WO2001065896A1 - Direct electrostatic printing method and device for manufacturing printed circuit boards - Google Patents

Direct electrostatic printing method and device for manufacturing printed circuit boards Download PDF

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Publication number
WO2001065896A1
WO2001065896A1 PCT/SE2001/000446 SE0100446W WO0165896A1 WO 2001065896 A1 WO2001065896 A1 WO 2001065896A1 SE 0100446 W SE0100446 W SE 0100446W WO 0165896 A1 WO0165896 A1 WO 0165896A1
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WO
WIPO (PCT)
Prior art keywords
toner particles
pattern
circuit board
printed circuit
charged toner
Prior art date
Application number
PCT/SE2001/000446
Other languages
French (fr)
Inventor
Masayyuki Ishii
Koichi Saito
Yukihoro Ohzeki
Original Assignee
Array Ab
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Array Ab filed Critical Array Ab
Priority to AU2001237866A priority Critical patent/AU2001237866A1/en
Publication of WO2001065896A1 publication Critical patent/WO2001065896A1/en

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
    • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
    • B41J2/385—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by selective supply of electric current or selective application of magnetism to a printing or impression-transfer material
    • B41J2/41—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by selective supply of electric current or selective application of magnetism to a printing or impression-transfer material for electrostatic printing
    • B41J2/415—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by selective supply of electric current or selective application of magnetism to a printing or impression-transfer material for electrostatic printing by passing charged particles through a hole or a slit
    • B41J2/4155—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by selective supply of electric current or selective application of magnetism to a printing or impression-transfer material for electrostatic printing by passing charged particles through a hole or a slit for direct electrostatic printing [DEP]
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
    • G03G15/00—Apparatus for electrographic processes using a charge pattern
    • G03G15/65—Apparatus which relate to the handling of copy material
    • G03G15/6588—Apparatus which relate to the handling of copy material characterised by the copy material, e.g. postcards, large copies, multi-layered materials, coloured sheet material
    • G03G15/6591—Apparatus which relate to the handling of copy material characterised by the copy material, e.g. postcards, large copies, multi-layered materials, coloured sheet material characterised by the recording material, e.g. plastic material, OHP, ceramics, tiles, textiles
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K3/00—Apparatus or processes for manufacturing printed circuits
    • H05K3/02—Apparatus or processes for manufacturing printed circuits in which the conductive material is applied to the surface of the insulating support and is thereafter removed from such areas of the surface which are not intended for current conducting or shielding
    • H05K3/06—Apparatus or processes for manufacturing printed circuits in which the conductive material is applied to the surface of the insulating support and is thereafter removed from such areas of the surface which are not intended for current conducting or shielding the conductive material being removed chemically or electrolytically, e.g. by photo-etch process
    • H05K3/061—Etching masks
    • H05K3/065—Etching masks applied by electrographic, electrophotographic or magnetographic methods
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
    • G03G2215/00—Apparatus for electrophotographic processes
    • G03G2215/00362—Apparatus for electrophotographic processes relating to the copy medium handling
    • G03G2215/00443—Copy medium
    • G03G2215/00523—Other special types, e.g. tabbed
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
    • G03G2217/00—Details of electrographic processes using patterns other than charge patterns
    • G03G2217/0008—Process where toner image is produced by controlling which part of the toner should move to the image- carrying member
    • G03G2217/0025—Process where toner image is produced by controlling which part of the toner should move to the image- carrying member where the toner starts moving from behind the electrode array, e.g. a mask of holes

Definitions

  • the invention relates to a method and an apparatus for pattern formation on a printed circuit board member. It especially refers to resist pattern formation, particularly soldering resist pattern. It further refers to conductive pattern formation and any other pattern that may be formed on a printed circuit board.
  • the invention also refers to a toner container holding toner particles for use in said method and apparatus.
  • Etching resist pattern formation on printed circuit boards is conventionally performed by means of coating a resist agent on a substrate which on it surface has a metal layer, usually copper, which can be dissolved by an etchant.
  • a photo mask is prepared having a pattern corresponding to the desired etching pattern, and is placed on the surface of the substrate. In this mask the portions that should remain after etching are transparent and the portions that should be removed at the etching are black.
  • ultraviolet exposure is performed through the mask the portions of the resist on the substrate corresponding to the transparent portions of the mask are polymerized and cured by the ultraviolet radiation. The non-cured resist material is then removed.
  • a solution that chemically dissolves the metal e g ferric chloride, cupric chloride and the like, is caused to act on the patterned surface, thereby removing the metal at the portion of the substrate where the resist pattern does not exist.
  • the etching resist film that is no longer needed is removed by peeling or oxidation.
  • a solder resist is a resist that protects a surface pattern on a printed circuit board and at the same time expose only mounting holes and electrical input-output terminals and is used for applying a solder to the exposed areas.
  • the solder resist pattern is conventio- nally formed by either a photo-printing method using ultraviolet curing in a corresponding way as disclosed above with respect to etching pattern formation or by a silk- screening method.
  • Such conventional resist pattern forming techniques involves several process steps, are complicated and requires expensive equipment. Moreover waste liquid and other waste that may pollute the environment are produced.
  • US-A-5,576,135 discloses a method and apparatus for forming etching resist patterns in which an electrostatic latent image is formed on a photosensitive rotating drum, a toner image is formed on said drum by developing the electrostatic image with a hot- melt toner and the toner image is transferred to a processing target member, e g a printed circuit board member.
  • US-A-4,897,326 discloses a method for forming a conductive pattern on printed circuit boards by forming an electrostatic latent image on a photosensitive rotating drum, applying an electrically conductive material on said latent image on the drum and transferring the so-distributed conductive material from the drum to the printed circuit board members.
  • the printing technique used in these two last cases is that of xerography, wherein latent electrostatic images formed on a charge retentive surface, such as a roller, are developed by a toner material to render the images visible, the images being subsequently transferred to a target member, usually paper but in the above cases a printed circuit board.
  • This process is called an indirect printing process since the images are first formed on an intermediate photo-receptor and then transferred to the target member.
  • EP-A-952 498 discloses the use of a direct electrostatic printing (DEP) process for forming an etching resist pattern on a conducting surface in a process for the production of printed circuit boards.
  • the conducting surface is a copper layer which makes the background electrode in the DEP process.
  • said printhead structure including a plurality of apertures and control electrodes arranged in conjunction to the apertures; -connecting voltage sources to said control electrodes to supply control potentials to said control electrodes to produce a pattern of electrostatic fields in accordance with the image information to selectively permit or restrict the transport of charged toner particles from the particle carrier through the apertures;
  • said image configuration corresponds to a resist pattern intended to be formed on the surface of the printed circuit board substrate.
  • Said resist pattern is especially a soldering resist pattern.
  • said image configuration corresponds to a conductive pattern intended to be formed on the surface of the printed circuit board substrate. According to still a further embodiment said image configuration corresponds to any pattern, characters, symbols and the like intended to be formed on the surface of the p ⁇ nted circuit board substrate.
  • the used toner particles should per se or after a hardening reaction resist a temperature of at least 150°C, preferably at least 200 °C and more preferably at least 250 °C, preferably during at least 3 minutes
  • the used toner particles contain a binding resin in the form of a thermoplastic or thermosettmg resin.
  • a thermo- setting binding resin is an epoxy resm.
  • the toner particles contain a binding resin in the form of a cyclic polyolefin.
  • Said cyclic polyolef is preferably a copolymer of an alicyclic compound, such as cyclohexene or norbornene and an alpha-olefm, such as ethylene, propylene or butylene.
  • the resm may during p ⁇ nting be in uncured form and the cu ⁇ ng takes place after the p ⁇ nting
  • the invention further refers to a direct electrostatic p ⁇ nting (DEP) apparatus for pattern formation on a printed circuit board member, said apparatus comp ⁇ smg an image forming apparatus in which an image information corresponding to a pattern which is to be formed on the p ⁇ nted circuit board substrate is converted into a pattern of electrostatic fields for modulating a transport of charged toner particles from a particle earner towards a back electrode member, said image forming apparatus including:
  • -a pnnthead structure arranged in said background elect ⁇ c field, including a plurality of apertures and control electrodes arranged in conjunction to the apertures, -control voltage sources for supplying control potentials to said control electrodes in accordance with the image information to selectively permit or restrict the transport of charged toner particles from the particle carrier through the apertures;
  • the invention further refers to a toner container holding toner particles for use in an an image forming apparatus.
  • Fig. 1 is a flow chart illustrating a conventional way of forming a resist pattern.
  • Fig. 2 is a flow chart illustrating etching resist formation according to the present invention.
  • Fig. 3 is a schematic view of an image forming apparatus in accordance with an embodiment of the present invention.
  • Fig. 4 is a schematic section view across a print station in an image forming apparatus, such as, for example, that shown in Fig. 3.
  • Fig. 5 is a schematic section view of the print zone, illustrating the positioning of a printhead structure in relation to a particle source and a printed circuit board substrate.
  • Fig. 6a is a partial view of a printhead structure of a type used in an image forming apparatus, showing the surface of the printhead structure that is facing the toner delivery unit.
  • Fig. 6b is a partial view of a printhead structure of a type used in an image forming apparatus, showing the surface of the printhead structure that is facing the intermediate transfer belt.
  • Fig. 6c is a section view across a section line I-I in the printhead structure of Fig. 6a and across the corresponding section line II-II of Fig. 6b. Detailed description of the embodiments
  • a substrate coated with a metal layer, e g copper, is in a resist forming step 55 coated with liquid resist forming agent or a resist film produced in advance
  • a heating step 56 the solvent is removed by evaporation
  • An etching pattern is formed in a pattern designing step 57 using CAD (Computer Aided Design) or the like.
  • the designed pattern is plotted in a plotting step 58 and the plotted-out pattern is photographed with a camera in a photographing step 59.
  • the photographed film is developed to form an exposure o ⁇ ginal or photo mask.
  • an exposing step 60 the exposure onginal (photo mask) is placed on the surface of the substrate, which is exposed to ultraviolet radiation through the mask. In this mask the portions that should remain after etching are transparent and the portions that should be removed at the etching are black. At the ultraviolet exposure the portions of the resist that correspond to the transparent portions of the mask are polyme ⁇ zed and cured.
  • a developing step 61 is performed for removing the non- set resist matenal.
  • the developing step is followed by a heating step 62 in which nnsmg solution and developing agent are evaporated and the adhesion force of the cured resist agent is increased.
  • the substrate is subsequently exerted to an etching step in which en etching solution that chemically dissolves the metal layer is caused to act on the patterned surface, thereby removing the metal on the portions where the metal layer is exposed.
  • the substrate is subsequently exerted to a soldenng step in which the substrate is immersed in melted soldenng tin or soldenng alloy
  • soldenng step in which the substrate is immersed in melted soldenng tin or soldenng alloy
  • the solder only adheres to those areas which are not covered by soldenng resist and which correspond to mounting holes and electncal input-output terminals.
  • the resist coating which is no longer needed, is removed by peeling or oxidation.
  • the resist pattern formation is performed in the schematic way illustrated by the flow chart of Fig. 2.
  • a resist pattern is formed in a pattern designing step 57 in a corresponding manner as in the prior art method.
  • a computerized image co ⁇ esponding to the resist pattern is formed in a subsequent step 64 and in a printing step 65 toner particles are deposited directly onto a printed circuit board substrate to form visible images. This is accomplished by so called direct electrostatic printing (DEP), which will be described in detail below.
  • the toner particles are preferably hardened (melted and cured) e g by UV irradiation, in a heating step 66.
  • the printed circuit board substrate is now provided with a resist pattern, especially a soldering resist pattern, and may then be further processed in a soldering process.
  • DEP differs from xerography in that an electric field is generated by electrical signals to cause toner particles to be deposited directly onto the image receiving member, usually paper, to form visible images without the need for those signals to be intermediately converted to another form of energy.
  • the characteristic feature of the DEP concept is the simultaneous field imaging and toner transport to produce visible images directly onto plain paper or any suitable image receiving substrate, in this case a printed circuit board substrate.
  • U.S Patent No. 5,036,341 discloses a direct electrostatic printing (DEP) device and a method to produce text and pictures with toner particles on an image receiving substrate directly from computer generated signals.
  • DEP direct electrostatic printing
  • Such a device generally includes a printhead structure provided with a plurality of apertures through which toner particles are selectively transported from a particle source to an image receiving medium due to control in accordance with an image information. Toner particles are held on the surface of the particle carrier by an adhesion force which is substantially related to the particle charge and to the distance between the particle and the surface of the particle earner.
  • the electrostatic field applied on a control electrode to initiate toner transport through a selected aperture is chosen to be sufficient to overcome the adhesion force to cause the release of an approp ⁇ ate amount of toner particles from the particle earner.
  • the electrostatic field is applied du ⁇ ng the time penod required for these released particles to reach sufficient momentum to pass through the selected aperture, whereafter the transported toner particles are exposed to the attraction force from the back electrode and intercepted by the image receiving substrate.
  • a background electric field is produced between a particle carrier and a back electrode to enable a transport of charged particles therebetween.
  • a pnnthead structure such as an electrode mat ⁇ x provided with a plurality of selectable apertures, is interposed in the background electric field between the particle earner and the back electrode and connected to a control unit which converts the image information into a pattern of electrostatic fields which, due to control in accordance with the image information, selectively open or close passages in the electrode matnx to permit or restnct the transport of charged particles from the particle earner.
  • the modulated stream of charged particles allowed to pass through the opened apertures are thus exposed to the background elect ⁇ c field and propelled towards the back electrode.
  • the charged particles are deposited on the image receivmg substrate, which according to the invention is a p ⁇ nted circuit board substrate, to provide lme-by-line scan p ⁇ nting to form a visible image corresponding to a resist pattern or other pattern that is to be formed on the p ⁇ nted circuit board substrate, e g a conductive pattern.
  • a p ⁇ nthead structure for use in direct electrostatic pnntmg may take on many designs, such as a lattice of intersecting wires arranged in rows and columns, or an apertured substrate of electrically insulating mate ⁇ al overlaid with a p ⁇ nted circuit of control electrodes arranged in conjunction with the apertures.
  • a pnnthead structure includes a flexible substrate of insulating mate ⁇ al such as polyimide or the like, having a first surface facing the particle carrier, a second surface facing the back electrode and a plurality of apertures arranged through the substrate.
  • the first surface is coated with an insulating layer and control electrodes are arranged between the first surface of the substrate and the insulating layer, in a configuration such that each control electrode surrounds a corresponding aperture.
  • the apertures are preferably aligned in one or several rows extending transversely across the width of the substrate, i.e. perpendicular to the motion direction of the image receiving substrate.
  • each single aperture is utilized to address a specific dot position of the image in a transversal direction.
  • the transversal print addressability is limited by the density of apertures through the printhead structure. For instance, a print addressability of 300 dpi requires a printhead structure having 300 apertures per inch in a transversal direction.
  • a direct electrostatic printing device includes a dot deflection control (D.C).
  • D.C dot deflection control
  • each single aperture is used to address several dot positions on an image receiving substrate by controlling not only the transport of toner particles through the aperture, but also their transport trajectory towards the image receiving substrate, and thereby the location of the obtained dot.
  • the D.C. method increases the print addressability without requiring a larger number of apertures in the printhead structure. This is achieved by providing the printhead structure with deflection electrodes connected to variable deflection voltages which, during each print cycle, sequentially modify the symmetry of the electrostatic control fields to deflect the modulated stream of toner particles in predetermined deflection directions. For instance, a D.C. method performing three deflection steps per print cycle, provides a print addressability of 600 dpi utilizing a printhead structure having only 200 apertures per inch.
  • an improved D.C. method provides a simultaneous dot size and dot position control.
  • This method utilizes the deflection electrodes to influence the convergence of the modulated stream of toner particles thus controlling the dot size.
  • Each aperture is surrounded by two deflection electrodes connected to respective deflection voltages Dl, D2, such that the electrostatic control field generated by the control electrode remains substantially symmet ⁇ cal as long as both deflection voltages Dl, D2 have the same amplitude
  • the amplitude of Dl and D2 are modulated to apply converging forces on toner particles as they are transported towards the image receiving medium, thus providing smaller dots
  • the dot position is simultaneously controlled by modulating the amplitude difference between Dl and D2 to deflect the toner trajectory towards predetermined dot positions
  • a pnnthead structure for use in D C methods generally includes a flexible substrate of electrically insulating mate ⁇ al such as polyimide or the like, having a first surface facing the particle earner, a second surface facing the back electrode and a plurality of apertures arranged through the substrate The first surface is overlaid with a first p ⁇ nted circuit including the control electrodes and the second surface is overlaid with a second p ⁇ nted circuit including the deflection electrodes Both printed circuits are coated with msulative layers Utilizing such a method, 60 micrometer dots can be obtained with apertures having a diameter m the order of 160 micrometer
  • an image forming apparatus in accordance with an embodiment of the present invention comprises at least one p ⁇ nt station 10, a transport belt member 11 supporting the pnnted circuit board members 13, and an adjustable holding element 12, which also constitute a back electrode member
  • the p ⁇ nt station is arranged m relation to the transport belt member 11 supporting the p ⁇ nted circuit board members 32
  • the holding element/back electrodes 13 are arranged to accurately positioning the transport belt 11 and the p ⁇ nted circuit board members 13 with respect to the p ⁇ nt station 10
  • the transport belt 11 is eliminated and the p ⁇ nted circuit board members 13 are conveyed past the print station 10 by some other optional transport means In the case of colour p ⁇ nting more than one, e g four different p ⁇ nting stations, are arranged after each other.
  • an intermediate image receiving member e g in the form of a transfer belt, conveyed past the print station.
  • the toner particles are deposited on said transfer belt.
  • the image formed on the transfer belt is then transferred to the printed circuit board member.
  • a print station in an image forming apparatus in accordance with the present invention includes a particle carrier/ particle delivery unit 3 preferably having a replaceable or refillable container 30 for holding toner particles, the container 30 having front and back walls (not shown), a pair of side walls and a bottom wall having an elongated opening 31 extending from the front wall to the back wall and provided with a toner feeding element 32 disposed to continuously supply toner particles to a developer sleeve 33 through a particle charging member 34.
  • the particle charging member 34 is preferably formed of a foam sponge or a roller made of or coated with a fibrous, resilient material.
  • the foam sponge is brought into mechanical contact with the peripheral surface of the developer sleeve 33 for charging particles by contact charge exchange due to triboelectrification of the toner particles through frictional interaction between the foam sponge and any suitable coating material of the developer sleeve.
  • the developer sleeve 33 is preferably made of metal coated with a conductive material or of rubber, and preferably has a substantially cylindrical shape and a rotation axis extending parallel to the elongated opening 31 of the particle container 30. Charged toner particles are held to the surface of the developer sleeve 33 by electrostatic forces essentially proportional to (Q/D) 2 , where Q is the particle charge and D is the distance between the particle charge centre and the boundary of the developer sleeve 33.
  • the charge unit may additionally include a charging voltage source (not shown), which supply an electric field to induce or inject charge to the toner particles.
  • a charging voltage source not shown
  • the method can be performed using any other suitable charge unit, such as a conventional charge injection unit, a charge induction unit or a corona charging unit, without departing from the scope of the present invention.
  • a metenng element 35 is positioned proximate to the developer sleeve 33 to adjust the concentration of toner particles on the penpheral surface of the developer sleeve 33, to form a relatively th , uniform particle layer thereon.
  • the metering element 35 may be formed of a flexible or rigid, insulating or metallic blade, roller or any other member suitable for providing a uniform particle layer thickness.
  • the metering element 35 may be of metal or a combination of rubber on metal.
  • the metenng element 35 may also be connected to a metenng voltage source (not shown) which influence the tnboelectn- fication of the particle layer to ensure a uniform particle charge density on the surface of the developer sleeve.
  • the onentation of the toner container 30 must be such that the metenng element 35 is not immersed in the toner
  • the developer sleeve 33 is a ⁇ anged in relation with a positioning device 40 for accurately supporting and maintaining the pnnthead structure 5 in a predetermined position with respect to the penpheral surface of the developer sleeve 33.
  • the positioning device 40 is formed of a frame 41 having a front portion, a back portion and two transversally extending side rulers 42, 43 disposed on each side of the developer sleeve 33 parallel with the rotation axis thereof.
  • the first side ruler 42 positioned at a upstream side of the developer sleeve 33 with respect to its rotation direction, is provided with fastening means 44 to secure the pnnthead structure 5 along a transversal fastening axis extending across the entire width of the pnnthead structure
  • the second side ruler 43 positioned at a downstream side of the developer sleeve 33, is provided with a support element 45, or pivot, for supporting the pnnthead structure 5 in a predetermined position with respect to the penpheral surface of the developer sleeve 33.
  • the support element 45 and the fastening axis are so positioned with respect to one another, that the printhead structure 5 is maintained in an arcuated shape along at least a part of its longitudinal extension.
  • That arcuated shape has a curvature radius determined by the relative positions of the support element 45 and the fastening axis and dimensioned to maintain a part of the pnnthead structure 5 curved around a co ⁇ esponding part of the penpheral surface of the developer sleeve 33.
  • the support element 45 is arranged in contact with the pnnthead structure 5 at a fixed support location on its longitudinal axis so as to allow a slight va ⁇ ation of the p ⁇ nthead structure 5 position in both longitudinal and transversal direction about that fixed support location, in order to accommodate a possible excentricity or any other undesired variations of the developer sleeve 33.
  • the support element 45 is arranged to made the printhead structure 5 pivotable about a fixed point to ensure that the distance between the printhead structure 5 and the peripheral surface of the developer sleeve 33 remains constant along the whole transverse direction at every moment of the print process, regardless of undesired mechanical imperfections of the developer sleeve 33.
  • the front and back portions of the positioning device 40 are provided with securing members 46 on which the toner delivery unit 3 is mounted in a fixed position to provide a constant distance between the rotation axis of the developer sleeve 33 and a transversal axis of the printhead structure 5.
  • the securing members 46 are arranged at the front and back ends of the developer sleeve 33 to accurately space the developer sleeve 33 from the corresponding holding element 12 of the transfer belt 1 facing the actual print station.
  • the securing members 46 are preferably dimensioned to provide and maintain a parallel relation between the rotation axis of the developer sleeve 33 and a central transversal axis of the corresponding holding member /back electrode 12.
  • a printhead structure 5 in an image forming apparatus in accordance with the present invention comprises a substrate 50 of flexible, electrically insulating material such as polyimide or the like, having a predetermined thickness, a first surface facing the developer sleeve, a second surface facing the transfer belt, a transversal axis 51 extending parallel to the rotation axis of the developer sleeve 33 across the whole print area, and a plurality of apertures 52 arranged through the substrate 50 from the first to the second surface thereof.
  • the first surface of the substrate is coated with a first cover layer 501 of electrically insulating material, such as for example parylene.
  • a first printed circuit comprising a plurality of control electrodes 53 disposed in conjunction with the apertures, and, in some embodiments, shield electrode structures (not shown) arranged in conjunction with the control electrodes 53, is arranged between the substrate 50 and the first cover layer 501.
  • the second surface of the substrate is coated with a second cover layer 502 of electrically insulating material, such as for example parylene.
  • a second printed circuit including a plurality of deflection electrodes 54, is a ⁇ anged between the substrate 50 and the second cover layer 502.
  • the printhead structure 5 further includes a layer of antistatic material (not shown), preferably a semiconductive material, such as silicium oxide or the like, arranged on at least a part of the second cover layer 502, facing the transfer belt 1.
  • the printhead structure 5 is brought in cooperation with a control unit (not shown) comprising variable control voltage sources connected to the control electrodes 53 to supply control potentials which control the amount of toner particles to be transported through the corresponding aperture 52 during each print sequence.
  • the control unit further comprises deflection voltage sources (not shown) connected to the deflection electrodes 54 to supply deflection voltage pulses which controls the convergence and the trajectory path of the toner particles allowed to pass through the corresponding apertures 52.
  • the control unit in some embodiments, even includes a shield voltage source (not shown) connected to the shield electrodes to supply a shield potential which electrostatically screens adjacent control electrodes 53 from one another, preventing electrical interaction therebetween.
  • the substrate 50 is a flexible sheet of polyimide having a thickness on the order of about 50 microns.
  • the first and second printed circuits are copper circuits of approximately 8-9 microns thickness etched onto the first and second surface of the substrate 50, respectively, using conventional etching techniques.
  • the first and second cover layers (501, 502) are 5 to 10 microns thick parylene laminated onto the substrate
  • the apertures 52 are made through the printhead structure 5 using conventional laser micromachining methods.
  • the apertures 52 have preferably a circular or elongated shape centered about a central axis, with a diameter in a range of 80 to 120 microns, alternatively a transversal minor diameter of about 80 microns and a longitudinal major diameter of about 120 microns.
  • the apertures 52 have preferably a constant shape along their central axis, for example cylindrical apertures, it may be advantageous in some embodiments to provide apertures whose shape vanes continuously or stepwise along the central axis, for example conical apertures
  • the p ⁇ nthead structure 5 is dimensioned to perform 600 dpi pnntmg utilizing three deflection sequences in each pnnt cycle, I e three dot locations are addressable through each aperture 52 of the p ⁇ nthead structure during each pnnt cycle Accordingly, one aperture 52 is provided for every third dot location in a transverse direction, that is, 200 equally spaced apertures per inch aligned parallel to the transversal axis 51 of the p ⁇ nthead structure 5
  • the apertures 52 are generally aligned in one or several rows, preferably in two parallel rows each comp ⁇ sing 100 apertures per inch Hence, the aperture pitch, I e the distance between the central axes of two neighbonng apertures of a same row is 0,01 inch or about 254 microns
  • the aperture rows are preferably positioned on each side of the transversal axis 51 of the p ⁇ nthead structure 5 and transversally shifted with respect to each other
  • the first pnnted circuit comp ⁇ ses control electrodes 53 each of which having a nng shaped structure surrounding the pe ⁇ phery of a corresponding aperture 52, and a connector preferably extending in the longitudinal direction, connecting the ⁇ ng shaped structure to a co ⁇ espondmg control voltage source
  • the control electrodes 53 may take on va ⁇ ous shape for continuously or partly surrounding the apertures 52, preferably shapes having symmetry about the central axis of the apertures
  • the control electrodes are advantageously made smaller in a transverse direction than m a longitudinal direction
  • the second pnnted circuit compnses a plurality of deflection electrodes 54, each of which is divided into two semicircular or crescent shaped deflection segments 541, 542 spaced around a predetermined portion of the circumference of a corresponding aperture 52
  • the deflection segments 541, 542 are arranged symmet ⁇ cally about the central axis of the aperture 52 on each side of a deflection axis 543 extending through the center of the aperture 52 at a predetermined deflection angle d to the longitudinal direction
  • the deflection axis 543 is dimensioned in accordance with the number of deflection sequences to be performed in each p ⁇ nt cycle in order to neutralize the effects of the belt motion during the p ⁇ nt cycle, to obtain transversally aligned dot positions on the transfer belt For instance, when using three deflection sequences, an approp ⁇ ate deflection angle is chosen to arctan(l/3), i.e.
  • each deflection electrode 54 has a upstream segment 541 and a downstream segment 542, all upstream segments 541 being connected to a first deflection voltage source Dl, and all downstream segments 542 being connected to a second deflection voltage source D2.
  • Numeral 6 denotes a cleaning unit for removal of residual charged particles from the pnnthead structure 5 after formation of the image.
  • Toner particles essentially consist of a binding resin, a colou ⁇ ng agent, electnc charge control agents (CCA).
  • the binding resin is the main component of a toner.
  • styrene acrylic resins and polyester resins are often used as binder resin.
  • the toner particles used per se or after a melting and cunng resists a temperature of at least 150°C, preferably at least 200°C and more preferably at least 250 °C, preferably dunng at least 3 minutes This could be accomplished by using toner particles that contain a binding resin in the form of a thermoplastic or thermosettmg resin, for example epoxy resins.
  • a suitable binding resins are amorphous cyclic polyolefmes
  • Other components of the binder resin could be polyester resms, epoxy resins, polyolefin resins, vinyl acetate group resms, vinyl acetate group copolymenzation resins, styrene acrylic resins, and other acrylic type resins.
  • Polyolefmes with the cyclic structure used herein are preferably copolymers of an alicyclic compound with double bonds, such as cyclohexene or norbornene and an alpha-olefm, such as ethylene, propylene or butylene for example.
  • the cyclic polyolefin is a copolymer of ethylene and norbornene These resms are amorphous, colourless, transparent and have a high transmissivity.
  • Polyolefmes with this cyclic structure are polymers obtained by polymenzation methods using for example metallocene group or Ziegler group catalysts.
  • Toner of the intended kind using a cyclic polyolefmes as a binding resm component are further disclosed in WO 97/05529 the disclosure of which is included herein as a reference.
  • the compatibility of the cyclic polyolefmes with other binder resin components and dispersabihty of a pigment (colouring agent) can be improved by coupling a carboxy group, a carboxyhc acid anhydnde, a hydroxy group and/or an amino group to the cyclic polyolefin.
  • the cyclic polyolefin is a copolymer of diene monomers, such as norbornadiene or cyclohexadiene
  • the carboxy group can be guided by a structure of cross linkage by addition of a metal, such as zmc, copper and calcium to the cyclic polyolefin resin.
  • a metal such as zmc, copper and calcium
  • Functional additives such as colouring agents, electric-charge control agents (CCA), waxes etc. are added to the binder resin for providing the desired toner composition.
  • Toner particles of the desired particle size are produced by conventional methods such as pulverization and classification.
  • cyclic polyolefines according to the invention as binding agent is that they withstand higher temperatures than e g the traditionally used polyesters, which means that the functional additives mentioned above may be admixed with the binding agent at higher temperatures and by that a lower viscosity. This gives a more homogeneous admixture of the additives in the binding agent. Besides and more important the toner particles will withstand the high temperatures during subsequent processing of the printed circuit board substrate, especially soldering.
  • the toner particles should preferably have a narrow particle size distribution with an average volume diameter comprised in the range of 3 to 30 ⁇ m, or depending on the resolution that is desired.
  • Small toner particles provides improved printing results as compared to larger toner particles and/or toner particles of varying size. Small particles melt over a smaller area after fusing, which makes it possible to print sharper dots, lines and images with small particles than with large particles. Another important advantage is that less toner particles are needed with smaller particle sizes.
  • colouring agents are carbon black, diazo yellow, copper phtalocyanine blue, quinacridone, carmine 6B, mono azo ed, perylene, green dye or pigment etc.
  • Examples of electric-charge control agents are a Nigrosine dye, a chrome complexity of a 5-di-tert-butyl salicylic acid, a quaternary ammonium salt, a triphenylmethane dye, an azo chrome complexity etc.
  • Examples of surface treatment additives on the toner particles are a colloidal silica, aluminum oxide, titanium oxide, barium stearate, calcium stearate, lauric acid barium etc.
  • the toner particles used must be of an electrically conductive material, for example a conductive metallic powder. They should in this case be covered with an insulating layer so that they may be electrically charged for the printing process. At the curing the insulation is broken so that the toner becomes conductive.
  • a higher printing speed than feeding speed of the printed circuit board substrate in order to achieve enough toner on the substrate during one print.
  • running the printer at 50 mm/s and the substrate feeding at 10 mm/s it would be possible to increase the toner transfer five times. This means that approximately 3000 dpi could be printed in vertical direction and up to 600 dpi in horizontal direction using the above described DEP apparatus.

Abstract

The invention refers to a method and an apparatus for pattern formation on a printed circuit board, especially resist pattern formation, such as etching resist pattern and soldering resist pattern. If further refers to conductive pattern formation and any other pattern that may be formed on a printed circuit board. A direct printing method and apparatus is used in which a computer generated image information corresponding to a pattern which is to be formed on the printed circuit board substrate (2) is converted into a pattern of electrostatic fields, which selectively transport electrically charged toner particles from a particle source (3) toward a back electrode (12) through a printhead structure (5), whereby by the charged toner particles are deposited in image configuration on the printed circuit board or an intermediate image receiving member caused to move relative to the printhead structure. The invention also refers to a toner container holding toner particles for use in said method and apparatus.

Description

DIRECT ELECTROSTATIC PRINΗNG METHOD AND DEVICE FOR MANUFACTURING PRINTED CIRCUIT BOARDS
Technical field
The invention relates to a method and an apparatus for pattern formation on a printed circuit board member. It especially refers to resist pattern formation, particularly soldering resist pattern. It further refers to conductive pattern formation and any other pattern that may be formed on a printed circuit board. The invention also refers to a toner container holding toner particles for use in said method and apparatus.
Background of the invention
Etching resist pattern formation on printed circuit boards is conventionally performed by means of coating a resist agent on a substrate which on it surface has a metal layer, usually copper, which can be dissolved by an etchant. A photo mask is prepared having a pattern corresponding to the desired etching pattern, and is placed on the surface of the substrate. In this mask the portions that should remain after etching are transparent and the portions that should be removed at the etching are black. When ultraviolet exposure is performed through the mask the portions of the resist on the substrate corresponding to the transparent portions of the mask are polymerized and cured by the ultraviolet radiation. The non-cured resist material is then removed. In a subsequent base material etching step a solution that chemically dissolves the metal, e g ferric chloride, cupric chloride and the like, is caused to act on the patterned surface, thereby removing the metal at the portion of the substrate where the resist pattern does not exist. In a final resist removing step, the etching resist film that is no longer needed is removed by peeling or oxidation.
A solder resist is a resist that protects a surface pattern on a printed circuit board and at the same time expose only mounting holes and electrical input-output terminals and is used for applying a solder to the exposed areas. The solder resist pattern is conventio- nally formed by either a photo-printing method using ultraviolet curing in a corresponding way as disclosed above with respect to etching pattern formation or by a silk- screening method. Such conventional resist pattern forming techniques involves several process steps, are complicated and requires expensive equipment. Moreover waste liquid and other waste that may pollute the environment are produced.
US-A-5,576,135 discloses a method and apparatus for forming etching resist patterns in which an electrostatic latent image is formed on a photosensitive rotating drum, a toner image is formed on said drum by developing the electrostatic image with a hot- melt toner and the toner image is transferred to a processing target member, e g a printed circuit board member.
US-A-4,897,326 discloses a method for forming a conductive pattern on printed circuit boards by forming an electrostatic latent image on a photosensitive rotating drum, applying an electrically conductive material on said latent image on the drum and transferring the so-distributed conductive material from the drum to the printed circuit board members.
The printing technique used in these two last cases is that of xerography, wherein latent electrostatic images formed on a charge retentive surface, such as a roller, are developed by a toner material to render the images visible, the images being subsequently transferred to a target member, usually paper but in the above cases a printed circuit board. This process is called an indirect printing process since the images are first formed on an intermediate photo-receptor and then transferred to the target member.
EP-A-952 498 discloses the use of a direct electrostatic printing (DEP) process for forming an etching resist pattern on a conducting surface in a process for the production of printed circuit boards. The conducting surface is a copper layer which makes the background electrode in the DEP process.
Summary of the invention
It is an object of the present invention to provide a method for pattern formation on a printed circuit board substrate that is less complicated than the known methods and can be performed at a higher production speed and that does not produce waste liquid and other waste that may pollute the environment. This has according to the invention been achieved by a direct electrostatic printing (DEP) method comprising the following steps: -converting an image information corresponding to a pattern which is to be formed on the printed circuit board substrate into a pattern of electrostatic fields including:
-modulating a transport of charged toner particles from a particle carrier towards a back electrode member; -producing a background electric field to enable a transport of said charged toner particles from said particle carrier towards said back electrode member;
-providing an apertured printhead structure in said background electric field, said printhead structure including a plurality of apertures and control electrodes arranged in conjunction to the apertures; -connecting voltage sources to said control electrodes to supply control potentials to said control electrodes to produce a pattern of electrostatic fields in accordance with the image information to selectively permit or restrict the transport of charged toner particles from the particle carrier through the apertures;
-conveying an image receiving medium in relation to the printhead structure for intercepting the transported charged toner particles in image;
-using charged toner particles which per se or after a hardening reaction resist the temperature of soldering tin or soldering alloy.
According to one embodiment said image configuration corresponds to a resist pattern intended to be formed on the surface of the printed circuit board substrate. Said resist pattern is especially a soldering resist pattern.
According to a further embodiment said image configuration corresponds to a conductive pattern intended to be formed on the surface of the printed circuit board substrate. According to still a further embodiment said image configuration corresponds to any pattern, characters, symbols and the like intended to be formed on the surface of the pπnted circuit board substrate.
Preferably the used toner particles should per se or after a hardening reaction resist a temperature of at least 150°C, preferably at least 200 °C and more preferably at least 250 °C, preferably during at least 3 minutes
According to a preferred embodiment the used toner particles contain a binding resin in the form of a thermoplastic or thermosettmg resin. One example of such a thermo- setting binding resin is an epoxy resm. According to another preferred embodiment the toner particles contain a binding resin in the form of a cyclic polyolefin. Said cyclic polyolef is preferably a copolymer of an alicyclic compound, such as cyclohexene or norbornene and an alpha-olefm, such as ethylene, propylene or butylene.
The resm may during pπnting be in uncured form and the cuπng takes place after the pπnting
The invention further refers to a direct electrostatic pπnting (DEP) apparatus for pattern formation on a printed circuit board member, said apparatus compπsmg an image forming apparatus in which an image information corresponding to a pattern which is to be formed on the pπnted circuit board substrate is converted into a pattern of electrostatic fields for modulating a transport of charged toner particles from a particle earner towards a back electrode member, said image forming apparatus including:
-a background voltage source for producing a background electπc field which enables a transport of charged toner particles from said particle earner towards said back electrode member;
-a pnnthead structure arranged in said background electπc field, including a plurality of apertures and control electrodes arranged in conjunction to the apertures, -control voltage sources for supplying control potentials to said control electrodes in accordance with the image information to selectively permit or restrict the transport of charged toner particles from the particle carrier through the apertures;
-an image receiving member caused to move in relation to the printhead structure for intercepting the transported charged particles in image configuration.
-said charged toner particles per se or after a hardening reaction resist the temperature of soldering tin or soldering alloy.
The invention further refers to a toner container holding toner particles for use in an an image forming apparatus.
Brief description of the drawings
Fig. 1 is a flow chart illustrating a conventional way of forming a resist pattern.
Fig. 2 is a flow chart illustrating etching resist formation according to the present invention.
Fig. 3 is a schematic view of an image forming apparatus in accordance with an embodiment of the present invention.
Fig. 4 is a schematic section view across a print station in an image forming apparatus, such as, for example, that shown in Fig. 3. Fig. 5 is a schematic section view of the print zone, illustrating the positioning of a printhead structure in relation to a particle source and a printed circuit board substrate.
Fig. 6a is a partial view of a printhead structure of a type used in an image forming apparatus, showing the surface of the printhead structure that is facing the toner delivery unit. Fig. 6b is a partial view of a printhead structure of a type used in an image forming apparatus, showing the surface of the printhead structure that is facing the intermediate transfer belt.
Fig. 6c is a section view across a section line I-I in the printhead structure of Fig. 6a and across the corresponding section line II-II of Fig. 6b. Detailed description of the embodiments
The invention will below be descnbed in detail, but firstly a conventional way of forming a resist pattern such as an etching resist pattern or a soldenng resist pattern on a pπnted circuit card by a photo-pπntmg method using ultraviolet setting will be explained with reference to Fig 1. A substrate coated with a metal layer, e g copper, is in a resist forming step 55 coated with liquid resist forming agent or a resist film produced in advance In a heating step 56 the solvent is removed by evaporation
An etching pattern is formed in a pattern designing step 57 using CAD (Computer Aided Design) or the like. The designed pattern is plotted in a plotting step 58 and the plotted-out pattern is photographed with a camera in a photographing step 59. The photographed film is developed to form an exposure oπginal or photo mask. In an exposing step 60 the exposure onginal (photo mask) is placed on the surface of the substrate, which is exposed to ultraviolet radiation through the mask. In this mask the portions that should remain after etching are transparent and the portions that should be removed at the etching are black. At the ultraviolet exposure the portions of the resist that correspond to the transparent portions of the mask are polymeπzed and cured. After the ultraviolet exposure a developing step 61 is performed for removing the non- set resist matenal. The developing step is followed by a heating step 62 in which nnsmg solution and developing agent are evaporated and the adhesion force of the cured resist agent is increased.
In case the resist pattern is an etching resist pattern the substrate is subsequently exerted to an etching step in which en etching solution that chemically dissolves the metal layer is caused to act on the patterned surface, thereby removing the metal on the portions where the metal layer is exposed.
In case the resist pattern is a soldenng resist pattern the substrate is subsequently exerted to a soldenng step in which the substrate is immersed in melted soldenng tin or soldenng alloy The solder only adheres to those areas which are not covered by soldenng resist and which correspond to mounting holes and electncal input-output terminals. In a final step the resist coating, which is no longer needed, is removed by peeling or oxidation.
According to the present invention the resist pattern formation is performed in the schematic way illustrated by the flow chart of Fig. 2. A resist pattern is formed in a pattern designing step 57 in a corresponding manner as in the prior art method. A computerized image coπesponding to the resist pattern is formed in a subsequent step 64 and in a printing step 65 toner particles are deposited directly onto a printed circuit board substrate to form visible images. This is accomplished by so called direct electrostatic printing (DEP), which will be described in detail below. The toner particles are preferably hardened (melted and cured) e g by UV irradiation, in a heating step 66. The printed circuit board substrate is now provided with a resist pattern, especially a soldering resist pattern, and may then be further processed in a soldering process.
Many of the methods used in DEP, such as particle charging, particle transport within the toner container, and particle fusing are similar to those used in xerography. However, DEP differs from xerography in that an electric field is generated by electrical signals to cause toner particles to be deposited directly onto the image receiving member, usually paper, to form visible images without the need for those signals to be intermediately converted to another form of energy. The characteristic feature of the DEP concept is the simultaneous field imaging and toner transport to produce visible images directly onto plain paper or any suitable image receiving substrate, in this case a printed circuit board substrate.
U.S Patent No. 5,036,341 discloses a direct electrostatic printing (DEP) device and a method to produce text and pictures with toner particles on an image receiving substrate directly from computer generated signals. Such a device generally includes a printhead structure provided with a plurality of apertures through which toner particles are selectively transported from a particle source to an image receiving medium due to control in accordance with an image information. Toner particles are held on the surface of the particle carrier by an adhesion force which is substantially related to the particle charge and to the distance between the particle and the surface of the particle earner. The electrostatic field applied on a control electrode to initiate toner transport through a selected aperture is chosen to be sufficient to overcome the adhesion force to cause the release of an appropπate amount of toner particles from the particle earner. The electrostatic field is applied duπng the time penod required for these released particles to reach sufficient momentum to pass through the selected aperture, whereafter the transported toner particles are exposed to the attraction force from the back electrode and intercepted by the image receiving substrate.
To perform a direct electrostatic pnnt g method in accordance with the present invention, a background electric field is produced between a particle carrier and a back electrode to enable a transport of charged particles therebetween. A pnnthead structure, such as an electrode matπx provided with a plurality of selectable apertures, is interposed in the background electric field between the particle earner and the back electrode and connected to a control unit which converts the image information into a pattern of electrostatic fields which, due to control in accordance with the image information, selectively open or close passages in the electrode matnx to permit or restnct the transport of charged particles from the particle earner. The modulated stream of charged particles allowed to pass through the opened apertures are thus exposed to the background electπc field and propelled towards the back electrode. The charged particles are deposited on the image receivmg substrate, which according to the invention is a pπnted circuit board substrate, to provide lme-by-line scan pπnting to form a visible image corresponding to a resist pattern or other pattern that is to be formed on the pπnted circuit board substrate, e g a conductive pattern.
A pπnthead structure for use in direct electrostatic pnntmg may take on many designs, such as a lattice of intersecting wires arranged in rows and columns, or an apertured substrate of electrically insulating mateπal overlaid with a pπnted circuit of control electrodes arranged in conjunction with the apertures. Generally, a pnnthead structure includes a flexible substrate of insulating mateπal such as polyimide or the like, having a first surface facing the particle carrier, a second surface facing the back electrode and a plurality of apertures arranged through the substrate. The first surface is coated with an insulating layer and control electrodes are arranged between the first surface of the substrate and the insulating layer, in a configuration such that each control electrode surrounds a corresponding aperture. The apertures are preferably aligned in one or several rows extending transversely across the width of the substrate, i.e. perpendicular to the motion direction of the image receiving substrate.
According to such a method, each single aperture is utilized to address a specific dot position of the image in a transversal direction. Thus the transversal print addressability is limited by the density of apertures through the printhead structure. For instance, a print addressability of 300 dpi requires a printhead structure having 300 apertures per inch in a transversal direction.
According to a preferred embodiment of the present invention, a direct electrostatic printing device includes a dot deflection control (D.C). According to that embodiment, each single aperture is used to address several dot positions on an image receiving substrate by controlling not only the transport of toner particles through the aperture, but also their transport trajectory towards the image receiving substrate, and thereby the location of the obtained dot. The D.C. method increases the print addressability without requiring a larger number of apertures in the printhead structure. This is achieved by providing the printhead structure with deflection electrodes connected to variable deflection voltages which, during each print cycle, sequentially modify the symmetry of the electrostatic control fields to deflect the modulated stream of toner particles in predetermined deflection directions. For instance, a D.C. method performing three deflection steps per print cycle, provides a print addressability of 600 dpi utilizing a printhead structure having only 200 apertures per inch.
According to a preferred embodiment, an improved D.C. method provides a simultaneous dot size and dot position control. This method utilizes the deflection electrodes to influence the convergence of the modulated stream of toner particles thus controlling the dot size. Each aperture is surrounded by two deflection electrodes connected to respective deflection voltages Dl, D2, such that the electrostatic control field generated by the control electrode remains substantially symmetπcal as long as both deflection voltages Dl, D2 have the same amplitude The amplitude of Dl and D2 are modulated to apply converging forces on toner particles as they are transported towards the image receiving medium, thus providing smaller dots The dot position is simultaneously controlled by modulating the amplitude difference between Dl and D2 to deflect the toner trajectory towards predetermined dot positions
A pnnthead structure for use in D C methods generally includes a flexible substrate of electrically insulating mateπal such as polyimide or the like, having a first surface facing the particle earner, a second surface facing the back electrode and a plurality of apertures arranged through the substrate The first surface is overlaid with a first pπnted circuit including the control electrodes and the second surface is overlaid with a second pπnted circuit including the deflection electrodes Both printed circuits are coated with msulative layers Utilizing such a method, 60 micrometer dots can be obtained with apertures having a diameter m the order of 160 micrometer
In order to clanfy the method and device according to the invention, some examples of its use will now be descπbed in connection with accompanying drawings
As is schematically shown in Fig 3, an image forming apparatus in accordance with an embodiment of the present invention comprises at least one pπnt station 10, a transport belt member 11 supporting the pnnted circuit board members 13, and an adjustable holding element 12, which also constitute a back electrode member The pπnt station is arranged m relation to the transport belt member 11 supporting the pπnted circuit board members 32 The holding element/back electrodes 13 are arranged to accurately positioning the transport belt 11 and the pπnted circuit board members 13 with respect to the pπnt station 10
In an alternative embodiment the transport belt 11 is eliminated and the pπnted circuit board members 13 are conveyed past the print station 10 by some other optional transport means In the case of colour pπnting more than one, e g four different pπnting stations, are arranged after each other.
According to a further embodiment there may be used an intermediate image receiving member, e g in the form of a transfer belt, conveyed past the print station. The toner particles are deposited on said transfer belt. The image formed on the transfer belt is then transferred to the printed circuit board member.
As shown in Fig.4, a print station in an image forming apparatus in accordance with the present invention includes a particle carrier/ particle delivery unit 3 preferably having a replaceable or refillable container 30 for holding toner particles, the container 30 having front and back walls (not shown), a pair of side walls and a bottom wall having an elongated opening 31 extending from the front wall to the back wall and provided with a toner feeding element 32 disposed to continuously supply toner particles to a developer sleeve 33 through a particle charging member 34. The particle charging member 34 is preferably formed of a foam sponge or a roller made of or coated with a fibrous, resilient material. The foam sponge is brought into mechanical contact with the peripheral surface of the developer sleeve 33 for charging particles by contact charge exchange due to triboelectrification of the toner particles through frictional interaction between the foam sponge and any suitable coating material of the developer sleeve. The developer sleeve 33 is preferably made of metal coated with a conductive material or of rubber, and preferably has a substantially cylindrical shape and a rotation axis extending parallel to the elongated opening 31 of the particle container 30. Charged toner particles are held to the surface of the developer sleeve 33 by electrostatic forces essentially proportional to (Q/D)2, where Q is the particle charge and D is the distance between the particle charge centre and the boundary of the developer sleeve 33.
Alternatively, the charge unit may additionally include a charging voltage source (not shown), which supply an electric field to induce or inject charge to the toner particles. Although it is preferred to charge particles through contact charge exchange, the method can be performed using any other suitable charge unit, such as a conventional charge injection unit, a charge induction unit or a corona charging unit, without departing from the scope of the present invention. A metenng element 35 is positioned proximate to the developer sleeve 33 to adjust the concentration of toner particles on the penpheral surface of the developer sleeve 33, to form a relatively th , uniform particle layer thereon. The metering element 35 may be formed of a flexible or rigid, insulating or metallic blade, roller or any other member suitable for providing a uniform particle layer thickness. The metering element 35 may be of metal or a combination of rubber on metal. The metenng element 35 may also be connected to a metenng voltage source (not shown) which influence the tnboelectn- fication of the particle layer to ensure a uniform particle charge density on the surface of the developer sleeve. The onentation of the toner container 30 must be such that the metenng element 35 is not immersed in the toner
As shown in Fig 5, the developer sleeve 33 is aπanged in relation with a positioning device 40 for accurately supporting and maintaining the pnnthead structure 5 in a predetermined position with respect to the penpheral surface of the developer sleeve 33. The positioning device 40 is formed of a frame 41 having a front portion, a back portion and two transversally extending side rulers 42, 43 disposed on each side of the developer sleeve 33 parallel with the rotation axis thereof. The first side ruler 42, positioned at a upstream side of the developer sleeve 33 with respect to its rotation direction, is provided with fastening means 44 to secure the pnnthead structure 5 along a transversal fastening axis extending across the entire width of the pnnthead structure
5. The second side ruler 43, positioned at a downstream side of the developer sleeve 33, is provided with a support element 45, or pivot, for supporting the pnnthead structure 5 in a predetermined position with respect to the penpheral surface of the developer sleeve 33. The support element 45 and the fastening axis are so positioned with respect to one another, that the printhead structure 5 is maintained in an arcuated shape along at least a part of its longitudinal extension. That arcuated shape has a curvature radius determined by the relative positions of the support element 45 and the fastening axis and dimensioned to maintain a part of the pnnthead structure 5 curved around a coπesponding part of the penpheral surface of the developer sleeve 33. The support element 45 is arranged in contact with the pnnthead structure 5 at a fixed support location on its longitudinal axis so as to allow a slight vaπation of the pπnthead structure 5 position in both longitudinal and transversal direction about that fixed support location, in order to accommodate a possible excentricity or any other undesired variations of the developer sleeve 33. That is, the support element 45 is arranged to made the printhead structure 5 pivotable about a fixed point to ensure that the distance between the printhead structure 5 and the peripheral surface of the developer sleeve 33 remains constant along the whole transverse direction at every moment of the print process, regardless of undesired mechanical imperfections of the developer sleeve 33.
The front and back portions of the positioning device 40 are provided with securing members 46 on which the toner delivery unit 3 is mounted in a fixed position to provide a constant distance between the rotation axis of the developer sleeve 33 and a transversal axis of the printhead structure 5. Preferably, the securing members 46 are arranged at the front and back ends of the developer sleeve 33 to accurately space the developer sleeve 33 from the corresponding holding element 12 of the transfer belt 1 facing the actual print station. The securing members 46 are preferably dimensioned to provide and maintain a parallel relation between the rotation axis of the developer sleeve 33 and a central transversal axis of the corresponding holding member /back electrode 12.
As shown in Fig.6a, 6b, 6c, a printhead structure 5 in an image forming apparatus in accordance with the present invention comprises a substrate 50 of flexible, electrically insulating material such as polyimide or the like, having a predetermined thickness, a first surface facing the developer sleeve, a second surface facing the transfer belt, a transversal axis 51 extending parallel to the rotation axis of the developer sleeve 33 across the whole print area, and a plurality of apertures 52 arranged through the substrate 50 from the first to the second surface thereof. The first surface of the substrate is coated with a first cover layer 501 of electrically insulating material, such as for example parylene.
A first printed circuit, comprising a plurality of control electrodes 53 disposed in conjunction with the apertures, and, in some embodiments, shield electrode structures (not shown) arranged in conjunction with the control electrodes 53, is arranged between the substrate 50 and the first cover layer 501. The second surface of the substrate is coated with a second cover layer 502 of electrically insulating material, such as for example parylene. A second printed circuit, including a plurality of deflection electrodes 54, is aπanged between the substrate 50 and the second cover layer 502.
The printhead structure 5 further includes a layer of antistatic material (not shown), preferably a semiconductive material, such as silicium oxide or the like, arranged on at least a part of the second cover layer 502, facing the transfer belt 1. The printhead structure 5 is brought in cooperation with a control unit (not shown) comprising variable control voltage sources connected to the control electrodes 53 to supply control potentials which control the amount of toner particles to be transported through the corresponding aperture 52 during each print sequence.
The control unit further comprises deflection voltage sources (not shown) connected to the deflection electrodes 54 to supply deflection voltage pulses which controls the convergence and the trajectory path of the toner particles allowed to pass through the corresponding apertures 52. The control unit, in some embodiments, even includes a shield voltage source (not shown) connected to the shield electrodes to supply a shield potential which electrostatically screens adjacent control electrodes 53 from one another, preventing electrical interaction therebetween. In a preferred embodiment of the invention, the substrate 50 is a flexible sheet of polyimide having a thickness on the order of about 50 microns. The first and second printed circuits are copper circuits of approximately 8-9 microns thickness etched onto the first and second surface of the substrate 50, respectively, using conventional etching techniques. The first and second cover layers (501, 502) are 5 to 10 microns thick parylene laminated onto the substrate
50 using vacuum deposition techniques. The apertures 52 are made through the printhead structure 5 using conventional laser micromachining methods. The apertures 52 have preferably a circular or elongated shape centered about a central axis, with a diameter in a range of 80 to 120 microns, alternatively a transversal minor diameter of about 80 microns and a longitudinal major diameter of about 120 microns. Although the apertures 52 have preferably a constant shape along their central axis, for example cylindrical apertures, it may be advantageous in some embodiments to provide apertures whose shape vanes continuously or stepwise along the central axis, for example conical apertures
In a preferred embodiment of the present invention, the pπnthead structure 5 is dimensioned to perform 600 dpi pnntmg utilizing three deflection sequences in each pnnt cycle, I e three dot locations are addressable through each aperture 52 of the pπnthead structure during each pnnt cycle Accordingly, one aperture 52 is provided for every third dot location in a transverse direction, that is, 200 equally spaced apertures per inch aligned parallel to the transversal axis 51 of the pπnthead structure 5 The apertures 52 are generally aligned in one or several rows, preferably in two parallel rows each compπsing 100 apertures per inch Hence, the aperture pitch, I e the distance between the central axes of two neighbonng apertures of a same row is 0,01 inch or about 254 microns The aperture rows are preferably positioned on each side of the transversal axis 51 of the pπnthead structure 5 and transversally shifted with respect to each other such that all apertures are equally spaced in a transverse direction The distance between the aperture rows is preferably chosen to correspond to a whole number of dot locations
The first pnnted circuit compπses control electrodes 53 each of which having a nng shaped structure surrounding the peπphery of a corresponding aperture 52, and a connector preferably extending in the longitudinal direction, connecting the πng shaped structure to a coπespondmg control voltage source Although a πng shaped structure is preferred, the control electrodes 53 may take on vaπous shape for continuously or partly surrounding the apertures 52, preferably shapes having symmetry about the central axis of the apertures In some embodiments, particularly when the apertures 52 are aligned in one single row, the control electrodes are advantageously made smaller in a transverse direction than m a longitudinal direction
The second pnnted circuit compnses a plurality of deflection electrodes 54, each of which is divided into two semicircular or crescent shaped deflection segments 541, 542 spaced around a predetermined portion of the circumference of a corresponding aperture 52 The deflection segments 541, 542 are arranged symmetπcally about the central axis of the aperture 52 on each side of a deflection axis 543 extending through the center of the aperture 52 at a predetermined deflection angle d to the longitudinal direction The deflection axis 543 is dimensioned in accordance with the number of deflection sequences to be performed in each pπnt cycle in order to neutralize the effects of the belt motion during the pπnt cycle, to obtain transversally aligned dot positions on the transfer belt For instance, when using three deflection sequences, an appropπate deflection angle is chosen to arctan(l/3), i.e. about 18,4; . Accordingly, the first dot is deflected slightly upstream with respect to the belt motion, the second dot is undeflected and the third dot is deflected slightly downstream with respect to the belt motion, thereby obtaining a transversal alignment of the pnnted dots on the transfer belt Accordingly, each deflection electrode 54 has a upstream segment 541 and a downstream segment 542, all upstream segments 541 being connected to a first deflection voltage source Dl, and all downstream segments 542 being connected to a second deflection voltage source D2.
Three deflection sequences (for instance: D1<D2, D1=D2; D1>D2) can be performed in each pπnt cycle, whereby the difference between Dl and D2 determines the deflection trajectory of the toner stream through each aperture 52, thus the dot position on the toner image.
Numeral 6 denotes a cleaning unit for removal of residual charged particles from the pnnthead structure 5 after formation of the image.
It is pointed out that the apparatus descnbed above and shown in the drawings only constitutes a non-limiting example of an image forming apparatus and the invention can be applied in any kind of image forming apparatuses according to the DEP concept.
Toner particles essentially consist of a binding resin, a colouπng agent, electnc charge control agents (CCA). The binding resin is the main component of a toner. In conventional toners styrene acrylic resins and polyester resins are often used as binder resin. According to the invention, especially in the case of forming soldenng resist patterns, it is be preferred that the toner particles used per se or after a melting and cunng resists a temperature of at least 150°C, preferably at least 200°C and more preferably at least 250 °C, preferably dunng at least 3 minutes This could be accomplished by using toner particles that contain a binding resin in the form of a thermoplastic or thermosettmg resin, for example epoxy resins.
Another example of a suitable binding resins are amorphous cyclic polyolefmes Other components of the binder resin could be polyester resms, epoxy resins, polyolefin resins, vinyl acetate group resms, vinyl acetate group copolymenzation resins, styrene acrylic resins, and other acrylic type resins.
Polyolefmes with the cyclic structure used herein are preferably copolymers of an alicyclic compound with double bonds, such as cyclohexene or norbornene and an alpha-olefm, such as ethylene, propylene or butylene for example. According to a preferred embodiment the cyclic polyolefin is a copolymer of ethylene and norbornene These resms are amorphous, colourless, transparent and have a high transmissivity. Polyolefmes with this cyclic structure are polymers obtained by polymenzation methods using for example metallocene group or Ziegler group catalysts.
Toner of the intended kind using a cyclic polyolefmes as a binding resm component are further disclosed in WO 97/05529 the disclosure of which is included herein as a reference.
The compatibility of the cyclic polyolefmes with other binder resin components and dispersabihty of a pigment (colouring agent) can be improved by coupling a carboxy group, a carboxyhc acid anhydnde, a hydroxy group and/or an amino group to the cyclic polyolefin. Furthermore when the cyclic polyolefin is a copolymer of diene monomers, such as norbornadiene or cyclohexadiene, the carboxy group can be guided by a structure of cross linkage by addition of a metal, such as zmc, copper and calcium to the cyclic polyolefin resin. It would also be possible to use thermoplastic resins which can withstand the high temperatures and are not washed away from the printed circuit boards or that the soldering tin penetrates under them.
Functional additives such as colouring agents, electric-charge control agents (CCA), waxes etc. are added to the binder resin for providing the desired toner composition. Toner particles of the desired particle size are produced by conventional methods such as pulverization and classification.
An important advantage of using cyclic polyolefines according to the invention as binding agent is that they withstand higher temperatures than e g the traditionally used polyesters, which means that the functional additives mentioned above may be admixed with the binding agent at higher temperatures and by that a lower viscosity. This gives a more homogeneous admixture of the additives in the binding agent. Besides and more important the toner particles will withstand the high temperatures during subsequent processing of the printed circuit board substrate, especially soldering.
The toner particles should preferably have a narrow particle size distribution with an average volume diameter comprised in the range of 3 to 30 μm, or depending on the resolution that is desired. Small toner particles provides improved printing results as compared to larger toner particles and/or toner particles of varying size. Small particles melt over a smaller area after fusing, which makes it possible to print sharper dots, lines and images with small particles than with large particles. Another important advantage is that less toner particles are needed with smaller particle sizes.
Examples of colouring agents are carbon black, diazo yellow, copper phtalocyanine blue, quinacridone, carmine 6B, mono azo ed, perylene, green dye or pigment etc.
Examples of electric-charge control agents are a Nigrosine dye, a chrome complexity of a 5-di-tert-butyl salicylic acid, a quaternary ammonium salt, a triphenylmethane dye, an azo chrome complexity etc. Examples of surface treatment additives on the toner particles are a colloidal silica, aluminum oxide, titanium oxide, barium stearate, calcium stearate, lauric acid barium etc.
In the case a conductive pattern is to be formed on the printed circuit board substrate the toner particles used must be of an electrically conductive material, for example a conductive metallic powder. They should in this case be covered with an insulating layer so that they may be electrically charged for the printing process. At the curing the insulation is broken so that the toner becomes conductive.
It may according to the invention be possible to use a higher printing speed than feeding speed of the printed circuit board substrate in order to achieve enough toner on the substrate during one print. By for example running the printer at 50 mm/s and the substrate feeding at 10 mm/s it would be possible to increase the toner transfer five times. This means that approximately 3000 dpi could be printed in vertical direction and up to 600 dpi in horizontal direction using the above described DEP apparatus.

Claims

1. A method for pattern formation on a pπnted circuit board member, compπsing
-converting an image information corresponding to a pattern which is to be formed on the pnnted circuit board substrate (13) into a pattern of electrostatic fields including:
-modulating a transport of charged toner particles from a particle earner (3 ) towards a back electrode member (12);
-producing a background electnc field to enable a transport of said charged toner particles from said particle earner towards said back electrode member;
-providing an apertured pnnthead structure (5) in said background electnc field, said pnnthead structure including a plurality of apertures (52) and control electrodes (53) arranged in conjunction to the apertures;
-connecting voltage sources to said control electrodes (53) to supply control potentials to said control electrodes to produce a pattern of electrostatic fields in accordance with the image information to selectively permit or restnct the transport of charged toner particles from the particle earner (3) through the apertures (52); and
-conveying the printed circuit board substrate (13) or an intermediate image receiving member in relation to the pnnthead structure (5) for intercepting the transported charged toner particles m image configuration
-using charged toner particles which per se or after a hardening reaction resist the temperature of soldering tin or soldenng alloy.
2. A method as claimed in claim 1, c h a r a c t e r i z e d i n that said image configuration corresponds to a resist pattern intended to be formed on the surface of the pnnted circuit board substrate (2).
3. A method as claimed in claim 2, c h a r a c t e r i z e d i n that said resist pattern is a soldenng resist pattern.
4. A method as claimed in any of the preceding claims, characterized in that said image configuration corresponds to a conductive pattem intended to be formed on the surface of the printed circuit board substrate (2).
5. A method as claimed in any of the preceding claims, characterized in that said image configuration corresponds to any pattern, characters, symbols and the like intended to be formed on the surface of the printed circuit board substrate (2).
6. A method as claimed in any of the preceding claims, characterized in using charged toner particles which per se or after a hardening reaction resists a temperature of at least 150°C, preferably at least 200°C and more preferably at least 250 °C, preferably during at least 3 minutes.
7. A method as claimed in claim 6, characterized in using toner particles containing a binding resin in the form of a thermoplastic or thermosetting resin.
8. A method as claimed in claim 7, characterized in using toner particles that are transported from said particle carrier (3) containing a binding resin in the form of an epoxy resin.
9. A method as claimed in claim 7, characterized in using toner particles that are transported from said particle carrier (3) containing a binding resin in the form of a cyclic polyolefin.
10. An image forming apparatus as claimed in claim 9, c h a r a c t e r i z e d i n that said cyclic polyolefines are copolymers of an alicyclic compound with double bonds, such as cyclohexene or norbornene, and an alpha-olefin, such as ethylene, propylene or butylene.
11. A method as claimed in any of the preceding claims, c h a r a c t e r i z e d i n using a printing speed that is higher than the feeding speed of the printed board circuit substrate.
12 An apparatus for pattern formation on a printed circuit board member, comprising an image forming apparatus in which an image information corresponding to a pattern which is to be formed on the printed circuit board substrate is converted into a pattern of electrostatic fields for modulating a transport of charged toner particles from a particle carrier (3) towards a back electrode member (12), said image forming apparatus including:
-a background voltage source for producing a background electric field which enables a transport of charged toner particles from said particle carrier (3) towards said back electrode member (12);
-a printhead structure (5) arranged in said background electric field, including a plurality of apertures (52) and control electrodes (53,54) arranged in conjunction to the apertures;
-control voltage sources for supplying control potentials to said control electrodes (53,54) in accordance with the image information to selectively permit or restrict the transport of charged toner particles from the particle carrier (3) through the apertures (52);
-the printed circuit board substrate (13) or an intermediate image receiving member is caused to move in relation to the printhead structure (5) for intercepting the transported charged particles in image configuration.
- said charged toner particles per se or after a hardening reaction resist the temperature of soldering tin or soldering alloy.
13. An apparatus as claimed in claim 12. characterized in that said charged toner particles per se or after a hardening reaction resists a temperature of at least 150°C, preferably at least 200°C and more preferably at least 250°C, preferably during at least 3 minutes.
14. A toner container holding toner particles for use in an image forming apparatus in which an image information corresponding to a pattern which is to be formed on the printed circuit board substrate is converted into a pattern of electrostatic fields for modulating a transport of charged toner particles from a particle carrier (3) towards a back electrode member (12), said image forming apparatus including:
-a background voltage source for producing a background electric field which enables a transport of charged toner particles from said particle carrier (3) towards said back electrode member (12);
-a printhead structure (5) arranged in said background electric field, including a plurality of apertures and control electrodes (53,54) arranged in conjunction to the apertures;
-control voltage sources for supplying control potentials to said control electrodes (53,54) in accordance with the image information to selectively permit or restrict the transport of charged toner particles from the particle carrier (3) through the apertures;
-an image receiving member (1) caused to move in relation to the printhead structure (5) for intercepting the transported charged particles in image configuration characterized in said charged toner particles per se or after a hardening reaction resist the temperature of soldering tin or soldering alloy.
15. A toner container as claimed in claim 14 characterized in that said toner container (30) contains charged toner particles which per se or after a hardening reaction resists a temperature of at least 150°C, preferably at least 200 °C and more preferably at least 250 °C, preferably during at least 3 minutes.
PCT/SE2001/000446 2000-03-02 2001-03-02 Direct electrostatic printing method and device for manufacturing printed circuit boards WO2001065896A1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU2001237866A AU2001237866A1 (en) 2000-03-02 2001-03-02 Direct electrostatic printing method and device for manufacturing printed circuit boards

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
SE0000680A SE0000680D0 (en) 2000-03-02 2000-03-02 Method and device for manufacturing printed circuit boards
SE0000680-9 2000-03-02

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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4897326A (en) * 1985-04-09 1990-01-30 Telettra-Telefonia Electronica E Radio, S.P.A. Process to manufacture printed circuit boards
US5576135A (en) * 1994-03-29 1996-11-19 Olympus Optical Co., Ltd. Processing method based on resist pattern formation, and resist pattern forming apparatus
EP0823676A1 (en) * 1996-08-08 1998-02-11 Agfa-Gevaert N.V. A method for direct electrostatic printing (DEP) on an insulating substrate
EP0952498A1 (en) * 1998-04-22 1999-10-27 Agfa-Gevaert N.V. Direct electrostatic printing process for forming a resist pattern on a conducting surface and use thereof in a fabrication process for printed circuit boards

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4897326A (en) * 1985-04-09 1990-01-30 Telettra-Telefonia Electronica E Radio, S.P.A. Process to manufacture printed circuit boards
US5576135A (en) * 1994-03-29 1996-11-19 Olympus Optical Co., Ltd. Processing method based on resist pattern formation, and resist pattern forming apparatus
EP0823676A1 (en) * 1996-08-08 1998-02-11 Agfa-Gevaert N.V. A method for direct electrostatic printing (DEP) on an insulating substrate
EP0952498A1 (en) * 1998-04-22 1999-10-27 Agfa-Gevaert N.V. Direct electrostatic printing process for forming a resist pattern on a conducting surface and use thereof in a fabrication process for printed circuit boards

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AU2001237866A1 (en) 2001-09-12

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