WO2010078611A1

WO2010078611A1 - Printed circuit board element having at least one laser beam stop element and method for producing a printed circuit board element

Info

Publication number: WO2010078611A1
Application number: PCT/AT2010/000004
Authority: WO
Inventors: Markus Leitgeb; Andreas Zluc; Alexander Kasper
Original assignee: At & S Austria Technologie & Systemtechnik Aktiengesellschaft
Priority date: 2009-01-09
Filing date: 2010-01-08
Publication date: 2010-07-15
Also published as: JP2012514859A; EP2386193A1; AT12321U1; JP5693468B2; CN102349360B; CN102349360A

Abstract

The invention relates to a printed circuit board element (1), in particular a multilayer printed circuit board element, comprising a plurality of dielectric layers (5, 6, 7) and conductor layers (8, 9, 10, 11), and comprising a dedicated laser beam stop element (14), which is different from the conductor layers (8, 9, 10, 11) on the inside of the printed circuit board element in order to prevent a laser beam used for drilling or cutting from penetrating deeper into the printed circuit board element, wherein the laser beam stop element is formed by laser beam energy-absorbing and/or -reflecting particles, and to a method for the production thereof.

Description

Printed circuit board element with at least one

Laser beam stop element and method for producing a printed circuit board element

Field of the invention

The invention relates to a printed circuit board element, in particular multilayer printed circuit board element, with a plurality of dielectric layers and conductor layers, and with at least one separate laser beam stop element in the interior of the printed circuit board element, around a laser beam used for drilling or cutting at a deep penetration into the Prevent PCB element.

Furthermore, the invention relates to a method for producing such a printed circuit board element.

Background of the invention

Circuit board elements are generally constructed of different layers which are adhesively bonded together, whereby a thermal pressing process can be used. In the case of multi-layer printed circuit board elements, so-called multilayer printed circuit board elements, a plurality of dielectric layers (insulating layers) and metallizations (conductor layers) are stacked on top of each other, thus producing conductive connections between electronic components at several levels. Usually, such printed circuit board elements are made of resin layers, e.g. Epoxy resin layers, and copper layers constructed, wherein at least two layers are provided.

For the production of conductive connections to internal components, bores up to predetermined depths are to be provided in such printed circuit board elements. If there is to be an electrical connection between conductive planes, the holes thus produced can subsequently be galvanically copper plated, for example. In general, often cutting or drilling of these circuit board elements is required with control of the depth of cut or drilling, for which cutting or drilling in usually a laser, such as a CO ₂ laser, is used. Although it is also possible to use a general depth control method, this is of limited use. For cutting and drilling with laser beams, for example, a copper layer inside the structure of the printed circuit board element serves to prevent the laser beam from penetrating deeper into the printed circuit board element, ie to stop the cutting or drilling process. Here, this stopping effect is based on the fact that copper layers or generally metal layers reflect very well in the visible or infrared light range; For example, a CO ₂ laser beam is reflected well on a copper layer. In contrast, a laser beam would cut copper in the UV range.

However, in the case of printed circuit board elements with already structured inner layers, the problem arises that the conductor layer (for example a copper layer) is only locally present due to structuring, but at other places the metallization is etched away so that, for example, two resin layers are directly connected to one another; Similarly, a solder mask can connect directly to an epoxy resin layer. In such places, where resin layers adjoin one another or a solder mask adjoins a resin layer, the above-described laser stop function is no longer present since the metallization required for this purpose is lacking. In these cases, it is difficult to determine the depth of cut or depth of the laser beam, i. its penetration into the structure of the printed circuit board element to control.

To remedy this situation, in the prior art (see US 4,931,134 A, JP 3-165594 A, JP 5-235556A and JP 2002-271039 A) the attachment of separate, additional laser beam stop elements, e.g. in strip form made of copper, which are intended to reflect the laser beam and thus prevent it from further penetrating into the laser plate element structure.

Summary of the invention

It is an object of the present invention to provide a printed circuit board element or a method as stated above, wherein an alternative, easy-to-install laser beam stop is used and it is possible, in the case of an already made patterning of inner layers, to ensure an efficient and reliable control of the depth of cut or depth of a laser beam inside a printed circuit board element.

To achieve this object, the invention provides a printed circuit board element as in claim 1 and a method as specified in claim 9. Advantageous embodiments and further developments are specified in the dependent claims.

In the present technique, therefore, a separate, "additional" stop element for the laser beam is also introduced, but this stop element is now formed with small particles which receive and / or reflect the laser beam energy, and whose size is in particular in the nm to μm. These particles consist in particular of a suitable metal, for example of gold, silver, copper, aluminum, tin and / or lead, but it is also possible to use other suitable refelective or fusible materials, for example ceramic particles. The particles, which may be, for example, spherical or platelet-shaped, are so small that the laser beam can not easily penetrate through the material of the layer, for example because of multiple reflection on the particles, if they are larger, or if the particles are not round but are platelet-shaped, or when a large proportion of particulate binder is present to the large particles with connect to each other, in which case this binder can not be reflected and penetrated by the laser beam. Even with such larger particles in the stop element, the reflection may be poor. In this way, it would be conceivable that with the laser beam enough energy can be introduced into the stop member to penetrate this, rather than that the laser beam is stopped. For small particles, however, on the one hand, the binder content can be very low, and on the other hand, the energy of the laser beam can be used to melt the material, or can be higher due to the higher proportion of particles, the reflection.

For the size of the particles can be taken as a standard, that the particles should have a "nano-character", ie the particles should have a size at which the melting point of the nanoparticles deviates from the melting point of the general printed circuit board material, for example, with particles of silver having a particle size of about 100 nm proved to be advantageous.

This own stop element can, at least in those places where the restriction of the depth of cut or depth of the laser beam is desired, but of course also be applied over the entire surface of the underlying layer; In particular, it can also be structured in a conventional manner. For structuring, a printing technique for local application, such as ink-jet printing, screen printing or the like, may preferably be used. A structuring is also possible if the material of the additional stop layer is equipped in a conventional manner photosensitive, so that then with the aid of a conventional photoprocess, the structuring can be performed. Also for this purpose, printing techniques, as indicated above, or other coating methods, for example: spraying, etc., can be used.

In the mechanism according to the present technology, with the use of small particles, the energy of the laser beam can also be used to completely or partially melt the particles, thereby stopping the laser beam at this point, except that the laser beam is similar on the known copper layer, completely or at least for the most part can be reflected. By the thermal contact of the particles in the laser beam impingement area, by the way, a cooling effect, a heat dissipation, is effected.

The present stop element is preferably provided as an additional layer part, in particular in the form of a paste, and used up, e.g. printed, this paste containing the small particles and the binder.

It is also conceivable, the stopper for stopping a laser beam in a layer above or below a removable Separating layer or between two removable separating layers. For example, such release liners are used to prevent overlying and underlying resin layers from sticking together. This is provided, for example, when a part of a substrate, ie a rigid resin layer, is to be subsequently removed in order to obtain a so-called rigid-flex printed circuit board, cf. For example WO 2008/098269 A, WO 2008/098270 A, WO 2008/098271 A and WO 2008/098272 A. The attachment of the stop element to or between the separating layers also has the advantage that it can be removed together with the separating layers.

On the other hand, the laser stop element can also be present as a separate, prefabricated film (tape) and, for example, laminated onto a resin layer or inserted into a resin layer. Also in this case, there is a layered, separate, independently of the conductor layers mounted laser stop element, which is attached as an additional layer.

A frequently particularly favorable embodiment is further characterized in that the present particles are or are incorporated directly as a filler in one of the layers of the printed circuit board element. For example, the particles may be introduced into a respective resin layer of the circuit board member, but they may be incorporated in or contained in the aforementioned separation layers, in which case the separation layer additionally functions as a stopper member; Similarly, in the aforementioned case of incorporation of filler nano-particles into a resin layer, the latter serves as a laser stop pest.

Incidentally, as a rule, a plurality of such stop elements will be present on a printed circuit board element as stop elements mounted in addition to conductor layers.

Brief description of the drawing

The invention will be further elucidated on the basis of preferred exemplary embodiments, to which, however, it should not be restricted, and with reference to the enclosed drawing. In detail in the drawing: Fig. 1 shows a per se known multilayer printed circuit board element in a very schematic cross section, wherein also only very schematically a laser beam for cutting or drilling a Kontaktierungslochs for a conductor layer is shown in the interior of the conductor element, wherein the laser beam to the inner conductor layer in a conventional manner (by reflection) is stopped;

Fig. 2 is a similar schematic cross-sectional view, but now compared to Fig. 1, the inner conductor layer is structured, so that the laser beam, when it is directed to a point where the inner conductor layer has no metal through the structuring, at a deeper Penetration is not hindered;

3 shows a comparable schematic cross section through a printed circuit board element, wherein, however, a separate stop element with small particles for stopping the laser beam is now provided;

Fig. 4 is a similar cross section, but here with only two PCB layers, again with an additional stop element is provided for the laser beam, but now between two removable separating layers;

Figure 4A is a cross-sectional view similar to Figure 4, but now with only a removable release liner on which an auxiliary stop member is mounted;

Fig. 5 shows a single layer with a resin layer and an attached, already structured conductor layer, as well as with a layer provided above with small particles, which form an additional layer for the production of a separate element for stopping a laser beam during cutting or drilling of the finished Printed circuit board element is provided; and

6 shows a multilayer structure with three layers still shown separately for the multilayer structure, wherein the middle layer corresponds to that according to FIG. 5, after the additional layer has been patterned in order to form the additional stop elements according to the invention. düng to form, and wherein schematically also the pressing of the individual layers to the multilayer printed circuit board element is illustrated.

Detailed description of preferred embodiments

In Fig. 1 is very schematic and not to scale a conventional per se structure of a multilayer printed circuit board element 1 is shown, wherein by way of example three layers 2, 3 and 4 are shown, but without the printed circuit board element structure should be limited thereto. Specifically, there are three resin layers 5, 6 and 7 made of, for example, epoxy resin as known per se, and may contain glass fibers for reinforcement. Further, in the example shown, there are four conductor layers (metal layers, usually copper layers) 8, 9, 10 and 11, two of which are 8, 11 on the outside of the structure, whereas the copper layers 9 and 10 are inside. Very schematically, a laser beam 12 is further indicated in Fig. 1; This laser beam 12 is used for drilling contact holes or for applying cuts, for example for removing parts of printed circuit board layers. Such a removal of printed circuit board layer parts is provided, for example, when flexible parts of the printed circuit board element are desired, that is to say a so-called rigid flex printed circuit board is to be produced. The penetration depth of the laser beam 12 is limited as shown in FIG. 1 by the inner copper layer 9, since this copper layer or metallization 9, the laser beam, such as a CO ₂ laser beam, well reflected. Due to this reflection on the copper layer 9, therefore, the laser beam 12 can not penetrate further into the interior of the structure of the printed circuit board element 1.

In general, metals used for conductor layers 8, 9, 10 and 11 reflect laser light in the visible or infrared range well; However, a laser beam in the UV range would cut a copper layer, for example. For such UV lasers, therefore, the penetration depth during drilling or cutting of circuit board elements is otherwise controlled, with special, non-metallic spacer material parts embedded in the layer structure, their function in providing a space or distance is located for the UV laser, and which can be destroyed during drilling or cutting with the UV laser. However, this method with the known "Distanzelmenten" is only suitable for a relatively slow cutting or drilling and requires the insertion of the spacer material in the interior of about the resin layers.

If, when cutting a printed circuit board element 1 with a laser beam 12 in the visible light range or in the infrared range, there is the situation that the inner conductor layer, e.g. the copper layer 9, already structured, cf. Fig. 2, wherein regions 13 are present in this conductor layer 9 without metal, so there is no reflection of the laser beam 12 on a metal surface, and the laser beam 12 penetrates deeper than intended in the circuit board element 1, as shown in Fig. 2. Although it would be conceivable to regulate the penetration depth of the laser beam 12 due to the control of the turn-on of the laser beam 12, but this method is too inaccurate and also depends u.a. from the thicknesses and materials of the respective layers, in particular the resin layers 5, etc., which may well vary.

If a solder mask is already provided at the location of the conductor layer 9 (or also the conductor layer 10, if there also should be structuring), metallization nevertheless still lacks at the locations 13, so that the penetration depth of the laser beam 12 is not without can be further controlled or limited.

To remedy this situation, at the required locations, namely, where later with the help of the laser beam 12, a cut or a hole to be applied, and where already the conductor layer, for example, the copper layer 9, is structured, a separate, independent, additional stop element - also called additional stop element 14 - attached; this auxiliary stopper 14 is mounted independently of (in addition to) the conductor layers, eg 9, and is formed with small particles which act as a laser beam stopper by reflecting the laser beam 12 thereon and / or its energy for reflowing is used by particles in this additional stop element 14. In FIG. 3, by way of example, such a locational The additional stop element 14 is shown in a metallization-free region 13 in an already structured conductor layer 9 of a printed circuit board element 1, which is otherwise constructed as shown in FIGS. 1 and 2.

The additive stopper 14 includes, as mentioned, small particles connected by a binder, which particles are so small that they melt earlier than the entire material complex. For example, silver particles and gold particles were tested for these "nano" particles, and it has been shown that good results can be achieved with silver particles and gold particles having a particle size of about 100 nm.

These small particles, whose size can extend into the micron range, are so small that in the stopper 14 and little binder is needed, which is advantageous because this binder is not useful for the stop function and may reflect the reflection of the Laser beam 12 hindered on the nano-particles. In the case of particles which are too large, a multiple reflection (or a relatively high proportion of binder increases absorption) can also occur due to the geometry of the particles, in which case penetration of the laser light through the region or the layer of the stop element 14 would be possible Laser beam nonetheless penetrates too deeply. Of importance for the present stop element 14 and its stop function are therefore the "smallness" of the particles in conjunction with the low binder content, or the reflection and absorption properties, in which case the energy of the laser beam 12 is also used, if necessary, the nano- Melting apart particles, except that the reflection at the stop element 14 can be comparable to that at a copper layer 9 (see Fig. 1), at any rate high.

Other materials for the nano-particles would be, for example, copper, tin, lead, aluminum, generally metals that can be made into the "nano" particles, but also ceramics.

For example, epoxy resins have proven suitable as binders; it may solvents based on α-terpin oil be used for the additional layer mass.

With such or similar binders and such nanoparticles as indicated, e.g. a layer mass can be produced in the form of a paste, which can be easily applied in the course of the production of the printed circuit board element 1 - as an addition to the other components. In particular, to apply this paste to the stop member 14, a variety of printing techniques, including screen printing or ink jet printing, and other coating techniques, e.g. also spray coating. One possibility is also to first apply the paste in the form of a surface layer and then to structure this surface layer, which can be done by means of known photo-exposure techniques (with subsequent development processes) if photosensitive properties are provided for the paste. This will be explained in more detail below with reference to FIGS. 5 and 6.

In operation, the energy of the laser beam 12 is absorbed by the small particles, which energy is used to partially or completely melt the particles. Furthermore, the laser beam 12 is partially or completely reflected. An advantage is further that, due to the thermal contact of the particles, the area where the laser beam 12 impinges is cooled, since heat is transported away by the particles.

The present laser beam stop 14 is particularly useful in applications where cuts are made in the printed circuit board element 1 by the laser beam 12, such as around a portion of a sheet, e.g. Layer 2 (see Fig. 1) so as to provide by removing the rigid resin part at this point a possible flexible printed circuit board area, as is known in the art.

When removing parts of layers of a printed circuit board element, it is also known, as mentioned at the beginning, to install removable separating layers so as to prevent layers from sticking together at this point. However, these separating layers do not act as such as stop elements for the laser beam 12. The provision of such separating layers, such as the separating layers 15, 16 in Fig. 4 or the individual separation layer 16 in FIG. 4A, can now be combined with the attachment of a laser beam stop element 14 as explained in principle with reference to FIG. 3, cf. 4 and 4A. In this case, it is possible to attach the additional or own stop element 14 between two separating layers 15, 16 (see FIG. 4), or to mount them on a separating layer 16 (see FIG. 4A). Of course, it would also be possible, depending on the circumstances, to provide the stop element 14 even below such a separating layer (eg 15 in FIG. 4) without attaching a further separating layer 16 underneath.

In the case of FIGS. 4 and 4A, for example, a part 17 of the upper layer 5 with 8 could be removed from the remaining printed circuit board element 1. This part 17 can be self-contained, e.g. its rectangle being formed by at least one separating layer 15, 16 and the stop element 14, and wherein the cut is made with the aid of the laser beam 12 around this part 17 in order to finally be able to remove the part 17. This is not shown in detail in FIGS. 4 and 4A, but in itself, apart from the present stop element 14, is conventional technology.

In Fig. 5, a layer, e.g. the layer 3 of the printed circuit board element 1 according to FIG. 1, with a resin layer 6 and an already structured conductor layer 9 applied thereon. As a result of the structuring, regions 13 are present in the conductor layer 9, where there is no more metallization. This situation according to FIG. 5 is provided for an inner layer of a multilayer printed circuit board element 1 approximately according to FIGS. 1 to 3.

For the attachment of the own stop elements 14 in the areas 13, a particle surface layer 14 'is now provided on the layer 3 in this example, for example, by brushing the paste and doctoring by spraying (spray-coa- ting), imprints or a similar known method can be done. This surface layer 14 'of the paste with the nano-particles and the binder is additionally equipped with a photosensitive element, for example a commercially available photoinitiator together with a binder to be crosslinked. As a result, by appropriate exposure through a mask, the surface layer 14 'partially cured and partially attackable for an etchant (or photographically developable) are designed so that in a subsequent etching (or development step), much as in the structuring of Conductor layers, eg 9, takes place, a structured additional layer is obtained as a stop element 14, cf. Fig. 6.

The inner layer 3 is then stacked as shown in FIG. 6 together with the outer layers 2, 4 (and optionally with other inner layers, which are not shown) in a conventional manner on each other and - usually in conjunction with other such layer packages in the Type of "book", as it is known per se - arranged in a press and then with heating, in order to connect the layers 2, 3 and 4 sticking together, pressed, see the press parts 18, 19 shown in Fig 6. (It should be mentioned here that, of course, there are also non-thermal connection possibilities which can also be used if the present additional stop elements 14 are installed.)

Such pressing can of course also take place if the additional stop elements 14 have been attached in a different manner, for example by screen printing, at the desired locations (ie "structured").

Another way of achieving the present stop elements 14 independently of the conductor layers 8, 9, 10, 11 is, for example, also to incorporate the aforementioned particles directly as fillers in suitable layers or layers in a suitable manner. The particles are thus in this case directly, as a "filler" in the resin system of a resin layer of the printed circuit board element or else optionally in a release layer 15 or 16 (in which case only one such release layer will be present), and the resin layer or Separation layer then acts as a laser stop layer or layer, ie as a laser stop element 14, again independently of the conductor layers 8, 9, 10, 11th Another possibility for providing a stop element 14 may be that prefabricated stop elements 14 are present as a film (tape), wherein these stop element films are laminated on a (resin) layer or inserted in the layer structure.

With the present additional stop elements 14 for the laser beam 12, the stop properties can be influenced via the reflection or absorption properties for which the particles and their size or shape are responsible, in particular. The advantage here is that these additional stop elements 14 can be mounted anywhere in the multilayer structure, namely where later limiting the penetration depth of the laser beam when cutting or drilling of the printed circuit board element 1 is desired. These variable application sites, as well as the flexible application methods, are of particular advantage. It has also proven to be favorable that a paste can be printed in layer form, with the nano-particles, or added to the circuit board element in another form, after which the conductor layers have been patterned and etched, without using a copper layer in the sense of a base layer is that can stop a laser beam. Upon impact of the laser beam 12 on the auxiliary stop element 14, the small particles are reflected as mentioned, or possibly partially or completely melted and sintered to prevent the laser beam from further penetration into the printed circuit board element.

If the invention has been explained above with reference to particularly preferred embodiments, it will be obvious that changes and modifications are possible within the scope of the invention. Thus, in the drawing, as far as described so far, the laser stop element 14 is always shown (approximately) in a plane with the already structured conductor layer 9. But it is just as conceivable and possible, the additional stop element 14 within a resin layer, for example 6; to attach, as for the sake of simplicity in Fig. 3 - for the sake of simplicity additionally - indicated by dashed lines. This is easily possible, in particular, when the resin layers consist, for example, of two layers before the pressing or gluing, as in the case of resin systems, for example Epoxy resin layers, which are formed from so-called prepregs, which are originally in film form and can be simply superimposed for pressing, about to achieve an increased insulation layer. In the case of a photosensitive paste paste, technologies are also applicable, whereby only a single-stage development process is used as the photographic process. As far as the additional layer mass is concerned, there are, for example, pastes or inks filled with aluminum particles, wherein the aluminum particles are of the order of a few micrometers (eg approx. 4 μm) and are approximately platelet-shaped, so as to provide a layered arrangement during application (printing). to achieve.

Claims

Claims:

1. printed circuit board element (1), in particular multilayer printed circuit board element, with a plurality of dielectric layers (5, 6, 7) and conductor layers (8, 9, 10, 11), and with at least one own, of the conductor layers (8, 9 , 10, 11) of a different laser beam stopping element (14) inside the printed circuit board element, around a laser beam (12) used for drilling or cutting at a deep penetration into the

Prevent printed circuit board element, characterized in that the laser beam stop element (14) is formed with laser beam energy absorbing and / or reflecting small particles.

2. Printed circuit board element according to claim 1, characterized in that the particles are coated with a binder, e.g. a resin, in particular epoxy resin, are bonded to a layer part.

3. Printed circuit board element according to claim 1 or 2, characterized in that the particles have a size in the nm to μm range.

4. printed circuit board element according to one of claims 1 to 3, characterized in that the particles have a spherical shape.

5. printed circuit board element according to one of claims 1 to 3, characterized in that the particles have a platelet shape.

A circuit board element according to any one of claims 1 to 5, characterized in that at least some particles of metal, e.g. Silver and / or gold.

7. printed circuit board element according to one of claims 1 to 6, characterized in that at least some particles of ceramic material.

8. printed circuit board element according to one of claims 1 to 7, characterized in that the stop element (14) is an imprinted layer part.

9. printed circuit board element according to one of claims 1 to 8, characterized in that the stop element (14) is photolithographically structured.

10. printed circuit board element according to one of claims 1 to 9, characterized in that the stop element (14) on or in a removable separating layer (15, 16) or between two removable separating layers (15, 16) is mounted.

11. Printed circuit board element according to one of claims 1 to 7, characterized in that the stop element (14) is formed by an inserted or laminated film.

12. printed circuit board element according to one of claims 1 to 7, characterized in that the stop element (14) by the locally in a layer (6) or layer (15, 16) is incorporated as a filler particles.

13. A method for producing a printed circuit board element (1) according to any one of claims 1 to 12, wherein prior to connecting layers (2, 3, 4) of the printed circuit board element own, of the conductor layers (8, 9, 10, 11) different stop element (14) is mounted at the desired location, after which the layers are pressed with the inclusion of the additional stop element (14), characterized in that the laser beam stop element (14) is formed with laser beam energy absorbing and / or reflecting particles.

14. The method according to claim 13, characterized in that the stop element (14) on or in a removable separating layer (15, 16) or between two removable separating layers (15, 16) is attached.

A method according to claim 13 or 14, characterized in that particles of metal, e.g. Silver and / or gold, are used.

16. The method according to any one of claims 13 to 15, characterized in that the stop element (14) in a Druckverfah- ren, eg screen printing, inkjet printing or the like. , is applied in layers.

17. The method according to any one of claims 13 to 15, characterized in that the stop element (14) in a Sprühbeschich- processing method is layered.

18. The method according to any one of claims 13 to 15, characterized in that the layered stopper member (14) is light-sensitively equipped and patterned in a Photoätztechik- or photodevelopment process before the other (n) layer (s) attached and the layers ( 2, 3, 4) are pressed.

Method according to any one of Claims 13 to 18, characterized in that the stop element (14) is in the form of a paste, e.g. with a resin, such as epoxy resin, as a binder, is applied.

20. The method according to any one of claims 13 to 15, characterized in that the stop element (14) is attached as a prefabricated film, which is inserted between layers (2, 3, 15, 16) or laminated to a layer (3, 16) ,

21. The method according to any one of claims 13 to 15, characterized in that the particles are incorporated as a filler locally in a layer (15, 16) or layer (6).