US3725836A - Thick film varistor and method for making the same - Google Patents
Thick film varistor and method for making the same Download PDFInfo
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- US3725836A US3725836A US00146624A US3725836DA US3725836A US 3725836 A US3725836 A US 3725836A US 00146624 A US00146624 A US 00146624A US 3725836D A US3725836D A US 3725836DA US 3725836 A US3725836 A US 3725836A
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01C—RESISTORS
- H01C17/00—Apparatus or processes specially adapted for manufacturing resistors
- H01C17/06—Apparatus or processes specially adapted for manufacturing resistors adapted for coating resistive material on a base
- H01C17/065—Apparatus or processes specially adapted for manufacturing resistors adapted for coating resistive material on a base by thick film techniques, e.g. serigraphy
- H01C17/06506—Precursor compositions therefor, e.g. pastes, inks, glass frits
- H01C17/06513—Precursor compositions therefor, e.g. pastes, inks, glass frits characterised by the resistive component
- H01C17/06533—Precursor compositions therefor, e.g. pastes, inks, glass frits characterised by the resistive component composed of oxides
- H01C17/06546—Oxides of zinc or cadmium
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T29/00—Metal working
- Y10T29/49—Method of mechanical manufacture
- Y10T29/49002—Electrical device making
- Y10T29/49082—Resistor making
- Y10T29/49099—Coating resistive material on a base
Definitions
- This invention relates to thick film varistor having finely divided particles of zinc oxide dispersed in glass and a pair of electrodes applied to said thick film and to a method for making the same.
- varistors such as silicon carbide varistor, silicon diode and selenium varistor.
- a varistor is defined as a non-ohmic resistor the electrical resistance of which varies with the applied voltage.
- the electric characteristics of such a varistor are expressed by the following equation:
- V is the voltage across the varistor
- I is the current flowing through the varistor
- C is a constant equivalent to the electrical resistance at a given voltage
- n is a numerical value greater than 1.
- the value which it is desired that C have depends upon the particular use to which the varistor is to be put. It is ordinarily desirable that the value of n be as large as possible since this exponent determines the degree to which the varistor departs from ohmic characteristics.
- V is defined as a voltage at a flowing current of I, milliampere through the varistor.
- the varistor voltage referred to hereinafter is a voltage at milliamperes of flowing current.
- the value of n is calculated from the relation 1:
- V, and V are the voltages at the currents I and I respectively.
- a principal object of this invention is to provide a thick film varistor which can be fired on an insulating base.
- Another object of this invention is to provide a method for making a thick film varistor.
- a thick film varistor having a thick film of finely divided particles of zinc oxide dispersed in a glass frit which bonds the par-- ticles together, and by providing electrodes on the thick film.
- the varistor can be made by preparing a paste of the zinc oxide particles, the frit, and a liquid vehicle, applying the paste to an insulating base, and' heating the paste to evaporate the liquid vehicle and then melt the particles of frit to bond the particles of zinc oxide together, and thereafter applying the electrodes.
- one electrode can be applied to the insulating base, the thick film formed thereon, and a second electrode applied to the surface of the thick film.
- FIG. 1 is a cross section, on greatly enlarged scale, of
- FlG. 2 is a cross section, on a greatly enlarged on a highly exaggerated scale, of a varistor according to another embodiment of the present invention.
- a thick film varistor according to the present invention comprises a thick film 3 applied to an insulating base 1 and a pair of electrodes 2 and 2.
- Said thick film 3 has finely divided particles of zinc oxide 4 dispersed in glass frit 5.
- the glass 5 is a bonding material for finely divided particles of zinc oxide 4 and may be composed of any glass capable of bonding said finely divided particles of zinc oxide 4 upon hardening.
- An operable composition for said thick film 3 is 30 to 95 wt.% of finely divided particles of zinc oxide and the remainder glass.
- a high amount of glass makes the electrical resistance of the resultant thick film 3 higher and a lower amount of glass results in poorer adherence of the thick film to the insulating base.
- FIG. 2 The structure of the thick film varistor of FIG. 1 can be modified as shown in FIG. 2.
- a thick film 3 having finely divided particles of zinc oxide 4 dispersed in glass frit 5 is sandwiched between two electrodes 2 and 2 one of which is formed on an insulating base 1.
- said one electrode 2 formed on said insulating base may be replaced by a suitable and available metal plate such as silver, platinum, titanium or nickel.
- a method for making a thick film varistor contemplated by the present invention comprises the following steps; providing a varistor paste having finely divided particles of zinc oxide and finely divided particles of glass frit, as a solid ingredients, dispersed in a liquid vehicle; applying said varistor paste to an insulating base; heating the applied varistor paste to evaporate said liquid vehicle and to melt and finely divided particles of glass frit whereby the melted glass frit bonds said finely divided particles of zinc oxide together and forms a thick film upon hardening; and providing said thick film with two electrodes.
- This method can be modified in the following way:
- the varistor paste is applied to an electrode formed on an insulating base or to a metal plate acting as an electrode.
- the subsequentsteps are similar to those mentioned above.
- Said varistor paste can be prepared by dispersing a uniform mixture of glass frit powder and zinc oxide powder, as solid ingredients, homogeneously in a liquid vehicle.
- the weight proportion of zinc oxide powder to glass frit powder in said mixture is 30 to 95 wt.% of zinc oxide and 5 to wt.% of glass frit powder.
- the liquid vehicle may vary widely in composition. Any inert liquid can be employed for this purpose, for example, water, organic solvents, with or without thickening agents, stabilizing agents, or the like, for example, methyl, ethyl, butyl, propyl or higher alcohols, the corresponding esters such as the carbitol acetates, propionates, etc., the terpenes and liquid resins, for example, pine oil, alpha-terpenol, and the like, and other liquids without limitation, the function of the liquid vehicle being mainly to form a liquid or paste of the desired consistency for application purposes.
- inert liquid can be employed for this purpose, for example, water, organic solvents, with or without thickening agents, stabilizing agents, or the like, for example, methyl, ethyl, butyl, propyl or higher alcohols, the corresponding esters such as the carbitol acetates, propionates, etc., the terpenes and liquid resins, for
- the liquid vehicles may contain volatile liquids to promote fast setting after application, or they may contain waxes, thermoplastic resins such as cellulose acetate butyrate, or wax-like materials which are thermofluid by nature whereby the composition can be applied to an insulating base while at an elevated temperature so as to set immediately upon contact with the insulating base.
- the amount of said liquid vehicle relative to solid ingredient can vary with the manner of application.
- the operable weight ratio of liquid vehicle to solid ingredient is to 45 wt.% of liquid vehicle and 55 to 90 wt.% of
- An advantageous weight ratio is to 30 wt.% of liquid vehicle and 70 to 85 wt.% of solid ingredient. it is preferable that the viscosity of the resultant paste be 500 to 2,000 poises.
- the varistor paste is applied in a uniform thickness to the insulating base or to the electrode surface. This may be done by any application method such as a stencil, spray, print, dip or brush method.
- the varistor paste applied to the insulating base is dried, if necessary, to remove the liquid vehicle and then fired in an electrical furnace at a temperature at which the glass frit fuses so as to bond the zinc oxide powder particles and to adhere firmly to the insulating base.
- the firing temperature may vary with the composition of glass frit. It is preferable to adjust the firing temperature so as to be 400 to 850C.
- Finelydivided zinc oxide powder is prepared by pul verization of sintered zinc oxide which is heated at a temperature of 1100 to l500C for 0.5 to 10 hours.
- the pulverization of zinc oxide powder can be achieved in accordance with well known techniques.
- Said sintered zinc oxide may be pre-crushed into granules having a diameter of few millimeters by a crushing machine equipped with a steel or iron pestle and mortar.
- the granules are further pulverized into fine powder with a fine crusher such as a ball mill or vibration mill etc.
- the preferable particle size of the zinc oxide powder is 0.5 to 10 microns.
- n is improved when said zinc oxide powder has incorporated therewith 0.1 to 8 mole percent of one member selected from the group consisting of bismuth oxide (Bi- 0 lead oxide (PhD) and barium oxide (BaO).
- the incorporation can be achieved by a well known ceramic technique. A mixture of zinc oxide powder and additives of a given composition is heated at a high temperature of ll00 to 1500C and then crushed into fine powder in a manner similar to that described above.
- An operable glass frit for use in the varistor paste can be borosilicate glass, lead borosilicate glass, zinc leadborate glass and bismuth borosilicate glass. Most advantageous is zinc leadborate frit having a composition consisting essentially of 55 to 85 wt.% of PbO, 10 to wt.% of H 0 and 5 to 20 wt.% of ZnO.
- Said glass'frit can be prepared in accordance with a per se well known glass frit technique.
- a mixtureincluding desired starting materials is heated to a high temperature so as to form a glass frit and is quenched in I cle size for the particles of the glass frit is 0.5 to 20 microns.
- the electrodes 2 and 2' may be formed by any suitaelectroless-plating of nickel metal. It has been discovered according to the invention that a higher n is obtained by using a silver paint electrode which has finely divided particles of silver'dispersed in bonding glass. Care should be taken that the softening temperature of said bonding glass is not higher than that of the glass frit of the varistor paste.
- the silver paint is prepared by dispersing a mixture of silver powder and bonding glass frit powder in a liquid vehicle. Said mixture is preferablycomposed of 50 to 95 wt.% of silver powder and 5 to 50 wt.% of bonding glass frit powder.
- the composition of the bonding glass frit powder is controlled of 60 to 80 wt.% so that it is bismuth oxide, 10 to 20 wt.% of boron oxide and 10 to 20 wt.% of silica.
- the method of preparing the silver paint are essentially similar to those for the varistor paste mentioned above.
- Example 1 I of B 0 and 13.8 wt.% of ZnO is pulverized into a fine powder having an average particle size of 3 microns.
- a uniform mixture of wt.% zinc oxide powder and 25 wt.% of glass frit is prepared by a well known method.
- the uniform mixture of these solid ingredients is mixed well with a liquid vehicle consisting of '15 wt.% of ethyl cellulose and 85 wt.% of carbitol acetate to form a varistor paste having a composition consisting of wt.% of solid ingredient and 20 wt.% of liquid vehicle.
- silver paint No. 6730 (silver paint l) from Dupont Co. in U.S.A. is appliedto an aluminum oxide ceramic insulating base by a stainless steel screen stencil with a 200 mesh and is fired in air at 800C for 10 minutes by a tunnel type kiln so as to form a silver paint electrode.
- the varistor paste is applied to said silver paint electrode and is fired in air at 800C for 10 minutes by the tunnel kiln.
- the resultant thick film has a thickness of about 20 microns.
- Thesilver paint 1 is applied to the varistor film and is fired at 800C in a manner similar to that described above to form an upper silver paint electrode having an active area of 6X6 mm.
- the thick film varistor has electrical properties shown for sample No. 1 in Table 1.
- Example 2 A varistor paste similar to that or Example l is apthick film varistor are shown for sample No. 2 in Table l.
- Example 3 differs from Example 2 only in that it has a different electrode from Example 2. After the thick film has been formed on the insulating base in a manner similar to that of Example 2, the thick film is provided with two electrodes of zinc film prepared by a well known vacuum evaporation technique. The dimensions of the electrodes are similar to that of Example 2.
- Example 4 Compositions of zinc oxide with 2 mol of bismuth oxide (Bi- 2 mol of lead oxide (PbO), and 2 mol of barium oxide (8210), respectively, are heated at l350C for 1 hour and then pulverized into fine powder having an average particle size of 2 microns by using a stamp mill for pre-crush and a ball mill for fine pulverization.
- the zinc oxide powder compositions are used for formation of thick film varistors.
- the other formation steps are exactly similar to those of example
- the resultant electrical characteristics of n and V of these thick film varisto rs are shown for samples No. 4, 5 and 6 in Table 1.
- Example 5 utilizes a different silver paint from Example l.
- the silver paint (silver paint 2) is composed of bonding glass frit powder, liquid vehicle and silver particles having in an average particle size of 1 micron. The weight proportions of said silver particles and glass frit are 85 wt.% and wt.%, respectively. The amount of liquid vehicle can be adjusted to provide a viscosity suitable for screen printing.
- the glass frit powder is of bismuth borosilicate glass having an average particle size of 4 microns and has a a composition of 15 t.% of B 0 15 wt.% of SiO and 70 wt.% of Bi O
- the thick film varistor is formed in the same manner as that of Example 1 by using said silver paint 2.
- n and V of this thick film varistor is shown for sample No. 7 in Table l.
- the silver paint 2 gives an improved n value as compared with the commercially available silver paint of Example 1.
- a thick film varistor consisting essentially of a thick film having 30 to 95 weight percent of finely divided particles of zinc oxide dispersed in 5 to weight percent of glass frit, said zinc oxide having incorporated therein 0.1 to 8 mole percent of one member selected from the group consisting of bismuth oxide, lead oxide and barium oxide, and a pair of electrodes applied to said thick film, said finely divided particles of zinc oxide being obtained by heating zinc oxide powder at a temperature of 1 100 to l500C and crushing the heated zinc oxide into finely divided particles.
- a thick film varistor consisting essentially of a thick film having 30 to 95 weight percent of finely divided particles of zinc oxide dispersed in 5 to 70 weight percent of glass frit and a pair of electrodes applied to said thick film, said finely divided particles of zinc oxide being obtained by heating zinc oxide powder at a temperature of l l00 to l500C and crushing the heated zinc oxide into finely divided particles.
- a method for making a thick film varistor comprising providing a varistor paste comprising, as solid ingredients, 30 to 95 weight percent of finely divided particles of zinc oxide and 5 to weight percent of finely divided particles of glass frit dispersed in a liquid vehicleyapplying said varistor paste to an insulating base; heating the applied varistor paste to evaporate said liquid vehicle and to melt said finely divided particles of glass frit, whereby the melted glass frit bonds said finely divided particles of zinc oxide together and 10.
- saidzinc leadborate glass consists essentially of 55 to 85 weight percent of lead oxide, 10 to weight percent of boron oxide and 5 to 20 weight percent of, zinc oxide.
Abstract
A thick film varistor having a thick film of finely divided particles of zinc oxide dispersed in a glass frit which bonds the particles together. Electrodes are provided on the thick film. The varistor is made by preparing a paste of the zinc oxide particles, the frit, and a liquid vehicle, and applying the paste to an insulating base. The paste is heated to evaporate the liquid vehicle and then melt the particles of frit to bond the particles of zinc oxide together. Thereafter the electrodes are applied. Alternatively, one electrode can be applied to the insulating base, the thick film formed thereon, and a second electrode applied to the surface of the thick film.
Description
United States Patent 1 1 1111 3,725,836 Wada et a1. 1 51 Apr. 3, 1973 [54] THICK FILM VARISTOR AND 3,220,881 11/1965 Yando ..338/21 x METHOD FOR MAKING THE SAME Inventors: Mitsuo wada, Kazuyuki Nishimoto, Masaki Aoki, Yoshio Iida, all of Osaka, Japan Matsushita Electric Industrial Co., Ltd., Kadoma, Osaka, Japan Filed: May 25, 1971 Appl. No.: 146,624
Assignee:
References Cited Primary Examiner-C. L. Albritton Attorney-Wenderoth, Lind & Ponack [57] ABSTRACT applied to the insulating base, the thick film formed thereon, and a second electrode applied to the surface of the thick film.
14 Claims, 2 Drawing Figures PATENTEUAPR3 ma ,7 5, 35
INVENTORQ MITSUO WADA KAZUYUKI NISHIMOTO MASAKI AOKI YOSHIIIDA ATTORNEYS THICK FILM VARISTOR AND METHOD FOR MAKING THE SAME This invention relates to thick film varistor having finely divided particles of zinc oxide dispersed in glass and a pair of electrodes applied to said thick film and to a method for making the same.
There have been known various varistors such as silicon carbide varistor, silicon diode and selenium varistor. Usually a varistor is defined as a non-ohmic resistor the electrical resistance of which varies with the applied voltage. The electric characteristics of such a varistor are expressed by the following equation:
where V is the voltage across the varistor, I is the current flowing through the varistor, C is a constant equivalent to the electrical resistance at a given voltage and n is a numerical value greater than 1. The value which it is desired that C have depends upon the particular use to which the varistor is to be put. It is ordinarily desirable that the value of n be as large as possible since this exponent determines the degree to which the varistor departs from ohmic characteristics. Generally a varistor voltage V is defined as a voltage at a flowing current of I, milliampere through the varistor. The varistor voltage referred to hereinafter is a voltage at milliamperes of flowing current. The value of n is calculated from the relation 1:
where V, and V are the voltages at the currents I and I respectively.
Conventional varistors are usually of a discrete type component. Varistors of the thick film type have not been known in the art. Recently so-called 1c, integrated circuits, have developed remarkably. Along with such development, resistors and capacitors have been constructed in such circuits in the form of a thick film. Consequently, the electronic industry has generated a demand for a thick film varistor for use in integrated circuits. I 1
Therefore, a principal object of this invention is to provide a thick film varistor which can be fired on an insulating base.
Another object of this invention is to provide a method for making a thick film varistor.
These objects are achieved by providing a thick film varistor having a thick film of finely divided particles of zinc oxide dispersed in a glass frit which bonds the par-- ticles together, and by providing electrodes on the thick film. The varistor can be made by preparing a paste of the zinc oxide particles, the frit, and a liquid vehicle, applying the paste to an insulating base, and' heating the paste to evaporate the liquid vehicle and then melt the particles of frit to bond the particles of zinc oxide together, and thereafter applying the electrodes. Alternatively, one electrode can be applied to the insulating base, the thick film formed thereon, and a second electrode applied to the surface of the thick film.
Other and further features of the present invention will be apparent upon consideration of the following detailed description taken together with the accompanying drawings, wherein FIG. 1 is a cross section, on greatly enlarged scale, of
a varistor according to the present invention; and
FlG. 2 is a cross section, on a greatly enlarged on a highly exaggerated scale, of a varistor according to another embodiment of the present invention.
Referring to FIG. 1, a thick film varistor according to the present invention comprises a thick film 3 applied to an insulating base 1 and a pair of electrodes 2 and 2. Said thick film 3 has finely divided particles of zinc oxide 4 dispersed in glass frit 5.
The glass 5 is a bonding material for finely divided particles of zinc oxide 4 and may be composed of any glass capable of bonding said finely divided particles of zinc oxide 4 upon hardening. An operable composition for said thick film 3 is 30 to 95 wt.% of finely divided particles of zinc oxide and the remainder glass. A high amount of glass makes the electrical resistance of the resultant thick film 3 higher and a lower amount of glass results in poorer adherence of the thick film to the insulating base.
- The structure of the thick film varistor of FIG. 1 can be modified as shown in FIG. 2. Referring to FlG. 2 wherein similar reference characters designate similar components to those of FIG. 1, a thick film 3 having finely divided particles of zinc oxide 4 dispersed in glass frit 5 is sandwiched between two electrodes 2 and 2 one of which is formed on an insulating base 1. In this structure, said one electrode 2 formed on said insulating base may be replaced by a suitable and available metal plate such as silver, platinum, titanium or nickel.
A method for making a thick film varistor contemplated by the present invention comprises the following steps; providing a varistor paste having finely divided particles of zinc oxide and finely divided particles of glass frit, as a solid ingredients, dispersed in a liquid vehicle; applying said varistor paste to an insulating base; heating the applied varistor paste to evaporate said liquid vehicle and to melt and finely divided particles of glass frit whereby the melted glass frit bonds said finely divided particles of zinc oxide together and forms a thick film upon hardening; and providing said thick film with two electrodes.
This method can be modified in the following way: The varistor paste is applied to an electrode formed on an insulating base or to a metal plate acting as an electrode. The subsequentsteps are similar to those mentioned above.
Said varistor paste can be prepared by dispersing a uniform mixture of glass frit powder and zinc oxide powder, as solid ingredients, homogeneously in a liquid vehicle. The weight proportion of zinc oxide powder to glass frit powder in said mixture is 30 to 95 wt.% of zinc oxide and 5 to wt.% of glass frit powder.
' The liquid vehicle may vary widely in composition. Any inert liquid can be employed for this purpose, for example, water, organic solvents, with or without thickening agents, stabilizing agents, or the like, for example, methyl, ethyl, butyl, propyl or higher alcohols, the corresponding esters such as the carbitol acetates, propionates, etc., the terpenes and liquid resins, for example, pine oil, alpha-terpenol, and the like, and other liquids without limitation, the function of the liquid vehicle being mainly to form a liquid or paste of the desired consistency for application purposes. The liquid vehicles may contain volatile liquids to promote fast setting after application, or they may contain waxes, thermoplastic resins such as cellulose acetate butyrate, or wax-like materials which are thermofluid by nature whereby the composition can be applied to an insulating base while at an elevated temperature so as to set immediately upon contact with the insulating base. 3
The amount of said liquid vehicle relative to solid ingredient can vary with the manner of application. For example, in a stencil screen printing method, the operable weight ratio of liquid vehicle to solid ingredient is to 45 wt.% of liquid vehicle and 55 to 90 wt.% of
solid ingredient. An advantageous weight ratio is to 30 wt.% of liquid vehicle and 70 to 85 wt.% of solid ingredient. it is preferable that the viscosity of the resultant paste be 500 to 2,000 poises.
The varistor paste is applied in a uniform thickness to the insulating base or to the electrode surface. This may be done by any application method such as a stencil, spray, print, dip or brush method.
The varistor paste applied to the insulating base is dried, if necessary, to remove the liquid vehicle and then fired in an electrical furnace at a temperature at which the glass frit fuses so as to bond the zinc oxide powder particles and to adhere firmly to the insulating base. The firing temperature may vary with the composition of glass frit. It is preferable to adjust the firing temperature so as to be 400 to 850C.
Finelydivided zinc oxide powder is prepared by pul verization of sintered zinc oxide which is heated at a temperature of 1100 to l500C for 0.5 to 10 hours. The pulverization of zinc oxide powder can be achieved in accordance with well known techniques. Said sintered zinc oxide may be pre-crushed into granules having a diameter of few millimeters by a crushing machine equipped with a steel or iron pestle and mortar. The granules are further pulverized into fine powder with a fine crusher such as a ball mill or vibration mill etc. The preferable particle size of the zinc oxide powder is 0.5 to 10 microns.
It has been discovered according to the present invention that the n is improved when said zinc oxide powder has incorporated therewith 0.1 to 8 mole percent of one member selected from the group consisting of bismuth oxide (Bi- 0 lead oxide (PhD) and barium oxide (BaO). The incorporation can be achieved by a well known ceramic technique. A mixture of zinc oxide powder and additives of a given composition is heated at a high temperature of ll00 to 1500C and then crushed into fine powder in a manner similar to that described above.
An operable glass frit for use in the varistor paste can be borosilicate glass, lead borosilicate glass, zinc leadborate glass and bismuth borosilicate glass. Most advantageous is zinc leadborate frit having a composition consisting essentially of 55 to 85 wt.% of PbO, 10 to wt.% of H 0 and 5 to 20 wt.% of ZnO.
Said glass'frit can be prepared in accordance with a per se well known glass frit technique. A mixtureincluding desired starting materials is heated to a high temperature so as to form a glass frit and is quenched in I cle size for the particles of the glass frit is 0.5 to 20 microns. I
The electrodes 2 and 2' may be formed by any suitaelectroless-plating of nickel metal. It has been discovered according to the invention that a higher n is obtained by using a silver paint electrode which has finely divided particles of silver'dispersed in bonding glass. Care should be taken that the softening temperature of said bonding glass is not higher than that of the glass frit of the varistor paste.
The silver paint is prepared by dispersing a mixture of silver powder and bonding glass frit powder in a liquid vehicle. Said mixture is preferablycomposed of 50 to 95 wt.% of silver powder and 5 to 50 wt.% of bonding glass frit powder. The composition of the bonding glass frit powder is controlled of 60 to 80 wt.% so that it is bismuth oxide, 10 to 20 wt.% of boron oxide and 10 to 20 wt.% of silica. The method of preparing the silver paint are essentially similar to those for the varistor paste mentioned above.
The following examples are given to illustrate certain preferred details of the invention, it being understood that the details of the examples are not to be taken as in any way limiting the invention thereto.
Example 1 I of B 0 and 13.8 wt.% of ZnO is pulverized into a fine powder having an average particle size of 3 microns. A uniform mixture of wt.% zinc oxide powder and 25 wt.% of glass frit is prepared by a well known method. The uniform mixture of these solid ingredients is mixed well with a liquid vehicle consisting of '15 wt.% of ethyl cellulose and 85 wt.% of carbitol acetate to form a varistor paste having a composition consisting of wt.% of solid ingredient and 20 wt.% of liquid vehicle.
Commercially available silver paint No. 6730 (silver paint l) from Dupont Co. in U.S.A. is appliedto an aluminum oxide ceramic insulating base by a stainless steel screen stencil with a 200 mesh and is fired in air at 800C for 10 minutes by a tunnel type kiln so as to form a silver paint electrode. a
The varistor paste is applied to said silver paint electrode and is fired in air at 800C for 10 minutes by the tunnel kiln. The resultant thick film has a thickness of about 20 microns. Thesilver paint 1 is applied to the varistor film and is fired at 800C in a manner similar to that described above to form an upper silver paint electrode having an active area of 6X6 mm. The thick film varistor has electrical properties shown for sample No. 1 in Table 1. In Table l, exponent n is calculatedjfrom relation 1 by using I =lmA. and I =l OmA. and V is the varistor voltage at the current I =l0mA.
Example 2 A varistor paste similar to that or Example l is apthick film varistor are shown for sample No. 2 in Table l.
Example 3 Example 3 differs from Example 2 only in that it has a different electrode from Example 2. After the thick film has been formed on the insulating base in a manner similar to that of Example 2, the thick film is provided with two electrodes of zinc film prepared by a well known vacuum evaporation technique. The dimensions of the electrodes are similar to that of Example 2.
The resultant electrical characteristics of n and V for this thick film varistor are shown for sample No. 3 in Table 1.
Example 4 Compositions of zinc oxide with 2 mol of bismuth oxide (Bi- 2 mol of lead oxide (PbO), and 2 mol of barium oxide (8210), respectively, are heated at l350C for 1 hour and then pulverized into fine powder having an average particle size of 2 microns by using a stamp mill for pre-crush and a ball mill for fine pulverization. The zinc oxide powder compositions are used for formation of thick film varistors. The other formation steps are exactly similar to those of example The resultant electrical characteristics of n and V of these thick film varisto rs are shown for samples No. 4, 5 and 6 in Table 1. It can be seen that the incorporation of Bi O improves the n value and increases the V as compared with the absence of zinc oxide from the thick film varistor of sample No. l. The incorporation of PbO or BaO improves the n value and decreases the V Example 5 '7 5 Example 5 utilizes a different silver paint from Example l. The silver paint (silver paint 2) is composed of bonding glass frit powder, liquid vehicle and silver particles having in an average particle size of 1 micron. The weight proportions of said silver particles and glass frit are 85 wt.% and wt.%, respectively. The amount of liquid vehicle can be adjusted to provide a viscosity suitable for screen printing. The glass frit powder is of bismuth borosilicate glass having an average particle size of 4 microns and has a a composition of 15 t.% of B 0 15 wt.% of SiO and 70 wt.% of Bi O The thick film varistor is formed in the same manner as that of Example 1 by using said silver paint 2.
The resultant electrical characteristics of n and V of this thick film varistor is shown for sample No. 7 in Table l. The silver paint 2 gives an improved n value as compared with the commercially available silver paint of Example 1.
Table 1 Sample Electrode Electrode No. ZnO Compositio'h 2" n V,.( volt) l pure ZnO Silver Silver 5 20 Paint 1 Paint 1 2 pure ZnO 5 450 3 pure ZnO Zinc film Zinc 4 400 film 4 ago, 2 mol.% Silver Silver 6 2S incorporated Paint l Paint 1 5 PhD 2 mol.% 7 l5 incorporated 6 BaO 2 mol.% 7 l0 incorporated 7 pure ZnO Silver Silver 8 2O Paint 2 Paint 2 *1 See FIG. land 2 What we claim is:
l. A thick film varistor consisting essentially of a thick film having 30 to 95 weight percent of finely divided particles of zinc oxide dispersed in 5 to weight percent of glass frit, said zinc oxide having incorporated therein 0.1 to 8 mole percent of one member selected from the group consisting of bismuth oxide, lead oxide and barium oxide, and a pair of electrodes applied to said thick film, said finely divided particles of zinc oxide being obtained by heating zinc oxide powder at a temperature of 1 100 to l500C and crushing the heated zinc oxide into finely divided particles.
2. A thick film varistor consisting essentially of a thick film having 30 to 95 weight percent of finely divided particles of zinc oxide dispersed in 5 to 70 weight percent of glass frit and a pair of electrodes applied to said thick film, said finely divided particles of zinc oxide being obtained by heating zinc oxide powder at a temperature of l l00 to l500C and crushing the heated zinc oxide into finely divided particles.
3. A thick film varistor as claimed in claim 2, wherein said glass frit consists essentially of a glass selected from the group consisting of borosilicate glass lead borosilicate glass, zinc leadborate glass and bismuth borosilicate glass.
4. A thick film varistor as claimed in claim 3, wherein said zinc leadborate glass consists essentially of 55 to weight percent of lead oxide, 10 to 25 weight percent of boron oxide and 5 to 20 weight percent of zinc oxide.
5. A thick film varistor as claimed in claim 2, wherein at least one of said two electrodes is a silver paint electrode.
6. A thick film varistor as claimed in claim 5, wherein said silver paint electrode consists essentially of 50 to 95 weight percent of silver powder and 5 to 50 weight percent of glass frit, said glass frit consisting essentially of 60 to 80 weight percent of bismuth oxide, 10 to 20 weight percent of boron oxide and 10 to 20 weight percent of silica.
7. A method for making a thick film varistor comprising providing a varistor paste comprising, as solid ingredients, 30 to 95 weight percent of finely divided particles of zinc oxide and 5 to weight percent of finely divided particles of glass frit dispersed in a liquid vehicleyapplying said varistor paste to an insulating base; heating the applied varistor paste to evaporate said liquid vehicle and to melt said finely divided particles of glass frit, whereby the melted glass frit bonds said finely divided particles of zinc oxide together and 10. A method for making a thick film varistor as claimed in claim 9, wherein saidzinc leadborate glass consists essentially of 55 to 85 weight percent of lead oxide, 10 to weight percent of boron oxide and 5 to 20 weight percent of, zinc oxide.
11. A method for making a thick film varistor as claimed in claim 7, wherein said finely divided particles of zinc oxide are made by heating zinc oxide powder at a'temperature of ll00 to 1500C and'crus'hing the heated zinc oxide into finely divided particles.
12. A method for making a thick film varistor as claimed in claim 11, wherein said zinc oxide powder has incorporated therein 0.1 to 8 mole percent of a member selected from the group consisting of bismuth oxide, lead oxide and barium oxide.
l3.- A method for making a thick film varistor as claimed in claim 7, wherein at least one of said two electrodes is a silver paint electrode.
14. Amethod for making a thick film varistor as claimed in claim 13, wherein said silver paint electrode consists essentially of to 95 weight percent of silver powder and 5 to 50 weight percent of glass frit, said glass frit consisting essentially of to weight percent of bismuth oxide, 10 to 20 weight percent of boron oxide and 10 to 20 weight percent of silica.
Claims (13)
- 2. A thick film varistor consisting essentially of a thick film having 30 to 95 weight percent of finely divided particles of zinc oxide dispersed in 5 to 70 weight percent of glass frit and a pair of electrodes applied to said thick film, said finely divided particles of zinc oxide being obtained by heating zinc oxide powder at a temperature of 1100* to 1500*C and crushing the heated zinc oxide into finely divided particles.
- 3. A thick film varistor as claimed in claim 2, wherein said glass frit consists essentially of a glass selected from the group consisting of borosilicate glass, lead borosilicate glass, zinc leadborate glass and bismuth borosilicate glass.
- 4. A thick film varistor as claimed in claim 3, wherein said zinc leadborate glass consists essentially of 55 to 85 weight percent of lead oxide, 10 to 25 weight percent of boron oxide and 5 to 20 weight percent of zinc oxide.
- 5. A thick film varistor as claimed in claim 2, wherein at least one of said two electrodes is a silver paint electrode.
- 6. A thick film varistor as claimed in claim 5, wherein said silver paint electrode consists essentially of 50 to 95 weight percent of silver powder and 5 to 50 weight percent of glass frit, said glass frit consisting essentially of 60 to 80 weight percent of bismuth oxide, 10 to 20 weight percent of boron oxide and 10 to 20 weight percent of silica.
- 7. A method for making a thick film varistor comprising providing a varistor paste comprising, as solid ingredients, 30 to 95 weight percent of finely divided particles of zinc oxide and 5 to 90 weight percent of finely divided particles of glass frit dispersed in a liquid vehicle; applying said varistor paste to an insulating base; heating the applied varistor paste to evaporate said liquid vehicle and to melt said finely divided particles of glass frit, whereby the melted glass frit bonds said finely divided particles of zinc oxide together and forms a thick film upon hardening; and providing said thick film with two electrodes.
- 8. A method for making a thick film varistor as claimed in claim 7, wherein said varistor paste is applied to an insulating base having one of said two electrodes formed thereon.
- 9. A method for making a thick film varistor as claimed in claim 7, wherein said finely divided particles of glass frit consist essentially of a member selected from the group consisting of borosilicate glass, lead borosilicate glass, zinc leadborate glass and bismuth borosilicate glass.
- 10. A method for making a thick film varistor as claimed in claim 9, wherein said zinc leadborate glass consists essentially of 55 to 85 weight percent of lead oxide, 10 to 25 weight percent of boron oxide and 5 to 20 weight percent of zinc oxide.
- 11. A method for making a thick film varistor as claimed in claim 7, wherein said finely divided particles of zinc oxide are made by heating zinc oxide powder at a temperature of 1100* to 1500*C and crushing the heated zinc oxide into finely divided particles.
- 12. A method for making a thick film varistor as claimed in claim 11, wherein said zinc oxide powder has incorporated therein 0.1 to 8 mole percent of a member selected from the group consisting of bismuth oxide, lead oxide and barium oxide.
- 13. A method for making a thick film varistor as claimed in claim 7, wherein at least one of said two electrodes is a silver paint electrode.
- 14. Amethod for making a thick film varistor as claimed in claim 13, wherein said silver paint electrode consists essentially of 50 to 95 weight percent of silver powder and 5 to 50 weight percent of glass frit, said glass frit consisting essentially of 60 to 80 weight percent of bismuth Oxide, 10 to 20 weight percent of boron oxide and 10 to 20 weight percent of silica.
Applications Claiming Priority (4)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GB1637571 | 1971-05-21 | ||
US14662471A | 1971-05-25 | 1971-05-25 | |
FR717119069A FR2138453B1 (en) | 1971-05-21 | 1971-05-26 | |
NL717107731A NL150936B (en) | 1971-05-21 | 1971-06-04 | METHOD OF MANUFACTURING A VARISTOR OF THE THICK-FILM TYPE. |
Publications (1)
Publication Number | Publication Date |
---|---|
US3725836A true US3725836A (en) | 1973-04-03 |
Family
ID=27446109
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US00146624A Expired - Lifetime US3725836A (en) | 1971-05-21 | 1971-05-25 | Thick film varistor and method for making the same |
Country Status (4)
Country | Link |
---|---|
US (1) | US3725836A (en) |
FR (1) | FR2138453B1 (en) |
GB (1) | GB1346851A (en) |
NL (1) | NL150936B (en) |
Cited By (29)
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US4001757A (en) * | 1973-08-14 | 1977-01-04 | Matsushita Electric Industrial Co., Ltd. | Method for detecting a reducing material in a gas phase |
DE2627930A1 (en) * | 1975-06-23 | 1977-01-13 | Gen Electric | PROCESS FOR MANUFACTURING THICK FILM VARISTORS FROM METAL OXIDES |
US4041436A (en) * | 1975-10-24 | 1977-08-09 | Allen-Bradley Company | Cermet varistors |
US4064475A (en) * | 1976-07-12 | 1977-12-20 | Allen-Bradley Company | Thick film varistor and method of making the same |
US4069465A (en) * | 1976-07-12 | 1978-01-17 | Allen-Bradley Company | Cylindrical varistor and method of making the same |
DE2740808A1 (en) * | 1976-09-13 | 1978-03-16 | Gen Electric | METAL OXYD VARISTOR |
DE2735484A1 (en) * | 1977-08-05 | 1979-02-15 | Siemens Ag | METHOD OF MANUFACTURING THICK FILM VARISTORS |
DE2921497A1 (en) * | 1978-07-20 | 1980-01-31 | Hermsdorf Keramik Veb | SUBSTRATE FOR CERAMIC SEMICONDUCTOR RESISTORS AND PRODUCTION METHODS |
US4333861A (en) * | 1976-11-26 | 1982-06-08 | Matsushita Electric Industrial Co., Ltd. | Thick film varistor |
US4460622A (en) * | 1981-02-27 | 1984-07-17 | Taiyo Yuden Co., Ltd. | Electroconductive paste to be baked on ceramic bodies to provide capacitors, varistors or the like |
US4460624A (en) * | 1981-09-04 | 1984-07-17 | Thomson-Csf | Process for the manufacture of thick layer varistors on a hybrid circuit substrate |
US4946709A (en) * | 1988-07-18 | 1990-08-07 | Mitsubishi Denki Kabushiki Kaisha | Method for fabricating hybrid integrated circuit |
US5059570A (en) * | 1989-08-17 | 1991-10-22 | Bp Chemicals Limited | Process for preparing a vanadium/titanium based catalyst suitable for olefin polymerization |
US5248452A (en) * | 1989-07-11 | 1993-09-28 | Ngk Insulators, Ltd. | Process for manufacturing a voltage non-linear resistor |
US5250281A (en) * | 1989-07-11 | 1993-10-05 | Ngk Insulators, Ltd. | Process for manufacturing a voltage non-linear resistor and a zinc oxide material to be used therefor |
US5250229A (en) * | 1991-10-10 | 1993-10-05 | E. I. Du Pont De Nemours And Company | Silver-rich conductor compositions for high thermal cycled and aged adhesion |
US5269971A (en) * | 1989-07-11 | 1993-12-14 | Ngk Insulators, Ltd. | Starting material for use in manufacturing a voltage non-linear resistor |
US5594406A (en) * | 1992-02-25 | 1997-01-14 | Matsushita Electric Industrial Co., Ltd. | Zinc oxide varistor and process for the production thereof |
US6232144B1 (en) * | 1997-06-30 | 2001-05-15 | Littelfuse, Inc. | Nickel barrier end termination and method |
US20050141166A1 (en) * | 2003-12-25 | 2005-06-30 | Hidenori Katsumura | Method of manufacturing ESD protection component |
US20050184387A1 (en) * | 2004-02-25 | 2005-08-25 | Collins William D.Iii | Ceramic substrate for a light emitting diode where the substrate incorporates ESD protection |
US20070128822A1 (en) * | 2005-10-19 | 2007-06-07 | Littlefuse, Inc. | Varistor and production method |
US20070171025A1 (en) * | 2004-04-02 | 2007-07-26 | Hidenori Katsumura | Component with countermeasure to static electricity |
US20080030296A1 (en) * | 2004-09-15 | 2008-02-07 | Epcos Ag | Varistor Comprising an Insulating Layer Produced From a Loading Base Glass |
EP1956612A1 (en) * | 2007-02-09 | 2008-08-13 | SFI Electronics Technology Inc. | Ceramic material used for protection against electrical overstress and low-capacitance multilayer chip varistor using the same |
EP1993108A1 (en) * | 2007-05-18 | 2008-11-19 | Bee Fund Biotechnology Inc. | Material composition having a core-shell microstructure used for a varisator |
CN101071666B (en) * | 2007-06-22 | 2010-06-09 | 赑丰生技股份有限公司 | Low-capacitance layered wafer rheostat and overvoltage protection material thereof |
US20100189882A1 (en) * | 2006-09-19 | 2010-07-29 | Littelfuse Ireland Development Company Limited | Manufacture of varistors with a passivation layer |
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IE47121B1 (en) * | 1977-07-29 | 1983-12-28 | Gen Electric | Stabilized varistor |
US4146677A (en) * | 1977-08-18 | 1979-03-27 | Trw Inc. | Resistor material, resistor made therefrom and method of making the same |
AU524277B2 (en) * | 1979-11-27 | 1982-09-09 | Matsushita Electric Industrial Co., Ltd. | Sintered oxides voltage dependent resistor |
JPS57194479A (en) * | 1981-05-25 | 1982-11-30 | Ngk Insulators Ltd | Heating element |
FR2523993A1 (en) * | 1982-03-24 | 1983-09-30 | Cables De Lyon Geoffroy Delore | Silk screen printing paste contg. metal oxide(s) as active materials - used for varistor prodn. |
US5742223A (en) | 1995-12-07 | 1998-04-21 | Raychem Corporation | Laminar non-linear device with magnetically aligned particles |
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- 1971-05-21 GB GB1637571A patent/GB1346851A/en not_active Expired
- 1971-05-25 US US00146624A patent/US3725836A/en not_active Expired - Lifetime
- 1971-05-26 FR FR717119069A patent/FR2138453B1/fr not_active Expired
- 1971-06-04 NL NL717107731A patent/NL150936B/en not_active IP Right Cessation
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US3052573A (en) * | 1960-03-02 | 1962-09-04 | Du Pont | Resistor and resistor composition |
US3220881A (en) * | 1960-11-30 | 1965-11-30 | Gen Telephone & Elect | Method of making a non-linear resistor |
Cited By (37)
Publication number | Priority date | Publication date | Assignee | Title |
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US4001757A (en) * | 1973-08-14 | 1977-01-04 | Matsushita Electric Industrial Co., Ltd. | Method for detecting a reducing material in a gas phase |
DE2627930A1 (en) * | 1975-06-23 | 1977-01-13 | Gen Electric | PROCESS FOR MANUFACTURING THICK FILM VARISTORS FROM METAL OXIDES |
US4041436A (en) * | 1975-10-24 | 1977-08-09 | Allen-Bradley Company | Cermet varistors |
US4064475A (en) * | 1976-07-12 | 1977-12-20 | Allen-Bradley Company | Thick film varistor and method of making the same |
US4069465A (en) * | 1976-07-12 | 1978-01-17 | Allen-Bradley Company | Cylindrical varistor and method of making the same |
DE2740808A1 (en) * | 1976-09-13 | 1978-03-16 | Gen Electric | METAL OXYD VARISTOR |
US4333861A (en) * | 1976-11-26 | 1982-06-08 | Matsushita Electric Industrial Co., Ltd. | Thick film varistor |
DE2735484A1 (en) * | 1977-08-05 | 1979-02-15 | Siemens Ag | METHOD OF MANUFACTURING THICK FILM VARISTORS |
US4186367A (en) * | 1977-08-05 | 1980-01-29 | Siemens Aktiengesellschaft | Thick film varistor and method of producing same |
DE2921497A1 (en) * | 1978-07-20 | 1980-01-31 | Hermsdorf Keramik Veb | SUBSTRATE FOR CERAMIC SEMICONDUCTOR RESISTORS AND PRODUCTION METHODS |
US4460622A (en) * | 1981-02-27 | 1984-07-17 | Taiyo Yuden Co., Ltd. | Electroconductive paste to be baked on ceramic bodies to provide capacitors, varistors or the like |
US4460624A (en) * | 1981-09-04 | 1984-07-17 | Thomson-Csf | Process for the manufacture of thick layer varistors on a hybrid circuit substrate |
US4946709A (en) * | 1988-07-18 | 1990-08-07 | Mitsubishi Denki Kabushiki Kaisha | Method for fabricating hybrid integrated circuit |
US5248452A (en) * | 1989-07-11 | 1993-09-28 | Ngk Insulators, Ltd. | Process for manufacturing a voltage non-linear resistor |
US5250281A (en) * | 1989-07-11 | 1993-10-05 | Ngk Insulators, Ltd. | Process for manufacturing a voltage non-linear resistor and a zinc oxide material to be used therefor |
US5269971A (en) * | 1989-07-11 | 1993-12-14 | Ngk Insulators, Ltd. | Starting material for use in manufacturing a voltage non-linear resistor |
US5059570A (en) * | 1989-08-17 | 1991-10-22 | Bp Chemicals Limited | Process for preparing a vanadium/titanium based catalyst suitable for olefin polymerization |
US5250229A (en) * | 1991-10-10 | 1993-10-05 | E. I. Du Pont De Nemours And Company | Silver-rich conductor compositions for high thermal cycled and aged adhesion |
US5594406A (en) * | 1992-02-25 | 1997-01-14 | Matsushita Electric Industrial Co., Ltd. | Zinc oxide varistor and process for the production thereof |
US6232144B1 (en) * | 1997-06-30 | 2001-05-15 | Littelfuse, Inc. | Nickel barrier end termination and method |
US20050141166A1 (en) * | 2003-12-25 | 2005-06-30 | Hidenori Katsumura | Method of manufacturing ESD protection component |
US7189297B2 (en) * | 2003-12-25 | 2007-03-13 | Matsushita Electric Industrial Co., Ltd. | Method of manufacturing ESD protection component |
US7768754B2 (en) | 2004-02-25 | 2010-08-03 | Philips Lumileds Lighting Company, Llc | Ceramic substrate for light emitting diode where the substrate incorporates ESD protection |
US20050184387A1 (en) * | 2004-02-25 | 2005-08-25 | Collins William D.Iii | Ceramic substrate for a light emitting diode where the substrate incorporates ESD protection |
US7279724B2 (en) * | 2004-02-25 | 2007-10-09 | Philips Lumileds Lighting Company, Llc | Ceramic substrate for a light emitting diode where the substrate incorporates ESD protection |
US20070297108A1 (en) * | 2004-02-25 | 2007-12-27 | Philips Lumileds Lighting Company, Llc | Ceramic Substrate for Light Emitting Diode Where the Substrate Incorporates ESD Protection |
EP1580809A3 (en) * | 2004-02-25 | 2008-07-09 | Philips Lumileds Lighting Company LLC | Ceramic substrate incorporating an ESD protection for a light emitting diode |
US20070171025A1 (en) * | 2004-04-02 | 2007-07-26 | Hidenori Katsumura | Component with countermeasure to static electricity |
US7864025B2 (en) * | 2004-04-02 | 2011-01-04 | Panasonic Corporation | Component with countermeasure to static electricity |
US20080030296A1 (en) * | 2004-09-15 | 2008-02-07 | Epcos Ag | Varistor Comprising an Insulating Layer Produced From a Loading Base Glass |
US8130071B2 (en) * | 2004-09-15 | 2012-03-06 | Epcos Ag | Varistor comprising an insulating layer produced from a loading base glass |
US20070128822A1 (en) * | 2005-10-19 | 2007-06-07 | Littlefuse, Inc. | Varistor and production method |
US20100189882A1 (en) * | 2006-09-19 | 2010-07-29 | Littelfuse Ireland Development Company Limited | Manufacture of varistors with a passivation layer |
EP1956612A1 (en) * | 2007-02-09 | 2008-08-13 | SFI Electronics Technology Inc. | Ceramic material used for protection against electrical overstress and low-capacitance multilayer chip varistor using the same |
EP1993108A1 (en) * | 2007-05-18 | 2008-11-19 | Bee Fund Biotechnology Inc. | Material composition having a core-shell microstructure used for a varisator |
CN101071666B (en) * | 2007-06-22 | 2010-06-09 | 赑丰生技股份有限公司 | Low-capacitance layered wafer rheostat and overvoltage protection material thereof |
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Also Published As
Publication number | Publication date |
---|---|
NL150936B (en) | 1976-09-15 |
GB1346851A (en) | 1974-02-13 |
NL7107731A (en) | 1972-12-06 |
FR2138453B1 (en) | 1973-05-25 |
FR2138453A1 (en) | 1973-01-05 |
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