JP4413096B2 - Photosensitive conductive paste - Google Patents

Description

  The present invention relates to a photosensitive conductive paste used when a fine wiring pattern or the like is formed on a ceramic substrate, a glass substrate, or a heat resistant resin substrate.

In recent years, electrical and electronic devices, particularly circuit boards, are required to be smaller, higher density, higher definition, and higher reliability. It has been requested.
Then, the photosensitive electrically conductive paste which has a photosensitive organic component and metal powder as an essential component, and contains metal microparticles with a particle size of 0.4 micrometer or less in the range of 10-100 mass% in the total amount of metal powder is proposed ( Patent Document 1).
JP 2004-54085 A

  Although the conventional photosensitive conductive paste can be thickened and finely processed to some extent, there is a problem that the range of the heat treatment temperature cannot be widened and the degree of freedom of the manufacturing method cannot be increased. In addition, since there is a possibility that the metal fine particles do not contact sufficiently, there is a big problem that the reliability cannot be improved.

  The present invention has been made in view of the above, and it is an object of the present invention to provide a photosensitive conductive paste capable of widening the range of the heat treatment temperature and improving the reliability by sufficiently contacting metal particles. Yes.

In the present invention, in order to solve the above-mentioned problems, a first binder that is insolubilized in the developer by irradiation with either ultraviolet rays or electron beams, and a heat of 50 ° C. or more than the thermal decomposition temperature of the first binder. A second binder having a high decomposition temperature, and metal particles having an average particle diameter of 0.05 to 0.5 μm,
The second binder is prepared from only a polyimide resin, a polyamideimide resin, a polyetherimide resin, and their precursors, and the mixing ratio of the second binder to the first binder is determined by the tap porosity of the metal particles. And
The aspect ratio of the metal particles is 1.0 to 1.5, and the ratio of the average particle diameter of the metal particles in the range of ± 0.05 μm is 30% by mass or more.

  Here, the first binder in the claims may be cured by irradiation with ultraviolet rays (UV) and insolubilized in the developer, or cured by irradiation with electron beams (EB) to form the developer. It may be insolubilized. The tap porosity is a value obtained by subtracting from 1 a value obtained by dividing the tap density of the metal particles by the true density of the metal. The photosensitive conductive paste is used at least for computers, PC cards, mobile phones, mobile terminals, color television ceramic substrates, glass substrates, heat resistant resin substrates, circuit boards, and the like. A sensitizer, a polymerization inhibitor, a leveling agent, a dispersant, a thickener, a precipitation inhibitor, and the like are added to this photosensitive conductive paste as necessary.

According to the present invention, there is an effect that the setting range of the heat treatment temperature can be widened, and the reliability can be improved by sufficiently contacting the metal particles . Moreover, since the capacity | capacitance of a 2nd binder is made into the tap porosity of a metal particle or less and a metal particle is made to contact reliably, resistance reduction is attained.

  Hereinafter, a preferred embodiment of the present invention will be described. The photosensitive conductive paste in the present embodiment includes a photocurable binder 1 (first binder) that is insolubilized in a developer upon irradiation with ultraviolet rays, and the binder. A heat-resistant binder 2 (second binder) having a thermal decomposition temperature higher by 50 ° C. or higher than the thermal decomposition temperature of 1 and metal particles having a fusion start temperature of 300 ° C. or lower in thermomechanical analysis (TMA) And heat treatment such as firing is performed when forming a fine wiring pattern.

  The decomposition temperature of the binder 1, the decomposition temperature of the binder 2, and the heat treatment temperature are set such that the decomposition temperature of the binder 1 <the heat treatment temperature <the decomposition temperature of the binder 2.

  The binder 1 is made of an ultraviolet curable resin composition that can be developed with water, an alkaline aqueous solution, a solvent, or the like, preferably a resin composition that can be developed with an alkaline aqueous solution from the viewpoint of resolution and workability, and heat treatment such as baking. Sometimes removed. The binder 1 comprising such a resin composition is prepared from an alkali-soluble resin, a crosslinkable monomer or oligomer having an unsaturated double bond, and a photopolymerization initiator.

  As the alkali-soluble resin, for example, an acrylic copolymer having an acidic group such as carboxylic acid and an ethylenically unsaturated group is optimal. Examples of the acidic group component include acrylic acid, methacrylic acid, 2-methacryloyloxyethyl succinate, 2-acryloyloxyethyl succinate, 2-methacryloyloxyethyl phthalate, 2-acryloyloxyethyl phthalate, and the like.

  As ethylenically unsaturated components, methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, n-propyl acrylate, n-propyl methacrylate, isopropyl acrylate, isopropyl methacrylate, n-butyl acrylate, n-butyl methacrylate, sec-butyl acrylate , Sec-butyl methacrylate, isobutyl acrylate, isobutyl methacrylate, tert-butyl acrylate, tert-butyl methacrylate, allyl acrylate, allyl methacrylate, benzyl acrylate, benzyl methacrylate, cyclohexyl acrylate, cyclohexyl methacrylate and the like.

  As the alkali-soluble resin, various copolymers of the above components and other monomers can be used as long as the alkali developability is not impaired.

  The crosslinkable monomer having an unsaturated double bond is a compound having at least one ethylenically unsaturated double bond, reacts with a radical generated from a photopolymerization initiator by light irradiation, and has a solubility in an alkali developer. Reduce to form a pattern.

  Specifically, allyl acrylate, benzyl acrylate, butoxyethyl acrylate, butoxyethylene glycol acrylate, cyclohexyl acrylate, dicyclopentanyl acrylate, 2-ethylhexyl acrylate, glycerol acrylate, glycidyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl Acrylate, isobornyl acrylate, isooctyl acrylate, lauryl acrylate, 2-methoxy acrylate, methoxyethylene glycol acrylate, phenoxyethyl acrylate, stearyl acrylate, ethylene glycol diacrylate, diethylene glycol diacrylate, 1,4-butanediol diacrylate, 1, 5-Pentanediol Diacryl 1,6-hexanediol diacrylate, 1,3-propanediol diacrylate, 1,4-cyclohexanediol diacrylate, 2,2-dimethylolpropane diacrylate, glycerol diacrylate, tripropylene glycol diacrylate, Glycerol triacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, ethylene oxide modified pentaerythritol tetraacrylate, propylene oxide modified pentaerythritol triacrylate, triethylene glycol diacrylate, polyoxypropyltrimethylolpropane triacrylate , Butylene glycol diacrylate, 1,2,4-butane Riol triacrylate, 2,2,4-trimethyl-1,3-pentanediol diacrylate, 1,10-decanediol dimethyl acrylate, pentaerythritol hexaacrylate and the above acrylate replaced with methacrylate, γ-methacryloxypropyl tri Examples include methoxyplan, 1-vinyl-2-pyrodrine and the like. Two or more kinds of the crosslinkable monomers may be combined.

  The photopolymerization agent is not particularly limited as long as it can be used for an ordinary negative photolithograph. Specifically, benzophenone, methyl o-benzoylbenzoate, methyl 4-dimethylaminobenzoate, 4,4-bis (dimethylamine) benzophenone, 4,4-bis (diethylamine) benzophenone, α-aminoacetophenone, 4, 4-dichlorobenzophenone, 4-benzoyl-4-methyldiphenyl ketone, dibenzyl ketone, 1-hydroxy-cyclohexyl-phenyl-ketone, fluoresson, 2,2-diethoxyacetophenone, 2,2-dimethoxy-1,2-diphenyl Ethan-1-one, 2-hydroxy-2-methyl-1-phenylpropan-1-one, pt-butyldichloroacetophenone, thioxanthone, 2-methylthioxanthone, 2-chlorothioxanthone, 2-isopropylthioxanthone, diethylthio Xanthone, benzyldimethyl ketal, benzyl-methoxyethyl acetal, benzoin, benzoin methyl ether, benzoin butyl ether, anthraquinone, 2-t-butylanthraquinone, 2-amylanthraquinone, β-chloroanthraquinone, anthrone, benzanthrone, dibenzosuberone, methylene Anthrone, 4-azitobenzalacetophenone, 2,6-bis (p-azidobenzylidene) cyclohexanone, 2,6-bis (p-azidobenzylidene) -4-methylcyclohexanone, 2-phenyl-1,2-butadion-2- (O-methoxycarbonyl) oxime, 1-phenyl-propanedione-2- (o-ethoxycarbonyl) oxime, 1-phenyl-propanedione-2- (o-ethoxycarbonyl) o Shim, 1-phenyl-3-ethoxy-propanetrione-2- (o-benzoyl) oxime, mihira-ketone, 2methyl-1 [4- (methylthio) phenyl] -2-morpholinopropan-1-one, naphthalene Sulfonyl chloride, quinoline sulfonyl chloride, N-phenylthioacdrine, 4,4-azobisisobutyronitrile, diphenyl disulfide, benzthiazole sulfide, triphenylphosphine, bis (2,4,6-trimethylbenzoyl) -phenyl Although it is phosphine oxide, camphorquinone, etc., it is also possible to use 2 or more types together.

  When there is a possibility that the transmission of ultraviolet rays may be inhibited, bis (2,4,6-trimethylbenzoyl) -phenylphosphine oxide or 2-methyl-1 [4- (methylthio) phenyl] -2- Preferably morpholinopropan-1-one is used. Further, 1-hydroxy-cyclohexyl-phenyl-ketone or 2,2-dimethoxy-1,2-diphenylethane-1-one may be used in combination.

  The binder 1 has a 5% mass reduction temperature in the range of 200 to 350 ° C. in thermal mass spectrometry. This is because when the temperature is lower than 200 ° C., it is difficult to obtain high conductivity based on fusion of metal particles. Conversely, when it exceeds 350 ° C., the use range of the binder 2 is narrowed, and the implementation range of the manufacturing method of the present embodiment is narrowed.

The binder 2 is selected in relation to the binder 1, and the blending ratio (capacity) is set to be equal to or less than the tap porosity of the metal particles. The binder 2 preferably has a larger difference in mass decrease temperature. From this viewpoint, a polyimide resin, a polyamideimide resin, a polyetherimide resin, and a precursor thereof are used. The tap porosity is a value obtained by subtracting from 1 a value obtained by dividing the tap density of metal particles by the true density of the metal. For example, in the case of silver particles having a tap density of 6.0 g / cm ³ , since the true density of silver is 10.5 g / cm ³ , the tap porosity is 0.429 (= 42.9%).

  As the metal particles, gold or silver particles having high conductivity are used, and particularly low-cost silver particles having excellent availability, conductivity, and oxidation resistance are preferably used. The metal particles are preferably surface-treated with various dispersants and do not cause secondary aggregation. The dispersant is preferably of a type that decomposes and volatilizes in the heat treatment step.

  When the metal particles are silver particles, the silver particles are adjusted to have an average particle diameter of 0.05 to 0.5 μm as measured based on the laser diffraction method so that the selection range of the resin and the like is not narrowed. The aspect ratio (aspect ratio) is formed into a substantially spherical shape of 1.0 to 1.5, and the ratio of the average particle size in the range of ± 0.05 μm is set to 30% by mass or more.

  The reason why the average particle diameter of the metal particles is in the range of 0.05 to 0.5 μm is that when the average particle diameter is less than 0.05 μm, it is necessary to increase the amount of addition in order to ensure conductivity. Conversely, when the average particle diameter exceeds 0.5 μm, the light transmittance is adversely affected and a fine pattern cannot be obtained. Moreover, it is because high temperature is required in order to obtain conduction by fusion of metal particles.

  The reason why the aspect ratio of the metal particles is 1.0 to 1.5 is based on the reason that when the aspect ratio deviates from this range, the light transmittance deteriorates and it becomes difficult to form a fine pattern. In measuring this aspect ratio, the metal particles are dispersed in a suitable dispersion medium and magnified and observed with a microscope or the like, the major axis and minor axis of each particle are measured, and the aspect ratio is calculated using the ratio of major axis / minor axis. Average value.

  As for the particle size variation of the metal particles, it is preferable that the ratio included in the range of the average particle size ± 0.5 μm is 30% by mass or less. This is based on the reason that when the particle size variation of the metal particles exceeds the range, small metal particles enter between the large metal particles, and it becomes difficult to obtain good light transmittance. The fusion start temperature of metal particles and the heat treatment temperature are set such that the fusion start temperature of metal particles <the heat treatment temperature.

  When using such a photosensitive conductive paste to form a fine wiring pattern on the surface of a glass substrate, first, the photosensitive conductive paste is applied to the surface of the glass substrate by a screen printing method or the like, for a predetermined time. It is heated and dried, exposed through a negative type mask, and developed with an alkaline aqueous solution or the like as a developer. When development with the developer is completed and the pattern is formed in this way, it is washed with water and dried, baked in a programmable oven, electric furnace, belt furnace, held for a predetermined time, and then cooled down to completely adhere to the surface of the glass substrate. A fine wiring pattern can be formed.

  According to the above, since the thermal decomposition temperature difference between the binders 1 and 2 is 50 ° C. or more, the setting range of the heat treatment temperature can be widened, and the conditions for removing only the binder 1 can be obtained very easily. Moreover, since it hardens | cures by irradiation of an ultraviolet-ray, a fine pattern with a line | wire width of 20 micrometers or less can be obtained by exposure development. Moreover, since the heat-resistant binder 2 is mix | blended with the photosensitive electrically conductive paste and it remains after heat processing, it becomes possible to obtain high reliability. Moreover, since the capacity | capacitance of the binder 2 is made into the tap porosity of a metal particle or less, and a metal particle is made to contact reliably, resistance reduction is attained.

Furthermore, since the metal particles are silver particles, and the average particle diameter of the silver particles is 0.05 to 0.5 μm, the heat treatment is performed at a low temperature of 300 ° C. or less instead of the conventional high temperature of 500 ° C. to 800 ° C. Silver particles are fused and conducted, and a low resistance of 1 × 10 ⁵ Ω · cm or less can be obtained. At this time, since the binder 1 is decomposed and removed and the volume is reduced, the chance of contact with the silver particles can be remarkably increased, and thus high reliability can be greatly expected. Furthermore, since the silver particles are fused at a low temperature of 300 ° C. or lower, no large and expensive heating device is required, and a long time is not required for temperature rise or cooling.

Examples of the photosensitive conductive paste according to the present invention will be described below together with comparative examples.
While producing the photosensitive electrically conductive paste of an Example and a comparative example, respectively, using these, the test pattern of Examples 1-7 and the test pattern of Comparative Examples 1-4 are each produced, The resolution regarding these, resistance value, The peel resistance was evaluated and summarized in Table 1.

Example 1
First, binder 1, binder 2, and silver particles shown in Table 1 were mixed with methoxybutyl acetate as a solvent at a volume ratio described in the table to prepare a photosensitive conductive paste, and the prepared photosensitive conductive paste was thickened. The coating was applied to 1.1 mm soda lime glass using a bar coater and dried with a hot air dryer at 50 ° C. for 30 minutes to form a dried coating film having a thickness of 20 μm.

  “UV” in Table 1 is an alkali-soluble resin of a styrene-maleic anhydride copolymer system, polyethylene glycol dimethacrylate as a crosslinkable monomer, and bis (2,4,6-trimethylbenzoyl) -phenyl as a photopolymerization initiator. 5 parts by mass of phosphine oxide and 1-hydroxy-cyclohexyl-phenyl-ketone are added to a total of 100 parts by mass of the alkali-soluble resin and the crosslinkable monomer. “PI” in the table is a polyimide resin [manufactured by Maruzen Petroleum: trade name BANI-H].

Next, a pattern part in which regions of 10 μm / 10 μm, 15 μm / 15 μm, 20 μm / 20 μm, 30 μm / 30 μm, 40 μm / 40 μm, and 50 μm / 50 μm are formed in 20 mm □, and a 20 mm × 50 mm transmission part A glass photomask having a thickness of 2 was adhered to the dried coating film, and UV exposure was performed using a Fresnel lens type parallel light exposure machine equipped with a metal halide lamp so as to obtain an integrated light amount of 8000 mJ / cm ² . After UV exposure in this manner, development was performed with a 1.0% by mass aqueous sodium carbonate solution to form a pattern, thereby obtaining an intermediate.

Next, in order to perform heat treatment, an intermediate was set in a programmable oven, and the temperature was raised from room temperature at a heating rate of 10 ° C./min. After reaching the heat treatment temperature shown in Table 1, the temperature was maintained for 60 minutes. After holding for 60 minutes, it was cooled to 180 ° C. at a cooling speed of 10 ° C./min, taken out from the programmable oven, and allowed to cool at room temperature to prepare a test pattern.
The “cured depth” in Table 1 refers to the depth from the surface of the test pattern, which is a wiring pattern, to the inside, and the thickness of the surface layer portion of the test pattern cross section before development heat treatment and hardly eroded by the developer. The thickness can be obtained by observing with an optical microscope or the like.

Examples 2-7
Basically the same as in Example 1, but the average particle size and aspect ratio of the silver particles of the photosensitive conductive paste are changed, the photoinitiator is removed from the UV, or the 5% mass reduction temperature is changed. did.

However, in Example 6, a nickel foil having a thickness of 25 μm was etched to produce a mask having the pattern part and the transmission part, and an EB irradiation apparatus with an acceleration voltage of 200 kV was used, and the irradiation dose was 500 kGy. .
In Table 1, “EB” in Example 6 is obtained by removing the photoinitiator from “UV”. “UV (2)” of Example 7 in the same table is obtained by adding a photopolymerization initiator similar to “UV” to a trisphenol methane type epoxy acrylate oligomer having an acid value of 100 (mg · KOH / g). .

Comparative Examples 1-4
Basically the same as in Example 1, but the average particle size of silver particles, the heat treatment temperature, the fusion start temperature, the aspect ratio were changed, and the 5% mass reduction temperature was changed.
“UV (3)” in Table 1 is obtained by adding a photopolymerization initiator similar to “UV” to a phenol novolac epoxy acrylate oligomer having an acid value of 100 (mg · KOH / g).

Evaluation of Resolution, Resistance Value, and Peeling Resistance (1) Evaluation of Resolution In the pattern area having the same line / space, it was set to the minimum without disconnection or short circuit.
(2) Evaluation of Resistance Value Volume resistivity was measured by a four-end needle method using Loresta HP (manufactured by Dia Instruments: trade name) using a solid region formed by a 20 mm × 50 mm transmission part.

(3) Evaluation of peel resistance A grid pattern is formed by drawing 11 lines each in 1 mm pitch and width and with a cutter knife in a solid area, and an adhesive tape is attached to the grid pattern and peeled, and divided into 100 pieces. In each region, the number of fractions adhered to the adhesive tape was counted. The peel resistance was evaluated at the initial stage and after being left at 60 ° C. and 95% RH for 1000 hours.

Results For the test pattern of Example 1, extremely good resolution, resistance value, and peel resistance could be obtained.
With respect to the test pattern of Example 2, since silver particles having a high fusion starting temperature and a large average particle diameter were used, the resistance value was slightly increased, but there was no problem in practical use, and good resolution and resistance were obtained. Value and peel resistance could be obtained.
About the test pattern of Example 3, since silver particle | grains with low fusion start temperature and a small average particle diameter were used, resistance value became low and the resolution and peeling resistance were also favorable.

For the test pattern of Example 4, since silver particles having a large aspect ratio were used, the curing depth was reduced and the resolution was 20 μm. However, this was a sufficient value depending on the application, and good resolution, resistance value, Peel resistance was obtained.
For the test pattern of Example 5, since silver particles having a small average particle diameter were used, the curing depth was reduced and the resolution was 15 μm, but this was a sufficient value depending on the application, and good resolution and resistance value. The peel resistance was obtained.

About the test pattern of Example 6, although the silver particle with a small average particle diameter was used, it became the hardness for the whole thickness by EB irradiation, and the favorable resolution, resistance value, and peeling resistance were obtained.
For the test pattern of Example 7, a binder 2 having a lower 5% mass loss temperature was used, but there was no particular problem, and extremely good resolution, resistance value, and peel resistance could be obtained.

On the other hand, for the test pattern of Comparative Example 1, silver particles having a fusion start temperature of 320 ° C. and a large average particle diameter were used, so that sufficient electrical conductivity could not be obtained by heat treatment at 280 ° C.
About the test pattern of the comparative example 2, the same material as the comparative example 1 was used, and the heat processing temperature was set as high as 350 degreeC, and the resistance value of the practical level was obtained. However, at such a heat treatment temperature, use of a resin base material, combined use with other parts, an insulating film, etc. is almost impossible, resulting in a problem that the application is very limited.

For the test pattern of Comparative Example 3, since silver particles having a very high fusion start temperature were used, sufficient electrical conductivity could not be obtained by heat treatment at 280 ° C.
About the test pattern of the comparative example 4, the same material as the comparative example 3 was used, and the heat processing temperature was set as high as 450 degreeC, and the resistance value of the practical level was obtained. However, use of a resin base material, combined use with other parts, insulating films, etc. is almost impossible at such a heat treatment temperature, resulting in a problem that the application is very limited, and only extremely poor peeling resistance is obtained. I couldn't.

Claims (1)

A first binder that is insolubilized in the developer by irradiation with either ultraviolet light or electron beam, a second binder that has a thermal decomposition temperature higher by 50 ° C. or more than the thermal decomposition temperature of the first binder, and an average Metal particles having a particle size of 0.05 to 0.5 μm,
The second binder is prepared from only a polyimide resin, a polyamideimide resin, a polyetherimide resin, and their precursors, and the mixing ratio of the second binder to the first binder is determined by the tap porosity of the metal particles. And
A photosensitive conductive paste characterized in that the aspect ratio of the metal particles is 1.0 to 1.5, and the ratio of the average particle diameter of the metal particles included in the range of ± 0.05 μm is 30% by mass or more.