JP2000082332A - Conductive paste composition for via filling - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a conductive paste composition having excellent reliance on electric connections and equipped with a characteristic required of a via filling conductive paste composition. SOLUTION: No more than 5 pts.wt. solvent is contained compared with 100 pts.wt. in total of the components A-D, and the viscosity is made not more than 1000 Pa.s. the component A consists of 86-95 pts.wt. silver-covered copper particles of such a structure that copper particles whose mean particle size ranges from 1 to 10 μm are coated with silver wherein the silver content as the coating relative to the total amount of the copper particles and silver coating is 0.5-20 wt.%, while the component B consists of 2-8 pts.wt. liquid-state epoxy resin having two or more epoxy radicals, and the component C consists of 2-8 pts.wt. phenol resin of resol type, and the component D consists of 0/5-5 pts.wt. hardening agent for epoxy resin.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductive paste composition for filling a via hole of a printed wiring board to electrically connect layers.

[0002]

2. Description of the Related Art In recent years, as electronic devices have become smaller, lighter, and thinner, the density of printed wiring boards used and the number of layers have been remarkably advanced.

On the other hand, as shown in FIG. 1, a conventionally used multilayer printed wiring board has a single printed circuit board 1 laminated in multiple layers, and is provided by penetrating the multilayer printed wiring board. Generally, by plating the through holes 2, electrical connection between the layers is formed by the plated through holes. In FIG. 1, reference numeral 3 denotes a printed wiring. In this plated through hole, it is necessary to perform plating on the through hole of the multilayer substrate and plating on the hole serving as an inner via hole between individual layers. This inner via hole is, for example, as shown in FIG.
These holes are provided in the base material 5 of a single printed circuit board 4 constituting a multilayer board. In the case of the printed circuit board 4, copper foils 6 constituting a wiring pattern are fixed to both surfaces thereof.

However, the plating of the through hole 2 and the plating of the inner via hole 7 are both wet processes called plating, which complicates the manufacturing process. Further, when a through hole is formed, component mounting of a printed wiring board is required. Is considerably restricted, and high-density component mounting cannot be performed.

Therefore, recently, a method of making electrical connection between layers by using a conductive paste has been proposed and put into practical use. According to this method, electrical connection is possible between individual layers and at arbitrary positions, and the mounting density is dramatically improved.

[0006] As a conductive paste used in a conventional printed wiring board, a conductive paste for a jumper circuit, a conductive paste for an EMI shield, or a conductive paste for a through hole is known. However, these conductive pastes have not been used for filling vias. This is because these conductive pastes were not specially designed for filling vias.

[0007]

The properties required for the conductive paste composition for filling vias in printed wiring boards are as follows. Increasing the contact probability of metal particles to reduce via connection resistance Having appropriate viscosity characteristics for screen printing The conductive paste composition and copper foil must adhere firmly In the conductive paste filled in vias No voids or cracks are generated during migration. Must not easily migrate between adjacent vias. Conductive paste composition has an appropriate life. Sufficient reliability (withstands solder shock test and heat cycle test). As a prior art, Japanese Patent Application Laid-Open No. 7-176846 (hereinafter referred to as “Prior Art 1”) discloses that the average particle diameter is 0.
5 to ²⁰ μm, the specific surface area of which is 0.1 to 1.5 m ² /
g of conductor filler 80-92% by weight, normal temperature viscosity 15Pa
A conductive paste composition for filling via holes, comprising 8 to 20% by weight of an epoxy resin containing two or more epoxy groups in an amount of not more than s and 0.5 to 5% by weight of a curing agent is disclosed. However, although the prior art 1 discloses an epoxy resin as a resin component to be used, the epoxy resin alone cannot suppress an increase in electrical resistance when a conductor is oxidized.

On the other hand, Japanese Patent Application Laid-Open No. 56-8892 (hereinafter referred to as "Prior Publication 2") discloses that a composite metal powder obtained by coating copper powder with silver is used as a conductive paste for a printed wiring board. I have. However, the invention disclosed in the prior art 2 is for the purpose of preventing the phenomenon that silver is transferred to the solder at the time of soldering, and the reliability of the electrical connection between the copper particles is low. The use of an epoxy resin or a resol-type phenol resin as a binder is not described because it is not aimed at improvement.

By the way, if copper particles are used as a conductor, it is economically advantageous to noble metals such as gold, silver and palladium, and copper is less susceptible to price changes due to fluctuations in demand as these noble metals. There are benefits. Further, copper has a characteristic that electric resistance is lower than nickel, tin, and lead. On the other hand, copper has a drawback that its operation reliability is inferior because it is more easily oxidized than gold, silver, palladium, nickel, tin and lead. Particularly, in an atmosphere of high temperature and high humidity, the copper paste connected to the via is gradually oxidized, so that the electric resistance is increased. In a remarkable case, the printed wiring may be disconnected.

As described above, no conductive paste composition having excellent properties has been provided as a via-filling conductive paste composition.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has been developed in order to improve the reliability of electrical connection between copper particles when the copper particles are used as a conductor component. As a result of sufficient experiments and technical studies to obtain the appropriate conditions for the conductive paste for via filling with respect to the ratio of each compounded component, the results were achieved. An object of the present invention is to provide a conductive paste composition which is excellent and has characteristics required for the above-mentioned conductive paste composition for via filling.

[0012]

In order to achieve the above-mentioned object, a conductive paste composition for filling a via of a printed wiring board according to the present invention is based on 100 parts by weight of the following components A to D in total. Contains 5 parts by weight or less of solvent and has a viscosity of 10
It is characterized by being equal to or less than 00 Pa · s. A A silver-coated copper particle having an average particle diameter of 1 to 10 μm coated with silver and having a silver content of 0.5 to 20% by weight based on the total amount of the copper particle and the coated silver is 86 to 86%. 9
5 parts by weight B 2 to 8 parts by weight of liquid epoxy resin having two or more epoxy groups C 2 to 8 parts by weight of resole type phenolic resin D Hardening agent of epoxy resin is 0.5 As described above, copper particles are easily oxidized in a high-temperature and high-humidity atmosphere. Therefore, there is a disadvantage that the electric resistance is increased. Therefore, the present invention, while maintaining as much as possible the characteristics of copper particles that low cost and relatively low electrical resistance, in order to compensate for the disadvantage of copper is easily oxidized,
By coating the surface of the copper particles with silver, the oxidation of copper in an atmosphere of high temperature and high humidity is suppressed, and even when the copper particles are partially exposed to the surface despite coating silver. Can reduce copper particles oxidized by the reducing power of the resole type phenol resin, and can suppress an increase in electric resistance.

In order to keep the electric resistance low, the proportion of silver to the total amount of copper particles and silver coated on the surface thereof is required to be at least 0.5% by weight. The copper particles are easily oxidized and the electric resistance increases. On the other hand, when the ratio of silver exceeds 20% by weight, oxidation of the copper particles is less likely to occur, but the silver ratio is increased to increase the cost, and silver migration is more likely to occur, resulting in an electric connection between vias. Connection reliability decreases. Therefore, the ratio of silver to the total amount of copper particles and silver covering the surface is preferably 0.5 to 20% by weight, more preferably 2 to 15% by weight.

The particle size of the copper particles coated with silver is 1 to 10
μm is preferred. The reason for this is to provide a viscosity characteristic suitable for screen printing. As the copper particles, those produced by an electrolytic method, a reduction method, or an atomizing method are preferably used. This is because the copper particles produced by these methods satisfy the above-mentioned particle size range, have a small specific surface area, and have an almost spherical shape.

As a method of coating the surface of the copper particles with silver, a method of coating the surface of the copper as uniformly as possible by a plating method is preferable. When the copper is exposed due to uneven plating, the exposed copper portion is oxidized. Progresses, and the electrical resistance increases. Therefore, it is preferable to perform plating so as to prevent uneven plating.

The silver-coated copper particles as described above are preferably blended in an amount of 86 to 95 parts by weight in order to function as a conductor.

Typical liquid epoxy resins having two or more epoxy groups include bisphenol A type epoxy resin, bisphenol F type epoxy resin, alicyclic epoxy resin, amine type epoxy resin, naphthalene skeleton epoxy resin, and dimer. There is a liquid epoxy resin such as an epoxy resin in which an acid is glycidyl-esterified, but basically, these resins can be appropriately mixed and used. This liquid epoxy resin has excellent electrical insulation properties but does not have a reducing function. Therefore, when used in combination with the resole type phenol resin described below, the defects of the resole type phenol resin are suppressed, and the resol The characteristics of the mold phenol resin can be utilized.

Although the resole type phenol resin is a resin having excellent reducibility, if only the resole type phenol resin is used as a binder resin, the resin itself is brittle, and when used as a conductive paste for filling vias, the effect of a heat cycle is reduced. As a result, the electrical connection reliability decreases. In addition, since the resol-type phenol resin is generally solid, it must be dissolved in a solvent before use, and if the amount of the solvent required for dissolution is large, it is not suitable as a conductive paste for via filling. Therefore, it is preferable to use a resin obtained by mixing a liquid epoxy resin and a resol-type phenol resin, and the weight mixing ratio is preferably liquid epoxy resin: resole-type phenol resin = 1 to 4: 4 to 1, and this ratio is used. It depends on the type of liquid epoxy resin and resol type phenol resin.

As the curing agent, a general curing agent can be used. Amine-based curing agents such as dicyandiamide and carboxylic acid hydrazide; urea-based curing agents such as 3- (3,4-dichlorophenyl) -1,1-dimethylurea; phthalic anhydride, pyromellitic anhydride, and hexahydrophthalic anhydride And acid anhydride-based curing agents such as methylnadic anhydride, and aromatic amine-based (amine adduct) curing agents such as diaminodiphenylmethane and diaminodiphenylsulfone. Among these, a solid latent curing agent is particularly preferable from the viewpoints of stability and workability of the composition. Here, the solid latent curing agent is
By raising to a predetermined reaction temperature and then cooling to room temperature, several types of amine components and epoxy resin are reacted to some extent to form particles of the resin, and the active groups such as amines are encapsulated in the three-dimensional structure of the polymer. The reaction is stopped in a state where the resin particle surface has partially reacted, and can be stored at room temperature for a long time without changing the characteristics, and when heated to a predetermined temperature or more, the resin particles are melted or dissolved, A substance having a function in which an encapsulated active group appears, starts a reaction at the same time, and cures quickly.

The above-mentioned liquid epoxy resin and resol type phenol resin are preferably blended in an amount of 2 to 8 parts by weight in order to ensure electrical connection reliability.
In order to perform a predetermined curing function, the curing agent should be 0.5 to 5
It is preferable to mix by weight. However, if the amount of the organic binder composed of the liquid epoxy resin, the resole-type phenol resin and the curing agent is too large, the electric resistance increases, while if the amount is too small, the paste cannot be formed. The amount is 5-1
Preferably it is 4 parts by weight.

The solvent is basically for adjusting the viscosity of the conductive paste composition. However, if the boiling point is too low, the solvent dries during filling of the via and the viscosity increases, making printing impossible. Therefore, those having a boiling point of 150 ° C. or more are preferable. Examples include butyl cellosolve, butyl cellosolve acetate, ethyl cellosolve, ethyl cellosolve acetate, butyl carbitol, butyl carbitol acetate, ethyl carbitol, ethyl carbitol acetate, and 2,2,4-trimethylpentanediol monoisobutyrate. It is possible, but not limited to these.

The amount of the solvent is preferably as small as possible. This is because the conductive paste is dried after drying the solvent after filling the vias, sandwiched between the copper foils from both sides, and heat-cured for interlayer connection. If the filling volume is small, it will be difficult to make an electrical connection, or if the solvent remains, voids will occur inside the via when sandwiched between copper foils and thermoset, resulting in poor electrical connection. It is.

However, on the other hand, the viscosity of the conductive paste composition at the time of printing needs to be 1000 Pa · s or less from the viewpoint of printability, so that a solvent may need to be added in some cases. Even in this case, the amount of the solvent to be added is preferably 5 parts by weight or less based on 100 parts by weight of the silver-coated copper particles and the organic binder.

If the amount of the solvent exceeds 5 parts by weight, the volumetric shrinkage of the conductive paste after drying becomes large and the electrical connection becomes unstable.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An example in which the conductive paste composition of the present invention is actually used will be described. That is,
Drilling, punching, laser or the like is used to make holes in a prepreg (made of glass epoxy, paper phenol, composite, aramid epoxy, etc.) on a printed circuit board, and the holes are filled with the conductive paste composition of the present invention. . After drying, a copper foil is laminated from both sides, and the layers are connected by heating and pressing, and a circuit is formed later by etching to form a substrate. In addition, to make a multilayer substrate, a prepreg filled with the conductive paste composition of the present invention is laminated on the substrate prepared as described above, and a copper foil is laminated thereon, heated and cured, and then etched. Circuits can be formed to create a multilayer substrate. By sequentially repeating this process, a substrate having a desired multilayer structure can be formed.

As described above, the conductive paste composition of the present invention can be used for filling the vias of the prepreg to establish electrical connection between layers.

As another form, it can be used as a conductive paste for filling through holes for electrical connection between layers of a printed wiring board having a circuit formed by heat curing.

[0028]

EXAMPLES The conductive paste composition for filling vias according to the present invention will be specifically described below. Table 1 shows details of the metal powder used.

[0029]

[Table 1]

The metal powders shown in Table 1 and the organic binders and solvents shown in Table 2 below were blended in the proportions (parts by weight) shown in Table 2 and kneaded with a three-roll mill to form a paste.

The epoxy resin used was a mixture of Bisphenol A type Epicoat 828 (Yuika Shell Epoxy) and Bisphenol F type Epicoat 807 (Yuika Shell Epoxy) in a weight ratio of 3 to 7. .

The resol type phenol resin is PL-22.
11 (manufactured by Showa Polymer Co., Ltd.) was used.

The curing agent is an amine adduct type curing agent MY
-24 (manufactured by Ajinomoto Co.) was used.

As a solvent, butyl carbitol acetate was used.

As the prepreg, a composite type, that is, an epoxy resin and an alumina powder are blended at a ratio of 12% by weight and 88% by weight, processed into a sheet having a thickness of 200 μm, and punched into the sheet. A hole having a diameter of 200 μm was formed. This sheet is in a prepreg state and is not completely cured.

Then, the paste shown in Table 2 was filled in the holes of the sheet and dried at 120 ° C. for 5 minutes. Then, a copper foil (thickness: 18 μm) was sandwiched from both sides of the sheet using a hot press at a temperature of 180 ° C. By heating and pressing at a pressure of 50 kg / cm ² for 60 minutes, a plate with copper on both sides (double-sided copper-clad plate) was prepared.

This double-sided copper-clad plate was etched by a known method to form an electrode pattern. Table 2 shows the electrical resistance per via hole. This substrate was subjected to PCT (pressure cooker test: 121 ° C., 100 hours)
The electric resistance per via hole was measured, and the change in the rate of increase from the initial resistance value was calculated (0% indicates that the resistance value did not change, and 100% indicates that the initial resistance value doubled). To indicate that it has.)

[0038]

[Table 2]

Table 2 shows that those having a via resistance of 3 mΩ or less and a rate of change of resistance after PCT of 100% or less are good.

The copper particles having no silver coating as in Comparative Example 1 have a low via resistance, but a very large change in resistance after PCT.

Further, when copper particles coated with 30% by weight of silver as in Comparative Example 2 are used, there is no problem in resistance value change after PCT, but the production cost is increased, which is not economical. .

In Comparative Example 3, the organic binder was 15
Since the weight is large, the via resistance is large.

In Comparative Example 4, since the organic binder was too small at 3 parts by weight, the paste could not be formed even when the solvent was added up to 5 parts by weight.

In Comparative Examples 5 and 6, since the added amount of the solvent was as large as 7 parts by weight with respect to 100 parts by weight of the silver-coated copper particles and the organic binder, the via resistance was high and the change in resistance after PCT was 1000%. That's all.

When the epoxy resin was used alone as in Comparative Example 7, the change in resistance after PCT was large.

Further, when the resole type phenol resin was used alone as in Comparative Example 8, the paste viscosity became too large and the via could not be filled with the paste.

When the paste amount is reduced by increasing the amount of the solvent to 8 parts by weight as in Comparative Example 9, the via can be filled with the paste, but the via resistance is high, and the resistance after PCT is high. The change was also extremely large.

In contrast to these comparative examples, Examples 1 to 13
Shows good results because the composition is composed of silver-coated copper particles, an organic binder, and a solvent within the range of the present invention, so that the via resistance is low and the resistance change after PCT is small.

[0049]

According to the present invention, it is possible to provide a conductive paste composition having excellent electrical connection reliability and having the characteristics required for a conductive paste composition for via filling.

[Brief description of the drawings]

FIG. 1 is a perspective view of a multilayer printed wiring board.

FIG. 2 is a sectional view of a single printed circuit board.

[Explanation of symbols]

 1, 4 ... single printed circuit board 2 ... through hole 3 ... printed wiring 5 ... base material 6 ... copper foil 7 ... inner via hole

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H05K 3/40 H05K 3/40 K

Claims (3)

[Claims] 1. A conductive paste composition for filling a via of a printed wiring board, comprising a solvent of 5 parts by weight or less based on a total of 100 parts by weight of the following components A to D, and having a viscosity of 1000 Pa -A conductive paste composition for filling vias, wherein the composition is not more than s. A 86 to 95 silver-coated copper particles in which silver is coated on the surface of copper particles having an average particle diameter of 1 to 10 μm, and the ratio of silver to the total amount of copper particles and coated silver is 0.5 to 20% by weight.
Parts by weight B liquid epoxy resin having two or more epoxy groups is 2 to 8 parts by weight C resole type phenol resin is 2 to 8 parts by weight D curing agent of epoxy resin is 0.5 to 5 parts by weight 5 parts by weight 2. The conductive paste composition for filling vias according to claim 1, wherein the silver-coated copper particles are obtained by coating silver on copper particles produced by an electrolytic method, a reduction method or an atomizing method. 3. The conductive paste composition for filling vias according to claim 1, wherein the silver-coated copper particles are obtained by coating silver on the surface of copper particles by plating.