JP2002289038A - Conductive paste composition for use in filling via - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a conductive paste for use in filling via, which does not form uncured part and has good conductivity, superb storage stability, good properties for filling process to via and characteristics necessary as a conductive paste for filling via. SOLUTION: The conductive paste composition comprises a conductive filler having an average particle diameter of 1.0-10 μm and a cationic polymerized resin composition which is prepared by preliminarily dissolving a cation polymerization catalyst in a liquid epoxy resin having at least two epoxy groups.

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 via filling.

[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 in the wiring. Migration is unlikely to occur between adjacent vias. The conductive paste composition has an appropriate life. Sufficient reliability (withstands solder shock test and heat cycle test). Japanese Patent Application Laid-Open No. 56-8892 (hereinafter referred to as "Prior Art 1") describes the use of a composite metal powder obtained by coating copper powder with silver as a conductive paste for a printed wiring board. I have. However, the invention disclosed in the prior art 1 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 as a binder is not described because it is not aimed at improvement.

Further, Japanese Patent Application Laid-Open No. 7-176846 (hereinafter referred to as “prior art 2”) discloses that the average particle size is 0.5 to 2 μm.
80-92% by weight of a conductive filler having a specific surface area of 0.1-1.5 m ² / g, a normal temperature viscosity of 15 Pa · s or less, and an epoxy resin containing two or more epoxy groups.
20% by weight and 0.5 to 5 solid heat latent hardener
There is disclosed a conductive paste composition for filling via holes, which contains wt%. However, the prior art 2 has the following disadvantages because a heating latent curing agent is used as a curing agent for an epoxy resin.

[0009] That is, the heating latent curing agent is a function that, when mixed with an epoxy resin and a curing agent, can be stored for a long time at room temperature without changing its characteristics, and quickly cures when heated to a predetermined temperature or higher. Which means
This heating latent curing agent is a powder in which the active surface of the curing agent powder is reacted (blocked) with an epoxy resin or the like in advance or encapsulated in order to have a heating potential. Even if it is not uniformly dissolved and is dispersed in a non-uniform manner, it may be difficult to impregnate and uncured portions may be formed. In addition, when filling a via with a small diameter, if the particle size of the hardener powder is large, the hardener powder excludes the conductive filler, so the filling rate of the conductive filler is reduced, and good conductivity is obtained. May not be possible, and sometimes there is a risk of disconnection. On the other hand, when the particle diameter of the hardener powder is small, the paste viscosity becomes high, and the workability of filling the via is deteriorated.
If this filling property is poor, it is necessary to repeat the filling operation many times, and the risk of entrapment of air bubbles during filling increases. Furthermore, even though it has the heating potential, the active site remains on the powder surface, so that thickening is inevitable even during storage at room temperature, and refrigerated storage is required.

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.

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 situation, and has sufficient experiments and techniques for obtaining appropriate conditions as a conductive paste for filling vias with respect to conductive fillers, their components and their ratios. As a result of a thorough study, it was possible to achieve the object, without the occurrence of uncured portions, good conductivity, excellent workability to fill vias, good storage stability. Another object of the present invention is to provide a via-filling conductive paste composition having all the properties required for the above-described via-filling conductive paste composition.

[0013]

In order to achieve the above object, a conductive paste composition for via filling according to the present invention has a conductive filler having an average particle size of 1.0 to 10 μm and two or more epoxy groups. It is characterized by containing a cationically polymerizable resin composition obtained by previously dissolving a cationic polymerization catalyst in a liquid epoxy resin as an essential component.

The conductive filler is preferably contained in the conductive paste composition at a high concentration. I mean,
This is because conduction reliability needs to be maintained even when resistance of the via hole is reduced by increasing the probability of contact between the conductive fillers and when substrate distortion due to thermal or mechanical stress is applied. For that purpose, the particle size of the conductive filler should be 10
It is preferably at most 1 μm, and more preferably at least 1 μm in order to obtain viscosity characteristics suitable for screen printing.

As the conductive filler, a noble metal such as gold, silver and palladium, or a base metal such as copper, nickel, tin and lead can be used, but two or more of these can be used in combination. As the shape of the conductive filler, any shape such as a sphere or a flake can be used as long as it has the above characteristics.

A characteristic feature of the present invention is that a cationic polymerization catalyst is used as a curing agent for a liquid epoxy resin having excellent electric insulation. When heated, the cationic polymerization catalyst decomposes a salt to produce cations, which become active species, and polymerize and cure epoxy groups. In particular, in the present invention, since the cationic polymerization catalyst is dissolved in the liquid epoxy resin in advance, the cationic polymerization catalyst is easily dissolved uniformly in the liquid epoxy resin, and an uncured portion does not occur. In addition, since the cationic polymerization catalyst is not present in the resin as a powder, the filling rate of the conductive filler can be increased without removing the conductive filler, and good conductivity can be obtained. The cationic polymerization catalyst can obtain a good cured product with a small amount of use, so that the paste viscosity does not increase, the viscosity characteristics suitable for printing and filling can be expected, and the workability of filling the vial of the paste composition is good. It is. In addition, the cation polymerization catalyst has a responsiveness to heat, and the reaction proceeds when heated to a certain temperature or higher, and the storage stability at room temperature is good.

As the cationic polymerization catalyst, for example,
Sulfonium-phosphonium-pyridinium-SbF ₆
Salts, sulfonium -SbF ₆ salt, dimethyl sulfonium salts, antimony pentachloride - acetyl chloride complex, diaryl - iodonium salt - di-benzyloxy salts, boron halide - tertiary amine adduct can be used include benzyl sulfonium salts. Of these, onium salts are preferred as a result of various studies. When the amount of the cationic polymerization catalyst is 0.5% by weight or more, there is an inconvenience that undissolved components remain when dissolved in the liquid epoxy resin. Therefore, the content thereof is less than 0.5% by weight in the paste composition. It is preferred that In addition, when the content of the cationic polymerization catalyst is large, voids are generated due to reaction heat accompanying rapid reaction during heat curing, and there is a disadvantage that electrical connection becomes poor, so that the cationic polymerization catalyst has a disadvantage. The content is preferably not more than 0.3% by weight in the paste composition,
More preferably, the content is not more than weight%. In order for the cationic polymerization catalyst to exhibit a function as a curing agent for the liquid epoxy resin, at least 0.02
It is preferable to contain 5% by weight or more.

The amount of the cationic polymerization catalyst dissolved in 100 parts by weight of the liquid epoxy resin is preferably 0.5 to 6 parts by weight. If the amount of the cationic polymerization catalyst dissolved is less than 0.5 part by weight, the curing of the epoxy resin becomes insufficient. The cationic polymerization catalyst can be dissolved up to about 15 parts by weight, but if the cationic polymerization catalyst is excessively dissolved, the viscosity of the resin itself increases, and as a result, the viscosity of the paste also increases. Gets worse. In addition, an excessive amount of the catalyst causes rapid heat generation at the time of heat curing, which causes a void in a via. For the reasons described above, when used as a conductive paste for filling vias, it is preferable that the cationic polymerization catalyst be dissolved in the range of 0.5 to 6 parts by weight based on 100 parts by weight of the liquid epoxy resin.

The mixing ratio of the cationically polymerizable resin composition in which the cationic polymerization catalyst is dissolved in the total paste composition is 5 to 5.
It is preferably 14% by weight. If the content is more than 14% by weight, it becomes difficult because the contact between the conductive particles having conductivity is hindered by the resin existing between the particles, and the conductivity required for the via cannot be obtained. On the other hand, if the blending ratio of the cationically polymerizable resin composition in the total paste composition is less than 5% by weight, the bonding strength of the resin for maintaining the contact between the conductive particles having conductivity is insufficient, and the contact between the particles is reduced. It becomes difficult to maintain, and the conductivity required for the via cannot be obtained. For the reasons described above, the proportion of the cationically polymerizable resin composition in which the cationic polymerization catalyst is dissolved in the total paste composition is preferably 5 to 14% by weight, and
More preferably, it is 0% by weight.

Among the conductive fillers, copper powder is preferred in terms of stable supply and low cost. However, as mentioned above,
Copper is easily oxidized, and in particular, copper particles are easily oxidized in an atmosphere of high temperature and high humidity. Therefore, there is a disadvantage that the electric resistance is increased. Therefore, the present invention maintains the characteristics of copper particles, which are relatively low-cost and has relatively low electric resistance, as much as possible, and covers the surface of copper particles with silver in order to compensate for the disadvantage of copper that is easily oxidized. Further, oxidation of copper in an atmosphere of high temperature and high humidity can be suppressed.

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% by weight in order to fulfill the function as a conductor.

The liquid epoxy resin having two or more epoxy groups is typically a bisphenol A epoxy resin, a bisphenol F epoxy resin, an alicyclic epoxy resin, an amine epoxy resin, an epoxy resin having a naphthalene skeleton, or a 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. If necessary, a single-tube epoxy resin can be added.

Although a solvent is generally used to adjust the viscosity of the conductive paste composition, the present invention does not require a solvent. This is because the viscosity can be reduced by increasing the amount of the low-viscosity liquid epoxy resin (eg, polyethylene glycol diglycidyl ether, alicyclic epoxy resin, phenyl glycidyl ether, etc.) as necessary. is there.

The absence of a solvent has the following advantages. This is because the conductive paste composition is dried in the vial after the vial is filled with the solvent, and is sandwiched between both sides with copper foil, and is thermally cured to form an interlayer connection. In addition, if the solvent remains, there is an inconvenience that voids are generated inside the via when the resin is sandwiched between copper foils and cured by heat, resulting in poor electrical connection. This is because no points occur.

However, on the other hand, the viscosity of the conductive paste composition during printing needs to be 1000 Pa · s or less from the viewpoint of printability, so that the viscosity may need to be adjusted. In this case, as described above, the compounding amount of the low-viscosity liquid epoxy resin may be adjusted as needed.

In the present invention, it is preferable to add a phenol resin as required. This phenolic resin functions as an antioxidant and is 0.5% by weight.
The content is preferably as described above, and the content is preferably 5.0% by weight or less because viscosity characteristics suitable for printing and filling are provided.

Further, other additives can be blended. For example, about 0.1% by weight of ethylene oxide adduct of higher fatty acid can be added as a dispersant.

[0031]

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 interlayer electrical connection of a printed wiring board on which a circuit is formed by heat curing.

[0034]

EXAMPLES Examples of the conductive paste composition for filling vias of the present invention will be specifically described below along with comparative examples. Used silver-coated copper particles, liquid epoxy resin, phenolic resin and curing catalyst (curing agent) in respective amounts (% by weight)
Is shown in Table 1 below.

[0035]

[Table 1]

In Table 1, silver-coated copper particles are copper particles having a diameter of 5 μm produced by a reduction method and coated with 5% by weight of silver based on the total amount of copper particles and silver.

The liquid epoxy resin comprises a bisphenol F type epoxy resin, an alicyclic epoxy resin, and 1,6-hexanediol diglycidyl ether, and is represented by symbols A, B and C, respectively.

The phenol resin is a terpene-modified phenol resin.

The curing catalyst (curing agent) is as described below. Example 1-5 and Comparative Example 1,
As for No. 2, before preparing the paste composition, a cationic polymerization catalyst (Sun-Aid SI-10 manufactured by Sanshin Chemical Industry Co., Ltd.) was used.
0) was previously dissolved in a liquid epoxy resin having the above composition at 40 ° C., and for Comparative Example 3-7, a powder hardener (amine-adduct-type latent heat hardener, Ajinomoto (MY-24) was dispersed in the paste composition.

The above components were blended in the blending amounts (% by weight) shown in Table 1 and kneaded with a three-roll mill to form a paste.

No solvent was used.

The prepreg is 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, a paste having the composition shown in Table 1 was filled in the holes of the sheet, dried at 120 ° C. for 5 minutes, and heated to a temperature of 200 using a hot press with copper foil (thickness 18 μm) sandwiched from both sides of the sheet. By heating and pressing at a temperature of 50 ° C. and a pressure of 50 kg / cm ² for 60 minutes, a plate having copper on both sides (double-sided copper-clad plate) was prepared.

The double-sided copper-clad plate was etched by a known method to form an electrode pattern having a thickness of about 25 μm. Table 2 below shows the initial viscosity, the viscosity after storage, the rate of change in viscosity, the adhesion, the volume resistivity, and the resistance per via hole.

The viscosity after storage refers to the viscosity after storage at 10 ° C. for one week. The viscosity change rate is a value obtained by dividing the viscosity after storage by the initial viscosity in percentage (%).

The adhesion and the volume resistivity were measured according to the procedure described below. That is,
A sample substrate for evaluation was prepared according to the following procedure, and the adhesion and volume resistivity of each paste composition shown in Table 1 were measured.

First, a printed pattern 8 as shown in FIG. 3 was formed on a 96% alumina substrate using a 200 mesh screen. The print pattern 8 includes a wiring pattern 9 having an aspect ratio of 75 and five pads 10 of 2 mm × 2 mm. Next, as shown in FIG. 4, an aluminum rivet 11 having a diameter d of 4 mm was placed only on the pad 10 in the print pattern formed on the alumina substrate 12. Then, the alumina substrate 12 on which the aluminum rivets 11 were mounted was heated in a hot air dryer at 200 ° C. for 30 minutes to cure the conductive paste. The volume resistivity and adhesiveness of the evaluation sample prepared as described above were determined as follows.

The volume resistivity was calculated from the resistance value, the film thickness and the aspect ratio actually measured from each wiring pattern 9. Regarding the adhesion, the aluminum rivet 11 placed on the pad 10 on the evaluation alumina substrate was horizontally pressed by a tensile tester (not shown) as shown by an arrow 13 in FIG. It was determined by measuring the maximum stress when the aluminum rivet 11 was separated (peeled off).

[0049]

[Table 2]

In the numerical values shown in Table 2, it is preferable that both the initial viscosity and the viscosity after storage be 500 Pa · sec or less. The adhesiveness is preferably in a range of 30 N (Newton) or more, and the volume resistivity is 2 × 10 ⁻⁴ (Ωc
m) or less is a preferred range, and the via resistance per hole is preferably 3 mΩ or less.

The following points are clear from Table 2. (1) In Comparative Example 1, since the amount of the curing catalyst added was too large, voids were generated due to reaction heat generated due to a rapid reaction at the time of heat curing of the liquid epoxy resin, and the via resistance was increased. Was. (2) In Comparative Example 2, since the amount of the curing catalyst added was too large, and both the initial viscosity and the viscosity after storage were too high, the vias could not be filled and printing could not be performed. (3) In Comparative Example 3, the viscosity was slightly higher than that of Example 2 in which the curing catalyst had the same addition amount, and the curing agent was not sufficiently cured due to the small addition amount of the curing agent, and the via resistance value was increased. Was. (4) In Comparative Example 4, the initial viscosity and the viscosity after storage are slightly higher, and the via resistance value is higher. (5) In Comparative Example 5, since the amount of the curing agent added was too large, and both the initial viscosity and the viscosity after storage were too high, the vias could not be filled and printing could not be performed. (6) In Comparative Example 6, the viscosity was higher than that of Example 5 in which the curing catalyst had the same addition amount, the via filling property was poor, and the curing agent was not sufficiently cured due to the small addition amount of the curing agent. The resistance value has increased. (7) The sample of Comparative Example 7 did not become a paste and could not even measure the viscosity.

In contrast to Comparative Examples 1-7, Example 1
5 to 5 contain a cationically polymerizable resin composition in which a cationic polymerization catalyst having a formulation within the range of the present invention is dissolved in a liquid epoxy resin in advance, so that the viscosity is low and the adhesion is excellent.
The volume resistivity and the via resistance are low, and all the characteristics show good results.

[0053]

According to the present invention, the uncured portion does not occur, the conductivity is good, the workability of filling the via is excellent,
It is possible to provide a conductive paste composition having good storage stability and having characteristics required as 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.

FIG. 3 is a plan view showing a print pattern for evaluating a characteristic value of the conductive paste composition of the present invention.

FIG. 4 is a cross-sectional view showing a state where an aluminum rivet is placed on a pad of the characteristic value evaluation print pattern of FIG. 3;

[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 8 printed pattern 9 wiring pattern 10 pad 11 aluminum rivet 12 alumina substrate

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01B 1/00 H01B 1/00 C H05K 1/11 H05K 1/11 N 3/46 3/46 NS F Terms (reference) 4J002 CC032 CC042 CD021 CD031 CD051 CD131 CD171 DA076 FA086 FB076 FB286 FD116 FD142 GJ02 GQ02 HA08 4J036 AA02 AC01 AD08 AH04 AJ07 AJ08 DA01 DA02 DA05 DC38 FA02 FB07 GA03 GA04 GA22 GA23 GA17 JA05 JA05 JA05 JA05 5E346 AA15 AA43 CC32 CC39 FF07 FF18 GG19 HH07 HH31 5G301 DA03 DA05 DA06 DA10 DA11 DA13 DA42 DA55 DA57 DD01

Claims (7)

[Claims] An essential component is a conductive filler having an average particle size of 1.0 to 10 μm, and a cationically polymerizable resin composition obtained by previously dissolving a cationic polymerization catalyst in a liquid epoxy resin having two or more epoxy groups. A conductive paste composition for filling vias, characterized in that: 2. The conductive filler has an average particle diameter of 1 to 10 μm.
2. The conductive paste composition for via filling according to claim 1, wherein the surface of the copper particles is silver-coated copper particles, wherein silver is coated on the surface of the copper particles, and the ratio of silver to the total amount of copper particles and silver is 0.5 to 20% by weight. . 3. The conductive paste composition for filling vias according to claim 1, wherein the content of the cationic polymerization catalyst is less than 0.5% by weight. 4. The conductive paste composition for via filling according to claim 1, wherein the content of the cationic polymerization catalyst is 0.3% by weight or less. 5. The conductive paste composition for filling vias according to claim 1, wherein the content of the cationic polymerization catalyst is 0.2% by weight or less. 6. The conductive paste composition for via filling according to claim 1, wherein the cationic polymerization catalyst is an onium salt-based catalyst. 7. The conductive paste composition for filling vias according to claim 1, further comprising a phenol resin.