JPH11222549A - Paste for filling through-hole - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a paste for filling through-holes which is excellent in workability in filling through-holes and can inhibit the shrinkage of a cured item in a reflow step in soldering. SOLUTION: A paste 4 comprising an epoxy resin compsn. and at least either an inorg. filler or a metal filler is used. The epoxy resin used contains 10-50 pts.wt. amine-type epoxy resin. In addition to the amine-type epoxy resin, at least either a phenol novolak epoxy resin or a bisphenol A epoxy resin is incorporated. Spherical silica is pref. as the inorg. filler; and a sphenrical copper powder, as the metal filler. The heating temp. in a hole filling step is pref. 120-170 deg.C; and that in a reflow step, pref. 230-280 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a paste for filling through holes which is used to fill through holes provided in a printed wiring board. INDUSTRIAL APPLICABILITY The paste of the present invention is useful for a high-density printed wiring board, particularly a multilayer printed wiring board, and is used for various information and communication printed wiring boards exposed to severe use conditions such as a build-up IC package for an MPU. Can be.

[0002]

2. Description of the Related Art In printed wiring boards and laminates having through holes for conducting conduction between the front and back of a substrate, through holes serving as through holes are provided in an insulating substrate, a copper-clad laminate, or the like. Is subjected to metal plating to form a conductor layer. Then, the through-hole is filled with a filling paste. Printed wiring boards having such through holes are disclosed in Japanese Patent Application Laid-Open Nos. 62-224996 and 63-137499. These wiring boards and the like are mainly used for consumer use. However, in MPU IC packages requiring high reliability, those having such through holes are not used, and ceramic wiring boards and the like are not used. in use.

[0003]

However, in recent years, there has been an increasing demand for higher densities or multilayers in printed wiring boards and the like. Wiring boards and laminated boards having through holes are also used in MPU IC packages. It has come to be. When a chip is mounted on this MPU IC package, when a conventional paste for consumer use is filled in the through-hole, a crack 51 is generated in the build-up layer 5 on the through-hole 2 as shown in FIG. There is. It is generally considered that the cause of the crack generation in the build-up layer is caused by a difference in thermal expansion between the substrate 1 and the paste 4.

Therefore, the present inventors have examined using a large number of pastes whose thermal expansion has been specified, but failed to suppress the occurrence of cracks. Therefore, the inventors considered that there was another cause of the occurrence of the crack and made various studies. As a result, the cracks are formed in the hole filling process, and the cured product is further hardened and shrunk in the solder reflow process, and the shrinkage remains as it is after cooling. Was found to be caused by doing

SUMMARY OF THE INVENTION The present invention solves the above-mentioned conventional problems, and further suppresses further shrinkage of the cured product generated in the hole filling step after cooling in the solder reflow step, thereby preventing cracks in the build-up layer. An object of the present invention is to provide a paste for filling through holes that is sufficiently prevented. Another object of the present invention is to provide a through-hole filling paste having low viscosity, excellent fluidity, and low water absorption by using a specific epoxy resin in combination. By using such a paste, it is possible to easily fill the through-hole, without causing poor filling, and sufficiently suppressing the occurrence of cracks in the build-up layer.

[0006]

The paste for filling a through hole according to the first invention is a paste for filling a through hole used to fill a through hole of a printed wiring board, the paste having an epoxy resin and a curing agent. It contains an epoxy resin composition and a filler, and the epoxy resin contains an amine type epoxy resin.

The above-mentioned “paste for filling through-holes”
The above-mentioned "epoxy resin composition" having an epoxy resin and a curing agent as a resin component is contained. This epoxy resin contains the above-mentioned “amine type epoxy resin”. By using this amine-type epoxy resin, the occurrence of cracks in the build-up layer can be sufficiently suppressed. The amine type epoxy resin has an effect of suppressing the occurrence of cracks as described above and has a low viscosity. for that reason,
The viscosity of the obtained paste is also reduced, and the workability at the time of filling the through holes is greatly improved. Furthermore, since the viscosity is low, a large amount of filler can be compounded, and the occurrence of cracks in the build-up layer can be suppressed more reliably.

As the amine type epoxy resin, a tetrafunctional epoxy resin such as tetraglycidylaminodiphenylmethane, tetraglycidyl metaxylylenediamine or the like can be used. In addition, trifunctional epoxy resins such as triglycidyl metaaminophenol and triglycidyl paraaminophenol can also be used. Further, a bifunctional epoxy resin such as diglycidylaniline and diglycidyl orthotoluidine can also be used.

Although the epoxy resin having a smaller number of functional groups has a lower viscosity, the epoxy resin is preferably more polyfunctional in order to suppress shrinkage of the cured product in the solder reflow step. However, in the case of tetrafunctional, the cured product has high rigidity, and cracks may occur in the cured product itself. Considering these viscosities and hardnesses, among these amine type epoxy resins, as in the second invention, they are liquid at normal temperature, that is, at a temperature of about 20 to 30 ° C., particularly about 23 to 25 ° C., A trifunctional amine epoxy resin having a low viscosity and a high glass transition point of a cured product obtained by curing the paste is preferred. Further, as in the third aspect, the viscosity is lower, the workability when filling the paste into the through-holes is excellent, the filling is not defective, and the generation of cracks in the build-up layer is sufficiently suppressed. Functional triglycidyl paraaminophenol is particularly preferred.

Since the amine type epoxy resin has high water absorption, the cured body may have high water absorption in the filling process. Therefore, it is preferable to use another epoxy resin having low water absorption. Examples of the epoxy resin having a low water absorption include a polyphenol type epoxy resin. In particular, when at least one of a phenol novolak epoxy resin and a bisphenol A epoxy resin is used as in the fourth invention, the shrinkage of the cured product in the solder reflow step is further reduced, which is preferable. Furthermore, when the phenol novolak type epoxy resin is used alone, the viscosity of the paste becomes considerably high. However, the viscosity of the paste is reduced by using the phenol novolak type epoxy resin in combination with the amine type epoxy resin, and a more practical paste is obtained. be able to.

When the total amount of the epoxy resin is 100 parts by weight, the amount of the amine type epoxy resin is preferably 10 to 50 parts by weight, particularly 15 to 45 parts by weight, and more preferably 20 to 40 parts by weight. When the amount of the amine type epoxy resin is less than 10 parts by weight, the viscosity of the paste does not become sufficiently low, and the workability at the time of filling the through-hole is reduced, which may cause a defective filling. On the other hand, when the amount of the amine type epoxy resin exceeds 50 parts by weight, water absorption becomes high, and problems such as cracks may be generated in the cured product or its surroundings during the reliability evaluation.

The paste 2 for filling a through hole of the present invention 2
The viscosity at 5 ° C. is preferably 10,000 poise or less, particularly 7000 poise or less, and more preferably 5000 poise or less as in the fifth invention. This viscosity is 10,000
Exceeding the poise is not preferable because the workability when filling the paste into the through-holes is reduced and a filling failure may occur.

The shrinkage ratio of the second cured product generated in the solder reflow process to the first cured product generated in the filling process is preferably 0.1% or less as in the fifth invention. If the shrinkage exceeds 0.1%, cracks may occur in the build-up layer after cooling in the solder reflow process or in a reliability test or the like thereafter. The contraction rate can be calculated by reading the contraction length from the chart of the thermomechanical analyzer. Furthermore, since this paste does not require a volatile solvent or the like, the volatile content during curing in the filling process is very small, and this also suppresses the generation of bubbles in the first cured product generated in the filling process.

The above-mentioned shrinkage ratio is determined by heating a 100 μm thick film made of this paste at 150 ° C. for 5 hours, curing it, and then using this film to obtain a 5 mm width.
When the temperature was increased from 23 ° C. to 270 ° C. in a state where a load of 5 g was applied in the length direction of the sample, and then lowered to 23 ° C., Can be calculated by the following equation. Shrinkage (%) = [270 ° C.
Length of specimen at 23 ° C before heating up to -27
The length of the specimen at the time when the temperature was raised to 0 ° C. and then lowered to 23 ° C.] / The length of the specimen at 23 ° C. before the temperature was raised to 270 ° C. × 100

This method does not actually fill the through-hole with the paste, cure the paste, and evaluate the shrinkage in the solder reflow process. However, when a paste having a shrinkage rate of 0.1% or less measured by this method is filled in the through-hole, cured in the filling step, and then heated and cooled in the solder reflow step, cracks in the build-up layer may occur. It has been confirmed that the occurrence of phenomena can be sufficiently suppressed. By such a simple method, a paste that can be practically used and a paste that cannot be practically used can be easily separated. It is to be noted that the above rate of temperature rise and temperature fall is preferably 1 to 5 ° C./min, particularly 1 to 3 ° C./min, and more preferably 2 ° C./min. Further, it is preferable to immediately lower the temperature after raising the temperature to 270 ° C.

As the above-mentioned "curing agent", a high-temperature curing type is used, and a catalyst-based curing agent is preferable in consideration of the flow characteristics of the paste or a decrease in viscosity. In particular, as in the sixth invention, an imidazole-based curing agent that has a sufficiently long pot life and can obtain a practical paste is more preferable. As high temperature curing type curing agents, other than these, acid anhydrides,
Boron trifluoride and the like are known, but these are not preferred because they have high reactivity with the amine type epoxy resin and shorten the pot life of the paste. The content of the imidazole-based curing agent is preferably 0.5 to 10 parts by weight, particularly 1 to 8 parts by weight, and more preferably 3 to 7 parts by weight, based on 100 parts by weight of the epoxy resin composition.

In the paste using an epoxy resin as the resin component as in the present invention, it is preferable that the heating temperature in the filling step is 120 to 170 ° C. and the heating temperature in the solder reflow step is 230 to 280 ° C.
If the heating temperature in the filling step is less than 120 ° C., the epoxy resin is not sufficiently cured, which is not preferable. on the other hand,
If the heating temperature exceeds 170 ° C., cracks in the build-up layer in the solder reflow step can be suppressed, but cracks may occur in the cured body itself in a subsequent heat cycle test or the like. Further, if the heating temperature in the solder reflow step is lower than 230, an IC chip or the like cannot be mounted. On the other hand, if the heating temperature exceeds 280 ° C., the epoxy resin may be thermally degraded, which is not preferable.

In order to suppress shrinkage of the cured product generated in the solder reflow step, a filler is mixed with the paste. As the “filler”, as in the seventh invention,
An inorganic filler or a metal filler may be used, or these may be used in combination. In order to suppress the shrinkage of the cured product, an inorganic filler is more preferable, but the purpose can be sufficiently achieved even with a metal filler.

The inorganic filler includes, without particular limitation, those used as fillers for epoxy resins, such as silica, mica, calcium carbonate, alumina, iron oxide, electrolytic iron powder, slate powder, and talc. Can be done. Among these inorganic fillers, silica having a small coefficient of thermal expansion is more preferable. In order to contain a larger amount of inorganic filler while suppressing an increase in the viscosity of the paste, a spherical inorganic filler such as spherical silica is particularly preferable. Further, by treating the surface of the inorganic filler with a silane coupling agent, the affinity with the epoxy resin can be improved, and the water absorption of the cured product generated in the filling process can be reduced.

As the metal filler, a filler made of powder such as copper, silver and a mixture thereof can be used. As the metal filler, it is preferable to use a filler in which at least half or more of the metal powder is a spherical powder in order to suppress an increase in the viscosity of the paste when the metal filler is contained in a large amount. Further, it is more preferable to use a metal filler obtained by soft etching a spherical copper powder or a metal filler obtained by a blackening treatment. Due to this blackening treatment, a needle-like coating made of copper oxide is formed on the surface of the powder particles and roughened, and the adhesion between the resin and the copper powder is increased by the improvement of the anchor effect and the chemical affinity. . Further, by treating the surface of the metal filler with a silane coupling agent having an epoxy group, the affinity between the epoxy resin and the metal filler can be increased. In particular, by using an epoxy silane having an epoxy group on the hydrophobic group side, the water absorption of the cured product generated in the filling process can be reduced.

These fillers are preferably contained in a large amount in order to suppress shrinkage of the cured product generated during solder reflow. However, care must be taken so that the increase in the viscosity of the paste does not reduce the workability when filling the through-holes. For example, in the case of silica, if the paste is 100 parts by weight,
Preferably, the content is about parts by weight. If it contains silica in this range, a paste having an appropriate viscosity is obtained, and the workability when filling the through holes is excellent,
No defective filling occurs. Further, generation of cracks in the build-up layer can be sufficiently suppressed. In addition, when the metal filler and the inorganic filler are used in combination, the amount ratio is not particularly limited, and the fluidity of the paste is not practically reduced so that it becomes a problem. Adjust it.

The viscosity of this paste can be from 1000 to 5000 poise, especially 1000 to 3500 poise, and its water absorption is 0.5 to 1.0%, especially 0.5 to 0.8%. It can be. Furthermore, the viscosity and the water absorption rate are low as described above, and the shrinkage rate of the cured product in the solder reflow is 0.01 to 0.1%, particularly 0.1 to 0.1%.
The content can be set to 0.01 to 0.08%, further 0.01 to 0.05%. In addition, a paste having a higher performance with a viscosity of 1000 to 3000 poise, a water absorption of 0.1 to 0.2%, and a shrinkage of less than 0.01% can be obtained.
The methods for measuring the viscosity, the water absorption and the shrinkage are the same as those in the examples described later.

Further, if necessary, this paste
Various additives can be contained. Such additives include antifoaming agents, leveling agents, antioxidants and the like. These additives can be contained in appropriate amounts as long as the properties of the paste are not impaired.

When the paste for filling through-holes containing the amine type epoxy resin of the present invention is used, the reason why the shrinkage of the cured product generated in the solder reflow process is suppressed is not clear, but is presumed as follows. . That is, general-purpose epoxy resins such as bisphenol A type epoxy resin and bisphenol F type epoxy resin are composed of linear flexible molecules. on the other hand,
Amine-type epoxy resins such as triglycidyl para-aminophenol are composed of bulky molecules, and when cured, steric hindrance restricts the movement of the molecules, and the shrinkage in the solder reflow process is very small at 0.1% or less. Generation of cracks in the build-up layer is sufficiently suppressed.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to examples. Examples 1 to 4 and Comparative Examples 1 to 4 (1) Preparation of paste 95 parts by weight of the following epoxy resin and an imidazole-based curing agent (trade name “2E4MZ-C manufactured by Shikoku Chemicals Co., Ltd.)
N ") 100 parts by weight of the epoxy resin composition consisting of 5 parts by weight, the following inorganic filler and a part thereof, and a metal filler were added in addition to the metal filler in the ratio shown in Table 1, and these were mixed and passed through. A hole filling paste was prepared.

Trifunctional amine type epoxy resin (triglycidyl paraaminophenol) (trade name "E-152", manufactured by Yuka Shell Co., Ltd., represented by "AP" in Table 1) Bifunctional amine type epoxy resin (Diglycidyl aniline) (manufactured by Nippon Kayaku Co., Ltd., trade name "GAN", represented as "AN" in Table 1) Phenol novolak type epoxy resin (trade name "E-152", manufactured by Yuka Shell Co., Ltd.) ), And in Table 1 are represented as “PN”. )

Bisphenol A type epoxy resin (same as above)
The product name is “E-828”), and is represented as “BPA” in Table 1. ) Bisphenol F type epoxy resin (same product name "E-
807 ”) and in Table 1 are represented as“ BPF ”. 1,6 hexanediol diglycidyl ether (same as above)
Product name “YED216”), and in Table 1, “16H”
It expresses. )

(A) Inorganic filler (1) Spherical silica, average particle size 1.6 μm; trade name “SO-E5” manufactured by Tatsumori Co., Ltd., “S16” in Table 1
It expresses. (2) Spherical silica, average particle size 0.5 μm;
O-E2 "and in Table 1 are represented as" S05 ". (B) Metal filler (1) Spherical copper powder, average particle size 10 μm; trade name “SFR-CU”, manufactured by Japan Atomize Processing Co., Ltd .;

[0029]

[Table 1]

(2) Viscosity, water absorption and shrinkage of the paste for filling through holes The viscosity, water absorption and shrinkage of the paste prepared in (1) were measured by the following methods. The results are also shown in Table 1. Viscosity: Measured at 25 ° C. with a rotating cylinder viscometer. Water absorption: Measured according to JIS K 6911. Shrinkage: The paste was formed into a film having a thickness of 100 μm, and cured by heating at 150 ° C. for 5 hours. Thereafter, a test piece having a length of 20 mm and a width of 5 mm was prepared, and the distance between the chucks was set to 15 mm, and a load of 5 g was applied in the length direction of the test piece.
After heating at a rate of 2 ° C./min to 23 ° C. at the same rate
Temperature. From the obtained chart of the thermomechanical analyzer, the shrinkage length [reading of the length on the chart at 23 ° C. before heating—reading of the length on the chart at 23 ° C. after cooling (unit: μm)] Was read, and the shrinkage length was divided by the length of the test piece before the temperature was raised to obtain a shrinkage ratio.

(3) Workability at the time of filling the through-hole and the presence or absence of cracks in the formed cured product The paste prepared in (1) is screen-printed on the through-hole provided in the printed wiring board by the screen printing method. The mixture was filled, heated at 150 ° C. for 5 hours in the atmosphere, cured, and the filling state was visually observed. When the filling condition was good, a multilayer printed wiring board was prepared using this printed wiring board, and passed through a solder reflow furnace adjusted to 260 ° C. for 10 minutes to check for the occurrence of cracks. It was confirmed visually. The results are also shown in Table 1.

According to the results shown in Table 1, in Examples 1 to 4, which are within the scope of the first invention, the viscosity, the water absorption and the shrinkage are small, and a paste with excellent performance is obtained. In particular, in Examples 1 to 2 and 4 corresponding to the second and third inventions, pastes having lower viscosity were obtained. Furthermore, in Examples 1 to 4, the condition of the filled paste was good, and no crack was observed. A
In Example 4, in which P and BPA were used in a quantitative ratio of 70:30, and an appropriate amount of spherical silica and spherical copper powder were used in combination, the viscosity was sufficiently low, the shrinkage was very small, and a more excellent paste was obtained. It turns out that it has been obtained.

On the other hand, in Comparative Example 1 using only BPF as the epoxy resin, the shrinkage was large, and cracks occurred in the cured product. In Comparative Example 2 using only PN,
Although the shrinkage was small, the viscosity was high, and poor filling was observed in some parts. Furthermore, as an epoxy resin,
In Comparative Example 3 in which a small amount of 16H, which is generally used as a reactive diluent, was used in combination, the viscosity was reduced and the filling property was improved, but the shrinkage was large and cracks occurred. Also, B
In Comparative Example 4 using only PA, the viscosity was high and poor filling was observed in part. In Example 4 and Comparative Example 4, the reason why the water absorption was very small was that the apparent numerical value calculated was small due to the weight of the spherical copper powder mixed in a large amount.

[0034]

According to the first aspect of the present invention, it is possible to obtain a paste for filling a through hole, which has a low viscosity, is excellent in workability of filling a through hole, and does not cause defective filling. If this paste is used, the shrinkage of the cured product in the length direction of the through hole in the solder reflow process is small, and the occurrence of cracks in the build-up layer can be sufficiently suppressed.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a state in which a crack has occurred in a build-up layer of a multilayer printed wiring board.

[Explanation of symbols]

1; multilayer board; 2; through hole; 3; plating layer;
Paste, 41; filler, 5; build-up layer, 5
1; crack, 6; via hole.

Claims (7)

[Claims] 1. A paste for filling a through hole used in filling a through hole of a printed wiring board, the paste containing an epoxy resin composition having an epoxy resin and a curing agent and a filler, wherein the epoxy resin is A paste for filling through holes, comprising an amine type epoxy resin. 2. The paste for filling a through hole according to claim 1, wherein the amine type epoxy resin is a trifunctional epoxy resin which is liquid at room temperature. 3. The paste for filling a through hole according to claim 1, wherein the amine type epoxy resin is triglycidyl paraaminophenol. 4. The paste for filling a through hole according to claim 1, wherein the epoxy resin contains at least one of a phenol novolak type epoxy resin and a bisphenol A type epoxy resin. 5. A paste having a viscosity at 25 ° C. of 1
0000 poise or less, and the shrinkage in the length direction of the through-hole of the second cured body generated by heating and cooling the first cured body generated by heating in the hole filling step in the solder reflow step is 0. .
The paste for filling a through hole according to any one of claims 1 to 4, which is 1% or less. 6. The paste for filling a through hole according to claim 1, wherein the curing agent is an imidazole-based curing agent. 7. The paste for filling a through hole according to claim 1, wherein the filler is at least one of an inorganic filler and a metal filler.