JP3405914B2 - Paste for filling through holes - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a through hole filling paste which is used by filling a through hole 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 communication printed wiring boards exposed to harsh usage conditions such as MPU build-up IC packages. You can

[0002]

2. Description of the Related Art In a printed wiring board and a laminated board having through holes for conducting the front and back of a board, a through hole serving as a through hole is provided in an insulating board or a copper clad laminated board, and an inner wall of the through hole is formed. Is plated with metal to form a conductor layer. Then, the through-hole is filled with a filling paste. Printed wiring boards and the like having such through holes are disclosed in JP-A-62-224996 and JP-A-63-137499. Although these wiring boards and the like are mainly used for consumer use, those having such through holes are not used in the IC package for MPU that requires high reliability, and ceramic wiring boards and the like are used. It is used.

[0003]

However, in recent years, there has been an increasing demand for higher density or multiple layers in printed wiring boards and the like, and wiring boards and laminated boards having through holes are also used in IC packages for MPU. It has started to be done. When a chip is mounted on this IC package for MPU, if a conventional consumer paste is filled in the through hole, a crack 51 is generated in the buildup 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 due to the difference in thermal expansion between the substrate 1 and the paste 4.

Therefore, the present inventors have studied using a large number of pastes whose thermal expansion has been specified, but were unable to suppress the occurrence of cracks. Therefore, it is considered that there is another cause for the occurrence of this crack, and various investigations were made. As a result, this crack causes the cured body generated in the hole filling process to further cure in the solder reflow process and shrink, and this shrinkage remains as it is even after cooling, so tensile stress occurs in the thickness direction of the build-up layer. It was found that it was caused by doing.

The present invention solves the above-mentioned conventional problems and further suppresses shrinkage of a hardened body formed in a hole filling step after cooling in a solder reflow step, and cracks are generated in a buildup layer. It is an object of the present invention to provide a through-hole filling paste that is sufficiently prevented. Another object of the present invention is to provide a paste for through-hole filling, which has a low viscosity, excellent fluidity, and low water absorption by using a specific epoxy resin together. By using such a paste, it is possible to easily fill the through holes, no defective filling occurs, and the occurrence of cracks in the buildup layer is sufficiently suppressed.

[0006]

A through-hole filling paste of the first invention is a through-hole filling paste which is used by filling a through hole of a printed wiring board, the paste having an epoxy resin and a curing agent. An epoxy resin composition and a filler are contained, and the epoxy resin comprises an amine type epoxy resin and a polyphenol type epoxy resin.
It is characterized by containing a resin .

The "through hole filling paste" is
The above "epoxy resin composition" containing an epoxy resin and a curing agent as a resin component is contained. This epoxy resin includes the above-mentioned "amine type epoxy resin". By using this amine type epoxy resin, it is possible to sufficiently suppress the occurrence of cracks in the buildup layer. The amine-type epoxy resin has a function of suppressing the generation of cracks as described above and has a low viscosity. for that reason,
The viscosity of the obtained paste also decreases, and the workability in filling the through holes is greatly improved. Furthermore, since the viscosity is low, a large amount of filler can be blended, and the occurrence of cracks in the buildup layer can be suppressed more reliably.

As the amine type epoxy resin, a tetrafunctional epoxy resin such as tetraglycidylaminodiphenylmethane or tetraglycidyl metaxylylenediamine can be used. Further, a trifunctional epoxy resin such as triglycidyl metaaminophenol or triglycidyl paraaminophenol can also be used. Further, a difunctional epoxy resin such as diglycidyl aniline or diglycidyl orthotoluidine may be used.

The less functional groups these epoxy resins have, the lower the viscosity is. However, in order to suppress the shrinkage of the cured product in the solder reflow process, more multifunctional ones are preferable. However, when the resin is tetrafunctional, the cured product has high rigidity, and cracks may occur in the cured product itself. Considering these viscosity and hardness together, among these amine type epoxy resins, as in the second invention, it is liquid at room temperature, that is, at 20 to 30 ° C., particularly at 23 to 25 ° C., A trifunctional amine type epoxy resin having a low viscosity and a high glass transition point of a cured product obtained by curing the paste is preferable. Further, as in the third invention, the viscosity is lower, the workability at the time of filling the paste into the through hole is excellent, the filling failure does not occur, and the generation of cracks in the buildup layer is sufficiently suppressed. Functional triglycidyl paraaminophenols are particularly preferred.

Since this amine type epoxy resin has high water absorption, the water absorption of the cured product in the hole filling step may be high. Therefore, it is preferable to use another epoxy resin having low water absorption in combination. Examples of the epoxy resin having low water absorption include polyphenol type epoxy resin. Particularly, it is preferable to use at least one of the phenol novolac type epoxy resin and the bisphenol A type epoxy resin as in the fourth aspect of the invention, because the shrinkage of the cured body in the solder reflow step becomes smaller. Further, when the phenol novolac type epoxy resin is used alone, the viscosity of the paste becomes considerably high, but the viscosity of the paste is lowered by the combined use 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 amine type epoxy resin is preferably 10 to 50 parts by weight, more preferably 15 to 45 parts by weight, further 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, the workability at the time of filling the through holes is deteriorated, and filling failure may occur. On the other hand, when the amount of the amine type epoxy resin exceeds 50 parts by weight, the water absorbency becomes high and problems such as cracks may occur in the cured product or its periphery during the reliability evaluation.

2 of the paste for filling through holes according to the present invention
The viscosity at 5 ° C. is preferably 10,000 poises or less, particularly 7,000 poises or less, and further preferably 5000 poises or less, as in the fifth invention. This viscosity is 10,000
If it exceeds the poise, the workability at the time of filling the through-hole with the paste is deteriorated, and filling failure may occur, which is not preferable.

Further, the shrinkage rate of the second cured body produced in the solder reflow step with respect to the first cured body produced in the hole filling step is preferably 0.1% or less as in the fifth aspect of the invention. If the shrinkage ratio exceeds 0.1%, cracks may occur in the buildup layer after cooling in the solder reflow step, or in a reliability test thereafter. This shrinkage ratio can be calculated by reading the shrinkage length from the chart of the thermomechanical analyzer. Furthermore, since this paste does not require a volatile solvent or the like, the volatile content at the time of curing in the hole filling step is very small, and this also suppresses the generation of bubbles in the first cured body generated in the hole filling step.

With respect to the above-mentioned shrinkage ratio, a film made of this paste and having a thickness of 100 μm is heated at 150 ° C. for 5 hours to be cured, and thereafter, a width of 5 mm is obtained using this film.
When a sample of No. 2 was prepared, and then the sample was heated from 23 ° C. to 270 ° C. with a load of 5 g applied in the longitudinal direction, the temperature was lowered to 23 ° C. It can be calculated by the following equation. Shrinkage rate (%) = [270 ° C
Length of specimen at 23 ° C before heating up to -27
The length of the sample when the temperature was lowered to 23 ° C. after the temperature was raised to 0 ° C.] / The length of the sample at 23 ° C. before the temperature was raised to 270 ° C. × 100

This method does not evaluate the shrinkage rate in the solder reflow step by actually filling the paste into the through hole and curing it. However, when the through hole is filled with a paste having a shrinkage ratio of 0.1% or less measured by this method, the paste is cured in the hole filling step, and then heated in the solder reflow step and cooled, cracks in the build-up layer occur. It has been confirmed that the occurrence of is sufficiently suppressed. By such a simple method, a paste that can be put to practical use and a paste that cannot be put to practical use can be easily selected. The rate of temperature increase and decrease is preferably 1 to 5 ° C / minute, particularly 1 to 3 ° C / minute, and more preferably 2 ° C / minute. Further, it is preferable to immediately lower the temperature after raising the temperature to 270 ° C.

As the above-mentioned "hardening agent", a high temperature hardening type is used, and a catalyst type hardening agent is preferable in consideration of the flow characteristics of the paste, the decrease in viscosity and the like. In particular, as in the sixth aspect of the invention, an imidazole-based curing agent having a sufficiently long pot life and capable of obtaining a practical paste is more preferable. As a high temperature curing type curing agent, in addition to this, an acid anhydride,
Boron trifluoride and the like are known, but they are not preferable because they have high reactivity with an 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, more preferably 1 to 8 parts by weight, and further 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 hole 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 hole filling step is lower 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 process can be suppressed, but cracks may occur in the cured product itself in subsequent heat cycle tests and the like. Furthermore, if the heating temperature in the solder reflow process is less than 230, it is not possible to mount an IC chip or the like. On the other hand, if the heating temperature exceeds 280 ° C., the epoxy resin may be thermally deteriorated, which is not preferable.

A filler is mixed in the paste in order to suppress the shrinkage of the hardened body produced in the solder reflow process. As the “filler”, as in the seventh invention,
Inorganic filler may be used or metal filler may be used
It may be, these may be used in combination. In order to suppress the shrinkage of the cured product, an inorganic filler is more preferable, but a metal filler can sufficiently achieve the purpose.

As the inorganic filler, silica, mica, calcium carbonate, alumina, iron oxide, electrolytic iron powder, slate powder, talc, and the like which are used as fillers for epoxy resin are not particularly limited. Can be made. Among these inorganic fillers, silica having a small coefficient of thermal expansion is more preferable. Further, in order to contain a larger amount of inorganic filler while suppressing an increase in the viscosity of the paste, spherical inorganic filler such as spherical silica is particularly preferable. Furthermore, by treating the surface of this 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 hole filling step can be reduced.

Further, as the metal filler, it is possible to use a filler made of powder such as copper, silver and a mixture thereof. As this metal filler, it is preferable to use a filler in which at least half the amount thereof is spherical powder in order to suppress an increase in the viscosity of the paste when a large amount is contained. Further, it is more preferable to use a metal filler obtained by soft etching spherical copper powder or a metal filler subjected to blackening treatment. By this blackening treatment, a needle-shaped 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 enhanced by the improvement of the anchor effect and 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 epoxysilane having an epoxy group on the hydrophobic group side, it is possible to reduce the water absorption of the cured product generated in the hole filling step.

It is preferable that these fillers are contained in a large amount in order to suppress the shrinkage of the hardened body generated in the solder reflow. However, it is necessary to consider that the workability at the time of filling the through holes does not decrease due to the increase in the viscosity of the paste. For example, in the case of silica, 60 to 90 when the paste is 100 parts by weight.
It is preferable to set the content to about parts by weight. By containing silica in this range, a paste having an appropriate viscosity can be obtained, which is excellent in workability when filling through holes,
No filling failure will occur. Furthermore, the occurrence of cracks in the buildup layer can be sufficiently suppressed. 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 practically not so lowered as to cause a problem. Adjust it.

The viscosity of this paste can be from 1000 to 5,000 poises, especially from 1000 to 3500 poises, and its water absorption is from 0.5 to 1.0%, especially from 0.5 to 0.8%. Can be Further, 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.
It can be set to 01 to 0.08%, further 0.01 to 0.05%. Further, it is possible to obtain a paste having a better performance with a viscosity of 1000 to 3000 poise, a water absorption rate of 0.1 to 0.2%, and a shrinkage rate of less than 0.01%.
The methods for measuring the viscosity, the water absorption rate, and the shrinkage rate are the same as those in Examples described later.

In addition, this paste may contain, if necessary,
Various additives can also be included. Examples of such additives include antifoaming agents, leveling agents and antioxidants. These additives can be contained in appropriate amounts as long as the characteristics of the paste are not impaired.

When the through-hole filling paste containing the amine type epoxy resin of the present invention is used, the reason why the shrinkage of the hardened body generated in the solder reflow step is suppressed is not clear, but it 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 and flexible molecules. on the other hand,
Amine type epoxy resins such as triglycidyl paraaminophenol are composed of bulky molecules, and during curing, the movement of the molecules is restricted by steric hindrance, and the shrinkage rate in the solder reflow process is very small, 0.1% or less, Generation of cracks in the buildup layer is sufficiently suppressed.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below with reference to Examples. Examples 1 to 3, Comparative Examples 1 to 4 and Reference Example 1 (1) Preparation of paste 95 parts by weight of the following epoxy resin and an imidazole curing agent (manufactured by Shikoku Kasei Co., Ltd., trade name "2E4MZ-C")
N ") 5 parts by weight of an epoxy resin composition containing 100 parts by weight of the following inorganic fillers and some of them in addition to the above metal fillers in a weight ratio shown in Table 1 and mixed to obtain a through mixture. A hole filling paste was prepared.

Trifunctional amine type epoxy resin (triglycidyl paraaminophenol) (trade name "E-152" manufactured by Yuka Shell Co., Ltd., represented as "AP" in Table 1) Bifunctional amine type epoxy resin (Diglycidylaniline) (manufactured by Nippon Kayaku Co., Ltd., trade name "GAN", represented as "AN" in Table 1) Phenol novolac type epoxy resin (manufactured by Yuka Shell Co., Ltd., trade name "E-152") ), In Table 1, it is represented as "PN". )

Bisphenol A type epoxy resin
The product name is "E-828"), and is shown as "BPA" in Table 1. ) Bisphenol F type epoxy resin (same as the trade name "E-
807 "), and in Table 1 is represented as" BPF ". ) 1,6 hexanediol diglycidyl ether (the same,
Product name "YED216"), "16H" in Table 1
Express. )

(A) Inorganic filler (1) Spherical silica, average particle size 1.6 μm; manufactured by Tatsumori Co., Ltd., trade name “SO-E5”, “S16” in Table 1.
Express. (2) Spherical silica, average particle size 0.5 μm;
It is represented by "O-E2" and "S05" in Table 1. (B) Metal filler (1) Spherical copper powder, average particle size 10 μm; product name “SFR-CU” manufactured by Japan Atomize Co., Ltd., and represented by “C10” in Table 1.

[0029]

[Table 1]

(2) Viscosity, Water Absorption and Shrinkage of Through Hole Filling Paste 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 rate: Measured according to JIS K 6911. Shrinkage rate: The paste was formed into a film having a thickness of 100 μm and heated at 150 ° C. for 5 hours to be cured. After that, a sample with a length of 20 mm and a width of 5 mm was prepared, the chuck distance was set to 15 mm, and a load of 5 g was applied in the length direction of the sample.
After heating up to 2 ℃ / min at the same rate, then at the same speed at 23 ℃
The temperature was lowered to. From the chart of the thermomechanical analyzer obtained, the shrinkage length [length reading on the chart at 23 ° C. before temperature increase-length reading on the chart at 23 ° C. after temperature decrease (unit: μm)] Was read, and this shrinkage length was divided by the length of the test piece before heating to obtain the shrinkage rate.

(3) Workability in filling the through holes and presence / absence of cracks in the resulting cured product The paste prepared in (1) is applied to the through holes provided on the printed wiring board by screen printing. It was filled, heated in air at 150 ° C. for 5 hours to be cured, and the filling state was visually observed. If the filling condition was good, a multilayer printed wiring board was prepared using this printed wiring board and passed through a solder reflow furnace whose temperature was controlled at 260 ° C for 10 minutes to check for the occurrence of cracks. It was visually confirmed. The results are also shown in Table 1.

From the results shown in Table 1, it is understood that in Examples 1 to 3 which are within the scope of the first invention, the paste having excellent viscosity, water absorption rate and shrinkage rate was obtained. Furthermore, in these Examples 1 to 3 , the condition of the filled paste was good, and no crack was observed.
Incidentally, in Example 3 in which AP and BPA were used in a ratio of 70:30 and a proper amount of spherical silica and spherical copper powder were used in combination, the viscosity was sufficiently low, and the shrinkage ratio was also very small, which was more excellent. It can be seen that a paste is obtained.

On the other hand, in Comparative Example 1 in which only BPF was used as the epoxy resin, the shrinkage rate was large and cracks were generated in the cured body. In Comparative Example 2 using only PN,
Although the shrinkage rate was small, the viscosity was high and some poor filling was observed. Furthermore, as an epoxy resin, this PN
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 decreased and the filling property improved, but the shrinkage ratio was large and cracks occurred. Also, B
In Comparative Example 4 in which only PA was used, the viscosity was high, and defective filling was partially observed. In addition, in Example 4 and Comparative Example 4, the reason why the water absorption rate was very small was that the calculated apparent numerical value was small because of 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 through-hole filling paste which has a low viscosity, is excellent in workability for filling a through hole, and does not cause defective filling. When this paste is used, the shrinkage rate in the length direction of the through hole of the cured body in the solder reflow step is small, and the occurrence of cracks in the buildup layer can be sufficiently suppressed.

[Brief description of drawings]

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

[Explanation of symbols]

1; multilayer substrate, 2; through hole, 3; plating layer, 4;
Paste, 41; Filler, 5; Build-up layer, 5
1; crack, 6; via hole.

Continuation of the front page (56) Reference JP 5-171008 (JP, A) JP 9-241419 (JP, A) JP 4-12595 (JP, A) (58) Fields investigated (Int .Cl. ⁷ , DB name) C08L 63/00-63/10 H01B 1/22 H05K 1/09 H05K 3/40

Claims (7)

(57) [Claims] 1. A through-hole filling paste used to fill 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, the epoxy resin comprising: A through-hole filling paste comprising: an amine-type epoxy resin and a polyphenol-type epoxy resin . 2. The paste for filling through holes 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 through holes according to claim 1, wherein the amine type epoxy resin is triglycidyl paraaminophenol. 4. The polyphenol type epoxy resin is
The through-hole filling paste according to any one of claims 1 to 3, which contains at least one of a phenol novolac type epoxy resin and a bisphenol A type epoxy resin. 5. The viscosity of the paste at 25 ° C. is 1
The through-hole filling paste according to any one of claims 1 to 4, which has a poise of 0000 poise or less. 6. The through-hole filling paste according to claim 1, wherein the curing agent is an imidazole curing agent. 7. The through-hole filling paste according to claim 1, wherein the filler is an inorganic filler.