JPH0892352A - Sealing resin composition for plastic ball grid array - Google Patents

Abstract

PURPOSE: To provide the subject composition causing little warpage defect and containing a specific polyfunctional epoxy resin, a phenolic novolak resin hardener, a cure accelerator, an inorganic filler and a silicone oil and/or a silicone rubber at specific ratios. CONSTITUTION: This sealing resin composition contains (A) a polyfunctional epoxy resin of formula I (R is H, methyl or t-butyl; (n) is an integer of 1-10), (B) a phenolic novolak resin hardener having an average polymerization degree of >=3, (C) a cure accelerator, (D) >=72wt.% (based on the total composition) of an inorganic filler and (E) >=2.0wt.% (based on the total composition) of a silicone oil and/or a silicone rubber of formula II (R1 is Cn H2n -COOH, H, etc.; R2 is benzene, ethyl, etc.; 5<=k+1+m<=300; any of (k), (l) and (m) are not zero). The cured product of this composition preferably has a glass transition temperature of >=180 deg.C, an elastic modulus of <=1400kgf/mm<2> at normal temperature and a thermal expansion coefficient of <=1.4×10<-5> / deg.C at normal temperature.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a sealing resin composition for a plastic ball grid array.

[0002]

2. Description of the Related Art Conventionally, an item that has been required in order to make a logic LSI into a device is to support a large number of pins. Devices such as QFP have been required to have various technical problems for the purpose of increasing the number of pins. For example, when the pin pitch is 0.3 mm or less, troubles during mounting increase. Even if it is mounted with a slight deviation, it becomes defective, and a very time-consuming process of removing and mounting again is required. Further, as the number of pins increases, the package size also keeps expanding, and the increase in mounting area has become a big problem. In order to solve these problems, a plastic ball grid array called OMPAC (trade name) from Motorola, Inc. in the United States (hereinafter referred to as B
GA) was developed. The outline of the BGA will be described with reference to FIG. FIG. 2 is a sectional view of the BGA. An IC chip 3 is mounted with silver paste on the surface of a circuit board 1 made of a laminated plate of epoxy resin, polyimide resin or the like, and the IC chip 3 is sealed with a sealing resin composition 2, and then the lower surface of the circuit board 1 is covered with pins. Instead, a solder ball 5 is attached.
The shortest distance between the solder balls at present is 1 mm, which is easier to mount than the pin pitch of the QFP. Furthermore, since the mounting area is small and the heat dissipation is good, there is a cost advantage when the pin count increases, and BGA is starting up with considerable momentum mainly in the United States. However, BGA also has a drawback, and the biggest problem is that the package warps easily due to the difference in thermal expansion coefficient between the encapsulating resin composition and the circuit board. In order to solve this, various encapsulating resin compositions have been developed, but the warpage has not been completely resolved (for example, JP-A-5-67705).

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a sealing resin composition suitable for a BGA package with less warpage.

[0004]

According to the present invention, an epoxy resin composition for mounting a semiconductor element on a surface of a circuit board with a silver paste and sealing the mounted product has a large amount represented by the formula (A) (1). Functional epoxy resin,

[0005]

[Chemical 3]

(B) Phenolic novolac resin curing agent having an average degree of polymerization of 3 or more, (C) curing accelerator, (D) total composition containing 72% by weight or more of an inorganic filler, and (E) total composition And the silicone oil represented by the formula (2)

[0007]

[Chemical 4]

A sealing resin composition for a plastic ball grid array, which comprises 2.0% by weight or more of silicone rubber. The cured product of the encapsulating resin composition has a glass transition temperature of 180 ° C. or higher, an elastic modulus of 1400 kgf / mm ² or less at room temperature, and a thermal expansion coefficient of 1.4 × 10 ⁻⁵ / ° C. or less at room temperature. However, the warpage of BGA when molded is extremely low, and a good BGA device can be obtained.

In order to reduce the warpage of BGA, we have focused on the three physical properties of the cured resin of the encapsulating resin composition, namely the glass transition temperature, the elastic modulus at room temperature and the coefficient of thermal expansion at room temperature, based on our findings. What kind of physical property values are necessary for the physical properties of slag are investigated using the method of thermal stress analysis by the finite element method. Figure 1
[FIG. 1] is a perspective view of a molded product in which a circuit board 1 made of an epoxy resin laminate, which is a part of the structure of a BGA at the time of thermal stress analysis and actual evaluation, and a sealing resin composition 2 are integrated,
The size of the circuit board 1 is 24 mm × 24 mm, the thickness thereof is 0.4 mm, and the size of the cured sealing resin composition 2 is 2.
It is 0 mm × 20 mm and its thickness is 0.8 mm. Table 1 shows the results of BGA warpage analysis by the finite element method assuming the three physical property values of the glass transition temperature, the elastic modulus at room temperature and the thermal expansion coefficient at room temperature of the cured encapsulating resin composition. Summarizing these results, the physical properties of the encapsulating resin composition effective in preventing warpage of BGA are that the glass transition temperature is 180 ° C. or higher (TM
A). The elastic modulus at room temperature is 1400 kgf / mm ² or less (3-point bending method). That is, the coefficient of thermal expansion at room temperature is 1.4 × 10 ⁻⁵ / ° C. or less (TMA). When the encapsulating resin composition satisfying the above-mentioned three physical property values was used, the warp of the molded product of FIG. 1 was as small as 200 ppm or less, and it was judged that it is sufficiently practical for BGA.

Based on these results, the encapsulating resin composition having various physical properties with respect to the three physical properties and the circuit board having the shape shown in FIG. 1 were integrally molded, and the actual warpage was measured. Table 2 shows the measurement results of the warp actually evaluated. This result agrees well with the calculation result of the finite element method, and proves that the above-mentioned three physical property values are correct. Curing conditions Low pressure transfer molding at 175 ° C, 70 Kg / c
It was integrally molded under a molding condition of m ² for 120 seconds, and was further treated as a post-mold cure at 175 ° C. for 8 hours, and subjected to the following test. Measuring method of glass transition temperature and thermal expansion coefficient at room temperature (T
MA method) TMA-100 manufactured by Seiko Co., Ltd. is used. The test piece size is 5 x 5 x 5 mm. 0 ~ 300 ℃ 5 ℃ / min
Measured at the rate of temperature rise. Measurement method of elastic modulus at room temperature (3-point bending method) Orientec Co., Ltd. OCT-10T is used. Test piece size 80 x 10 x 5 mm. The span is 64 mm,
The load speed is measured at 2 mm / min. Warpage measurement method (surface roughness meter) Tokyo Seimitsu Co., Ltd. Surfcom 1500A is used. The molded parts were fixed and the maximum warpage was monitored. FIG. 3 is a schematic diagram showing the warp amount of the BGA package.

Based on these results, the above three items were used as the target physical property values, and intensive investigations were made on the resin composition, and it was confirmed that the use of the encapsulating resin composition described below was effective in preventing warpage of BGA.

Each component of the encapsulating resin composition of the present invention will be described below. The polyfunctional epoxy resin used in the present invention is represented by the formula (1). R in the formula is the same or different atom or group selected from hydrogen, methyl group and tertiary butyl group. n = 1 to 10, and when it exceeds 10, the resin viscosity is too high and the moldability is deteriorated. As long as it has these structures, you may use it individually or in mixture. In order to improve the moisture resistance of the encapsulating resin composition, it is desirable that impurity ions such as Cl ions and Na ions as impurities are minimized. Further, if the glass transition temperature of the cured encapsulating resin composition is within the range of not higher than 180 ° C., it may be used in combination with various epoxy resins such as brominated epoxy resin, orthocresol novolac type epoxy resin and biphenyl type epoxy compound. Absent.

The phenol novolac resin curing agent used in the present invention has an average degree of polymerization of 3 or more because the glass transition temperature of the cured encapsulating resin composition must be 180 ° C. or higher in order to prevent warpage of BGA. Need to be If the average degree of polymerization is less than 3, the glass transition temperature of the encapsulating resin composition will be less than 180 ° C., and the warpage of BGA will increase. In order to improve the moisture resistance of the encapsulating resin composition, it is desirable that impurity ions such as Cl ions and Na ions as impurities are as small as possible, and the hydroxyl equivalent is preferably 90 to 150 g / eq for improving the curability. .

The curing accelerator used in the present invention may be any one as long as it accelerates the reaction between the epoxy group and the hydroxyl group, and those generally used for sealing resins can be used. For example, 1,8-diazabicycloundecene, triphenylphosphine, benzyldimethylamine, 2-methylimidazole and the like can be mentioned, and they may be used alone or in combination.

As the inorganic filler used in the present invention, fused silica powder, spherical silica powder, crystalline silica powder, alumina and the like can be used, but a mixture of fused silica powder and spherical silica powder is particularly desirable. The inorganic filler must be contained in the total composition in an amount of 72% by weight or more. 7 inorganic fillers
The encapsulating resin composition containing 2% by weight or more has a thermal expansion coefficient of 1.4 × 10 ⁻⁵ / ° C. or less, which is a target value, and BGA warpage is reduced. If the inorganic filler content is less than 72% by weight, the thermal expansion coefficient of the encapsulating resin composition will be large, and the warpage when molded for BGA will be large, and the characteristics of the encapsulating resin composition will be significantly impaired. On the other hand, if the content of the inorganic filler exceeds 82% by weight, the fluidity at the time of molding decreases, which is not practical.

The silicone oil used in the present invention is a compound having a structure represented by the formula (2). Equation (2)
The silicone oils having various structures represented by can be used alone or as a mixture. In order to improve the moisture resistance of the resin composition, it is desirable that impurity ions such as Cl ions and Na ions as impurities be as small as possible, and further that the volatile content be as small as possible in order to improve moldability.

In the silicone oil having the structure of the formula (2), R _{1 of} the side chain is either carboxylic acid, epoxy, cyclohexyl type epoxy, polyalkylene oxide or hydrogen, and R ₂ is phenyl group or phenethyl group. It is either a group or an ethyl group. Silicone oils that do not have these functional groups are not sufficiently compatible with the epoxy resin, bleed out on the surface of the molded product and stain the surface of the molded product, and a good molded product cannot be obtained. Further, the degree of polymerization of the silicone main chain is 6 or more (k + l + m = 5 or more), 301
It is indispensable to be the following (k + l + m = 300 or less). If the degree of polymerization is less than 6, the low elastic modulus will not be expressed and B
The warp of GA becomes large and the desired performance cannot be obtained. When the degree of polymerization exceeds 301, the compatibility of the silicone oil with the epoxy resin is poor, so that the surface of the molded product bleeds out and the surface of the molded product is soiled.

The silicone rubber used in the present invention is not particularly limited as long as it has a chemical structure mainly composed of dimethylsiloxane, but in order to improve the flow characteristics of the resin composition, the average particle diameter is 5 to 50 μm. It is preferably spherical. Further, those having polar reactive groups such as epoxy, silanol, and mercapto on the particle surface are more desirable. Further, in order to improve the moisture resistance of the resin composition, C as an impurity is used.
It is desirable that the amount of impurity ions such as l ion and Na ion is as small as possible, and further that the volatile content is as small as possible in order to improve moldability. It is essential that the silicone oil and / or the silicone rubber be contained in the entire composition in an amount of 2.0% by weight or more. These components are effective in reducing the elastic modulus of the encapsulating resin composition. By blending 2.0% by weight or more in the entire composition, the elastic modulus of the encapsulating resin composition can be lowered and the elastic modulus at room temperature can be 1400.
It can be less than or equal to kgf / mm ² . This can reduce the amount of BGA warpage. However, when it exceeds 6.0% by weight, the tableting property of the tablet is remarkably deteriorated although the molding property and the characteristic are not problematic, and the handling problem occurs. When used in combination, the compounding ratio of silicone oil and silicone rubber is not particularly limited, and there is no problem in moldability and reliability when silicone oil alone or silicone rubber alone is used.

The resin composition of the present invention contains a polyfunctional epoxy resin, a phenol novolac resin curing agent, a curing accelerator, an inorganic filler, a silicone oil and / or a silicone rubber as essential components. Various additives such as a silane coupling agent, a flame retardant such as antimony trioxide and hexabromobenzene, a coloring agent such as carbon black and red iron oxide, and a release agent such as natural wax and synthetic wax may be appropriately blended. . Further, in order to produce the encapsulating resin composition of the present invention as a molding material, a polyfunctional epoxy resin, a phenol novolac resin curing agent, a curing accelerator, an inorganic filler, a silicone oil and / or a silicone rubber, and other additives are used. Can be sufficiently and uniformly mixed with a mixer or the like, and then melt-kneaded with a hot roll, a kneader or the like, cooled and pulverized to obtain a sealing material.

The present invention will be specifically described below with reference to examples. Example 1 Composition below Polyfunctional epoxy resin A of formula (1) (R is shown in Table 6) (softening point 60 ° C., epoxy equivalent 170) 12.6 parts by weight phenol novolac resin curing agent (softening point 100 ° C., Hydroxyl equivalent 105, average degree of polymerization 4.0) 8.2 parts by weight Fused silica powder (average particle size 15 μm) 10.0 parts by weight Spherical silica powder (average particle size 20 μm) 63.0 parts by weight Silicone oil A (R ₁ , R ₂ , k, l and m are shown in Table 6) 1.2 parts by weight Silicone rubber A (average particle size 10 μm, spherical) 1.0 parts by weight Triphenylphosphine 0.3 parts by weight Carbon black 0.3 parts by weight Parts Antimony trioxide 2.0 parts by weight Carnauba wax 0.3 parts by weight Brominated phenol novolac type epoxy resin 1.1 parts by weight are mixed at room temperature with a mixer, and then a biaxial low temperature is applied at 70 to 100 ° C. Were kneaded with, it was milled after cooling the molding material. The obtained molding material is tabletized, and the circuit board of FIG. 1 and this material are 175 ° C. and 70 kg / in a low-pressure transfer molding machine.
Integral molding was performed under conditions of mm ² and 120 seconds, and post-mold cure was further performed at 175 ° C. for 8 hours to obtain a molded product. The evaluation results are shown in Table 3.

Evaluation Method Warpage Evaluation of BGA: The amount of warpage of the obtained molded product was evaluated using a surface roughness meter. Evaluation of stains on the surface of the molded product: Oil stains on the surface of the molded product were visually observed for the obtained molded products.

Examples 2 to 6 Compounding was performed according to the formulation shown in Table 3, molding materials were obtained in the same manner as in Example 1, and evaluated in the same manner. Polyfunctional epoxy resin B (softening point 60 ° C., epoxy equivalent 180, R is shown in Table 6),
Polyfunctional epoxy resin C (softening point 65 ° C, epoxy equivalent 2
00 and R are shown in Table 6). The evaluation results are shown in Table 3. Comparative Examples 1 to 13 Compounding was performed according to the formulations shown in Tables 4 and 5, molding materials were obtained in the same manner as in Example 1, and evaluated in the same manner.

[0023]

[Table 1]

[0024]

[Table 2]

[0025]

[Table 3]

[0026]

[Table 4]

[0027]

[Table 5]

[0028]

[Table 6]

[0029]

According to the present invention, it is possible to obtain a BGA package with extremely small warpage, which was not possible with the prior art. When this resin composition is used for encapsulation of electric and electronic parts, BGA with less warpage causes less troubles when mounting on a circuit board and can be mounted promptly, resulting in quality improvement, process reduction, and cost reduction. It has a great effect on saving.

[Brief description of drawings]

FIG. 1 is a perspective view of a molded product obtained by integrally molding a circuit board made of an epoxy resin laminate used for evaluation of the present invention and a sealing resin composition. The size of the circuit board is 24 mm × 24 mm.
The thickness is 0.4 mm, the size of the cured encapsulating resin composition is 20 mm × 20 mm, and the thickness is 0.8 mm.
Is.

FIG. 2 is a cross-sectional view of a plastic ball grid array.

FIG. 3 is a schematic diagram showing a warp amount of a plastic ball grid array.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location H01L 23/31

Claims (2)

[Claims] 1. An epoxy resin composition for mounting a semiconductor element on a surface of a circuit board with a silver paste and encapsulating the mounted product is a polyfunctional epoxy resin represented by the formula (1): (B) a phenol novolac resin curing agent having an average degree of polymerization of 3 or more, (C) a curing accelerator, (D) the total composition contains 72% by weight or more of an inorganic filler, and (E) the composition contains the formula Silicone oil represented by (2) And / or a silicone rubber content of 2.0% by weight or more, which is a sealing resin composition for a plastic ball grid array. 2. The cured product of the encapsulating resin composition according to claim 1, which has a glass transition temperature of 180 ° C. or higher and an elastic modulus of 14 at room temperature.
A sealing resin composition for a plastic ball grid array, which has a physical property of 00 kgf / mm ² or less and a thermal expansion coefficient at room temperature of 1.4 × 10 ⁻⁵ / ° C. or less.