Epoxy resin composition

Abstract: Provided herein is an epoxy resin composition which comprises a curable epoxy resin, a hardener, and a block copolymer formed by the reaction of a triphenol-alkane type resin or a polymer thereof with a specific organopoly­ siloxane. It provides a cured product having a high glass transition point, a low coefficient of expansion, good crack resistance, and less liability to exerting stress to the semiconductor devices. It exhibits its distinct performance when used as a sealing compound for semiconductor devices, especially in the case where the element is bonded directly to a printed circuit board or heat sink. It is very little liable to warp the semiconductor device sealed with it.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention: The present invention relates to an epoxy resin composition which provides a cured product having a high glass transition point, an extremely low coefficient of expansion, good crack resistance, and low stress. More particularly, it is concerned with an epoxy resin composition suitable for use as an encapsulator for semiconductor devices. 2. Description of the prior Art: An epoxy resin composition which is composed of a curable epoxy resin, a curing agent, and a variety of additives is used for encapsulating semiconductor devices because it is superior to other thermosetting resins in moldability, adhesion, electrical properties, mechanical properties, and moisture resistance. It needs to meet new requirements arising from the recent advance in semiconductor devices. With the development of smaller and thinner electronic machines and equipment, the package of semiconductor devices has become diversified. On the other hand, the electronics technology has produced semiconductor devices in which semiconductor elements are bonded directly to a printed circuit board or heat sink. Such semiconductor devices encounter some problems when encapsulated with a conventional epoxy resin composition because of the difference in coefficient of thermal expansion between the printed circuit board and the epoxy resin composition. The difference in coefficient of thermal expansion exerts a great stress on the semiconductor element, resulting in the cracking and deformation, which deteriorate the performance and appearance of the element. In order to solve this problem, the present assignee has proposed an epoxy resin composition composed of a curable epoxy resin and an organopolysiloxane (Japanese Patent Laid-open No. 129246/1981) and an epoxy resin composition incorporated with a block copolymer composed of an aromatic polymer and organopolysiloxane (Japanese Patent Laid-open No. 21417/1983). These epoxy resin compositions produce a lower level of stress than the conventional ones. However, there are some instances where even these new epoxy resin compositions do not meet severe requirements for an encapsulator of sophisticated semiconductor devices. Thus there still is a demand for a new encapsulator which is more reliable and less liable to exert stress to the semiconductor element. The present invention was completed under the above-mentioned circumstance. Chemical Abstract, vol. 101, no. 6, August 6, 1984, abstract no. 39 326 q describes cured epoxy resin compositions composed of glycidyl ethers and tris(hydroxyphenyl)alkanes (hardeners). SUMMARY OF THE INVENTION It is an object of the present invention to provide a new epoxy resin composition which has good flowability and provides a cured product having a high glass transition point, a low coefficient of thermal expansion, good crack resistance, and less liability to exerting stress to the semiconductor element. To achieve the above-mentioned object, the present inventors carried out a series of researches which led to the findings that an epoxy resin composition incorporated with a copolymer formed by the reaction of a compound represented by the formula (1) below or an oligomer thereof with a specific organopolysiloxane represented by the formula (2) below, provides a cured product having a glass transition point 10 to 20°C higher than that of the conventional cured product, a lower coefficient of thermal expansion, good crack resistance, and less liability to exerting stress to the semiconductor devices. This epoxy resin composition exhibits its distinct performance when used as an encapsulator for semiconductor devices, especially in the case where the element is bonded directly to a printed circuit board or heat sink. In other words, it is very little liable to warp the semiconductor device encapsulated with it. Thus the epoxy resin composition of the present invention can be advantageously applied to semiconductor devices of DIP type, flat pack type, PLCC type, and SO type, and also to semiconductor devices in which the element is bonded directly to a printed circuit board or heat sink. According to the present invention, there is provided an epoxy resin composition which comprises a curable epoxy resin, a curing agent, and a block copolymer formed by the reaction of an aromatic compound or an oligomer thereof with an organopolysiloxane represented by the formula (2) below having at least one = SiR³ group per molecule R³ a R⁴ b SiO (4-[a+b])/2 (2) (where R³ denotes a hydrogen atom, halogen atom, hydroxyl group, alkoxyl group, or a monovalent hydrocarbon group having 1 to 10 carbon atoms substituted with groups selected from -NH₂, -NHCH₃, -Cℓ and -SH; R⁴ denotes a monovalent organic group having 1 to 10 carbon atoms of the same or different kind; 0.001≦a≦2, 1≦b<3, and 1.001≦a+b≦3.), characterized in that said aromatic compound is represented by the formula (1) below (wherein R¹ denotes a hydrogen atom, or a monovalent organic group having an alkenyl group; R² denotes a monovalent hydrocarbon group having 1 to 10 carbon atoms of the same or different kind; X denotes a halogen atom; ℓ denotes an integer of 1 or 2; m and n each denote an integer of 0 to 2; and ℓ+m+n≦5 ). BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic perspective view of a semiconductor device used to measure the amount of warpage. Fig. 2 is a sectional view of a warped semiconductor device. DETAILED DESCRIPTION OF THE INVENTION The invention will be described in more detail in the following. The epoxy resin composition of the present invention is composed of a curable epoxy resin, a curing agent, and a block copolymer formed by the reaction of a compound of the formula (1) or an oligomer thereof with an organopolysiloxane of the formula (2). One component used for preparing the copolymer of the present invention is a compound represented by the formula (1) below or an oligomer thereof. (where R' denotes a hydrogen atom, or a monovalent organic group having an alkenyl group; R² denotes a monovalent hydrocarbon group having 1 to 10 carbon atoms of the same or different kind; X denotes a halogen atom; ℓ denotes an integer of 1 or 2; m and n each denote an integer of 0 to 2; and ℓ+m+n≦5 ) Examples of the R¹, which is a monovalent organic group having an alkenyl group, include and -CH₂ CH=CH₂. Examples of the R², which is a monovalent hydrocarbon group, include a methyl group, ethyl group, propyl group, allyl group, i-propyl group, t-butyl group, octyl group, and nonyl group. The oligomer of the compound (1) may preferably be a dimer, a trimer or a tetramer of the compound (1). Examples of the compound (1) and the oligomer thereof include the following compounds. These compounds can be synthesized according to the process disclosed in U.S.-A-4,394,496. Another component used for preparing the copolymer is an organopolysiloxane represented by the formula (2) below. R³ a R⁴ b SiO (4-[a+b])/2 (2) (where R³ denotes a hydrogen atom, halogen atom, hydroxyl group, alkoxyl group, preferably having 1 to 5 carbon atoms, or a monovalent hydrocarbon group having 1 to 10 carbon atoms substituted with groups selected from -NH₂, -NHCH₃, -Cℓ and -SH; R⁴ denotes a monovalent organic group having 1 to 10 carbon atoms of the same or different kind; 0.001≦a≦2, 1≦b<3, and 1.001≦a+b≦3. ) Examples of the R³, which is a substituted monovalent hydrocarbon group, include: -CH₂NH₂, -CH₂CH₂CH₂NH₂, and ClCH₂CH₂CH₂-. Examples of the R⁴, which is a monovalent organic group, include a methyl group, ethyl group, phenyl group, and benzyl group. The organopolysiloxane represented by the formula (2) has at least one ≡SiR³ group per molecule. Examples of such a compound include: [(CH₃)₂ SiO]₃ [CH₃HSiO]₂ [C₆H₅ SiO 3/2 ]₅ The copolymer used in the present invention is prepared from a compound represented by the formula (1) or an oligomer thereof and an organopolysiloxane represented by the formula (2) through the reaction shown in the following. In the above equations, R⁵ represents: -H and Y represents a halogen atom, hydroxyl group, and alkoxyl group; R⁶ represents a divalent hydrocarbon group such as methylene, ethylene, and propylene: and p represents 0 or 1. The block copolymer mentioned above is incorporated into an epoxy resin composition composed of a curable epoxy resin and a curing agent. The amount of the copolymer may be 1 to 100 parts by weight, preferably 2 to 60 parts by weight, for 100 parts by weight of the total amount of the epoxy resin and curing agent. With an amount less than 1 part by weight, the copolymer is not effective in the improvement of the epoxy resin composition (such as glass transition point, crack resistance, and flowability). With an amount in excess of 100 parts by weight, the copolymer may lower the mechanical strength of the epoxy resin composition. According to the present invention, the curable epoxy resin is one which has two or more epoxy groups per molecule. It is not specifically limited in molecular structure and molecular weight so long as it is capable of curing with a curing agent mentioned later. Any known ones can be used. They include, for example, epoxy novolak resins such as one synthesized from epichlorohydrin and bisphenol, triphenol-alkane type epoxy resin or polymer thereof, alicyclic epoxy resin, and epoxy resins having halogen atoms (such as chlorine and bromine). These epoxy resins may be used alone or in combination with one another. The above-mentioned epoxy resin may be used in combination with a monoepoxy compound according to need. Examples of the monoepoxy compound include styrene oxide, cyclohexene oxide, propylene oxide, methylene glycidyl ether, ethyl glycidyl ether, phenyl glycidyl ether, allyl glycidyl ether, octylene oxide, and dodecene oxide. Examples of the curing agent include amine-type curing agent such as diaminodiphenyl-methane, diaminodiphenylsulfone, and metaphenylenediamine; acid anhydride-type curing agents such as phthalic anhydride, pyromellitic anhydride, and benzophenone tetracarboxylic anhydride; phenol novolac-type curing agents having two or more hydroxyl groups per molecule such as phenol novolak and cresol novolak; and triphenol alkanes. The curing agent may be used in combination with an accelerator which promotes the reaction of the curing agent with the epoxy resin. Examples of the accelerator include imidazole and derivatives thereof, tertiary amine derivative, phosphine derivatives, and cycloamidine derivatives. The curing agent and accelerator may be used in ordinary amounts, although the amount of the curing agent may preferably be 20 to 100% based on the equivalent of the epoxy group of the epoxy resin. The epoxy resin composition of the present invention may be incorporated with an inorganic filler. It may be selected from a wide variety according to the application of the epoxy resin composition. Examples of such an inorganic filler include natural silica (crystalline or amorphous silica), synthetic high-purity silica, synthetic spherical silica, talc, mica, silicon nitride, boron nitride, and alumina. They may be used alone or in combination with one another. The amount of the inorganic filler is not specifically limited. It should preferably be 100 to 1000 parts by weight for 100 parts by weight of the total amount of epoxy resin and curing agent. With an amount less than 100 parts by weight, the resulting epoxy resin composition may decrease in stress and have low crack resistance. With an amount in excess of 1000 parts by weight, the resulting epoxy resin composition has such poor flowability that the inorganic filler is not readily dispersed. The epoxy resin composition of the present invention may be incorporated with a variety of additives according to its intended use and application. Examples of the additives include waxes, fatty acids (e.g., stearic acid), release agent (e.g., metal salt), pigment (e.g., carbon black), dye, antioxidant, flame retardant, and surface treating agent (e.g., γ-glycidoxypropyltrimethoxysilane). The epoxy resin composition of the present invention should be prepared such that the cured product has a coefficient of expansion smaller than 2.0 x 10⁻⁵ /°C, preferably smaller than 1.9 X 10⁻⁵/°C, at 25 to 180°C. The epoxy resin composition is used for encapsulating semiconductor devices of such type that the semiconductor elements are bonded directly to a printed circuit board. It prevents the semiconductor devices from warping, twisting, or cracking. Thus it prevents the semiconductor devices from becoming deteriorated in performance. The epoxy resin composition of the present invention is prepared by mixing the above-mentioned components at 70 to 95°C using a kneader, roll mixer, extruder, or the like. The resulting mixture is cooled and crushed. The sequence of adding the components is not specifically limited. As mentioned above, the epoxy resin composition of the present invention is composed of a curable epoxy resin, a curing agent, and a block copolymer obtained from the reaction of a compound represented by the formula (1) or an oligomer thereof with an organopolysiloxane represented by the formula (2). It provides a cured product having good mechanical properties (such as flexural strength and flexural modulus), a low coefficient of expansion, a high glass transition point, and good crack resistance. By virtue of this feature, it is advantageously used for encapsulating semiconductor devices such as ICs and LSIs of DIP type, flat pack type, PLCC type and SO type, transistors, thyristors and diodes. It is especially suitable for semiconductor devices of such type that the semiconductor element is bonded directly to a heat sink or printed circuit board. The semiconductor devices encapsulated with the epoxy resin composition of the present invention are very little subject to warpage and have extremely good dimensional stability. In addition, the composition of the present invention may also be applied to hydrid ICs of full mold type. For encapsulating semiconductive devices, conventionally employed molding techniques such as, for example, transfer molding, injection molding and casting techniques may be used. Preferably, the molding temperature for the epoxy resin composition is in the range of from 150 to 180°C and the post curing is effected at a temperature of from 150 to 180°C for 2 to 16 hours. To further illustrate the invention, and not by way of limitation, the following examples are given. The block copolymers used in the examples and comparative examples were prepared as shown in the following production examples. PRODUCTION EXAMPLES 1 to 4 (Preparation of block copolymers) In a 500-ml four-neck flask equipped with a reflux condenser, thermometer, stirrer, and dropping funnel were placed 75 g of the organic compound (a kind of the compound (1)) as shown in Table 1, 0.10 g of chloroplatinic acid solution (containing 2% platinum and modified with 2-ethylhexanol), 100 g of methyl isobutyl ketone, and 200g of toluene. After complete dissolution of the organic compound, reaction was carried out by azeotropic dehydration for 1 hour. To the reaction product was added 25 g of an organopolysiloxane represented by the formula below from the dropping funnel over 2 hours. Reaction was continued for 6 hours under refluxing. The reaction product was washed with water and the solvent was distilled away under reduced pressure. Thus there were obtained four block copolymers shown in Table 1. Production Example 1 2 3 4 Organic compound i ii iii iv Block copolymer I II III IV Properties Brown opaque solid Brown opaque solid Brown opaque solid Brown clear solid Viscosity of 50% MIBK solution (cs. 25°C) 28 32 40 25 Ignition loss (%, 150°C/1 hr) 0.84 0.72 0.80 0.73 Organic compound (i) Organic compound (ii) Organic compound (iii) Organic compound (iv) (where q/r=12/1 ) PRODUCTION EXAMPLES 5 to 7 (preparation of block copolymers) In the same four-neck flask as used in Production Example 1 to 4 were placed 75 g of the organic compound (a kind of the compound (1)) shown in Table 2, 0.05 g of triphenyl phosphine, and 200 g of diethylene glycol dimethyl ether. After complete dissolution of the organic compound, 25 g of an organopolysiloxane represented by the formula below was added through the dropping funnel over about 20 minute, while keeping the flask at 130±5°C. Reaction was continued at the same temperatures for 4 hours. The reaction product was washed with water and the solvent was distilled away under reduced pressure. Thus there were obtained three flask copolymers shown in Table 2. Production Example 5 6 7 Organic compound v vi vii Block copolymer V VI VII Properties Brown opaque solid Brown opaque solid Brown opaque solid Viscosity of 50% MIBK solution (cs. 25°C) 20 21 18 Ignition loss (%, 150°C/1 hr) 0.93 0.87 0.88 Organic compound (v) Organic compound (vi) Organic compound (vii) Epoxidized cresol novolac EOCN 1020-65 (a product of Nippon Kayaku) EXAMPLES 1 to 5 and COMPARATIVE EXAMPLES 1 to 3 Eight kinds of epoxy resin compositions were prepared by uniformly melting and mixing the components shown in Table 3 using a two-roll mixer. The thus obtained epoxy resin compositions were examined for the following six items of performance. The results are shown in Table 3. (1) Spiral flow Measured at 160°C and 6.86 MPa (70 kg/cm²) using a mold conforming to the EMMI standard. (2) Mechanical properties (flexural strength and flexural modulus) Measured using a specimen (10 by 4 by 100mm) molded under the conditions of 160°C, 6.86 MPa (70 kg/cm²), and 3 minutes, followed by post-curing at 180°C for 4 hours, according to JIS K6911. (3) Coefficient of expansion and glass transition point Measured using a dilatometer. A specimen (4 mm in diameter and 15 mm long) was heated at a rate of 5°C per minute. (4) Crack resistance Measured by subjecting IC package specimens (50 pieces) to 50 heat cycles, each cycle consisting of 1 minute at -196°C and 30 seconds at 260°C. The specimen was prepared by bonding a silicon chip measuring 9.0 by 4.5 by 0.5 mm to a 14-pin IC frame (42 alloy), followed by molding with the epoxy resin composition at 160°C for 3 minutes and post-curing at 180°C for 4 hours. (5) Deformation of aluminum electrodes Measured by subjecting IC package specimens to 200 heat cycles, each cycle consisting of 1 minute at -196°C and 30 seconds at 260°C. The specimen was prepared by bonding a silicon chip measuring 3.4 by 10.2 by 0.3 mm (provided with deposited aluminum electrodes) to a 14-pin IC frame (42 alloy), followed by molding with the epoxy resin composition at 180°C for 2 minutes and post-curing at 180°C for 4 hours. (6) Warpage A semiconductor device as shown in the figure was prepared by transfer molding under the conditions of 165°C, 6.86 MPa (70 kg/cm²), and 2 minutes. Warpage (δ) that took place after post curing at 180°C for 4 hours was measured. In the figures, there are shown glass epoxy resin 1, semiconductor element 2, and encapsulator 3. It is noted from Table 3 that the epoxy resin composition of the present invention provides a cured product having a high glass transition point, good crack resistance, and a low coefficient of expansion. It is also noted that the epoxy resin composition when used as an encapsulator has a minimum of liability to deforming aluminum electrodes in a semiconductor device and to warping a semiconductor device.

Claims: An epoxy resin composition which comprises a curable epoxy resin, a curing agent, and a block copolymer formed by the reaction of an aromatic compound or an oligomer thereof with an organopolysiloxane represented by the formula (2) below having at least one = SiR³ group per molecule R³ a R⁴ b SiO (4-[a+b])/2 (2) (where R³ denotes a hydrogen atom, halogen atom, hydroxyl group, alkoxyl group, or a monovalent hydrocarbon group having 1 to 10 carbon atoms substituted with groups selected from -NH₂, -NHCH₃, -Cℓ and -SH; R⁴ denotes a monovalent organic group having 1 to 10 carbon atoms of the same or different kind; 0.001≦a≦2, 1≦b<3, and 1.001≦a+b≦3 .), characterized in that said aromatic compound is represented by the formula (1) below (wherein R¹ denotes a hydrogen atom, or a monovalent organic group having an alkenyl group; R² denotes a monovalent hydrocarbon group having 1 to 10 carbon atoms of the same or different kind; X denotes a halogen atom; ℓ denotes an integer of 1 or 2; m and n each denote an integer of 0 to 2; and ℓ+m+n≦5 ). The epoxy resin composition as claimed in Claim 1, characterized in that the content of the block copolymer is 1 to 100 parts by weight per 100 parts by weight of the total amount of the curable epoxy resin and curing agent. The epoxy resin composition as claimed in Claim 1, characterized in that an inorganic filler is blended in an amount of from 100 to 1000 parts by weight per 100 parts by weight of the total of said curable epoxy resin and said curing agent.

Inventors: SHIOBARA TOSHIO, TOMIYOSHI KAZUTOSHI, SHIOBARA, TOSHIO, TOMIYOSHI, KAZUTOSHI
Applicants: CITIZEN WATCH CO LTD, SHINETSU CHEMICAL CO, CITIZEN WATCH CO. LTD., SHIN-ETSU CHEMICAL CO., LTD.
Application year: 1988
Main classification: C08L63
IPC codes: C08L63, H01B3, C08G59, C08L83, H01L23