Maleimide resin composition and resin encapsulated semiconductor device manufactured using the composition

Abstract: Characteristic is in containing a maleimide resin with a content of 0.2 weight percent or less of an organic acid, a phenolic resin, and a combination of a basic catalyst and a peroxide as a curing catalyst. In addition, additives as a mold release agent such as a polyethylene wax and an inorganic filler are contained. The maleimide resin composition is prepared in such a manner that a part of the phenolic resin is preblended with the curing catalyst in advance of other components, while the remainder of the phenolic resin is added to the maleimide resin to prepolymerize, and then, the preblend and the prepolyer are blended the other components. The maleimide resin composition has excellent moldability by improvement of curing characteristics through combined use of a basic catalyst and a peroxide as a curing agent. Besides, a resin encapsulated semiconductor device manufactured by encapsulating a semiconductor element with the resin composition has excellent heat resistance and moisture-resistance reliability.

Description: This invention relates to a maleimide resin composition suitably allowing encapsulation of a semiconductor element and to a resin encapsulated semiconductor device manufactured using the composition. Recently, rapid increase is progressing in fining various function units of a semiconductor element and in size of the element. An epoxy resin composition containing a thermosetting epoxy resin as a resin component and a phenolic resin as a curing agent is widely used for resin encapulation of the semiconductor element. A flat package-type IC, for example, a gate array called ASIC (Application specific IC) and a standard cell-type LSI, encapuslated with the resin composition described above is mounted on a substrate by processes of vapor phase re-flow, infrared re-flow, and soaking in solder. In these process, the package is exposed to high temperature (ca. 215-260°C). Then, in the resin encapsulated semiconductor encapsulated with said epoxy resin composition, very small amount of water permeated through resin to inside abruptly evaporates allowing to crack the encapsulating resin. Crack developed to outside spoils moisture-resistance reliability of the resin encapsulated semiconductor to make a great problem. Besides, a phenomenon occurs to disturb to mount the package due to swelling of the encapsulating resin. Inside the semiconductor element encapsulated with the resin composition in the processes described above, the following problems frequently occurs: crack occurred in PSG (phoshor silicate glass) and SiN (silicon nitride) used as a passivation film formed on a wiring layer of aluminum; cutting of Au bonding wires. For measures for these problems, the following requirements have increased intensively for the encapsulating resin used for manufacturing a large package. 1) To decrease stress against an object encapsulated with the encapsulating resin and to increase adhesion of encapsulating resin to PSG, SiN, polyimde film, and lead frame. 2) To give high-temperature strength corresponding to mounting temperature and high-temperature strength with moisture absorbance to the encapsulating resin and to reduce moisture absorbance. On the basis of the above views, utilizing for main resin components of the encapsulating resin composition is being evaluated for such as maleimide resins, PPS (polyphenylene sulfide) resin, PPO (polyphenylene oxide) resin, and a liquid crystal polymer. Recent candidates of the encapsulating resin proposed are combined resins of maleimide and epoxy resins or amino-bis-maleimide resin made by combining bis-maleimide resin and 4,4'-diaminodiphenylmethane. Generally, encapsulation of a semiconductor element using these maleimide resins is made by molding a resin composition containing a maleimide resin as a main component of resin, a phenolic resin as a curing agent component, a curing catalyst, and other additives such as an inorganic filler and a flame-retardant, employing normal molding process, such as transfer molding. Such maleimide resin compositions, containing as a curing catalyst, a basic hardening catalyst and an organic peroxide, are described in, for example, JP-A 1 254 735, JP-A 63 191 833, JP-A 1 213 335, JP-A 62 072 722 and JP-A 1 213 336. It is said that the additional reaction of the phenolic resin to double bonds of the maleimide resin contained in the resin composition and the mutual reaction of maleimide resins occur in the molding process to cure the composition by polymerization of the maleimide resin resulting in the yield of the encapusulating resin moldings. The following problems occur at resin encapsulation of a semiconductor element using the maleimide resin composition described above. In comparison with the epoxy resin composition containing a phenolic resin as a curing agent, the maleimide resin composition shows less curing characteristics, because the reaction between the maleimide resin and the phenolic resin slowly progresses in said maleimide resin composition. Hence, molding resin for encapsulating requires long time to result in remaining non-reacted components and in decrease in mold release characteristics from a mold used. In addition, monomer and low molecular substance remain in the resin composition to make stain on the mold. The encapsulating resin moldings results in problem such as inferior appearance. Consequently, though use of the maleimide resin composition for resin encapsulation of a semiconductor element solves problems in the use of the conventional epoxy resin composition, the use causes a problem of very inferior properties such as moldability. An object of the present invention is to improve such as curing characteristics of a maleimide resin composition used for encapsulation of a semiconductor element. To be more specific, the present invention is intended to provide a maleimide resin composition having increased mouldability so as to reduce moulding time, less staining of a mould during the moulding process, increased releasability from a mould, and improved external appearance of mouldings. Another object of the present invention is to provide highly reliable resin encapsulated semiconductor device having resin encapsulation with the maleimide resin composition showing better mouldability as described above. The object is achieved according the present invention by a maleimide resin composition comprising a maleimide resin, a phenolic resin, and a curing catalyst, said curing catalyst being a combination of a basic catalyst and a peroxide, the maleimide resin composition being characterised in that the content of organic acid therein does not exceed a value of 0.2 weight percent when said value is analysed by extracting said organic acid using hot water treatment of said maleimide resin under the condition of 95°C for 20 hours or more. Still further, the present invention provides a resin encapsulated semiconductor device manufactured by encapsulating a semiconductor element with a maleimide resin composition in accordance with the present invention. This invention can be more fully understood from the following detailed description when taken in conjunction with the accompanying drawings, in which: Fig. 1 shows a sectional view showing structure of a resin encapsulated semiconductor device according to the present invention. The following is the detailed description of a maleimide resin composition in accordance with the present invention. It is said that in a maleimide resin composition according to the present invention, the additional reaction of the phenolic resin being a curing agent component to double bonds of the maleimide resin being a main component of resin and the mutual reaction of the maleimide resin occur place through the function of the curing catalyst, and the resin composition is cured by progress of polymerization of the maleimide resin to form a cured product. Though the maleimide resin is not particularly restricted in the present invention, for example, a N,N'-substituted bismaleimide compound represented by general formula (1) given below or poly(phenylene methylene)polymaleimide represented by general formula (2) given below can be used. where, X represents a divalent hydrocarbon group such as an alkylene group, a cyclo-alkylene group, and a monocyclic or polycyclic arylene group, or a divalent hydrocarbon group combined by a divalent atomic group such as -CH 2 -, -CO-, -SO 2 -, and -CONH-.) where, m represents an integral of 1 to 5. To be more specific, the maleimide resin used in the present invention includes, for example, N,N'-phenylenebismaleimide, N,N'-hexamethylene-bismaleimide, N,N'-diphenylmethanebismaleimide, N,N'-oxy-di-p-phenylenebismaleimide, N,N'-4,4'-benzophenonebismaleimide, N,N'-p-diphenylsulfonebismaleimide, N,N'-(3,3' dimethyl)methylene-di-p-phenylenebismaleimide, poly(phenylmethylene)polymaleimide, 2,2'-bis(4-phenoxyphenyl)propane-N,N'-bismaleimide, bis(4-phenoxyphenyl)sulfone-N,N'-bismaleimide, 1,4-bis(4-phenoxy)benzene-N,N'-bismaleimide, 1,3-bis(4-phenoxy)benzene-N,N'-bismaleimide, 1,3-bis-(3-phenoxy)benzene-N,N'-bismaleimide. These maleimide resins can be used singly or in combination. The maleimide resin can contain a trace amount of an organic acid. The organic acid referred to is that remaining in the resin when the purity thereof is insufficient; examples of such organic acids are acetic acid. maleic acid. fumaric acid, and fatty acids. These organic acids can be extracted from the resin by hot water treatment of the maleimide resin under the condition of 95°C for 20 hours or more and can be analyzed by an ion chromatography and a liquid chromatography. In the maleimide resin composition of the present invention, the organic acid content of the maleimide resin has a great influence on the properties of a cured product when it is moulded. Namely, a large amount of an organic acid left due to insufficient purity of the maleimide resin, reduces moisture-resistance of the cured product. Corrosion of an Al wiring layer on a semiconductor chip is increased in the case of encapsulation of a semiconductor element with a resin composition containing maleimide resin containing a large amount of an organic acid. Consequently, organic acid content in the maleimide resin should be not more than 0.2 weight per cent or preferably not more than 0.1 weight per cent in values determined by the extracting and analyzing methods described above. The method for obtaining a bismaleimide resin of sufficient purity is the direct dehydration and cyclisation of the bismaleamic acid by heating, without acetic anhydride as reaction solvent. Phenolic resin is used as a curing agent component in the maleimide resin composition of the present invention. For example, novolak type phenolic resin may be used. Any novolak type phenolic resin having two or more phenolic hydroxyl groups in a single molecule can be used. More specifically, types of novalak resin which may be used in the present invention include phenolic novolak resin, cresol novolak resin, t-butyl phenolic novolak resin, nonyl phenolic novolak resin, phenolic aralkyl resin, dicyclopentadien phenolic novolak resin. Particularly, phenolic resins having a group reactive to a maleimide resin, such as amino group, allyl group, vinyl group, and acryl group, can be used. Among these phenolic resins, phenolic novolak resin is particularly preferable in terms of mouldability and strength. To be more specific, examples of phenolic resin, and in particular novolak type phenolic resins marketed include: Shonol BRG-555 (Showa High Polymer Co., Ltd., softening point 68°C, melting viscosity 2.4 ps at 125°C), Shonol BRG-556 (Showa High Polymer Co., Ltd., softening point 80°C, melting viscosity 1.8 ps at 150°C), Shonol BRG-557 (Showa High Polymer Co., Ltd., softening point 87°C, melting viscosity 3.0 ps at 150°C), Shonol BRG-558 (Showa High Polymer Co., Ltd., softening point 97°C, melting viscosity 6.2 ps at 150°C), Varcum TD-2131 (Dai Nippon Ink, kk, softening point 80°C, melting viscosity 3.3 ps at 150°C), and Varcum TD-2093 (Dai Nippon Ink, kk, softening point 100°C, melting viscosity 30 ps at 150°C). The phenolic resin contained in the maleimide resin composition according to one embodiment of the present invention is allyl phenolic resin represented by general formulae (3), (4), or (5) given below. where, R represents -CH 2 -CH = CH 2 ; n and 1 are positive integers. When an allyl phenolic resin is contained in the maleimide resin compound of the present invention, the content of allyl phenol monomer contained in the allyl phenolic resin is preferably 1000 ppm or less to reduce the volatility of components at melting. Preferable examples of allyl phenol monomers allowing to use in the present invention are SH-140A (Mitsubishi Petrochemical Co., Ltd.), SH-150A (Mitsubishi Petrochemical Co., Ltd.), and XPSF-4488 (Gunei Chemical Industry Co., Ltd.). It is preferred that the content of the phenolic resin in the maleimide resin composition of the present invention is 10 to 50 weight percent based the maleimide resin content. A content of phenolic resin below 10 weight percent increases the melting viscosity of the maleimide resin composition to result in unloading and wire flow at moulding. On the other hand, the content of the phenolic resin over 50 weight percent makes curing characteristics of the resin composition unsatisfactory and causes the heat resistance of a cured and moulded product to be reduced. Besides, a more preferable content of the phenolic resin is 20-40 weight percent based on the maleimide resin content. In the maleimide resin composition of the present invention, a binary catalyst including a basic catalyst and a peroxide is used as a curing catalyst. As the basic catalyst, for example, organic phosphine compounds, imidazole compounds or their derivatives, and DBU (1,8-diazabicyclo (5,4,0)undecene-7) or its phenolic salt are used. These compounds can be used singly or in comination as the need arises. The specific organic phosphines include, for example, trimethylphosphine, triethylphosphine, tributylphosphine, triphenylphosphine, tri(p-methylphenyl)phosphine, tri(nonylphenyl)phosphine, methyldiphenylphosphine, butylphenylphosphine, tricyclohexylphosphine, 1,2-bis(diphenylphosphine)ethane, and bis(diphenylphosphine)methane. These organic phosphine compounds can be used singly or in combination. The specific imidazole compounds include, for example, 2-methylimidazole, 2,4-dimethylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, and 2-heptadecylimidazole. The phenolic salt of DBU is exemplified by SA-853 (Sanapuro). The specific peroxides which may be used in the composition of the present invention may, for example, include diallyl peroxides such as di-t-2,5-dimethyl-2,5-di-t-butyl peroxyhexane; peroxy esters such as t-butyl peroxy acetate, t-butyl peroxy phthalate, t-butyl peroxy benzoate, 2,5-dimethyl-2,5-dibenzoyl peroxyhexane, and t-butyl peroxy-2-ethyl hexanoate; diacyl peroxides such as acetyl peroxide, isobutyryl peroxide, decanoyl peroxide, lauroyl peroxide, 3,5,5-trimethylhexanoyl peroxide, benzoyl peroxide, and di-2-ethylhexyl peroxy dicarbonate; hydroperoxides such as t-butyl hydroperoxide, cumene hydroperoxide, and p-methane hydroperoxide; ketone peroxides such as methylethyl ketone peroxide and cyclohexanone peroxide; peroxy ketals such as 1,1-bis(t-butyl peroxy)cyclohexane and 1,1-bis(t-butyl peroxy)-3,3,5-trimethyl cyclohexane. These peroxides can be used singly or in combination. In the maleimide resin composition of the present invention, the total content of the curing catalyst is preferably 0.1 to 10 weight percent based on the total content of the maleimide resin (main component of resin) and the phenolic resin (curing agent component). If the content of curing catalyst is below 0.1 weight percent, reaction of the maleimide resin to the phenolic resin is insufficient and insufficient curing occurs. Hence, electrical characteristics of cured and moulded product, i.e. an encapsulating resin moulded, are substantially reduced. On the other hand, a content of curing catalyst above 10% causes a reduction in heat resistance, moisture-resistance, and electrical characteristics of the cured and moulded product. The most preferable content of curing catalyst is 0.5 to 5 weight percent depending on the total content of the maleimide resin and the phenolic resin. The content of peroxide is preferably 10 to 50 weight percent based on the content of the basic catalyst. A peroxide content below 10 weight percent promotes a polymerixing reaction of maleimide resin (bismaleimide) which is insufficient, so as to result in a reduced mouldability of the resin composition, and to inhibit improvement of, for example, heat resistance of a cured product. On the other hand, a peroxide content over 50% considerably lowers moisture-resistance and electrical characteristics of a cured product. In addition, in order to make most effective use of the basic catalyst and the peroxide in combination and to obtain excellent performances of the maleimide resin composition, such as curing characteristics, mouldability, and heat resistance, moisture resistance, and electrical characteristics of a cured product yielded, the content of the peroxide is preferably 20 to 30 weight percent depending on the content of the basic catalyst. The maleimide resin composition of the present invention is particularly suitable for encapsulating a semiconductor element, for which it usually contains an inorganic filler in addition to essential components described above. The inorganic filler may, for example, be quartz glass powder, crystalline silica powder, glass fiber, talc, alumina powder, calcium silicate powder, calcium carbonate powder, barium sulfate powder, and magnesia powder. Among these fillers, the most suitable are quartz powder and crystalline silica powder. The content of the silica powder can be in the range of 50 to 85 weight percent based on the content of the maleimide resin composition with proper combination of ground silica, globular silica, and fumed silica. A content of the inorganic filler below 50 weight percent increases the thermal coefficient of expansion of a cured product finally obtained, causing insufficient thermal impulse resistance. On the other hand, if the content of inorganic filler is over 85 weight percent, the fluidity of the maleimide resin composition is insufficient to result in wire flow, bed flow and unloading. In the maleidmide resin composition of the present invention, various waxes can be added as a mould release agent to increase its mouldability. Suitable waxes for this purpose are, for example, polyethylene series waxes, i.e. waxy materials containing a main component of polyethylene with a molecular weight of 500 to 4000. The polyethylene series waxes are generally called a polyethylene wax. In addition, other suitable waxes are those having a carbonyl group as a polar group introduced by oxidizing denaturation of denaturation with acid. In the present invention, polyethylene series waxes having a softening point of 65 to 140°C are particularly preferably. The content of the wax contained in the maleimide resin composition of the present invention should be 0.2 to 19 parts by weight, preferably 0.5 to 5 parts by weight, based on 100 parts by weight of the resin composition. If the wax content is less than 0.2 parts by weight, releasability of a cured product from a mould is reduced. On the other hand, if the content is over 19 parts by weight, a mould can become stained, primarily by bleeding wax contained in the resin composition. For reference, in the maleimide resin composition of the present invention, ester series waxes such as carunauba wax and fatty acid amide series waxes can be added and a combination of these waxes and polyethylene series waxes can also be used. Organosyloxane bismaleimide can be added to the maleimide resin composition of the present invention in order to improve adhesion of the cured and moulded composition to a polyimide protecting film and to an insulating film such as SiO 2 and SiN formed on the surface of a semiconductor element. In addition, additives containing silicon rubber or silicon gel as a main component or MBS or ABS as a main component can be added in order to give low stress to a cured and moulded product. As another component, a flame-retardant, such as an epoxy halide resin and antimony trioxide, a colorant such as carbon powder, or a coupling agent can be added, if necessary. The following is a detailed explanation of the preparation process for a maleimide resin composition according to the present invention. In preparing the maleimide resin composition of the present invention, it is generally preferable that a part or all of the phenolic resin, being a component of a curing agent, is preblended with the curing catalyst containing a basic catalyst and a peroxide in advance of other components, in order to improve mouldability of the resin composition. Specifically, prior to blending other components, a part or all of the phenolic resin and a part or all of the curing catalyst are dissolved and blended (preblending) to yield them in uniform and clear state. Subsequently, this blend is cooled and powdered by grinding to obtain a phenolic resin containing the curing catalyst. After this process, the phenolic resin containing the curing catalyst, the maleimide resin, the remainder of the phenolic resin, the remainder of the curing catalyst (when a part of the phenolic resin and a part of the curing catalyst are preblended), and as the need arises, other components such as an inorganic filler and additives, are melted and kneaded together, and then ground into powder form so as to obtain the maleimide resin composition of the present invention. In the process described above, when reference is made to the curing catalyst being preblended, note that both or either of the basic catalyst and the peroxide can be used. However, it is more preferable that both the basic catalyst and the peroxide are preblended with the phenolic resin in order to improve dispersability of the curing catalyst in the resin composition. The temperature at which preblending is performed should be the softening point of the phenolic resin used, or higher. The temperature is preferably in the range so as to retain catalytic activity by thermal decomposition of the peroxide contained in the curing catalyst. In the preblending, when a part of the phenolic resin used and the curing catalyst are blended, the remainder of the phenolic resin, prepolymerized by adding it to maleimide resin as a main component of resin, can be used for the preparation of the maleimide resin composition. On this occasion, the amount of phenolic resin preblended with the curing catalyst should be preferably 1 to 50 weight percent depending on the total amount of phenolic resin used for the preparation of the maleimide resin composition. When the amount of preblended phenolic resin is less than I weight percent based on the total amount of phenolic resin used for preparing the maleimide resin composition, dispersion of the curing catalyst during preblending is insufficient, such that the effect of preblending is severely reduced. On the other hand, if the amount of preblended phenolic resin is more than 50 weight percent based on the total amount of phenolic resin used for preparing the maleimide resin composition, the amount of phenolic resin remaining for pre-polymerization with the maleimide resin is too low and the operational performance of the pre-polymerization is reduced. The particularly preferable amount of phenolic resin used for preblending is 3 to 40 weight percent based on the total amount of phenolic resin amount used for the preparation of the maleimide resin composition. Preferably, in the maleimide resin composition of the present invention, the combined result of preblending a part of said phenolic resin with the curing catalyst and pre-polymerizing the remainder of the phenolic resin with the maleimide resin, improves dispersiblity of the curing catalyst to result in improvement of curing characteristics of the maleimide resin composition. In the preparation of the maleimide resin composition of the present invention, there are the following possible methods for preblending a part or whole of the phenolic resin with the curing catalyst and for melting and kneading of remaining components: melting and kneading using a heated roll; melting and kneading using a kneader; melting and kneading using an extruder; blending using a special blender after grinding; and a suitable combination of these methods may be used. The resin encapsulated semiconductor device of the present invention is manufactured by encapsulating a semiconductor element with the maleimide resin composition described previously, which contains an inorganic filler, according to conventional method. Fig. 1 shows a sectional structure of an example of a resin encapsulated semiconductor device of the invention. In the figure, 1 shows a semiconductor chip mounted on an island 2. On the surface of the semiconductor chip 1, plural bonding pads 3 are formed and these and a lead frame 4 of an outer terminal are connected each other using a bonding wire 5. The individual device composed of a semiconductor element and parts such as a lead frame is encapsulated as covered with an encapsulating resin 6. As the encapsulating resin 6 in the present invention, the resin composition containing the maleimide resin, the phenolic resin, the combination of the basic catalyst and the peroxide as a curing catalyst, and the inorganic filler described previously is used. Although the most common method of this type of resin encapsulation is low pressure transfer molding, resin encapsulation by injection molding, compression molding, and casting is possible to employ. On this occasion, after-curing at 175°C or higher is preferred after the molding. The maleimide resin composition of the present invention can be applied to a thermoresistance plywood, and a thermoresistance adhesive and a thermoresistance paint, which are obtained by adding a diluting solvent to the composition, as well as use for the resin encapsulation of a semiconductor element. The maleimide resin composition of the invention has a characteristic of combined use of the basic catalyst and the peroxide as the curing catalyst. Between them, the peroxide has a function of a radical polymerization intiator, which reacts to double bonds of the maleimide resin so as to promote polymerization among molecules of the resin. On the other hand, the basic catalyst primarily promotes additional reaction of the phenolic resin being a curing agent to the maleimide resin. On the contrary, sole use of the basic catalyst as the curing catalyst leaves unreacted double bonds in the maleimide resin to result in insufficient progress of its polymerization. Sole use of the peroxide as the curing catalyst inhibits enough progress of reaction between the phenolic resin and the maleimide resin. In the maleimide resin composition of the present invention, both reactions of the mutual polymerization of the maleimide resin and the additional reaction of the phenolic resin to the maleimide resin are promoted to improve its curing characteristics. Consequently improvements are achieved for moldability of the resin composition such as shortening of molding time, reducing stain of a mold, and improvement of mold release characteristics of a cured product from a mold to result in obtaining an encapsulating resin mold having good external appearance. A cured product has properties of heat resistance, moisture-resistance reliability, and electric characteristics appropriate for an encapsulating resin. In the preparation process of the maleimide resin composition of the present invention, preblending a part or whole of the phenolic resin being a curing agent with the curing catalyst, prior to blending with other components, allows to make improvement of dispersability of the curing catalyst in the resin composition. Thus, when resin encapsulation of a semiconductor element with the maleimide resin composition is performed, progress of the additional reaction of the phenolic resin to the maleimide resin and the mutual reaction of the maleimide resin is promoted to make curing characteristics of the resin composition better. Therefore, improvement is also realized for moldability of the resin composition and for various performances of a cured product obtained, as well as those mentioned above. In the maleimide resin composition of the present invention, its curing characteristics is further improved by preparing the maleimide resin composition in such a manner that a part of the phenolic resin is preblended with the curing catalyst in advance of other components, while the remainder of the phenolic resin is added to the maleimide resin to prepolymerize, and then, the preblend is blended with the other components. Besides, on the basis of the characteristics of maleimide resin, high reliability in performances such as heat resistance and moisture-resistance is applied to the resin encapsulated semiconductor device, as mentioned above, manufactured using the maleimide resin composition of the present invention as encapsulating resin. The followings are detailed explanations of the invention on the basis of Examples and Comparative Examples. Content ratios of components used in the following Examples and Comparative Examples are all expressed in weight percent. First, 100 g of a novolak type phenolic resin, Shonol BRG-556 (available from Showa High Polymer Co., Ltd., softening point 80°C) was charged in a separable flask and was melted at 120°C followed by dissolving a curing catalyst of the (a) to (f) described below into the melted mixture. Thus, preblending of the phenolic resin with the curing catalyst were performed. (a) 25 g of triphenyl phosphine (used for the Examples 1 and 4, and Comparative Examples 5 and 6); (b) 6 g of dicumyl peroxide (used for Examples 2 and 5); (c) 25 g of triphenyl phosphine, and 6 g of dicumyl peroxide, (used for Examples 3 and 6 to 8); (d) 40 g of 2-methylimidazole, and 6 g of dicumyl peroxide, (used for Examples 9); (e) 30 g of 1,8-diazabicyclo (5,4,0) undecene-7, and 6 g of dicumyl peroxide (used for Example 10); (f) 25 g of dimethylphenyl phosphine, and 6 g of dicumyl peroxide (used for Example 11). Subsequently, clarity and uniformity of each of these blends was confirmed and the blend was poured into a stainless vat to cool and grind. Finally, six kinds of phenolic resins containing curing catalyst are obtained. Next, according to the following method, the maleimide resin compositions of Examples 1 to 11 and Comparative Examples 1 to 7 were prepared with components in content ratios showed in the following Table 1 (Examples 1 to 11) and Table 2 (Comparative Examples 1 to 7). Specifically, first, pre-polymerization was performed by blending a phenolic resin, which had not been preblended with the curing catalyst, with the maleimide resin. Besides, melted silica powder GR-80T (available from Toshiba Ceramics Co., Ltd.) as an inorganic filler was treated using epoxy silane coupling agent A-187 (available from Nihon Unicar Co., Ltd.) in a Henschel mixer. Next, all components containing these are put in the mixer to treat for five minutes and kneaded with a roll heated 110°C. Following to this process, the kneaded mixture was cooled, grirded, and made in tablets to obtain maleimide composition of each Examples 1 to 11 and Comparative Examples 1 to 7. In the maleimide resin composition of Examples 1 to 11, a basic catalyst and a peroxide are added as a curing catalyst. Here, Examples 1 and 4 employed the phenolic resin containing curing catalyst made by preblending the curing catalyst of (a), Examples 2 and 5 employed the phenolic resin containing curing catalyst made by preblending the curing catalyst of (b), Examples 3 and 6 to 8 employed the phenolic resin containing curing catalyst made by preblending the curing catalyst of (c), Example 9 employed the phenolic resin containing curing catalyst made by preblending the curing catalyst of (d), Example 10 employed the phenolic resin containing curing catalyst made by preblending the curing catalyst of (e), Example 11 employed the phenolic resin containing curing catalyst made by preblending the curing catalyst of (f). On the other hand, in the maleimide resin composition of Comparative Examples 1 to 7, either a basic catalyst or a peroxide is added as a curing catalyst. In Comparative Examples 1 to 4 and 7, no preblending was performed for a curing catalyst and a phenolic resin; Comparative Examples 5 and 6 were preblended. The content of an organic acid in the maleimide resin used for the resin composition was measured according to the method described previously. The values of them are showed in Table 1 and 2. Molding was performed for maleimide resin composition, which had been prepared described above, of Examples 1 to 11 and Comparative Examples 1 to 7 by low pressure transfer molding machine at molding temperature of 180°C. The molded product obtained was checked concerning the following measures of moldability. Molding time: evaluation of swelling of cull, releasability of a molded product from a mold; Hardness immediately after molding: measurement using Barcol impresser (#935); Mold releasing load: load at releasing a molded product from a mold was measured by using a push-pull gage after molding using a mold for measurement of mold releasing load; Stain of a mold: evaluation by observing of a mold surface after 50 shots of molding of the same compositon using the same mold; Observation of external appearance of a molded product. The results are showed in Table 3 for Examples 1 to 11 and in Table 4 for Comparative Examples 1 to 7. It is clear from the results shown in Tables 3 and 4 that the external appearance of the molded product of the maleimide resin composition of the present invention is superior to those of Comparative Examples. The molded product obtained by the resin composition of the present invention shows excellent moldabilitys such as short time for molding and low 0 to 9 kg values of mold releasing load. The maleimide resin compositions of Examples 7 to 11 containing polyethylene waxes as mold release agent shows particularly low mold-releasing load to result in excellent moldability. Subsequently, at 200°C for eight hours, test samples were formed by after-curing molded products of maleimide resin compositions of Examples and Comparative Examples. The chips were applied to measurements of the following physical properties. Gelling time (175°C) Glass transition point Thermal expansion coefficient High temperature strength (215°C) Water absroption (135°C, 85% RH, 20 hours) The results of these measurements are showed in the following Table 3 and Table 4. It is clear from Tables 3 and 4 that the physical properties of the molded product of the maleimide resin compositions according to the present invention are superior to those of Comparative Examples. For the purpose to evaluate performance as encapsulating resin, QFP (Quad Flat Package) having 184 pins was manufactured by encapsulating a test element of chip size 15 mm square with the maleimide resin composition of the present invention and Comparative Examples. The resin encapsulated semiconductor device was applied to after-curing at 200°C for eight hours, followed by with moisture-absorbing treatment at 85°C humidity 85% for 168 hours and VPS (vaper phase re-flow treatment at 215°C) was finally carried out. Crack reaching outside of the encapaulating resin was observed for the resin encapsulated semiconductor device immediately after VPS. Moisture-resistance reliability test was done in a pressure cracker under 121°C and 2 atms. for the resin encapsulated semiconductor device so as to evaluate occurrence of inferior products. The results are showed in the following Table 3 and Table 4. It is clear from the results showed in the Table 3 and 4 that the resin encapsulated semiconductor device manufactured using the maleimide resin composition of the present invention as the encapsulating resin is superior to that manufactured using the maleimide resin composition of Comparative Examples in moisture-resistance characteristic. From the results of the Comparative Examples 1, 4, and 7, it is suggested that moisture resistance reliability of the resin encapsulated semiconductor device reduces when an organic acid is more contained in the maleimide resin used. As described in detail above, the maleimide resin composition of the invention has very improved curing characteristics to result in excellent moldability. Thus, according to the invention, when a semiconductor element is encapsulated with the maleimide resin composition, the resin encapsulated semiconductor device can be provided with good external appearance of the molded encapsulating resin mold to result in high reliability. In addition, the maleimide resin composition of the invention is an encapsulating material providing the better characteristics of heat resistance and thermal impulse resistance and meeting requirement of moisture-resistance reliability and trend of thinning to a future resin encapsulating semiconductor device to result in bringing great value to industries.

Claims: A maleimide resin composition comprising a maleimide resin, a phenolic resin, and a curing catalyst, said curing catalyst being a combination of a basic catalyst and a peroxide, the maleimide resin being characterised in that the content of organic acid therein does not exceed a value of 0.2 weight percent when said value is analysed by extracting said organic acid using hot water treatment of said maleimide resin under the condition of 95°C for 20 hours or more. The maleimide resin composition according to claim 1, which further comprises an inorganic filler. The maleimide resin composition according to claim 1, characterised in that a polyethylene wax is added as a mold release agent. The maleimide resin composition according to claim 1, characterised in that said basic catalyst is one selected from a group consisting of organic phosphine compounds, imidazole compounds or derivations thereof, and DBU (1,8-diazabicyclo (5,4,0) undecene-7) or its phenoic salts. A resin encapsulated semiconductor device manufactured by encapsulating a semiconductor element with a maleimide resin composition comprising a maleimide resin, a phenolic resin, a combination of a basic catalyst and a peroxide as a curing catalyst, and an inorganic filler, characterised in that said maleimide resin composition contains no more than 0.2 weight percent of organic acid when said organic acid content is analysed by extracting said organic acid using hot water treatment of said maleimide resin compound under the condition of 95°C for 20 hours or more. The resin encapsulated semiconductor device according to claim 5, characterised in that polyethylene wax as mold release agent is added to said maleimide resin composition. The resin encapsulated semiconductor device according to claim 5, characterised in that said basic catalyst contained in said maleimide resin composition is one selected from a group consisting of organic phosphine compounds, imidazole compounds or derivatives thereof, and DBU (1,8-diazabicyclo (5,4,0) undecene-7) or its phenolic salts.

Inventors: FUJIEDA SHINETSU, HIGASHI MICHIYA, SHIMOZAWA HIROSHI, YOSHIZUMI AKIRA, FUJIEDA, SHINETSU, HIGASHI, MICHIYA, SHIMOZAWA, HIROSHI, YOSHIZUMI, AKIRA, FUJIEDA, SHINETSU, C/O INTELLECTUAL PROPERTY DIV., HIGASHI, MICHIYA, C/O INTELLECTUAL PROPERTY DIV., Shimozawa, Hiroshi, c/o Intellectual Property Div., YOSHIZUMI, AKIRA C/O INTELL. PROPERTY DIV.
Applicants: TOSHIBA KK, KABUSHIKI KAISHA TOSHIBA
Application year: 1991
Main classification: C08L79
IPC codes: C08L61, H01L23, C08K5, C08L79, H01B3, C08L35