Stock material or miscellaneous articles – All metal or with adjacent metals – Composite; i.e. – plural – adjacent – spatially distinct metal...
Reexamination Certificate
2001-04-04
2003-02-18
Dawson, Robert (Department: 1712)
Stock material or miscellaneous articles
All metal or with adjacent metals
Composite; i.e., plural, adjacent, spatially distinct metal...
C257S786000, C257S789000, C257S793000, C257S795000, C523S443000, C525S523000, C528S121000
Reexamination Certificate
active
06521354
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an epoxy resin composition of good moldability and high reliability favorable for semiconductor encapsulation, and also to a semiconductor device.
BACKGROUND OF THE INVENTION
Epoxy resins have good heat resistance, moisture resistance, electrical properties and adhesiveness, and, when combined with various additives, they can be formulated into different types of compositions having desired properties. Therefore, they are utilized for industrial materials including paints, adhesives, electric insulators, etc.
For sealing and encapsulating electronic circuit members of semiconductor devices and others, for example, hermetic sealing with metals or ceramics as well as resin encapsulation with phenol resins, silicone resins or epoxy resins has heretofore been proposed. Resins usable for such semiconductor encapsulation are generally referred to as sealant resins. Above all, resin encapsulation with epoxy resins is the most popular in the art, in view of the balance of their economical advantages, productivity and physical properties. In general, a transfer-molding process is employed for sealing and encapsulating semiconductor chips with epoxy resins. Briefly, a curing agent, a filler and other additives are added to an epoxy resin, and the resulting composition is applied to semiconductor chips aligned in a mold.
The necessary characteristics of epoxy resin compositions for semiconductor encapsulation are high reliability and good moldability. For their reliability, for example, the resin compositions must be resistant to moisture; and for their moldability, the resin compositions must be flowable and must be softened when heated, and must not form burrs when molded.
The moisture resistance referred to herein is meant to indicate that, when resin-sealed semiconductors are left in high-temperature high-humidity environments, no moisture penetrates into the sealant resin and into the interface between the sealant resin and the resin-sealed lead frame to damage the semiconductors. The degree of integration of semiconductors is increasing these days, and the sealant resins for semiconductors are desired to have higher moisture resistance.
For improving the moisture resistance of sealant resins, a silane coupling agent is generally added to them. Concretely, a method of adding an epoxy silane to sealant resins (Japanese Patent Publication No. 17640/1987); a method of adding a mercaptosilane thereto (Japanese Patent Laid-Open No. 153357/1980); and a method of adding thereto an aminosilane having a secondary amino group (Japanese Patent Laid-Open No. 218736/1990) have been proposed.
A method of increasing the purity of sealant resins by removing impurities from epoxy resin, curing agents and other constituent components to thereby improve the moisture resistance of the thus-purified sealant resins has also been proposed (Japanese Patent Laid-Open No. 212224/1982).
The recent technology for mounting semiconductor packages on a printed circuit board is toward automatic high-density package mounting, for which the surface mount technology (SMT) of directly soldering semiconductor packages on the surface of a substrate is being popular in place of the conventional plated through-hole (PTH) mount technology of inserting lead pins into the through-holes of a substrate. With that, the semiconductor packages to be mounted on a substrate range from conventional dual in-line packages (DIP) to thin-film flat plastic packages (FPP) suitable for high-density surface mounting. Above all, TSOP, TQFP and LQFP having a thickness of at most 2 mm are the mainstreams for the recent FPP, as meeting the advanced microfabrication in the art. In that situation, they are more readily influenced by external factors such as temperature and humidity, and their reliability including soldering heat resistance, high-temperature reliability and heat-resistance reliability will be a matter of greater importance.
Solder reflow surface mounting is generally employed for SMT. The method comprises putting semiconductor packages on a substrate followed by exposing them to a high temperature not lower than 200° C. so that the solder previously applied onto the substrate is melted to thereby fix the packages on the surface of the substrate. In the surface-mounting method, the semiconductor packages are entirely exposed to such a high temperature. In this case, if the moisture resistance of the sealant resin used in the packages is not good, the moisture absorbed by the resin will explosively expand while the packages are heated at such a high temperature for solder reflow, and the package will be cracked. Therefore, the moisture resistance of sealant resins for semiconductor encapsulation is a matter of great importance.
For protecting the environment, the recent tendency in the art is toward using lead-free solder. The melting point of lead-free solder is high, and therefore the reflow temperature thereof is also high. In that situation, sealant resins for semiconductor encapsulation are desired to have higher soldering heat resistance and higher moisture resistance than before.
It is generally known that increasing the proportion of a filler in a sealant resin effectively results in enhancing the soldering heat resistance of the resin. This is because the resin component of the sealant resin is reduced whereby the moisture resistance of the sealant resin is enhanced and the moisture absorption thereof decreases. However, this is problematic in that, if the proportion of the filler in a sealant resin is larger than 90% by weight, the fluidity of the sealant resin greatly lowers, thereby causing other problems of package encapsulation failure and stage shifts. In addition, the reduction in the resin component in a sealant resin causes still other problems of resin-to-lead frame adhesion failure and package peeling in reflow treatment.
The object of the present invention is to solve the problems with epoxy resin compositions noted above and to provide a resin composition having the advantages of improved reliability including soldering heat resistance, improved moldability including fluidity, and improved reflow resistance to ensure good adhesion to lead frames, thereby enabling resin encapsulation of semiconductors at higher solder reflow temperatures.
DISCLOSURE OF THE INVENTION
The invention provides an epoxy resin composition comprising (A) an epoxy resin, (B) a curing agent and (C) a filler, which is characterized in that the epoxy resin (A) contains an epoxy compound (a) of chemical formula (I) mentioned below, that the filler (C) contains spherical silica and that the filler (C) accounts for from 88 to 96% by weight of the entire resin composition, and provides a semiconductor device.
BEST MODES OF CARRYING OUT THE INVENTION
The constitution of the invention is described in detail hereinunder.
In the invention, the epoxy resin (A) contains, as the essential ingredient, a bisphenol F-type epoxy resin (a) of formula (I) mentioned below. Containing the bisphenol F-type epoxy resin (a), the viscosity of the sealant resin of the composition lowers and the moldability thereof greatly improves. Preferably, the content of the bisphenol F-type epoxy resin (a) falls between 50 and 100% by weight of the epoxy resin (A).
Depending on its use, the resin composition may contain two or more different types of epoxy resins. For good heat resistance enough for semiconductor encapsulation, however, it is desirable that the resin composition contains any of cresol-novolak-type epoxy resins and bishydroxybiphenyl-type epoxy resins having an epoxy equivalent of at most 500, preferably at most 300.
In the invention, the proportion of the epoxy resin (A) preferably falls between 2.5 and 5.0% by weight of the entire resin composition.
The curing agent (B) for use in the invention is not specifically defined, so far at it reacts with and cures the epoxy resin (A). Concretely, it includes, for example, novolak resins such as phenol-novolak, cresol-novolak, etc.; bisphenol compounds such as biphe
Niwa Katsuhiro
Shimizu Hiroo
Tanaka Masayuki
Aylward D.
Dawson Robert
Schnader Harrison Segal & Lewis LLP
Toray Industries Inc.
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