Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2000-11-09
2001-11-27
Dawson, Robert (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C257S789000, C257S794000, C257S795000, C428S620000, C523S444000
Reexamination Certificate
active
06323263
ABSTRACT:
This invention relates to liquid epoxy resin compositions for use with semiconductor devices as potting and coating materials, and more particularly, to liquid epoxy resin compositions having improved storage stability and interstitial infiltration and suitable for use with flip-chip type semiconductor devices as underfill material.
BACKGROUND OF THE INVENTION
With the advance of electric equipment toward smaller size, lighter weight and higher performance, the semiconductor mounting technology has changed from the pin mating type to the surface mounting which now becomes the mainstream. One bare chip mounting technology is flip-chip (FC) mounting. The flip-chip mounting is a technique of providing an LSI chip on its circuit pattern-bearing surface with several to several thousands of electrodes, known as bumps, of about 10 to 100 microns high and joining the chip to electrodes on a substrate with a conductive paste or solder. Then the sealing material used for the protection of FC devices must penetrate into gaps of several tens of microns (typically about 40 to 20 &mgr;m) defined by bumps between the substrate and the LSI chip. Conventional liquid epoxy resin compositions used as the underfill material for flip-chip devices are generally composed of a liquid epoxy resin, a curing agent and an inorganic filler. Of these, the most predominant is a composition in which a large amount of inorganic filler is blended in order to provide a matching coefficient of linear expansion with those of semiconductor chips, substrates and bumps for increased reliability.
The flip-chip underfill materials with high loading of inorganic filler suffer from very low productivity since they penetrate into a narrow gap, usually of about 40 to 20 &mgr;m, at a very slow rate. There is a desire to overcome this problem. It is presumed that the inorganic filler can accommodate the narrow gap penetration as its particle size decreases. However, the cured composition loaded with inorganic filler of a smaller particle size tends to peel and crack because the cured product has an increased modulus of elasticity to prevent easy relaxation of stresses therein.
SUMMARY OF THE INVENTION
An object of the invention is to provide a novel and improved liquid epoxy resin composition having improved interstitial infiltration, curing into a low modulus product and suitable in sealing semiconductor devices therewith in a reliable manner.
According to the invention, there is provided a semiconductor-sealing liquid epoxy resin composition, comprising (A) a liquid epoxy resin, (B) a curing agent, and (C) an inorganic filler. The inorganic filler contains up to 1% by weight of particles having a particle size of at least 45 &mgr;m, has a mean particle size of 1 to 5 &mgr;m, and has a particle size distribution having a peak in a particle size range of 0.5 to 2 &mgr;m and a peak in a particle size range of 5 to 10 &mgr;m wherein the content in % by weight of particles falling within the particle size range of 0.5 to 2 &mgr;m divided by the content in % by weight of particles falling within the particle size range of 5 to 10 &mgr;m is from 1 to 20. The composition exhibits improved interstitial infiltration and has a low modulus of elasticity in the cured state.
Spherical silica is typically used as the inorganic filler in the underfill material because of its flow. If the filler contains a substantial amount of particles which are larger than the gap, such large particles are intercepted at the gate to further reduce the infiltration cross-section and exacerbate the infiltration capability. By substantially removing particles having a maximum particle size of 45 &mgr;m or greater and controlling the mean particle size to the range of 1 to 5 &mgr;m, there are obtained particles which can effectively penetrate through the narrow gap. Any increase in modulus of elasticity due to a reduction of particle size is precluded by a choice of particle size distribution. The particles have a particle size distribution having a peak in a particle size range of 0.5 to 2 &mgr;m and a peak in a particle size range of 5 to 10 &mgr;m. Additionally, the ratio of the content (X) in % by weight of particles falling within the particle size range of 0.5 to 2 &mgr;m to the content (Y) in % by weight of particles falling within the particle size range of 5 to 10 &mgr;m is controlled to the range from 1/1 to 20/1. This choice is effective for achieving stress relaxation in the cured composition.
The semiconductor-sealing liquid epoxy resin composition exhibits effective interstitial infiltration and cures into a product having a low modulus of elasticity.
REFERENCES:
patent: 4877822 (1989-10-01), Itoh et al.
patent: 4902732 (1990-02-01), Itoh et al.
patent: 5089440 (1992-02-01), Christie et al.
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patent: 6083774 (2000-07-01), Shiobara
Kuwabawa Haruyoshi
Shiobara Toshio
Sumita Kazuaki
Aylward D.
Birch & Stewart Kolasch & Birch, LLP
Dawson Robert
Shin-Etsu Chemical Co. , Ltd.
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