A resin-encapsulated semiconductor device is of the structure wherein a silicon chip on a die pad is encapsulated with a molding resin. The rear surface of the die pad remote from the silicon chip, preferably the entire surfaces of the elements are treated with a primer, typically a silane coupling agent and a low stress epoxy resin encapsulant is used, preventing the encapsulating resin from separating and cracking upon subsequent dipping in solder bath.

An epoxy resin composition useful for sealing a semiconductor device includes 100 parts by weight of epoxy resin, 30-75 parts by weight of phenolic resin, 320-570 parts by weight of silica powder, and 2-30 parts by weight of styrene-butadiene-methyl methacrylate copolymer. The surface of the silica powder is treated, at room temperature, by 0.05-1.00% by weight of silane coupling agent, 0.05-1.00% by weight of a silicone base surface active agent, and 0.15-3.00% by weight of thermosetting silicone rubber.

A rubber-modified phenolic resin composition contains a novolak-type phenolic resin in which at least one modifying agent selected from the group consisting of an ABS resin and an MBS resin is homogeneously dispersed. The composition has good impact resistance and thermal shock resistance. The composition is prepared by adding at least one modifying agent described above to a novolak-type phenolic resin which is heated and melted at its softening point or more, so that the modifying agent is homogeneous dispersed in the resin. The resin composition is suitably used as a curing agent for an epoxy resin encapsulant for sealing electronic devices.

A silicone resin for sealing a semiconductor chip. A cured silicone resin, which is obtained by curing the silicone resin at a given temperature, has a percent elongation, after fracture, measured at a room temperature, not less than 4% of a penetration number at room temperature. A semiconductor device sealed with the silicone resin, when subjected to a heat cycle or a vibration test, provides resistance to cracking, forming of voids, and interfacial peeling-off. The cured silicone resin may have a penetration number not less than 10 and not more than 80 and a loss elasticity not less than 17% of the storage elasticity. A resin member made of the cured silicone resin and sealing a semiconductor chip may include a filler, such as silica or alumina, having a coefficient of linear thermal expansion lower than that of the cured silicone resin.

Plastic (or resinous) materials used to package (or support) electronic devices typically have thermal coefficients of expansion exceeding that of the device to be packaged. A "loading" material (agent) having a coefficient of expansion significantly less than the "base" plastic material (molding compound), less than that of the die, and preferably zero or negative over a temperature range of interest, is mixed with the "base" plastic material to produce a plastic molding compound with a lower overall thermal coefficient of expansion. Titanium dioxide, zirconium oxide and silicon are discussed as loading agents. The loading material is mixed into the plastic molding compound in sufficient quantity to ensure that the resulting mixture exhibits an overall thermal coefficient of expansion that is more closely matched to that of the electronic device. Reduction of the absolute thermal coefficient of expansion of the plastic material (independent of any matching criteria) additionally serves to reduce thermal stress cracking of plastic package bodies during rapid thermal cycling, such as occurs during vapor soldering.