Abstract: Phosphonium borate compounds of formula (1) are novel. R1, R2, R3 and R4 each are a monovalent organic group having an aromatic or heterocyclic ring or a monovalent aliphatic group, at least one of R1, R2, R3 and R4 which are bonded to phosphorus atom and at least one of R1, R2, R3 and R4 which are bonded to boron atom are each an organic group derived by releasing a proton from a proton donor selected from among an aromatic carboxylic acid having at least one carboxyl group, an aromatic carboxylic acid having at least one acid anhydride group and at least one carboxyl group, a phenol compound having at least one phenolic hydroxyl group, an aromatic compound having at least one carboxyl group and at least one phenolic hydroxyl group, and an aliphatic carboxylic acid having at least one carboxyl group. The phosphonium borate compounds are useful as a latent curing catalyst for epoxy resin compositions.

Abstract: In an epoxy resin composition comprising an epoxy resin, a curing agent, and an inorganic filler, there are blended a salt of trimellitic anhydride with 1,8-diazabicyclo(5.4.0)undecene-7 as a curing accelerator and a mercapto-containing silane coupling agent. The composition is shelf stable and smoothly flowing and cures into a product having improved adhesion, moisture resistance and electrical properties. The composition is suitable for the encapsulation of semiconductor devices.

Abstract: A thermosetting resin composition contains (A) a mixture of an imide compound having an allyl-free maleimide group and an imide compound having an allyl-containing imide group, (B) an epoxy resin, (C) a phenolic resin, and optionally, (D) an aromatic polymer/organo-polysiloxane copolymer. Component (B) and/or (C) includes a compound containing a naphthalene ring having a double bond conjugated with an aromatic ring. The composition is easily workable and well adhesive and cures to products having improved mechanical strength, hot-water resistance, low thermal expansion, and minimized water absorption.

Abstract: An epoxy resin composition comprising an epoxy resin, a curing agent, a substantially pure alpha-alumina filler, and a silicone-modified epoxy or phenol resin is useful in encapsulating semiconductor devices. The composition can be molded and cured into a product having improved thermal conductivity and moisture resistance.

Abstract: A silicone composition adapted for impregnation of electronic parts comprising a vinyl group-containing organopolysiloxane, an organopolysiloxane having at least two hydrogen atoms bonded to silicon atoms in one molecule and a peroxide compound. The peroxide compound is soluble in both organopolysiloxanes and is contained in an amount of from 0.1 to 10 parts by weight per 100 parts by weight of the total of the organopolysiloxanes. The composition has a viscosity which is sufficient to allow easy impregnation, and is in the range of from 20 to 400 centistokes at 25.degree. C.