Patent ID: 7309733

Claim:
An organopolysiloxane composition for use in the encapsulation and sealing of precision electronic parts, comprising 100 parts by weight of an organopolysiloxane represented by the average compositional formula R 1 a SiO (4-a)/2 wherein R 1 is the same or different and is selected from substituted or unsubstituted monovalent hydrocarbon groups of 1 to 12 carbon atoms and “a” is from 1.90 to 2.05, the organopolysiloxane being blocked with hydroxyl groups or organoxy groups at both ends of the molecular chain and having a viscosity at 25° C. of at least 24 mPa·s, 2 to 50 parts by weight of a crosslinking agent which is a silane or siloxane compound having at least two hydrolysable groups in a molecule, 0.01 to 10 parts by weight of a curing catalyst selected from the group consisting of alkyltin esters, titanates, titanium chelates, organometallic compounds, aminoalkyl group-substituted ammonium salts, alkyl metal salts of lower fatty acids, dialkylhydroxylamines, and silane and siloxane compounds having a guanidyl group, and 0.05 to 0.4% by weight of a metal powder having an average particle size of 0.01 to 10 μm which is sulfidable with sulfur-containing gas, wherein when a precision electronic part is encapsulated or sealed with the cured composition, the metal powder in the cured composition is sulfided with sulfur-containing gas for thereby preventing or retarding the corrosion of the precision electronic part with the sulfur-containing gas.