Organopolysiloxane composition, cured product thereof, electronic component sealing agent, electronic component, and method for protecting semiconductor chip

An organopolysiloxane composition, comprising:

• (A) 100 parts by mass of an organopolysiloxane having, on average, at least two alkenyl groups bonded to silicon atoms per molecule and having a viscosity at 25° C. in a range of 10 to 10,000 mPa·s;
• (B) 10 to 80 parts by mass of an organopolysiloxane resin expressed by the following formula:
• where each R1 is independently a monovalent hydrocarbon group having 1 to 10 carbon atoms and not containing an aliphatic carbon-carbon double bond;
• R2 is a hydrogen atom or an alkyl group having 1 to 10 carbon atoms;
• and a, b, and c are numbers satisfying 0.35≤a≤0.55, b=1-a, and 0≤c≤0.05,
• the mass loss rate when exposed to 200° C. for 1 hour being 2.0 mass % or less relative to the mass of component (B);
• (C) an organohydrogenpolysiloxane having at least two hydrogen atoms bonded to silicon atoms in each molecule and having a viscosity at 25° C. in a range of 2 to 10,000 mPa·s in an amount such that the number of hydrogen atoms bonded to silicon atoms per alkenyl group bonded to silicon atoms in the entire composition is 0.5 to 2.0;
• (D) a hydrosilylation catalyst in an amount sufficient to react and cure components (A) to (C);
• and optionally
• (E) 0 to 10 parts by mass of a reaction product of (e1) an alkali metal silanolate and (e2) at least one salt selected from chlorides expressed by M1Cly and carboxylates expressed by (R4COO)yM1 where R4 represents the same or different monovalent hydrocarbon groups, M1 is cerium or a mixture of rare earth elements mainly composed of cerium, and y is 1 to 3, depending on the valence of M1.