Curable silicone composition for sealing an optical semiconductor element, method of producing a resin-sealed optical semiconductor element, and resin-sealed optical semiconductor element

A curable silicone composition for sealing an optical semiconductor element, the composition comprising:

• (A) an organopolysiloxane that has a viscosity at 25° C. of 50 to 100,000 mPa·s, that has at least two silicon-bonded vinyl groups in one molecule, that has C1-10 alkyl for the other silicon-bonded organic groups therein, and that lacks a siloxane unit represented by the following formula:
• SiO4/2;
• (B) an organopolysiloxane represented by the following average unit formula:
• (ViR2SiO1/2)a (R3SiO1/2)b (SiO4/2)c (HO1/2)d
• wherein Vi is a vinyl group;
• each R is independently a C1-10 alkyl group;
• and a, b, c, and d are each positive numbers that satisfy:
• a+b+c=1, a/(a+b)=0.15 to 0.35, c/(a+b+c)=0.53 to 0.62, and d/(a+b+c)=0.005 to 0.03, at from 15 to 35 mass % of the total of components (A) and (B);
• (C) an organopolysiloxane that has at least three silicon-bonded hydrogen atoms in one molecule, that has C1-10 alkyl for the silicon-bonded organic groups therein, and that contains from 0.7 to 1.6 mass % of silicon-bonded hydrogen atoms, in a quantity that provides from 0.8 to 2.0 moles silicon-bonded hydrogen atoms in this component per 1 mole of the total vinyl groups in components (A) and (B);
• and
• (D) a hydrosilylation reaction catalyst, in a quantity sufficient to cure the composition;
• wherein a viscosity at 25° C. of the composition lacking component (D) is from 3,000 to 10,000 mPa·s and, letting η25° C. be this viscosity in mPa·s and letting η100° C. be a viscosity in mPa·s at 100° C. of the composition lacking component (D), a value of the following formula:
• Log10 η100° C./Log10 η25° C.
• is 0.830 to 0.870.