Resin composition, prepreg, resin sheet, metal-clad laminate, printed wiring board, multilayer printed wiring board and semiconductor device

A resin composition comprising:

• (A) an epoxy resin,
• (B) a cyanate resin and
• (C) an onium salt compound as essential components,
• wherein the onium salt compound (C) is a compound selected from the group consisting of the following formulae (2), (3) and (4):
• wherein P is a phosphorus atom;
• each of R1, R2, R3 and R4 is an organic group having a substituted or unsubstituted, aromatic or heterocyclic ring or is a substituted or unsubstituted aliphatic group;
• wherein R1 to R4 are identical or different from each other;
• X1 is an organic group bonding to substituents Y1 and Y2;
• X2 is an organic group bonding to substituents Y3 and Y4;
• wherein X1 and X2 are identical or different from each other;
• each of Y1 and Y2 is a group resulting from a proton-donating substituent through release of a proton;
• wherein Y1 and Y2 in the same molecule bond to a silicon atom to form a chelate structure;
• each of Y3 and Y4 is a group resulting from a proton-donating substituent through release of a proton;
• wherein Y3 and Y4 in the same molecule bond to a silicon atom to form a chelate structure;
• Y1, Y2, Y3 and Y4 are identical or different from each other;
• and
• Z1 is an organic group having a substituted or unsubstituted, aromatic or heterocyclic ring or is a substituted or unsubstituted aliphatic group;
• wherein P is a phosphorus atom;
• B is a boron atom;
• each of R1, R2, R3 and R4 is an organic group having substituted or unsubstituted, aromatic or heterocyclic ring or is a substituted or unsubstituted aliphatic group;
• wherein R1 to R4 are identical or different from each other;
• each of R5, R6, R7 and R8 is selected from the group consisting of an organic group having a substituted or unsubstituted, aromatic or heterocyclic ring, a substituted or unsubstituted aliphatic group, and an n(n≧1)-valent proton donor having in a molecule at least one or more protons which can be released from the molecule;
• and R5 to R8 are identical or different from each other;
• wherein P is a phosphorus atom;
• B is a boron atom;
• each of R1, R2, R3 and R4 is an organic group having a substituted or unsubstituted, aromatic or heterocyclic ring or is a substituted or unsubstituted aliphatic group;
• wherein R1 to R4 are identical or different from each other;
• X3 is an organic group bonding to substituents Y5 and Y6;
• X4 is an organic group bonding to substituents Y7 and Y8;
• wherein X3 and X4 are identical or different from each other;
• each of Y5 and Y6 is a group resulting from a proton-donating substituent through release of a proton;
• wherein Y5 and Y6 in the same molecule bond to a boron atom to form a chelate structure;
• each of Y7 and Y8 is a group resulting from a proton-donating substituent through release of a proton;
• wherein Y7 and Y8 in the same molecule bond to a boron atom to form a chelate structure;
• and
• Y5, Y6, Y7 and Y8 are identical or different from each other;
• wherein an amount of the cyanate resin (B) is in the range of 0.25 to 9.00 with respect to an amount of the epoxy resin (A) being 1;
• and
• a content of the onium salt, compound (C) is in the range of 0.01 to 10% by weight with respect to a total amount of the epoxy resin (A) and the cyanate resin (B).