Resin composition, copper foil with resin, dielectric layer, copper clad laminate sheet, capacitor element and printed wiring board with built-in capacitor

A resin composition comprising

• a resin component and
• a dielectric filler,
• wherein the resin component comprises
• an epoxy resin composed of a biphenyl novolak epoxy resin,
• an active ester resin, which is a curing agent that reacts to cure the epoxy resin, and
• an aromatic polyamide resin containing a phenolic hydroxyl group;
• wherein 100 parts by weight of the resin component comprises 22 to 46 parts by weight of the epoxy resin, 20 to 60 parts by weight of the aromatic polyamide resin and 18 to 34 parts by weight of the active ester resin,
• wherein the resin composition has an insulation retention time of 500 hours or more, and
• wherein the insulation retention time is determined by etching two sides of a copper clad laminate including a dielectric layer composed of the resin composition in cured state to form a circular circuit pattern with a diameter of 0.5 inches, soldering lines to upper and lower electrodes of the circuit pattern, connecting the lines to a tester for measurement of migration of ionized copper, placing the circular circuit pattern in a chamber having a temperature of 85° C. and a humidity of 85% RH, and applying a voltage of 3 V to the circular circuit pattern to measure time while a dielectric resistance is maintained at 1×105Ω or more.