Patent ID: 8216668

Claim:
A resin composition used for forming an insulating layer of a multilayer printed wiring board, comprising an inorganic filler having an average particle diameter from 0.01 μm to 0.45 μm and present in an amount from 30 weight % to 75 weight %, an epoxy resin having a weight-average molecular weight of 5,000 or less and present in an amount from 10 weight % to 40 weight %, and a phenoxy resin having a weight-average molecular weight from 10,000 to 70,000, wherein the resin composition has a property to be cured by heating to form a layer having a thickness of 10 to 100 μm, the layer having a surface roughness parameter Rvk value from 0.1 μm to 0.8 μm, measured after roughening treatment in which the layer is dipped in a swelling agent made of an aqueous solution containing 20 to 60 wt % of dimethylene glycol monobutyl ether and 0.1 to 1.0 wt % of sodium hydrate and having a temperature from 50 to 90° C. for 3 to 20 minutes, and then the layer is dipped in a roughening agent made of an aqueous solution containing 5.0 to 15.0 wt % of permanganate and 1.0 to 10.0 wt % of sodium hydrate and having a temperature from 60 to 90° C. for 3 to 40 minutes.