Patent ID: 7294393

Claim:
A sheet material used as an insulating film of a wiring board, comprising: a first layer made of a first insulating material wherein the first insulating material contains an aramid fiber or a fluorine-containing polymer; and a second layer laminated on the first layer, the second layer being made of a second insulating material which is porous polyimide, the second insulating material having a tensile rupture strength of 100 MPa or more at 23° C. and a tensile rupture elongation of 10% or more at 23° C. and providing a ratio (a/b) of 2.5 or less, assuming that a tensile rupture strength of the second layer at −65° C. is a (MPa) and a tensile rupture strength at 150° C. is b (MPa); wherein the polyimide contains a benzophenone skeleton.