Heat-resistant electrical insulating layer

A copper-clad substrate for use in the fabrication of printed circuit boards, comprising an electrical insulating substrate having a copper foil bonded to each surface thereof, wherein said electrical insulating substrate consists essentially of a polycondensed fused polycyclic, polynuclear aromatic resin and glass fibers, said polycondensed fused polycyclic, polynuclear aromatic resin being prepared by a polycondensation reaction of a starting material with a crosslinking agent in the presence of an acid catalyst, wherein the starting material is selected from the group consisting of fused polycyclic aromatic hydrocarbons which may have a hydroxyl group as a ring substituent and mixtures of a fused polycyclic aromatic hydrocarbon and a monocyclic aromatic hydrocarbon both of which may have a hydroxyl group as a ring substituent and wherein the crosslinking agent is an aromatic compound having at least two hydroxymethyl or halomethyl groups as ring substituents, and said electrical insulating substrate having a long-term heat resisting temperature of about 260.degree. C. said temperature determined as the highest temperature at which the weight loss after 1000 hours of aging in air was within 2% by weight;

• a dielectric constant at 1 MHz of about 3.7;
• and a water absorption of about 0.4% or less as measured by immersion in water for 24 hours at 25.degree. C.

A semiconductor device comprising a semiconductor and an electrical insulating film on said semiconductor, wherein the electrical insulating film consists essentially of a polycondensed fused polycyclic, polynuclear aromatic resin prepared by a polycondensation reaction of a starting material with a crosslinking agent in the presence of an acid catalyst, wherein the starting material is selected from the group consisting of fused polycyclic aromatic hydrocarbons which may have a hydroxyl group as a ring substituent and mixtures of a fused polycyclic aromatic hydrocarbon and a monocyclic aromatic hydrocarbon both of which may have a hydroxyl group as a ring substituent and wherein the crosslinking agent is an aromatic compound having at least two hydroxymethyl or halomethyl groups as ring substituents, said electrical insulating film having a long-term heat resisting temperature of about 260.degree. C., said temperature determined as the highest temperature at which the weight loss after 1000 hours of aging in air was within 2% by weight;

• a dielectric constant at 1 MHz of about 3.1;
• and a water absorption of about 0.4% or less as measured by immersion in water for 24 hours at 25.degree. C.