Process for producing fire retardant and heat resistant copper-clad laminated board, and varnish therefor

A process for producing a fire retardant and heat resistant copper-clad laminated board, which comprises the steps of:

• (1) impregnating a base material with a varnish comprising a solvent, at least one maleimide compound and/or resin containing at least one maleimide group represented by the formula (I):
• ##STR8##
• 0. 1 to 10% by weight, based on the resin content of the varnish, of at least one halogenated diphenyl ether compound containing at least eight halogen atoms and represented by the formula (II):
• ##STR9## wherein X.sub.1 to X.sub.10 each independently is a chlorine atom, a bromine atom, a hydrogen atom, a methyl group, an ethyl group, an n-propyl group, an iso-propyl group or an amino group;
• (2) drying the impregnated base material to prepare a prepreg;
• and
• (3) contact-bonding under heat and pressure a required number of sheets of the prepreg placed in contact relationship and one sheet of copper foil placed thereon or two sheets of copper foil sandwiching the same.