TECHNOLOGY FOCUS - POLYMERS - Preferred Composition: The triazine ring-containing cresol novolak phenolic resin is a triazine ring-containing cresol novolak phenolic resin having a nitrogen content of 12-22 wt.%. The ratio of the total number of hydroxyl groups in the triazine ring-containing cresol novolak phenolic resin and the phenolic hydroxyl group-containing phosphorus compound to the number of epoxy groups in the novolak epoxy resin is 0.6-1.3. The ratio of the weight of the novolak epoxy resin to the weight of the carboxylic acid-modified acrylonitrile butadiene rubber particles is 88/12-98/2. The amount of the phenolic hydroxyl group-containing phosphorus compound is 1.5-2.5 wt.%, based on the total weight of the first four components, in terms of a phosphorus atom. EXAMPLE - A glass cloth-base epoxy resin double-sided copper-clad laminate sheet was etched to prepare a circuit board having on one surface a circuit pattern. A varnish of an insulating resin composition comprising (pbw) biphenyl epoxy resin (80), carboxylic acid-modified acrylonitrile butadiene rubber particles (5), triazine ring-containing cresol novolak phenolic resin (9), phosphorus-containing compound (26), inorganic filler (40), imidazole derivative compound (0.24) and methyl ethyl ketone solvent (55), was prepared. The composition was applied to a polyethylene terephthalate film and dried at 100degreesC for 10 minutes to prepare a film roll. The film was laminated onto one surface of the circuit board so that the insulating resin was in contact with the first circuit pattern. For forming a second circuit pattern on the roughened surface of the first insulating layer, the circuit substrate was immersed in a catalyst solution for electroless plating. Annealing was conducted at 180degreesC for 30 minutes to form a conductor layer on the surface of the insulating layer. Next, an oxide film on the copper surface of the conductor layer was removed by polishing, and then an etching resist was formed and an unnecessary portion was etched. The etching resist was removed to form a second circuit pattern connected to the first circuit pattern through a via hole. A multilayer structure was then formed.