Multilayer printed wiring board

A process for producing a multilayer printed wiring board which comprises forming an etching resist at the part where circuit is to be formed on a laminate of copper-clad insulating substrates containing reinforcing fiber, etching away the unnecessary copper foil to make an insulating circuit board, preparing at least two pieces of such insulating circuit board, placing between said insulating circuit boards an interlaminar insulating layer which is B-staged, has a B-stage resin flow of less than 1%, with the difference in glass transition point between the adjoining insulating layers being not greater than 60.degree. C., and contains no reinforcing fiber, integrally laminating them by heating under pressure, drilling the obtained laminate, forming a plated conductor layer by electroless plating to make an interlayer circuit board, preparing at least two pieces of such interlayer circuit board, placing between said interlayer circuit boards an interlaminar insulating layer which is B-staged, has a B-stage resin flow of less than 1%, with the difference in glass transition point between the adjoining insulating layers being not greater than 60.degree. C., and contains no reinforcing fiber, integrally laminating them by heating under pressure, providing an etching resist over the whole surface of the obtained laminate, drilling the laminate to form holes to a section where connection is necessary, and forming a plated conductor layer by electroless plating.

A process for producing a multilayer printed wiring board which comprises forming an etching resist at the part where interlayer circuit is to be formed on one side of a laminate of copper-clad insulating substrates containing reinforcing fiber, forming an etching resist over the entire surface of the other side, etching away the unnecessary copper foil on the inner layer side to make an insulating circuit board, preparing a pair of such insulating circuit boards, placing therebetween an interlaminar insulating layer which is B-staged, has a B-stage resin flow of less than 1%, with the difference in glass transition point between the adjoining insulating layers being not greater than 60.degree. C., and contains no reinforcing fiber, integrally laminating them by heating under pressure, drilling the obtained laminate to form holes to a section where connection is required, forming a plated conductor layer by electroless plating, forming an etching resist to the shape of circuit on the copper surface on the inner layer side, forming an etching resist over the entirety of the copper surface on the outer side, etching away the unnecessary copper on the embedded side to make two interlayer circuit boards, placing therebetween an interlaminar insulating layer which is B-staged, has a B-stage resin flow of less than 1%, with the difference in glass transition point between the adjoining insulating layers being not greater than 60.degree. C., and contains no reinforcing fiber, integrally laminating them by heating under pressure, drilling the obtained laminate to form holes to a necessary section for connection, forming a plated conductor layer by electroless plating, forming an etching resist to the shape of circuit on the outermost layer, and etching away the unnecessary copper.