Process for manufacturing printed wiring boards

Claim 1

A process for manufacturing a printed wiring board, comprising the steps of: forming a laminated board by laminating an internal printed wiring board which is provided with wiring on both surfaces thereof to external printed wiring boards which are provided with wiring on both surfaces thereof, first through-holes which are provided through said external printed wiring boards and prepreg sheets which are sandwiched between said internal printed wiring board and each of said external printed wiring boards so that said first through-holes are filled with the prepreg; selectively providing said laminated board with second through-holes therethrough which are formed at positions not superposed on said first through-holes; forming a first copper plating layer by a first electroless plating step on the surfaces of said laminated board which include the inner faces of said second through-holes, surfaces of the outer layers of said laminated board and surfaces of the prepreg filled in the first through-holes, respectively; selectively forming an alkali-soluble photoresist film on said first copper plating layer; forming by a second electroless plating step, a second copper plating layer thicker than said first copper plating layer selectively covered by said alkaline-soluble photoresist film as a mask; removing said photoresist film with an alkaline solution to expose said first copper plating layer; and removing the thus exposed first copper plating layer by etching back to expose said wiring on the surface of said laminated board; and forming on said exposed wiring a solder resist film which remains as the final product.