Method for producing multilayer wiring substrate and multilayer wiring substrate

A method for producing a multilayer wiring substrate, the method comprising:

• (1) forming a laminated body comprising an insulating resin layer and a polymer adhesive layer, on a surface of a first wiring substrate comprising a metal wiring thereon, in which the polymer adhesive layer comprises a polymer precursor comprising a functional group that forms an interaction with a plating catalyst or a precursor thereof, and a reactive group capable of forming a bond with an adjacent layer on the first wiring substrate side;
• (2) applying energy in a patterned manner to a region outside of a via connection portion on the surface of the laminated body, to form a patterned polymer adhesive layer, in which the polymer precursor is bonded to the insulating resin layer, at the energy-applied region;
• (3) applying a plating catalyst or a precursor thereof to the patterned polymer adhesive layer, and carrying out a first electroless plating treatment, to form a second metal wiring on the surface of the patterned polymer adhesive layer;
• and
• (4) forming a via by utilizing the patterned second metal wiring as a mask, and subsequently carrying out a desmear treatment.