Method for manufacturing wiring substrate

A method for manufacturing a wiring substrate, comprising:

• forming a resin insulating layer on a first conductor layer such that the resin insulating layer covers the first conductor layer;
• applying a roughening treatment on a surface of the resin insulating layer on an opposite side with respect to the first conductor layer;
• covering the surface of the resin insulating layer with a protective layer after the roughening treatment on the surface of the resin insulating layer;
• forming an opening in the resin insulating layer after the roughening treatment on the surface of the resin insulating layer such that the opening penetrates through the resin insulating layer and exposes a portion of the first conductor layer;
• applying a dry desmear treatment comprising a plasma treatment on an inner surface of the resin insulating layer in the opening such that the dry desmear treatment is applied in a state in which the surface of the resin insulating layer is covered by the protective layer;
• and
• forming a second conductor layer on the surface of the resin insulating layer such that the second conductor layer is formed in contact with the surface of the resin insulating layer and that a via conductor is formed in the opening of the resin insulating layer,
• wherein the applying of the roughening treatment comprises wet processing using a chemical on the surface of the resin insulating layer, and the applying of the dry desmear treatment comprises applying the dry desmear treatment on the inner surface of the resin insulating layer in the opening before the forming of the second conductor layer.