Printed wiring board

A printed wiring board comprising:

• a first insulating layer having a first main surface;
• a first copper layer disposed on the first main surface;
• an adhesion layer disposed on the first main surface so as to cover the first copper layer;
• a second insulating layer having a second main surface and a third main surface and disposed on the adhesion layer such that the second main surface faces the adhesion layer;
• a second copper layer disposed on the third main surface;
• and
• a third copper layer,
• wherein a through-hole reaching the first copper layer is formed in the second insulating layer, the second copper layer, and the adhesion layer,
• the third copper layer is disposed on the first copper layer inside the through-hole, on an inner wall surface of the through-hole, and on the second copper layer located around the through-hole,
• a single copper layer is disposed on the inner wall surface of the through-hole, and the single copper layer is the third copper layer.