Manufacturing method of multilayer printed wiring board and multilayer printed wiring board

A manufacturing method of a multilayer printed wiring board comprising:

• forming, in a first single-sided metal-foiled laminate sheet having a first insulating resin film and a first metal foil on a front face of the first insulating resin film, a first adhesive protective layer having a first adhesive-agent layer that covers a rear face of the first insulating resin film and a first protective film that is laminated on the adhesive-agent layer;
• forming a first bottomed via hole having a bottom face with the first metal foil exposed therefrom by partially removing the first adhesive protective film and the first insulating resin film;
• first printing of filling a conductive paste into the first bottomed via hole by a printing method;
• peeling off the first protective film from the first adhesive-agent layer and causing a part of the conductive paste filled in the first bottomed via hole to protrude from the first adhesive-agent layer, thereby obtaining a first wiring substrate;
• forming, in a double-sided metal-foiled laminate sheet having a second insulating resin film and second and third metal foils respectively provided on a front face and a rear face of the second insulating resin film;
• a first piercing mask and a first reception land by patterning the second metal foil and forming a second piercing mask and a second reception land by patterning the third metal foil;
• attaching a first adhesive protective film having a weak adhesive layer formed on one side thereof to the double-sided metal-foiled laminate sheet in such a way that the weak adhesive layer contacts with a front face of the second insulating resin film and buries the patterned second metal foil;
• attaching a second adhesive protective film having a weak adhesive layer formed on one side thereof to the double-sided metal-foiled laminate sheet in such a way that the weak adhesive layer contacts with a rear face of the second insulating resin film and buries the patterned third metal foil;
• forming a first bottomed step via hole having a middle part with the first piercing mask exposed therefrom and a bottom face with the second reception land exposed therefrom by partially removing the first adhesive protective layer and the second insulating resin film;
• forming a second bottomed step via hole having a middle part with the second piercing mask exposed therefrom and a bottom face with the first reception land exposed therefrom by partially removing the second adhesive protective layer and the second insulating resin film;
• second printing of filling a conductive paste into the first bottomed step via hole by a printing method;
• third printing of filling a conductive paste into the second bottomed step via hole by a printing method;
• peeling off the first adhesive protective film from the second insulating resin film and causing a part of the conductive paste filled in the first bottomed step via hole to protrude from the first piercing mask, and peeling off the second adhesive protective film from the second insulating resin film and causing a part of the conductive paste filled in the second bottomed step via hole to protrude from the second piercing mask, thereby obtaining a second wiring substrate;
• forming, in a second single-sided metal-foiled laminate sheet having a third insulating resin film and a fourth metal foil on a rear face of the third insulating resin film, a second adhesive protective layer having a second adhesive-agent layer that covers a front face of the third insulating resin film and a second protective film that is laminated on the second adhesive-agent layer;
• forming a second bottomed via hole having a bottom face with the fourth metal foil exposed therefrom by partially removing the second adhesive protective layer and the third insulating resin film;
• fourth printing of filling a conductive paste into the second bottomed via hole by a printing method;
• peeling off the second protective film from the second adhesive-agent layer and causing a part of the conductive paste filled in the second bottomed via hole to protrude from the second adhesive-agent layer, thereby obtaining a third wiring substrate;
• and
• laminating in which the first to third wiring substrates are laminated in such a way that a protruding part of the conductive paste filled in the first bottomed via hole of the first wiring substrate comes into contact with a protruding part of the conductive paste filled in the first bottomed step via hole of the second wiring substrate and a protruding part of the conductive paste filled in the second bottomed via hole of the third wiring substrate comes into contact with the second reception land of the second wiring substrate, and the laminated first to third wiring substrates are heated to be integrated with one another.