Filling method of conductive paste and manufacturing method of multi-layer printed circuit board

1. A filling method of conductive paste, comprising:

a process of preparing a metal foil clad laminated sheet having an insulative base material having a first principal surface and a second principal surface opposite to the first principal surface and a metal foil provided on the second principal surface of the insulative base material;

a process of providing a protective film on the first principal surface of the metal foil clad laminated sheet;

a boring process of partially removing the protective film and the insulative base material, and thereby, forming a bottomed via hole having the metal foil exposed on its bottom face;

a groove forming process of removing the protective film from a surface to a midway thereof to form a conductive paste flowing groove having the bottomed via hole exposed on its bottom face;

a housing member preparing process of preparing a housing member in which a conductive paste injecting channel and a vacuum evacuating channel are provided and has an opening face on which one end of each of the conductive paste injecting channel and the vacuum evacuating channel opens;

a housing member disposing process of disposing the housing member on the protective film such that the opening face opposes the protective film, and thereby, causing the conductive paste injecting channel and the vacuum evacuating channel to communicate with a conductive paste flowing space defined by the bottomed via hole, the conductive paste flowing groove and the opening face of the housing member;

a process of depressurizing the conductive paste flowing space via the vacuum evacuating channel;

a filling process of injecting conductive paste into the conductive paste flowing space via the conductive paste injecting channel, and thereby, filling an inside of the bottomed via hole with the conductive paste; and

a process of peeling off the protective film with the conductive paste flowing groove on its surface to remain the conductive paste in the bottomed via hole and to cause part of the conductive paste with which the bottomed via hole is filled to protrude, wherein

in the boring process, a plurality of the bottomed via holes are formed, and

in the groove forming process, the conductive paste flowing groove is formed so as to join the plurality of bottomed via holes.

2. The filling method of conductive paste according to claim 1 , wherein

during the filling process, pressure larger than injection pressure of the conductive paste is exerted with respect to the housing member in a direction of the protective film.

3. The filling method of conductive paste according to claim 1 , further comprising

a process of partially removing the protective film and the insulative base material, and thereby, forming a dummy bottomed via hole, the dummy bottomed via hole communicating with the conductive paste flowing space and positioned between the bottomed via hole and the vacuum evacuating channel in a state where the housing member is disposed on the protective film, wherein

in the filling process, injection of the conductive paste is ended at a time point when the conductive paste flows in the dummy bottomed via hole.

4. The filling method of conductive paste according to claim 3 , wherein

in the housing member preparing process,

the housing member is prepared in which a monitoring through hole whose one end opens on an opening face positioned above the dummy bottomed via hole in a state where the housing member is disposed on the protective film and which penetrates the housing member in a thickness direction of the metal foil clad laminated sheet is provided, a transparent material being hermetically fitted into the monitoring through hole, and

in the filling process,

the injection of the conductive paste is ended at a time point when it is detected that the conductive paste flows in the dummy bottomed via hole via the monitoring through hole.

5. The filling method of conductive paste according to claim 1 , wherein

in the housing member preparing process,

the housing member is prepared in which a monitoring through hole whose one end opens on an opening face positioned above the bottomed via hole in a state where the housing member is disposed on the protective film and which penetrates the housing member in a thickness direction of the metal foil clad laminated sheet is provided, a transparent material being hermetically fitted into the monitoring through hole, and

in the filling process,

injection of the conductive paste is ended at a time point when it is detected that an inside of the bottomed via hole is filled with the conductive paste via the monitoring through hole.

6. The filling method of conductive paste according to claim 1 , wherein

viscosity of the conductive paste at 20 to 30° C. is 500 to 2000 dPa·sec.

7. The filling method of conductive paste according to claim 1 , wherein

in the filling process, a conductive paste that does not contain a volatile solvent is used.

8. The filling method of conductive paste according to claim 1 , wherein

in the groove forming process, the conductive paste flowing groove is formed in a traversable manner so as to pass through the plurality of bottomed via holes one-by-one, and

the conductive paste flowing groove has a shape without a branch or a junction entirely from one end corresponding to the conductive paste injecting channel to another end corresponding to the vacuum evacuating channel.