Process for producing a multi-layer wiring board

A process for producing a multi-layer wiring board comprising:

• (a) forming a first wiring circuit layer on a first surface of a first insulating board;
• (b) forming via hole conducting passages in a soft second insulating board containing a thermosetting resin by forming via holes, and filling said via holes with a conducting paste, the via hole conducting passages having first and second ends opening to a first and a second surface of the second insulating board, respectively;
• (c) forming a second wiring circuit layer buried in the first surface of the second insulating board by transferring thereon a conducting layer formed on a transfer sheet in a manner to close the first end of said via hole conducting passages;
• and
• (d) laminating the second insulating board obtained in step (c) on the first surface of the first insulating board in a manner that the second end of said via hole conducting passages are closed by the first wiring circuit layer,
• wherein during the lamination in step (d), the thermosetting resin in the second insulating board is oozed out into the via hole conducting passages.

A process for producing a multilayer wiring board comprising:

• (A) forming a first wiring circuit layer on a first insulating board;
• (B) laminating on said first wiring circuit layer, a second soft insulating board having via hole conducting passages formed by filling via holes with a conducting paste obtained by dispersing metal particles in a binder composed of a thermosetting resin;
• and
• (C) forming a second wiring circuit layer buried in a surface of the second insulating board by transferring thereon a conducting layer formed on a transfer sheet in a manner to close open portions of said via hole conducting passages,
• wherein after said second wiring circuit layer is formed, a pulse current is supplied into the via hole conducting passages in the second insulating board, so that the metal particles are weld-joined in the conducting paste and that said metal particles are weld-joined to the second wiring circuit layer.

A process for producing a multi-layer wiring board comprising:

• (a) forming a first wiring circuit layer on a first surface of a first insulating board;
• (b) forming via hole conducting passages in a soft second insulating board containing a thermosetting resin by forming via holes, and filling said via holes with a conducting paste obtained by dispersing metal particles in a binder composed of a thermosetting resin, the via hole conducting passages having first and second ends opening to a first and a second surface of the second insulating board, respectively;
• (c) forming a second wiring circuit layer buried in the first surface of the second insulating board by transferring thereon a conducting layer formed on a transfer sheet in a manner to close the first end of said via hole conducting passages;
• and
• (d) laminating the second insulating board obtained in step (c) on the first surface of the first insulating board in a manner that the second end of said via hole conducting passages are closed by the first wiring circuit layer,
• wherein after said second wiring circuit layer is formed, a pulse current is supplied into the via hole conducting passages in the second insulating board, so that the metal particles are weld-joined in the conducting paste and that said metal particles are weld-joined to the second wiring circuit layer.