PURPOSE: To mount a high-density (ultra-high density) multi-chip module substrate on a printed wiring board by improving a connecting and fixing structure (bonding structure) between a printed wiring board and a multi-chip module substrate (MCM) having high-density connecting terminals.

CONSTITUTION: On a multi-chip module substrate 30 mounting a plurality of IC chips 33a, 33b and 33c, an external terminal portion 31 and a plurality of electrodes 32 on the rear surface of said module substrate 30 are provided; and a plurality of electrode portions 12 and a plurality of electrode portions 32 provided on the corresponding multi-chip module substrate 30 are electrically connected and fixed on this multi-chip module mounting type printed wiring board.