It is well known that a multi-chip flip-chip package includes a plurality of flip chips with the bumps and a substrate for directly flip-chip mounting. In U.S. Pat. No. 6,507,098, Lo et al. disclosed a structure of a multi-chip stack package, which comprises a plurality of flip chips mounted on one surface of substrate. Each flip chip has a plurality of bumps on an active surface thereof for flip-chip (C4) mounting on the same surface of the substrate. The substrate is demanded to supply a large enough area for mounting the flip chips. However, the multi-chip flip-chip package can't achieve a vertical stack with the plurality of the flip chips. In addition, the substrate is a well-known printed circuit board (PCB), the minimum pitch of bump pads of the PCB substrate is about 200 μm (micrometer) according to current PCB technology, it is difficult to manufacture the substrate with pitch of bump pads less than 150 μm by means of PCB process. However the wiring pitch of the integrated circuits of the flip chip has reached 0.1 μm up-to-now which means that the chip size becomes smaller and smaller, and the bumps on the flip chip are more crowded. Normally the pitch of bumps of the flip chip is around 150 μm, even near to 70˜90 μm for special design, so the pitch of bumps of the flip chip and the pitch of bump pads of the PCB become unmatchable. Therefore, the yield of mass production of multi-chip flip-chip package cannot reach the acceptable range because it is not easy to make a substrate with bump pads in tiny pitch.
In U.S. Pat. No. 5,923,090, Fallon et al. also disclosed another well-known stacked multi-chip package. The package comprises an integrated circuit chip by wire bonding and a flip chip. The integrated circuit chip is attached to a substrate, and the flip chip is mounted on a major surface of the integrated circuit chip. The integrated circuit chip has an extra circuitry (C4 connection pad) on the major surface different from a normal chip in order to bond the flip chip. Pads on periphery of the major surface of the integrated circuit chip are connected with the substrate by bonding wires. It is necessary that size of the integrated circuit chip is larger than that of the flip chip. But it is very hard to design the C4 connection pads, bond pads and extra circuitry on the major surface of the integrated circuit chip.