Transfer and non-transfer stacking technologies based on chip-to-wafer self-asembly for high-throughput and high-precision alignment and microbump bonding

Two types of high-throughput and high-precision multichip-to-wafer 3D stacking approaches are demonstrated: one is non-transfer stacking and the other one is transfer stacking. Both the stacking approaches employ a self-assembly technologies using liquid surface tension. In the former stacking scheme, large number of chips having 20-μm-square Cu/SnAg microbumps are directly self-assembled face-down on an interposer wafer, like flip-chip bonding. On the other hand, in the latter stacking scheme, the many chips having the microbumps are self-assembled face-up on a carrier wafer with bipolar electrodes for electrostatic chucking. Then, the latter chips are transferred from the carrier to another interposer in wafer-level processing. The alignment accuracies are evaluated and compared between the two stacking approaches. The resulting daisy chains show good electrical properties comparable to conventional flip-chip bonding.