Direct multichip-to-wafer 3D integration technology using flip-chip self-assembly of NCF-covered known good dies

We demonstrated surface tension-driven self-assembly and microbump bonding using NCF (non-conductive film)-covered chips with Cu/Sn-Ag microbumps for highthroughput and high-yield direct multichip-to-wafer 3D integration. The NCF is a promising candidate to completely fill gaps between fine-pitch microbumps, and is essential for realizing highly-reliable microbump-to-microbump interconnections. Here, by applying the self-assembly method with strong water surface tension, the NCF-covered chips were precisely aligned to hydrophilic assembly sites defined on host Si substrates in a face-down manner with alignment accuracies of approximately 1 μm. The self-assembled chips having Cu/Sn-Ag microbumps covered with NCF were thermally compressed to obtain electrical joints between the chips and substrate after the self-assembly process. The resulting daisy chains showed good electrical characteristics with contact resistance of 53 mΩ/joint.