Development and Characterizations of Fine Pitch Flip-Chip Interconnection Using Silver Sintering

Flip-chip interconnects made of silver are promising candidates to overcome the intrinsic limits of solder-based interconnects and match the demand for increased current densities of high-performance microprocessors. Dip-based interconnects have been demonstrated to be a promising approach to form electrical interconnects by sintering paste between copper pillars and pads. However, the quality of the process is limited by residual porosity and poor performances of the sintered joint formed between the pillar and the pad during sintering if a pressure > 50 MPa is not applied in order to decrease the final porosity. In this study, development has been focused on varying key dipping process parameters allowing a pressureless sintering process. Dip-transfer process was optimized on test vehicle and has shown electrical continuity over 700 interconnections with diameter down to 50 μm. We demonstrate high reliability of the process with microstructural observations, tomography X and thermal cycle up to 200 cycles without breakdown.