Morphology of Low-Temperature All-Copper Interconnects Formed by Dip Transfer

Flip-chip interconnects made entirely from copper are needed to overcome the intrinsic limits of solder-based interconnects and match the demand for increased current densities. To this end, dip-based all-copper interconnects are a promising approach to form electrical interconnects by sintering copper nanoparticles between the copper pillar and pad. However, the remnant porosity of the copper joint formed between the pillar and the pad limits the performance of this technology. Moreover, the applicability of this technology in the printed circuit board (PCB) industry is endangered by thermo-mechanical stresses that arise during the sintering and by the unknown compatibility with standard finishing layers used to prevent the oxidation of the copper. This work reports three main advances in dip-based all-copper interconnect technology. First, a reduction in the porosity level of the copper joint is obtained by application of pressure during the bonding. Second, a decrease of the bonding temperature to 160 °C is achieved. Third, the compatibility of this technology with standard finishing layers is demonstrated.