Thermal gradient-induced full intermetallic joints formation for chip bonding

Solid-liquid interdiffusion bonding (SLID) acts as a promising stacking process for three-dimensional integrated circuit (3D IC) tacking, but nevertheless is plagued with low throughput. In this work, a new speed solid-liquid interdiffusion bonding process is proposed to improve the bonding reliability. Different from the homogeneous bonding temperature, a temperature gradient superposition is applied across the joint in the new process. Firstly, the new method is 5–7 times faster than that of the traditional bonding process, depending on the bonding temperatures and times. On the other hand, the asymmetric dissolution of Cu/Sn-3.0Ag-0.5Cu/Cu (Cu/SAC305/Cu) solder joints induced by large temperature gradient (0.1 °C/μm) leads the asymmetric growth of intermetallic compounds (IMCs) at the cold end. Besides, the morphologies of IMCs layer transforms from scallop-like grains to columnary grains at the cold end. In addition, the shear property of the solder joints obviously increases with the extension of the bonding times. The bonding mechanism of the solder joints is provided and experimentally confirmed in this work.