Formation mechanism for the interface between Cu and Sn formed by magnetic pulse welding

The formation of interfacial intermetallic compounds (IMCs) such as Cu6Sn5, Cu3Sn or platelet -shaped Ag3Sn which are formed in reflow soldering process will directly destroy the soldering reliability. Magnetic pulse welding (MPW), as a solid state welding technique can effectively restrain or even impede the formation of interfacial IMCs. In this paper, Cu and Sn dissimilar metals were welded by MPW under the discharge energy from 17 to 31 kJ. The typical wavy interface and metal jet flow were found in all samples. When the discharge energy reached 31 kJ, a typical gradient nanograined (GNG) interface has been observed to undergo an evolution from a sub -micron secondary solid solution of Cu6.26Sn5 IMCs to a nanoscale secondary solid solution of Cu81Sn22 IMCs, followed by the formation of nanoscale equiaxed alpha-Cu grains, and ultimately leading to the deformed elongated nanoscale alpha-Cu grains. This discontinuous distribution of the aforementioned phases occurs specifically at the interface of the 23 kJ_1.5 mm sample. In contrast, when subjected to a discharge energy of 17 kJ, there were no indications of a secondary solid solution of Cu6.26Sn5 IMCs or elongated nanoscale alpha-Cu grains. However, a discontinuous secondary solid solution of Cu81Sn22 IMCs was observed to form at the Cu/Sn interface under these conditions. Based on these findings, the utilization of microprojection welding (MPW) techniques involving Cu and Sn-based solder in the microscale is anticipated to serve as a highly efficient and automated technology within the field of electronic micropackaging.