Study on mechanical properties and microstructure reliability of composite solder under multiple reflow and high-temperature storage

With the development of integrated circuit packaging from single chip packaging to multi-chip packaging, the number of interconnection levels increases and the number of welding increases significantly. The problem of solder joint remelting becomes more and more serious in the process of multistage interconnection. Transient liquid phase composite solder has attracted wide attention due to its low temperature welding and high temperature service performance, but there are few studies on its reliability under long-term service conditions. SnPb solder plays an important role in highly reliable integrated circuits because of its good tin whisker inhibition and electromigration resistance. In this paper, two SnPb-Cu composite solders were welded and stored at high temperature for many times, and their mechanical properties and microstructure were obtained. The experimental results show that: (1) with the increase of reflow times, the shear strength of solder joint increases first and then decreases, and the shear strength reaches the maximum after one reflow. The fracture mode of solder joint is a mixture of ductile fracture and brittle fracture. (2) The IMC thickness of the welding interface increases with the increase of the number of reflow, which is proportional to the square root of the number of reflow. (3) The shear strength of solder joint decreases with the increase of storage time, and remains stable after a certain time. (4) The microstructure in the solder joint coarsened obviously with the process of high temperature storage, and the interface IMC thickened.