Facile preparation of Cu foam/Sn composite preforms for low-temperature interconnection of high-power devices

A simple and low-cost Cu foam/Sn composite preform was proposed for the low-temperature interconnection of high-power devices. The composite preform was prepared by pressing a Cu foam as the skeleton between two Sn foils as low-melting point metals with different pressures. The composite preform retains the high re-melting temperature superiority of transient liquid phase (TLP) bonding, as well as shortens the reflow time of intermetallic compounds (IMCs). The microstructures of the bondlines and the electrical and mechanical properties of the composite preform pressed at different pressures were studied. After sintering at 260 °C, the interconnection layer becomes denser with the increasing pressures of composite preform, and the bondline is composed of mainly Cu₆Sn₅, Cu₃Sn and Ag₃Sn phase. When the pressure of the composite preform increases from 200 to 400 MPa, the electrical resistivity decreases and the shear strength of bonded joints increases. At the pressure of 400 MPa, the electrical resistivity and the shear strength are 8.83 μΩ cm and 36.4 MPa, respectively, which are far better than the traditional Sn performs. Furthermore, two fracture failure models were obtained to analyze the breaking mechanism of the bonding joints under different sintering temperatures.