Revealing the strengthening mechanism of Cu–Sn composites joint fabricated via in-situ reaction for power electronic packaging

The growing demand for advanced materials for high-temperature connections has seen a substantial increase in response to the greater integration and enhanced power of electronic devices, especially in the electric vehicle sector. Our investigation presents an innovative solder alloy comprising copper-tin (Cu–Sn) for high-power electronic devices, achieved through the cross-accumulative rolling (CAR) technique with transient liquid phase (TLP) pathway. This results in the successful creation of Cu–Sn composite joints, reinforced with high melting point intermetallic compounds (IMCs), Cu6Sn5 and Cu3Sn. Our findings reveal the formation of a unique heterogeneous lamellar structure at the interface of Cu micro-particles (Cu MPs) and Sn during the stacked layer growth process. These distinct microstructures are primarily governed by diffusion-assisted nucleation mechanisms. Notably, the composite joint displays an elevated-temperature tensile strength of 43.01 MPa, with the spatial distribution of Cu MPs and the size of IMCs significantly influencing the mechanical strength of the joint. The observed strain hardening in Cu MPs offsets the strength reduction resulting from the formation of microcracks in the IMCs, leading to a notably enhanced joint strength. Theoretical analysis and examination of the fracture morphology confirm that the uniform distribution of Cu MPs, resulting in an alternating arrangement of soft and hard phases, is a key factor contributing to the superior strength of the joint. These results provide a valuable strategy for creating IMCs that are suitable for applications in the field of power semiconductor device packaging.