Shearing properties of low temperature Cu-In Solid-Liquid Interdiffusion in 3D package

With the rapid development of three-dimensional integrated circuit packaging technology, through silicon via (TSV) has been used to bond the stacked chips. Cu-In Solid-Liquid Interdiffusion (SOLID) low temperature bonding is a promising process for TSV stacked chip interconnection. In this paper, shearing properties of Cu/In/Cu SOLID bonding joints was studied. A specific Cu-In solder joint was designed for the test. The samples used in shear test were bonded at two different temperatures, 260 °C and 360 °C, for three different time, including 40min, 160min and 360min, respectively. Scanning Electron Microscope(SEM) and Energy-dispersive X-ray(EDX) were used to observe the fractured morphologies after shear test. The results reveal that shear strength of Cu-In solder joints increases as bonding time prolonged for samples bonded at 260°C, while the strength of samples bonded at 360°C stay constant as the bonding time increases. Fracture observation after shear test showed that fracture mode of solder joints is brittle fracture. Cleavage fracture is mainly found in solder joints bonded at 260°C. There are many tongue-patterns found on the fracture of solder joints bonded at 260°C for 360 min. Cleavage fracture is preferred for solder joints bonded at 360°C for both 40 min and 160 min, found at Cu₂In phase. Comparatively, for those bonded at 360°C for 360 min, both intergranular fracture and cleavage fracture were found.