High-temperature shear strength of solid-liquid interdiffusion (SLID) bonding: Cu-Sn, Au-Sn and Au-In

Solid-Liquid Interdiffusion (SLID) bonding is a promising bonding technique, particularly for high-temperature applications. Based on intermetallics as the bonding medium, the bonds are stable at temperatures far above the processing temperature which is in the range of normal solder temperatures. This work confirms experimentally this high-temperature stability through shear strength testing as function of temperature (room temperature to 300 °C) for three different SLID systems: Cu-Sn, Au-Sn and Au-In. All three systems remain solid within the tested temperature range, as expected, but they show remarkably different temperature dependence of mechanical strength: Au-Sn SLID bonds show strongly decreasing shear strength with temperature (but at 300 °C it is still well above the MIL-STD requirement); Cu-Sn SLID bonds show only small changes; whereas Au-In SLID bonds show increased shear strength at 300 °C, accompanied with a change in fracture mode from brittle to ductile. All three behaviours can be explained from the phase diagrams with the actual phases in use.