A study on temperature dependence in gold-gold ͑Au-Au͒ thermocompression bonding was performed. Gold studs were bonded to two kinds of surfaces-cofired gold on alumina and electroless nickel covered with immersion Au on silicon. A critical bonding temperature was observed for both substrates. No bonding occurs when the temperature is below this threshold value, whereas bond strength increases with bonding temperature beyond the threshold. This critical temperature can be related to the activation of organic films on the bonding surfaces. Under similar bonding conditions, the critical temperature is lower for a harder substrate than for a softer substrate, primarily because of larger interfacial shear stresses. This is supported by the observation on the interfacial shear stress distribution at the bonding interface based on finite element simulation models of substrates with different hardness.

Low temperature interconnection is a critical component of 3D integration and packaging technology. In this study, we investigate the characteristics of thermocompression metal bonding using gold stud bumps formed on Si die in the temperature range of 100-300 °C and the pressure range of 200–600 g/bump. We observed a critical bonding temperature below which bonding did not occur and above which shear strength improves linearly with bonding temperature. This critical temperature can be interpreted to be the onset of the break-up of organic barrier films while the linear rise in shear strength can be attributed to the increase in the true bonded area. Above this critical temperature, the tensile strength of the Au-Au bond exhibits a maximum with increasing bonding pressure. This can be related to the pressure dependence of the interfacial stress distribution and its effect on unbonded radius, r. SEM fractographs of the failed surfaces suggest a combination of cohesive and adhesive failures along the bonded interface.