Analysis of Cold Bonding at Gold-Gold Contact in a Thermal Switch

Cold pressure bonding at the gold-gold interface of a thermal switch was analyzed. There are conditions under which the gold-gold interface can cold bond and stick together, constituting a failure of the switch. The objectives of this study were to quantitatively understand the bonding phenomenon, to improve the design and fabrication for eliminating the concern for cold bonding, and to conduct a fundamental study of the mechanisms for cold pressure bonding. Using the contact mechanics method and principles for solid-state joining, an analysis of the gold-gold contact in the thermal switch has been conducted to find out stress levels at the interface, conditions for yielding, and interface diffusion driven by the pressure difference at the contact interface. A model involving two gold-coated copper anvils with a pressure applied was set up. The pressure-driven interface diffusion was identified as the controlling mechanism for the bonding process. At the microscopic level, plastic deformation occurred at the tips of the asperity, and a local bonding was shown to occur. The bonded area was shown to be influenced significantly by the temperature, pressure, and roughness of the surfaces.