Leak rate and reliability of low temperature thin-film indium bonding

This paper shows the high performance of low-temperature thin-film indium bonding in terms of reliability, temperature stability, and leak rates. The bonding was performed at low temperatures between 60°C and 140°C, avoiding flux or any other pretreatment of the surface (e.g. formic acid). Through patterning of the indium and the applied pressure, the indium is squeezed out of its oxide shell and forms a strong, 1-2 μm-thick bond. Materials, designs of the bond rings, and bonding parameters have been varied and compared according to the tensile strength of the bonds which lie between 10 and 25 MPa. Leak rate measurements were performed with samples bonded at 140 °C and at 60 °C and both show high hermeticity. No leak could be detected with samples bonded at 140 °C and stored at 125°C for 5 weeks.