A fluxless Sn-In bonding process achieving high re-melting temperature

In this paper, we report a new alternative to the conventional solder. It is based on In-Sn multilayer composite design. This is a fluxless, oxidation-free, and most important of all, non-eutectic soldering technique that can achieve a remelting temperature significantly higher than the bonding temperature. The In-Sn non-eutectic multilayer alloy so designed has the composition of 13.9 atomic % In and 86.1 atomic % Sn. The SEM and EDX analyses performed on the joint cross section clearly indicate a uniform joint thickness of 9μm, while the joint microstructure is clearly visible and nearly void-free. The EDX results obtained also successfully demonstrate that the entire joint is heavily Sn-rich, as what we have anticipated. It ranges from 175 to 190°C. The results clear show that the joint composition is heavily Sn-rich, a very significant advantage from which it maximizes the temperature tolerance the device package can possibly handle.