Eutectic Bonding with Au/Sn

Author: Sascha Lohse

Abstract: Eutectic Gold/Tin (Au/Sn) is a hard solder alloy particularly suitable for demanding micro- and optoelectronic applications. They are available in different forms, such as preforms, solder paste or as sputtered depot.

Eutectic bonding with Au/Sn provides a number of advantages, e.g. high stability, high melting temperature, excellent resistance to corrosion, good wetting behavior, high thermal conductivity and high surface tension. If process gas is integrated into the process, the use of flux is not required, meaning that during bonding of e.g. optical components the risk of pollution is diminished.

Au/Sn eutectic bonded packages are used in many automotive and aerospace applications, in medical and military devices, during lid sealing and in most applications intended for mobile use.
As the melting point is rather high, eutectic bonding with Au/Sn is often combined with other soldering processes such as Indium bonding. When performing sequential bonding or step bonding processes, the use of different melting point materials will prevent previous joints from melting.