Gold/tin alloys around the eutectic composition are used as solders. The eutectic composition occurs at 80% gold, 20% tin, or 30at% tin. However, compositions from 80/20 to 70/30 gold/tin are used.
Gold/tin eutectic solders are classified as hard solders and are also suited to packaging of microelectronic and optoelectronic devices due to their excellent thermal and mechanical properties combined with their low reflow/melting temperature.
The use of solder preforms is cheap to perform, but alignment and thickness control are difficult to control. Furthermore, solder deposited in this way is easily oxidised, which may compromise the integrity of the bond.
Vacuum deposition techniques such as sputtering offer improved process control and reduce the chance of oxidation. However, they take longer to perform and are more expensive.
Electroplating of gold/tin has also been used as an alternative to more conventional solder deposition processes like solder preforms and evaporation/sputtering.