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.
The 80/20 gold/tin eutectic composition:
• Reflows at 280°C
• If used in a vacuum or under a forming gas, soldering can be achieved without the use of a chemical flux
• Exhibits good wettability
• High yield strength
• Resistant to creep
• Corrosion resistant
• Good thermal conductivity
As mentioned above gold/tin alloys are used as solders as well as for hybrid, photonic, microelectronic and photoelectronic device packaging.
As a solder the gold/tin eutectic alloy is used to bond opto/microelectronic devices to ceramic carriers as part of the packaging process.
Primary author: AZoM.com