Au/Sn is commonly used as a Pb-free solder to attach Au surfaces. The 80/20 alloy melts at 280°C, and can be used with a mild flux or a reducing atmosphere. Another key point of 80Au/20Sn solder is that it has a tensile strength of 40,000psi. This material's high melting point, combined with the non-hazardous nature of Au and Sn have made it very popular for Pb-free assemblies that must endure subsequent Pb-free reflow temperatures (~245°C).