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High Temperature Gold Based Lead Free Solder
Keywords: Solder, Lead Free, Gold base solder
With the conversion from tin-lead solders to the SAC lead free solders, soldering processing temperatures have substantially increased. These higher soldering temperatures have the potential of reflowing ceramic packages that have been hermetically sealed, or any devices that have previously been soldered with conventional 80%Au 20%Sn solder. This change to lead free soldering has led to a need for a Gold Tin solder with a higher melting point and reflow temperature, than the conventional 80%Au 20%Sn electronic solder which is a eutectic at 278C. To create a solder with a higher melting point, we examined the effects of minor Germanium and/or Indium additions to the standard AuSn solder composition, in an effort to raise its Liquidus and Solidus to 300C. To study the melting temperatures of the AuGeSn and AuInSn ternary phase diagrams near the binary 80%Au 20%Sn solder target, we made a series of ternary alloys with up to 6% Ge or 6% In. We found that additions of Germanium increased the Liquidus but unfortunately decreased the Solidus, leaving these ternary alloys vulnerable to reflow during subsequent lead free SAC alloy soldering. Successful alloys were created by adding Indium to the 80%Au 20%Sn binary solder, generating a ternary eutectic solder with a single melting point of 300C. This patent pending ternary eutectic solder provides a higher temperature safety factor for subsequent SAC soldering processes.
Heiner Lichtenberger, VP - Technology
Williams Advanced Materials
Buffalo, NY
USA


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