Sandia researcher Tom Crenshaw sets up a specimen in a test frame that will pull a solder joint apart to determine its tensile strength. He co-authored a paper that won the Best of Proceedings category in the Surface Mount Technology Association’s International 2012 Best Papers conference. (Photo by Lloyd Wilson)

A few years ago, researchers asked Sandia’s geothermal group to develop electronics to monitor well conditions in field operations—withstanding high temperatures and pressures, excessive vibrations, and other extreme environments.

Most brazing processes occur at a peak temperature above about 700° C, while most soldering occurs below 350° C, leaving high-temperature electronics few filler materials from which to choose. “So there’s this no man’s land in which the only materials that are available are aluminum-based brazing alloys that melt at about 600° C,” said Paul Vianco (Metallurgy and Materials Joining Dept.). But aluminum-based alloys are difficult to process for electronics.

Sandia first investigated the gold-silver-germanium alloy about 15 years ago for another project that was later closed down. The alloy’s fundamental mechanical and processing properties are nearly fully characterized. That’s important because it saves about two years of development that would be required to establish how well the alloy makes a reliable solder joint, Vianco said. “All that’s done,” he said. “We have the preliminary work completed that allows us to consider this material for a range of applications, including downhole electronics.”

In addition, the gold-silver-germanium alloy is lead-free, making it environmentally friendly for geothermal work in countries moving away from materials that contain lead.

Read the  Sandia news release.