Assessing the Reliability of High Temperature Solder Alternatives

Alternatives to solder suitable for operating temperatures above 175°C or so include sintered Ag as well as fused nano-particles of Ag or Cu, and micron-scale Cu particles fused with and bonded together by Ag nano-particles. The nature of these is very different from that of common solder materials, but assessments of their long term reliability too often rely on the same (or similar) accelerated test protocols and implicit interpretations. This can easily become misleading. Systematic studies are ongoing to develop a mechanistic understanding of the evolution of damage and failure in the kinds of metallic structures achieved by the fusion of nano-particles at temperatures of 200 — 300°C. For a start, our focus has been on the CuantumFuseTM material originally developed at the Advanced Technology Centre of the Lockheed Martin Space Systems Company and now being further developed and marketed by Kuprion Inc., but preliminary results suggest that generic conclusions and recommendations may apply to the other alternatives as well. Accelerated testing is of course only of use to the extent that it reveals something about the anticipated performance under realistic service conditions. The materials in question all exhibit significant porosity, nano-particles leading to both nanocrystallinity and nano-porosity. This has major consequences for their behavior in cycling and long term exposure to elevated temperatures, all of which should be taken into account when defining test protocols and interpreting test results.