Understanding Tin Plasmas: A New Approach to Tin Whisker Risk Assessment

This study examines the mechanisms governing sustained tin plasma formation in vacuum as well as at atmospheric pressure. The authors have experimentally demonstrated that sustained tin plasmas can form in vacuum at DC power supply voltages as low as 4 V, and present a qualitative model for the observed voltage and current signatures associated with tin plasma formation. Engineering estimates were developed to help quantify tin whisker risk as a function of power supply voltage. Implications for space applications are also discussed. At high pressures, the authors found that sustained tin plasmas can form both in nitrogen and air. These plasmas tend to remain spatially localized because the heat generated can lower the air density in a small region, sustaining the plasma in that area and causing pernicious metal destruction. Thus the risk associated with using tin whisker-containing components at one atmosphere may be comparable to, or possibly worse than, the already-known high risk in vacuum.