Extreme Cold-Temperature High-Strain Rate Properties of SAC Solder Alloys
Pradeep Lall, Vikas Yadav, Vishal Mehta, Jeff Suhling, Ken Blecker
Abstract
Electronics in a number of harsh environments may be subjected to very-low operating temperatures in conjunction with high strain rates. Examples include the automotive underhood environment, in which electronics on-engine and on- transmission may be exposed to low temperatures for sustained period in addition to high strain-rates resulting from engine vibration and road shocks. Further, electronics in downhole applications may be mounted just before the drill tip and be exposed to high strain rate resulting from the deep-well drilling in addition to exposure to extreme cold-temperatures while drilling in cold-climates. Transition of the industry to leadfree solder alloys for second level interconnects has necessitated the fundamental studies for long-term reliability assurance of products in harsh environments. There is scarcity of data for solder alloys at extreme cold temperatures and high-strain rates in the neighborhood of 1-100 per sec. Low strain-rate mechanical properties for SAC allots have shown degradation. In this paper, SAC105 and SAC305 leadfree solder alloys have been tested and studied at several lower surrounding temperature starting from - 65C up to +200C, with high strain rates. The prepared lead-free alloy specimen after reflowing, have been tested at strain rates of 10, 35, 50, and 75 per sec. The calculated experimental data has been fit to the Anand Viscoplasticity model. In order to assess the predictive power of the model, the model predictions from computed parameters have been compared with experimental data.