Effect of aging on the high strain rate mechanical properties of SAC105 and SAC305 leadfree alloys

Electronics subjected to shock and vibration may experience strain rates of 1-100 sec^-1. High strain rate data is scarce for leadfree solders at strain rates in the range of 1-100 sec^-1, typical of drop-impact, shock and vibration. A new experimental method has been developed to achieve constant strain rate in the neighborhood of 1 to 100 sec^-1 during the entire deformation history. SAC105 and SAC305, which are two of the widely used leadfree alloys, have been tested at strain rates of 10, 35, 50 and 75 per sec. Effect of aging on the high strain rate properties has also been quantified by subjecting the test specimen to thermal aging for varied periods of time at various temperatures. The leadfree solders have been exposed to constant temperatures of 25°C, 50°C, 75°C, 100°C and 125°C for 1 day, 30 days and 60 days prior to high strain-rate test. Full-field strain in the specimen has been measured using high speed imaging at frame rates up to 75,000 fps in combination with digital image correlation. The cross-head velocity has been measured prior-to, during, and after deformation to ensure the constancy of cross-head velocity. Experimental data for the unaged and the aged specimen has been fit to the non-linear Ramberg-Osgood model using two methods.