ELECTRICAL CHARACTERIZATION OF THERMAL VACUUM GROWN SUBMICRON-THICK SN WHISKERS

Abstract

Submicron-thick Sn whiskers were electrically characterized. The whiskers were grown from a 500 nm thick Sn layer on a Cu substrate, which was kept in a thermal vacuum chamber (50 ◦C and 8.3 × 10− 6 mbar for 1000 h) to simulate the space circumstances. First, the electrical parameters were measured in ambient conditions by welding the whisker to a sample holder. Next, a real circumstance was simulated when whiskers touched a conductive surface using a probing method in a vacuum. The average breakdown voltage was 10–12 V. Two types of I-V characteristics of the whisker were observed: an abrupt breakdown in the case of needle-type whiskers and a slower breakdown in the case of nodule-type whiskers. Nodule-type whiskers had a relatively larger current capacity than needle-type whiskers. TEM investigations showed that both whisker types were mono-crystalline, but the nodule-type whiskers were more oxidized and contained more Cu/Cu6Sn5 inclusions than the needle-type whiskers, which explains the electrical differences. In ambient conditions, a whisker can conduct more than three times larger current (over 100 mA) than in vacuum due to the thermal management effect of the ambient air. The space industry can use the obtained electrical parameters for risk analyses and the development of short-circuit protection systems.