Tin whisker growth from low Ag content micro-alloyed SAC solders

In this paper the tin whisker growth properties of lead-free SAC (SnAgCu) solder alloys were investigated. There different alloys were studied: two micro-alloyed SAC (SnAgCu+Bi+Sb) and the widely applied SAC305 as reference. FR4 test board was developed for 18 pieces of 0805 chip resistor components. Solder joints were fabricated on imm-Sn surface finish. The samples were aged in elevated temperatures and different humidity levels to induce the tin whisker formation. Three kinds of aging conditions have been used: 85°C/85RH%, 105°C/100RH% and 105°C/20RH%. The test duration was 3000 hours. Whisker growth was checked after every 500 hours by scanning electron microscope. It was shown that the lead-free SAC solder alloys can also develop tin whiskers and the whiskering ability depends on the composition of the SAC solders.