Relation between tin whiskering ability Sn/Ag/Cu solder alloys and current load

This paper presents the relation between the tin whiskering ability of lead-free Sn/Ag/Cu (SAC) solder alloys and the current load. For the investigation three solder alloy was applied: two low Ag content micro-alloyed SAC (SnAgCu+Bi+Sb with different wt%) and the widely known SAC305. FR4 test board was used for 60 solder joints on copper pads coated with immersion tin surface finish. The solder joints were loaded with different current levels: 0, 0.1, 0.2, 0.5, 1, and 1.5 A. The solder joints were aged in 85°C/85RH% elevated temperatures and humidity to induce the tin whisker growth. The duration of the test was 3000 hours. Whisker growth was studied by Scanning Electron Microscope (SEM) after every 500 hours. The lead-free SAC solder alloys have produced tin whiskers during the investigation. The results showed that the whiskering ability of the SAC alloys considerably depends on the applied current load and not only on the composition of the alloys.