Whisker Development from SAC0307-Mn07 Solder Alloy

In this study, the whisker growth from SAC0307-Mn07 solder alloy was investigated. To get fast information, an ultra-thin film was vacuum evaporated from the examined solder alloy onto Cu substrates. The evaporated layer was $\sim 100 - 150$ nm thick in average with the same grain size. The layers were kept at room temperature for 28 days. Whisker growth was monitored by scanning electron microscope with some days frequency, and the layer structure under the whisker was examined on focused ion beam cuts. The large mechanical stress on the Sn layer due to the intermetallic layer growth initiated the whisker growth right after the layer deposition. However, it stopped after 2 weeks since the intermetallic grains consumed the ultra-thin Sn layer. The whisker density was extremely high $(\sim 24 \, 000 pcs./mm^{2}$). Most of the whiskers were the short nodule and hillock type, which does not mean risk in microelectronics. Therefore, the alloying of Mn into the high Sn content solder alloys have a positive effect on the reliability of the solder joints.