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 ~100-150nm 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 (~24000 pcs./mm2). 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

ELECTRICAL CHARACTERIZATION OF ß→α-Sn TRANSITION IN HIGH TIN CONTNET SOLDER ALLOYS WITH DIFFERENT INOCULATORS

The identification of allotropic transition of the metallic β-Sn to non-metallic α-Sn in Sn-rich solders joints is crucial for electronics working in sub-zero temperatures. This phenomenon was characterized by electrical resistance measurements in SnCu1 and Sn99Ag0.3Cu0.7 alloys inoculated with InSb, CdTe and α-Sn. Samples were stored at -18°C for 10 weeks. The transition showed characteristic differences at the different alloys and inoculators, like different nucleation, growth and the saturation stages. Although the presence of α-Sn initiates the transition faster than the other inoculators, but the higher diffusion rate of the non-tin inoculators results in much more serious destruction of the samples. The results of the electrical resistance measurements were validated with metallurgical cross-sections

Early Stage Whisker Development from Sn Thin Film on Cu Substrate

The Sn thin film on Cu substrate has high Sn whisker growth susceptibility because of the intensive Cu6Sn5 intermetallic formation at the Sn-Cu interface. In this study, the whisker development on vacuum evaporated Sn thin film deposited on Cu substrates was investigated, starting directly from the Sn deposition. The aim was to obtain more information about the whiskering behavior of Sn thin film in the early stage of the life cycle. For the study, 99.99% pure tin was vacuum evaporated onto Cu substrates. Two different Cu substrates were applied with different surface roughness to investigate the effect of surface roughness on the whisker development. The average thickness of the evaporated Sn layer was ~2 μm. Samples were stored at room temperature for 10 weeks. Whisker development was observed by scanning electron microscope. It was found that the large compressive stress in the Sn layer because of the intermetallic formation initiates the whisker development even after 1 day of the Sn layer deposition. Almost only filament type whiskers were detected. The characteristics of the whisker density showed exponential saturation up to 10 days of the study, while the length of the whiskers was growing further still the end of the study. It was also found that the surface roughness of the Cu substrate affects the rate of whisker growt