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20 SMT Magazine • January 2017 ure on the post-thermal samples was limited to two part locations, and was associated with lift- ed pads at each of those locations. Several locations of brittle fracture on the ENEPIG samples were selected for further evalu- ation. Analysis of the PB pad surface using EDS indicates that the remaining sur- face is predominantly nickel, with a small amount of tin. The materi- al exposed on the solder joint side of the fracture surface was mea- sured to have a high level of tin, but also up to 0.79% by weight Pd and 17.5% by weight Au (as well as low levels of Pb and Ni). These values varied based on the area se- lected (Figure 11 for an example). Analysis of an overall solder joint in cross section showed 0.5% by weight Pd and 3.3% by weight Au. Considering the volume of solder that was applied to the joint, this level of overall Pd is consistent with the Pd layer thicknesses mea- sured on the PBs, but the level of Au is higher than expected. It was anticipated that the part had an ENIG finish, which would Figure 10: Brittle fracture surface on PB pad with small amount of solder remaining around perimeter. Figure 11: Cross-section and EDS analysis of brittle fracture surface (solder side). EVALUATION OF THE USE OF ENEPIG IN SMALL SOLDER JOINTS