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34 SMT Magazine • May 2014 derfill, slightly better for HP in compare to MP samples. But as it can be seen in the interval chart of Figure 3, the statistical significance was not convincing. Summarized can be concluded that HP-ENIG surfaces have at least no negative impact to the drop shock resistance. Well known from previous studies is the positive effect of Cu defined (CuD) pads in comparison to solder mask defined (SMD) pads. Due the fact that the influence of solder mask/underfill interaction surpasses the influ- ence of the pad design (Figure 5), the differ- ence between CuD and SMD pads is statistical- ly not so obvious in the case of underfill, but is the major impact for samples without underfill (Figure 4). mECHaNICaL RELIaBILITy continues feATuRe Table 2: Test vehicle build-up.