Effects of NiP Nodule Interfacial Morphology on Solder-Ball-Joint Reliability
The reliability of a solder ball joint is significantly affected by the properties of its NiP surface finish. In this study, a solder ball joint is prepared using an Sn–4.0 wt%Ag–0.5 wt%Cu (SAC405) solder ball and an electroless NiP/electroless Pd/immersion Au (ENEPIG) plating process on a Cu pad, and the NiP surface finish is then investigated using scanning electron microscopy (SEM), atomic force microscopy (AFM), focused ion beam (FIB) analysis, and high-speed shear (HSS) testing. The NiP-nodule test samples exhibit various interfacial morphologies in response to three fabrication variables: the NiP thickness; the Pd activation time; and the Cu sub-layer roughness. The interfacial morphology is measured based on the ratio of the nodule radius (r) to the distance (D) between the two nodule centers. The results indicate that the HSS energy of an SAC405 solder ball joint is strongly affected by r/D, and increases with increased r/D. Interestingly, we find that corrosion occurs at nodule boundaries with small r/D. Hence, we estimate the boundary energies for each observed r/D value. It should be noted that boundary corrosion occurs at a relative total surface energy of more than 0.4835. This result provides evidence that the retention of higher r/D plays a critical role in improving the robustness of solder ball joints.
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Document Type: Short Communication
Publication date: 01 August 2017
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- Nanoscience and Nanotechnology Letters (NNL) is a multidisciplinary peer-reviewed journal consolidating nanoscale research activities in all disciplines of science, engineering and medicine into a single and unique reference source. NNL provides the means for scientists, engineers, medical experts and technocrats to publish original short research articles as communications/letters of important new scientific and technological findings, encompassing the fundamental and applied research in all disciplines of the physical sciences, engineering and medicine.
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