Despite the importance of lead-free solders in modern environmentally friendly packaging, few studies have been conducted on their mechanical reliability at the wafer level. In the present study, high-speed die shear tests were conducted to investigate the effects of strain rate on the shearing resistance and fracture mode of Sn-3wt%Ag-0.5wt%Cu solder joints on electroless Ni-P/immersion Au surface finish pads. The results indicated that the solder joints underwent ductile and mixed ductile-brittle fracture at low (<855 s −1 ) and high (>25,385 s −1 ) strain rates, respectively. Thus, the overall shear stress-strain curve can be divided into three areas according to Hollomon's law, starting from low strain rates: area I, 100% ductile fracture of the solder itself; area II, mixed ductile-brittle fracture resulting in a ductile-brittle transition region; and area III, 100% brittle fracture at the interface between the intermetallic compound and the Ni-P layer.
In this study, reliability assessment of the IMC layer of the ultra-fine-pitch FC-BGA(Flip-Chip Ball Grid Array) is conducted. The samples are prepared to reveal the differences in the adhesion forces of the IMC layer by dissimilarly establishing each plating thickness for surface finish(Ni/Pd/Au). The hardness and thickness of a P-rich Ni layer, which is known as the weakest section in ENPIG surface, are measured using the nanoindentation and TEM analysis. The degree of adhesion of the IMC layer under each experimental condition is evaluated and the metal plate shear test is performed for verification. The results showed significant correlations between the hardness and thickness of the IMC later and the high fraction defectives of the brittle fractures whose IMC layer had low hardness.
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