Surface Finish Effects on Fracture Behavior of Sn–4Ag–0.5Cu Solder Joints
The effect of various surface finishes on the interfacial fracture toughness of SAC405 solder joints under shock loading conditions was investigated using sandwich compact tension specimens. The surface finishes investigated in this study were organic solderability preservative (OSP), immersion silver (ImAg), nano-tin dispersed in an organic carrier (OrM), and gold over nickel (NiAu). It was found that the ImAg surface finish appears to enhance the fracture toughness, while the NiAu surface finish appears to have no effect compared to bare copper. For the OSP and OrM surface finishes, more data will need to be collected to reach a conclusion regarding their effect. The effects on fracture toughness could not be attributed to the thickness or morphology of the intermetallic compound layer found at the solder joint interface. Future work will focus on understanding the mechanisms by which immersion silver enhances the fracture toughness. Overall, the results of this study may help designers make more informed decisions about which surface finishes can be used to reduce shock failures in consumer electronic devices.
KeywordsLead free solder Surface finish Fracture toughness
The authors gratefully acknowledge financial support from Intel Corporation and the Oregon Metals Initiative. Furthermore, the authors would like to thank Jim Kenny of Cookson Electronic for providing the surface finishes, Professor Tae-Kyu Lee of Portland State University for several useful discussions, and Joel Walenza-Slabe for helping with the aluminum evaporation.
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