NiSn4 Formation in As-Soldered Ni-Sn and ENIG-Sn Couples

作者：Belyakov S A^*; Gourlay C M

来源：Journal of Electronic Materials, 2012, 41(12): 3331-3341.

DOI：10.1007/s11664-012-2277-1

• Microstructure
• Pb-free soldering
• metastable
• NiSn4
• intermetallics
• solidification

Most research on Sn-Ni solder reactions has focused on the interfacial reactions with the substrate, whereas the microstructure which develops above the intermetallic layers has not been studied in detail. This paper shows that nonequilibrium NiSn4 forms during solidification of the bulk solder in Sn-Ni and Sn-electroless nickel immersion gold (ENIG) solder reactions. With both substrates, the bulk solder solidified to contain Sn-NiSn4 eutectic and primary Ni3Sn4 crystals, and the interfacial layers contained a Ni3Sn4 reaction layer on the Sn side. It is found that Cu, present from dissolution of Cu through cracks in the ENIG layer, promotes the formation of Sn-Ni3Sn4 eutectic. Thus, Sn-ENIG couples contained both Sn-NiSn4 and Sn-Ni3Sn4 eutectic. It is further shown that NiSn4 is not stable at soldering temperatures and that, during isothermal holding at 270 degrees C to 220 degrees C, NiSn4 transforms into Ni3Sn4 and liquid or beta-Sn.

• 出版日期2012-12