Microstructural Study of Interfacial Reactions Between Liquid Sn and Electroless Fe-Ni Alloys

摘要

Interfacial reactions between liquid Sn and electroless xFeNiP alloys (where x is the at.% of Fe) were investigated to determine the suitability of electroless Fe-Ni films as a potential under-bump metallization in solder interconnections. It was found that the interfacial reactions depended strongly on the Fe percentage in the electroless Fe-Ni alloys. The FeSn_2 compound layer was observed at the interface of alloys with high atomic percentage of Fe, such as 55 at.% and 75 at.%, while both FeSn_2 and Ni_3Sn_4 layers were found at the interface at low Fe concentration such as 25 at.%. The growth rate of interfacial intermetallic compounds and the amount of intermetallic whiskers grown on the FeNiP coatings decreased with increasing Fe percentage. The presence of FeSn_2 phase in Fe-Ni alloys at different Fe concentrations was believed to result from the lower Gibbs free energy for FeSn_2 formation in the Sn/FeNiP system, while the variation in the growth rate of the intermetallic layer with Fe concentration was related to the different growth rates of FeSn_2 and Ni_3Sn_4 compounds.