Wetting and reaction of Sn-2.8Ag-0.5Cu-1.0Bi solder with Cu and Ni substrates |
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Authors: | M J Rizvi Y C Chan C Bailey H Lu M N Islam B Y Wu |
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Affiliation: | (1) Department of Electronic Engineering, City University of Hong Kong, Kowloon, Hong Kong;(2) School of Computing and Mathematical Sciences, University of Greenwich, SE10 9LS London, United Kingdom |
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Abstract: | The wettability of newly developed Sn-2.8Ag-0.5Cu-1.0Bi lead-free solder on Cu and Ni substrates was assessed through the
wetting balance tests. The wettability assessment parameters such as contact angle (ϑc) and maximum wetting force (Fw) were documented for three solder bath temperatures with three commercial fluxes, namely, no-clean (NC), nonactivated (R),
and water-soluble organic acid flux (WS). It was found that the lead-free Sn-2.8Ag-0.5Cu-1.0Bi solder exhibited less wetting
force, i.e., poorer wettability, than the conventional Sn-37Pb solder for all flux types and solder bath temperatures. The
wettability of Sn-2.8Ag-0.5Cu-1.0Bi lead-free solder on Cu substrate was much higher than that on Ni substrate. Nonwetting
for Sn-2.8Ag-0.5Cu-1.0Bi and Sn-Pb solders on Ni substrate occurred when R-type flux was used. A model was built and simulations
were performed for the wetting balance test. The simulation results were found very close to the experimental results. It
was also observed that larger values of immersion depth resulted in a decrease of the wetting force and corresponding meniscus
height, whereas the increase in substrate perimeter enhanced the wettability. The wetting reactions between the solder and
Cu/Ni substrates were also investigated, and it was found that Cu atoms diffused into the solder through the intermetallic
compounds (IMCs) much faster than did the Ni atoms. Rapid formation of IMCs inhibited the wettability of Sn-2.8Ag-0.5Cu-1.0Bi
solder compared to the Sn-Pb solder. |
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Keywords: | Wettability Sn-2 8Ag-0 5Cu-1 0Bi wetting force contact angle flux surface tension finite element modeling intermetallic compounds |
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