Effect of alloying element on wettability and mechanical properties of SN-0.7CU solder
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Date
2016-06
Authors
Koh Lian Jun
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Abstract
Sn–0.7Cu eutectic solder has been successfully applied to practical production of consumer products, due to its cost that is only 1.3 times higher than Sn-Pb solder. However, Sn–Cu has been reported to exhibit somewhat inferior mechanical properties and wettability compared to Ag containing lead free solder alloys. In this work, 1.0wt% In and 0.1wt% Fe had been added into Sn-0.7Cu eutectic solder, and the effect of alloying element on thermal behavior, bulk microstructure, wettability and mechanical properties were studied. The effect of isothermal aging (150℃ and 180℃, for 100h, 250h and 500h) on IMC thickness was studied as well. Addition of In had lowered the melting temperature of Sn-0.7Cu. In contrast, addition of Fe led to an increased in melting temperature. From the SEM and EDX analysis, addition of In and Fe had grain refinement effect on microstructure of solder. Addition of Fe also led to the formation of 𝐹𝑒𝑆𝑛2 IMCs. Addition of In improved the wettability of solder samples, however Fe addition led to slight decrease in wettability, but still having better wettability compared to eutectic Sn-0.7Cu solder. The shear strength of samples improved as In and Fe added. But In addition led to higher fracture strain compared to Fe addition. From SEM and EDX analysis, aging had led to the formation and growth of 𝐶𝑢6𝑆𝑛5 and 𝐶𝑢3𝑆𝑛 IMC, and this had increase the thickness of IMC layer. According to IMC thickness measurements, Sn-0.7Cu-1.0In sample showed the lowest IMC thickness while Sn-0.7Cu-1.0In-0.1Fe showed the highest IMC thickness. The presence of In in had reduce the growth rate of IMC layer, as it showed lowest growth rate constant among the solder samples.