Abstract
A lead-free Sn-2.5Ag-0.7Cu base solder with different weight percentages of bismuth (0, 1, 2.5, 5) was used. Thermal properties, microstructure, wettability and mechanical properties were investigated. By decreasing the degree of undercooling, microstructure improved, the eutectic structure become finer and the size of β-Sn and intermetallic compounds decreased. By the addition of bismuth to SAC257 solder, the spreading ratio increased from 80.46% to 85.97, indicating an improvement in wettability. In order to investigate the joint properties, alloy solders were bonded to copper substrate, and the structure of the interface, tensile-shear strength and the fractured surfaces were studied. It was observed that the thickness of the intermetallic compounds of Cu6Sn5 at the interface decreased with the addition of bismuth, and the lowest thickness of the interfacial IMCs was found in the SAC257-1Bi solder joint, which decreased about 14% compared to the base solder. Also, the Cu/SAC257-1Bi/Cu bond had the highest tensile-shear strength and elongation percentage among the alloy solders, which has a tensile-shear strength of about 30% and an elongation percentage of about 38% higher than the base solder joint.
Highlights
Zhang et al.[16] studied the effect of Zn on the wettability of Sn-3.8Ag-0.7Cu solder
The results showed that the addition of silver and iron, only reduced the diffusion coefficient, while in the case of gold and nickel, the reaction layer changed to (Cu, Au)6Sn5 and (Cu, Ni)6Sn5, respectively, and even in the case of nickel, the curvature of IMC growth did not show any other parabolic behavior with time, indicating a change in the growth mechanism[18]
The melting temperature is one of the critical factors for solder selection in microelectronic industries, for this reason, this should be taken into consideration to improve the base solder properties[21,22]
Summary
Zhang et al.[16] studied the effect of Zn on the wettability of Sn-3.8Ag-0.7Cu solder They have shown an increase in the wettability of the mentioned solder by adding up to 0.8 wt.% Zn, but decreasing at higher percentages. Adding alloying elements to the SAC solders have three major effects on the interface reactions and the formation of IMCs18:. These elements generally fall into two general categories: (a) Elements that only affect the activity of the elements participating in the interactions of the interface, and these elements do not affect the formation of these phases.
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