| Summary: | The increased use of electronic devices has increased the usage of solder
connections. Lead, the prime solder hitherto used, is hazardous to human health and
the environment. Thus, replacing Sn-37Pb with a lead-free solder is one of the most
important issues in the electronics industry. As such, the characteristics of In-Bi-Sn
and In-Bi-Zn compared with that of the Sn-Ag-Cu solder alloy were studied. In the
differential scanning calometry analysis, In-Bi-Sn and In-Bi-Zn system alloys
presented a low melting temperature of 61.3 °C and 72.3 °C, respectively. Surface
tension and contact angle of In-Bi-Sn and In-Bi-Zn lead-free solder alloys were
measured on Cu substrate and different surface finishes at 100, 120 and 140 °C
reflow. Sessile drop measurements showed that the contact angle depended on the
reflow temperature. The contact angle gradually decreased from 30.76° to 17.25° as
reflow temperature increased from 100 to 140 °C and for In-Bi-Sn and In-Bi-Zn
solder alloy on Cu substrate, ranged from 58° to 7° after wetting on Ni/Cu substrate
at the same reflow temperature range (100 to 140°C). Energy-dispersive X-ray
analysis found two layers of intermetallic compound in the In-Bi-Sn solder alloy:
Cu6Sn5 and Cu11In9 (scallop shaped) and Cu11In9 (brightly coloured) with Cu and
Sn/Cu substrate. The IMC between the In-Bi-Zn solder alloy could be observed:
Cu5Zn8 (continuous planar) and Cu11In9, a minor IMC layer with Cu and Sn/Cu
substrate. However, only one type of IMC was formed between both solders (In-Bi-
Sn and In-Bi-Zn) and Ni/Cu substrate, which was InNi2. As the reflow temperature
increased, the shear strength of the In-Bi-Sn and In-Bi-Zn solder alloys on Cu, Ni/Cu
and Sn/Cu joints improved due to reduced contact angle and larger spreading area.
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