Spreading Behaviour and Joint Reliability of Sn-0.3Ag-0.7Cu Lead-Free Solder Alloy on Nickel Coated Copper Substrate as a Function of Reflow Time

Solder joint directly interfaces electrically, mechanically and thermally with numerous electronic components in electronic assemblies. Sn-Ag-Cu lead-free solder alloys for electronic assembly are being driven by the environmental issues concerning the toxicity of lead. In the present study, spreading behaviour, evolution of intermetallic compounds during solidification of Sn-0.3Ag-0.7Cu solder alloy on Ni coated Cu substrate and the related joint strength were studied as a function of reflow time. Experiments were carried out for various reflow times of 10, 100, 300 and 500 s at a reflow temperature of 270 A degrees C. The solder alloy exhibited improvement in wettability on the substrate at longer reflow times. An increase in the IMC (CuNi)(6)Sn-5 thickness was observed for samples reflowed up to 300 s and the thickness decreased for samples reflowed for 500 s. IMC layer formed were about 0.3, 1.15, 2.03, 1.94 mu m during 10, 100, 300 and 500 s of reflow time respectively. The joint shear test was performed to assess the integrity of the Sn-0.3Ag-0.7Cu solder solidified on Cu substrates. The maximum joint strength was observed for samples reflowed for 100 s.