Characterisation of the interfacial morphology of explosive welded tin and copper plates under isothermal ageing

What is it about?

After the ban on toxic lead (Pb) in solder alloys, Pb-free solder alloys are extensively used in the applications of electronic packaging, with tin (Sn) comprising over 90% of the composition. The formation of an intermetallic layer at the solder/substrate interface due to chemical bonding is a common phenomenon. However, during continuous service conditions, the growth of the IMC layer may affect the electrical and thermal properties. In real conditions, the IMC thickness associated with ageing is very important. This is because the reliability of the joint is allied to the growth of the IMC layer. Therefore, investigating the formation of intermetallic layers during joining and ageing is challenging. In the current research, Sn/Cu plates were welded using controlled underwater shock waves without the formation of intermetallic phases. Further, studies on the evolution of interfacial morphology in isothermally heat-treated tin/copper joints over extended periods were also assessed.

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Why is it important?

The wavy interface significantly affects the morphology of the IMC interface. IMC growth of all the samples obeyed thermally activated diffusion-controlled mechanism. Plates welded at a water distance of d = 40 mm exhibited a faster IMC growth rate, and d = 30 mm had the slowest rate. The growth of the intermetallic layer will be impeded if the interface exhibits a larger wavy interface.