Effect of substrate surface condition on thermal cycling behaviour of lead-free solders

Chen, Wei Keat (2014) Effect of substrate surface condition on thermal cycling behaviour of lead-free solders. Project Report. Universiti Teknikal Malaysia Melaka, Melaka, Malaysia. (Submitted)

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Abstract

Lead-free solder is a new generation material which introduced for the replacement of conventional lead containing solder in the purpose of environmental friendly. In electronic packaging industry, the reliability of solder joint not only depends on the solder material but include the surface finish. This study will focus on the microstructural analysis and characterization of the effect of thermal cycling behaviour to the lead-free solder with different types of surface finish. The solder material used is SAC 305 which composed of tin, silver, and copper. The surface finishes included in this study were bare copper, immersion tin, and electroless nickel immersion gold. The main aim was to determine the microstructure of the solder and the intermetallic compounds formed in different types of surface finish after thermal cycling test is applied which affecting the performance and lifetime of solder joint. The effect of surface finish and the intermetallic compounds to the crack initiation and propagation behaviour in the influenced of thermal cycles is analyzed in this research. After thermal cycling test, the samples were cross sectioned, grinded and polished. Nanoindentation is carried out to compare and examine the effect of thermal cycling to the samples with the as-received samples. Then, the morphology of the sample was reveal under Scanning Electron Microscopy in order to inspect the crack propagation behaviour in the solder. X-ray diffraction analysis is performed to understand about the effect of intermetallic compound formation in the solder joint. In addition, the samples undergo Energy Dispersive X-ray for compositional and elemental analysis of intermetallic compound layer. From the analysis, ENIG displayed most serious impact from thermal cycling and ImSn shows highest tendency for IMC to grow. The study also shows that the cracking phenomena happened in low thermal cycles and the mechanism is analyzed.

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