Protrusion and whisker growth on tin coated copper substrate under stresses

Tin thin films were coated on copper substrates using chemical method. Tin coated copper specimens under continuously applied compressive and tensile stresses were oxidised at 100°C for 8 days. Protrusion and whisker growth behaviour of tin coated copper specimens was characterised by scanning electron microscope, X-ray diffractometer and transmission electron microscope. The results show that continuously applied compressive stress on tin coated copper specimens would enhance the growth of whisker while tensile stress would reduce whisker growth. A SnO2 layer was formed during oxidation and intermetallics of Cu3Sn and Cu6Sn5 were formed between SnO2 layer and copper substrate, which built up the residual compressive stresses in the coated tin layer. Continuously applied stress on the specimens can change the magnitude of residual compressive stress in coated tin layer, which affects the driving force for protrusion and whisker formation and growth.