Three-dimensional analysis of the interface between an Sn-8wt.%Zn-3wt.%Bi solder and a substrate by using an angle-lapping method

Abstract

The validity of application of the angle-lapping method to investigate the microstructure between an Sn-8wt.%Zn-3wt.%Bi Pb-free solder and an Auimmersed Ni-7.0%P plate or a Cu substrate was studied using transmission electron microscopy. The method enabled a three-dimensional analysis of the interface layers. The morphology of the Au layer was clarified as an intermetallic compound with Zn with numerous voids that looked like cracks spreading in all directions. Sn and Bi could diffuse into the interface layer only when the Ni-P plate was used, but Ni did not diffuse actively and formed a narrow interface layer. When a Cu substrate was used, Cu diffused, rather than Sn or Bi, and formed a relatively wide interface layer. These results were obtained with the angle-lapping method.