TEM observation of interfaces in a solder joint in a semiconductor device

Abstract

Microstructure of a joint between a Pb–Sn eutectic solder and an electroless Ni–8 mass% P has beenexamined using transmission electron microscopy. Four layers, i.e. Ni3Sn4, Ni48Sn52, Ni2SnP and Ni–20 mass% P, are formed between the solder and the electroless Ni–8 mass% P. Among them, Ni48Sn52 and Ni2SnP were found for the first time in a solder joint. Spherical voids are formed at the interface between Ni48Sn52 and Ni2SnP, and columnar voids are formed at the interface between Ni2SnP and Ni–20 maas% P. From the analysis of the migration of the respective interfaces observed during in situ heatingexperiments, it is concluded that these voids are Kirkendall voids formed due to the difference in diffusivity of Ni across the interfaces. Fracture takes place at either of those interfaces during a dropping test.