A TEM observation of solder joints of an electronic device

An interface between a eutectic solder and an under-bump metal (UBM) fabricated by electroless NiP and Au plating was examined using transmission electron microscopy (TEM). The purpose of this study is to analyze a formation and intermetallic compounds which formed by solder attaching near the solder joint. The sample observed was a ball-grid-array (BGA) type semiconductor package, which was fabricated by making use of a printed-wiring board (PWB) for a package substrate. The observation was carried out on 2 kinds of sample, i.e. those before and after solder attachment. Ni3P crystalline was observed in NiP layer with before solder attaching samples. Two binds of new alloy phase were observed at the interface of the solder joints. One is Ni48Sn52 and the other is Ni2SnP. Ni2SnP layer had only 0.2 mu m in thickness, so it was considered to be difficult detecting this layer by other observation method. Focused Ion Beam (FIB) technique was applied to preparing the foil specimens.