Ion bombardment methodology for lead free solder microstructure characterization

In the paper, the ion bombardment skill was adopted in analyzing various lead free solder microstructures to compare Ag effect, Cu effect as well as Ni dopant addition effect by way of following SEM observation. The ball grid array package attached with lead free ball is subject to SMT with lead free (SAC387) paste on the PCB. After mechanical polishing, the test vehicle is further subject to ion milling cutting to make the surface flat enough to be observed. In order to highlight the microstructure difference due to different ingredient composition in the Sn, Ag, Cu and dopant, a proprietary ion bombardment skill to replace conventional chemical etching is conducted to the sample, so that the different phase can be demonstrated due to the selective physical etching effect. In parallel, the conventional chemical etching after mechanical polishing is also conducted for the comparison of the microstructure observation in Sn-1.2Ag-0.5Cu-0.05Ni candidate. The new methodology combining the features of cross section and ion bombardment for the microstructure characterization of lead free solder interconnect will be recommended for the industry reference.