The application of a focused ion beam (FIB) mill equipped with a microsampling unit to a tin-plated specimen was reported briefly. Tin-plating has a serious problem: Whiskers are liable to grow on the surface of tinplates. In order to clarify the mechanism of the whisker growth, detail characterisation is conducted using transmission electron microscopy (TEM). However, it is difficult to prepare specimens for TEM observation without the influences of mechanical damages. It was demonstrated that FIB etching was successfully used to observe a three-dimensional microstructure by scanning ion microscopy (FIB-imaging) and to prepare thin films for TEM observation. The observation has revealed the formation of precipitates of Ni(3)Sn(4) that is considered to be strongly related to the whisker growth.