Observations of continuous tin whisker growth in NdSn3 intermetallic compound

In situ observation of tin whisker growth in NdSn3 compound was carried out by using an optical microscope (OM) and scanning electron microscopy (SEM). The growth rate of Sn-whisker from NdSn3 is shown to be rapid (approximately 8-15 A/s) during exposure to room ambience, and it is accompanied by formation of a new compound, Nd(OH)(3), as was confirmed by x-ray diffraction. This reaction between the Sn-RE compound and trace water in room ambience has significant influence on whisker growth. There is an electron irradiation effect on whisker growth; that is, whiskers stopped growing after being observed in SEM. Therefore, it is suggested that OM be used rather than SEM to observe the continuous whisker growth. In discussion, the driving force per Sn atom for whisker growth is estimated as 1 x 10(14) N in accordance with the whisker growth rate, and its apparent force originates from a chemical potential gradient between the released Sri atoms and the whisker.