Investigating whisker growth on immersion tin surface finishing

The aim of this research is to examine the whiskering ability of immersion tin layers in natural and elevated temperatures and elevated or decreased humidity environments. Immersion tin layer with 2 μm layer thickness on copper substrate has been tested. Five different groups of samples has been investigated: a reference in room environment (25 °C/ 50% RH), two hot and dry circumstances in 50 °C and 105 °C temperature with 15% Relative Humidity (RH) and two hot and wet circumstances in 40 °C and 105 °C temperature with 92% RH and 100% RH respectively. The whisker growth was observed by using Scanning Electron Microscopy (SEM). The structure of the whiskers and the tin layer were also examined with FIB (Focused Ion Beam). It is shown that the immersion tin layer is also capable of growing tin whiskers. Most of the detected whiskers were the so called “nodule” types, approximately 3-9 μm long with 1-2 μm thickness.