Tin whisker growth from Sn-Cu (0–5 wt%) surface finishes

The aim of this research is to examine the whisker growth behaviour of tin-copper alloy surface finishes in highly oxidizing environment. Samples from copper base substrates were plated with 10 μm thick tin-copper alloys between 0 and 5 wt% copper content (with 1% steps) by solder dipping technology. Two types of aging were being used to accelerate the whisker appearance; these were an elevated humidity and temperature condition (85°C/85%RH) and a Highly Accelerated Stress Test (HAST 105°C/100%RH) up to 2400 hours in order to keep the samples in highly corrosion environment. The whisker growth was observed by using Scanning Electron Microscopy (SEM) and was evaluated by the morphology of the whiskers, by the average and maximum whisker length and the average whisker density. Results indicate differences in whisker growth depending on the test circumstances and on the copper content. The series of tests has shown that the different test circumstances induce different whiskering mechanisms and the significance in whisker formation of humidity and melting temperature of the plating alloy were also proven.