Title of Document : TIN WHISKER RISK ASSESSMENT STUDIES

Title of Document: TIN WHISKER RISK ASSESSMENT STUDIES Tong Fang, Doctor of Philosophy, 2005 Directed By: Professor Michael G. Pecht Department of Mechanical Engineering As a result of the global transition to lead (Pb)-free electronics, pure tin and high tin lead-free alloys have been widely adopted by the electronics part manufacturers as the materials of terminal finishes. However, electrically conductive tin whiskers have been found to develop in pure tin or high tin alloy finished surfaces, resulting in a reliability concern. Experimental results and observation appear to support the hypothesis that the driving forces for whisker formation is compressive stress. However, no accepted model and accelerated factors are available to describe and predict whisker growth. Though the issue of metal whiskers has been studied for over 60 years, currently there is no an industry-wide accepted methodology to quantify tin whisker risk. In this dissertation, a tin whisker risk assessment algorithm, which mainly focuses on bridging risk, is developed. The goal of this risk assessment algorithm is to provide a practical methodology for the electronics industry to quantify the failure risks posed by tin whiskers on tin-plated electronic products. This algorithm assessES tin whisker bridging risk quantitatively as a function of time. Probabilistic and statistical methods are applied to quantify the risk parameters, such as whisker density and length, related to assess tin whisker risk. Monte Carlo technique is the basic tool to sample the whiskers and assess the bridging risk. Two experiments are designed and conducted to simulate bridging failures caused by fixed and broken free whiskers. The methods to collect the information of the risk parameters are demonstrated. Prediction of whisker growth and tin whisker bridging risk is conducted based on the collected information. Error analyses on the differences between simulation and experimental results are provided. TIN WHISKER RISK ASSESSMENT STUDIES