The Relation Between Tin Whisker Growth and Stresses,Temperatures

• Main Authors: Tung-Hsien Lin, 林東賢
• Other Authors: Chih-Kuang Jack Lin
• Format: Others
• Language: zh-TW
• Online Access: http://ndltd.ncl.edu.tw/handle/43045037290305807530

碩士 === 國立中央大學 === 機械工程研究所碩士在職專班 === 95 === The purpose of this study is to investigate the tin whisker growth behavior on bright tin-plated copper under different applied stresses at room temperature (RT) and 50 ℃. Scanning electron microscopy (SEM) was employed to observe the tin whisker growth behavior under the given testing conditions. Although tin whiskers were observed on the surfaces subjected to applied tensile stresses, they were shorter than those present on the surfaces without applied stress or with applied compressive stresses. Apparently, the applied tensile stresses could counterbalance the residual compressive stresses in the tin layer to a certain extent and reduce the driving force for tin whisker growth. However, the applied tensile stresses could not completely prevent formation of tin whisker. At RT, the observed whisker length did not consistently increase with an increase in the magnitude of the applied compressive stress. An applied compressive stress with a magnitude greater than the yield strength of tin caused a reduction in the observed whisker length but an increase in whisker density. This might be due to a greater number of surface cracks or imperfections induced by a larger applied compressive stress. Such surface defects could serve as a path for whiskers to initiate. For tin surfaces under application of compressive stresses at 50 ℃, whiskers with a wider bottom and greater length were generally observed, as compared to those formed at RT under the same applied compressive stress. A longer whisker growth period was also found for the specimens tested at 50 ℃. This might be attributed to a greater effect of recovery and recrystallization on the growth of tin whisker at 50 ℃. On the tin surface without applied stress at 50 ℃, both needle and nodule types of whiskers were observed. As no mechanical stresses were applied, the plastic deformation caused by residual compressive stresses was smaller, leading to a less extent of recrystallization. In this regard, some of the whiskers grew to become a needle shape, as compared to those present at tin surfaces with applied compressive stresses at 50 ℃.