本研究主旨在探討銅試片鍍光澤錫後，在不同外加應力及溫度條件 下錫鬚生長之行為，並利用掃描式電子顯微鏡(SEM)觀察錫鬚之變化，以 了解外加應力及溫度與錫鬚生長之關係。實驗結果顯示，在室溫下承受 外加拉應力之試片表面發現長度較短之小結狀錫鬚，其長度比無外加應 力的試片短，主要是由於外加之拉應力抵消部份試片內部既存的壓應力 所致，但此機制無法完全避免錫鬚產生。試片在室溫中承受不同外加壓 應力，其表面均發現有較明顯的錫鬚生長，其分佈密度隨外加壓應力數 值的增加而增高，但外加壓應力的數值越高並沒有造成錫鬚長度也呈一 致性遞增的趨勢，主要是由於較高外加應力造成氧化錫表面出現較多缺 陷，這些缺陷促使更多錫鬚生成，亦導致多數錫鬚長度無法增長。在50 oC 環境中承受外加壓應力之試片表面均生成基地寬度較大之錫鬚，此類型 錫鬚之成長不僅是長度的變化，還包括基地寬度的增加，且成長期較長， 主要是由於在高溫環境中，外加應力、熱應力及錫-銅介面反應產生內部 應力促使晶粒再結晶與晶粒成長，並持續提供錫鬚成長之驅動力等機制 所致。在50 oC 環境中無外加應力之試片，其表面出現典型細長針狀錫鬚 與基地寬度較大之錫鬚共存之現象，細長針狀錫鬚長度最長為209.5 μm， 主要是由於在無外加應力條件下之試片塑性變形程度比承受外加壓應力 之試片低，導致材料再結晶程度亦隨之降低，造成部分晶粒未能完全成 長為大晶粒所致，而高溫環境中熱應力及IMC 較快之生長速率所引發之 較大壓應力分別經由成長及未成長之晶粒釋放，形成細長針狀錫鬚與基 地寬度較大之錫鬚同時存在情形。 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 ℃.
