以臨場穿透性電子顯微鏡研究通電導致之錫晶鬚成長及錫晶粒旋轉

Abstract

由於環保意識的抬頭，傳統含鉛銲錫將禁止使用，並以無鉛銲錫取代之。採用無鉛銲錫作為引腳 架的表面塗層時，引腳架的表面會有錫晶鬚生成，當不同接腳的引腳架接通時，將會使得元件短路， 甚至燒毀，此一問題嚴重影響相關封裝的可靠度。這已經是數十年來困擾封裝業的議題。 綜觀過去的研究成果，都是在錫晶鬚生成後觀察，推論其生成原因。本計劃將採用即時觀測的穿 透式電子顯微鏡(In-situ TEM)技術，在TEM 腔體內，直接對試片通電，直接錄影觀測錫晶鬚的成長 現象，包括原子的擴散供給、晶粒的消長以及晶粒旋轉等特性。藉由觀測所得的結果建立完整的錫晶 鬚成長機制，提供錫晶鬚生長之基礎科學。目前已經得到清大材料系陳力俊教授的首肯，可以使用該 TEM，也獲得交大材料系吳文偉教授的支持，能夠提供在操作該TEM 的幫忙。特別是也獲得杜經寧 院士的幫忙，願意提供國際合作來幫忙分析結果。本計劃將更深入研究錫晶鬚成長之機制，藉由高技 術性的即時觀測掃描式電子顯微鏡，將於錫晶鬚成長之同時，直接錄影觀測在電遷移作用下銲錫的原 子移動、差排滑移以及晶粒旋轉等特性，以建立一套完整之錫經鬚成長機制，很有機會在此議題的研 究做一個關鍵性的突破，也會是一個很有影響力的研究。

Due to the concern of environmental protection, the conventional solders, which contain lead, are forbidden. Instead, lead-free solders are adopted. If the lead-free is applied as surface finish of leadframes, tin whiskers will grow out of the surface of leadframe. When two whiskers from different frames are connected, a short circuit will happen, which may lead to the breakdown of electronic devices and products. It is a serious reliability issue. Among researches published in past years, the tin whiskers were investigated after the whiskers were grown. Thus no enough information can be obtained on how they were grown. Thus, the growth mechanism is not clear. In this project, with adopted in-situ observation in transmission electron microscopy, we can apply current inside the TEM chamber and record the TEM image simultaneously. Thus, some important information including the supply of tin atom by diffusion, the growth and shrinkage of tin grains and the rotation of tin grains can be observed directly. We have obtained the permission from Prof. LJ Chen in National Tsing Hua University for using the in-situ TEM. We will work with Prof. WW Wu in National Chiao Tung University since he is an expert on the in-situ TEM. In addition, we will work with Prof. King-ning Tu since he is an well-known expert on whisker growth. This proposal has a good chance to have a breakthrough on the growth mechanism and the impact of this research may be quite high.