當銅引腳的表面接合銲錫改成無鉛時，自發性生成的錫晶鬚成為電子產業很頭痛的問題。自發性的錫晶鬚來自於兩個不可逆的反應，且同時有兩種驅動力驅使銅與錫兩種不同種原子同時擴散。受到濃度梯度的化學勢影響，銅快速擴散進入錫，由於化學反應產生Cu6Sn5 介金屬化合物會產生壓應力。此壓應力梯度又將驅使錫原子擴散以釋放映力而長出錫晶鬚，因此錫晶鬚為一無應力的晶體。表面錫所生成的原生氧化層在錫晶鬚成長扮演重要腳色。產業界已有許多建議阻絕錫晶鬚生成。本計畫提出一創新構想，利用微胞的概念，以溶膠-凝膠法製備奈米氧化錫粉末，將此粉末塗佈於銲錫表面，並對錫的微結構進行改質。錫的再結晶溫度很低，於室溫即可發生。若可藉由外加奈米氧化錫減緩其再結晶及成長的驅動力，則晶粒可維持於奈米尺度。錫晶鬚由於其表面能的關係，所生成的直徑幾乎都在數微米的尺度，無法生成奈米晶鬚，因此控制微結構可視為方法之一。同時奈米氧化錫氧化錫亦有機會破壞原生氧化錫的緻密程度，則空缺的供應將源源不絕，錫原子能很容易地釋放應力。此計畫提供一個兼具實務以及基礎研究的課題。 ; Spontaneous Sn whisker growth on Cu leadframe finished with Pb-free solder is a serious reliability problem in electrical and electronic devices. The spontaneous growth is an irreversible process, in which there are two atomic fluxes driven by two kinds of driving force. The Cu atoms diffuse from the leadframe into the solder finish driven by chemical potential gradient to form intermetallic compound of Cu6Sn5 in the grain boundaries of the solder, and the growth of the compound at room temperature generates a compressive stress in the solder. To relieve the stress, a flux of Sn atoms driven by the stress gradient diffuses away to grow a spontaneous Sn whisker which is stress-free. No doubt the protective surface oxide of Sn plays an important role. Several approaches have been proposed to stop the whisker growth. This project proposes an innovative method to inhibit the growth of whisker by spraying a tin layer of nano SnO2 particle. The concept of micelle provides the way to make these nano-particles by sol-gel method. The nano SnO2 particle might stop the fast recrystallization and growth of Sn at room temperature and keep the grain at Sn matrix to be nano size. The way it prevents whisker growth is due to the diameter of whisker has a lower limit due to surface energy. Another benefit is the weakening of surface oxide of Sn matrix. With broken oxide film, the supply of vacancy is continuous. Therefore the stress will not be built up. The project provides a link between fundamental academic research and the application in industry. ; 研究期間 9708 ~ 9807
