Synchrotron Radiation X-Ray Measurement of Residual Stress in Sn Films and the Effect on Kinetic Analysis of Sn Whisker Growth

• Main Authors: Hao Chen, 陳灝
• Other Authors: 吳子嘉
• Format: Others
• Language: en_US
• Published: 2016
• Online Access: http://ndltd.ncl.edu.tw/handle/svpq59

博士 === 國立中央大學 === 化學工程與材料工程學系 === 104 === Spontaneous Sn whisker growth is one of the most serious reliability problems for electronic devices. Sn and Cu are commonly used in electronic packaging, and they easily form intermetallic compounds (Cu6Sn5) at room temperature, inducing compressive stress, which is the main force that drives the spontaneous growth of Sn whiskers from Sn films. The electronic product tends to be smaller and thinner than the preceding design, and the demands for high reliability devices are increasing. The risk of Sn whiskers increases with each new design iteration. Manufacturers must understand the growth mechanisms of Sn whiskers to minimize the problems, but the unpredictability of Sn whisker growth caused difficulties for research. To effectively discuss the growth mechanisms of Sn whiskers, a lithography process was used to control the positions of Sn whiskers by creating arrays of weak spots on Sn film surfaces. This study discusses how Sn film microstructures affect the kinetics of spontaneous Sn whisker growth and qualitatively analyzes Sn whiskers with various microstructures. The result indicates a strong correlation between the whisker diameter and grain size of the films. The whisker diameters were confined depended on the sizes of the Sn grains. The results directly evidenced that both the thickness and grain size of Sn films can influence the growth of Sn whiskers. Additionally, thickness has a greater effect on whisker growth than grain size does. Since Sn whisker growth is a spontaneous phenomenon that combines continuous processes of stress generation and relaxation, biaxial stress in the films was measured using synchrotron radiation X-ray. The stress evolution during annealing was correlated with the growth kinetics. An incubation period was observed, during which the compressive stress in the films built up and the whiskers nucleated. From the thermodynamic relationship between the growth kinetics of the Sn whiskers and the microstructures of the films, an equation was formulated to predict the growth of the Sn whiskers from various microstructures of the films. According to the results, increasing the thickness and grain size of Sn films would inhibit the growth rates of whiskers and suppress the formation of whiskers. Through this method, the electronic packaging industry can enhance device reliability.