Mechanism of Microvoid Formation and Their Prevention in Micro-scale Joints

• Main Authors: Chih-Tsung Chen, 陳智琮
• Other Authors: Cheng-En Ho
• Format: Others
• Language: zh-TW
• Published: 2016
• Online Access: http://ndltd.ncl.edu.tw/handle/14697506059305099229

碩士 === 元智大學 === 化學工程與材料科學學系 === 104 === In recent years, as electronic products tend to lighter and higher performance, the development of the size in transistors becomes more difficult. In order to offers a much greater vertical interconnect density, 3D IC (three-dimensional integrated circuits) is the most commonly used technology. The advance micro-scale joints for 3D IC have a diameter of about few tenths μm with various solder thicknesses ranging from 10 μm to about 30 μm. The reduction in the joints size might induce: (1) a complete transformation of “solder” joints into “intermetallic compound (IMC)” joints (i.e., IMC joints), which are brittle in nature and might seriously deteriorate the mechanical reliability of micro-joints; (2) voids formation that will probably degrade the micro-joints reliability. In this study, we observed voids formation mechanism and its prevention in Cu/solder/Cu and Cu/Ni/solder/Cu structure, respectively. In early stage, the phase transformation induced volume shrinkage measured in Cu-Sn solder reactions. As the isothermal aging time increased, it was found that voids continue formed in the micro-joints. The reason of voids formation is micro-joints not under space confinement that some of Sn diffused to the side wall of Cu pillar. According to electron backscatter diffraction (EBSD) analysis, IMC grains growing from opposite directions have not merged into one single grain that caused the grain boundary. The grain boundary becomes the Sn surface diffusion path that Sn may diffuse to the Cu pillar wall. The correlation between Sn surface diffusion and voids formation will discussed in this study.