The Effect of Tin Grain Orientations and Grain Boundaries during Current Stressing on Cu6Sn5 Formation

• Main Authors: Lin, Yu-Lung, 林玉龍
• Other Authors: Chen, Chih
• Format: Others
• Language: zh-TW
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/80963185072561693058

碩士 === 國立交通大學 === 材料科學與工程學系所 === 102 === As electronic devices become more functional and miniaturization, the microelectronic industry is facing a lot of challenges. The fabrication process is encountering many physical limitations. In order to keep up with Moore’s law, the 3D-IC packaging technology is a promising solution to the limitatons. Microbumps are one of the possible solutions for 3D-IC packaging. The bump diameter shrinks to 20μm and the bump height decreases to about 10-15μm . As a result, the number of solder grains in a microbump is limited, and these few grains may affect the reliability of microbumps. It is well known that the diffusion is the key factor for intermetallic compounds (IMCs) formation, void formation and electromigration (EM). Previous researches reported that the diffusion of Ni in solder is highly anisotropic. The different Sn grain orientations can cause different failure modes for solder joints with Ni under bump metallization (UBM) during current stressing. Therefore, the Sn grain orientation is a critical problem for the reliability of 3D IC microbumps. However, no researches reported the anisotropic diffusion of Cu in solder under EM. In this study, we used flip-chip samples with 30μm bump height to study the Sn grain orientation effect on Cu diffusion by Electron Backscatter Diffraction (EBSD). The stressing condition was 1.17 x 10P4P A/cmP2 Pat 140 PoPC. Even though the anisotropy of Cu in Sn is not as large as Ni in Sn, the effect of Sn grain orientation on Cu-Sn IMC formation was still obvious. If the c-axis of Sn grain was aligned with along electron flow, the IMCs and the Cu UBM dissolved quickly at cathode side and the IMCs accumulated at anode side. Even when the channels of scallop CuR6RSnR5R closed, this phenomenon was unchanged. But if the c-axis of Sn grain was normal to electron flow, the CuR6RSnR5R formed along Sn grain boundary and the growth rate depended on the angle of grain boundary. Therefore, the Sn grain boundary also played an important role in the IMCs formation besides the Sn grain orientation.