Interfacial Reaction between Ni Substrate and Lead Free Solder for 3D IC Application

• Main Authors: Mei-Shih Kuo, 郭楣詩
• Other Authors: Chen-Hung Robert Kao
• Format: Others
• Language: zh-TW
• Published: 2012
• Online Access: http://ndltd.ncl.edu.tw/handle/70911843549080757336

碩士 === 國立臺灣大學 === 材料科學與工程學研究所 === 100 === For 3D IC applications, solder volume reduction is a significant issue in the chip-to-chip micro bumping process. For the reason, solder joints can contain a large portion of the intermetallic compounds （IMCs）. Many new issues must occur due to the reduction of solder volume; however, they are yet to be sufficiently revealed. This study aims to uncover effects caused by the miniaturization of solder volume on the Ni-Sn solid liquid reactions and solid state reactions. According to Ni/Sn（10μm）/Ni experimental results, the miniaturized solder volume has less impact on the species and growth rate of the IMCs. The grains are still polycrystalline at the interface after solder was totally consumed in solid liquid reaction. A number of voids were observed at the interface in solid state reaction, which were related with IMC characteristics, reaction volume shrinkage and diffusion characteristics. The gold embrittlement issue should be rediscussed under small solder volume condition. When the gold concentration reaches to 1.3wt%, continuous Ni3Sn4 /（Au1-x, Nix）Sn4 interface will be observed. However, Sn-1.3wt% Au just corresponds to 50nm thickness of Au in 10μm solder. Applying solder alloy of Sn-3.9Au-0.5Cu in Ni/Soldr/Ni, the continuous Ni3Sn4 /（Au1-x, Nix）Sn4 interface still observed. Thus, with the miniaturized solder volume to 10μm, the Au thickness should be thinner than 50nm, and Cu concentration should be higher . One of the choices is to use the asymmetric structure of Ni/solder/Cu, which can supply enough Cu to form （Cu, Au, Ni）6Sn5 and prevent continuous （Au1-x, Nix）Sn4 forming at the interface.