Electrical properties of AU-GE solder under high temperature

• Main Author: Lau, Fu Long
• Other Authors: Gan Chee Lip
• Format: Theses and Dissertations
• Language: English
• Published: 2014
• Subjects: DRNTU::Engineering::Materials::Electronic packaging materials
• Online Access: https://hdl.handle.net/10356/61875
• Institution: Nanyang Technological University

Ruggedized electronics are defined as electronics that can withstand harsh operating environment. A key requirement for ruggedized electronics is reliability. One of the areas for reliability study is solder interconnects. Solder is used to deliver electric signal and power, and is a critical component in electronics package assembly. Operating under high temperature may impact its electrical property. Another reliability issue in solder interconnect is electromigration (EM). This issue will worsen with increasing current density due to miniaturization, or with a higher operating temperature as required in ruggedized electronics. The use of high temperature solders is relatively new with limited research, and this work aims to understand their reliability physics. The effect of thermal aging on the electrical resistivity of bulk Au-Ge and electrical resistance on Au-Ge solder joint was studied. It is observed that the electrical resistivity in bulk Au-Ge will decrease with aging and stabilize to a lower value. This is due to the effect of Au grain growth which reduces the grain boundaries that leads to lesser electrons scattering. On the other hand, electrical resistance in Au-Ge solder joint increases after aging. This is contributed by the growth of intermetallic compound (IMC), and micro voids in electroless-Ni (P) layer. Ni will react with Ge to form IMC that contributes to the increase in electrical resistance. This study concludes that Au-Ge is potential candidates as a high temperature solder interconnection for ruggedized electronics, but its reliability is compromised by the Ni diffusion barrier. Lastly, EM behavior in Au-Ge was also studied. It shows that EM results in void growth that leads to open failure, and polarity growth of IMC at the interface. Polarity growth causes the IMC growth to be enhanced at the anode side, while IMC growth is retarded at the cathode side during the EM stressing. This will further degrade the reliability of the Au-Ge solder under high temperature and current density.