Compositional dependence of Sn-Zn solder on the intermetallic compound (IMC) growth kinetics with Cu at thin film scales

• Main Author: Hidajat, Vincent Sebastian.
• Other Authors: Gan Chee Lip
• Format: Final Year Project
• Language: English
• Published: 2013
• Subjects: DRNTU::Engineering
• Online Access: http://hdl.handle.net/10356/52244
• Institution: Nanyang Technological University

The development of lead-free solders in microelectronics packaging industry attracts both manufacturers and researchers to study the effect of alloying elements to the reliability of solder joint. One of the most important factors to be examined is the growth of intermetallic compound (IMC) layer in the interfacial region between conductor metal and solder alloy. By studying the thermodynamic and kinetic aspects of the IMC layer, one can compare the interfacial activities between different device packages under a given environmental condition. In this project, the effect of zinc concentration to the growth of IMC in Cu/Sn-Zn system was evaluated. The conventional ex-situ heating followed by cross-section analysis not only suffers in accuracy, but the experimental setup is also tedious. A simple yet efficient method to quickly investigate IMC growth kinetics in Cu/Sn-Zn system was demonstrated in this study. By observing the optical colour change of copper, one can quickly evaluate the growth kinetics of intermetallic layer. From our experiment, we found that the addition of zinc replaces the growth of Cu6Sn5 and Cu3Sn IMC layers into a single Cu5Zn8 layer. The threshold concentration was found to be 2%at zinc for it to be the main diffusing species in Cu/Sn-Zn system. We also concluded that Cu5Zn8 IMC layer has a lower activation energy than the former Cu-Sn IMC layers. However, as zinc concentration is increased further, the diffusion rate of solder increases and thus accelerates the formation of Cu5Zn8 IMC layer. Therefore, Zn content in the solder has to be carefully controlled to allow the fastest/slowest IMC growth in the solder joint.