Abstract: The Cu/Sn/Cu-xZn (x=0,5,20 wt.%) solder joints were chosen as research object to study the effect of Zn content on the liquid-solid interfacial reactions during isothermal reflow and reflow under temperature gradient (TG). During isothermal reflow, the intermetallic compounds (IMCs) at the two ends of the micro solder joints grow symmetrically. With the increase of Zn content, the thickness of the IMCs at the two ends of the micro solder joints decreased slightly, indicating that the addition of Zn to the Cu substrate had no significant effect on the growth of the interfacial IMCs during isothermal reflow. During reflow under TG, the IMCs at the cold and hot ends grew asymmetrically. As the Zn content increased, the thickness of the IMCs at the cold end decreased significantly, indicating that the addition of Zn had a significant inhibiting effect on the growth of IMCs at the cold end interface. This is due to the fact that the addition of Zn reduced the thermomigration induced atomic flux for the IMC growth at the cold end. In addition, it was found that the formation of a Cu(Sn,Zn) layer at the interface more effectively suppressed the dissolution of the hot end substrate, resulting in a sharp decrease in the growth rate of the cold end IMCs of the Cu/Sn/Cu-20Zn micro solder joints. Based on the interfacial IMC growth behavior with reflow time, the growth kinetics of the IMCs at the two ends of the Cu/Sn/Cu-xZn micro solder joints during isothermal reflow and reflow under TG was obtained.

Key words: electronic packaging, Cu-Zn substrates, interfacial reactions, thermonigration, IMCs growth