Effect of Thermal Aging on the Reliability of Interconnected Nano-Silver Solder Joints

Abstract

Due to the growing demand for ultra-high-density integrated circuits in the integrated circuit industry, flip-chip bonding (FCB) has become the mainstream solution for chip interconnection. In flip-chip bonding (FCB), however, alloy solder is no longer adequate to meet the high heat dissipation demands of high-power devices with over 100 kW/cm2 in power density due to its low reflow temperature. Nano-silver solder, on the other hand, exhibits superior thermal and electrical conductivity, making it an excellent alternative to traditional solder for FCB. This study explored nano-silver’s thermal reliability and electrical performance as a solder material. The following results were obtained through temperature cycle (with temperatures ranging from −55 to 150 °C) and high-temperature storage experiments (with applied temperatures of over 170 °C). The results indicate that as the duration of the high-temperature storage increased, the grain continued to coarsen, resulting in an average pore size transition from 0.004 to 0.072 μm2. A strong correlation coefficient of 0.9913 was observed between the duration of high-temperature exposure and the porosity within the time range of 0–200 h. Following the reliability test, the shear strength of the nano-silver interconnect samples showed varying degrees of decrease. The bonding effect with the nano-silver layer can be enhanced, and the thermal reliability can be improved by depositing Ni/Ag on the surface of Cu, making it less prone to cracking. Regarding the electrical performance, the square resistance of the nano-silver interconnect structures increased by 35% after the reliability test. This indicates a significant degradation in the electrical reliability of nano-silver interconnects under temperature stress.