Influence of Temperature and Current Stressing on Cu‐Sn Intermetallic Compound Growth Characteristics of Lead‐Free Microbump

Abstract

A numerical analysis of the Cu flux on Cu/Sn/Cu is successfully used to establish kinetic models that are verified with reported data. Kinetic models are adopted to discuss the polarity effect of intermetallic compounds (IMCs) growth at different alloying stages. The models reveal that, before Sn solder is depleted during thermal aging, the net thermodiffusion Cu flux in Cu6Sn5 is over three times larger than that in Cu3Sn. While coupling with current stressing, the IMCs thickness increases from parabola‐like curves to a linear‐like relationship. The degree of influence decreases in the order of Cu6Sn5 on anode, Cu6Sn5 on cathode, Cu3Sn on anode, and Cu3Sn on cathode. Electromigration Cu flux in Sn is the critical factor that accelerates the anode's Cu6Sn5 growth, and its influence on the growth rate over 1000 times that on the anode's Cu3Sn. After Sn solder is depleted, Cu6Sn5 gradually converts into Cu3Sn, and its thickness is linearly decreases with square root of annealing time. When coupling with a current density of 1.0 × 105 A cm−2, the thickness ratio of Cu3Sn/Cu6Sn5 reduces from 1:2 to 1:6. Remarkably, irrespective of whether current exists or not, the depletion of Cu6Sn5 always takes much longer than that of Sn solder.