Effects of Initial Morphology on Growth Kinetics of CuSn at SAC305/Cu Interface during Isothermal Aging.

Solder/Cu joints are important components responsible for interconnection in microelectronics. Construction of the solder/Cu joints through liquid/solid (L/S) reactions accompanies the formation of the Cu-Sn intermetallic compounds (IMCs) at the joint interface. The CuSn IMC exhibits remarkable distinctions in thickness and morphology upon increasing the L/S reaction time. Effects of the initial characteristics of thickness and morphology on the growth kinetics of CuSn during subsequent isothermal aging were investigated. SAC305 solder was reflowed on a Cu electroplated layer at 265 °C for 1 to 60 min to produce the CuSn IMC with different thickness and morphology at the SAC305/Cu interface. The as-fabricated SAC305/Cu joint samples were aged at 200 °C for 72 to 360 h to investigate the growth kinetics of CuSn. The results show that the initial characteristics of thickness and morphology significantly influenced the growth kinetics of CuSn during the subsequent solid/solid (S/S) reaction. A prolonged L/S reaction time of 60 min (L/S-60) produced a scallop-type CuSn IMC with a larger grain size and a thicker thickness, which reduced the quantity of fast diffusion path (grain boundary) and the magnitude of concentration gradient, thus slowing down the growth rate of CuSn. According to the growth kinetics analysis, the growth rate constant of CuSn could be remarkably reduced to 0.151 µm/h for the L/S-60 sample, representing a significant reduction of 70 % compared to that of the L/S-1 sample (0.508 µm/h for L/S reaction time of 1 min).