Effects of temperature gradients on the growth kinetics of CoSn3 at Co-P/Sn/Co-P interface

Abstract

In this paper, the interfacial reaction of Co- P/Sn/Co-P solder joints at temperature gradients of 1110°C/cm and 1620°C/cm was studied. After stressing for 400h at 1110°C/cm, the average intermetallic compound (IMC) thickness of cold and hot end increased from 4.162μm and 4.249μm to 6.012μm and 4.838μm, respectively, with a total growth of 2.439μm. After stressing for 400h at 1620°C/cm, the average IMC thickness of cold and hot end increased from 3.569μm and 3.799μm to 5.981μm and 4.286μm, respectively, with a total growth of 2.899μm, indicated that the larger temperature gradient was more likely to induce the growth of full CoSn 3 IMC joints. The power rate empirical function h= K•tn was used to calculate the relationship between IMC thickness and stressing time. The time index of interfacial CoSn 3 growth at the hot and cold end under 1110°C/cm was 0.12 and 0.05, respectively, while the index under 1620°C/cm was 0.17 and 0.04, respectively, the growth mechanism of CoSn 3 were all controlled by grain boundary diffusion. With the increase of temperature gradient, the time index ratio of CoSn3 growth of the cold end and hot end increased from 2.4 to 4.25, indicated that the larger temperature gradient is more favorable for inducing asymmetric growth of interfacial CoSn3 IMC. Therefore, the extreme temperature gradients can induce the growth of CoSn3 IMC in solder joints, which supplies the significant theoretical foundation and reference for the potential application of full IMC solder joints.