Evolution of Interfacial Intermetallic Compounds in Ni/Sn-xCu/Ni Micro Solder Joints Under Thermomigration During Soldering
Ning ZHAO1(),Jianfeng DENG1,Yi ZHONG1,Luqiao YIN2
1 School of Materials Science and Engineering, Dalian University of Technology, Dalian 116024, China 2 Key Laboratory of Advanced Display and System Applications, Ministry of Education, Shanghai University, Shanghai 200072, China
Cite this article:
Ning ZHAO,Jianfeng DENG,Yi ZHONG,Luqiao YIN. Evolution of Interfacial Intermetallic Compounds in Ni/Sn-xCu/Ni Micro Solder Joints Under Thermomigration During Soldering. Acta Metall Sin, 2017, 53(7): 861-868.
The effect of Cu content on the evolution of intermetallic compounds (IMCs) in Ni/Sn-xCu/Ni (x= 0.3, 0.7, 1.5, mass fraction, %) micro solder joints during soldering at 240 ℃ under a temperature gradient of 1045 ℃/cm was investigated. Asymmetrical growth and transformation of interfacial IMCs and asymmetrical dissolution of Ni substrate were clearly observed. In Ni/Sn-0.3Cu/Ni micro solder joints, though the interfacial IMC remained as the initial (Ni, Cu)3Sn4, asymmetrical IMC growth between cold and hot ends occurred, i.e., the (Ni, Cu)3Sn4 IMC at the cold end was obviously thicker than that at the hot end. In Ni/Sn-0.7Cu/Ni and Ni/Sn-1.5Cu/Ni micro solder joints, the interfacial IMC gradually transformed from the initial (Cu, Ni)6Sn5 into (Ni,Cu)3Sn4. Meanwhile, the transformation at the cold end lagged behind the hot end, namely asymmetrical transformation phenomenon occurred. Moreover, the transformations at the cold and hot ends in the Ni/Sn-1.5Cu/Ni micro solder joints both lagged behind those in the Ni/Sn-0.7Cu/Ni micro solder joints. Based on the analysis of the Cu and Ni atomic fluxes for the IMC growth at both cold and hot ends, the thermomigration (TM) direction was confirmed to be from the hot end towards the cold end. The Cu concentration in the micro solder joints had a significant effect on the main TM element, and thus affected the growth and transformation behavior of the interfacial IMCs at the two ends. In addition, TM promoted the diffusion of Ni atoms into solder at the hot end, which accelerated the dissolution of the hot end Ni substrate. Most of the dissolved Ni atoms migrated to the cold end and participated in interfacial reaction locally. On the contrary, TM inhibited the diffusion of Ni atoms at the hot end, resulting in no obvious dissolution of the cold end Ni substrate.
Fund: Supported by National Natural Science Foundation of China (No.51675080) and Key Laboratory of Advanced Display and System Applications, Ministry of Education (Shanghai University) (No.P201601)
Fig.1 Schematics of Ni/Sn-xCu/Ni micro solder joint (a) and experimental configuration for thermomigration (b)
Fig.2 Simulated temperature distribution in the liquid solder layer of the micro solder joint
Fig.3 SEM images of the as-soldered Ni/Sn-xCu/Ni micro solder joints with x=0.3 (a), x=0.7 (b) and x=1.5 (c)
Fig.4 SEM images of the Ni/Sn-0.3Cu/Ni micro solder joints after reflowed on hot plate for 3 min (a), 15 min (b), 30 min (c) and 60 min (d)
Fig.5 SEM images of Ni/Sn-0.7Cu/Ni micro solder joints after reflowed on hot plate for 3 min (a), 15 min (b), 30 min (c) and 60 min (d)
Fig.6 SEM images of Ni/Sn-1.5Cu/Ni micro solder joints after reflowed on hot plate for 3 min (a), 15 min (b), 30 min (c) and 60 min (d)
Fig.7 Thicknesses of intermetallic compounds (IMCs) at both cold and hot ends in the Ni/Sn-xCu/Ni micro solder joints as a function of reaction time
Fig.8 Schematic of Cu and Ni atomic fluxes in Ni/Sn-xCu/Ni micro solder joint during reflow on a hot plate (JTM, JChem and JDis are the atomic fluxes induced by thermomigration, chemical potential, and Ni dissolution, respectively)
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