PHASE FIELD SIMULATION ON MICROSTRUCTURE EVOLUTION AND GROWTH KINETICS OF Cu6Sn5 INTERMETALLIC COMPOUND DURING EARLY INTERFACIAL REACTION IN Sn/Cu SOLDERING SYSTEM
KE Changbo1,2(), ZHOU Minbo2, ZHANG Xinping2
1 School of Mechanical and Automotive Engineering, South China University of Technology, Guangzhou 510640 2 School of Materials Science and Engineering, South China University of Technology, Guangzhou 510640
Cite this article:
KE Changbo, ZHOU Minbo, ZHANG Xinping. PHASE FIELD SIMULATION ON MICROSTRUCTURE EVOLUTION AND GROWTH KINETICS OF Cu6Sn5 INTERMETALLIC COMPOUND DURING EARLY INTERFACIAL REACTION IN Sn/Cu SOLDERING SYSTEM. Acta Metall Sin, 2014, 50(3): 294-304.
In the continuous pursuit of miniaturization, multifunction and high-reliability of electronic products and devices, the packing density has been increasing and the dimension of solder joints has been scaling down. In electronic packaging, during the soldering process being employed to Sn-based solders, an intermetallic compound (IMC) layer is formed between molten solder and pad (or under bump metallization, UBM), whose morphology and thickness as well as growth kinetics play an important role in controlling the service performance of the solder joints, in particular for solder interconnects with the decreasing size where the interfacial IMC layer takes up a high volume fraction in the solder joint. Thus, characterizing the morphology change and growth kinetics of interfacial IMC layer is very important to optimize the soldering process and evaluate the reliability of solder interconnects. In this study, a multi-phase-field model is applied to intensively account for the effect of grain boundary diffusion coefficient () and IMC/liquid interfacial energy on the morphology evolution and and growth kinetics of IMC. The simulation results show that Cu6Sn5 grains grow up and contact with each other exhibiting a scallop-like morphology which can be influenced by both the grain boundary diffusion coefficient and IMC/liquid interfacial energy. The IMC growth process exhibits three stages, including the initial stage associated with Cu6Sn5 grain broadening followed by the transition stage characterized by scallop shape formation and the last normal growth stage dominated by IMC layer thickening and concurrent Cu6Sn5 grain coarsening. It is also found that the IMC layer thickness increases with grain boundary diffusion coefficient but decreases with IMC/liquid interfacial energy, while the scallop average width decreases with grain boundary diffusion coefficient and increases with IMC/liquid interfacial energy. The relationships between IMC layer thickness/width and reaction time can be well fitted by an exponential growth law, in which the large grain boundary diffusion coefficient combined with (where is the grain boundary energy) can produce precise growth exponent closing to that in the ideal solid-liquid interface reaction.
Fund: Supported by National Natural Science Foundation of China (Nos.51275178 and 51205135) and Specialized Research Fund for the Doctoral Program of Higher Education of China(No.20110172110003) and Fundamental Research Funds for the Central Universities (No.2013ZM0026)
Fig.4 Curves of IMC layer thickness (a) and average width of Cu6Sn5 scallop-type grains (b) vs time for different grain boundary diffusion coefficients
Fig.5 Exponential curves fitting for IMC layer thickness vs time during normal growth stage for different grain boundary diffusion coefficients
IMC layer thickness
Scallop average width
R2
KW
nW
R2
2.0×103Dη
35.44
0.35
0.998
23.16
0.32
0.997
2.0×102Dη
28.80
0.37
0.997
25.54
0.27
0.991
Dη
22.52
0.40
0.991
16.27
0.48
0.989
Table 2 Exponential fitting results of variations of IMC layer thickness and average width of Cu6Sn5 scallop-type grains with time during normal growth stage for different grain boundary diffusion coefficients
Fig.6 Microstructure of IMC layer with different levels of interfacial energy (t=6 s) (a) =0.08 J/m2 (b) =0.15 J/m2 (c) =0.24 J/m2 (d) the energy balance relationship in triple junction point ( θ is the semi-dihedral angle)
Fig.7 Curves of IMC layer thickness (a) and average width of Cu6Sn5 scallop-type grains (b) vs time for different levels of interfacial energy (DGB=2.0×103Dη)
σηL/ J/m2
IMC layer thickness
Average width of Cu6Sn5 grain
R2
KW
nW
R2
0.24
25.76
0.36
0.994
26.32
0.19
0.998
0.15
35.44
0.35
0.998
23.16
0.32
0.997
0.08
36.83
0.42
0.997
27.76
0.23
0.998
Table 3 Exponential fitting results of variations of IMC layer thickness and average width of Cu6Sn5 scalloptype grains with time during normal growth stage for different levels of interfacial energy
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