Comparative Study on Solid-State and Metastable Liquid-State Aging for SAC305/Cu Joints

doi:10.1007/s40195-018-0789-2

Abstract

Abstract:

In order to study the influence of the physical state of solder on the interfacial reaction of dip-soldered Sn-3.0Ag-0.5Cu/Cu system, two kinds of experiments were designed, including: (1) solid-state aging between the solder and Cu substrate; (2) liquid-state aging between the metastable supercooled liquid-state solder and Cu substrate. The aging times were 30, 60, 120 and 180 min, respectively, and the aging temperature was 8 °C lower than the melting point of the Sn-3.0Ag-0.5Cu (SAC305) alloy (217 °C). The experimental data revealed that the physical state of the solder obviously affected the formation of the intermetallic compound (IMC), and resulted in the difference in the diffusion of atoms on the interface between the SAC305 solder and Cu substrate. The IMC interface after aging for 30 min presents unique characteristics compared with that of the sample after dip soldering. The IMC interface of solid-state aged SAC305/Cu couple is relatively planar, while the IMC interface under metastable supercooled liquid-state aging conditions presents scallop-like shape.

Key words: Lead-free solder, Supercooling, Metastable liquid state, Aging, Intermetallic compound

Shuang Li, Xiao-Wu Hu, Wei-Guo Zhang, Yu-Long Li, Xiong-Xin Jiang. Comparative Study on Solid-State and Metastable Liquid-State Aging for SAC305/Cu Joints[J]. Acta Metallurgica Sinica (English Letters), 2019, 32(5): 629-673.

Figures/Tables 10

Fig. 1 Time-temperature curves a-c and exothermic curves a1-c1 of SAC305/Cu-soldered samples under conditions of reflowing a, a1, solid-state aging at 209 °C for 60 min b, b1 and metastable supercooled liquid-state aging at 209 °C for 60 min c, c1

Fig. 2 Cross-sectional microstructures of SAC305/Cu solder joints after dip soldering for 3 s a, solid state aged for 30 min b and metastable supercooled liquid aged for 30 min c and EDS analysis of spectrums 1 d and 2 e from Fig. 1c

Fig. 3 Cross-sectional microstructures of SAC305/Cu solder joints under solid-state aging a-c and metastable supercooled liquid aging d-f for 60 min a, d, 120 min b, e, 180 min c, f

Fig. 4 Schematic diagram of nanochannels between Cu6Sn5 grains

Fig. 5 XRD pattern of SAC305/Cu solder joint aged at 209 °C for 60 min under supercooled metastable liquid-state condition

Fig. 6 Morphologies of SAC305/Cu interfacial compound grains aged at 209 °C under conditions of solid-state aging a, c, e, g and metastable supercooled liquid aging b, d, f, h for 30 min a, b, 60 min c, d, 120 min e, f, 180 min g, h

Table 1 IMC thickness (μm) with increasing aging time under various aging state

Aging time (min)	Solid-state aging	Metastable supercooled liquid aging
30	3.17	6.25
60	3.84	9.53
120	4.41	11.27
180	4.87	12.23

Fig. 7 Relationships of total IMC thickness on SAC305/Cu interfaces with square root of aging time on different aging conditions

Table 2 Average grain diameter (μm) with increasing aging time under various aging state

Aging time (min)	Solid-state aging	Metastable supercooled liquid aging
30	3.87	10.69
60	4.84	13.60
120	5.25	16.28
180	5.88	21.08

Fig. 8 Plots of Cu6Sn5 grain mean diameters (d) versus aging time (t) on logarithm coordinates at different physical state

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