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| ELECTROCHEMICAL CORROSION BEHAVIOR AND DENDRITE GROWTH OF Sn-0.7Cu SOLDER ON FR-4 PRINTED CIRCUIT BOARD PLATED WITH Cu |
| HUA Li1,2, GUO Xingpeng1, YANG Jiakuan2 |
1. School of Chemistry and Chemical Engineering, Huazhong University of Science and Technology, Wuhan 430074
2. School of Environmental Science and Engineering, Huazhong University of Science and Technology, Wuhan 430074 |
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Abstract Electrochemical corrosion characteristics and dendrites growth of lead-free Sn-0.7Cu solder on FR-4 printed circuit board plated with Cu were investigated by potentiodynamic polarization coupled with scanning electron microscope, energy dispersion X-ray analysis and X-ray diffraction analysis. The results showed that the corroded metal in solder alloy was primarily Sn, and the corrosive current density increased with electric field intensity increasing. In low electric field, uniform corrosion took place, while in high electric field, the inhomogeneous corrosion existed. “Bridge interconnection” caused by dendrite growth severely impacted on the reliability of electronic products due to short circuit. Results of EDAX analysis indicated that on dendrites the content of Cu was larger than Sn, which implied the electromigration and deoxidization capacity of Cu2+ were larger than those of Sn2+. There was crystal tropism characteristics for dendrite growth: the orientations with fastest growth rate were from four directions, the growth was spiraled from inter to outer, and the favor tropisms of crystal particles on dendrites were (411) and (220). The stronger the electric field intensity, the faster the growth of dendrites, the shorter the bridge time. The bridge time of two electrodes with 3 mm fine-pitch after dendrite growth was respectively 12.5 h for 8 V, 20.4 h for 5 V, 28.5 h for 3 V, and 39.6 h for 1 V. XRD showed that the primary corrosive products were SnO2，SnCl4, while the contents on dendrites were Sn，SnO2，SnCl4，Cu，CuCl2.
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Received: 16 October 2009
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Corresponding Authors:
GUO Xingpeng
E-mail: guoxp@mail.hust.edu.cn
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