Article

Journal of Electronic Materials

, Volume 35, Issue 1, pp 89-93

Microstructure, solderability, and growth of intermetallic compounds of Sn-Ag-Cu-RE lead-free solder alloys

  • C. M. T. LawAffiliated withDepartment of Physics and Materials Science, City University of Hong Kong
  • , C. M. L. WuAffiliated withDepartment of Physics and Materials Science, City University of Hong Kong
  • , D. Q. YuAffiliated withDepartment of Physics and Materials Science, City University of Hong KongDepartment of Materials Engineering, Dalian University of Technology
  • , L. WangAffiliated withDepartment of Materials Engineering, Dalian University of Technology
  • , J. K. L. LaiAffiliated withDepartment of Physics and Materials Science, City University of Hong Kong

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Abstract

The near-eutectic Sn-3.5 wt.% Ag-0.7 wt.% Cu (Sn-3.5Ag-0.7Cu) alloy was doped with rare earth (RE) elements of primarily Ce and La of 0.05–0.25 wt.% to form Sn-3.5Ag-0.7Cu-xRE solder alloys. The aim of this research was to investigate the effect of the addition of RE elements on the microstructure and solderability of this alloy. Sn-3.5Ag-0.7Cu-xRE solders were soldered on copper coupons. The thickness of the intermetallic layer (IML) formed between the solder and Cu substrate just after soldering, as well as after thermal aging at 170°C up to 1000 h, was investigated. It was found that, due to the addition of the RE elements, the size of the Sn grains was reduced. In particular, the addition of 0.1wt.%RE to the Sn-3.5Ag-0.7Cu solder improved the wetting behavior. Besides, the IML growth during thermal aging was inhibited.

Key words

Lead-free solder rare earth (RE) elements solderability test intermetallic layer