Journal of South China University of Technology (Natural Science Edition) ›› 2016, Vol. 44 ›› Issue (5): 8-14.doi: 10.3969/j.issn.1000-565X.2016.05.002

• Electronics, Communication & Automation Technology • Previous Articles     Next Articles

A Probe into Microstructure of Sn/SnPb Mixed-Assembly Soldered Joints Under Isothermal Aging

ZHOU Bin1,2 LI Xun-ping2 EN Yun-fei2 LU Tao3 HE Xiao-qi2 YAO Ruo-he1   

  1. 1.School of Electronic and Information Engineering,South China University of Technology,Guangzhou 510640,Guangdong,China; 2.Science and Technology on Reliability Physics and Application of Electronic Component Laboratory,The Fifth Electronics Research Institute of the Ministry of Industry and Information Technology,Guangzhou 510610,Guangdong,China; 3.Reliability Research and Analysis Center,The Fifth Electronics Research Institute of the Ministry of Industry and Information Technology,Guangzhou 510610,Guangdong,China
  • Received:2015-11-09 Revised:2016-01-08 Online:2016-05-25 Published:2016-04-12
  • Contact: 姚若河(1961-)，男，教授，博士生导师，主要从事集成电路系统设计、半导体物理及器件研究． E-mail:phrhyao@scut.edu.cn
  • About author:周斌(1981-)，男，博士生，高级工程师，主要从事电子元器件及封装可靠性研究． E-mail:zhoubin722@163． com
  • Supported by:
    Supported by the National Defense Pre-Research Foundation of China(51319070102)，the Natural Science Foundation for Distinguished Young Scholars of Guangdong Province(2015A030306002) and the Natural Science Foundation of Guangdong Province(S2013040011597)

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Abstract: In order to improve the process compatibility and long-term reliability of Sn/SnPb mixed-assembly sol- dered joints,board-level circuits with daisy chain structures were designed,on which Pb-free QFPs (Quad Flat Packages) were assembled with SnPb solder paste through a typical reflow process.Then,a isothermal aging ex- periment of the assembled samples was carried out for 1500h.Moreover,the microstructure,electric performance and mechanical performance of the mixed-assembly soldered joints before and after the aging were analyzed,through which the growth mechanism of IMC (Intermetallic Compounds) at both sides of soldering interfaces and its effect on the electric and mechanical performances of soldered joints were explored.The results show that (1) the growth of Cu6Sn5  andCu3Sn IMC at soldering interfaces exhibits an excellent linear relationship with the square root of aging time,and the decomposition reaction of Cu6Sn5  is the primary growth mechanism of Cu3Sn IMC at soldering interfaces; (2) the Pb phase gathering in soldering interfaces in the aging process cuts off the diffusion pathway of Sn atom and thereby inhibits the further growth of interface IMC; and (3) the coarsening of β-Sn size,the accumulation of Pb-rich phase and the quick growth of interface IMC layer with intrinsic brittleness all result in the decrease of tensile strength of soldered joints,and the thickness of layered IMC reflects the mechanical per- formance of soldered joints to some extent.

Key words: mixed assembly, soldered joint, isothermal aging, intermetallic compounds, reliability