Morphology and Growth of Intermetallics at the Interface
of Sn-based Solders and Cu with Different Surface Finishes |
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Authors: | Ruihong Zhang Fu Guo Jianping Liu Hao Shen Feng Tai |
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Affiliation: | (1) College of Materials Science and Engineering, Beijing University of Technology, Beijing, 100124, People’s Republic of China |
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Abstract: | Several types of surface finishes have been applied on Cu substrates in an effort to facilitate bonding and improve the reliability
of lead-free solder joints. In the current research, the effects of printed circuit board surface finishes on the reliability
of the solder joints were investigated by examining the morphology and growth behavior of the intermetallic compounds (IMCs)
between Sn-based solders and different surface finishes on Cu. Three types of Cu substrates with different surface finishes
were fabricated in this study: organic solderability preservative (OSP)/Cu, Ni/Cu, and electroless nickel immersion gold (ENIG)/Cu.
Sn-3.5Ag and Sn-3.0Ag-0.5Cu were used as the solders. In the experiment, the solder joint specimens were aged isothermally
at 150°C for up to 1000 h. Experimental results revealed that the OSP surface finish promoted the interdiffusion between Cu
and Sn during soldering. The composition and morphology of the IMC layer at the solder/Ni/Cu interface were sensitive to the
Cu concentration in the solder. Meanwhile, the solder joints with different morphological features of the IMCs exhibited significant
differences in shear strengths. The Au-containing ENIG surface finish affected the shear strength of the solder joint significantly
at the initial stage of isothermal aging. |
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Keywords: | IMC surface finishes microstructure shear strength |
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