The Paton Welding Journal, 2020, #6, 27-30 pages
Effect of Co addition on interface reaction between Sn–Ag–Cu solder and Cu substrate
Jianxin Wang, Yun Zhou and Taikun Fan
Jiangsu Provincial Key Laboratory of Advanced Welding Technology,
Jiangsu University of Science and Technology,
Zhenjiang, Jiangsu, China. E-mail: wangjx_just@126.com
Abstract
Sn−Ag−Cu (SAC) alloys are considered as the most promising Pb-free solders in electronic industry. The solidification
microstructure and interface reaction behaviors of SAC alloys are therefore of fundamental importance for the service
reliability of electronic devices. This is particularly true for these SAC alloys with low silver contents, partially because
the coarsened interfacial intermetallics (IMCs) of these low-Ag SAC alloys with higher surface tension than conventional
near-eutectic SAC alloys. As a result, it is desirable to refine the grain size of interfacial IMCs between low-Ag
alloys and common substrates such as Cu. In this work, the effects of addition of trace amount of Co on the interface reaction
between both conventional SAC305 and low-Ag SAC107 alloys on Cu substrate have been studied by reflowing
experiments at temperature close to 260 °C. In addition, effects of Co additions on the solid state growth of interfacial
IMCs have been studied at 150 °C after ultra-long annealing treatment for 384h, 768, and 1536h. Both top-view and
cross-section micro-graphs have been obtained using electron microscopes. It has been found that addition of trace
amount of Co can significantly refine the interfacial Cu6Sn5 IMCs grains after reflow process and impede the growth of
Cu3Sn after annealing treatment. This attributed to the replacement of Cu atoms by Co atoms in Cu6Sn5 crystals, which
in turn depresses the diffusion of Cu and impedes the transformation from Cu6Sn5 to Cu3Sn during aging.
Keywords: lead-free solder, Sn−Ag−Cu, intermetallic compound, microstructure
Received 26.05.2020
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Suggested Citation
Jianxin Wang, Yun Zhou and Taikun Fan (2020) Effect of Co addition on interface reaction between Sn–Ag–Cu solder and Cu substrate.
The Paton Welding J., 06, 27-30.