Abstract
In this work we studied the initial microstructure and microstructural evolution of eutectic Au-Sn solder bumps on Cu/electroless Ni/Au. The solder bumps were 150–160 m in diameter and 45–50 m tall, reflowed on Cu/electroless Ni/Au, and then aged at 200°C for up to 365 days. In addition, Au-Ni-Sn-alloys were made and analyzed to help identify the phases that appear at the interface during aging. The detailed interfacial microstructure was observed using a transmission electron microscope (TEM). The results show that the introduction of Au from the substrate produces large islands of-phase in the bulk microstructure during reflow. Two Au-Ni-Sn compounds are formed at the solder/substrate interface and grow slowly during aging. The maximum solubility of Ni in the—phase was measured to be about 1 at.% at 200°C, while Ni in the-phase is more than 20 at.%. The electroless Ni layer is made of several sublayers with slightly different compositions and microstructures. There is, in addition, an amorphous interaction layer at the solder/electroless Ni interface.
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Song, H.G., Ahn, J.P. & Morris, J.W. The microstructure of eutectic Au-Sn solder bumps on Cu/electroless Ni/Au. J. Electron. Mater. 30, 1083–1087 (2001). https://doi.org/10.1007/s11664-001-0133-9
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DOI: https://doi.org/10.1007/s11664-001-0133-9