Abstract
Transient liquid phase bonding has been proven to offer exceptional joining strength and dependable high temperature service in chip stacking applications. Nevertheless, conventional Cu/Sn/Cu transient liquid phase bumps had shortcomings, such as smooth phase boundaries and coarsening grains. In this study, the variation of microstructure in Cu/Sn-3.0Ag-0.5Cu/Cu, Cu/Sn-3.0Ag-0.5Cu/Ni, and Ni/Sn-3.0Ag-0.5Cu/Cu transient liquid phase bonds with the sizes less than 10 μm before and after long term aging were investigated. Due to the dissolution of Ni atoms from the substrates at the cold or hot end, the structure exhibited randomly-oriented and small-sized grains. After 1000 h aging treatment, the Ni-containing specimen still retained the abundant grain structure and appeared network-like morphology of Cu3Sn near phase boundaries. Additionally, the shear testing was applied in the aged samples, Ni-doped joints demonstrated better mechanical properties than Ni-free joining. The enhancement of shear strength was attributed to Ni addition, retaining the advantageous grain structure. This present work showed that doping Ni to micro-bumps could halt the deterioration of grain structure over extended usage of electronic devices in 3D-IC technology.
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