A low temperature and low pressure fluxless bonding of plateless Cu-Cu substrates has been achieved by transient liquid phase sintering of Ag and Sn-Bi eutectic powder mixture in a formic acid reducing environment. The effects of Sn-Bi addition amount and sintering temperature to the shear strength and microstructure were investigated. Remelting temperature of the sintered paste was also examined. Shear strength of 30 weight percentage added Sn-Bi that was sintered at 250°C was over than 20 MPa. The microstructure varied with the Sn-Bi addition amount, however, mainly consisted of Ag solid solution and/or Ag-Sn intermetallic compounds (IMCs), Bi-rich phase and Cu-Sn IMCs. No remelting event at Sn-Bi eutectic temperature was observed and the remelting temperature shifted to approximately 262°C, implying the possibility for higher operation temperature although the processing was performed at lower temperature.