Low-temperature Cu-Cu bonding by self-reduction of particle-free Ag ion paste

We proposed a low-temperature Cu-Cu bonding method by a new type of self-reducible Ag ion paste in this paper. The Ag ion paste is free of any particles or precipitates, which can be easily prepared and stored. Because of its high dispersion characteristic, the Ag ion paste can also be uniformly coated or written on substrates. With a heating temperature of 200 °C in the air, the Ag ion paste can be reduced to pure Ag file after 10 min, the excessive organic solvents and byproducts in the reducing reaction were volatilized. By using the Ag ion paste as a bonding interlayer, the Cu-Cu interconnect can also be achieved at 200 °C and under a bonding pressure of 1 MPa. After bonding, the Cu-Cu interface was observed and the shear strength of the joint was tested. From the characterization, the Cu-Cu interconnect was confirmed to be a compacted structure, with a high bonding strength over 20 MPa. Due to the high melting point, high electrical and thermal conductivity of Ag, the proposed Ag ion paste represents a strong application prospect in high-power device packaging.