A study on the low temperature sintering-bonding through in-situ formation of Ag nanoparticles using Ag2O microparticles

Based on the rapid sintering characteristic of nanoparticles at a relatively low temperature, a novel bonding process using Ag metallo-organic nanoparticle paste has been proposed. This paste is considered as an alternative for lead-rich high temperature solder. However, further decrease of bonding temperature and pressure is required for industrial application. Additionally, the cost of Ag nanoparticle preparation is relatively high. In this paper, Ag₂O powders were mixed with triethylene glycol (TEG) as a reducing agent to form a paste, which was used to bond the Ag-coated Cu bulks. The TEG shew its reducibility to Ag₂O at temperature as low as 110 °C. It could be inferred that when the paste was heated above 110°C, in-situ formation of Ag nanoparticles would occur in the sintering process. With the increasing of sintering time and temperature, more and more Ag nanoparticles would be formed and sintered. The effects of sintering-bonding temperature and external bonding pressure on joint strength and microstructures were studied. The shear strength increased with sintering temperature and reached up to about 22MPa at sintering temperature of 250°C under pressure of 2MPa. In addition, the strength first increased with pressure and then began to decrease under 5MPa. Moreover, the microstructures of the joints were observed and analyzed by FE-SEM.