Die sinter bonding in air using copper formate preform for formation of full-density bondline
(Department of Materials Science and Engineering, Seoul National University of Science and Technology, 232 Gongneung-ro, Nowon-gu, Seoul 139-743, Korea)
Abstract: Pressure-assisted sinter bonding was performed in air at 250-350 °C using a preform comprising copper formate particles to form a bondline that is sustainable at high temperatures. H2 and CO generated concurrently by the pyrolysis of copper formate at 210 °C during the sinter bonding removed the native oxide and other oxides grown on bulk Cu finishes, enabling interface bonding. Moreover, Cu produced in situ by the reduction of Cu(II) accelerated the sinter bonding. Consequently, the bonding achieved at 300-350 °C under 5 MPa exhibited sufficient shear strength of 20.0-31.5 MPa after 180-300 min of sinter bonding. In addition, an increase in pressure to 10 MPa resulted in shear strength of 21.9 MPa after an extremely short time of 30 s at 250 °C, and a near-full-density bondline was achieved after 300 s. The obtained results indicate the promising potential of the preform comprising copper formate particles for high-speed sinter bonding.
Key words: structural materials; microstructure; mechanical properties; copper formate preform; sinter bonding; pyrolysis