Compressive Sinter Bonding in Air Between Cu Finishes Using Paste Containing Composite Ag₂O-Cu Filler

A Ag₂O-Cu composite filler was adopted as a sintering material between Cu finishes under compression to achieve the high-speed bonding of dies in an air atmosphere via a cost-effective paste and finish process. The commercial Cu particles had an average size of 2 μm, and the synthesized Ag₂O particles were in the submicrometer range with an average size of 210 nm. The Ag₂O particles in the paste started decomposing at ∼150 °C, and the liquid-type reductant in the paste effectively reduced the oxide layers on the Cu particles as well as the upper and lower Cu finishes during bonding. Therefore, the in situ-generated active Ag and fresh Cu surfaces enabled significantly rapid sinter bonding under 5 MPa compression. Only 30 s of bonding at 300 °C was required to achieve an excellent shear strength of 27.8 MPa in the created bond-line, while 90 s of bonding produced a near-full-density structure with a strength of 41.9 MPa despite solid-state sintering when the 3:7 (Cu particles:Ag₂O particles) mixing ratio was used. Well-dispersed Ag₂O particles did not create a non-sintered interface or form large voids upon outgassing during decomposition. The out-diffused Cu was reoxidized after sintering with Ag, forming irregularly dispersed Cu₂O shells that remained in the microstructure of the full-density bond-line. Graphical Abstract: [Figure not available: see fulltext.].