Low-temperature nano-Ag bonding below 150 °C via reductive surface activation of an organic-free film

Achieving high-strength die attach below 150 °C process temperature using nano-Ag paste remains a great challenge, primarily due to the insufficient atomic diffusion driving force and the presence of organic additives in conventional nano-Ag pastes. In this work, an organic-free nano-Ag film combined with a Pt-catalyzed formic acid atmosphere was firstly proposed for low-temperature die attachment. A high shear strength of 45.3 MPa was achieved at 150 °C under a pressure of 5 MPa for 30 min. Notably, even when the bonding temperature was reduced to 100 °C, a shear strength of 21.2 MPa was still obtained. These results demonstrate a substantial improvement in bonding strength over existing low-temperature nano-Ag sintering studies conducted at similar temperatures. TEM and XPS analyses reveal that the Pt-catalyzed formic acid atmosphere effectively reduces the oxidative amorphous shell on the nano-Ag particle surfaces, leading to the formation of a crystalline surface layer at the bonding temperature. Reactive molecular dynamics simulations further demonstrate that the oxidative amorphous shell suppresses atomic kinetic energy, thereby significantly retarding neck growth and densification during sintering. This work establishes an effective strategy for achieving low-temperature nano-Ag bonding through the combination of organic-free films and reductive surface activation.