Cu nanoparticle paste has become one of the alternative materials for conventional high-temperature packaging, but this sintering process is significantly inhibited by copper oxides. In this paper, the activated formic acid atmosphere was used to achieve high-strength Cu–Cu bonding at low temperature. When sintered at a temperature of 275 °C for 30 min with a pressure of 5 MPa, a shear strength of more than 70 MPa was achieved. In contrast to formic acid atmosphere, the hydrogen radicals generated by activated formic acid atmosphere facilitated the rapid evaporation of the solvent during preheating process. Moreover, the hydrogen radicals effectively reduced of the oxides on the surface of the Cu nanoparticle resulting in a higher shear strength. This Cu nanoparticle sintering method has great potential in the field of power device integration in future.

Polymer adhesives have emerged as a promising dielectric passivation layer in hybrid bonding for 3D integration, but they raise misalignment problems during curing. In this work, the synergistic effect of oxygen plasma surface activation and wetting is utilized to achieve bonding between completed cured polyimides. The optimized process achieves a void-less bonding with a maximum shear strength of 35.3 MPa at a low temperature of 250 °C in merely 2 min, significantly shortening the bonding period and decreasing thermal stress. It is found that the plasma activation generates hydrophilic groups on the polyimide surface, and the wetting process further introduces more −OH groups and water molecules on the activated polyimide surface. The synergistic process of plasma activation and wetting facilitates the bridging of polyimide interfaces to achieve bonding, providing an alternative path for adhesive bonding in 3D integration.

A novel bonding process using Ag agglomerates paste prepared by Ag₂O reduction has been proposed, which solved the problem of Cu substrate oxidation in the conventional Ag₂O sintering process for Cu–Cu bonding. By applying the Ag agglomerate paste to Ag–Ag bonding, a shear strength of 28.3 MPa at 150 °C was obtained. Further studies showed that the optimum sintering temperature was at 225 °C, and a shear strength of 46.4 MPa was obtained. In addition, a shear strength of 20 MPa was obtained at 225 °C for Cu–Cu bonding. Compared to common Ag pastes, the results in this paper revealed that the sintering behavior of Ag agglomerates was unique, and the sintering mechanisms for Ag–Ag and Cu–Cu bonding were also discussed.

Polymer adhesives have emerged as a promising dielectric passivation layer in hybrid bonding for 3D integration while they raise misalignment problems during curing. In this work, the synergistic effect of oxygen plasma surface activation and wetting is utilized to achieve bonding between completed cured polyimides. The optimized process achieves a void-less bonding with a maximum shear strength of 35.3 MPa at a low temperature of 250 °C in merely 2 min, significantly shortening the bonding period and decreasing thermal stress. It is found that the plasma activation generated hydrophilic groups on the polyimide surface, and the wetting process further introduced more -OH groups and water molecular on the activated polyimide surface. The synergistic process of plasma activation and wetting facilitate bridging polyimide interfaces to achieve bonding, providing an alternative path for adhesive bonding in 3D integration.