Cu-Cu bonding is always conducted at high temperature and high pressure in reductive atmosphere to eliminate the influence caused by oxidation. Herein, a novel low-pressure sinterable Cu nanoparticle (Cu-NPs) paste was developed using Cu Metal Organic Decomposition (MOD) ink as solvent and surface modifier. The Cu MOD ink in paste introduced in Cu nanoparticle paste not only eliminated the surface oxidation of Cu-NPs, but also modified Cu-NPs with Cu atoms due to the thermal decomposition during sintering process. As a result, robust Cu sinter joints for die-attachment could be realized at a low pressure of 0.4 MPa in non-reductive nitrogen atmosphere. Using the paste with 20 wt.% Cuf addition in solvent, a relative high shear strength of 17.1 MPa could be achieved at 300 °C, which is about 3.8 times higher than that sintered without MOD ink (4.5 MPa). When bonding temperature rose to 350 °C, even higher shear strength over 20 MPa was obtained. The bonding strength was comparable to the traditional Pb-5Sn solder alloy, promising its industrial potential.
The reliability of Cu bonding technology in three-dimensional integration packaging is limited by high sintering temperatures and the growth of oxide at the joining interface. Hence, we propose a bionic adhesion interface of creeper sucker on the Cu substrate and covered with monolayer graphene, which increases the shear strength by 3 times compared to the conventional flat Cu substrate. The covered graphene layer effectively inhibits the generation of oxide at the joint interface and maintains a high shear strength after aging at 300 °C for 48 h Nanoscale Cu particles could reduce the chemical potential energy of the substrate surface , and stable bonding was achieved at 200 °C under a pressure of 2 MPa. Molecular dynamics simulation models reveal crystal structure evolution and residual stresses during the sintering process . This work demonstrates that bionic microstructures applied to copper bonding play an important role in interface enhancement, resulting in reliable bonding of Cu substrate at low temperatures. The method proposed here can provide insight into diversified applications including high-power light-emitting diodes soldering, SiC electronic devices, and flexible electrode interconnects.
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