•Ag–Cu nanopaste formulated by Ag and Cu nanoparticles with organic compounds.•A die-attach material for SiC device that operates at temperature exceeds 400°C.•The nanopaste has low hardness, low Young’s modulus and high bonding strength.•A study on the bonding attributes of nanopaste at a different metallization.•Microstructures reveal interaction between nanopaste and metallization layers. In this work, mechanical properties of Ag–Cu nanopaste that formulated by mixing Ag and Cu nanoparticles with organic compounds have been reported. Various weight percents of Cu nanoparticles (20–80wt%) had been loaded in the nanopaste, in which an increasing trend for hardness, stiffness and Young’s modulus were recorded with the increment of Cu loading. When the nanopaste was used to bond two pieces of Cu substrates, a declining of bonding strength has been recorded with an increasing of Cu loading. For metallization studies, Ag and Au coatings on Cu substrate have displayed the highest (52.6MPa) and the lowest (34.4MPa) bonding strength, respectively. The values of bonding strength were found to have a close relationship with the interface microstructure between the nanopaste and metallization layer on the substrate. Finally, the nanopaste was used to attach a SiC die on a substrate with either Ag or Au coating. The entire bonding structure has undergone a thermal aging test, whereby the thermal-aged microstructure was in agreement with the microstructure of metallization studies.