We explored the properties and performance of copper-based metallic nanoparticle paste (MNPs) for interconnects applications in 3D heterogeneous integration. A patterning method was developed to process micron sized sintered MNPs structures. This enables the fabrication of IC interconnect test structures to characterise specific resistivity sintered MNPs and the contact resistances of sintered MNP to bulk copper (bCu) which was respectively 78.4 mOhm.micrometer and 0.23 Ohm.micrometer2. In situ XRD analysis showed no oxidation of MNPs at processing temperatures below 100 °C. When Copper based MNPs are sintered under forming gas conditions, no oxidation of copper is measured. With in situ TEM at a temperature range of 220 - 260 oC local melting of copper nanoparticles was observed. This is in agreement with the electrical measurements, the resistivity and contact resistance are considerably reduced when MNPs is sintered in this temperature range. Copper-based MNPs is successfully applied as die attach and wafer to wafer (W2W) bonding. However, for W2W bonding, the specific contact resistance was 800 Ohm.micrometer2.@en