In Situ-Formed Nano-Cu Pathways in Binders Endowing Pastes High Conductivity with Low Metal Content

Although adding binders could significantly improve the adhesion between metal pastes and polymer substrates, they also considerably decrease the conductivity of printed circuits, limiting their applications in printed electronics. This study innovatively adds a copper (Cu) precursor to the paste to solve this problem. Cu nanoparticles are formed on the surface of Cu flakes and within the binders due to their in situ decomposition characteristics. The decomposed Cu nanoparticles construct more conductive pathways that improve the conductivity of the printed circuits. Furthermore, this study employs an orthogonal test to investigate the relationship between the formulation of pastes and the performance of printed circuits, optimizing the proportion of the Cu precursor and binders based on these results. Compared to conventional pastes that consist solely of Cu fillers, binders, and solvents, the paste developed in this study exhibits high conductivity, which is approximately 2.6 times that of the pure Cu flake paste at low metal content around 40%. Thus, with more binders, the printed circuits not only met the 5B level according to ASTM D3359 standards but also showed excellent electrical properties after curing at 200 °C for 5 min, achieving a resistivity as low as 331 μΩ·cm. Additionally, the paste exhibited outstanding performance in the application of heaters and ultrabroadband (UWB) antennas, further confirming its considerable potential for commercial printed circuits.