Direct patterning of electrical wiring on three-dimensional plastic substrate under ambient air conditions

Electronic devices are being produced in substantial quantities and have become an essential component of our daily existence. Furthermore, interest in printed electronics has increased due to the straightforwardness of the manufacturing process, decreased expenses, and diminished ecological footprint. Despite these advantages, there are still some challenges in the field of printed electronics. In this study, a process for manufacturing electrical wiring on a three-dimensional (3D) plastic substrate was developed using a pneumatic dispenser that utilizes a continuous-wave laser for laser sintering, and enables rapid and selective sintering at ambient temperature and pressure. The metal paste consists of spherical Ag-coated Cu with a diameter of 5–10 µm, Sn-Bi powders, and epoxy binders and has a high viscosity. In addition, a thermo-mechanical characterization of the metal paste was performed to explain the metallurgical bonding behavior during sintering. Using a pneumatic-based dispenser equipped with a rotary valve, a high-viscosity metal paste was precisely patterned at a pressure of 1.0 bar and a dispensing speed of 5 mm/s. The patterned metal paste was then sintered with a continuous-wave laser to achieve electrical conductivity. When sintering with a power of 5 W and a scanning speed of 5 mm/s, at which the induced temperature is 280 ℃, a specific resistivity of 0.193 mΩ·cm was determined. Under these conditions, the metal paste was directly patterned and sintered onto a 3D plastic substrate as electrical wiring, and LEDs were then affixed to the substrate to validate the interconnections’ functionality. In addition, the feasibility of industrial applications was demonstrated by fabricating a garnish model for automotive interiors.