Direct printing of electrical connections from metal melts using StarJet technology

We present a novel approach for maskless generation of conductive connections by direct printing of molten metal (e.g. solders). This approach utilizes a pneumatically actuated printhead based on the so-called StarJet technology [1, 2], with a reservoir containing molten metal and a star-shaped nozzle chip, allowing for the deposition of liquid metal lines and thus the direct printing of conductive connections. In this work, the printhead is used as a means to connect Au pads on PCBs. The electrical properties of the pad-to-pad connection of Au-pads on PCBs with test structures and the pad-to-line transition resistance are experimentally evaluated. The printed metal lines exhibit a width of about 80 μπι on PCBs. Printed connections with pad-to-pad distances from 0.1 to 3.00 mm exhibit resistances from 28 to 208 ιηΩ depending on the length of printed lines. Pad-to-line transition resistances amount up to 60 πιΩ. This is in the same range as observed for Aluminum wire-bonds (25 μπι in diameter), indicating sufficient electrical contact of the printed lines to the surface.