Inkjet-printed vertical interconnects for ultrathin system-on-package technology

This study investigated inkjet-printed vertical interconnect vias with silver ink for ultrathin system-on-package technology. Inkjet-printing parameters such as droplet spacing, jetting frequency, number of droplets, and substrate temperature were determined based on surface morphology of the vias. The interval time between multipass printings was used to evaporate the solvent and avoid ink overflow. Two-step inkjet printing was used to fill a drilled via with aspect ratio of 1 (100 μm depth/diameter) that resembles the frustum of a cone. First, the via is printed on the substrate using 1 kHz jetting frequency and 30 μm droplet spacing at 60 °C and 125 passes. The jetting frequency and droplet spacing are then increased to 3 kHz and 40 μm and the passes up to 200 to increase the printing length for filling up the via. Inkjet-printed vertical interconnection was fabricated for ultrathin packages applications.