Inkjet printing of electrical vias

Inkjet printing of planar and via (through-hole) electrical interconnections is developed to be incorporated into a roll-to-roll manufacturing line. The specific roll-to-roll machine uses rotary RMPD^® technology, self-alignment of bare LED dies, and inkjet printing of the electrical connections to the LEDs dies. The key problem to be solved is the inkjet printing of electrical connections through via holes with vertical walls Xaar126-50pL industrial inkjet printheads were used to print silver nano particle ink at 0.1 m/s to connect through LED vias of 90 μm diameter and up to 50 μm depth. While high throughput sintering techniques are desirable for the specific roll-to-roll machine standard convection oven sintering was applied for the proof of principle described here. Sintering at temperatures as low as 135°C for 30 min prevented damage to the substrate and LED dies and yielded electrical connections that allowed to drive LEDs with 20 mA at 3V under emission of bright green light.