Inkjet printed nano-particle Cu process for fabrication of re-distribution layers on silicon wafer

As of late, attention has been paid towards usage of copper nano-particle inks instead of silver or gold nano-particle inks in the field of printed electronics, the main reason being its good conductivity with respect to its bulk material price. However, there are inherent challenges with using copper inks. One of the most crucial challenges is the reactive nature of copper nano-particles, which easily forms a non-conductive oxide layer. To combat this, the process of sintering the printed copper inks should be performed either in vacuum or an inert environment, which is difficult and costly. Laser sintering provides digital high energy-density alternative for oven sintering, which is fast enough so that the oxide layer does not have enough time to form. In this work, we have studied the sintering of inkjet printed copper ink on silicon substrate using continuous-wave 808nm diode laser. The output power and the scanning velocity of the laser as the main sintering parameters were varied in order to study their effect on the electrical resistance of the samples. A sheet resistance of about 300 mΩ/□ was measured. The tests were conducted in room conditions and the sintered patterns were analyzed using optical microscope and scanning electron microscope (SEM).