Surface grafting of epoxy polymer on CB to improve its dispersion to be the filler of resistive ink for PCB

Abstract

In this paper, we report a novel and efficient method of promoting the dispersing uniformity of carbon black (CB) in epoxy polymer substrate of PCB (printed circuit board) by chemical grafting. The reported method shows the promising capability in the application of advanced printable resistor ink. By taking advantage of the functionalized CB surfaces, the grafting reaction of epoxy polymer on CB particles was investigated with Fourier-transform infrared spectroscopy (FT-IR), transmission electron microscope (TEM) and thermo gravimetric analysis (TGA). FT-IR spectra evidenced the polymerization of epoxy resin with coupling agent and TEM investigation directly confirmed the polymerization occurred on CB surface. The polymerization occurred on the limited part of the CB surfaces to form a network-structure polymer to reside on the CB particles and hence greatly improved CB dispersion in ink as evidenced in ink-droplet spreading verification on glass and PCB resin substrates. On the other hand, the polymer grafting has limited effect on the increasing of the as-cured ink filled with the grafted CBs. Finally, the cross-section observation also confirmed the dispersion improvement and sheet resistance uniformity due to epoxy polymer grafting on PCB substrate, indicating the prospective candidate as embedded resistors for PCB. Keywords: Grafting, Carbon black (CB), Epoxy polymer, Resistive ink, Printed circuit board (PCB)