Conductive ink for through hole application

Silver through-hole (STH) technology is a method to create an electrical interconnect between the top and the bottom of a printed circuit board (PCB). STH technology has gained and is continually gaining acceptance worldwide because the process is low-cost, reliable, and environmentally benign. The detailed process for the through-hole connection is described in this paper. Even though the technology to produce STH boards is mature, the performance of current through-hole ink relies on different types of PCB´s. Exposure to solder baths or to thermal cycling becomes problematic with the stability of electrical conductivity. This problem is associated with different types of metal fillers, resin systems, and PCB´s. For example, the electrical resistance of the ink on FR2 substrate gradually increases after each solder bath dip. A fundamental study has been conducted to investigate the hole-resistance drift after each solder bath dip, TMA and DMA have been used to characterize CTE´s and curing performances of the ink and PCB substrates. A failure mechanism has been proposed and confirmed by experiments. Experimental results demonstrated that a hole-resistance drift on FR2 substrate is caused by several factors. First, the higher thermal expansion of the substrate itself stretches the coating layer. Second, the continued curing causes the resin matrix to be fixed at higher temperature. Finally, the CTE´s of the conductive ink and the PCB substrate mismatch