Effect of surface roughness on paper substrate circuit board

The European Union (EU) implemented the waste electrical and electronic equipment (WEEE) and restriction of hazardous substances (RoHS) directives in July 2006. To fulfil the environmental ethos of these EU directives, a printed circuit board (PCB) was developed based on a currently mass-manufactured board, but using a substrate of paper card, with interconnecting tracks added using conductive ink via a printing process. Components were bonded to the tracks using electrically conductive adhesives via an industry-based manufacturing line. During this investigation, paper card substrates of varying surface roughness were examined to establish the effect of substrate surface roughness for printing an interconnecting pattern for single-sided boards. Four degradable card substrate types with surface roughness values varying from 0.25 to 2.66 μ m were trialled. The impact of substrate surface roughness on track resistance was investigated and a correlation between increased substrate roughness and a reduction in track resistance was established, a reduction in track resistance of up to 56% was observed. Flammability analysis of the substrates was performed in accordance with BS61189-2, while mechanical, electrical, and functional tests were undertaken inline with international standards. The developed PCBs were deemed to have met this established criteria, thus opening the possibility of producing a WEEE/RoHS-compliant environment-friendly PCB.