Long-term stability of resistors embedded in printed circuit board

This paper presents principle of manufacturing process of thin-film resistors embedded in printed circuit boards (PCB) as well as their chosen electrical and stability properties. Test structures were fabricated on FR-4 laminate with Ohmega-Ply^® technique basing on nickel-phosphorus alloy (NiP). The thickness of resistive foil was 0.4 μm and 0.1 μm with sheet resistance 25 Ω/sq. and 100 Ω/sq., respectively. Moreover, part of the samples was covered with two different types of cladding - Resin Coated Copper (RCC) or Laser Drillable Prepreg (LDP). The long-term stability of components was determined basing on resistance changes during ageing tests. The resistance was measured in two cases: at room temperature after keeping of samples at elevated temperature and/or humidity or directly during heating of resistors on hot plate. The measurements were carried out for structures after fabrication process as well as for resistors trimmed with Nd-YAG laser or treated with voltage pulses.