Conduction mechanisms in contaminant layers on printed circuit boards

AC impedance methods have been utilized to explore surface conduction mechanisms on printed circuit boards (PCBs) containing various types of solder flux contaminants. Residues from water-soluble, rosin-based, and no-clean fluxes were analyzed and evaluated for their potential impact on reliability. Impedance data for intentionally contaminated PCBs having several circuit line geometries were obtained at different relative humidities. An equivalent circuit model is presented that fits the data obtained. It is used to evaluate and distinguish among ohmic, kinetic, and diffusion effects and to predict the environmental conditions that may be detrimental for various line geometries.