Dielectric breakdown characteristics of flux-contaminated printed circuit boards in different environmental conditions.

Abstract

One common failure type for high voltage industrial products is dielectric breakdown. The dielectric strength through air between metallic traces of printed circuit boards (PCBs) depends on environmental parameters (temperature and humidity) and the presence of surface contamination (i.e. flux residues). With the development of soldering technologies, fluxes used nowadays no longer require cleaning, these are so-called no-clean fluxes. In our research, we investigated how the use of this type of flux affects the breakdown voltage on a test PCB under different environmental conditions. Temperature and humidity were controlled within a wide range, and the breakdown voltages measured on clean and contaminated surfaces were compared under these conditions. We found that no-clean flux residues significantly (almost by 20%) decrease the dielectric strength of PCBs. Under humid conditions (at 80% relative humidity) the breakdown voltage was typically lower by ∼25% in case of both clean and contaminated PCB surfaces.