Feasibility Study of OSEE Inspection for Flux Residue on Electronics Assemblies

The technique of Optically Stimulated Electron Emission (OSEE) is considered as a method of inspecting printed circuit based electronics assemblies for flux residue immediately following production soldering. The technique has been used for several years by NASA and its contractors in the refurbishment of solid rocket motors for the Space Shuttle. The application to copper substrates and soldered copper substrates has shown sensitivity to small amounts of residues of some solder fluxes. The technique was extended for inspection of insulating substrates used in printed wiring board (PWB) construction by altering the measurement procedure to include charge replacement, thereby attaining measurement reproducibility. The results indicate that OSEE inspection of electronic assemblies for flux residues is feasible. An inspection based on this technology subjects the inspected object only to photons of ultra‐violet light and immersion in an inert gas, such as argon. It is potentially rapid enough to provide 100% inspection of boards processed on a production line, and it has potential spatial resolution of less than 1 micron.