THE CHEMICAL NATURE OF BROMIDE-CONTAINING CONDUCTIVE ANODIC FILAMENT
Authors: A. Caputo, L.J. Turbini, and D.D. Perovic Company: University of Toronto, Materials Science and Engineering Date Published: 5/16/2008
ICSR (Soldering and Reliability)
Abstract: Conductive anodic filament (CAF) is a failure mode in printed wiring boards (PWBs) which occur under high humidity and high voltage gradient conditions. The filament, a copper salt, grows from anode to cathode along the epoxy-glass interface. Ready et al have identified the salt as atacamite, Cu2(OH)3Cl. They have also shown that for solder fluxes containing high bromide concentration, a bromide containing CAF compound forms. Using a hot air solder level (HASL) fluid containing high bromide content a bromide containing CAF compound was created. This compound was characterized using transmission electron microscopy (TEM) to be Cu2(OH)3Br and the electrochemical pre-cursors for its formation have been discussed. In addition, it has been shown using FTIR that the polyglycol constituent from the flux diffuses into the board during soldering. Ion chromatography was used to show that bromide ions from the flux also diffuse into the board material during soldering.