A novel test circuit for automatically detecting electrochemical migrationand conductive anodic filament formation

The rapid growth of the global electronics manufacture environment has brou ght about the onset of a variety of new, untested materials and processing chemicals. The interactions between substrates and processing chemicals tha t can occur during manufacture, storage and use must be assessed in order t o determine long-term reliability. Surface insulation resistance (SIR) test ing is a standard industry technique used to assess the interactions betwee n processing chemicals (e.g., soldering fluxes) and substrates. SIR test me thod conditions vary in terms of the temperature and the humidity used to a ccelerate the normal failure modes. Typically, a 45 to 50 volt bias is appl ied to an interdigitated comb pattern, and periodic SIR measurements are ma de using a 100 volt test. Pass/fail criteria based solely on SIR electrical values, (e.g., 100 M Ohm) however are inadequate. Often the electrical mea surement fails to reveal the presence of surface dendrites due to contamina nts related to processing chemicals. This failure occurs because the dendri te burns out between electrical readings when the circuit continues to be b iased at 50 volts. A new "linear test circuit" has been developed to overco me this deficiency. The circuit uses an operational amplifier to detect the formation of a surface dendrite between electrodes on the comb pattern. Wh en the dendrite shorts the circuit, voltage to the comb pattern is removed. Thus, the presence of the dendrite is captured electrically, and the dendr ite is preserved for further analysis. This paper will present the circuit used and data showing its' effectiveness at detecting both surface dendrite s and subsurface conductive anodic filament formation.