Electrochemical Model for Corrosion of Conductors on Ceramic Substrates

A quantitative model for electrochemical corrosion of conductors on microelectronic substrates was developed from fundamental principles such as Faraday´s and Ohm´s laws. The principal parameters are properties of electrode materials, geometry, and the surface resistivity of adsorbed moistured films. The time-to-fail calculation is linearly proportional to the surface (sheet) resistivity and inversely proportional to dc voltage between electrodes. Calculations based on data from published literature are presented as examples to illustrate the model. The relationship of surface resistivity to contamination of adsorbed moisture films by anions, primarily chlorides is discussed. Experiments are described in which surface resistivity is increased greatly by conformal coatings of polymers such as silicone junction coating and a polyamideimide. The silicone was shown to be superior because of its greater resistance to delamination from the substrate in high temperature and relative humidity (RH) exposures, due to higher bonding energies.