The role of electrochemical migration and moisture adsorption on the reliability of metallized ceramic substrates

Data presented here have resulted from an extensive investigation into fundamental mechanisms involved in electrochemical migration and dendrite growth on metallized ceramic substrates. Significant new results are presented, and pertinent data from previous studies are outlined to provide a comprehensive, coherent analysis of the complex process of electrochemical migration. A number of critical issues are addressed including formation of an absorbed moisture layer and the effect of humidity on the thickness and conductivity of this layer. Migration has been quantified by examining dendrite morphology and dendrite growth rates. Morphology and growth rates are nearly identical for immersion tests in both bulk and thin layer electrolytes, but is quite different in absorbed layers of moisture. Immersion tests are still useful in determining the effects of solution variables that would be difficult or impossible to quantify in adsorbed moisture layers. In addition the maximum velocity theory for predicting dendrite growth rates can be used for predicting general trends, but requires further refinement for more precise predictions. Clearly the most important parameters affecting reliability are the adsorption of moisture combined with surface contamination.

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