Influence of Sodium Chloride and Potassium Fluoride on Electrochemical Properties of Aluminum Copper Interdigital Structures

Abstract

This paper evaluates the electrochemical properties of aluminum (0.5 w%) copper alloy metallized test chip surfaces with interdigital structures and distances between 3 and 20 μm, regarding sodium chloride and potassium fluoride contamination in the range of 1011–1016 ions per cm2 at high humidity (85%) and high temperature (85 °C). These accelerated tests result in leakage currents and impedance values which show a significant change above a contamination limit value of 1014 ions per cm2 for both salts i.e., the leakage current starts to increase well above a few pico amperes, and the impedance decreases significantly. This contamination level can be seen as a turning point, after which devices can undergo for example signal shifts or corroded metal tracks over lifetime. But not only the start point of an increase in leakage current decides about the harmfulness of the contamination, other important influences are deliquescence and how high the leakage current gets at its maximum. Therefore, even with the same starting point, the risk evaluation is not the same for sodium chloride and potassium fluoride.