Effect of Moisture and Contaminants on the Dielectric Constant of Thin-Film Alumina Substrates

Abstract

ABSTRACTThe dielectric properties of substrate materials constitute key parameters that determine the selection, reliability and design of sophisticated modern electronic devices. Two important factors affecting the reliability of electronic devices are the adsorption of moisture from the atmosphere, and contaminants like airborne particles (dust), flux residues, gaseous pollutants, residues from rinsing and cleaning unit operations etc. Any variation in the dielectric properties due to moisture and/or contaminants would be detrimental to the performance of an electronic package.Among the inorganic materials, alumina represents an optimal combination of electrical properties for many low and high-frequency applications. In this paper, the dielectric constant of thin-film alumina substrates has been measured over a wide frequency range (100 Hz to 3 GHz) as a function of relative humidity. The changes in the dielectric constant when the alumina substrates are contaminated with different contaminants like CuC12, CuSO4, organic acids etc. and exposed to various relative humidity levels for different lengths of time have also been measured. The effect on the dielectric constant when the contaminated substrates are treated with surfactants like oleic acid and dodecyl amine and exposed to different relative humidity levels is also presented. An important observation is that at a relative humidity level of approximately 70% there is a sudden increase in the dielectric constant of the contaminated alumina substrates. Results are also presented for the measured moisture adsorption using Thermo-Gravimetric Analysis in pure alumina, alumina contaminated with CuCI2 and contaminated alumina treated with dodecyl amine. It is shown that the measured dielectric constant is consistent with the amount of moisture adsorption that decreases on treatment with the surfactant.