Development of Screen-Printed Impedance Sensor and Detections of Wiring Corrosion and Dew Condensation

Abstract

The pitch of wiring on printed circuit boards has become finer for the development of small and lightweight electronic devices. Due to the finer pitch of wire, dew condensation causes a short circuit of wiring easier and there is a risk of breaking the wiring due to slight corrosion. It is crucial to develop a sensor for monitoring dew condensation and corrosion of wiring in order to prevent these corrosion phenomena. Our group 1) has developed a corrosion monitoring sensor with screen printing techniques. This sensor, which has a comb-like structure of silver wiring on the boards, can monitor dew condensation environments using electrochemical impedance spectroscopy (EIS) because of the change of impedance spectra with condensation condition. Aiba 2) et al. have fabricated printed –type corrosion monitoring sensor which can evaluate amount of dew condensation. This sensor, which has wiring of a reference resistance by coating anticorrosion, can quantitatively evaluate dew condensation by standardizing the output impedance from the sensor with reference resistance. In this study, monitoring corrosion sensor that can accurately detect corrosion of wiring and dew condensation was developed using screen printing.Polyimide was used for a substrate of the developed sensor, and silver wiring was printed on the substrate by using screen printing. The silver wiring consists of two parts. The upper and lower parts have comb-like structure and two parallel straight lines, respectively. Corrosion of wiring and dew condensation can be detected by the upper and the lower patterns, respectively. UV irradiation was performed for 10 minutes in an oxygen atmosphere only on the substrate to make hydrophilic partially.Dew condensation on the surface of the corrosion sensor was detected by measuring impedance spectra. The measurements were performed in the chamber that temperature and the relative humidity were set at 25 ℃ and 90 %, respectively. The frequency range of impedance measurements were from 10 mHz to 10 kHz. The amplitude of voltage modulation for the sensor was 10 mV. The voltage during the measurements was set at 0 V.In impedance spectra of the sensor without UV ozone treatment, although dew condensation occurred, the wiring did not short circuit and impedance spectrum remained on the real number axis. On the other hand, in impedance spectra of the sensor with UV ozone treatment, impedance spectrum of capacitive semicircle attributed to short circuit of wiring due to dew condensation was observed, that is, it was possible to detect dew condensation with high sensitivity. References I. Shitanda, A. Okumra, M. Itagaki, K. Watanabe, Y. Asano, Sensor Actuat B-Chem, 139, 292 (2009).A. Aiba, N. Fujii, Y. Hoshi, I, Shitanda, M. Itagaki, J. Electrochem, Soc., 165, C743 (2018).