LOW FREQUENCY IMPEDANCE INVESTIGATION ON AN EPOXIDE RESIN
Author: Jane M. Terry Company: Georgia Institute of Tech Date Published: 4/28/1997
Surface Mount International
Abstract: Low frequency impedance spectroscopy (105 to 10-4 Hz) was used to investigate the effects of elevated temperature and humidity on the electrical and chemical stability of a resin and the stability of the resin-electrode interface. Experiments focused on the characterization of an unfilled epoxide resin used as a polymer matrix in a conductive adhesive. A temperature of 85°C and a relative humidity of 85% were used to accelerate degradation mechanisms in the resin and to place impedance levels within the operating window of the instrumentation. The results of this investigation identified bulk and interracial conduction paths and reflected on the reliability of the resin in an electronic application. Impedance studies on samples containing tin/lead and gold-plated electrodes immersed in resin provided information on degradation mechanisms, occurring at the resin-electrode interface Research on conductive adhesives is still in an early phase. Previous studies in the literature have focused on the electrical and mechanical properties of individual adhesives and have given little material description of the resin in terms of chemical make-up. In this study, impedance results are correlated with the chemical make-up of the epoxide resin under investigation. The chemical make-up of the polymer affects the degree of moisture absorption. Free and bound hydrophilic moieties within a resin will increase the driving force for moisture ingress. Moisture ingress affects the resistivity and adhesive strength of polymers and their ability to protect substrates from corrosion. Insitu impedance spectroscopy is a suitable technique to study the degree of moisture ingress, and its effects on conduction processes in the resin and on resin-adherent interfaces.