Electrical characteristics of an ACF bond as a function of temperature and humidity aging

A commercial Hitachi anisotropic conducting film (ACF) was used to form the electrical interconnection between aluminum pads on a glass plate substrate, and electrolysis tin coated copper pads on a polyimide flexible circuit. These interconnections were aged over 1,400 hours at 85°C and 79% relative humidity. Throughout the thermal aging period a variety of electrical properties were measured. Electrical resistance of the ACF bonds was monitored in situ providing a continuous record of the resistance increase toward failure. The specimens were periodically brought back to ambient and dried out to monitor the resistance recovery and how other electrical properties were affected due to aging. A continuous resistance monitoring during the temperature ramp provided the temperature coefficient of resistance as a function of aging. The other electrical properties measured at ambient conditions were the voltage coefficient of resistance, both at low currents and at high currents, where self-heating occurred, the magnitude of 1/f noise, and the thermopower. As will be explained, each of these electrical properties provides an independent measurement of critical interconnection parameters