Thermal cycling of anisotropically conductive adhesive interconnections in demanding sensor applications

Sensor components are increasingly used in electronic applications. One example of such a sensor is a humidity sensor. The attachment process of humidity sensors can be challenging as the sensor structure needs to be open to the environment. The use of solders is often prevented by sensor materials and structures. Consequently, anisotropically conductive adhesives (ACAs) are interesting attachment materials for such sensor interconnections. In this study, the attachments of humidity sensors onto FR-4 substrates with two different substrate thicknesses were done with three different ACAs. The reliability was studied in a temperature cycling test between -40^oC and +125 °C up to 10,000 cycles. The results showed that excellent reliability can be achieved with this kind of interconnection structure. Thinner substrate further increased the reliability, but excellent reliability can also be reached with rigid substrate if optimal bonding parameters are used. However, significant differences were found in the reliability of interconnections made with different ACAs.