Behavior of Humidity Sensors Attached With Anisotropic Electrically Conductive Adhesives in Corrosive Environment

Sensors are used increasingly in different applications. In some of these applications, they need to be able to tolerate harsh environments and also operate for long periods of time. One of the most challenging environments is corrosive media which may be present in many applications. In this paper, the reliability of humidity sensors attached to an FR-4 substrate was studied using a salt spray test to determine their tolerance for corrosion. Because of their structure, the attachment methods for the sensor components were restricted. Consequently, the sensor components were attached using flip chip technology with two different anisotropic conductive adhesives (ACAs). Afterward, the reliability of the sensor components was investigated using the salt spray test. During testing resistance of the ACA interconnection was measured in real time. To extract the failure mechanism, an extensive failure analysis was performed with scanning electron microscopy. The main failure mechanism was found to be corrosion of a polymer film in the sensor component. The results showed that ACA is promising material for sensor attachments, as most of the sensor components were able to withstand a considerable period of time under the salt spray test without failures.