Usability of ECA materials in high temperature sensor applications

In electronics applications sensors are often used in challenging environments such as high temperature and humidity. For a sensor to perform reliably under such conditions stable attachment methods are needed. However, sensor structures may differ from typical silicon chip configuration and materials, which may make their attachment challenging. In this work the attachment of temperature sensors with electrically conductive adhesives (ECAs) was studied. The sensors were attached to a flexible polyimide substrate with different ECAs and exposed to three different step stress tests. In the step stress tests the temperature was ramped from 180°C to 260°C with different dwell times. Typically ECAs are not applied at this high temperature region. However, it was found that the adhesives could withstand exposure to high temperatures for surprisingly long periods of time. The weakest link in the structure was not necessarily the ECA but the copper pad, which oxidized at the high temperature and reacted with the adhesive layer of the substrate. This reaction formed a mix of copper oxide and the adhesive which migrated within the structure. Severe delamination between the sensor chip and the copper pads was also observed.