High temperature reliability of electrically conductive adhesive attached temperature sensors on flexible polyimide substrates

The attachment and packaging of temperature sensors may be challenging due to their structure and materials. Sensing requires a structure which is open to the environment and the materials often differ from those used in silicon-based electronics. Thus, traditional attachment techniques and materials such as soldering may be inappropriate. Polymer-based electrically conductive adhesives (ECA) are an alternative. The operating environment of a sensor may, however, be very demanding. Very little research data is available on the use of ECAs in challenging conditions, thus restricting their use in many applications. This study tested the behaviour of temperature sensors attached with ECAs onto flexible polyimide (PI) substrates in thermal storage at 200 °C. More than 1000 h of testing without failures were conducted on the ECA sensor structures. Good high temperature reliability therefore seems to be possible with ECAs. However, the PI substrate was observed to be critical to reliability. An adhesive layer used in the PI substrate reacted at the test temperature and severe oxidation of the copper pads and reaction between the materials consequently destroyed the interconnection and caused failures.