Reliability assessment of COB technology for extreme low temperature environment

Chip-on-board (COB) technology is a viable approach for miniaturization in space electronics. Although COB technology has been widely used in many commercial products, comprehensive and systematic studies are needed for space application. Temperature extremes (-125degC to +85degC) that the Mars Science Laboratory (MSL) electronics will be exposed to pose challenges in spacecraft electronics design using COB technology. The cyclic nature (1500 cycles) of the temperature environment will further aggravate the condition and introduce accumulation of the damage. Existing military standards for electronics design and test can no longer provide sufficient reliability credits for the electronics exposing to such extremely low temperatures. Potential failures induced by the unique environment of the Mars mission must be assessed to ensure long-term reliability of the electronics, which is crucial for the success of the mission. To understand the root cause of failures of the electronics in the severe Mars temperature environment, fundamental knowledge of material properties and their impact on the electronics are crucial. This paper summarizes a comprehensive study conducted on the COB technology that will be used in the MSL motor controller electronics. An extensive test matrix is designed and developed, and thermal cycle tests (-125degC to +85degC) are conducted to identify the failure mechanisms in the extreme temperature environment on Mars. Relevant materials are tested to and beyond the -125degC limit for their properties and application feasibilities. Failures observed during the thermal cycle test, failure mechanism identifications, as well as test results will be presented in this paper. The overall objective of this study is to identify potential failure mechanisms and assess reliability of the COB technology, to ensure survivability and functionality of the electronics through the Mars mission