Electronic packaging for extended Mars surface missions

Abstract

Extended Mars missions require vehicles to survive a large number of extended temperature cycles. To address this issue for electronics, previous strategies have placed electronics in a "warm electronics box" where thermal management is more easily maintained. However, that strategy limits number and location of electronics. An alternative strategy allows electronics to be remotely located on actuator and wheel arms with no heating, which has the advantage of distributed control. This strategy requires the electronics to survive the Martian extremes of -120 to +20/spl deg/C for the duration of the mission. In addition, wheel motor controllers were mounted directly on the motor casing extending the temperature range on the warm side to +85/spl deg/C (including some margin). Since missions may last 18 months or more and with day-night cycles on Mars at about 26 hours this means exposure to approximately 500 cycles. Typical testing is performed to 3/spl times/ the number of cycles giving the electronics a testing requirement of -120 to +85/spl deg/C for 1,500 cycles. A chip on board strategy was selected and a parallel approach of materials characterization and physics of failure with engineering experimentation is being used to address the issues of a large temperature swing with many cycles. A full factorial experiment, designed to highlight expected failure modes from the physics of failure analysis, is being conducted. The experiment is designed to evaluate different substrate materials, different die attach materials and different encapsulants or coatings. Combinations of these materials are being evaluated on a test vehicle with a range of die sizes in an effort to determine lifetime and to verify failure modes. Initial results were presented.