Low Temperature Thermal Cycle Survivability and Reliability Study for Brushless Motor Drive Electronics

Abstract

This paper presents a survivability and reliability investigation for integrated actuator and brushless motor drive electronics packaging and components under an extreme low temperature and high thermal cycle environment. A universal brushless motor drive electronics assembly has been designed, built, and thermal cycle tested for use in Mars, Moon, and asteroid type cold environments without the need for any active thermal control. The assembly uses electronic part types and chip-on-board electronic packaging technology that allow operation at temperatures down to -180/spl deg/C. The thermal cycle capability of the assembly has been demonstrated to be in excess of 2010 cycles from -120/spl deg/C to 85/spl deg/C, over a 210/spl deg/C total temperature swing. Future space missions will require electronic and actuator systems on a planet, asteroid or Moon surface to function beyond the established reliability limits of currently used components and materials systems. In support of this target application, the Jet Propulsion Laboratory (JPL) has performed a series of experiments to test the reliability of actuators, sensors, electronic components, and electronic packaging designs to provide input to the detailed flight design of a universal brushless motor drive electronics and integrated actuator assembly. These experiments started with the use of a chip-on-board electronic packaging strategy due to its inherent advantage of improved high functionality with minimal circuit board area compared with standard packaged electronic components. Initial electronic packaging experiments were comprised of various sized chip devices with gold wire bonds. The second phase of electronic packaging experiments conducted at JPL consisted of power devices with large diameter wire bonds as well as various surface mount resistor devices. Full factorial experiments were designed to find the most reliable combinations of substrate type, component attach method and encapsulation. The surviving material combinations after a minimum of 1500 thermal cycles were utilized to form the basis of the packaging and electronic component detailed design approach used in the universal brushless motor drive electronics design. Electrical failures were defined as open circuits. A failure analysis procedure was applied by defining the failure mechanism and applying a risk mitigation. After 1500 cycles, the packaged assembles were cycled to exceed 2010 cycles and additional material considerations were made. In addition, selected components were functionally tested over the temperature range of +100/spl deg/C to -180/spl deg/C and cold soaked at -150/spl deg/C for 1000 hours for reliability. A design for reliability method was also developed at the component and circuit level for electronics operating at extreme low temperatures.