Method of isothermalization for passive elements in an electronics system

This paper describes a method for obtaining a uniform temperature condition for multiple passive electronic elements, without active control, in an assembly that undergoes large temperature fluctuations due to power cycling. It describes a specific system in which the temperature of several electronics filters had to be controlled to within 1°C of each other in a Space-based electronics assembly. Because the absolute temperature of the filters was allowed to vary somewhat, and the filters dissipated very little heat, an entirely passive method could be used. A passive control system feature is desirable as it minimized the cost, power consumption and complexity of the system. However, due to the passive nature of the method a great deal of attention had to be given to the design of the thermal isolation of the filters from the surrounding environment. Many important factors had to be considered such as the conductive coupling through the printed wiring board to other electronic parts, which dissipate heat, the radiation paths, and the transient response of the surrounding assembly during an operational orbit cycle. The thermal design process required to produce a robust thermal control system is discussed in detail. The testing that was performed to verify the design, the results and the correlation of the results to model predictions are also discussed