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Thermal Analysis

Thermal Analysis. Lindy Ahr Southwest Research Institute (210) 522-3212 lahr@swri.org. Purpose. Spacecraft Electronics must have the highest reliability High Junction Temperatures reduce reliability Electronics Allowable Maximum Junction Temperatures are derated to increase reliability

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Thermal Analysis

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  1. Thermal Analysis Lindy Ahr Southwest Research Institute (210) 522-3212 lahr@swri.org

  2. Purpose • Spacecraft Electronics must have the highest reliability • High Junction Temperatures reduce reliability • Electronics Allowable Maximum Junction Temperatures are derated to increase reliability • Thermal Analysis is used to keep the Electronic Component Temperatures below the derated temperature

  3. Requirements Compliance Matrix

  4. Thermal Assumptions • Chassis dissipates waste heat through conduction via mounting flanges to spacecraft. • Heat transfer from each electronic module into the housing is through the card guides in the form of conduction • Individual components with 50 milliwatts, or greater power dissipation, are explicitly modeled with the remainder of the power from components being averaged across the board • Component conduction is via thermal epoxy for surface mount IC’s, solder connections for surface mount leadless devices and pins for through-hole devices that do not receive epoxy or other thermal treatment • All circuit boards have dedicated thermal planes of 4 ounces of copper in addition to power and ground planes • Power dissipation on boards is taken as nominal expected for all boards. This assumes that worst case dissipations for the entire assembly would not exceed this condition.

  5. Steady-State Analysis Approach • TAK 2000 finite difference software used to model the enclosure. • Power from modules are used as heat sources at the respective nodes in the enclosure model. • Steady-state temperature profile of the housing was determined and used as boundary conditions on the card models. • Electronics modeling package in TAK 2000, PC Analyze, was used to construct card models. • Card models are comprised of parallel conductors representing the board substrate and the thermal plane, and conductors representing the edge guides. • An equivalent conductance for the board-card guide-wedge clamp-housing thermal path was determined and input into the PC Build models.

  6. Power Dissipation for Electronics Modules

  7. Thermal Network Diagram of TCU Chassis

  8. Steady State Temperature of the Chassis

  9. POW Steady State Board Temperature

  10. CPU Steady State Board Temperature

  11. CPU Component Temperatures

  12. DIG Steady State Board Temperature

  13. ANA Steady State Board Temperature

  14. Summary • Insufficient information to accurately model the POW, DIG and ANA Card Modules. Board with uniformly distributed power were modeled. Board Temperatures were plotted. • CPU Card Module Results indicate that all analyzed device temperatures meet derating guidelines for junction temperatures for the Flight Hot Temperature Case.

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