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Electronics Cooling

Electronics Cooling. Reference: Cengel, Heat Transfer, 2 nd Edition, Chapter 15. Introduction. All electronic components generate heat due to I 2 R (joule heating) Modern integrated circuits (ICs) approaching 10 10 components/chip heat fluxes up to 100 W/cm 2

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Electronics Cooling

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  1. Electronics Cooling Reference: Cengel, Heat Transfer, 2nd Edition, Chapter 15 ME 259

  2. Introduction • All electronic components generate heat due to I2R (joule heating) • Modern integrated circuits (ICs) • approaching 1010 components/chip • heat fluxes up to 100 W/cm2 • Failure rate of electronic devices increases exponentially with operating temperature • Silicon p-n junctions • Absolute limit of 125C for “safe” operation • 85C desirable for extended life ME 259

  3. Supporting Electronic Equipment • Chip Carrier • heat flow paths • junction-to-case thermal resistance (Rjc) • Printed Circuit Board (PCB) • Single-sided • Double-sided • Multilayer • Enclosure • sealed • vented ME 259

  4. Common Cooling Methods • Conduction cooling • copper “heat frames“ attached to PCB • copper layers and “vias” within multilayer PCBs • Air Cooling with or w/o heat sinks • natural convection & radiation • forced convection with fans • Liquid cooling • direct immersion • indirect (hxer, pump) ME 259

  5. Electronics Cooling Models • Component Model • Semiconductor device • Heat sink, mini-fan, heat pipe, hxer • PCB • Enclosure Model • Chassis assembly • Environment • Air Flow Model • Chassis-mounted fans • Air intakes, exhausts, • Shrouds, ducted flow • System Model • Combines component, enclosure, and air flow models ME 259

  6. Component Model • Physical system • Thermal circuit • Typical values • Analysis ME 259

  7. Enclosure Model • Physical system • Thermal Circuit • Analysis ME 259

  8. Air Flow Model • Physical system: • Thermal Circuit • Analysis ME 259

  9. System Model • Thermal circuit • Analysis ME 259

  10. Example • Given: Enclosure containing 16 TO-3 style power transistors, mounted in sets of four, on four EG&G 435 series heat sinks. Transistor specsEnclosure specs Rjc = 7.0 C/W L = 60 cm Rcs = 0.09 C/W H, W = 20 cm qc = 10 W t = 3 mm Tj,max = 125 C k = 0.4 W/m-K ho = 10 W/m2-K To = 25 C o = 0.8 Heat Sink specs Find: Fan flow rate needed to keep Tj below 125C ME 259

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