Electronics cooling
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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

Electronics Cooling

Reference: Cengel, Heat Transfer,

2nd Edition, Chapter 15

ME 259


Introduction

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


Supporting electronic equipment

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


Common cooling methods

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


Electronics cooling models

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


Component model

Component Model

  • Physical system

  • Thermal circuit

  • Typical values

  • Analysis

ME 259


Enclosure model

Enclosure Model

  • Physical system

  • Thermal Circuit

  • Analysis

ME 259


Air flow model

Air Flow Model

  • Physical system:

  • Thermal Circuit

  • Analysis

ME 259


System model

System Model

  • Thermal circuit

  • Analysis

ME 259


Example

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/WL = 60 cm

    Rcs = 0.09 C/WH, W = 20 cm

    qc = 10 Wt = 3 mm

    Tj,max = 125 Ck = 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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