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CHE/ME 109 Heat Transfer in Electronics

CHE/ME 109 Heat Transfer in Electronics. LECTURE 20 – ELECTRONICS COOLING FUNDAMENTALS. BACKGROUND - VACUUM TUBES. FUNCTION LIKE DIODES TEMPERATURES FOR THE TUNGSTEN (WITH A DASH OF THORIUM) FILAMENT (CATHODE) CAN RUN UP TO 2400 C HEAT LOADS ARE THE RANGE OF 100's TO 1000's W WERE TYPICAL

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CHE/ME 109 Heat Transfer in Electronics

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  1. CHE/ME 109 Heat Transfer in Electronics LECTURE 20 – ELECTRONICS COOLING FUNDAMENTALS

  2. BACKGROUND - VACUUM TUBES • FUNCTION LIKE DIODES • TEMPERATURES FOR THE TUNGSTEN (WITH A DASH OF THORIUM) FILAMENT (CATHODE) CAN RUN UP TO 2400 C • HEAT LOADS ARE THE RANGE OF 100's TO 1000's W WERE TYPICAL • TUBES ARE STILL FABRICATED AND STILL IN USE • AMPLIFIERS FOR INSTRUMENTS • HIGH POWER ( >10000 W) HIGH FREQUENCY (> 50 MHz) USE TUBE BASED UNITS http://www.electrontubes.net/industrial.htm

  3. BACKGROUND - TRANSISTORS • LOWER POWER OPERATION FOR THE SAME FUNCTION AS TUBES • MATERIALS OF CONSTRUCTION ALLOW OPERATION AT RELATIVELY HIGH TEMPERATURES • LED TO DEVELOPMENT OF INTEGRATED CIRCUITS AND MICROPROCESSORS http://media.digikey.com/photos/Intersil%20Photos/20-16-SOIC.jpg

  4. INCREASING HEAT LOAD • POWER ELECTRONICS AND TELECOMMUNICATION DEVICES • HIGHER DEVICE DENSITIES • PROBABILITY IS FOR CONTINUED INCREASES IN HEAT FLUXES https://vicariousconversations.com/~vicario1/MWT/img/wiki_up/heat.JPG

  5. THERMAL MANAGEMENT H • ATTEMPTS TO BALANCE HEAT LOADS AND COOLING CAPABILITIES • GENERAL FORMS OF COOLING FOR DEVICES ON BOARDS • CONDUCTION - THROUGH CONNECTION TO BOARDS AND THEN TO HEAT SINKS • CONVECTION - BOTH NATURAL AND FORCED USING HEAT SINK TECHNOLOGY • RADIATION – INTERNAL AND EXTERNAL SOURCES

  6. THERMAL MANAGEMENT IN SATELLITES • Young-Keun, C., et. al., A Study on Thermal Modeling and Heat Load Mitigation for Satellite Electronic Components, 15th Annual AIAA/USU Conference on Small Satellites, Utah State University Research Foundation, 2001 (http://www.smallsat.org/proceedings) • PRIMARY HEAT DISSIPATION VIA CONDUCTION AND RADIATION • NEED TO CONSIDER LOCAL HEAT LOAD FOR EACH COMPONENT • ONE METHOD MAY BE TO INCREASE HOUSING THICKNESSES TO ENHANCE CONDUCTION TRANSFER • ALSO ANALYZE THE EFFECT OF COMPONENT LAYOUT

  7. THERMAL MANAGEMENT IN SATELLITES

  8. FABRICATION OF ELECTRONIC DEVICES • DEVICES ARE MOUNTED ABOVE THE PCB DUE TO DIFFERENT COEFFICIENTS OF THERMAL EXPANSION • JUNCTION TEMPERATURES ARE THE MAXIMUM IN THE DEVICE • CALCULATED FROM

  9. CHIP CARRIER • CAN BE USED FOR THERMAL MANAGEMENT • TYPICAL DEVICE SCHEMATIC FOR FLIP-CHIP PLASTIC BALL GRID ARRAY PACKAGE (SOLDER TECHNIQUE) http://www.electronics-cooling.com/assets/images/2003_Feb_A1_Figure3.jpg

  10. MECHANISMS FOR HEAT DISSIPATION • INVOLVE ALL THREE MODES OF HEAT TRANSFER • CONDUCTION THROUGH THE PINS TO THE BOARD (THE MORE PINS, THE HIGHER THE RATE OF CONDUCTION) • CONVECTION TO THE SURROUNDING AIR • RADIATION TO THE SURROUNDINGS http://www.njr.co.jp/pdf/ee/ee05007.pdf

  11. JUNCTION TO CASE RESISTANCE • CONTROLLED BY THE BONDING AGENT PROPERTIES • ALSO AFFECTED BY THE GEOMETRY OF THE SYSTEM • COOLING THROUGH THE PCB • PCB’s CAN BE FABRICATED WITH HEAT FRAMES TO CONDUCT HEAT AWAY FROM THE DEVICES • THE HEAT FRAME IS CONNECTED TO A COLD PLATE, WHICH SERVES AS A HEAT SINK.

  12. THERMAL STUDY FOR A BOARD • HEAT LOADS ON THE BOARDS ARE ADDITIVE, SO THE MAXIMUM TEMPERATURE IS TYPICALLY IN THE CENTER OF THE BOARD http://www.thermoanalytics.com/applications/electronics.html

  13. THERMAL STUDY FOR A BOARD http://www.thermoanalytics.com/applications/electronics.html

  14. CASE AND OTHER COMPONENTS • BOARD CONFIGURATION IN THE CASE IS A FACTOR IN THERMAL MANAGEMENT • AIR FLOW PATTERNS ARE AFFECTED BY RELATIVE LOCATION OF BOARDS AND OTHER EQUIPMENT • LOCATION OF VENTS CAN IMPACT THE FLOW IN THE UNIT • VERY HIGH HEAT DENSITY UNITS, CPU’s AND POWER SUPPLIES, MAY HAVE LOCAL FAN COOLING • LAYOUT SHOULD ALLOW FOR MAXIMUM COOLING BY THE METHODS THAT ARE NOT DEPENDENT UPON A MOTOR • RADIATION • CONDUCTION • NATURAL CONVECTION

  15. COOLING LOADS • HEAT BALANCE REQUIRES THAT HEAT IS DISSIPATED AT THE RATE IT IS GENERATED AT STEADY STATE • MOST DESIGNS INCLUDE SOME INSURANCE TO ALLOW FOR COOLING RATES ABOVE THAT ANTICIPATED IN DESIGN SERVICE

  16. THERMAL ENVIRONMENT • THE RANGE OF ENVIRONMENTS TO WHICH THE SYSTEM WILL BE EXPOSED MUST BE CONSIDERED • NATURAL CONVECTION WILL NOT WORK WELL IN SPACE DUE TO LOW GRAVITY • FORCED CONVECTION WILL NOT WORK IN A VACUUM • AIRCRAFT TYPICALLY EXPERIENCE A RANGE OF PRESSURE AND TEMPERATURE CONDITIONS ON EACH FLIGHT

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