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 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

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

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

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

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

THERMAL MANAGEMENT IN SATELLITES

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

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

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

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.

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

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

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

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

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