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

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

4. INCREASING HEAT LOAD POWER ELECTRONICS AND TELECOMMUNICATION DEVICES
HIGHER DEVICE DENSITIES
PROBABILITY IS FOR CONTINUED INCREASES IN HEAT FLUXES

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 (
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)

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

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

13. THERMAL STUDY FOR A BOARD

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