1. Electronics Cooling MPE 635
Mechanical Power Engineering
Dept.

2. Course Goals
1. To establish fundamental understanding of heat transfer in electronic equipment.
2. To select a suitable cooling processes for electronic components and systems.
3. To increase the capabilities of post-graduate students in design and analysis of cooling of electronic packages.
4. To analysis the thermal failure for electronic components and define the solution.

3. Part-A
Main topics
Introduction to electronics cooling and thermal packaging
Introduction to basic modes of heat transfer
Conduction heat transfer and extended surfaces in electronic devices
Transient conduction
Natural convection heat transfer (i.e. PCB cooling)
Forced convection heat transfer (Internal and External flow )
Fan performance
Radiation heat transfer and its applications in electronic devices
Solving the electronics cooling problems with EES software
Electronics cooling problems
Solution of selected electronics cooling problems

4. 1. Introduction to electronics cooling and thermal packages
Thermal management importance in the electronic product development
Heat sources in electronic products:
-Power dissipated through electric resistances
P=I2R
-Switching power dissipation in transistors

5. Case Study Every personal computer contains a CPU.
The CPU clock and speed progress with time, the clock speed was increased from 200 MHz to 2 GHz from 1998 to due to this improvement, the CPU packages should also be improved to accommodate the increase in heat dissipation.
You are required to study the various heat sinks and the required fan for thermal management for the Pentium® Processors from the MMX generation until the 4th generation.

6. Reliability and temperature
Recent studies of electronic equipment have shown that the field reliability of equipment is temperature related.
The failure rate model may be competitively described by the Arrhenius-type model
Where the coefficients Ai, Bi, and Ei are independent of temperature.

7. Reliability and temperature
Typical junction temperatures for equipment presently operating in a large number of field applications.

8. Liquid Cooling System Consideration
System Types
-direct cooling system
The coolant flows over the component to remove heat from the surface and as such must be capable of sustaining a voltage gradient
Efficient means of heat removal because the coolant is closest to the heat source.
In addition, moisture absorption can lead to a chemical breakdown in some coolants, which in turn lowers the flash point, hence creating a potential safety hazard.

9. Liquid Cooling System Consideration
System Types
-Direct cooling system (cont.)
Restrictions
- Necessity for the maintenance of coolant purity
- The system must be absolutely airtight in order to prevent air or moisture from degrading the heat transfer performance of the coolant.
- Extreme care is thus required in selecting a dielectric for direct cooling applications.

10. Liquid Cooling System Consideration
System Types
-Direct cooling system (cont.)
Common Examples of Direct Liquid Cooling
Application
Coolant
Cray-2 supercomputer
FC.77
Laser target illumination for electro-optical systems
FC-104, EGW, deionized water
Radar transmitter and TWTs on F-15 and F-16 fighter aircraft and others
C25R
Antenna and klystron tubes for E3-AWACS radar system
FC-77, EGW
TWTs on F-16 and ATF radars
C25R, PAO

11. Liquid Cooling System Consideration
System Types
-Indirect cooling system (cold-plate cooling)
No requirement on the voltage drop.
Suitable for commercial applications
May be used in antenna array modules having solid-state circuitry and in high-heat flux power supply modules in aircraft applications.

12. Liquid Cooling System Consideration
Coolant Selection Parameters
- FOM (Figure of Merit)
- Toxicity
- Maximum wet wall temperature
- Flammability
- Cost
- Material compatibility
- Corrosion
- Pressure drop characteristics
- Water absorption sensitivity

13. Liquid Cooling System Consideration
Pressure drop and pump requirements
- For the viscous pressure drop through the heat exchanger core, neglecting the entrance and exit losses,
the velocity head term () is replaced by (), where G is the mass flow per unit area, kg/m2.s, a more commonly used heat exchanger parameter.

14. Liquid Cooling System Consideration
Pressure drop and pump requirements
the velocity head term () is replaced by (), where G is the mass flow per unit area, kg/m2.s, a more commonly used heat exchanger parameter.

15. AIR COOLING SYSTEM Induced or Draft Cooling Forced Cooling
For small heat dissipation applications, the prime mover of the air cooling system may be the draft or circulation created by density variations.
Forced Cooling
The prime movers are fans or blowers . For The general classification of blowers is best defined in terms of specific speed. Specific speed, Ns, is expressed by the equation
Where:
Q (in ft3/min) and the pressure Δp (in inches of water)

16. AIR COOLING SYSTEM Fans and Blowers
Range of specific speeds for various Fans and blowers
Fan and blower impeller designs