Why Thermal Management?

1. Why Thermal Management? References: Sergent, J., and Krum, A., Thermal Management Handbook for Electronic Assemblies, McGraw-Hill, 1998 And Yeh, L.T., and Chu, R.C., Thermal Management of Microelectronic Equipment: Heat Transfer Theory, Analysis Methods, and Design Practices, ASME Press, New York, 2002.

2. Size and Performance Trends • Higher levels of integration in semiconductors • More multichip modules • Faster speeds, smaller devices • Leads to both more heat generation and higher heat densities

3. Increase in Circuit Complexity Yeh and Chu, 2002

4. Major Causes of Electronics Failures Yeh and Chu, 2002

5. Types of Failures • Soft failures: Properties change, changing performance outside the specs • Resistors, capacitors, transistors, leakage currents • Example: bipolar transistor gain can change by a factor of 3 over the military temperature range Sergent and Krum, 1998.

6. Types of Failures, cont. • Hard failures: component doesn’t work at all • Corrosion, chemical reactions, intermetallic compound formation • Cracking caused by different coefficient of thermal expansions • Breakdown of materials

7. Classification of Temp-Related Failures Sergent and Krum, 1998.

8. Yeh and Chu, 2002

9. Other common (non-temp-related) failures • Due to mechanical interconnections: poor wire bonds, die bonds, lead frame bonds, etc.; bonds not fully formed or incompatible materials • Due to manufacturing defects in active devices: impurities in semiconductors, pinholes in insulating oxide, etc. • Due to electrical overstress: overstress during operation or else exposure to electrostatic discharge • Due to chemical reactions: corrosion or formation of intermetallic compounds; exacerbated by high temperatures

10. Designer Reaction to Thermal Issues • Two common reactions • Underestimate of component temps, resulting in too little cooling, leading to failure • Overkill – cooling a system much more than needed, leading to excessive cost and increased size and noise • To properly design the system, we need to know the following • How and where heat is generated • How to estimate the temperature • How to remove the heat • We’ll focus on these three issues in class!