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 doesnt 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
• Well focus on these three issues in class!