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.

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

Increase in Circuit Complexity Yeh and Chu, 2002

Major Causes of Electronics Failures Yeh and Chu, 2002

Types of Failures Soft failures: Properties change, changing performance outside the specs 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.

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

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

Yeh and Chu, 2002

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 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 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 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 Due to chemical reactions: corrosion or formation of intermetallic compounds; exacerbated by high temperatures

Designer Reaction to Thermal Issues Two common reactions Two common reactions Underestimate of component temps, resulting in too little cooling, leading to failure 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 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 To properly design the system, we need to know the following How and where heat is generated How and where heat is generated How to estimate the temperature How to estimate the temperature How to remove the heat How to remove the heat We’ll focus on these three issues in class! We’ll focus on these three issues in class!