Electronics Cooling Mechanical Power Engineering Dept.

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=I 2 R -Switching power dissipation in transistors

Automotive Electronics Electronic content in cars and trucks has significantly increased in the last 30 years. Much of the functional content of these vehicles is now generated or controlled by electronic systems. History of typical engine control modules (ECMs)

Examples of thermal requirements for various products Cost/Performance 2004 RF Chip Thermal Requirements -Power Dissipation - 100W -Temperatures: Junct = 150C; Ambient = 45C -Chip Size - 3mm x 1mm 0.3mm -Wireless Module = 10 Chips, 1kW -Thermal “Space Claim” x 150 x 150mm -Thermal Resistances: Spreading (Chip Level) = 0.6K/W Internal Convective (Chip Level) = 0.2K/W External Convective (Module Level) = 0.25K/W

Thermal Packaging, Future Forecasting Future Thermal Packaging Needs -Higher Power Dissipation -Higher Volumetric Heat Density -Market-Driven Thermal Solutions -Air as the Ultimate Heat Sink -Environmentally-Friendly Design Future Thermal Packaging Solutions -Thermo-fluid Modeling Tools -Integrated Packaging CAD -Compact Heat Exchanger Technology -Design for Manufacturability/Sustainability -“Commodity” Refrigeration Technology -Thermal Packaging Options and Trends

Aims of thermal control PREVENT CATASTROPHIC FAILURE -Electronic Function -Structural Integrity PROVIDE ACCEPTABLE MICROCLIMATE -Device Reliability -Packaging Reliability -Prevent Fatigue, Plastic Deformation and Creep SYSTEM OPTIMIZATION -Fail Safe or Graceful Degradation -Multilevel Design -Reduction of “Cost of Ownership”

Modes of heat transfer

Conduction Conduction heat transfer as diffusion of energy due to molecular activity. Conduction in liquids and solids ascribed to molecules vibration (solids), translational and rotational (liquids)

Conduction Fourier’s law

Thermal convection The heat transfer by convection is described by the Newton's law of cooling:

Thermal convection convection heat transfer ranges Process h(w/m2.k) Free convection - gases liquids Forced convection - gases liquids 50-20,000 Convection with two phase - boiling or condensation ,000

Thermal radiation The mechanism of heat transfer by radiation depends on the transfer of energy between surfaces by electromagnetic waves in the wave length interval between 0.1 to 100 μm. Radiation heat transfer can travel in vacuum such as solar energy. Radiation heat transfer depends on the surface properties such as colors, surface orientation and fourth power of the absolute temperature (T 4 ) of the surface. The basic equation for radiation heat transfer between two gray surfaces is given by

There exists an analogy between the diffusion of heat and electrical charge. Just as an electrical resistance is associated with the conduc­tion of electricity, a thermal resistance may be associated with the conduction of heat. Analogy between Heat Transfer and Electric Circuits

Series Circuits: By analogy

Parallel Circuit:

Combined Modes of Heat Transfer Combined Convection and Radiation

Combined Modes of Heat Transfer