Materials and Design for Advanced Heat Spreader and Air Cooling Heat Sinks

Abstract

Air cooling is the simplest and principal method of thermal management most widely used for a variety of electronic systems ranging from portable electronics to large business systems. The advantages of air cooling are its ready availability and ease of application. Air cooling usually dissipates heat through heat spreaders and heat sinks. Low-power electronic systems are conveniently cooled by natural convection and radiation. When natural convection is not adequate, the forced convection is adopted by a fan or blower to blow the air through the enclosure that houses the electronic components. Various heat spreading methods have been widely used in electronic packaging. Heat spreaders are usually used in die level packaging to spread heat from the microprocessor chip into the package. Spreaders are commonly used within electronic enclosures to move heat from discrete components to the walls of the enclosure. Materials and process technologies to make heat spreaders have been involved in metallic heat spreaders ( 5,000 W/m K), and oscillating flow heat spreaders (up to 120,000 W/m K). Heat sinks can usually be divided into active and passive. Active heat sinks utilize power and are usually a fan type, or liquid cooling or some other Peltier cooling device. Passive heat sinks are fully reliable, usually made of a metal such as aluminum-finned radiator that dissipates heat through convection. Next generation heat sinks and leading-edge materials in air-cooled heat removal have been developed and are increasing, such as high thermal conductivity polymers, carbon-based composites, sintered metallic powders, phase-change compounds, synthetic diamonds, and strand-oriented graphite materials. Composite heat sinks are emerging and getting increased attention since nanotechnology can be applied. This chapter will review materials and design for advanced heat spreaders and air cooling sinks, including the concept of air cooling, spreading and constriction resistance analysis, heat spreader classification and materials selection, and overview of design, materials, and processing of air cooling heat sinks.