Thermal Control for High Density Packaging

Direct cooling of semiconductor components is limited to very low power levels due to the small surface area of the components. Free air convection is limited to about 0.5 watts per square inch while forced air cooling can increase the allowable power levels to 5 watts per square inch. Forced convection with liquid coolants is required for higher power levels. Pressure drop is genrally not a problem due to the low velocities and large duct sizes. Indirect cooling permits more efficient thermal design of heat exchangers. Forced-air cooling can handle heat loads up to 10 watts per square inch. Above this level, liquid is required. Pressure drop is a major factor in forced-air cooling and extended surfaces must be carefully designed. Nucleate boiling presents component access problems. However, it offers the possibility of an order of magnitude increase in power dissipation when compared to forced convection in the same liquid.