Capabilities and Limitations of Air Cooled Avionic Packages

Currently, avionics equipment depends primarily on forced air cooling for thermal control. The electronic parts are mounted on cards which are enclosed in an electronic enclosure to facilitate packaging and cooling of high density electronic packages found in present day avionics equipment. Three types of thermal designs, classified according to how air is used to cool the cards, are commonly used. The three types are air impingement cooled, conduction to coldwall, and flow through cooling in the card itself. The cooling capacity of the designs vary, with air impingement cards having the least cooling capacity and the flow through cards having the highest cooling capacity. Flow through cards are capable of cooling electrical power densities of up to 3098 watts/m² (2 watts/in²) and 7.06 × 10⁴ watts/m³ (2000 watts/ft³) of volume. Although fairly high power density levels can be cooled with forced air cooling, the practical limit of power density that can be adequately cooled may soon be exceeded, because of the continuing trend toward higher electronic packaging density. Methods of estimating cooling capacities for the above designs are presented herein as well as the limitations imposed when cooling with forced air.