Aspects of the circuit board thermal design

Several factors such as copper density, number of copper layers, surface properties, connectors, etc., determine the thermal behavior of the printed circuit board. Due to the number of parameters it is impossible in a straight forward manner to determine the equilibrium temperature for any part of the board. For the successful operation of the electronics design only a certain, usually quite narrow, temperature range is available. This range varies in the course of the mission typically allowing greater temperature variations in the non-operational mode. The more important, and from the design point of view, more interesting is the thermal behavior of the electronics in the operational mode. For this purpose we have developed a thermal design procedure for printed circuit boards to be used as an aid and support in electronics design. The procedure is based on digital copper density information gathered from scanned electronics blueprints using SAUNAr Thermal Design Program together with a special MathCadr program to modify SAUNAr for the space environment. An iterative procedure gives the temperatures on the circuit board with 1 cm spatial resolution and 2 - 5 C temperature accuracy in an informative graphical output, together with all statistical information stored in file, if so wished. The principles, operations needed and some results gained are presented in this document.