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The purpose of this paper is to give the nonspecialist some tools he can use to gain insight into some of the complex thermal problems encountered in electronic assemblies. Some causes of thermal problems in electronic components and assemblies are briefly reviewed on a fundamental level. This review includes a discussion of some basic thermal parameters, the effect of the thermal environment on other physical parameters, and ways the thermal environment affects the operating characteristics and life of electronic assemblies. Most of the paper is devoted to specific thermal design and cooling problems. Techniques are presented which can be used to determine the thermal stresses that develop in some assemblies during soldering, shipping, and storage; and to determine the cyclic thermal stresses that develop during normal operation. In addition, some fundamentals of heat transfer from minute electronic components by conduction, convection, and radiation are reviewed, and techniques are described that can be used to predict the heat transfer from both single and multiple sources. Experimental and analytical studies are cited to illustrate each topic discussed. For example, experimental data are presented to show the effect temperature has on the coefficient of thermal expansion and the compliance of epoxy-glass composites and its effect on stress relaxation in solder, These data are then used to analyze the form of the stresses that exist in a plated-through hole during soldering and temperature cycling.