Now that a number of techniques exist which permit the fabrication of circuits with a theoretical packing density of 1 million or more circuits per cubic foot, thermal design is an essential initial consideration. In most cases the drive toward microminiaturization is based on the need for a large number of circuits in a small weight and volume. If present circuit designs are taken as the basis for microminiaturization, it can be shown that with most materials being considered the temperature will rapidly rise to the point where circuits will become inoperative. This paper outlines some of the basic considerations in terms of heat conductivity of materials, maximum safe working temperatures, and circuit power levels as dictated by current devices. A method is described whereby a proposed design configuration can be computer-analyzed in terms of isothermal lines and maximum hot spot temperatures and decisions made on that basis as to which type of cooling is most appropriate.

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