A simple equation for heat spreading angle is derived which is useful for cases with a single layer\nthermal spreader. The derivation starts with Fourier�s heat transfer law. Heat spreading in two\ndimensions is then introduced which results in a quadratic equation relative to spreading angle.\nThe result is a closed form equation for heat spreading angle. Calculations using the equation are\ncompared to 3D finite element simulations which show agreement acceptable for most practical\napplications and over a wide range of physical dimensions and thermal conductivities. A normalized\ndimensional parameter is defined which is used to generate a curve fit equation of the\nspreading angle. A three step procedure is then presented which allows the calculation of the\nspreading angle and temperature rise in the thermal spreader. The result has application for initial\ncalculations of temperature rise in microwave hybrid modules and electronic packages such\nas heat sinks for high power amplifiers. This is because it is common for these types of modules\nand packages to use a single layer heat spreader in copper-tungsten (CuW) or copper-molybdenum\n(CuMo) connected to a cold plate. An important benefit of this method is that it allows microwave\nhybrid designers and high power amplifier packaging engineers a method to quickly\nperform trade studies to determine the maximum mounting temperature for integrated circuits.
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