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For a Surface Mount Diode

In a surface mount application, the diode is mounted to a ceramic substrate or PC board. The heat generated in the junction of the diode flows through the end tabs or formed leads directly to the substrate or PC board. The thermal impedance of the diode (given in the diode data sheet) is added to the thermal resistance of the substrate or PC board to obtain the total thermal impedance of the package. See Figure 3 for a typical surface mount configuration.

Total Package Thermal Impedance

j-ms = jc + substrate
where jc = Thermal impedance from diode junctions to the substrate
substrate = Thermal impedance through the pc board or substrate

The total thermal impedance of the package is the sum of the thermal impedance from the diode junctions to the internal surface of the pc board or substrate, plus the thermal impedance through the substrate to the external mounting surface.

In order to assure reliable operation, heat generated by the diode must be transmitted away from the base plate, PC board, or mounting surface. Common methods of conducting heat away from mounting surfaces include forced-air cooling, the use of water-cooled base plates, and oil operation. All of these methods help to maintain a constant operating temperature.

Last revised: 03 Aug 2012