7/8/2023 0 Comments Power transistor case![]() a printed circuit board or an external heatsink.Ĭonvection is defined as the transfer of heat via a fluid, which may be a liquid or gas, as in the surrounding air. At this point heat may be further transferred by conduction through any solid material the device is in contact with, e.g. For a packaged semiconductor device the majority of the heat will be transferred by conduction: from the heat source at the device’s core through the semiconductor substrate, the lead frame to which the chip is attached, and through the molding material that encapsulates the device to its external surface. ![]() There are three basic mechanisms by which heat is dissipated from an electronic device: conduction, convection and radiation. The inaccuracies that can arise from using the thermal information provided in the datasheet will be highlighted along with an alternate method of determining the key junction temperature of a device. This article will look at the mechanisms by which heat is normally dissipated, aiming to understand in what way these apply to semiconductor devices and in turn how the semiconductor manufacturers specify the thermal performance of their products. The packaging of semiconductor devices further complicates the means by which heat can be dissipated so it is important to understand the various processes involved and the way in which thermal information is provided in device datasheets. Whatever the cause, losses in semiconductor devices generate heat that has to be dissipated if the junction temperature is to be kept within acceptable limits for correct device operation. Even in the off-state, losses due to transistor leakage currents can be significant in devices such as microprocessors that have to use small geometry processes in order to pack millions of transistors into a single integrated circuit. ![]() Conduction losses are due to the device’s internal resistance that, no matter how low it is, will result in a power loss when a current is flowing. Switching losses occur during the interval between the on- and off-states of a junction, when there is both a voltage across the device terminals and a current flowing through it. Semiconductor devices are not perfect - all diodes and transistors are characterized by power losses due to switching and conduction. ![]() Author: Siva Uppuluri, Applications Engineer ![]()
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