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Powerful bipolar microwave transistors (PBT) operate, as a rule, in conditions close to the limiting ones, which requires controlling the release of heat from the active region of the crystal to the transistor body and further to the environment. One of the most efficient is the control of PBT heat characteristics, including the dependence of the heat resistance - the device body on the electrical mode parameters. However, the quantitative evaluations of connection of defects with measuring the heat parameters of devices in literature are absent. In the work the results of modeling using the COMSOL Multiphysics software the temperature distribution in the structures of a power bipolar microwave transistor (PBT), with defects of electrophysical and thermal nature have been presented. The dependences of the maximum overheating of the crystal working surface on the size and location of the defects have been obtained. It has been shown that the temperature dependence of power density released in the structure of PBT leads to a nonlinear dependence of the maximum and average temperature of the crystal surface on the total power dissipated in PBT. The developed thermal models can serve as the basis for creating the methods for diagnosing the PBT of thermoelectric characteristics and identifying the defective products. The comparative measurements of thermal characteristics of the serial high-power microwave transistors of the KT920B type with no defects and with an artificially introduced electrophysical-type defect in a diode switch-on using a T3Ster meter have shown that the thermal resistance of the body-to-case PBT with the defects has increased by 25-40% compared to the thermal resistance of the defect-free device. In this case, the thermal characteristics of PBT in the diode switching on of the «base-collector» transition are more sensitive to structural defects than in the diode switching on of the emitter-base transition, and more preferable for the purposes of diagnosing the PBT quality.
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The important factor, determining the functional properties, the limiting modes of operation and reliability of hetero-transient LEDs with the high-Ohm substrate is an account of heat release in it. A nonlinear thermoelectric model of InGaN/LED, taking into account the Joule heat release in the semiconductor substrate has been presented. The distribution of the potential on the elements of the structure and the current dependence of the thermal resistance of the semiconductor device structure have been obtained. The model adequacy has been confirmed by comparison of the calculated and experimental dependences of the thermal resistance of the powerful LED structure on the total current. The presented heat-electric model of LED diode accounting the Joule heat release permits to calculate its thermal resistance. The adequacy of the developed model has been experimentally verified.
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Thermal methods of quality control of the plated-through hole (PTH) of printed circuit board (PCB) are based on thermal models. However, known thermal models of PTH take no account of heat transfer to PCB material thus not allowing for PTH heat characteristic tying up with adhesion quality. In this work, an axisymmetric thermal model of a single-layer PCB PTH under one-sided heating conditions is considered. It was shown that the ratio of the temperature increments of the upper (heated) and lower end of the PTH in the considered range of heating power does not depend on the power level. A linear thermal equivalent scheme of the PTH has been proposed, which includes the longitudinal thermal resistance of the PTH metallization, determined by the parameters and quality of the metallization layer, the thermal resistance, which determines the convection heat exchange between the ends of the PTH with the adjacent PCB surface and the environment, and the thermal resistance of the area of the PCB material adjacent to the PTH, depending on the quality of the metallization adhesion and the PCB dielectric. Thermal equivalent circuit parameters determined by the ratio of the temperature increment of the upper and lower ends of the PTH and their difference can serve as the basis for the development of a nondestructive inspection procedure for PTH quality control by way of its unilateral heating, for example, by a laser beam.
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The model of the thermal defeat of the semiconductor microwave diode by powerful microwave impulse with the temperature dependent density of power has been presented. The distribution of the maximum temperature on semiconductor structure depending on duration of the impulse radiation has been found.
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