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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Radiators. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Ham Radio Technologies 10.1. Purpose of radiators- remove heat from semiconductor devices, which allows to reduce the temperature of pn-junctions and thereby reduce its effect on the operating parameters of devices. Lamellar, ribbed and pin radiators are used. To improve heat dissipation, a semi-conductive device is best attached directly to the radiator. If electrical isolation of the device from the chassis is necessary, the radiator is mounted on the chassis through insulating gaskets. The heat-radiating capacity of the radiator depends on the degree of blackness of the material (or its surface) from which the radiator is made:
The greater the degree of blackness, the more efficient the heat dissipation will be. 10.2. pin heatsink - a very efficient heat sink for semiconductor devices. For its manufacture, sheet duralumin with a thickness of 4-6 mm and aluminum wire with a diameter of 3-5 mm are required. On the surface of the pre-treated radiator plate, the holes for the pins, the leads of the transistors (or diodes) and the mounting screws are marked with a center punch. The distance between the centers of the holes (pitch) for the pins in a row and between rows should be equal to 2-2,5 diameters of the aluminum wire used. The diameter of the holes is chosen in such a way that the wire enters them with the smallest possible gap. On the reverse side, the holes are countersinked to a depth of 1-1,5 mm. A mandrel is made from a steel rod 80-100 mm long and V-10 mm in diameter, for which a hole with a diameter 0,1 mm larger than the wire diameter is drilled at the end of the rod. The depth of the hole should be equal to the height of the future radiator pins.
Rice. 10.1. Crimp for radiator pins Then the required number of pin blanks is cut. To do this, a piece of wire is inserted into the hole of the mandrel and cut off with wire cutters so that the length of the end protruding from the mandrel is 1-1,5 mm greater than the thickness of the plate. The mandrel is clamped in a vice with the hole up, a pin blank is inserted into the hole, on the protruding end of which a plate is put on the front side and riveted with light hammer blows, trying to fill the countersink recess. Thus, all the pins are installed. A pin heatsink can also be made using a slightly different way of inserting the pins into the holes in the base plate. A steel crimp is made, the drawing of which for pins with a diameter of 3 and a length of up to 45 mm is shown in fig. 10.1. The working part of the crimp should be hardened. The pin is inserted into the hole in the radiator base, the base is placed on the anvil, a crimp is put on top of the pin and hit with a hammer. An annular groove is formed around the pin, and the pin itself is tightly planted in the hole. If it is necessary to make a double-sided radiator, then two such crimps are required: a pin is inserted into one of them, installed on the anvil with the hole up, the radiator base is strung, and the second crimp is put on top. With a hammer blow on the upper crimp, the pin is fixed from both sides at once. In this way, it is possible to manufacture radiators from both aluminum and copper alloys. And finally, the pins can be installed using soldering. To do this, take copper or brass wire with a diameter of 2-4 mm as a material. One end of the pin is tinned for a length greater than the thickness of the plate by 1-2 mm. The diameter of the holes in the plate should be such that the tinned pins fit into them without much effort. Liquid flux is introduced into the base holes (Table 9.2), pins are inserted and each of them is soldered with a powerful soldering iron. At the end of the work, the radiator is washed with acetone.
Rice. 10.2. Radiator for a powerful transistor 10.3. Copper Sheet Radiator1-2mm thick can be made for powerful transistors such as P210, KT903 and others in similar cases. To do this, a circle with a diameter of 60 mm is cut out of copper, holes are marked in the center of the workpiece for mounting the transistor and its leads. Then, in the radial direction, a circle is cut with scissors for metal by 20 mm, dividing it into 12 parts along the circumference. After installing the transistor, each sector is turned 90° and bent up. 10.4. Radiator for high power transistorstype KT903, KT908 and others in similar cases can be made of aluminum sheet 2 mm thick (Fig. 10.2). The indicated dimensions of the radiator provide the area of the radiating surface sufficient for power dissipation on the transistor up to 16 W.
Rice. 10.3. Radiator for a low-power transistor: a - sweep; b - general view 10.5. Radiator for low power transistorscan be made from sheet red copper or brass 0,5 mm thick in accordance with the drawings in fig. 10.3. After making all the cuts, the reamer is rolled into a tube using a mandrel of the appropriate diameter. Then the workpiece is tightly put on the transistor case and pressed with a spring ring, having previously bent the side mounting ears. The ring is made of steel wire with a diameter of 0,5-1 mm. Instead of a ring, you can use a band of copper wire. Then the side ears are bent down, the incised "feathers" of the workpiece are bent outward to the desired angle - and the radiator is ready. 10.6. Radiator for transistors series KT315, KT361can be made from a strip of copper, aluminum or tin with a width of 2-3 mm more than the width of the transistor case (Fig. 10.4). The transistor is glued into the radiator with epoxy or other adhesive with good thermal conductivity. For better thermal contact between the transistor case and the radiator, it is necessary to remove the paintwork from the case at the points of contact, and install it in the radiator and glue it with the minimum possible gap. Install the transistor with the heatsink on the board, as usual, while the lower edges of the heatsink should rest against the board. If the width of the strip is 7 mm, and the height of the radiator (made of tinned sheet 0,35 mm thick) is 22 mm, then at a dissipation power of 500 mW, the temperature of the radiator at the place where the transistor is glued does not exceed 55 °C. 10.7. Fragile metal heatsinkfor example, from sheet duralumin, they are made in the form of a set of plates (Fig. 10.5). In the manufacture of gaskets and radiator plates, it is necessary to ensure that there are no burrs on the edges of the holes and on the edges of the plates. The contacting surfaces of the gaskets and plates are carefully ground on fine-grained sandpaper, laying it on a flat glass. If it is not required to isolate the transistor housing from the device housing, then the radiator can be mounted on the wall of the device housing or on the internal partition without insulating gaskets, which ensures more efficient heat transfer.
10.8. Mounting diodes type D226 on the radiatoror on a heat sink. The diodes are fixed with a flange. The cathode lead is bitten off at the very base and the bottom is carefully cleaned on a fine-grained sandpaper until a clean, even surface is obtained. If it is necessary to leave the cathode terminal, then a hole is drilled in the radiator for the terminal, the varnish is removed from the bottom with acetone and the side (rim) of the diode is carefully filed flush with the bottom for better thermal contact between the diode and the radiator. 10.9. Thermal Contact Improvementbetween the transistor and the heatsink will provide more power dissipation on the transistor. Sometimes, especially when using cast radiators, it is difficult, and sometimes even impossible, to remove shells and other surface defects at the place of thermal contact (to improve it). In this case, a lead gasket will help. The lead plate is carefully rolled or flattened between two smooth flat bars to a thickness of about 10,5 mm and the gasket is cut to the required size and shape. Both sides of it are cleaned with a fine-grained sandpaper, installed under the transistor and the assembly is tightly compressed with screws. The gasket should not be thicker than 1 mm, as the thermal conductivity of lead is low. 10.10. Blackening of aluminum radiators.To improve the heat transfer efficiency of the radiator, its surface is usually made matte and dark. An affordable way of blackening is the treatment of the radiator in an aqueous solution of ferric chloride. To prepare the solution, an equal volume of ferric chloride powder and water is required. The radiator is cleaned of dust, dirt, thoroughly degreased with gasoline or acetone and immersed in a solution. Keep in the solution for 5-10 minutes. The color of the radiator is dark grey. Processing must be carried out in a well-ventilated area or outdoors. Did you know? 10.11.The thermal regime of low-power transistors can be facilitated by putting a torus ("steering wheel") on the metal case of the transistor - a spiral twisted from copper, brass or bronze wire with a diameter of 0,5-1,0 mm. 10.12.A good heatsink can be the metal case of the device or its internal baffles. 10.13.The flatness of the heatsink pad is checked by smearing the base of the transistor with some paint and applying it to the surface of the pad. Protruding contact areas. the radiator pads will be painted. 10.14. To ensure good thermal contact, the surface of the transistor adjacent to the radiator can be lubricated with a non-drying lubricant, such as silicone. This will reduce the thermal resistance of the contact by one and a half to two times. 10.15.To improve cooling conditions, the radiator must be positioned so as not to interfere with convection air flows: the radiator fins are vertical, and the side on which the transistor is located must be on the side, and not below or above. Author: tolik777 (aka Viper); Publication: cxem.net
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