Soldering iron for microsoldering. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Ham Radio Technologies

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In recent years, radio amateurs have increasingly had to deal with very small surface-mount radio components, as well as with factory-made equipment in which printed circuit boards are extremely densely mounted. In such conditions, it is difficult to use even miniature soldering irons with a tip diameter of 2,5 ... 3 mm.

I bring to the attention of readers a low-power electric soldering iron, which allows you to dismantle and mount parts on the board of an electronic watch and other similar devices under a magnifying glass. The soldering iron has a replaceable copper working rod with a diameter of 1,5 mm and is powered by an isolating step-down transformer. Supply voltage - 12...14 V.

The heating element of the soldering iron is of a closed type, that is, it is protected from contact with atmospheric oxygen; this ensures the durability of the soldering iron. The base of the element is a tube made of tin or sheet brass (in extreme cases, copper) 0,2 mm thick, rolled up on a mandrel with a diameter of 1,5 mm. A drill shank is suitable as a mandrel. Tube length - 30...35 mm. The edges should meet butt, without overlap.

Then a coating is prepared, which, after hardening, will become both an insulator and an element that mechanically fixes the assembled heater parts. 10-20 g of dry talcum powder (you can use baby powder) is poured into a small plastic vessel and silicate glue (also known as "liquid glass") is added dropwise with constant stirring. The finished coating should have the density of a regular dough and adhere well to a metal surface.

The tube is covered with a thin uniform layer of coating and rolled with a piece of plywood or sheet plastic on a flat surface sprinkled with talc. The thickness of the coating layer should be close to 0,5 ... 1 mm. With a smaller thickness, it is difficult to ensure reliable insulation of the heater wire from the tube along its entire length, and with a larger thickness, the heating element assembly will turn out to be too thick.

It is best to dry the workpiece in a gas stove oven for two to three hours. The temperature is slowly increased to 100 °C, and at the end of drying, the workpiece is heated to 150 °C. Drying too fast can cause the coating to blister or peel off.

It is best to determine the required temperature and drying time experimentally. It is necessary to strive to ensure that the dried coating is continuous and dense, does not crumble when winding the wire. Then the thickness of each coating layer can be made minimal, which will make it possible to make a heating element, and hence its casing, of a very small diameter - no thicker than a pencil.

It is also important to note that a thin first layer of coating transfers heat better from the electric heater coil to the soldering rod than a thick one. In other words, the spiral during operation will heat up to a lower temperature, so it will last longer.

The remains of the coating should not be thrown away - it can be stored in a sealed container for a long time. If it thickens, add glue and mix thoroughly.

A piece with a resistance of 0,2 ohms is cut off from a coil of nichrome wire with a diameter of 0,25 ... 10 mm (measured with an ohmmeter) with a margin of 15 mm from one end and 50 mm from the other - for connection with a flexible cord. The total length of the piece usually does not exceed 300...350 mm.

This wire is wound on a dried tube with such a pitch that the winding begins and ends five millimeters from the ends of the tube. It is advisable to first carry out a simple calculation of the number of turns, the winding pitch and the length of one turn (based on the diameter of the tube). To prevent the wound wire from unraveling, the first and last turns should be fixed with thin threads (they will burn out when the soldering iron is turned on).

The winding leads (one 15 mm long and the other 50 mm long) are tucked into the tube and the winding is coated with the same coating, after which it is rolled and dried. After the workpiece has dried, the long lead is wrapped in one and a half to two turns around it towards the short lead and tucked into the tube along with it.

The workpiece is coated again, rolled and dried. Care must be taken to ensure that the leads do not touch the metal tube of the heater. After drying, the coating is removed from the workpiece, the excessively protruding ends of the tube are filed with a file and its channel is cleaned. Try to insert a soldering rod. It should fit tightly, but without too much effort, into the tube.

Then, rigid copper conductors are attached to the winding terminals with a tight twist, to which a flexible soldering iron cord will be soldered during final assembly. The twisting points can be wound with glass yarn and impregnated with the same coating, only more liquid. Ceramic or glass insulating tubes should be put on copper conductors.

The heater casing is a suitable thin-walled tube. In extreme cases, the tube is easy to bend from tin. The tube should tightly fit the heating element, for which it is wrapped with fiberglass or thin asbestos in the right places, and one or two clamping rings are put on the tube from the outside.

The handle can be made of wood, textolite or heat-resistant plastic. To reduce the transfer of heat from the heater casing to the handle, two through holes with a diameter of 3 mm are drilled in the casing tube near the handle.

The soldering rod is made of rigid copper wire with a diameter of 1,5 mm. Rod length - 40 mm. At a distance of 15 mm from the sting, two dents are made on the rod with round-nose pliers or a hammer - the local thickening serves as a limiter when the rod is inserted into the heater.

Do not overhang more than 15mm. This will hardly increase the service life of the soldering rod, but it will add inconvenience in using the soldering iron. The end of the rod will not be rigid enough - it will bend when pressed radially, when soldering massive parts, the time for heating the junction and melting the solder will noticeably increase.

To prevent the rod from jamming in the heater tube, before each turning on the soldering iron, remove the rod, pour out the scale and insert it into place. If after a while the fastening of the rod loosens so much that it interferes with work, you should not bend or flatten it, it is better to make a new one.

The length of the finished soldering iron is 150 mm. Power - about 12 watts. To power the soldering iron, a vertical scan transformer TVK - 110LM from old tube TVs is suitable without alteration. A winding with pin numbers 220 and 1 is connected to the network - 2 V, and the soldering iron is powered from winding 3 - 5 (voltage without load is about 13 V).

Nevertheless, it is much more convenient to power the soldering iron through a trinistor power regulator. On the same TVK-1 10LM, without disassembling it, carefully, so as not to damage the insulation, wind one layer of wire PEV - 2 0,8 in any direction. Connect this winding in series according to winding 3 - 5, the total voltage should be approximately 17 V. This voltage is quite sufficient for the normal operation of the power regulator.

If you set the regulator to the maximum, the soldering iron will operate in the mode of increased tip temperature against the norm - in some cases, such a mode is necessary. Under normal soldering conditions, the power should be reduced slightly, and during breaks in work, significantly, up to 50%. This power regulator is handy.

Author: A.Naumov, Chapaevsk, Samara region

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