Features of assembly and installation of electrical circuits. reference Information

Features of assembly and installation of electrical circuits

Background

It is impossible to tell about all the features of this work in a note, but you need to know the most important rules before you start manufacturing any radio engineering design for the first time.

Many circuits use micropower microcircuits made using CMOS technology (series 561, 1561, 564), as well as field-effect transistors. All these parts, until they are installed on the board, are afraid of static electricity. On a person, it is formed due to the friction of clothing and can exceed a potential of 1000 V. Therefore, before touching these parts, it is necessary to put on a grounded bracelet or at least touch the heating battery metal with your hand. Parts that are afraid of static electricity should be stored in metal foil or in special boxes. To protect field-effect transistors, their conclusions can be wrapped with a bare wire, which is removed during installation. Mounting these parts on the board is best done last, after installing all the other parts.

The assembly of the printed circuit board begins with the installation of elements that require mechanical fastening. At the same time, it is sometimes necessary to expand the holes and grooves, and it is inconvenient to do this with already installed parts.

All installed parts must not have scratches, cracks, dents or any other mechanical damage on the body. Even if such details work, it does not mean that it will last long. The parts are installed so that they do not touch each other.

The soldering iron is best used with a grounded tip, and the temperature of the tip should be around 270°C. If it is much higher, then the solder on the tip quickly burns out and becomes gray, and at normal temperature, the molten solder does not lose its mirror shine, which remains even after it cools. Such soldering provides a high-quality electrical connection.

To speed up soldering, liquid alcohol-rosin flux is used - it destroys the oxide film on the surface of the leads of the parts. Flux can be easily made on your own by dissolving a piece of rosin in alcohol in a ratio of about 1:10.

When soldering the elements, in order not to overheat them, the soldering iron with solder on the tip touches the leads for no more than 3 seconds. At the same time, it is convenient to hold the elements themselves with tweezers. For better soldering, it is useful to pre-irradiate the leads of parts before installation on the board. When installing the elements, their conclusions are bent so that the marking is visible. This will come in handy when you set up the device and understand installation errors.

Some parts (diodes, zener diodes, electrolytic capacitors, etc.) have polarity, and it must be observed during installation. It is most easy to make a mistake with the installation of electrolytic capacitors, especially imported ones, since it is difficult to find reference information on them, and the polarity is not indicated on the case.

In this case, it is convenient to use a circuit that will allow you to easily determine its polarity by the minimum leakage current of the capacitor.

Features of assembly and installation of electrical circuits

Leakage is measured indirectly by the voltage drop across the resistor R1 after the charge of the connected capacitor is completed. The voltage supplied from the power supply must not exceed the allowable operating voltage for the capacitor. If the polarity of the capacitor is connected incorrectly, the leakage will be 10 ... 100 times greater than the correct one. A voltmeter for these measurements is needed with a large input resistance, for example B7-38A.

After soldering is completed, we shorten the protruding leads of the parts and wash off the remains of rosin with a solvent, which will allow us to control the quality of the installation: there should be no drops of solder and inter-track shorts on the board.

Publication: radioman.ru

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