SMD-resistors: description, marking

SMD (Surface Mounted Devices) in English means "surface mounted device". SMD-components are ten times smaller in size and weight than traditional parts, due to this, a higher density of their mounting on the printed circuit boards of devices is achieved. In our time, electronics is developing at a tremendous pace, one of the directions is a reduction in the overall dimensions and weight of the instruments. SMD-components - due to their size, cheapness, high quality - have become very widespread and are increasingly replacing the classic elements with wire leads.

The photo below shows the SMD resistors placed on the PCB. It can be seen that, due to the small size of the elements, a high density of mounting has been achieved. Conventional parts are inserted into special holes in the board, and SMD-resistors are soldered to the contact tracks (pins) on the printed circuit board surface, which also simplifies the development and assembly of radioelectronic devices. Thanks to the possibility of hanging the installation of radio components, it became possible to produce printed circuit boards not only by double-sided, but also multilayered, outwardly reminiscent of puff cake.

In industrial production, the soldering of SMD components is carried out by the following method: a special soldering thermal paste (flux mixed with solder powder) is applied to the contact tracks of the board, after which the robot has the necessary elements, including SMD-resistors. The parts adhere to the solder paste, then the board is placed in a special oven where it is heated to the required temperature, at which the solder in the paste melts, the flux evaporates. In this way, the parts fit into place. After this, the circuit board is removed from the furnace and cooled.

For soldering components such as SMD at home, you need the following tools: tweezers, awl, nippers, magnifying glass, syringe with a thick needle, soldering iron with a thin sting, hot air soldering station. Consumables require solder, liquid flux. It is advisable, of course, to use a soldering station, but if you do not have it, you can get by with a soldering iron. When soldering the main thing is to prevent overheating of the elements and the printed circuit board. To ensure that the elements do not move and do not stick to the soldering iron, they should be pressed against the board with a needle.

SMD-resistors are presented quite in a wide range of nominal values: from one Ohm to thirty megaohm. The operating temperature of such resistors ranges from -550 ° C to +1250 ° C. The power of SMD-resistors reaches 1 W. With increasing power, the overall dimensions increase . For example, SMD resistors rated at 0.05 W have overall dimensions of 0.6 * 0.3 * 0.23 mm, and a power of 1 W is 6.35 * 3.2 * 0.55 mm.

Marking of such resistors is of three types: with three digits, with four digits and with three symbols:

- The first two digits indicate the value of the resistor value in Ohm, and the last one - the number of zeros. For example, the marking on resistor 102 means 1000 Ω or 1 kΩ.

- The first three digits on the resistor indicate the nominal value in Ohm, and the last one - the number of zeros. For example, the marking on resistor 5302 means 53 kΩ.

- The first two symbols on the resistor indicate the nominal value in Ohm, taken from the table above, and the last character indicates the multiplier value: S = 10-2; R = 10-1; B = 10; C = 102; D = 103; E = 104; F = 105. For example, the marking on resistor 11C means 12.7 kΩ.