SMD-resistors: description, marking

SMD (Surface Mounted Devices) in translation fromEnglish 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 huge 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 SMD resistors placed on the PCB.

It can be seen that, due to the small sizehigh density of assembly is achieved. Ordinary parts are inserted into special holes in the board, and SMD-resistors are soldered to contact tracks located on the surface of the printed circuit board (pins), which also simplifies the development and assembly of radioelectronic devices. Due to the possibility of hanging the installation of radio components, it became possible to produce printed circuit boards not only with two-sided, but also multilayered, outwardly reminiscent of puff cake.

В промышленном производстве пайка SMD-компонентов is made by the following method: on the contact tracks of the board a special soldering thermal paste (flux mixed with solder powder) is applied, 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 that, the PCB is removed from the furnace and cooled.

For soldering components such as SMD in householdthe following tools will be needed: tweezers, an awl, nippers, a magnifying glass, a syringe with a thick needle, a soldering iron with a thin sting, a 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 widerange of nominal values: from one Ohm to thirty megaohm. The operating temperature of such resistors varies 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.

The 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 in Ohms, and the last - the number of zeros. For example, the marking on the resistor 102 means 1000 ohms or 1 kOhm.

- 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.

- Первые два символа на резисторе указывают на the nominal value in Om taken from the table given 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.