SMD (Surface Mounted Devices) in English means "surface mounted device". SMD components are dozens of times smaller in size and weight than traditional parts, due to this, a higher density of their mounting on printed circuit boards of devices is achieved. In our time, electronics is developing at a tremendous pace, one of the directions is to reduce the overall dimensions and weight of devices. SMD components - due to their size, low cost, high quality - have become 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 mounting density is achieved. Ordinary parts are inserted into special holes in the board, and SMD resistors are soldered to contact tracks (spots) located on the surface of the printed circuit board, which also simplifies the development and assembly of electronic devices. Thanks to the possibility of surface mounting of radio components, it became possible to produce printed circuit boards not only double-sided, but also multi-layered, resembling a layer cake.
In industrial production, 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 places elements in the right places, including SMD resistors. The parts stick 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 and the flux evaporates. Thus, the details fall into place. After that, the printed circuit board is taken out of the oven and cooled.
To solder SMD components at home, you will need the following tools: tweezers, an awl, wire cutters, a magnifying glass, a syringe with a thick needle, a soldering iron with a thin tip, a hot air soldering station. Of the consumables, solder, liquid flux are needed. It is advisable, of course, to use a soldering station, but if you do not have one, 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. In order for the elements not to move and not stick to the tip of the soldering iron, they should be pressed against the board with a needle.
SMD resistors are presented in a fairly 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 1W. As power increases, overall dimensions increase. For example, 0.05W SMD resistors are 0.60.30.23mm, and 1W are 6.353.20.55mm.
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 1k ohms.
- The first three digits on the resistor indicate the nominal value in ohms, and the last one indicates the number of zeros. For example, the marking on the 5302 resistor means 53 kOhm.
- The first two characters on the resistor indicate the nominal value in ohms, taken from the table above, and the last character indicates the value of the multiplier: S=10-2; R=10-1; B=10; C=102; D=103; E=104; F=105. For example, the marking on a 11C resistor means 12.7 kOhm.
