SMD code
The miniaturization of electronic components, especially SMD components, has prompted manufacturers to mark them with letters and numbers instead of colors. Since the shape of the SMD component does not usually allow any conclusions to be drawn about its function and certainly not about its characteristic values, such components are given a special code, the SMD code.
So that the manufacturer of an SMD component can be identified during development and production, there is a two- digit abbreviation of the manufacturer's name. For example," AD" stands for Analog Devices," FA" for Fairchild or" MO" for Motorola.
The SMD code for resistors and capacitors
Resistors and capacitors have a two-, three- and four-digit code which indicates the resistor or capacitor value and its tolerance. Resistors and capacitors with a two-digit SMD code have tolerances of 5%. Such an identifier consists of a letter and a digit. The letter indicates the value resulting from the standard series. The standard series starts with the letter "A", which corresponds to the value 1.0, "B" stands for the value 1.1, "C" for 1.2 and so on until "Z", which corresponds to 9.1. If they are lowercase letters, then they are intermediate values such as 1.5, 2.0, 2.5, 3.0, and so on. The following digit indicates the power of ten, using picofarad as the base for capacitors. Thus, the two-digit SMD code C4 corresponds to a resistance value of 12 kilo-ohms or a capacitance of 12 nF.
Three-digit numbers mean that the resistor has a tolerance of 5%, For three-digit numbers, the first two digits are the resistance value, and the third digit indicates the number of zeros.
Components with four-digit SMD code have a tolerance of 1%. The first three digits indicate the resistance value and the fourth indicates the power of ten. Examples: the three-digit number 105 corresponds to a resistance value of '10 * 10^5', i.e. 1 mega-ohm with a tolerance of 5 %. The four-digit number 2372 corresponds to a resistance value of `237 * 10^2`, i.e. 23700 or 23.7 kilo- Ohm.
Exceptions for SMD codes
There is one more exception in the marking, which still has an "R" in the designation. The "R" only serves as a comma. If 4R3 is marked, this means a resistance value of 4.3 Ohm, if R43 is marked, the resistance value is 0.43 Ohm.
In the case of capacitors, the dielectric strength is indicated either directly or by a letter; the numerical value corresponds to that of the resistors. However, a distinction is made between tantalum capacitors and electrolytic capacitors. The value indication on tantalum capacitors refers to picofarads, that of electrolytic capacitors to microfarads. The letter designation is also different. For example, if the letter "E" on tantalum capacitors stands for a dielectric strength of 16 volts, then the same letter "E" on an electrolytic capacitor stands for 25 volts.