PCB Technical - PCBA capacitance identification method

PCBA capacitance identification method
1. Capacitors are generally represented by "C" plus a number in the circuit (for example, C25 represents a capacitor numbered 25).

A capacitor is a component composed of two metal films close together and separated by an insulating material in the middle. The characteristic of the capacitor is mainly to block the direct current and pass the alternating current. The size of the capacitor capacity is the size that can store electrical energy. The obstructive effect of the capacitor on the AC signal is called capacitive reactance, which is related to the frequency and capacitance of the AC signal.

Capacitive reactance XC=1/2πf c (f represents the frequency of the AC signal, C represents the capacitance)

2. Capacitance identification method

The identification method of capacitance is basically the same as that of resistance, which can be divided into three types: direct marking method, color marking method and number marking method. The basic unit of capacitance is expressed in Fara (F), and other units are: millifarad (mF), microfarad (uF), nanofarad (nF), picofarad (pF). Among them: 1 farad=103 millifarad=106 microfarad=109 nanofarad=1012 picofarad

The capacitance value of a large-capacity capacitor is directly marked on the capacitor, such as 10 uF/16V

The capacitance value of a small capacity capacitor is indicated by letters or numbers on the capacitor 6

Letter notation: 1m=1000 uF 1P2=1.2PF 1n=1000PF

Digital representation: generally use three digits to indicate the size of the capacity, the first two digits indicate the effective digits, and the third digit is the magnification.

For example: 102 means 10*102PF=1000PF 224 means 22*104PF=0.22 uF

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3. Capacitor capacity error table

Symbol F G J K L M

Allowable error ±1% ±2% ±5% ±10% ±15% ±20%

For example: a ceramic capacitor of 104J means that the capacity is 0.1 uF and the error is ±5%.

4. Fault characteristics

In the actual maintenance, the failure of the capacitor is mainly manifested as:

(1) Open circuit failure caused by pin corrosion.

(2) Open circuit failure of desoldering and virtual welding.

(3) Small capacity or open circuit failure caused by liquid leakage.

(4) Leakage, serious leakage and breakdown faults.
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