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Capacitors Basic Guide: A Beginner's Manual for PCB Assembly Electronics Enthusiasts


Capacitors are one of the essential printed circuit board components, ranging from large circuits to small electronic motherboards, all need capacitors. The so-called capacitor is an electronic component that holds and releases electric charge.

Electronic Printing Circuit Board Capacitor

Capacitors Working Principle

The function of the capacitor is to store energy, which can convert unstable electric energy into stable electric energy and transmit it to the circuit. An ideal capacitor itself does not consume electrical energy, it releases as much energy as it absorbs. When the input voltage fluctuates, the capacitor will generate current because it will be charged or discharged. When the voltage is stable, no current will be generated, which is called "blocking DC and communicating with AC".

● Charging of Capacitors

When a capacitor is connected to the positive and negative terminals of a power supply, the positive terminal attracts negative charges and the negative terminal attracts positive charges. This causes the charges on the two conductor plates to separate, creating an electric field. This process is called charging, and there is a short charging current in the circuit during the charging process.

For a charged capacitor, there is an electric field between the two plates, and the potential difference is U. The electric energy obtained from the power supply is stored in the electric field. This energy is called electric field energy. Capacitors have the ability to store charge and electric field energy.

Charging of Capacitors

● Discharging of Capacitors

When the capacitor is disconnected from the power source, the capacitor starts to discharge. Charge flows from one conductor plate to the other, and the electric field gradually decreases until the capacitor is completely discharged.
After discharge, there is no electric field and the potential difference between the two plates, and the electric field can be converted into other forms of energy.

Discharging of Capacitors

● The Working Principle Formula of Capacitor Expresses:

Q = CV
Q represents the amount of charge stored in the capacitor, C represents the capacitance value of the capacitor, and V represents the voltage of the capacitor. This formula describes the relationship between the amount of charge a capacitor stores and its capacitance and voltage.

Labeling method of main parameters of the capacitor

Capacitance (capacity): Indicates the amount of charge a capacitor can store, usually in Farads (F). The marking method of capacitance value can be a combination of numbers, letters or numbers + letters. For example, 1uF means 1 microfarad, and 100nF means 100 nanofarad.

Labeling Method of Capacitor in Printed Circuit Board

● Direct Labeling Method

Electrolytic capacitors or larger non-polar capacitors: nominal capacity, rated voltage and allowable deviation.
Small non-polar capacitors: nominal capacity, rated voltage and allowable deviation.
Capacity unit: microfarad (μF), nanofarad (nF), picofarad (pF)
·1p2 means:1.2 pF;
·1n means: 1 000 pF;
·10n means: 0.01 μF;
·2μ2 means: 2.2 μF.

● Digital Annotation Method

The digital marking method generally uses three digits to indicate the capacity of the capacitor, and the unit is pF. Among them, the first two digits are effective figures of the capacitance, and the third digit is the multiplier, but when the third digit multiplier is 9, it means ×10 -1.
·101  means: 10 × 101 = 100 pF
·102  means: 10 × 102 = 1 000 pF
·103  means: 10 × 103 = 0. 01μF
·104  means: 10 × 104 = 0.1μF
·223  means: 10 × 103 = 0. 022μF
·474  means: 10 × 104 = 0. 47μF
·159  means: 10 × 10–1 = 1. 5 pF  

● Color Scale Method

Color scale method: Mark the color ring or color point on the capacitor to indicate the capacitance and allowable deviation.
· Four-ring color scale method: the first and second rings represent effective values, the third ring represents the multiplier, and the fourth ring represents the allowable deviation (ordinary capacitor).
· Four-ring color scale method: the first and second rings represent effective values, the third ring represents the multiplier, and the fourth ring represents the allowable deviation (ordinary capacitor).
· Brown, black, orange, and gold Indicate that its capacitance is 0.01 μF, and the tolerance is ±5%
· Brown, black, black, red, brown means that its capacitance is 0.01 μF, and the tolerance is ±1%

Capacitors Commonly Used In PCB

● Surface Mount Capacitors

Surface mount capacitors are capacitors that are mounted directly on the surface of a circuit board, featuring small size and suitability for mass production.
Uses: They are widely used in applications such as coupling, decoupling, filtering and voltage regulation in electronic equipment.

Surface Mount Capacitors In Printing Circuit Board

● Ceramic Capacitors

Ceramic material is used as the medium, a layer of metal (silver) film is coated on the surface of the ceramic, and then it is used as an electrode after high-temperature sintering. Features of small size, high-frequency response, and low cost. Ceramic capacitors are divided into Class 1 dielectric (NPO, CCG); Class 2 dielectric (X7R, 2X1) and Class 3 dielectric (Y5V, 2F4) ceramic capacitors.
Uses: Mainly used in high-frequency electrical printing circuits board.

● Aluminum Electrolytic Capacitors

Polarized aluminum electrolytic capacitors are formed by winding an aluminum foil with an oxide film (positive electrode) and a liner paper soaked in an electrolyte, together with a cathode (negative electrode) foil laminate. The external package has tube type and vertical type and there are blue or black plastic sleeves outside the aluminum shell.
Uses: It is usually used for filtering, decoupling, signal coupling, time constant setting, DC blocking, etc. in DC power lines or medium and low-frequency lines in PCB

Aluminum Electrolytic Capacitor in Printed Circuit Board Assembly

● Tantalum Capacitor

A tantalum capacitor is a type of capacitor that uses tantalum metal as the electrode material and tantalate as the electrolyte.
Tantalum capacitors are widely used in:
·Tantalum capacitors are used in mobile devices such as smartphones, tablets, and portable audio equipment for PCB stabilization and power management.
·Tantalum capacitors are often used in communication equipment, such as base stations, communication modules and network equipment, to provide efficient power filtering and decoupling functions
·Due to their high reliability and high-temperature resistance, tantalum capacitors are widely used in electronic equipment applications in aerospace, military and defense fields.

Tantalum Capacitor in PCB Assembly

● Polyester Capacitors

Polyester capacitors use polyester film as a medium and have a non-polar capacitor with a positive temperature coefficient (that is, when the temperature rises, the capacitance becomes larger).
Uses: Polyester capacitors usually have good high-temperature resistance and can work normally in higher-temperature environments. Used in electronic printing circuit board assembly, such as computer equipment, consumer electronics, etc.

Polyester Capacitors

● Polypropylene Capacitors

A negative temperature coefficient non-polar capacitor made of non-polar polypropylene film as the medium. There are two types: non-sealed (commonly used for encapsulation with colored resin paint) and sealed (encapsulation with metal or plastic casing).
Due to their low loss and good frequency characteristics, polypropylene capacitors are often used in electrical printing circuits board that require high precision and stable performance, such as precision measuring instruments and audio amplifiers, etc.

Polypropylene Capacitors in Printed Circuit Board Assembly

● Organic Polymer Capacitors

Organic polymer capacitors are high-performance capacitors with high capacitance, low ESR (equivalent series resistance), and long service life. They are used in high-performance electronics for applications such as high-frequency energy storage, power filtering, and PCB stabilization.

Organic Polymer Capacitors in Printing Circuit Board Assembly

● Electrolytic capacitors (Tantalum Capacitors)

Electrolytic capacitors are capacitors with high capacitance and small volume, suitable for high-frequency energy storage and decoupling applications. They are commonly used in fields such as mobile devices, communication equipment and computer circuits

Labeling Method of Capacitor in PCB


In printing circuit board manufacturing and printing circuit board assembly, capacitors have many other functions and applications, such as power management, signal transmission, filtering, voltage regulation, energy storage and circuit stability. The specific application depends on the requirements of the PCB design and the characteristics of the capacitor.
Therefore, the selection of the appropriate capacitor type and parameters is based on factors such as PCB board design requirements, voltage range, frequency response, and space constraints.

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