An electronic device that uses coils is referred to as a coil PCB. These coils can be used in transformers, inductors, motors, and other electronic devices. In order to create PCB coils, conductive traces are printed on a substrate, for instance, they can be fiberglass or FR4, and then wound together into a coil.
A coil is simply a general term for a wire wound around it. Although it has nothing to do with electricity, a coiled spring is sometimes called a "coil spring."
In other words, a coil is a shape in which a wire is wound round and round.
When a current flows through a conductor, a concentric magnetic field is generated around the conductor.
A magnetic field has the characteristic of being generated clockwise when viewed from the direction of current flow.
A component called a coil (inductor) uses the magnetic field generated when this current flows.
A coil (inductor) has two major roles, one of which is to store energy. The other role is to prevent AC current from flowing (which depends greatly on the frequency).
When a voltage is applied to a coil and a current is passed through it, something called “magnetic flux " is generated.
This is the same as the magnetic flux of a magnet. This magnetic flux remains even if the external power supply is disconnected.
This means that the coil was magnetized by passing a current through it. In other words, electrical energy is changed to magnetic energy and stored inside the coil.
The amount of magnetic energy stored is determined by this inductance and is measured in henries (H). When a "direct current" is passed through a coil, the coil acts as a conductor after interrupting the flow for a moment, allowing the direct current to flow smoothly.
However, "alternating current" is a current that periodically changes in magnitude and direction over time.
When a current tries to flow through the coil, the magnetic field generated by that current crosses the other windings, causing an induced voltage and trying to prevent the current from changing.
In particular, when the current suddenly increases, an electromotive force is generated in the opposite direction of the current, that is, in the direction that reduces the current, preventing the current from increasing. Conversely, if the current tries to decrease, it works in the direction of increasing.
In the case of alternating current, the direction of the current keeps changing, so the coil keeps trying to block it.
In this way, coils have the property that they act like resistance to alternating current, and the higher the frequency, the more difficult it is to flow.
According to the winding structure, they can be divided into three main types: wound coils, laminated coils, and thin film coils.
A "wound coil" is made by winding an insulated copper wire around a plastic bobbin or ferrite core in a spiral like a spring.
A "laminated coil" is a stack of layers of conductive metal printed on a sheet or substrate. It is compact and has excellent high frequency characteristics. A "thin film coil" is a coil formed of a metal film that is even thinner than printing using sputtering or vapor deposition technology.
Coils used in printed circuit boards are basic components of electronic circuits that are also used in place of power supplies. It is thanks to coils that not only home appliances around us, but also precision instruments such as smartphones, personal computers, and cameras operate with a stable voltage.
Therefore, in this article, we will summarize the roles that coils play in printed circuit boards and introduce the types of coils.
Coils used in printed circuit boards are electronic components that store and discharge electricity in circuits. It is a part that is sometimes used as a power supply itself, and plays an essential role in printed circuit boards.
In addition to storing electricity, coils have other functions such as stabilizing voltage, eliminating noise, and passing alternating current instead of direct current.
The number of parts mounted on one board varies depending on the function of the electronic device, but it is believed that coils account for 30% to 40% of all mounted parts.
By having a coil on a printed circuit board, it is possible to use the electricity of electronic equipment efficiently, so it is an electronic component that is required for all purposes.
The structure of a coil consists of an insulator sandwiched between two metal plates. The insulator in the middle is a material that does not conduct electricity, but polyethylene, polypropylene, ceramics, etc., which has a high dielectric constant, is used as dielectrics.
The two outer metal plates are conductors, so they conduct electricity and act as electrodes. By applying a voltage to the coil, the two metal sheets become + and - electrodes, respectively, and attract each other like a magnet across the insulator.
Eventually, as the voltage continues to be applied, the metal plate is filled with charges that do not flow through the insulator, leaving no room for new charges to flow in.
In this state, even if the voltage is stopped, the charge remains on the metal plate because the metal plates attract each other positively and negatively. This is the state of storing electricity.
The capacity of a metal plate to store an electric charge is called "capacitance." The capacitance varies depending on the properties of the insulator becomes larger.
Along with the recent miniaturization of electronic devices, coils have also been developed, such as those that are wrapped like a coil and sealed in a case, and those that are alternately stacked with multiple layers of metal plates and insulators. It has been.
From here, we will introduce the types of coils used in printed circuit boards.
A ceramic coil is a coil that uses ceramic with a high dielectric constant as an insulator.
Since different ceramics have different dielectric constants, their resistance and capacity change due to temperature changes, but they tend to be heat resistant and are often used in small, high-frequency circuits.
About 500 ceramic coils are used in smartphones and about 800 in notebook computers and tablet devices.
Electrolytic coils do not use a sheet-like dielectric material between two metal plates like a general coil increase.
Since there is no insulator, the distance between the electrodes is shortened and the capacitance can be increased.
However, while it is possible to increase the capacity, if too much voltage is applied, or if there is a problem such as electricity flowing in the opposite direction of plus and minus, phenomena such as explosion or heat generation that lead to damage to the substrate will occur, so caution is required. .
A film coil uses a plastic film as the dielectric. Polyester, styrol, and polypropylene are used for plastic films, and heat resistance, cold resistance, and insulation resistance vary depending on the material.
Generally, these coils tend to have good temperature characteristics and are highly accurate, so they are often used in audio circuits.
A variable coil, as the name suggests, is a coil whose capacitance can be changed.
The insulator is sandwiched between two metal plates, which is similar to the coils introduced so far. It is a mechanism to change
In the past, they were used for amateur radio and radio tuning, but now the tuning process in equipment has been digitized, and the use of variable coils has almost disappeared. Now it is only manufactured for some electronic work.
If the board is bent while soldering the coil to the printed circuit board or after soldering, the coil may crack.
Therefore, it is necessary to place the coils so that stress is not applied as much as possible due to bending of the printed circuit board.
Placing a coil parallel to the direction of stress, as shown above, will result in direct flexure. Therefore, place the coil perpendicular to the direction in which the stress acts.
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