The printed circuit board is the provider of electrical connections for electronic components. It has a history of more than 100 years; its design is mainly layout design; the main advantage of using circuit boards is that it greatly reduces wiring and assembly errors, improves the level of automation and production labor rate.

As an important electronic component, the printed circuit board[^1] is the support of electronic components[^2]. Due to its important role in the field of electronic components, it is called an "electronic aircraft carrier" by many people.

Now, communication products, computers and almost all other electronic products use printed circuits. The development and improvement of printed circuit technology has created conditions for the invention that changed the face of the world-the advent of integrated circuits[^3]. With the development of science and technology, printed circuit boards are widely used in military, communications, medical, electric power, automobiles, industrial control, smart phones, wearable and other high-tech fields.

How was the printed circuit invented?

The inventor of the printed circuit is Paul Eisler of Austria. Eisler is an electrical engineer who has studied printing technology. When he made the circuit board, he drew the electronic circuit diagram by imitating the plate-making method in the printing industry, and then etched the circuit diagram on a copper foil insulating board. The unnecessary copper foil was etched away, leaving only the conductive circuit. In this way, the electronic components were connected through the circuit formed by the copper foil. In 1936, Eisler successfully assembled a radio using this method.

Eisler's invention was valued by the US military, so the printed circuit was first used in the proximity fuse. The proximity fuse is a radio fuse invented by American physicist Van Allen during World War II. It is installed on anti-aircraft shells and emits radio waves when used. As long as the target enters the killing range, the reflected radio waves can detonate the shells. This fuse requires many electronic components to be compactly installed in a very small device, so a printed circuit is used. The anti-aircraft shells equipped with proximity fuses used by the Allies dealt a devastating blow to German aircraft, and printed circuits have since become known to the world.

Why are printed circuits so important?

The advantage of printed circuits is that there is no need to solder on the circuit board again and again, eliminating a lot of complicated manual wiring operations, and can achieve high precision, greatly improving the production efficiency, stability and profit margin of the circuit board. The printing industry can reduce large pictures to make plates, and printed circuits can also reduce electronic circuit diagrams to make plates, thus preparing the conditions for the production of integrated circuits. Today, all computers and all electronic products use printed circuits.

Printed circuits are electronic circuits that connect electronic components to each other by etching or photosensitive conductor patterns on an insulating substrate by printing means. It can already use an automatic plotter to quickly draw conductor patterns directly on a glass plate for plate making, and then print them out. Printed circuits make mass production of electronic equipment simple and easy, making electronic equipment consistent in performance, stable in quality, and compact in structure. Without the printed circuit process, electronic equipment since the 1950s would not have made such great progress.

Circuit boards have a history of more than 60 years since their invention. History shows that without circuit boards and electronic circuits, flight, transportation, atomic energy, computers, aerospace, communications, home appliances, etc., all of these would not be possible.

The reason is easy to understand. Chips, ICs, and integrated circuits are the food of the electronic information industry. Semiconductor technology reflects a country's level of industrial modernization and guides the development of the electronic information industry. The electrical interconnection and assembly of semiconductors (integrated circuits, ICs) must rely on circuit boards.

What are the different types of circuit boards?

According to the number of layers of the circuit board, it can be divided into single-sided boards[^4], double-sided boards[^5], four-layer boards, six-layer boards, and other multi-layer circuit boards.

What is a single-sided board?

On the most basic PCB, the parts are concentrated on one side, and the wires are concentrated on the other side. Because the wires only appear on one side, this type of PCB is called a single-sided board. Because single-sided boards have many strict restrictions on designing circuits (because there is only one side, the wiring cannot cross and must go around a separate path), only early circuits used this type of board.

What are the characteristics of double-sided boards?

This type of circuit board has wiring on both sides, but to use the wires on both sides, there must be an appropriate circuit connection between the two sides. This "bridge" between circuits is called a via. A via is a small hole filled or coated with metal on the PCB, which can be connected to the wires on both sides. Because the area of a double-sided board is twice that of a single-sided board, a double-sided board solves the difficulty of wiring interlacing in a single-sided board (it can pass through the via to the other side), and it is more suitable for use in more complex circuits than a single-sided board.

What are the advantages of multi-layer boards?

In order to increase the area that can be wired, multi-layer boards[^6] use more single- or double-sided wiring boards. A printed circuit board with one double-sided board as the inner layer and two single-sided boards as the outer layer, or two double-sided boards as the inner layer and two single-sided boards as the outer layer, is alternately connected through a positioning system and insulating adhesive materials, and the conductive patterns are interconnected according to the design requirements. The printed circuit board becomes a four-layer or six-layer printed circuit board, also known as a multi-layer printed circuit board. The number of layers of the board does not mean that there are several independent wiring layers. In special cases, empty layers will be added to control the thickness of the board. Usually, the number of layers is an even number and includes the two outermost layers. Most motherboards have a structure of 4 to 8 layers, but technically, it is possible to achieve a PCB board with nearly 100 layers. Large supercomputers mostly use motherboards with quite a few layers, but because such computers can be replaced by clusters of many ordinary computers, super-multilayer boards have gradually been discontinued. Because the layers in the PCB are tightly combined, it is generally not easy to see the actual number, but if you look closely at the motherboard, you can still see it.

The components used in multilayer boards are mostly surface-mount components[^7], which have the following characteristics:

1. When used in conjunction with integrated circuits, the whole machine can be miniaturized and the weight of the whole machine can be reduced;

2. The wiring density is improved, the spacing between components is reduced, and the transmission path of the signal is shortened;

3. The number of component soldering points is reduced, the failure rate is reduced,

4. The shielding layer is added, and the signal distortion of the circuit is reduced;

5. The introduction of a ground heat dissipation layer can reduce local overheating and improve the reliability of the whole machine.

[^1]: Understanding printed circuit boards is crucial for grasping modern electronics and their applications.
[^2]: Explore the various electronic components that make up devices and their functions.
[^3]: Discover the significance of integrated circuits in modern technology and their impact.
[^4]: Gain insights into the basic structure and limitations of single-sided circuit boards.
[^5]: Explore the benefits of double-sided boards in complex circuit designs.
[^6]: Discover how multi-layer boards enhance wiring capacity and performance in devices.
[^7]: Learn about the advantages of using surface-mount components in modern circuit boards.