What is a PCB?
Abstract: What is PCB in electronics? What does it do? Which electronic devices use circuit boards? I believe that these questions may bother many people who do not know about PCB. Now FS Technology will inform you and hopefully answer all of these questions, with knowledge from the basic concept to the development history. Next, let’s understand some basic PCB concepts by watching the below YouTube video.
What is PCB?
PCB is an informal term as it stands for printed circuit board, but previously, it was known as PWB, a more accurate term that stands for printed wiring board. However, as the concept between circuit and wiring has become blurred over time, this term has become less and less used. A PCB refers to conductive paths, tracks, or signal traces etched through copper sheets on a non-conductive substrate to support and electrically connect electronic components together. We can understand PCB as the carrier of components. The reason electronic products can function properly is due to the electronic components that are connected to each other through the traces on a PCB board. These traces help realize the electrical connection between the components. When you search for what a PCB means on Google, your results may also push you towards the meaning of PCBA. Although there is only a one-letter difference between PCB and PCBA, the meanings of these two terms are completely different. A PCB represents the bare board, which is often seen as the ‘green board’ that does not function and contains no components. On the other hand, PCBA means PCB assembly and the components are mounted on the bare board through surface mount technology (SMT), through-hole technology (THT) and other assembly technologies.
Composition of PCB Bare Board
The above image showcases the intricate details of a PCB bare board, comprising various elements such as the substrate, copper foil, pad, via, solder mask, and letter identification. To enhance your comprehension of printed circuit board definitions, let us delve into these elements in a more technical manner:
- Substrate: The primary component of a circuit board, typically fabricated from a non-conductive material like fiberglass-reinforced epoxy. It serves as a foundation for supporting and securing electronic components.
- Copper foil: This refers to the conductive layer present on the PCB. Manufacturers create the required circuit pattern by etching processes and then employ chemical or mechanical methods to affix it to the substrate. This facilitates the interconnection of wires among electronic components.
- Pad: These are the portions on the PCB that establish connections with component pins. They often appear as circular or square shapes and enable both electrical and mechanical connections.
- Via hole: Also known as through-hole, these are apertures on the substrate utilized for interconnecting circuits at different levels. They provide electrical connections for DIP components and are indispensable for the manufacturing and assembly of multilayer circuits.
- Solder mask: In everyday circuit boards, the solder mask ink used is typically green, resulting in a green-colored appearance. The solder mask is applied on the board’s surface to shield the circuit from contamination, oxidation, and mechanical stress.
- Silkscreen: In the aforementioned image, you can prominently observe numerical digits and characters. These markings represent the silkscreen layer, which serves to indicate component positions, pin functions, circuit diagram identification, and other relevant information.
How PCB Present in Electronic Applications
With the above text, you probably already have a certain understanding of the concept of PCB, or at least a basic understanding of what is a circuit board, right? But even if you have already looked through all the electronic devices around you, it may still be difficult to find a printed circuit board. As previously mentioned, a PCB usually refers to the bare board whereas the application of printed circuit boards in electronic products is called the PCBA board. A PCBA board refers to the fully assembled or soldered board after the completion of component placement and soldering. There is a saying on the internet that “without PCBs, it would be impossible to progress in technology today.” This is because PCBs are so widespread in our lives that they are the basic building block of most electronic devices. From your door opener (single layer) to your smartphone (6 layers) and to your computer and server (60 layers), they all run on PCB.
With the development of the manufacturing industry, the progress of medical technology is obvious to all. Looking back, in the era of underdeveloped technology, doctors used artificial pulse signals to judge patients’ conditions by observing words and expressions. However, it is now possible to use tiny medical electronic devices injected into the human body to observe the patient’s condition.
Since the outbreak of the COVID-19 pandemic, there has been a significant surge in demand for teletherapy devices, ventilators, and temperature testers within the medical industry. These products, without exception, necessitate higher standards of test accuracy, signal transmission performance, and compactness.
First and foremost, the adoption of HDI and SMT is considered paramount in achieving heightened density and reduced size for medical PCBA. These advanced technologies enable the integration of more components within a limited space, ensuring the efficient functionality of medical devices.
Furthermore, given the direct impact of these products on human health, it becomes imperative for PCB manufacturers to possess industry certifications and adhere to rigorous testing protocols. Meeting the highest standards of quality and reliability is crucial to guarantee the safety and effectiveness of medical devices.
Lastly, the growing prevalence of implantable electronics and wearable medical devices necessitates PCB with enhanced flexibility. This requirement has led to the emergence of rigid-flex PCB, which combines the advantages of both rigid and flexible boards. Such PCB enables seamless integration with various medical applications, accommodating the dynamic nature of implantable and wearable electronics.
You read that right, small PCB boards used in the aerospace industry have pivotal positions. You may be wondering much about this, but when you really understand how a PCB board works, you will understand and accept this fact. Aeroplanes, satellites, drones and other avionics would not be possible if they were still connected using ancient components and technology. The circuit boards used in the aerospace industry are qualitatively different from those used in our daily lives as they are smaller and more complex products. This kind of PCB is often quite difficult to manufacture and is impossible to produce unless it is by a professional PCBA company.
First and foremost, stringent requirements are imposed on the number of PCB layers. While consumer electronics typically require PCB with up to 10 layers, the aerospace industry demands significantly more complex and reliable devices. As a result, manufacturers must undertake multiple stacking processes to accommodate these specific applications. It is important to note that each addition of two layers (as all multi-layer boards have an even number of layers) significantly increases manufacturing complexity and the likelihood of failure.
Moreover, as previously mentioned, the primary function of a PCB is to serve as a platform for electronic components. To meet the functional requirements of PCB used in aerospace applications, it becomes necessary to integrate a larger number of components onto a smaller board. This poses significant challenges, as integrating more components is inherently difficult and the associated integrated circuits (ICs) are often expensive.
The earliest applicable field of PCBs is the military industry, and the United States first used it in military tape recorders. With the advancement of military technology to meet changing customer needs, more and more equipment integrates advanced computerized technology. Contrastingly, ordinary SMT technology has proved difficult to meet the requirements of military PCB. They require the electrical and mechanical properties inherent in flexible and rigid-flexible packaging and resultantly, these types of electronic packages can withstand thousands of pounds of gravity without failing.
Why PCB is Favored by Electronics Manufacturing Industry
Circuit boards have been around for nearly 100 years. Not only did PCBs not show any signs of a need to be replaced over the long years, but it was used more and more widely. In the electronics manufacturing industry, PCB as a carrier for electronic components has unique advantages:
- High density: The development of the PCB has always been in line with the trend of society. With the dependence of human beings on miniature electronic devices, PCBs show a trend of high density. With the advancement of IC integration and the development of assembly technology, the electronic component density of PCB has reached its peak.
- High reliability: The production and assembly process is very complicated. During the whole PCB manufacturing process, the manufacturer needs to carry out many tests. Take a turnkey PCBA company like FS Technology as an example. In addition to the most basic manual inspection and AOI inspection, we also need to carry out a series of ageing tests, functional tests, etc. The lifespan of PCB boards from the FS Technology factory can reach 20 years.
- Designability: The application field of electronic products is very wide. In addition to the common mobile phones and watches used in daily life, there are many electronic products that are dedicated to high temperature, high pressure and humid environments. For different application fields, the designability of PCB is the premise that electronic products can meet the different needs of different scenarios.
- Productivity: The PCB factory adopts a modern management model, through strict quality management and professional technical means, to achieve a standardized production process, high-volume assembly, and fully automatic mechanized production. This ensures the consistency of product quality.
- Assimilability: The turnkey factory is equipped with SMT and THT technologies, which can carry out standardized assembly of various components on bare boards, and perform automated and large-scale batch assembly. As far as the assembly workshop of FS Technology is concerned, in addition to 7 fully automatic SMT production lines, we can also meet manual plug-in and mixed assembly. Even for large-volume DIP assembly orders, we can also achieve an automated Through hole PCB assembly process.
- Maintainability: PCBA finished products are of standardized design and large-scale production, so even if the system fails, the turnkey company can quickly, easily and flexibly replace your products and quickly restore the system to proper working order.
What Types of Circuit Boards are There
Printed circuit boards can be classified in different ways: the number of layers, dimensions, materials, functions, etc. In this article, FS Technology mainly explains the meaning of PCB in electronic products, so we will classify it by the number of layers below so that you can easily understand the types of circuit boards.
This is the most basic and simplest type of PCB. After the bare board is assembled by a turnkey PCBA company, the electronic components are concentrated on one side of the board and the wires are concentrated on the other side. Since single-sided PCBs are subject to many severe restrictions on circuit design, this kind of board is more likely to appear in the early stage of circuit board development.
This is a type of PCB with wiring on both sides. Since wires are required on both sides of the board, we must build bridges for them – Vias. Vias are small holes in the PCB that are covered with metal, which connect the wires on both sides of the circuit board. Double-sided PCB solves the problem of interleaving wiring when manufacturers make single-sided PCB, and it is used on more complex circuits than single-sided PCB.
This type is a more difficult PCB to manufacture and its difficulty and price may increase with increasing number of layers. Multilayer PCB makes multiple single- or double-sided boards the inner layers of a multi-layer board through lamination technology. Compared with the first two PCB types, multi-layer boards can realize more wiring area, so they are widely used in a large variety of electronic products. The number of layers of the multi-layer board may only be displayed as an even number due to the lamination method, which is a mistake that many people who do not understand printed circuit boards will make during planning.
PCB Development History
The development of PCB can be said to be very rapid. Humans never knew what a PCB was back then, and it has taken a century for PCBs to become the core of the electronics industry. Before the advent of circuit boards, electrical connections between circuit board components were made through bulky wire connections. This ancient connection method not only wastes material but also complicates the connections between lines. The history of printed circuit boards is as follows.
- 1925s: American inventor Charles Ducas patented the first circuit design when he stenciled a conductive material onto a flat board.
- 1936s: Paul Eisler makes the first printed circuit board for a military radio.
- 1943s: Eisler etched circuits into copper foil on a glass-reinforced non-conductive substrate.
- 1944s: The United Kingdom and the United States cooperated for the first time in military weapons.
- 1948s: In order to popularize PCB and apply it to daily life, the United States first disclosed PCB technology.
- 1950s: Transistors are introduced to the electronics market in order to reduce the size of electronic products. This move makes the PCB easier to integrate and improves the safety of electronic products.
- 1950s-1960s: Double-sided PCB is introduced, with electronic components on one side and logo printing on the other. Zinc sheets are incorporated into the PCB design and feature corrosion-resistant materials and coatings to prevent degradation.
- 1960s: HDI PCB is realized, and IC is introduced into electronic design. This move enables the bare PCB board to carry thousands of electronic components, which greatly improves the power, speed and safety of electronic equipment. Manufacturers program the required functions into smaller chips through IC programming, so that the number of circuit board components used is reduced, thereby reducing the size of the PCBA board. Humans face a new difficulty: how to make welding stronger.
- 1970s: PCB is renamed PWB. Because the acronym for the printed circuit boards is the same as the acronym for the environmentally harmful chemical PCBs, this confusion leads to public confusion and community health concerns.
- 1970s to 1980s: Newly developed solder masks of thin polymer materials become the standard manufacturing method for PCB. A photo-imageable polymer coating was subsequently developed that can be applied directly to circuits, dried and subsequently modified by exposure to further increase circuit density.
- 1980s: A new assembly technology called Surface Mount Technology is developed. This soldering directly to small pads on the PCB, without the need for holes, is quickly becoming the standard in PCBA manufacturing. SMD components are rapidly gaining popularity, becoming the industry standard, and striving to replace through-hole components, again increasing functional power, performance, and reliability, and reducing electronics manufacturing costs.
- 1990s: Computerized design automates many steps in PCB design and facilitates increasingly complex designs using smaller, lighter components.
- 2000s: PCB became smaller, and lighter, with higher layers and more complexity. Multilayer and flex circuit designs allow for more operational functions in electronic devices, and PCB is getting smaller and less expensive.
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