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What is a Printed Circuit Board (PCB)? | Its Structure And Types

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What is a Printed Circuit Board?

Printed Circuit Board or PCB is a board with the purpose of connecting electronic components. It consists of alternating layers of conductive copper and layers with non-conductive material for insulation purposes.

Every electronic device requires a printed circuit board with different electronic components to fulfill the desired action. 

Two methods are used to mount components on the surface of the substrate, called Surface Mount Technology (SMT) and Through-Hole Technology (THT).

The PCB makes the connection between the electronic components attached to its surface. The components could be connectors, diodes, resistors, capacitors, semiconductors, radio devices, and many more.

pcb

The above gives you a general understanding of what a printed circuit board is.

PCB sounds easy. But that's far too few of it.

You may need to know more. 

So I will explain its structure and types one by one.

Please keep patient to read...

Structure of Printed Circuit Board

A printed circuit board has an inner layer and an outer layer. During PCB manufacturing, on the inner layers are left thin traces of copper that connects the circuit components. Once the copper traces are ready, the insulation material is laminated to the layers and the board is completed.

The electronic components are later added to the outer layers of the board after all the layers are already laminated together.

In the below illustration, you can see the layers of a single-layered printed circuit board.

pcb structure

Now we are ready to briefly review each of the layers:

1. Rigid Copper Clad Laminate

    The copper layer is a thin foil of copper. It is laminated to the board with adhesive and heat. It is commonly applied on both sides on a double-sided printed circuit board. A two-layered or double-sided board means that there are two copper layers in the structure. You can find PCBs with only one or more than 16 copper layers!

2. FR4

    FR4 is a reinforced epoxy laminate material. It is the base substrate of the printed circuit boards. It is an extremely durable material and there are different thickness types. Some PRBs, especially the cheaper ones, are made from other materials and they lack the FR4 durability.

3. Solder Mask

    Have you ever wondered why the PCB boards are green? Because of the solder mask layer. This is the top layer above the copper foil and it gives the printed boards their green color. The main purpose of this layer is to insulate the copper traces from accidentally contacting any solders or metal. Just the common color is green, but have in mind that the solder mask could be manufactured in nearly all possible colors.

4. Silkscreen

    On top of the solder mask, a white silkscreen layer is applied. It is used to insert any numbers, symbols, or letters as instruction like a guideline for people to better understand the board. Again, any color can be used and there are PCBs with yellow, red, or even black silkscreen.

As we now cover all the layers and we have a basic understanding of how the PCB boards are created and how they work, it is time to reveal the different types.

Types of Printed Circuit Boards

The general construction and build of a printed circuit board could be done in three different ways - single-sided, double-sided, and multi-layered. Down below we are going to review the most common types of printed circuit boards.

Single-Layer PCBs

    Single-sided or single-layered is the same when referring to PCBs. These types of boards are the easiest to design. They are used for a variety of applications including radio equipment, calculators, solid-state drive, and in simple electronics compared to multi-layered circuit boards.

    There is a high volume of orders for these types of printed circuit boards. This is because of the wide range in which they find applications and that they can be purchased at low prices.

Double-Layered PCBs

    The interesting thing here is that the double-layered PCBs have holes drilled through the board to allow the circuits on one side to connect with circuits on the other.

    However, holes are not the only alternative to connect circuits located on both sides. Surface-mount technology is another way to achieve that.

    In general, many small leads are soldered to the board and used as a wiring surface. In that case, the board is using less space and it is capable of more functions. Double-sided PCBs are used, for instance, in instrumentation, LED lighting, vending machines, power supplies, automobile dashboards, and more.

Multi-Layered PCBs

    When there are three or more double-layered PCBs together, it is called a multi-layered board. They are glued together by specialized glue and carefully secured preventing heat damage. In fact, the largest printed circuit board ever built is over 50 layers thick!

    These types of multi-layered boards are extremely beneficial for data storage, GPS technology, medical equipment, and even satellite systems.

High-Frequency PCBs

    Here we are referring more to a finished design, rather than a type, but it is still beneficial to know. Those types of printed circuit boards are designed specifically to transmit high-frequency signals that surpass over one gigahertz.

    There are some specifications when designing high-frequency printed circuit boards:

    • Water Absorption - This is taken under consideration when a specific order has been made for a board that will be used in wet environments. In the basic designs, a high amount of water intake can affect the board’s proper functionality and lead to a loss.
    • Dielectric Loss - It is directly affecting the quality of the transmitted signal. Even a small amount of dielectric loss can lead to a significant signal waste.

Rigid PCBs

    This type originated around the idea of preventing the board from twisting. Rigid PCBs are made of the solid substrate material and, just for reference, you can check your computer motherboard. Probably the Rigid PCBs are the most manufactured boards! They can be single, double, or multi-layered, up to 10 individual layers.

Flexible PCBs

    Flexible PCBs are made of a material that can flex and move like plastic. Again, they can be single, double, or multi-layered, but they cost more, as they need to be printed on a flexible material. The flexibility is one of the main benefits of these types of boards. They weigh less, and their material is waterproof, corrosion, and high-temperature resistant.

Referring to the types of the printed circuit boards, PCBONLINE has an extremely strong technical strength to manufacture advanced circuit boards, such as the HDI, high-frequency, ceramic, multilayered, etc. It provides one-stop PCB manufacturing and assembly, with free PCB and assembly sample!

PCBONLINE’s capability:

  • Layer: 1 ~ 42
  • Laminate: normal Tg/high-Tg/lead-free/halogen-free
  • Surface finishing: OSP/HASL/LF HASL/immersion ENIG/immersion tin/immersion silver
  • Board thickness: 0.15 ~ 3.2 mm
  • Max board size: 500 × 580 mm
  • Copper thickness: (inner finish copper) 1-4oz, (outer finish copper) 1-7oz
  • Min. line width/spacing: 0.0635 mm/0.0635 mm
  • Min. CNC drilling size: 0.15 mm
  • Min. laser drilling size: 0.075 mm
  • HDI stack up: 1+N+1, 2+N+2, 3+N+3

Printed Circuit Board (PCB) Application

Printed circuit boards provide us with a variety of capabilities and they find different applications in almost everything electrical or electronic.

Industrial Use

    Many manufacturing facilities have electronic components that require printed circuit boards to achieve the end-design. PCBs are found in industrial equipment such as presses, ramps, assembly machines, and more.

    In the automotive industry, many vehicle systems such as navigation, media devices, control systems, and monitors are using PCBs.

    Printed circuit boards also find applications in medical devices, such as CT scanners, X-Ray screens, and blood pressure monitors. All of the scanning equipment, medical instruments, and monitors contain PCBs.

Home Applications

    The most common application of printed circuit boards is in consumer electronics. In fact, PCBs are the heart of every electronic device, such as mobile phones, computers, workstation, navigation, TV, microwave, coffee machine, refrigerator, and even your smartwatch.

What is Next for Printed Circuit Boards?

The PCBs are continuing to drive towards a compact and smaller design with increased capabilities. Some speculations regarding the future of the PCBs may be the integrated circuit chips or the tree-dimensional molded plastic board.

Most of the predictions for the PCBs future are strongly focused on the following:

  • PCB Auto Places - Most of the printed circuit boards today include an auto-router in their design. The whole idea is to make the automation process easier. Autoroutes are difficult to create and implement, taking a lot of time and work.

    The time that the automatization saves is later lost when autoroutes are designed. Many manufacturers are now looking at an auto place as the resolution. Autoplacers make the manufacturing process easier and automatization much faster.

    With the idea of integrated CAD systems the PCB design technology is on a rise recently. The auto places need both mechanical and electrical design aspects, the CAD system applies in both realms and it is necessary to make the auto places more beneficial and efficient.

  • 3D Printed Electronics - This is probably the most exciting technical invention in the recent decade! It is already beneficial for a variety of industries. I mention this because 3D printing electronics have changed the way we look at electronics forever. That technology will revolutionize the way electronics systems are created in the future, and the same goes for the PCBs.
  • PCB Cameras - Printed circuit board cameras or also called board cameras are specific in that they are mounted directly on the circuit board. In order to fit a camera into a PCB, it has to be very small. In fact small enough that it can fit in about any electronic device. That type of camera might be the future for PCB designs.

Conclusion

The content in this article is summarized in an accessible manner so that everyone can get a better sense of PCBs. The truth is that all this is far more complex than it looks like and if you are interested to order printed circuit boards, navigate to PCBONLINE, for online quotations and more information.

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