What is a Printed Circuit Boards (PCB)?

 Printed circuit boards (PCBs) are the foundational building block of most modern electronic devices.  Whether simple single layered boards used in your garage door opener, to the six layer board in your smart watch, to a 60 layer, very high density and high-speed circuit boards used in super computers and servers, printed circuit boards are the foundation on which all of the other electronic components are assembled onto.

Semiconductors, connectors, resistors, diodes, capacitors and radio devices are mounted to, and “talk” to one another through the PCB.

PCB’s have mechanical and electrical attributes that make them ideal for these applications.  Most PCB’s manufactured in the World are rigid, roughly 90% of the PCB’s manufactured today are rigid boards. Some PCB’s are flexible, allowing the circuits to be bent and folded into shape, or sometimes they are used where the flexible circuit will survive hundreds of thousands of flex cycles, without any break in the circuits.  These flexible PCB’s comprise roughly 10% of the market.  A small subset of these types of circuits are called rigid flex circuits, where one part of the board is rigid – ideal for mounting and connecting components, and one or more parts are flexible, providing the advantages of flexible circuits listed above.

A rapidly emerging PCB technology, separate from the ones above, is called printed electronics – typically very simple, very low cost, circuits that reduce electronic packaging expense to the level that electronic solutions can be developed to solve problems never considered before.  They are often used in electronics for wearable applications, or disposable electronic devices – opening many opportunities for creative electrical designers.

Conventional PCB’s can be as simple as a single layer of circuitry or can go to fifty layers or more.  They consist of electrical components and connectors linked via conductive circuits – usually copper, with the purpose of routing electrical signals and power within and between devices.

PCB’s were developed in the early 20th century but have had a continued escalated development in technology since then.  The advancement and widespread adoption of technology in PCBs has paralleled the rapid advancement in semiconductor packaging technology and has enabled industry professionals to invest in smaller and more efficient electronics.

Founded in 1977, Printed Circuits LLC has since become a ground-breaking printed circuit board manufacturer.  Originally manufacturing all types of PCB’s, they drove towards specialization in rigid flex and flexible circuit manufacturing in the mid 1990’s. Our broad selection of PCB designs, enables us to serve a wide range of industries around the world, including military, medical, aerospace, computer, telecommunications, and instrumentation. Here we provide a comprehensive overview of printed circuit boards to provide relevant background information for what we do.

Why Are Printed Circuit Boards Used?

Compared to traditional wired circuits, PCBs offer a number of advantages. Their small and lightweight design is appropriate for use in many modern devices, while their reliability and ease of maintenance suit them for integration in complex systems. Additionally, their low cost of production makes them a highly cost-effective option.

These qualities are some of the reasons PCBs find application across industries, including within the following markets:


Medical electronics have significantly benefited from the introduction of PCBs. The electronics in computers, imaging systems, MRI machines and radiation equipment all continue to advance in technology from the electronic capability in PCB’s.

The thinner and smaller size of flexible and rigid flex PCBs allows for the manufacture of more compact and lightweight medical devices, such as hearing aids, pacemakers, implantable devices, and truly tiny cameras for minimally invasive procedures. Rigid-flex PCBs are a particularly ideal solution when looking to decrease the size of complex medical devices, as they eliminate the need for the flex cables and connectors that take up valuable space in more intricate systems.


Rigid, flexible and rigid flex PCBs are commonly employed in the aerospace industry for instrument panels, dashboards, flight controls, flight management and safety systems. The growing number of advances in aerospace technology have increased the need for smaller, more complex PCBs for use in aircraft, satellites, drones, and other aerospace electronics. Flexible and rigid flex circuits offer exceptional durability and mission survivability due to the elimination of connectors.  This makes them suitable for use in high-vibration applications, while their small and lightweight design reduces the overall equipment weight and, consequently, fuel consumption requirements. For applications where dependability is paramount, they serve as a highly reliable solution.


In the military sector, PCB’s are used in equipment frequently exposed to heavy impact, shock and vibration applications, such as military vehicles, ruggedized computers, modern weapons, and electronics systems (e.g., robotics, guidance, and targeting systems). As military technology advances to meet changing customer demand, more equipment integrates advanced computerized technology, requiring both the electrical and mechanical performance that is inherent in flex and rigid flex packaging. These types of electronic packaging can withstand thousands of pounds of g-force without failure.

Industrial and Commercial

The use of PCBs in industrial and commercial electronics has revolutionized everything from manufacturing to Supply Chain management – increasing information, automation and efficiency. In general, they are a reliable means of directing equipment in increasingly automated facilities, enhancing production while decreasing labor costs. Flexible and rigid flex PCB’s enable manufacturers to produce increasingly smaller and lighter products with greater functionality and much higher reliability, such as drones, cameras, mobile electronics, and ruggedized computers.

Custom Printed Circuit Boards

Nearly all PCBs are custom designed for their application. Whether simple single layered rigid boards, to highly complex multilayered flexible or rigid flex circuits, PCB’s are designed using special software called CAD for computer aided design.  The designer uses this software to place all of the circuits and connection points, called vias, throughout the entire board.  The software knows how each of the components need to interact with each other, and any specific requirements as well – such as how they need to be soldered to the PCB.

When the designer is done, the software exports two critical components, with which we will build their boards. The first is called gerber files, which are electronic artwork files that show every single circuit in the PCB, where exactly it goes, on every single layer of the board.  The gerber files will also contain drill files, showing us where exactly to drill the holes to make all the via connections we discussed earlier.  They will also contain soldermask and nomenclature files – which are discussed later, as well as a file that shows us exactly how to cut out the perimeter of their board.

All PCB designers – whether rigid, flexible, or rigid flex – use these files to communicate to PCB manufacturers exactly how they want their boards built.  They include one other item that is critical for the PCB fabricator – a fabrication print.  The fabrication print carefully details all the requirements of the boards, that are not in the gerber files. The fabrication print for example will detail what materials we are to use building their board, what size drilled holes they would like, any special manufacturing instructions or specifications we need to meet, and miscellaneous information like what color soldermask or nomenclature they would like.

With these two components, we can build a custom board, that meets the customer’s requirements exactly.  As PCBs are highly customizable, they can be designed and manufactured to various flexibilities, sizes, and configurations to fit almost any application.

Printed Circuit Board Materials

The primary materials used in the manufacture of PCBs are fiberglass or plastic substrates, copper, solder mask, and nomenclature ink.

Fiberglass & Plastic Substrates
PCBs can be constructed on rigid or flexible base materials depending on the intended PCB design. Rigid PCBs often use FR4 or polyimide fiberglass, while flexible circuits and rigid-flex flexible layers typically use high-temperature polyimide films.

Common plastic substrates for flexible circuits include polyimide (PI), liquid crystal polymer (LCP), polyester (PET), and polyethylene naphthalate (PEN). The purpose of the substrate is to provide a non-conductive base upon which the conductive circuits can be constructed and insulated from one another. Polyimide and LCP laminates are typically used in high reliability or high signal speed applications.  Polyester and polyethylene napthalate laminates are primarily chosen for their low cost, and usually are just single layers of circuitry.

Due to its high electrical conductivity, copper is the most used conducting material for circuitry in PCBs. The laminates described above, all come with thin sheets of copper foil laminated to one or both sides of the plastic.  The fabricator then uses the gerber files supplied by the designer, to image and etch the circuits to meet the customer’s requirements. The thickness and number of layers required are largely dependent upon the application for which the PCB will be used. multi-layered PCBs are constructed by alternating layers of copper circuitry and insulating materials to complete the PCB.

Soldermask is a liquid, usually an epoxy material, that is applied onto the outerlayers of rigid PCBs.  It is also commonly used on the rigid sections of rigid flex PCB’s.  Soldermask is primarily designed to insulate the copper circuits on outerlayers from oxidation from the environment.  Soldermask is also designed to control and retain the flow of solder when the components are assembled to the PCB.  Without soldermask, the liquid solder could flow out onto the surface of the PCB, connecting two adjacent circuits and short out the board.  The most common color for soldermask is green, but blue, black, red, amber, clear, white and many other colors exist as well.

Once the soldermask layers are completed, identifying information, marks and sometimes bar codes, are printed onto the soldermask.  These marks are called nomenclature, and they will also be defined by files that were included with the other gerber layers.  They are printed onto the solder mask to help assure accurate assembly of the PCB.

Printed Circuit Board Design
PCBs come in a variety of designs, so it is important to have a thorough understanding of the design process. Some of the key elements to consider when designing a PCB include:

Application for which the PCB will be used
Environment in which the PCB will operate
Amount of space and configuration required for installation
Flexibility of the PCB
Installation and assembly
Selecting the right PCB design to suit these considerations significantly impacts manufacturability, production speed, product yield, operation costs, and lead times.

For more insights into the design process – particularly for rigid flex systems, which we describe further down this page – download our free Rigid-Flex PCB Application & Design Guide.

When choosing a fabricator for your PCB needs, be sure that they have the appropriate accreditations, to ensure that they have the quality system, experience, industry recognition and ratings to assure your project’s success. At Printed Circuits, we make it our goal to meet and exceed industry standards and have obtained a wide range of certifications and accreditations to do so, including:

ITAR Registration
Printed Circuits ISO 9001:2015 Certification
We have also obtained UL 94 V-0 qualification for rigid-flex and flexible circuits, with the largest listing of UL ratings for rigid flex worldwide.  So, your boards can be 94 V-0 certified without additional testing (thus expediting the fabrication and delivery of our PCBs). For more information on the importance of UL qualification for rigid-flex PCBs, see our white paper “The Problem With UL Approval of Rigid-Flex Circuits”.

Printed Circuit Board Fabrication
The construction and fabrication of PCBs include the following steps:

Chemically imaging and etching the copper layers with pathways to connect electronic components
Laminating the layers together, using an bonding material, that also acts as electrical insulation, to create the PCB
Drilling and plating the holes in the PCB to connect all of the layers together electrically
Imaging and plating the circuits on the outside layers of the board
Coating both sides of the board with soldermask and printing the nomenclature markings on the PCB
The boards are then machined to the dimensions that are in the designer’s perimeter gerber file
Once complete, the PCB board is ready for components to be assembled to it.  Most commonly the components are attached to the PCB by soldering the components directly onto exposed traces – called pads – and holes in the PCB. Soldering can be done by hand, but more typically is accomplished in very high-speed automated assembly machines.

Two of the most common PCB assembly methods are surface-mount device (SMD) or thru-hole technology (THT). The use of either depends on the size of the components and the configuration of the PCB. SMD is useful for directly mounting small components on the exterior of the PCB, while THT is ideal for mounting large components through large pre-drilled holes in the board.

Types Of Printed Circuit Boards
Although all PCBs have the same fundamental objective, they are available in a wide range of designs and configurations to meet the needs of various applications. Some of the different types available on the market include:

Single sided rigid
Double sided rigid
Multi-layered rigid
Single layer flexible circuits
Double sided flexible circuits
Multi-layered flexible circuits
High frequency
The three most common types are:

1. Rigid PCBs
Rigid PCBs are constructed of a rigid fiberglass substrates, making them practical and inexpensive, but inflexible. They are easier and less expensive to manufacture than their more flexible counterparts but much less versatile and hard to fit into unusual geometries or small areas.

2. Flexible PCBs
Flexible PCBs feature relatively good bending and folding capabilities to fit into confined and oddly shaped spaces. This quality makes them highly versatile and able to be used to package smaller electronic devices. Additionally, as they are highly adaptable, the product does not have to be built to fit around the PCB’s restrictions. Compared to rigid PCBs, they can offer greater resistance to heat.

Rigid-flex PCBs combine the most attractive qualities of both rigid and flexible PCBs. Unlike the other two types of circuit boards, these PCBs contain all of the electronic interconnectivity buried within the board, thereby reducing the board’s weight and overall size. They are an excellent choice when ultra-light packaging is a key requirement. Additionally, they are more durable and reliable while retaining great strength and flexibility.

Quality PCBs From PCBSKY
Printed circuits boards enable professionals across a diverse set of industries to optimize the performance and production of their electronic systems. Through careful selection of materials and PCB fabricator, it is possible to create packaging for your electronic device, optimized for its end application.

At PCBSKY, we are a leading manufacturer of flex and rigid flex printed circuit boards. We take pride in our innovative solutions, and we regularly upgrade and expand our product offerings to address our customers’ unique specifications. Our decades of expertise and dedication to quality make us well-suited to meet each customer’s needs with high-quality PCB solutions.

For more information about our PCB capabilities, contact us today.


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