PCB

What is a Printed Circuit Board(PCB)?

pcb

A printed circuit board (PCB) or printed wiring board (PWB) is a laminated sandwich structure of conductive and insulating layers by PCBShare. PCBs have two complementary functions. The first is to affix electronic components in designated locations on the outer layers by means of soldering. The second is to provide reliable electrical connections (and also reliable open circuits) between the component's terminals in a controlled manner often referred to as PCB design. Each of the conductive layers is designed with an artwork pattern of conductors (similar to wires on a flat surface) that provides electrical connections on that conductive layer. Another manufacturing process adds vias, plated-through holes that allow interconnections between layers.

A circuit board is built with a dielectric core material with poor electrical conducting properties to ensure pure circuitry transmission and interspaced with extra layers of metal and dielectric as needed. The standard dielectric material used for circuit boards is a flame-resistant composite of woven fiberglass cloth and epoxy resin, known as FR-4, while the metal traces and planes for the circuitry are usually composed of copper.

Table of Contents

Basic Structure of Printed Circuit Board

The most basic printed circuit boards are the ones that contain copper tracks or interconnects just on one of its surfaces. These sorts of boards are known as 1-layer printed circuit boards or 1-layer PCBs. A single-layer printed circuit board has an inner layer and an outer layer.  In the below illustration, you can see the stack-up of a single-layered printed circuit board.

Basic Structure of Printed Circuit Board

 

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

FR4 (Substrate)

PCB substrate can be FR4, metal, or ceramic. FR4 is mostly used and 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 PCBs, especially the cheaper ones, are made from other materials and they lack FR4 durability.

 

Rigid Copper Clad Laminate (Copper Layer)

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!

 

Solder Mask

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.

 

Silkscreen

The white silkscreen layer is applied on top of the soldermask layer. The silkscreen adds letters, numbers, and symbols to the PCB that allow for easier assembly and indicators for humans to better understand the board. We often use silkscreen labels to indicate what the function of each pin or LED.

Silkscreen is most commonly white but any ink color can be used. Black, gray, red, and even yellow silkscreen colors are widely available; it is, however, uncommon to see more than one color on a single board.

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.

Common Types of Printed Circuit Boards

The printed circuit boards are classified into many different types depending of the number of layers that are available in the board and also the manufacturing process that was used. They are classified as follows:

Single-layer Printed Circuit Boards

This is the most common PCB with a single copper layer above its substrate. p1 The electrical components are placed on one side of this board. The conducting paths cannot intersect since it utilizes a single layer hence a lot of space is needed. Single sided PCBs are the basic type of circuit boards, which contain only one layer of substrate or base material. The layer is covered with a thin layer of metal, i.e. copper- which is a good conductor of electricity. These PCBs also contain a protective solder mask, which is applied on the top of the copper layer along with a silk screen coat. Some advantages offered by single sided PCB’s are: Single sided PCB’s are utilized for volume production and are low in cost. These PCBs are utilized for simple circuits such as power sensors, relays, sensors and electronic toys.

Double-layer Printed Circuit Boards

A thin layer of conducting copper layer is added on both sides of the boards and holes drilled through the board allow the metal parts to be connected across both layers.

pcbshare Double layer pcbs

These types connect the parts from one side to the other using one or two methods; ie THT or SMT.

Double sided PCBs have both the sides of the substrate featuring metal conductive layer. Holes in the circuit board allow the metal parts to be attached from one side to the other. These PCBs connect the circuits on the either side by either of the two mounting schemes, namely through-hole technology and surface mount technology. The through-hole technology involves inserting of lead components through the pre-drilled holes on the circuit board, which are soldered to the pads on the opposite sides. The surface mount technology involves electrical components to be directly placed on the surface of the circuit boards. Advantages offered by double sided PCBs are:

Surface mounting allows more circuits to be attached to the board in comparison to the through-hole mounting.

These PCB’s are utilized in a wide range of applications, including mobile phone system, power monitoring, test equipment, amplifiers, and many others.

Multilayer Printed Circuit Boards

This has more than two copper layers. Generally, a board featuring at least three layers will fall under this category.

pcbshare Multilayer PCBs

Multi-layer PCBs are printed circuit boards, which comprise more than two copper layers like 4L, 6L, 8L, etc. These PCBs expand the technology used in double sided PCB’s. Various layers of a substrate board and insulating materials separate the layers in multi-layer PCBs. The PCBs are compact sized, and offer benefits of weight and space. Some advantages offered by multi-layer PCBs are:

Multi-layer PCBs offer a high level of design flexibility.

These PCBs play an important role in high speed circuits. They provide more space for conductor pattern and power.

Rigid Printed Circuit Boards

Rigid PCBs refer to those types of PCBs whose base material is fabricated from a solid material and which cannot be bent. Some salient advantage offered by them:

pcbshare rigid pcbs

These PCBs are compact, which ensures the creation of variety of complex circuitry around it. 

Rigid PCBs offer easy repair and maintenance, as all the components are clearly marked. Also, the signal paths are well organized.

Flexible Printed Circuit Boards

Flexible PCBs are constructed on a flexible base material. These PCBs come in single sided, double-sided and multilayer formats. This helps in reducing the complexity within the device assembly. Some advantages offered by these PCBs are:

pcbshare Flex PCBs

These PCBs help save a lot of space, along with reducing the overall board weight.

Flexible PCBs helps in decreasing the board size, which makes it ideal for various applications where high signal trace density is needed.

These PCBs are designed for working conditions, where temperature and density is a main concern.

Rigid-flex Printed Circuit Boards

Rigid flex PCBs are the combination of rigid and flexible circuit boards. They comprise of multiple layers of flexible circuits attached to more than one rigid board.

pcbshare Rigid flex PCBs

These PCBs are precision built. Hence, it is used in various medical and military applications.

Being light-weight, these PCB offer 60% of weight and space savings.

High-Frequency PCBs

High-frequency PCBs are used in the frequency range of 500MHz – 2GHz. These PCBs are used in various frequency critical applications like communication systems, microwave PCBs, microstrip PCBs, etc.

How to Choose a Suitable Printed Circuit Board?

When choosing a suitable printed circuit board,the designers consider certain factors such as design size,mechanical strength,flexibility,weight,heat,and cost. 

PCB type is chosen as per the circuit design and the environment in which PCB has to operate. 

For example,complex circuits that cannot be assembled on a short PCB and need to bend can be built on multi-layer flexible PCBs. 

Similarly,for circuits that require a robust and lightweight base and excessively generate heat,aluminum .

PCBs are most suitable. 

However,for high-frequency circuits with a strong base,high-frequency rigid boards are the best option. 

This is how the circuit design significantly impacts the PCB selection. 

It is essential to understand that apart from the technical aspects of electronics,the designers have to consider the cost and feasibility.

Item Capability
Layer Count 1-40layers
Base Material KB. Shengyi, ShengyiSF305, FR408, FR408HR, IS410, FR406. GETEK, 370HR, IT180A, Rogers4350, Rogers400, PTFE Laminates(Rogers series, Taconic series, Arlon series, Nelco series). Rogers/Taconic/Aron/Nelco laminate with FR-4 material(including partial Ro4350B hybrid laminating with FR-4)
Board Type Backplane. HDI, High multi-layer blind&buried PCB. Embedded Capacitance, Embedded resistance board , Heavy copper power PC, Backdrill.
Board Thickness 0.2-5.0mm
Copper Thickness Min. 1/2 OZ, Max. 10 OZ
PTH Wall 25um(1mil)
Maximum Board Size 1100*500mm(43″*19″‘)
Min Laser drilling holes & pad 4mil
Min. Spacing/Tracing 2.7mil/2.7mil
Solder Mask Green. Black. Blue. Red, White, Yellow, Purple matte/glossy
Surface Treatment Flash gold(electroplated gold). ENIG, Hard gold, Flash gold, HASL Lead-free. OSP. ENEPIG, Soft gold, Immersion silver, Immersion Tin. ENIG+OSP, ENIG+Gold finger, Flash gold(electroplated gold)+Gold finger, Immersion silver+Gold finger, Immersion Tin+Gold finger
Min. Annular Ring 3mil
Aspect ratio 10:1(HASL Lead-free , HAS Lead, ENIG, Immersion Tin, Immersion silver, ENEPIG):8:1(OSP)
Impedance control ‡50hm(<500hm), +10%(≥500hm)
Other Techniques Blind/Buried Via Gold Fingers Press Fit Via in Pad Electrical Test

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.

Medical Devices

The healthcare sector is using growing numbers of PCBs as technologies advance, revealing new capabilities. PCBs play a role in devices used for diagnostics, monitoring, treatment and more. Special attention must be paid to ensuring reliability when producing medical PCBs because proper functioning can be critical to patient health. In many cases, PCBs must also meet strict standards for sanitation, especially those used for implants. Boards used for implants and many other applications, such as emergency room monitors, must also be relatively small. Because of this, many medical PCBs are high-density interconnect, or HDI.

Consumer Electronics

Smartphones, computers and the many other consumer products that people use daily require PCBs to function. As we add electronics to more of our products, PCBs become a bigger part of our daily lives.

Manufacturers are producing smaller and smaller smartphones and laptops that still have many advanced capabilities, which require small PCBs with a high volume of connections. PCBs used for consumer electronics also need to be relatively low-cost to keep the price of the final product low. Manufacturers also want reliable boards, because they need their products to function as expected to stay in business.

Industrial Equipment

Printed circuit board uses in the industrial sector vary widely. Electronic components power much of the equipment in manufacturing and distribution centers as well as other types of industrial facilities.The PCBs used in the industrial sector often need to be especially high-powered and be durable enough to withstand the harsh conditions that exist in industrial facilities.

PCBs may need to be resistant to rough handling, vibrating machinery, extreme temperatures or harsh chemicals. To meet this need for durability, industrial PCBs may be made with durable metals or thermal-resistant materials and be thicker than other kinds of PCBs. Industrial PCB assembly services may include thru-hole technology to increase durability.

Military and Defense Applications

The military uses PCBs for a wide range of applications, including communications equipment, computers, vehicles, firearms and more.

PCBs used for military applications must be exceptionally reliable and durable. They may be exposed to extreme conditions, and they could play a role in national security. The military uses materials such as high-temperature laminates, aluminum and copper because of their ability to withstand harsh conditions such as high temperatures. Anodized aluminum may be used because of its resistance to oxidation. Some military printed circuit board applications may also benefit from the enhanced reliability of thru-hole technology.

Fabrication considerations

Printed circuit board prototypes can be extremely helpful during the PCB manufacturing process because they provide a means of testing multiple aspects of the designed component before it is mass-produced. Finding a job shop with prototyping capabilities will help with overall PCB assembly.

When choosing a contract manufacturer for PCB fabrication and assembly, be sure that the fabrication shop can meet the turnaround time and technological expectations. Shops often specialize in one type of PCB or one type of mounting, so it’s important to find a shop that suits your production run needs. 

For example, when it comes to fabricating PCBs with small dimensions, smaller drills or laser technology are required. Other PCB specialty procedures, such as depth drilling and sequential lamination, may be offered by a fabrication shop, but if specialized processes are needed, be sure to check in advance. Sequential lamination requires that boards be laminated two at a time instead of as one large batch. Depth drilling is used when holes need to be drilled to a specific depth without breaking through the other side of the circuit board. Depending on its applications, a circuit board may also require special materials, so it’s important to find a manufacturer who can acquire those materials. Flexible and rigid-flex PCBs use materials such as plastic that can bend and move, to create lighter weight and PCBs for aerospace and medical applications. Manufacturers may also specialize in a specific industry.

The Benefits of PCBs

There are many benefits to using printed circuit boards. The first thing is that they allow for products to be smaller and more portable.

The circuits on a PCB can take up much less space than the individual components themselves, so you get a much smaller product in the end. This also makes it easier to put together different parts of your circuit and route traces where you need them to go.

Next, they’re very durable and long-lasting. They can take a lot of damage such as heat, moisture, or even physical force, without breaking apart. This makes them ideal for use in areas that are hazardous to electronics – like under the hood of an automobile where they are exposed to things like oil and water.

Allowing the boards to withstand these elements is crucial for ensuring it continues working properly, especially if it’s something critical like braking systems.

Thirdly, they’re extremely safe. The circuits on a PCB are encapsulated so that it’s almost impossible to touch two contacts at once with your bare skin. This eliminates the chances of you getting an electric shock from your device.

Fourthly, PCBs are very efficient and economical. They allow for devices to be made with fewer components, which in turn, saves on cost, for both yourself and your business.

Finally, PCBs are easy to repair and recycle. If a component on the board fails, it’s usually much easier to fix than if it were located elsewhere in the circuit. And when the board eventually reaches the end of its lifespan, it can be recycled without any negative environmental effects.

Without Printed Circuit Boards, our devices would not be able to function. They are essential in connecting different components and allowing for communication between them. Additionally, PCBs help protects these components from damage and interference.

printed circuit board FAQs

Why printed circuit board is needed?

Without Printed Circuit Boards, our devices would not be able to function. They are essential in connecting different components and allowing for communication between them. Additionally, PCBs help protects these components from damage and interference.

What are printed circuits used for?

After World War II, printed circuits replaced conventional wiring in much electronic equipment, such as radio and television sets, computers and control equipment, and airborne and guided-missile electronic systems.

How does a printed circuit board work?

PCB is an acronym for printed circuit board. It is a board that has lines and pads that connect various points together. In the picture above, there are traces that electrically connect the various connectors and components to each other. A PCB allows signals and power to be routed between physical devices.

How is a PCB made step by step?

Step 1: Design and Output.

Circuit boards should be rigorously compatible with, a PCB layout created by the designer using PCB design software. Commonly-used PCB design software includes Altium Designer, OrCAD, Pads, KiCad, Eagle etc. NOTE: Before PCB fabrication, designers should inform their contract manufacturer about the PCB design software version used to design the circuit since it helps avoid issues caused by discrepancies.

Step 2: From File to Film.

PCB printing begins after designers output the PCB schematic files and manufacturers conduct a DFM check. Manufacturers use a special printer called a plotter, which makes photo films of the PCBs, to print circuit boards. Manufacturers will use the films to image the PCBs. Although it's a laser printer, it isn't a standard laser jet printer. Plotters use incredibly precise printing technology to provide a highly detailed film of the PCB design.

Step 3: Printing the Inner layers: Where Will the Copper Go?

The creation of films in previous step aims to map out a figure of copper path. Now it's time to print the figure on the film onto a copper foil. This step in PCB manufacturing prepares to make actual PCB. The basic form of PCB comprises a laminate board whose core material is epoxy resin and glass fiber that are also called substrate material. Laminate serves as an ideal body for receiving the copper that structures the PCB. Substrate material provides a sturdy and dust-resistant starting point for the PCB. Copper is pre-bonded on both sides. The process involves whittling away the copper to reveal the design from the films.

Step 4: Removing the Unwanted Copper.

With the photo resist removed and the hardened resist covering the copper we wish to keep, the board proceeds to the next stage: unwanted copper removal. Just as the alkaline solution removed the resist, a more powerful chemical preparation eats away the excess copper. The copper solvent solution bath removes all of the exposed copper. Meanwhile, the desired copper remains fully protected beneath the hardened layer of photo resist.

Step 5: Layer Alignment and Optical Inspection.

Once the layers are placed together, it's impossible to correct any errors occurring on the inner layers. Another machine performs an automatic optical inspection of the panels to confirm a total absence of defects. The original design from Gerber, which the manufacturer received, serves as the model. The machine scans the layers using a laser sensor and proceeds to electronically compare the digital image with the original Gerber file.

Step 6: Layer-up and Bond.

In this stage, the circuit board takes shape. All the separate layers await their union. With the layers ready and confirmed, they simply need to fuse together. Outer layers must join with the substrate. The process happens in two steps: layer-up and bonding. The outer layer material consists of sheets of fiber glass, pre-impregnated with epoxy resin. The shorthand for this is called prepreg. A thin copper foil also covers the top and bottom of the original substrate, which contains the copper trace etchings. Now, it's time to sandwich them together.

Step 7: Drill.

The drills use air-driven spindles that turn at 150,000 rpm. At this speed, you might think that drilling happens in a flash, but there are many holes to bore. An average PCB contains well over one hundred bore intact points. During drilling, each needs its own special moment with the drill, so it takes time. The holes later house the vias and mechanical mounting holes for the PCB. The final affixation of these parts occurs later, after plating.

Step 8: Plating and Copper Deposition.

After drilling, the panel moves onto plating. The process fuses the different layers together using chemical deposition. After a thorough cleaning, the panel undergoes a series of chemical baths. During the baths, a chemical deposition process deposits a thin layer - about one micron thick - of copper over the surface of the panel. The copper goes into the recently drilled holes. Prior to this step, the interior surface of the holes simply exposes the fiber glass material that comprises the interior of the panel. The copper baths completely cover, or plate, the walls of the holes. Incidentally, the entire panel receives a new layer of copper. Most importantly, the new holes are covered. Computers control the entire process of dipping, removal and procession.

What was used before PCBs?

Most of these issues were directly addressed when PCBs went into regular production. 1920s – The early PCB material could be almost anything, from Bakelite and Masonite to plain old thin pieces of wood. Holes could be drilled into the material and flat brass wires would be riveted onto it.

Who invented PCBs?

The printed circuit board (PCB) is probably one of the most important inventions of the 20th century. The intellectual father of the printed circuit board was Paul Eisler.

Although the development leading up to the invention of the circuit board can be traced all the way back to the 1890s, the invention of the printed circuit board is credited to Paul Eisler, an Austrian inventor. Paul Eisler first developed the printed circuit board when he was working on a radio set in 1936, but circuit boards did not see mass usage until after the 1950s. From then onwards, the popularity of PCBs began rapidly growing.

Why are they green?

You may have noticed that the majority of printed circuit boards have a green colour and you’re probably wondering why. The green colour that you see on the circuit board is actually just the colour of the solder mask that is showing through the glass epoxy. The purpose of the solder mask is to protect the electronic traces underneath from moisture and dust. In reality, the solder mask can come in a variety of colours, such as orange, blue, and yellow, not just green.

There are a few reasons why the majority of circuit boards are green:

The green colour is believed to have been used as the regulation standard for PCBs when they were being used by the American military and it has spread to the rest of the world. The original colour of the glass epoxy is naturally green and the colour may still be used to stay conventional.

Ultimately, the green colour is largely used in the manufacturing of PCBs because engineers find it easier to look for faults in the trace lines.

Can PCBs be customized?

Did you know that printed circuit boards can be completely customised to your order? You can request a PCB company to design and manufacture circuit boards that completely ticks all of your requirements. For example, if you need to add more functionality to a device, then ordering a custom PCB may be better than a standard PCB. If you require PCB manufacturing, then take a look at our PCB fabrication services here.

One thought on “What is a Printed Circuit Board(PCB)?

  1. Avatar of Mark Mark说道:

    Thanks for your blog, nice to read. Do not stop.

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