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A printed circuit board (PCB) is a board that connects electronic components. It is the basic building block of any electronic design and has created game-changing possibilities in the world of technology. In 1925, American Charles Dukas devised and patented a way of electroplating an electrical path onto an insulated surface. The printed circuit board was born, opening the door to smaller, simpler, and less cumbersome designs.
This detailed guide will cover the ins and outs of printed circuit boards, including common applications, and what the future holds for this versatile piece of technology.
What is the history of the printed circuit board?
Paul Eisler, an Austrian refugee to Britain in 1936, is considered the real founder of the PCB. He developed and patented several applications that eventually grabbed the attention of the US military. The rest, as they say, is history.
PCBs have evolved from 1-layer boards to the 20+ layer boards found in your smartphone. They have interconnecting layers that allow the overall size to be reduced – think of the size of mobile phones in the 80s compared to the smartphones of today.
What does a printed circuit board do?
PCBs are used to mechanically support and electrically connect electric components. This is done with conductive pathways or signal traces engraved on copper sheets attached to non-conductive substrate. The different types of PCB mean they can be applied to anything from smartphones to manufacturing equipment like power drills.
Different types of printed circuit board
PCBs have evolved over time, facilitating different applications because of this. They can be split into several different types.
Single layer PCB
The simplest of all the PCB types, these boards have a single layer of conductive metal on one side of a non-conductive substrate.
Double layer PCB
These PCBs have a conductive layer on the top and bottom layer of a non-conductive substrate. These conductive sides can be joined using vias, which are plate holes in the substrate that connect to pads on each side.
A printed circuit board with three or more layers is known as a multi-layer PCB. Like a double layer PCB, there are conductive layers at the top and bottom of the substrate, plus additional layers sandwiched between non-conductive substrate. Although you can get up to 40-layer boards, most will typically be 4-, 6- or 8-layer boards.
You can also get:
- Rigid PCB: One of the most standard types of PCB, rigid circuit boards are inflexible and sturdy. Several layers make up the structure, including a substrate, copper, silkscreen, and solder mask layer.
- Flexible PCB: Unlike rigid PCB, flexible PCB has a circuit mounted onto flexible plastic substrates.
- Rigid-Flex PCB: These circuit boards combine rigid and flexible qualities, meaning you can fold and flex the board.
- High Density Interconnect (HDI) PCB: Known for having a larger circuitry density, HDI PCBs have a unique design that means they have smaller vias and capture pads, and higher connection pad densities.
- LED PCB: This is a specific type of circuit board used for a variety of lighting applications.
- Blank PCB: This is an empty circuit board without any components installed. They will not function while blank.
What is printed circuit board design software?
PCB design software creates the layouts for printed circuit boards. Electrical engineers use it regularly to not only create the design, but also to draw from previous PCB designs. The software allows you to route the electrical connectivity before it is then printed onto a chosen type of circuit board, whether that's a flexible PCB or an LED PCB.
What are the advantages of a printed circuit board?
The versatility of PCBs has created lots of opportunities in modern technology. Here are a few key advantages:
- They're compact: A single PCB is capable of connecting hundreds of components even on a tiny PCB.
- They're simple to repair: Diagnosing and repairing an issue is simple with a PCB. Because the board is built with labels showing the polarity of the components, it means you can easily replace parts when required.
- They're inexpensive: You can get quality PCBs at competitive prices.
- They help save time:PCBs take less time to connect components than a conventional board. Obviously, handy if you need to put a circuit together in a short amount of time!
- They're stable: Components are attached to PCBs using solder flux, which means that the components won't move when there's motion. This means the circuit is safer for frequent use.
If you want to go into more depth, take a look at our more detailed guide on PCBs.
What are printed circuit boards made of?
Printed circuit boards are made using the following materials:
- Copper: The conductivity of copper makes it a key component of a PCB as it aids signal transmission and heat transfer.
- Substrate: The exact material of the substrate depends on the type of PCB board you choose. The substrate secures the components onto the board.
- Solder mask: A thin layer of polymer, the solder mask protects the copper from oxidation and helps to prevent solder bridges forming.
- Silkscreen: This is the top layer of a PCB and is used as a guide for placing components onto the board.
Characteristics of a printed circuit board
A good quality PCB will have the following characteristics:
Consideration for hole wall thickness
The holes in a PCB, known as vias, are lined with copper and their thickness helps strengthen the resistance to expansion along the z-axis.
Copper cladding at industry standard
The copper cladding should align with the standards set by IPC-4101 criteria. This way, the tolerance helps to minimise divergence in the expected performance.
Not a speck of dust in sight
Even a speck of dirt on its surface can compromise the effectiveness of a PCB. They should be cleaned thoroughly throughout the manufacturing process, otherwise there are risks of poor connection.
Sufficient solder resistance layer
When the solder resistance layer has a good amount of thickness, it will be able to effectively support electrical insulation. On top of this, solder resistance material should be industry-approved. If it is poor quality, there are risks of the copper board being exposed to corrosive substances.
How is a printed circuit board designed and manufactured?
PCB manufacturing and assembly is an intricate task, but we have the tools to aid the process. To describe how they're created, we’ve taken a standard double layer PCB.
- First, you need to find a suitable CAD package, such as the DesignSpark PCB Software, to design your printed circuit board. This will allow you to create Gerber and NC Drill files. Each Gerber file represents a component necessary for PCB manufacture, including the copper layers, solder mask, and silkscreen data, the PCB outline, and the solder paste data for producing a laser stencil for assembly. The NC Drill file defines the location and size of each hole on the PCB – both PTH (pin through hole) and NPTH (non-pin through hole).
- The double-sided PCB is made of epoxy glass fibre (FR4) with copper foil on both sides. This is generally bought pre-prepared from suppliers. The FR4 material is fibreglass and gives the board its rigidity. To create a multi-layered PCB, combinations of the pre-made material are pressed together with other layers or non-copper clad FR4 (Prepreg) is used to isolate the copper layers from each other.
- In the PCB design stage, using the DesignSpark software, a drill or DRL file is created. This is the drill file containing the information used to drill the necessary holes.
- At this point there is no electrical connection between the layers. The hole walls need to be layered with copper. As the walls are non-conductive, a layer of copper is deposited chemically over the hole walls. This process, known as electroplating, is repeated until the copper thickness has reached its optimum for connectivity, typically 25um.
- The board is covered with photo-resist. This is a soft, photo-sensitive material. The copper film is placed over the board, aligned with the drills and the board is exposed to UV light. The unexposed areas of resist are removed by passing the boards through a developer solution leaving the copper track and pad pattern visible on the board.
- The next step is to deposit a coating over the exposed copper. This coating protects the copper on vias, component holes, and traces from being removed during the etching stage. The photo-resist is chemically stripped from the board before the copper is also chemically removed. The chemical will only remove the unused copper and not the copper protected by the coating. Once the coating is removed, exposing all the traces, component pads, and vias, this will leave you with the fundamental PCB
- Next, a layer of solder mask is added to both sides. It is generally green, although other colours are common. Using a similar process to the photo-resist, the areas for soldering are exposed. The solder mask insulates the copper and will only create contact where it is exposed. It also acts as a protector against oxidation and corrosion of the copper. The solder mask layers will include clearances around traces and vias.
- To identify the PCB, developers like to add print. The silk screen will be added at this stage using epoxy ink. Typically, this is white, although many coloured options are available.
- A layer of gold, silver or solder on the copper pads will be applied to all component pads and vias, giving the expected finish for the customer. This improves the solderability and protects these surfaces from oxidation. This is the final surface finish.
Once you know how to design and make a PCB, you can test it and create new PCBs using your existing design as a base. You can even sell your design.
Common applications of a printed circuit board
The versatility of PCBs means they can be applied across a range equipment used in different industries including:
- Consumer electronics: Smartphones, computers and home appliances, from microwaves to boilers, all rely on PCBs. You'll also find one below your computer keyboard – it's fundamental, allowing you to transfer data to the computer.
- LEDs: Whether it's for residential, automotive, or medical lighting, PCBs allow them to function.
- Automotive manufacturing:PCBs are applied to dashboard functions, sensors, and any screens or stereos.
- Industrial equipment: From manufacturing equipment like electric power drills to power equipment such as DC AC power inverters, PCBs are key in the industrial sector.
- Aerospace manufacturing: Communication equipment devices are crucial to the smooth operations of this industry and are powered using PCBs.
- Medical equipment:PCBs are essential for any medical imaging systems, from CAT to ultrasound scanners, as well as monitors for heart rate or blood pressure.
Can printed circuit boards be repaired?
A key advantage of printed circuit boards is that issues can be diagnosed and repaired with ease. The labels on the board help to identify any components that are causing the issue, allowing them to be replaced where required.
Depending on the type of damage incurred, the board can be changed to its original state, allowing you to start the process again. Alternatively, it can be repurposed in another device. The ease of PCB repair, as well as its adaptability, means that waste is kept to a minimum.
How to test a printed circuit board
There are several PCB-testing methods:
- In-Circuit Test (ICT): A reliable and widely used PCB test, this involves an in-circuit tester, which contains hundreds of thousands of drivers and sensors, plus a fixture and accompanying software. The fixture connects to the in-circuit tester and makes contact with the board through the pins attached. These pins connect to a point and relay information back to the tester. The software is used to instruct the components for the test and parameters can be set.
- Flying Probe Test: Otherwise known as the Fixtureless In-Circuit Test (FICT), this uses a simple fixture to secure the PCB while pins test relevant points with support from a software-controlled program.
- Boundary Scan Test: This test assesses the wire lines on a PCB and can help engineers test integrated circuits when the nodes aren't accessible.
- Functional Circuit Test: As the name suggests, this tests the function of the circuit to see whether a completed PCB performs as required. It is done at the end of the manufacturing plan.
How to clean a printed circuit board
A cleaning agent like isopropyl alcohol (IPA) can be used to clean a PCB. For the best outcome, this should be done with a small brush or even a Q-tip. The room should also be well-ventilated when using products like IPA.
The future of printed circuit boards
The evolution of the many industries that rely on PCBs means they won't be going anywhere anytime soon. There's scope for them to evolve and bring technological advances with them, opening endless opportunities. HDI PCBs, in particular, offer exciting possibilities. These are PCBs with a higher wiring density per unit than standard PCBs.
Further opportunities lie within 3D printing. 3D printed PCBs could revolutionise productivity and speed up technological advances even further. It creates the possibility for capacitors to be printed onto the PCB. This could also reduce circuit board footprints. Engineers will be able to bypass more time-consuming tasks if the right technology becomes an industry norm.