Printed circuit boards are an integral part of any electronic system that has a variety of integrated electronic components, from passive devices like resistors and capacitors to microprocessors and integrated circuits. All these components are placed on a green colour (common) printed circuit board that also provides mechanical strength to the components enabling the PCB to be mounted onto a bigger electronic system. To design a printed circuit board, several processes take place, including manufacturing, integrated circuit packaging, and the structure of the bare circuit board. All of these require domain expertise and understanding of the practical application to efficiently design and place the electronic components. The placement of these devices on a printed circuit board brings an efficient electrical system that can be deployed at scale in consumer products.
PCBs play an important role in our day-to-day lives as most of the electronic systems around us, including television sets, music systems, laptops, and even smartphones. All these devices have hundreds of miniature electronic components that are carefully mounted on a printed circuit board that uses copper conductors to create those electrical connections between the mounted components.
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A printed circuit board is an electronic assembly that holds components and provides a compact packaging for integrated electronic circuits to be deployed into an end product. These sandwich-like structures consist of insulating and conducting layers and slots to hold these electronic components in place. The electrical connection present between the components is due to the copper conducting lines known as traces. The components are soldered on the pads, completing the connection between the track and the component. A PCB helps compact the circuit by efficiently placing components and connecting them with tracks in multiple layers. The layers are stacked one above the other with an insulating layer between them. The different layers help route traces without intersecting each other. A PCB has two layers: a conducting layer generally made of copper and a non-conducting layer known as the substrate material. Above the substrate material, the PCB has the following parts:
Traces: These are conducting paths, generally made of copper used to electrically connect the components on the printed circuit board. A trace can be of different widths depending on the amount of current it will carry.
Pads: Pads are relatively thicker copper traces that are present around the leads of an electronic component. The lead of the component is soldered onto these pads to electrically connect them and also mechanically hold them in their place.
To make a PCB as compact as possible, several conducting copper layers are stacked over each other with insulating material (prepreg) between them. Based on the number of conducting layers present in a PCB, it is categorized as follows:
Single-layer PCB: A single-layer PCB is the most basic kind of PCB, consisting of a single copper layer over a substrate. Depending on the manufacturer, the tracks are either etched or printed on the substrate layer. They are generally used in electronics like toys, LED driver circuits, etc. These PCBs take up a lot of space because the tracks cannot overlap, and the components have to be spread out to accommodate tracks. To overcome these problems, double and multi-layered PCBs are used in applications that require compactness.
Double-layer PCB: In this type of PCB, they have a layer of copper present both above and below the substrate. One of the advantages of having both sides coated with copper as a conductive layer is to provide double the amount of area compared to a single-layer PCB of the same dimensions. This allows more space for the routing of traces and makes the complete circuit more compact. To connect the two layers, vias are placed through holes with conducting material, electrically connecting traces on different layers.
Multi-layer PCB: A PCB has more than two conducting layers as they consist of several double-sided boards stacked over each other and separated by insulating layers. All the layers are sandwiched over each other under high pressure and temperature. They are used in complex high-frequency electronic circuits like motherboards, microcontrollers, etc. The different layers of the PCB helps isolate high and low power lines from signal lines to prevent interference and loss of signals.
PCBs are made of various substrates and materials, and the substrate selection depends upon the operating conditions and application specifications. For PCB design, engineers choose the material based on the following factors such as dielectric constant, flame retardance, loss factors for high-speed applications, mechanical strength, and thermal performance. The core substrate that forms the middle layer in a PCB is called laminate, insulating in nature. The insulating media between two consecutive conducting layers is called prepreg.
The following are the materials used in PCB manufacturing:
Prepreg: A glass fabric is coated with resin and dried after going through a special machine called prepreg treaters. These are usually FR4 epoxy resin, polyimide, Teflon and several others. The glass is a mechanical substrate that holds the resin in place. When exposed to high temperatures, this resin begins to melt, and once the resin in the prepreg melts, it reaches a thermosetting point where it then re-hardens to become very rigid. Prepreg is used in manufacturing several things such as aircraft and boats.
Laminates: Also commonly referred to as copper-clad laminates that are composed of sheets of prepreg laminated together with heat and pressure. They also have sheets of copper foil on both sides, and once the resin is hardened, the PCB laminates are like a plastic composite with sheets of copper foil.
Solder mask: A solder mask is an insulating layer generally green in colour (although it can be customized based on the customer's needs). It is layered on top of the traces to prevent oxidation of the copper traces when exposed to moisture. They also prevent shorting the tracks if any conducting material is placed on a live PCB. Solder masks increase the life of a PCB and also provide space for applying the silkscreen.
Silkscreen: A silkscreen is a layer of ink trace to mark the boundary of components and name them. They make PCBs more readable and help with troubleshooting. They also help in customizing a PCB by adding logos and names of the company.
PCB is used in almost every electronic device, from LED lamps to mobile phones. PCB forms the heart of every electronic device today. As electronics and its application penetrate into almost all the industry, the application of PCBs increases. Almost every industry is looking for automation through advanced machinery, which causes more and more electronics to be used.
In the healthcare field, various electronic scanners, monitoring, and measuring equipment are used to monitor patients' health parameters. These machines are required to work with utmost precision and have high accuracy. Hence, high-density interconnect HDI PCBs are specially designed for this purpose. Certain applications also require frequent movement of parts; hence flexible laminates are used for the same.
Consumer electronics, such as smartphones, kitchen appliances, and entertainment systems, use PCB as the substrate. Due to mass production, the manufacturing of these PCBs is done at a low cost and high volume while maintaining quality and safety standards. FR4 epoxy type of laminates is generally used in consumer electronics applications. In industrial applications, machines, power converters, and power measuring devices are all designed for PCBs that can survive harsh heat, moisture, and chemicals. Polyimide laminate with doubly thick copper is generally used for such applications.
PCBA stands for printed circuit board assembly, which is completely different from a PCB, where there are just the tracks without the components attached. In simple words, a PCB is a blank board, while a PCBA has all the components mounted onto it. A PCB schematic is first designed in CAD software like Eagle, Altium, etc., after which it is manufactured. The end product of this process is a board over which tracks are printed along with a solder mask and silkscreen. This board cannot be used unless the electronic components are mounted on it. After mounting all the components at their respective locations as indicated by the silkscreen, an assembled printed circuit board (also called PCBA) that can be deployed is ready. As part of the PCBA design, nowadays, the manufacturers mainly use SMD components for the PCB to make it cost-efficient.
No components mounted
Components are mounted
Cannot be deployed
Can be deployed
Time taken to complete
Takes less amount of time
Takes comparatively more time
Compartmental anti-static packing
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For PCBA manufacturing, the sourcing of electronic components is an important part of the whole process before mounting them. These components are selected during the design phase of the PCB according to the requirements of the application. Components like resistors, capacitors, integrated circuits, and microprocessor chips are of two types based on the type of mounting: surface mounted and through-hole mounted.
For printed circuit board assembly, surface-mount technology (SMT) is an assembly process method in which surface-mount components are soldered on the surface of the PCB. This technology is generally used in multi-layered PCBs, which are required to be compact. The process first involves making the PCB and placing the solder paste on the leads, after which components are placed on the board. The PCB is then heated for the solder to melt and firmly hold the components in their place.
The thru-hole PCB assembly method is used to mount thru-hole components. The components have long leads that are inserted into holes that are drilled in the PCB. These components are generally bigger and cheaper as compared to surface-mounted components. The process first involves drilling holes in the PCB, after which the leads are inserted and then soldered onto the solder pads. The solder holds the component in its place and provides an electrical connection.
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PCBs are the foundation of modern-day electronic systems, and with an increase in industrial automation, PCBs will be much needed to serve the demand. Some of the key takeaway points are:
A PCB is a bare board made up of non-conductive substrate material with copper circuitry placed on both sides.
In the manufacturing process, the PCB board with more layers has a complex process and can be labor-intensive to produce. They are also expensive, and not many manufacturers will provide the service.
The difference between PCB and PCBA is that the PCB is a bare circuit board without any electronics components mounted on it, while in PCBA, the complete board is ready for deployment with all the passive and IC components mounted.