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PCB stands for Printed Circuit Board, a printed circuit board, which supports and connects electronic components, with copper paths or tracks, so that a circuit or product works as desired.
To make it easier for you to understand, as you read this article, you are surrounded by PCBs; you have several in your computer, monitor, mouse and also in your cell phone. Every electronic element is built using a PCB, or at least its interior.
What is a PCB?
A PCB is basically a physical support of insulating material, where electronic and electrical components are installed and interconnected with each other. These components can be chips, capacitors, diodes, resistors, connectors, etc. In this link you can find more information about the components. If you take a look inside a computer, you will see that there are multiple flat plates with a lot of components assembled to it, this is a motherboard and it is composed of a PCB and its components.
How does a PCB work?
To connect each element on a PCB we use a series of extremely thin copper conductive tracks that generate a conductor rail, they function as a cable. In the simplest circuits, we only have conductive tracks on one side or both visible sides of the PCB, but in more complete circuits we have electrical tracks and even components stacked in multiple layers of them.
The main support for these tracks and components is a combination of fiberglass reinforced with ceramic materials, resins, plastic and other non-conductive elements. Although components such as celluloid and conductive paint tracks are currently being used to manufacture flexible PCBs. It is a sector in constant changes and modifications that improve the performance of printed circuits.
The first integrated circuit board was built in 1936 by hand by engineer Paul Eisler for use in a radio. From then on, the processes were automated for large-scale manufacturing, first in radios, and then in all kinds of components.
PCB creation process
We already know what integrated circuit boards are made of, but it would be very interesting to know how they are made. What’s more, we can create a basic integrated circuit ourselves by buying one of these boards, but of course the process will be quite different from the one used in reality.
PCB design by software
It all starts with the PCB layout, tracing the electrical leads needed to connect the components, as well as enumerating how many layers are going to be needed in order to generate all the connections that are going to be needed for the components.
This process is performed using CAM computer software, such as TinyCAD or DesignSpark PCB, which is widely used in electronic engineering careers. Not only are the electrical tracks designed, but also the various labels are created to list the installed components and identify each connector.
All the necessary steps in the development process will be documented so that the manufacturer knows exactly what to do when the project is sent to him.
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Screen printing and photographic tracing
Once designed, we now pass the project directly to the manufacturer, where the physical creation of a PCB begins. The next process is called photographic tracing, by which a machine similar to a printer (photoplotter) traces by laser a graphic with the connection masks of the electronic elements.
A thin sheet of conductive metal about 7 thousandths of an inch thick is used for this purpose. These masks are then used to determine where the electronic components are attached. In more advanced processes, this process is done directly on the PCB with a printer that etches the connection masks with this metal.
Printing of PCB inner layers
The next thing that is done is the printing on the PCB of the various internal electrical tracks, with a special compound. This involves “painting” a negative of the electrical tracks onto the foil to create a conductive pattern with a photosensitive or dry film material. Well, this film that has been created is exposed to a laser or ultra violet light to remove the excess material and thus create a negative of the final circuit.
This process is performed if the PCB has inner layers with conductive tracks. In addition, this process will then be repeated on the outer layers of the PCB to create the final copper tracks and according to the circuit design.
Inspection and verification
Once the different layers of conductive tracks have been made, a machine will inspect that they are all correct and working properly. This is done in an automated way by comparing the original design with the physical printout to look for short circuits or broken tracks.
Oxide film and lamination
Each of the printed sheets with conductive tracks is oxide treated to improve the capabilities and durability of the copper tracks in each layer.
Thanks to the process, delamination of the different conductive layers and tracks on particularly sensitive PCBs or PCBs with a large number of components, such as those in computers, will be avoided.
The next thing to do is to build the final PCB, for this purpose each one of the circuit layers will be joined by means of fiberglass sheets with epoxy resin, Pértinax or any other method used. All this will be perfectly glued by means of a hydraulic press and this is how we will obtain the integrated circuit board.
Drilling of holes
In most cases we will need to drill a series of holes in the PCBs in order to join the different layers and copper tracks. We will also need complete holes to be able to attach electronic elements or different connectors or expansion slots.
The drilling process must be extremely precise to preserve the integrity of the PCB, so tungsten carbide heads are used, the hardest material available.
Metallization of orifices
In order for these holes to communicate with the various internal tracks, a plating process with a thin copper film will be required to provide the necessary conductivity. These plating will be between 40 and 60 millionths of an inch.
The PCB is now ready to trace the copper tracks on the outer sides of the PCB.
Outer track film and electroplating
Now we move on to create the outer conductive tracks, and for this we will follow the same procedure as for creating the inner tracks. First we create the dry film in the form of a negative of the final circuit. Then, using a laser, we create the spaces where the copper will be deposited to create the conductive tracks.
The PCB will then undergo an electroplating process, which involves bonding copper to the free areas of dry foil to form the PCB’s electrical tracks. The PCB is placed in a copper bath and the copper will adhere by electrolysis to the conductive patterns to create tracks as thin as 0.001 inches.
Another layer of tin will then be added on top of the copper layer to protect this chemical attack when we go to the SES orstrip-etch-stripprocess.
Strip etch strip
This is the penultimate step, we are going to remove the excess copper from the PCB, the excess will be the one that we have not bathed with tin. This way only the copper will be protected with tin.
Subsequently we must also remove the tin by means of a chemical treatment to finally leave only the copper tracks that will finally be the ones that will connect components and transport electricity.
Now another AOI process will verify that everything is correct to finally engrave the mask and the legend.
Solder mask and legend
Finally, a solder mask will be applied to the electronic circuit board so that the components can be soldered to the tracks correctly and exactly where they should go.
Then we also print the legend composed of the information that the designer wanted to provide on the PCB, such as connector names, element code, etc. In addition, the final design of the PCB will also be made with the colors that the manufacturer wants to give it, as we see in the gaming motherboards, etc.
Component welding and final testing
The PCB is ready and it only remains to add the components by means of high precision robot arms, and the corresponding slots. This way the board is ready to be tested electrically and check that it works correctly.