Printed circuit boards, also known as PCIs, are usually out of sight, but they are part of everything that involves technology. Computers, automated chairs (such as dentists), security systems, smartphones, toys, cars and showers are just a few examples of devices that take advantage of these full electronic components boards to perform their respective functionalities.
Although they are mostly hidden, you may have realized that PCIs are extremely important in our day to day lives. Tecmundo explains to its readers how these boards are produced. Put on your goggles and antistatic wrist strap and let's start the ride through a production line.
A printed circuit consists of a plate made up of layers of plastic and fibrous materials (such as phenolite, glass fibre, fibre and polyester film, among other polymers) that have thin films of metallic substances (copper, silver, gold or nickel). These films from the "tracks" or "tracks" that will be responsible for the conduction of electrical current by the electronic components.
These electrical impulses are transmitted to the components, enabling the operation of each part and, consequently, of the complete system formed by the PCI. The printed circuit boards had their origin in 1936 by the Austrian engineer Paul Eisler, although the fundamental technique for the development of PCIs came in the year 1903 with the researchers of the German inventor Albert Hanson.
Before exploring the manufacturing process of PCIs, it is important to make it clear that the steps described in this article may suffer variations among manufacturers. Each company has its procedures stipulated according to its structure and method of work. Our intention is to show how printed circuit boards are produced in a generic way.
Creation of electric scheme and drawing
The manufacturing process of a printed circuit board starts at a computer. Each PCI model is designed by engineers with expertise in electrical or electronics, using specific software.
The files originated, generally, in the formats CAD and CAM, form the electrical scheme of the plate, defining where the electric current should pass. These drawings will be used by production machines to select layers, drill holes, and create PCI "tracks" - steps that we'll look at in more detail later in this article.
With the PCI project duly revised, the first manufacturing procedure per se is drilling. Grouped into large panels, several fibrous plates (which will form the layers of the PCI) are drilled by large machines - some of which are capable of exceeding up to six panels at a time.
A thin sheet of foil can be placed on the panels to absorb and aid in the distribution of the heat caused by the perforation, avoiding possible damage to the plate. The number of bits used by the machines can vary, but in general, they have cartridges with 120 bits.
Chemical and copper bath
After the aluminium foil is removed, the panels are cleaned. At this stage of the process, the plates pass away from the contact with electrical currents, being restricted to coming in contact with chemical substances. The substances used are chosen according to the material of the plates and the metal films.
Then the still grouped PCIs proceed to containers filled with copper. Thus, the whole area of the plates, including inside the open holes in the drilling, will receive a very thin layer of this metal.
Application of photoresist film
The next step is the application of a photoresist film, a light-sensitive material that has the objective of creating a coating to protect the copper layer of the PCIs from the action of UV rays, avoiding possible oxidations and short circuits.
This is a step that requires great care. The storage environments of the exposed film-coated panels must be thoroughly sanitized so that foreign particles (such as dust) do not come into contact with the areas of the plates.
Subsequently, the panels receive a film that will determine the tracing of the "tracks" that will lead the electric current through the PCI. This new layer acts as a mask. It covers the parts of the surface of the plates that should not receive current, leaving only the positions of the components and the path that the chain should follow between them (the "trails") exposed.
Application of tin
The printed circuit boards follow to receive a reinforcement in the copper layer in the parts that have remained exposed, the "tracks" and holes from the drilling. The applications of the metallic substance are very fine, being thousandths of an inch thick.
Another metallic element enters into action: the tin. This substance is added to the points where newly bathed areas in copper remain exposed. It will serve as a protection for the contacts where the electronic components will be welded in the future.
Then, the PCIs proceed to the removal procedure of the photoresist film. The films are removed with machines, as the precision must be perfect not to affect other layers of the plates. The panels are then dipped into tanks with chemical components to remove the tin. At that moment, the structure that will be responsible for conducting the electric current is finished.
The plates leave for the process where they will receive the so-called solder mask, a type of lacquer consisting of polymers that give a coating capable of permanently protecting the copper traces of the PCIs. Finally, the plates gain the green colouration that we know.
The panels are exposed to UV lights so that the welding mask dries and they can be manipulated. The excess of the varnish is removed and the plates go to a greenhouse or oven to cure them at high temperatures.
The manufacturing process begins its final phase. The printed circuit boards go to a device that can be understood as a giant printer, in which they will have printed screenprinting (such as the product name, version, indications of the positions of the components and other information that will be useful in assembling the electronic components ). Again, the PCIs are resting in a greenhouse or kiln to dry the screenprint.
Finally, the plates are bathed in a welding stream - a substance that facilitates the welding procedure. The flow adheres only to the surface where the copper is still exposed. Removed the excess of this element, the panels can follow for the final quality inspection.
It is not only at the end of the production process that the plates are checked. The visual inspections, when the human being ascertains imperfections in the plates, can happen in several moments of the line, varying according to the manufacturer.
Usually, in addition to the last superficial check, at the end of production, the PCIs pass through machines that will test if the electric current is passing through the points specified in the initial design. Once this is done, the printed circuit boards can already be separated or sent in panels to the clients - which will insert the electronic components that will constitute the gadgets.
Did you get excited about the theme? Then you will be more excited to know that it is possible to make a printed circuit board at home without spending much and as a result that resembles the industrially produced PCIs.
Combining materials purchased in any stationery and some items we have in our homes, such as hair dryer, steel sponge, crepe tape, glue and transparencies, it is possible to put your electronics project into action. Check out how to proceed in this article published by Suraj Gehlot.