What is a PCB?How it Works

What is a PCBHow it Works

A Printed Circuit Board is the backbone of all the modern day electronic devices. Let’s explore what a PCB is and how these tiny circuits are manufactured. Let’s go. Early electronic components were manufactured and connected to each other manually using wires in a point to point construction. This manual construction lead to errors and difficulty in scaling up the production. Moreover, because these circuits were extremely complex, repairing one that had been damaged was an unreliable tedious task.

In 1936, Paul Eisler, a genius engineer who worked for a newspaper company recognized the hurdles. He invented the concept of printing conducting copper circuits on a non conductive board as shown here. Then connecting components over the traces, this is the very first PCB manufactured. However, a modern day PCB looks like this much more sophisticated, tiny and complex. A modern day PCB manufacturing starts from a simple copper flat sheet. Let’s see how this sheet evolves into a sophisticated electronic device in a detailed logical manner.

To start off, this layer of copper foil is laminated on a flat sheet of insulating glass fiber material. The glass fiber gives mechanical support to the PCB, this glass fiber will remain with the PCB till the end of the manufacturing process. This arrangement along with a protective aluminum sheet is first sent to drilling. Here some holes called registration holes are drilled. These holes serve as reference points for further alignment processes. Meanwhile, an engineer properly designs the circuit using computer aided simulations. Here’s some PCB design software, which generates design files called Gerber files.

Gerber files contain detailed 3d models of the PCB. Using these design files, the drilling machine drills different holes. These holes are used to attach the components into the board later on. After drilling, the boards are cleaned properly, so that no drilling residue is left behind. Now the most important step production of these tiny and complex copper traces. The best way to achieve this is by a chemical process called etching, where you have to cover the copper plate with a resistive mask, this resistive mask will have the same pattern of the circuit you want. Now if you dip this arrangement into an alkaline solution at 60 to 120 degrees Celsius, the area of copper uncovered by the resistive mask dissolves or is etched away. After this process is complete.

The protective mask is washed off as well. Thus we are left with only required traces of copper. The circuit prints on the resistive mask used in this process is obviously made with the help of a Gerber file. A UV light based technique is used for sticking the mask to the copper plate where it is needed. To achieve bulk manufacturing multiple masks are made in a single sheet. As you can see, the copper traces are very thin, hardly visible to the naked eye. To check the quality of the copper traces, the board’s go for an inspection. An operator with an optical inspection machine checks the quality of printed boards by taking pictures of them and comparing them with the design files.

The machine checks for broken or short circuited traces and the PCBs with damaged short circuited traces are rejected. If everything is good, then boards are moved to the next step. Have you ever wondered why a PCB is always green? This is to protect the board from oxidation and exposure to dust. a layer of solder mask resin protective coating is applied over the board. This layer gives the board its green hue, which has simply been universally adopted. The copper traces go hidden beneath the green layer after this operation, this new green resin added is insulating in nature.

You can see clearly that the resin will block the connection between copper trace on the edges of the holes and components. To avoid this issue, we have to remove the solder mask from the edges. The solder mask we added will adhere to the copper plate only if it undergoes a UV process. So the trick is simple. Just cover the edge area of the holes with a chemically resistant mask and go for the UV process. After this when you do the chemical dipping, the green mask of the edge areas will be removed As a final step a silkscreen is printed, which is nothing but a layer of visible ink trace used to identify the PCB components, markings, logos, symbols and so on. We are done.

We have manufactured a PCB starting from a simple copper plate, your PCB is ready to dispatch. In the industries the components are then placed and soldered using liquid tin. This process fixes the components to the copper pads on board. Next, final flying probe testing is done to check the connectivity between all the components traces and pads. The current PCB technology we explored was THT-(THROUGH HULE TECHNOLOGY) type. Even though this technology is good for educational purposes, THT-(THROUGH HULE TECHNOLOGY) is almost obsolete. The latest PCB technology is SMT based.


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