Printed Circuit Board (PCB)
A PCB is used to connect electronic components electrically. This is done by making conductive path ways for circuit connections by etching tracks from copper sheet laminated onto a non-conductive substrate.
A PCB consists of a conducting layer that is made up of thin copper foil. The insulating layer di-electric is laminated together with epoxy resin prepreg. The most commonly used PCB type is the FR-4. Boards may be single sided or double sided. Double sided PCB can be used to connect electronic components on both sides through through-hole plating. This is done by copper plating the walls of each hole so as to connect the conductive layers of the PCB.
Advantages of PCB over Bread-board
- You can get a much higher density board with PCB.
- You will find the PCB design to be more reliable than the one made on a bread board. The circuit will look neat without any wires popped up and will not fall apart.
- You can have very precise control over the circuit component you are using, and you can comfortably fit in odd shaped components that are difficult to fix on a bread board.
- For production of large volume of circuit boards, the costs become less and the soldering can be done by fully automated machines.
For PCB fabrication, some basic steps have to be followed. The detailed description on how to make PCB is explained below. The step by step procedure can be obtained by checking the following links.
PCB Etching Process | PCB Drilling | Conductor Plating | Solder Resist | PCB Testing |PCB Assembling
Take a look at the video below to get a brief idea about how a PCB is made.
Once you have decided which electronic circuit is to be made on a PCB, you will have to make the design for the board on your PC. You can use different PCB designing CAD softwares like EAGLE. The most important point to note is that everything has to be designed in reverse because you are watching the board from above. If you need the circuit to be designed on a PCB, the layout must have a 360 degree flip.
The next step is to print out the layout using a laser printer. You must take special care in the type of paper that you are going to use. Though a little expensive, photo basic gloss transparent papers are known to be the most suitable for the process.
You must also make sure that you are able to fit all your components on to the print. First take a copy of the print on ordinary paper and lay down all the IC’s and other components. The size of the layout must also fit the size of the PCB. Try to get the highest resolution when you are printing i on the paper. Always use black ink to take the layout. Increase the contrast and make the print more dark and thick. Do not take the print as soon as it comes out. Wait for some time for the ink to dry out.
The above said method is a little unprofessional, and thus the colour may not b dark enough that you may be able to see through it. There might also be a few spots here and there. But this is more than enough as long as it can block UV light compared to the blank area.
Cut the layout by leaving a generous amount of blank space. Place the paper layout on the PCB and apply some heat by pressing an iron box on top of the paper on to the printed circuit board. Apply pressure for some time and keep the PCB intact for a few minutes. Now the layout is attached to both the board and the paper. We have to get rid of the paper, so that it gets permanently attached to the board. The only way to do this is to soak it in water. After two minutes, peel off the first layer of paper. After two to three hours of soaking, take it out and rub it with your finger to remove all the paper bits off.
All PCB’s are made by bonding a layer of copper over the entire substrate, sometimes on both sides. Etching process has to be done to remove unnecessary copper after applying a temporary mask, leaving only the desired copper traces.
Though there are many methods available for etching, the most common method used by electronics hobbyists is etching using ferric chloride ir hydrochloric acid. Both are abundant and cheap. Dip the PCB inside the solution and keep it moving inside. Take it out at times and stop the process as soon as the copper layer has gone. After etching, rub the PCB with a little acetone to remove the black colour, thus giving the PCB a shining attractive look. The PCB layout is now complete.
The components that have to be attached to the multi-layered PCB can be done only by VIAS drilling. That is, a pated-through hole is drilled in the shape of annular rings. Small drill bits that are made out of tungsten carbide is used for the drilling. A dremel drill press is normally used to punch the holes. Usually, a 0.035 inch drill bit is used. For high volume production automated drilling machines are used.
Sometimes, very small holes may have to be drilled, and mechanical methods may permanently damage the PCB. In such cases, laser drilled VIAS may be used to produce an interior surface finish inside the holes.
The outer layer of the PCB contains copper connections (the part where the components are placed) which do not allow solderability of the components. To make it solderable, the surface of the material has to be plated with gold, tin, or nickel.
The other areas which are not to be solderable are covered with a solder resist material. It is basically a polymer coating that prevents the solder from bringing traces and possibly creating shortcuts to nearby component leads.
In industrial applications, PCB’s are tested by different methods such as Bed of Nails Test, Rigid Needle adaptor, CT scanning test, and so on. The basic of all tests include a computer program which will instruct the electrical test unit to apply a small voltage to each contact point, and verify that a certain voltage appears at the appropriate contact points.
PCB assembling includes the assembling of the electronic components on to the respective holes in the PCB. This can be done by through-hole construction or surface-mount construction. In the former method, the component leads are inserted into the holes drilled in the PCB. In the latter method, a pad having the legs similar to the PCB design is inserted and the IC’s are placed or fixed on top of them. The common aspect in both the methods is that the component leads are electrically and mechanically fixed to the board with a molten metal solder.
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