A printed circuit board (PCB) is the most widely used mechanical support and electrical connection of electronic parts of modern day circuits. Its base is made of a non-conductive substrate material, most of the time fiberglass, phenolic, or epoxy. Copper is laminated onto the substrate to serve as its conductor, then a soldermask is also coated onto the copper to form conductive paths and pads based on a detailed designer-made pattern.
There are three types of PCBs available in the market. These are referred to according to the number of copper conducting layers each one possesses. They are: Single sided, double sided, and multi-layer. For double sided and multi-layer, the different layers are linked to one another through plated holes named vias.
PCB assembly is the process of creating a PCB by bonding or laminating a substrate, conductor, and soldermask together, and adding a silkscreen layer on the outermost surface for labeling and as guidance mechanism in mounting the different components of an electronic circuit based on a specific design.
Once all the parts are soldered, mounted, and ready to be used, the printed circuit board is now similarly termed as a PCB assembly.
Two Ways to Mount Components
There are two ways to mount electronic components onto a PCB, and they are called through-hole technology and surface-mount technology. The most widely-used method at present is the surface-mount, as parts are directly soldered onto the surface of the board. This makes surface-mount technology ideal for the more compact designs that modern gadgets have today.
The through-hole method uses protruding lead legs from electronic parts to be inserted through holes in the circuit board. Afterwards, the legs are soldered onto it on the other side. This process greatly limited the space that can be utilized in a single PCB, but is still occasionally being used today for simpler circuit designs.
The PCB Assembly Process
The modern process of making a PCB is actually quite sophisticated, especially when fabricating the contemporary designs of today. Most of them need specialized tools and equipment and should be done in an extremely clean room for faster and more efficient mass production.
However, simpler designs can still be made manually, and there are many electronic enthusiasts who fabricate their own PCBs at home using practical DIY techniques.
Four layers are laminated together to form a single PCB. Starting from the center of the board, they are: substrate, conductor (typically copper), soldermask, and silkscreen.
Below is a simplified step-by-step process of making a PCB that is applicable for beginners to easily understand its concept.
1. After preparing the substrate, a copper layer is then coated on top of it. The copper layer is placed depending on the type of method used in creating the circuit pattern. The two methods are either additive or subtractive.
2. In the subtractive method, the entire surface of the substrate is laminated with copper, and then the undesired portions are etched away. The additive method is the opposite as the copper pattern is directly electroplated on the substrate.
3. After the copper pattern is securely bonded with the substrate, a solder mask is then laminated onto the board. This thin layer of polymer protects the board from oxidation and keeps the conductive parts of the circuit from touching one another.
4. A silkscreen layer is then coated on top of the board. This layer contains labels, names, designators, and sometimes specific instructions, on the parts that are to be mounted on the PCB assembly.
5. The next step is the mounting of circuit components, which, as mentioned above, can either be through-hole or surface-mount.
6. For through-hole, small holes are first drilled on the board where the components are to be inserted.
7. For surface-mount, drilling is no longer needed as the parts are directly soldered onto the circuit board.
8. After all the components are mounted, then the PCB assembly is finished and ready to be used for its intended purpose.
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