Working with PCBs – A Short Guide

Working with PCBs

Electronics is a fascinating subject, with a wide array of practical applications – from repairing household devices and appliances to designing electronic tools of one’s own. However, from the outside in the subject can be intimidating, especially when it comes to practical work. The mess of wires and inscrutable components that make up circuitry can seem impenetrable to the budding engineer. However, with a little understanding of what a PCB is and how it is best constructed, they become a lot easier to understand and even repair.

What is a PCB?

A PCB, or Printed Circuit Board, comprises layers of non-conductive material – generally a plastic – sandwiching conductive copper layers. A printing and etching process can turn these layers into pathways for electricity, as designed by an electronics engineer. As such, PCBs represent a bespoke, efficient, optimized way to create complex circuits with minimal footprint. PCBs come in many different shapes and sizes. The two most common are through-hole and SMD; through-hole has holes passing through contact points on the PCB, through which the wire ends of large components are threaded and soldered. SMD stands for Surface Mount Device, with vastly smaller iterations of the same component soldered directly onto the PCB’s surface. Here we will assume we are working with a through-hole PCB design, as they are the most common kinds of circuit-board for beginner projects.

Populating a PCB

Populating a PCB with the correct components is an easy enough task, but also easy to get wrong if not undertaken with due care and consideration. Ensuring you have all of the components, and that they are of the correct values and tolerances with reference to the circuit’s schematic, is a key preparatory task before you begin.

Populating your PCB in stages is the safest way to complete its circuit. Go component type by component type, starting with passive components: resistors first, then capacitors and inductors, then diodes. Place all of the relevant component type in their respective places, and solder one leg of each in place before going back over and soldering the other. This prevents any potential damage to the component from heat stress.

With all passive components in place, you can now begin to populate the PCB with active components, such as transistors and ICs. Working in stages like this reduces the chance of overheating any sensitive active parts of your circuit. With ICs, try to source IC sockets instead of soldering the ICs straight onto the PCB. Soldering a DIP socket in instead will prevent the possibility of damaging the IC, and also allow you to swap it out with ease later on.

Repairs and Troubleshooting

With understanding of PCBs and the process of building a circuit with one, they will now be a lot less intimidating to look at. In the event that your built circuit doesn’t work, or you receive a broken PCB to troubleshoot, simple observation of the schematic and board can help you reveal where the problem lies – and simple application of certain tools and techniques can help you in your repair efforts.

The visual check should be the first you carry out; look for any obvious cracks in the PCB traces or solder joints, or signs of burnt-out components. Remember that a burnt-out component is not necessarily the end of the circuit’s problems, but more likely a symptom of something wrong earlier in the circuit. If the circuit works intermittently, try flexing the PCB in your hands while powered. This can reveal bad or cold-soldered joints. Here, a desoldering pump comes in useful, allowing you to remove solder after re-heating with an iron. With such a pump, you can remove parts or simply re-solder existing parts to create a better contact. If no obvious solution appears from the above checks, a thorough signal-tracing inspection with a multimeter and oscilloscope can help you discover the exact point of failure, in tandem with the schematic.

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