PCB Capacitor-What You Should Know About It

by Howie Liu Electronics Engineer

Abstract

We can then have discrete capacitors alongside the PCB capacitor which may act as lumped capacitors that you can use to create a distribution system for your design.

Content

1. PCB Capacitor

2. Capacitor PCB symbol

3. Non PCB capacitor disposal

4. Non PCB capacitor

5. Decoupling capacitor PCB layout

6. Conclusion

1. PCB Capacitor

PCBs can behave like capacitors because a capacitor can be made up of 2 metal objects separated by a non-dielectric material. So the combination of PCB tracks, pads, components and pins should form a capacitor capable of destabilizing frequency oscillation. Also, closely ground planes and power provides the required decoupling capacitance. It is possible to use capacitors on the edge of your PCB, all you need are two copper planes to act as capacitors. We can then have discrete capacitors alongside the PCB capacitor which may act as lumped capacitors that you can use to create a distribution system for your design.

2. Capacitor PCB Symbol

Capacitors are used to store electric charges. It can be used in a circuit alongside other components such resistors and diodes. A capacitor is represented by the following symbol.

pcb capacitor1.png

When used in a circuit, it helps to block DC current but allows the AC signals to pass. The unpolarised capacitor will have a charge of less than 1µF and will be represented by the following symbol.

pcb capacitor.png

On the other hand variable capacitor which can suitably be used in radio, the tuner can be represented by the following symbols

pcb capacitor3.png

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3.PCB Capacitor Disposal

Disposing non PCB capacitors require that you comply with federal regulations that govern disposal. Already there is a document that assists the scrap yards with guidelines on how this can be done. Shredding and crushing is no longer an option since it contaminates the entire area where this is done. As a result, proper removal and storage of non-PCB capacitors minimize and prevents violation of the requirements.

Disposal Requirements

Alternatively, the capacitors could be disposed of by contracting a transporter who is permitted to transport PCB waste. Proper records must be kept including the date when the haul was picked, the number of drums the transporters name and the date of pick-up.

4.Non PCB Capacitor

The ban on the use of PCBs capacitors in 1979 meant that manufacturers had to substitute them with Di2-Ethylhexyl phthalate. This is a dielectric fluid found in non-PCB ballast capacitors. Currently, about 25 percent of capacitors contain DEHP.

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5.Decoupling Capacitor

How effective your design will depend on many factors including the effect of decoupling capacitor on the PCB. Typically, the design will have the top layer and the bottom layer on the sides of the chip. The vias are connected to the power plane and the ground. The top capacitors should be connected to the unbroken ground plane because of the advantage it comes with. Typically, they have the lowest impedance. Unfortunately, this arrangement may not work if we are looking for high-frequency signals. The layout should be good to ensure that the routing does not get into other signals. This is why the layout should consist of two layer boards.

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6.Conclusion

Notice that decoupling will provide a near reservoir energy to smooth out voltage whenever there is a change in the current that is being drawn. It is common for the power supply to take some time before responding to voltage because of inductance. The decoupling cap, therefore, has the duty to close the gap. It should be closer to the digital chip to be able to do this. Otherwise, the inductance in the leads could easily get in the way and make it difficult for the extra current to be delivered quickly.