Part 1: PCB design basics 4

Published:2011/8/24 2:25:00 Author:Amy From:SeekIC

Karol Walraven

Wrapping up

Continue by placing the com­ponents in their final location (Figure 5). If you ore short of space, check if the following tricks are of any help:

-Use SMD components. These are smaller (and therefore belter at higher frequencies) than leaded components and can be placed on the bottom of the circuit board, so they do not occupy space on the component side. In Figure 2b you can see that with respect to the area an SMD decoupling capaci­tor is absolutely superior to an ’ordinary’ decoupling (2a) capacitor.



Split large capacitors into two smaller capacitors. You can quite safely place the decoupling capacitor with the larger value a little fur­ther away because it pro­vides far the lower frequen­cies. Place a small (for example 10 to 100μF) capacitor close lo the com­ponent to where the power supply track runs.

Tips

Finally another few lips. Don’t give interference an opportunity to slip ’past’ the decoupling components. Fig­ure 6 illustrates what we mean by this.



If you are designing o double-sided PCB, then it is usual lo reserve one side as a ground plane. This makes the layout easier and works very well from an electrical perspective, because ground then becomes a real ground (= reference] as much as possible. When using leaded components each con­nection to ground is then made automatically. With SMDs you will have to make a manual connection with the aid of an additional via (a connection through the board from the top- lo the bottom side) which must be close to the ground pin of the SMD component. If you don’t do this the length of the ground trace could become too much!

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