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I just started PCB design today (using KiCad) so I don't have to deal with a mess of jumpers for a homemade 74xx CPU on a breadboard. In addition to what value and type of decoupling capacitors I should use, I'd like to know how to route them (how far from the chip, how much to place some chips, specific trace width/turns/via requirements, etc.)

JRE
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leosmi
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    Have you seen [Decoupling capacitors for 7400 type chips](https://electronics.stackexchange.com/questions/353567/decoupling-capacitors-for-7400-type-chips)? – Andrew Morton Apr 02 '22 at 09:55
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    if you're a complete beginner, first start by looking at existing designs. Luckily there's over 50 years worth of examples for 74xx series. – Kartman Apr 02 '22 at 10:01

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I hope and I wish that you have a great time in Kicad.

Don't worry too much about the particular capacitance - something like 10 nF to 100 nF sounds about right. One capacitor per IC package. As I generally try to have large areas of GND even on double-sided boards (i.e. just two layers) I generally put those caps close to the Vcc pin of each IC, and run a via to the "ground plane". I also place the parts such that they don't prevent me from soldering the IC's and capacitors = no problem if you add an extra mm or two. Or, I can place the caps on the underside (solder side) and the via goes to the Vcc pin.

Andrew Morton has linked to a nice topic where this is debated in more detail. If you're interested in further reading, google Murata C39E application note. Note that apart from capacitance, capacitors in the debated range feature a parasitic resonance that is relevant at the switching speeds of those devices - so a larger MLCC is not always better. And if you're into fast circuitry, you may want be aware of the anti-resonance phenomenon when combining multiple capacitors. See also the Kemet KSIM tool. But I'm probably fetching this a little too far already :-)

With many logic or mixed-signal chips, you typically find a recommended style of power blocking in the datasheet or in an application note (often with an example PCB layout). Not so with the generic 74xx family - I know.

frr
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