I have a question about this... is there really a difference between "route
so that power goes THROUGH the capacitor pad on its way to the chip" and
not? Does anyone have empirical evidence of this working vs not? Or is it
just something people have imagined?

Just curious as have not seen any tests around which prove the need for it.

Ryan




On 5 December 2017 at 07:16, Van Horn, David <
david.vanhorn@backcountryaccess.com> wrote:

> Plenty of good answers, and I'll throw in a "HELL YES" as well.
>
> I saw one instance of a product in production using an Atmel AVR, where
> there is a single pin which is an ADC AREF input only rather than a fully
> implemented I/O pin.
> The application didn't use the ADC at all, and the designer thought he
> didn't need that bypass cap.
> There was a box of boards which had failed production test, which had
> resisted all attempts to repair.
> I added the specified bypass cap and recovered 100% of those boards.
>
> If the data sheet specifies bypass caps, design them in.  If it doesn't,
> design them in anyway, you can always DNP (do not populate) in production=
..
>
> Bypasses are your friend.  Route them well, and don't skimp.   I use X2Y
> caps in critical applications. With any type of bypass cap I route so tha=
t
> power goes THROUGH the capacitor pad on its way to the chip, and the grou=
nd
> side of the cap returns directly to the nearest ground pin on the chip.
> Never a "tee" where the current has the option to go past the cap.
>
> Similarly with crystal loading capacitors, where I route them directly to
> the nearest ground pin on the chip and nothing else touches that trace
> until it joins all the ground pours at the chip ground pin.
> I have seen boards fail FCC testing hard because crystal caps were
> "grounded" into a 100 mil ground track that was about a quarter wavelengt=
h
> long at 400+ MHz.  The "ground" actually worked more like a shunt fed
> antenna. :-P
>
>
>
>
>
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