Advanced PCB - L2 - CPU fanout and decoupling
schad.rio , 10-07-2020, 12:05 PM
Had a quick question: In the lesson 2 video for Adv PCB, there is a mention not to use a series connections (but instead a star connection from the via) between decoupling caps but instead one VIA per power or GND connection (I have also seen this mentioned in youtube videos)
Given this CPU and the size of the decoupling caps in relationship to the location of the pins, I cant see how this is possible. I have done the CPU and decoupling fanout for this lesson multiple times & every time I reach a point where the caps (especially the bigger ones) are too far away from the VIAs in which they need to connect, resulting in having to connect in series the other pads of nearby caps...is this typical for dense boards with tons of decoupling caps where the BGA pitch doesn't allow for multiple caps to reach the VIAs?
robertferanec , 10-12-2020, 08:34 AM
Just try do your best. It is not always possible, sometimes you will need to connect more power pins together and use shared VIA. Larger caps can be a little bit further. And if you are not sure, have a look at reference design and check how they did it.
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