Display Your Know How: Decoupling Capacitor

Are these caps Mirrored as in on the bottom layer of the board under a BGA. ?

If that's the case then Picture C looks the best.

Best Regards,

That's correct, excellon1. The components are indeed placed underneath the IC, specifically on the bottom layer of the board.

I have had SI engineers request the the routing go from the pin to the cap then to the via:

...

if I remember correctly they thought this reduces Ground Bounce type of issues

I have had SI engineers request the the routing go from the pin to the cap then to the via:

...

if I remember correctly they thought this reduces Ground Bounce type of issues

Same engineers here.

For me,  pin->capacitor->via is usefull for analog circuit.

Tip: for numeric, ideal is to have loop's area between power and ground the smaller as possible.For bga, unfortunately no choice but to plca capacitor on opposite side of bga. For others, i take into account the pcb thickness (already use 5mm thick!)  to know the real loop area.

Thank you, DavidJHutchins, for sharing your expertise. I completely concur with your point.

Decoupling capacitors, strategically placed between the power supply pins and ground pins of an IC, provide a low-impedance pathway for current during switching transients. This effectively mitigates voltage fluctuations on both the power supply and ground lines.

Do you have any additional thoughts or insights to share on this topic?