power supply decoupling capacitor size
Hi
I have used this solution on several board with BGA package
1) Power plane
Each supply must have its own power plane.
For the internal supply its enough that its cover the BGA and the decouple capacitors
For IO supply its must also include all the area were the IO signals are.
The power pins shall be connected directly to the power plane.
2) Decouple capacitor
The general rule is one for each power pin.
The typical value is 0.1 uf or lower for more high speed signal
You have to look on the resonance frequency so the capacitor is working at your high speed signal.
On the BGA is not working with one capacitor for every power pin but instead you put as many as practical around the BGA, and inside (secondary side) if not a filled one.
You should also do a check with a good oscilloscope.
The version with multiple capacitor with different values in parallel I don’t recommend, because
the resonance frequency its so manufacture/batch depended.
Use only X7R or NP0 capacitors.
The capacitors shall be connected directly to the power plane.
3) Bulk capacitor
Depending how much current the BGA consumes and how near your power supply are,
you may need some bulk capacitors.
Use low ESR tantal capacitor
For more information you can read Dr. Howard Johnson articles at his excellent site
http://www.sigcon.com
Micron has also a technical note: Bypass Capacitor Selection,
http://download.micron.com/pdf/technotes/TN0006.pdf
jzo