How to better connect decoupling caps with BGA on top side?

[gandi]

Hi,

I am currently designing a board for a display that includes SDRAM, NOR flash, ethernet, USB,...
The board should "stick" on the back of the LCD panel, therefore I have to put all components
on the top layer.
I have positioned the caps on the outside of the BGA package and now I need some help
to determine which wiring strategy is better or which one is a no go.

Stackup: #1 High Speed, #2 GND Plane, #3 & #4 Low Speed, #5 Supply Plane, #6 High Speed

1. Using solid supply plane

2. Supply plane with keepout area and track for every supply pin


Is the first one bad for decoupling behaviour?
Does the second one need a GND plane in between to keep the impendance
of the tracks on layer #6?

BR Martin

[richard.cs]

I would definitely go for the first one. That's about as good as you'll get with components on one side (BGA pinouts are generally chosen on the assumption that you'll put the decoupling capacitors on the back).

[gandi]

Hi,

tank you for the quick response.  I will use the first pattern.