[PCB_FORUM] 0402 round pads

Gary
     I feel that the significance of this discussion has been missed.
 
The fact that you can imbed termination resistors and decoup caps into a
1mm BGA via grid on the back side is a very BIG DEAL!
The round pads enable you to do this. Maybe some other shape works also,
but not square or rectangle.
For every 2 vias you can fit one 0402 component.
No vias need to be removed.
Short is better whether your talking about caps or termination
resistors.
This technique may delay or reduce the need of moving to 0201 packages.
 
Build your 0402 alt symbol with 1 mm pad to pad spacing.
 
What we use is....
Pad size is .022".
Via size is .019".
Via to pad is .007 min.
Make the solder mask cover most of the via.
 
Of course I can't guarantee yield, but so far so good.
 
It would make placement easier to be using a metric database but not
vital.
If your on an inch database use the rat going to the pad to enable you
to place the part to the closest .0001 inch.
 
Barry Unruh

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