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Hi Nial
So your pads are placed in the PCB spaced between the vias, and you don't tent the vias? Did you have any issues with solder wicking into the vias?
I did try a small run of boards without tenting the vias. Inspection (flying probe and X-ray) showed there were a lot of poor contacts due to solder wicking into vias, resulting in a lot of manual rework.
The recommendation we received from SigmaTron was to tent the vias and place the 0402 caps (and any LVDS termination resistors) across the vias.
Cheers,
Dave
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That was badly explained (or you're being daft!).
An 0402 footprint with 0.5mm round pads at 1mm pitch can be placed on the back of the board to mirror a pair of BGA balls on the other side.
I drop the vias centrally between the BGA pads with a short stub to the pad on the top layer. I then connect the cap straight to the via on the bottom.
You'll often get a power input and GND BGA beside each other. This allows you to have a CAP directly across their associated vias on the bottom of the board.
All my vias under the BGA are tented, it's one of the things to check on my PCB signoff checklist!
Nial
Honored Contributor
