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Altera_Forum
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13 years ago

Power Delivery Network (PDN) Tool

Hi everybody, i know that PDN is just a base line guide for selecting decoupling caps. Until now i just used 100n 0402 caps on each power (VCCINT, VCCIO, VCC PLL and VCC GXB ) pin of the device...
Altera_Forum's avatar
Altera_Forum
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13 years ago

Hi Nial

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Just to follow this up, if you're using devices with 1mm BGA pitch then a footprint for 0402 caps can be created with round pads with 1mm centres.

On the back of the board these mirror the BGA pads on the top of the board and allow you to connect straight to the vias from the top layer.

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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