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On altera web page I read that there should be a decoupling cap on each vccint or vccio pin respectively. Do you have any thought on that? I am missing something?
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Once you have decided that you need to put a decoupling capacitor across a pair of BGA vias (between VCCINT or VCCIO and a ground via), then you should have the vias tented (epoxy filled prior to the last plating step for the bottom of the PCB ). If you're tenting one power via, you may as well tent all power vias (and remove the solder mask from the bottoms of the signal vias so you can probe them with an oscilloscope).
I personally recommend tenting the vias, and placing decoupling capacitors on every single power via.
If you want to see an example design that took this approach, see the documentation on this page:
http://www.ovro.caltech.edu/~dwh/carma_board/ (
http://www.ovro.caltech.edu/%7edwh/carma_board/)
The 1.2V core supply can implement a 60A load step while maintaining core regulation within the required data sheet specification.
The schematic and PCB design files are there. Feel free to download and look at them. The boards were manufactured by DDI (
http://www.ddiglobal.com) and assembled by SigmaTron (
http://www.sigmatronintl.com/).
Cheers,
Dave
Honored Contributor
