FPGA Tenting

[clive.seguna]

Dear All,

I am using an FPGA device with over 361 pins. I have routed these pins but I am not sure if I should tent all vias under the FPGA both in TOP and BOTTOM layers so to avoid shorts or other reliability problems during soldering or assembly of PCB. Additionally I am not quite sure if a solder mask expansion value of 3 mil for vias under FPGA is adequate ?

Further how do you indicate with Altium that the via should be filled ?
Under what conditions or When I should tent the vias?

Thanks for your help and guidelines.

Regards,
Clive

[mairomaster]

Speak to your assembler for this topic, they should give you a recommendation. The assemblers I am using always recommend tenting the vias under the BGAs. On the other hand, some of the manufacturer don't like tenting the vias, unless they fill them up first, because of acid entrapment. You might need to tent the vias if you are getting to think solder mask bridges between the vias and the pads. Normally those need to be at least 0.09 mm or more. If you can't achieve the appropriate value, you should tent the vias.

There is no way to indicate filled vias in altium, just tenting. You can specify the filling in the manufacturing notes.

[robertferanec]

I always tent VIAs too (on the whole PCB, not only under BGA).