Via in Pad Callout, VIPPO

[cjurczak]

I'm looking to utilize via in pad (VIPPO) for the first time.  I have some questions for those of you who have done this before.  I've got a 0.5mm pitch BGA, with a 0.3mm ball, so I'm targeting a 0.25mm pad.  Now for a couple of questions.

1.  Is there are common way to call out VIPPO on your fab drawing for the board supplier?

2.  Traditionally my suppliers wanted a minimum 3mil annual ring, on a 0.25mm (9.85mil) pad that would mean a <4mil drill, am I missing something.  I thought VIPPO was suited for fine pitch BGAs such as this. 

3.  When I specify VIPPO the via is filled, and plated over, is this done on one side or both sides?

4.  How do I identify which vias should be filled and plated to the board supplier? (I'm using Altium if that matters)

I'm sure to some of you this is old hat, but after all my experience in PCB design I've never had a need for VIPPO until now. 

[free_electron]

VIPPO is Via In Pad Plated Over. The hole is filled with an epoxy compound and then plated shut. You will see no hole. VIPPO is typically still mechanically drilled all the way through. once you drop to BGA with a pitch smaller than 0.6mm you need stacked vias. For a 0.5mm pitch BGA you need stacked and blind vias. You can not go all the way through the board ( you won't be able to do the fan out anyway.)

Without knowing more i can not really give any good advice.

what does the BGA grid look like. is this a 3x3 bga or a 15x15 bga ? how many active rings ? power / ground web ? how many layer board ? board thickness ? copper thickness ? are you using controlled impedance ?
If this bag has more than 4 rings you will need a 6 layer board with laser vias and dog-bone the breakout. you can use mechanical drill on the inner layers to save cost, but your outer layer will become laser.

you can PM me if you want. i have plenty of experience doing such boards.