Paste in Hole Process

Capillary action tends to suck out the solder and even balls on BGA. I have seen guidelines that capping the via with solder mask from the back side tends to prevent that, but is not reliable enough. Filling the via is possible but troublesome, so the recommendation was to avoid in-pad vias.

Late at night, by candle light, przemek klosowski penned this immortal opus:

I saw somewhere mentioned that with a fine enough drill the vias will plate shut. OTOH you'll have to talk nicely with the boardhouse since they don't appreciate it much.

- YD.

We put 4, 5, sometimes 7 into a power pad.

John

Part of the problem is that small amounts of the nasty acidic plating solution get trapped inside voids in the via. They tend to boil when you do the reflow, which is a Bad Thing.

Cheers,

Phil Hobbs