Is anybody using via-in-pad under a BGA successfully? Is this a specialized capability, or do most board houses have the capability to do micro-via's? How small does the via need to be in order to avoid solder wicking? I understand that in order for this to work well, it typically requires laser drilling.
Cellular and PDA architectures employ this technology all the time. You have to be careful with your board supplier as well as with your plugging approach. Leave the via unplugged, I guarantee voids in the solder joint. That leaves us with, "how do we plug the via?" I've seen and used a couple of approaches. One approach was to plug with a conductive epoxy. It worked ok but I didn't get the barrel fill that I hoped for 100% of the time. It was also expensive. Plugging with copper during the plating process can work but it can also trap plating solution in the via causing problems down the road. My advice to you is to find a supplier with good experience in this arena. Find out if they can plate up in a controlled manner that allows adequate fill of the via but will not trap plating solution. I know of a supplier who touts this but I don't know if it's right to give people plugs on this forum.