Microvias, Blind and Buried Vias
In the image, (A) shows an open via which we don't recommend at all. If you must do this, give us a call first to see if we can help you out. We have built boards like this, but we can't guarantee the work when we do and there are things you can do to make it better or worse.
(B) shows one of our favorite options; the copper capped via, also called a blind via by some. You can have the via hole filled with a variety of materials at the boards house for mechanical durability. If this is done properly, we can't even tell that a via exists.
(C) shows a micro via. This usually works pretty good, but you should still call us first to talk about it. Sometimes the solder paste or the BGA solder ball can flow down into the microvia leaving insufficient solder to make a good mechanical or electrical connection. Call us first.
(D) shows the buried and blind via. In this case, the via is completely isolated from the BGA pad so, as with (B), we don't really care.
Bury that viaspec, Bury that viaspec , bury it, bury it, bury it