From the comments on our earlier DIY BGA soldering teardown post, JesseJ points out the poison via effect that will also break the connection to the BGA.
Image above is from the previous post, depicting the capillarity effect where a via sucks the ball of solder in, and prevents contact to the BGA.
Just as a comment on the ‘other side of the coin’ when manufacturing an IC, vias can present an opposite problem with the same result. If all moisture isn’t ‘baked’ out of the wafer before the vias are processed, it is possible for some moisture to be ‘out-gassed’ at the via site breaking the metal via tube – also resulting in a poor/broken connection. This failure is sometimes called a ‘poison via’ and is the opposite of the capillary action on the PCB via, with the same result. Whooda thunk!
Via the comments.