GARTHWILSON wrote:
Nothing silkscreened should go onto a hole, as it makes a bunch of the silkscreened paste squish through, whether solderpaste or soldermask. This is why you don't put vias in solder pads (unless you actually
want a mess
). I was able to violate that rule on my memory modules because I solder them by hand, and I don't silkscreen solder paste onto them. I have no knowledge or experience in laying out boards for BGAs, but I suppose the chance of bridges underneath one would be greater if vias' rings are not masked; but then again you would want to put soldermask only on the ring, not pump it down the hole.
I found out something neat from a supplier yesterday. They now have a way to put vias in the SMT pads of a PC board without causing problems during assembly. It costs another $300 for the lot, but if we need the board smaller, putting the vias in the pads saves space. What I'm thinking of in your case EE (although the cost will be too high for many hobbyists) is your BGAs.
If you can put the via in a pad for a surface-mount part, you can save room. The problem used to be that a stencil was used for getting the solder paste on the SMT pads, and if there was a hole in the pad, a bunch of solder paste would squirt through the hold and make a mess. Now this board house can put a via in the pad, then put a plug in the hole after it's plated thru, then plate over the plug too, so mechanically it's like there's no via at all, except you've made the connection to one more other layers at that point, under the pad.
Additionally, instead of screening the solder paste on before applying the parts with the pick-and-place machine, they're using a process like ink jet to
print the solder paste onto the board, so they don't have to make the stencil anymore. That saves a little NRE charge. I imagine it saves some solder paste too.