Just a follow up concerning a decision made here a few hours ago. We have
decided to go with micro vias in our 30 mil pitch, 20 mil diameter BGA pads
instead of plating over the top and to avoid the sequential lamination
process, and associated costs and time factor. As some of us did this over a
year ago, there was enough evidence to get the right folks to make this
decision based on how well it worked when we came up with a paste and
profile preventing some outgassing problems.

Thieving no issue on our designs first because our outer dielectric
thickness is less than 5 mils, as yours must be, and the via diameter is
about 3 mils, as yours must be. Also, solder paste really not needed to
effect solder joints as the balls do that. The solder paste becomes the fill
and provides the compliance needed to "catch/capture" all the balls evenly
for good solder joint formation.

Hope this makes sense,

Earl Moon

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