In the good old days, using DFM/CE principles before they really existed, we
used sequential lamination for MLB's. Then we used a good electroless copper
process to do the plated hole walls while simultaneously "coating" over the
smooth hole opening in the SMT pad. Then we did normal electrolytic plating
over that giving a smooth finish with no indication a hole was in the pads.

Now, most good board shops simply fill the large vias with a conductive
epoxy/silver formulation. Then, the continue as above also giving no
indication a hole is in the pad.

Micro vias, in SMT pads, are the norm for higher density designs. If the via
is shallow enough, no problems are encountered. And on it goes.

MoonMan

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