Preferably, the larger diameter of {HEAD ~ the via opening edge portion} at {TAIL ~ an upper portion} of the via includes at most, an upper one third of the via opening depth 
Preferably , the larger diameter of { HEAD ~ the via opening edge portion } at { TAIL ~ an upper portion } of the via includes at most , an upper one third of the via opening depth
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH