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