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