Preferably, {HEAD ~ 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 the via opening depth 
Preferably , { HEAD ~ 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 the via opening depth
OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD 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 OTH OTH OTH OTH