The focus information of each solder ball is used to determine the distance to {HEAD ~ the tips} of {TAIL ~ each solder ball} 
of
The focus information of each solder ball is used to determine the distance to { HEAD ~ the tips } of { TAIL ~ each solder ball }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL