Through holes are formed when the beam penetrates through {HEAD ~ the entire thickness t} of {TAIL ~ the substrate} 18 
Through holes are formed when the beam penetrates through { HEAD ~ the entire thickness t } of { TAIL ~ the substrate } 18
OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH