The low dielectric constant insulation layer comprises {TAIL ~ a porous insulation layer}, preferably sandwiched between {HEAD ~ non porous upper and lower insulation layers} 
The low dielectric constant insulation layer comprises { TAIL ~ a porous insulation layer } , preferably sandwiched between { HEAD ~ non porous upper and lower insulation layers }
OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD