Hello Sona,

Sorry for the delay, I am trying to catch up on emails...  It appears that
the reference to 4.3 to 5.3 is the dielectric constant (Er or Dk).  Someone
placing this on the fab document is wrong (humble opinion of mine).  What
they are eluding to is 50% or less resin and if that is the case they should
have called out the core and pregs by part number.  Even then it would be a
first for me... someone requiring high Er.
I would call for Customer approval of book prior to fab.  Minimally clarify
if the Er range is an average or individual rating.  It is better to be a
"pain in the neck" fabricator on paper than one with rejected parts.

Boston Brad