ed:
the following is an explanation of the referenced slash sheets to 4101:

L/24:  note the Tg range of 150 to 200°, which translates to FR4's known as
high temperature or high performance, such as PCL's 370 or AlliedSignal's 406
or Nelco's 4105-6.  Their chemical makeup is generally 100% multifunctional
resin (un-blended with difunctional.)

(fyi, Polyclad's "standard material 1226FR is covered by /21.)

L/25:  this covers GE's GETEK version of a high temperature FR4, which has a
resin copolymer containing the thermoplastic PPO for lower Dielectric
Constant.

L/26:  Not a tetrafunctional.  This covers the BT type materials when you want
to use them for a drawing calling out type GF.  Note that BT is a blend of a
Cyanate Ester type resin with epoxy, which is the point of the "modified ...
epoxy resin" reference.  This slash sheet also allows other epoxy-based
materials with a higher Tg (170-220°) besides BT to be used.

FYI, slash 30 is intended to apply to BT materials also.  The ID Reference of
"MIL-S-13949/26 - GFT" is an error.  It should refer to 13949/24 and 26 - Type
GMN.

Hope this clears up some questions.
jimpaulus

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