> One more note: the fiberglass composite material which makes up modern
> circuit boards is often called FR-4. This stands for Flame Retardant
> 4. I believe that the raw fiberglass material is called G-10 but once
> they add the flame retardant chemicals to it, it is called FR-4.

Pretty much.
AIUI G-10 and FR4 use a different epoxy and G10 is mechanically
slightly superior to FR4 but FR4 is now almost exclusively used in
preference.
Both use a woven fibreglass material. (The fire retardation works by
incorporating bromides in the material which release Bromine at
combustion temperatures.

Quoting a PCB FAQ:  There are red and blue logos. Red is UL94-V0, blue
is UL94-HB. If you have a blue logo material, it is either XPC
(phenolic) or G10 (glass epoxy). In 1.50/1.60mm FR4 the logo is in the
middle layer (layer 4) of the common 8 layer construction. ie your
logo should be red if you think you have a fire extinguishing board. .

I wrote the following for  another thread a few days ago and decided
not to send it. Now seems a good time to use it :-)
__________

FR2 is paper with phenolic resin. Your standard cheap junk rubbish
boards. Punching (or using at all) not recommended. Beloved of Asian
manufacturers aiming at low cost. Nasty ability to split and radiate
cracks which may break copper tracks.

FR3 is essentially FR2 with epoxy rather than phenolic resin - still
paper. Good "punchability"
__________

FR4 is essentially glass - epoxy resin laminate.with bromides
incorporated to provide self extinguishing properties.
Usually routed rather than punched.

CEM3 (more Japan and some other Asia) is glass-epoxy but instead of a
woven fabric as in FR4 uses random non woven glass fibres. Instantly
distinguishable by its white colour. Equally as good as FR4.

G10 (often seen in older specs is glass-epoxy, different epoxy to FR4
and not flame retardant. Claimed more punchable than FR4 - not obvious
why.



           Russell McMahon
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