Bob,

The difference lies in the adhesive used
in each system.  "FR" has a filler added to
the adhesive to make it flame retardant 
(hence "FR").  If you are concerned with 
flamability, you should be using the "FR".  
LF has no UL rating for flamability or if 
it does, it isn't very good.  "LF" will
go up like a torch with a flame put to it.

Because of the flame retardant additive, the
flow of the adhesive is a little higher.  On
the other hand, the peel strength to copper
is also higher than the "LF".

The reason for the price break is that
"LF" is supplied as IPC class 3 material.
"FR" is supplied as IPC class 2 material.
The savings is mainly in the amount of tests
and documentation that DuPont needs to perform
on each lot of material.  About the only 
difference is that the "FR" adhesive flow 
is higher than IPC class 3 will allow.

One of the obvious differences when you get
your circuits is that the "FR" will visually
look different because the filler makes the
adhesive look milky yellow instead of the clear
appearance of the "LF".  A circuit made with
"FR" will be opaque when held up to a light.
Very similar to a circuit made with Rogers
R/flex 2005 in appearance.

In short,  the "FR" and the "LF" will produce
circuits that are identical in quality except
the UL rating (FR being superior).  The "FR"
laminate is IPC class 2, but my bet is that
your finished circuit is IPC class 2 as well
so you won't be giving up any quality but will
be getting a price break.  Go for it!

Darren Hitchcock
Merix Corporation
Forest Grove, OR
(503) 359-2658
[log in to unmask]



BOB HOENE <[log in to unmask]> Wrote:
| 
| 
| Would someone care to drop a brief tutorial regarding 
| the differences
| between Dupont's "LF" and "FR" flexible circuit 
| laminate materials? Our
| source is offering a substantial cost savings to use 
| "FR" but we are
| concerned about the usual issues of flex life cycles, 
| flamability, ect.
| 
| Thanks.
| Bob Hoene
| Marquette Electronics
|