My original post diverged into a couple of different directions.  Here are my observations and comments.

Halogen-free flame-retardant (HFFR) materials are available (at least for evaluation purposes).  We've looked at a couple and are still looking for the "right" material.  My problem is trying to find a material that matches a "No-flow" FR4 prepreg.  I've not found one.  I'm pretty certain Isola A11 is not halogen-free. 

These systems can rely on various mechanisms to provide flame resistance.  One of the best papers I've seen on this is "High Tg Bromine Free Laminates for PWB Applcations" by Marty Choate from IPC Expo in 2001.  It is available in the Technical Paper section of Isola's website.  He explains how bromine and the new alternatives work. 

https://www.isola-usa.com/isolaus.nsf/main?OpenFrameset

Phosphorous is one of the compounds that is used, though it seems it's fallen out of favor.  Some of the newer HFFR materials emphasize that they are "phosphorous free". 

I hope Geoff's comments on the "exclusion" of TBBA are true.  I'll have to look into it. 

Mike McMaster
RF Product Engineer
Merix Corporation
503-992-4263



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