[SI-LIST] : Impact of halogen-free boards

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From: Ole Segtnan (ole.segtnan@era.ericsson.se)
Date: Mon Nov 27 2000 - 07:34:05 PST


Hi all,

I would like to bring up the issue of halogen-free materials vs. signal
integrity.

Most of us will probably need to replace the traditional board materials
such as FR4 by halogen-free materials in the near future. As a result,
impedances, losses, etc. will change, but how? I would be grateful for
any experience, information and comments!

I realize that this may be a huge question but maybe we can break it in
two:

1/ Material "constants":
     - What are the values of epsilon, conductivity, etc. of these new
materials?
     - How do these "constants" vary with frequency?

2/ Impact on impedances, losses, etc.
     - Which changes are important?

One particular material was measured to differ in the following way
compared to FR4:
- epsilon increased by 10%
- loss tangent increased by 60%
No other significant differences were seen.

In my opinion, this will give the following effects:
- Signal velocity reduction (about 3%) is negligible.
- Impedance change can be compensated by means of track width.
- Increased dielectrical loss may be a problem.

Any comments?

Best Re

--
Ole Segtnan
Ericsson Radio Systems, Stockholm
Phone: +46 8 585 32 279

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