[SI-LIST] Re: FR4
- From: "Moran, Brian P" <brian.p.moran@xxxxxxxxx>
- To: "'si-list@xxxxxxxxxxxxx'" <si-list@xxxxxxxxxxxxx>
- Date: Wed, 11 Jul 2001 16:35:04 -0700
Rich,
If your question relates to what Er to use in calculating impedance and
velocity parameters, you need to cover a range of Er, usually something like
3.7 to 4.5, unless your vendor can provide something tighter than that.
Between raw material variance, lamination effects, and frequency effects, I
think thats about the best you can assume. For maximum accuracy you would
need to sweep the various stack parameters, including Er, with a field
solver to find the actual worst case impedance velocity corners for a given
stack up, but as a minimum you should define a low Z, max Er, min velocity
case, and a high Z, min Er, max velocity case for use in doing worst case
propagation delay or flight time simulations. There are two other corners
there as well if you want to use them.
Brian P. Moran
Signal Integrity Engineer
Intel Corporation
brian.p.moran@xxxxxxxxx
-----Original Message-----
From: Ritchey Lee [mailto:leeritchey@xxxxxxxxxxxxx]
Sent: Wednesday, July 11, 2001 2:46 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: FR4
Depends on what conditions are when the measurement is made. At the glass
to
resin rations used in multilaeyr PCBs and at the edge rates we all deal
with,
4.1 is much closer to the real number. Remember, there are two uses for er,
impedance calculations and velocity or propogation delay.
For the high laeyr count PCBs that I design daily, the resin ratio is so
high
that the er is closer to 3.7. This is probably true for most of us in 14
plus
layer situations.
Lee
Rich Peyton wrote:
> Thanks All,
>
> Before I got any replies I found a Reference that stated FR4= 4.5 +/-
0.5
> which is pretty close to all replies.
>
> Thanks,
> Rich
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx
> [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Martyn Gaudion
> Sent: Tuesday, July 10, 2001 4:57 PM
> To: si-list@xxxxxxxxxxxxx
> Cc: Rich Peyton
> Subject: [SI-LIST] Re: FR4
>
> Rich,
>
> Its well worth taking a look at the laminate vendors web sites.
>
> It is also worth noting that FR4 is a resin glass
> composite based on Glass with Er of around 6 and
> resin with Er of around 3.
>
> If you are designing differential traces on fine
> spacings you need to take this into account.
>
> Typically most fabricators use 4.3 or 4.2 for single
> ended designs, but for close spaced differential traces
> they use 3.6 to 3.8
>
> An explanation of this effect is here:
>
> www.polarinstruments.com/support/cits/AP139.html
>
> Kind regards
> Martyn Gaudion
>
> At 13:57 10/07/01 -0400, you wrote:
>
> >Hi
> >
> >what is the dielectric constant for FR4? Or a web site with listing of
> >typical materials and there constants?
> >
> >Thanks,
> >Rich
> >
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