[SI-LIST] Re: PC board materials
- From: "Istvan NOVAK" <istvan.novak@xxxxxxxxxxxxxxxx>
- To: <amp46@xxxxxxxxxxx>, "'SI Newsgroup'" <si-list@xxxxxxxxxxxxx>
- Date: Tue, 18 Nov 2003 21:27:54 -0500
Anand,
A brief summary:
The two fundamental electrical properties of dielectric PCB materials are
the dielectric constant and dielectric loss. The primary advantage of lower
dielectric constant (Dk) is lower propagation delay. Lower-Dk materials
also tend to be less frequency dependent (and more expensive). Dielectric
loss usually matters only at Gbps speeds, but because the attenuation due to
dielectric loss increases (slightly faster than) linearly with frequency, as
opposed to the conductive skin loss, which increases approximately with the
square root of frequency, at very high speeds dielectric loss is the primary
enemy. Again, lower dielectric loss materials tend to be more expensive.
Mosture absorption is another characteristics, which impacts signal quality,
because the effective dielectric constant of a hygroscopic material is more
dependent on environmental parameters. Other parameters are mostly process
related (Tg, X, Y, Z axis expansion coefficients, which tend to be different
in reinforced laminates and affect reliability) and they impact the overall
cost of the PCB. As usual, 'better' materials in any sense tend to be more
expensive.
I hope this helps to get you started.
Regards,
Istvan Novak
SUN Microsystems
----- Original Message -----
From: "Anand Mohan Pappu" <amp46@xxxxxxxxxxx>
To: "'SI Newsgroup'" <si-list@xxxxxxxxxxxxx>
Sent: Tuesday, November 18, 2003 5:57 PM
Subject: [SI-LIST] PC board materials
> Hi,
> Could someone tell me the difference between different board materials
> (like FR4 and TMM3)? Is the only difference the permittivity (Er) of the
> board material or is there anything else?
> Or in other words, what does a better printed circuit board constitute?
> Is it just that lower permittivity leads to lower capacitive coupling
> between different traces? Or is there more to it in the frequency domain
> - are the rise times of signals somehow affected by the traces of the
> new (better) board? Does the resistance of the traces play a role?
>
> *ANY* light on the issue will be gratefully appreciated.
>
> Anand
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