[PCB_FORUM] Documentation of material for manufacturing
- From: "Milostnik Matija IESMSD" <milostnik@xxxxxxxxxxx>
- To: <icu-pcb-forum@xxxxxxxxxxxxx>
- Date: Wed, 15 Sep 2004 21:44:54 +0200
Hello Folks,
Doing high speed design is a challenging task anyway, but even more is to write
the right documentation for the board producer. :-)
Up until recently we just gave the general board stackup and the dielectric
constant.
Now for better documentation we give an exact stackup and the dielectric
constant.
Our producer is asking us to specify in which tolerance we can give the
dielectric constant, similar to the board thickness, were we usually have +/-10%
Looking at the material qualities a +/-10% on dielectric constant would allow a
board producer to take a material ranging form E0=4.32 to E0=5.28 instead of
the E0=4.8 that we calculated with.
Even worse on the manufacturing tolerance. The prepreg usually involved in the
stackup can also change for +/-10% in thickness, either because the final
thickness is allowed to change this much, or because during pressing the
prepreg gets squeezed differently on different parts of the board, depending on
the density of the traces in the area.
Etching can also change impedance, but this is left to the board producer to
cope with, since mathematically speaking the most important influence are (in
order of importance):
1) Material properties and trace distance from planes (involves dielectric,
tangent loss, core and prepreg geometry)
2) Trace with (etching)
3) Trace height (choosing copper 1/2 once or 1/4 of once, finish)
My questions are:
-How do you specify the material properties.
-How much tolerance do you allow for dielectric constant.
-Do you specify a tangent loss to in the material specification (e.g. less than
0.020)
-Do you have any other method of specifying high speed designs, that have
worked for you.
-Does Cadence or ODB++ or other data interchange format help in any way
achieving better data transfer for the purpose of high speed designs?
Thanks for any help
Matija
Seid gegen den Krieg, nicht weil ihr Gewalt hasst, sondern
weil ihr den Frieden um so mehr liebt. J.M.Haig.
Matija Milostnik, Email: milostnik@xxxxxxxxxxx
IskraTEL Electronics, Ljubljanska 24a, SI-4000 Kranj, Slovenia
Tel: +386 4 207 2125, Fax: +386 4 20 21 552
www.IskraTEL-Electronics.si: The power of partnership
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