Hello Tim,

i have just seen your new layer-stackup for your 8-layer PCB.

But i'm wondering about the numbers of prepregs.
I think when you put 4 cores with copper on both sides together, you need
only 3 prepregs.

P.S.: If you are searching for a tool to calculate the impedance of PCBs,
try the program CITS25, which can be downloaded for free from
"www.polar.co.uk".


Best regards,

Florian Finsterbusch

--------------------------------------------
Lightmaze AG
Dipl.-Ing. (FH) Florian Finsterbusch
Erbachshof 8
D - 97249 Eisingen
Tel. (+49) 0 93 06 / 9 83 -1 70
Fax. (+49) 0 93 06 / 9 83 -1 12
E-Mail: [EMAIL PROTECTED]



> -----Urspr ngliche Nachricht-----
> Von: Tim Hutcheson [mailto:[EMAIL PROTECTED]]
> Gesendet: Mittwoch, 22. August 2001 23:25
> An: Protel EDA Forum
> Betreff: Re: [PEDA] Warping on small odd layer boards.
>
>
> Third try:  Using 8-layer board, 4 cores, 4 prepreg and a foil.
>
> Laminate:   (4x2) + (8x6) = 56 mils
> Copper: 2x(.7+.3) = 2 mils 1/2 oz copper plated to 1.0 for outer layers
> Copper: (7x.7) = 4.9 mils inner layer 1/oz copper
> Total:   56 + 2 + 4.9 = 62.9mils
>
> Impedance:  about 52-54 ohms for FR4, all traces.
>
> Since my source resistance is 53 ohms, I have less than 2% mismatch.
>
> For the price of the extra layers, I get a good match and have the  luxury
> of an extra routing layer and voltage plane to play with.
>
> Thanks for the help.
>
>
> Tim Hutcheson
> Institute for Human and Machine Cognition
> 40 S. Alcaniz St.
> Pensacola, FL.  32503
>

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