Subject: | |
From: | |
Reply To: | Leslie O. Connally |
Date: | Mon, 8 Feb 1999 08:30:50 -0600 |
Content-Type: | text/plain |
Parts/Attachments: |
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Well Scott, it looks like The IPC has a problem, I tried it and got the same
answer. It's funny because I tried some other balanced numbers and obtained
balanced Impedance values. There does seem to be a flaw in their model
calculations.
How about it Hugo, is someone looking in to the model?
Regards,
Les
> From: Scott Decker <[log in to unmask]>, on 2/5/99 9:26 AM:
> Hi All
> I have a question / problem....
> I recently used the Impedance calculator on IPC WEB site and
> found a very interesting problem. On one occasion a few weeks
> ago, I used the calculator to do a quick stackup for a board I'm
> working on. The results were fine and were used as a baseline
> for the FAB shop to find me the values they use. I was just showing
> another designer here this neat calculator and changed the values
> I used to the values that the FAB shop gave me. Guess What....
> The calculator came back with an un-balanced impedance value!
> This is a very strange problem. I put in a balanced stackup
> and the values for impedance were different from the top to the
> bottom by 5 ohms. Sure you say, that's the 10% but, why are the
> numbers different? Maybe some of you out their can try these numbers.
> First. 6 Layer Board.
> .5 oz on both outside layers and 1 oz on all inside signals and planes.
> .005" traces on all layers
> Dielectric thickness as follows:
> 6.5
> 10
> 18
> 10
> 6.5
> Er value of 4.2
> OK now you have the numbers, the impedance should be around 72 ohms.
> But Wait! The values I got were 77 72 72 72...... What Gives?
>
> Any Comments???
> I already herd that it's because the UV rays from the sun were hitting
> the top of the board more, but I don't think that's true....(:-}
>
> --
> Scott Decker
> Senior PCB Designer
>
> AKA: PadMasterson
> E-Mail: [log in to unmask]
> -----------------------------------------------------------------
>
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