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July 1998

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Subject:
From:
Scott Decker <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Thu, 23 Jul 1998 13:26:52 -0700
Content-Type:
text/plain
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text/plain (85 lines)
R. Christopher Lott wrote:

> First of all, I'm an engineer and don't do board layout every day.
> Please forgive what may be a dumb question...
>
> I have a nagging recollection in my mind that PWBs designed to
> MIL-STD-275 (now IPC-D-275) had a special requirement on the
> conductor routing.  Namely, that all conductor traces have to
> begin and end on a land.  That is, no conductor "tees" are
> permitted.
>
> Now that I may be making such a board, I reviewed both MIL-STD-275
> and IPC-D-275, and don't find this to be the case.  The only remotely
> similar remark is in section 5.3.1.2 Conductor Routing (from the IPC,
> but the MIL-STD has very similar wording):
>
>        "The length of a conductor between any two lands
>         should be held to a minimum."
>
> You would be really stretching things to get my "no tees" rule from
> that section.
>
> Question: Am I really losing it (entirely possible), or is/was there
> such a rule, and if so, where is it and under what circumstances is/was
> it invoked?
>
> Thanks,
>
> -Chris Lott
>
> --
>
> ************************************************************************
> R. Christopher Lott, P.E.                                  [log in to unmask]
> Huntsville, Alabama
> ************************************************************************
>
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 Chris,
   I don't think your losing it, if so well...... I'm not sure about the D-275 std because I don't have
one handy
but, tee's are OK as long as you don't create a problem with signal integrity. What I mean is, if your
working
on an RF board or some other high speed board/signal, you probably don't want tee's. If the signals are
not
fast edges, then the tee shouldn't hurt. Someone will correct me if I'm wrong, (and I may be) but when
processing
boards back when..... The tee's and 90's would trap the chemicals and cause problems. Now that being said,
I don't
really know just how true that was. Someone told me that and could have been pulling my leg. (Maybe that's
why
I go in circles so much?) On a personal note, I don't use tee's if I can help it. I just don't like them,
they look funny...
Hope this helps.

--
                 Scott Decker
              AKA: PadMasterson
        Praegitzer Design On Location at
         Enterprise Server Group CO3
              Intel Corporation
Ph: (503)-677-6582 E-MAIL: [log in to unmask]

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