FreeLists / si-list / [SI-LIST] Re: matching within 1 mil

["Jack Olson" <pcbjack@xxxxxxxxx>]

yes, I agree.
I was just "smiling" in public,
and for that, I apologize.

Overall, you are right. Part
of the discussion seemed
humorous to me, though...

seeya,
Jack


On 6/4/07, steve weir <weirsi@xxxxxxxxxx> wrote:
>
> Jack, while it is impossible to out calculate a computer, expertise is
> what we use to outperform results one gets from push button reliance on
> simplified assumptions built into most tools.  The first thing to know
> when deciding where to put resources is how much different trade-offs
> matter.  We are hardly alone in this view.  Two things that you will
> repeatedly hear from people like Eric Bogatin and Lee Ritchey is the
> importance of understanding how much changing a given parameter
> matters.  Eric spends a great deal of time in his book and in a number
> of his on-line seminars demonstrating this with real numbers.  When it
> comes to the differential trace matching, 1 mil is massive overkill.  If
> it really comes for free, great.  For reasons that have kind of gotten
> beat to death here, there are any number of cases where it isn't.  I
> think it is very wise of Bill to understand the metrics of this and
> other parameters in his designs so that he can make intelligent
> decisions when and if he needs to make trade-offs.
>
> Regards,
>
>
> Steve.
>
> Jack Olson wrote:
> > I don't know what software you use, but
> > in Mentor's AutoActiveRE constraint editor,
> > its easier to type "1" than it is to type "100"
> > That's two less keystrokes, bub!
> >
> > Do all the math you want, but if the router
> > can EASILY route to a tighter constraint,
> > LET IT.
> > If it has trouble, THEN you can loosen the belt.
> >
> > It doesn't really seem worth "venting" about.
> >
> > If anyone has constructive ways of educating
> > engineers not to out-think a computer, I'd like
> > to hear them
> >
> > regards,
> > Jack (a layout guy)
> >
> >
> > On 6/3/07, Bill Wurst <billw@xxxxxxxxxxx> wrote:
> >
> >> <snip>
> >>
> >> Today, we now have some interfaces where 100mils is no longer adequate.
> >> I know that because I take the time to go through the math, and will
> >> specify what I believe is appropriate given all of the other variations
> >> that can affect skew.  Here in lies the frustration:  more often than
> >> not, the layout designer will come back and say to me, "I know you only
> >> needed this matched to XXmils, but it was just as easy for me to match
> >> it to 1mil, so that's what I did."  Now, I have a hard time believing
> >> that it didn't involve a lot of extra work to get down to 1mil, but I'm
> >> not about to do his job for him nor do I wish to micro-manage him.  In
> >> all other respects, these folks are excellent at what they do, but this
> >> typical response makes me wonder why I went through the trouble of
> >> figuring out a more practical number in the first place.  Judging from
> >> the various responses, I'm not alone.  And I know that while the tool
> >> reports the lengths as matching to within 1mil, there may be as much as
> >> a few mils difference within the pad itself.  I know because I've sat
> >> down with designers and together we've discovered this.  (As an aside,
> >> it would be nice if CAD tools could report trace length minus the trace
> >> segments (or portions thereof) buried in pads.)
> >>
> >> Mainly I'm venting and not looking for a response, but if anyone has
> had
> >> similar experiences and can think of constructive ways of "educating"
> >> layout designers, I'd like their opinions.
> >>
> >> Regards,
> >>     -Bill
> >>
> >>
> >>       /************************************
> >>      /         billw@xxxxxxxxxxx         /
> >>     /                                   /
> >>    / Advanced Electronic Concepts, LLC /
> >>   /           www.aec-lab.com         /
> >>   ************************************
> >>
> >>
> >
> >
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> >
> >
>
>


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