kicad-developers team mailing list archive

[Adam Wolf <adamwolf@xxxxxxxxxxxxxxxxxxxx>]

Nick,

I have used trapezoidal pads to connect between PCB antennas and traces.
There are precise rules on trace thickness for antennas, and this let me
have one thing I could modify in the footprint to handle multiple different
feedline widths.

Adam Wolf
Cofounder and Engineer
W&L

On Wed, Nov 26, 2014 at 1:16 PM, Nick Østergaard <oe.nick@xxxxxxxxx> wrote:

> 2014-11-26 20:00 GMT+01:00 jp charras <jp.charras@xxxxxxxxxx>:
> > Le 26/11/2014 18:43, Nick Østergaard a écrit :
> >> This is indeed an annoyting bug, it has existed since 2009 at least.
> >> There is already a bug report about it. See:
> >>
> >> https://bugs.launchpad.net/kicad/+bug/1035621
> >
> > Sorry, but I already said why a trapezoidal pad is designed.
> >
> > The fact an user is thinking something is not expected is not a proof of
> > a bug.
>
> I do follow you, but I still thought it was worth linking this thread
> with the bug report.
>
> > Trapezoidal pads have a very specific purpose.
> > I am pretty sure a copper zone around tracks in a microwave design
> > breaks the design.
>
> Indeed, IIRC this special behaivour of the trapez pad is not described
> in the manual, so one could only assume it was a bug.
>
> On top of my head I can not come up with a design that requires a
> trapez pad instead of an oval, rectangular or circular pad. Maybe
> wayse could fill in, since he has them in his design.
>
> > So :
> > First, define the purpose of trapezoidal pads.
> > After, and depending on this purpose, decide if thermal reliefs are good
> > or not.
> >
> >>
> >> Nick
> >>
> >> 2014-11-26 18:03 GMT+01:00 jp charras <jp.charras@xxxxxxxxxx>:
> >>> Le 26/11/2014 17:18, Wayne Stambaugh a écrit :
> >>>> I just discovered something I never noticed before.  Trapezoidal SMD
> >>>> pads are not connected to zone files (see attached screen shot).  The
> >>>> zone fill also does not follow the contour of the pad outline.  Is
> this
> >>>> by design or should I file a bug report?
> >>>>
> >>>
> >>> Currently, this is by design.
> >>>
> >>> The primary goal of these trapezoidal pads is microwave applications.
> >>>
> >>> For these microwave applications, they are used to connect a large
> track
> >>> to a narrow pin ( transistor or IC) ( or a narrow track to a large pin)
> >>> *without discontinuity* of the copper width.
> >>> (A discontinuity between a track and a copper pad area can create
> signal
> >>> integrity issues. In fact any discontinuity on the signal path creates
> >>> issues, at very high frequencies )
> >>> A trapezoidal shape with an edge having the same size as the track, and
> >>> the opposite edge having the size of the transistor or IC pin does not
> >>> create discontinuity.
> >>> One could use also rectangular pads, and trapezoidal track segments to
> >>> avoid discontinuity, but Pcbnew does not know trapezoidal track
> >>> segments, mainly because they are not easy to handle in DRC.
> >>>
> >>> When you are using trapezoidal shapes for pads, you are expected
> connect
> >>> a track to these pads using the right edge, and the right track width
> >>> (or the right pad size)
> >>> If this is not the case, a rectangular pad or an oval pad is better
> >>> (more easy to use).
> >>>
> >>> Adding thermal relief to a trapezoidal shape creates discontinuity, and
> >>> the shape is no more a trapezoid.
> >>> In fact, using a trapezoidal shape for a pad in a copper zone has no
> >>> interest.
> >>>
> >>> For these reasons, I did not spent time to code thermal reliefs for
> >>> trapezoidal shapes.
> >>>
> >>> Of course, trapezoidal shapes can have now applications outside the
> >>> microwave applications, but I don't know these applications.
> >>>
> >>> --
> >>> Jean-Pierre CHARRAS
> >>>
> >>> _______________________________________________
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> >>
> >
> >
> > --
> > Jean-Pierre CHARRAS
> >
> > _______________________________________________
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