kicad-developers team mailing list archive

[Nick Østergaard <oe.nick@xxxxxxxxx>]

Den 26/11/2014 20.29 skrev "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.

Yes, this is what JPC pointed out. The issue here as I understand is
weather it should support trepez fill, instead of the rectangular zone fill
we see now, or not.

>
> 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
>> >>>
>> >>> _______________________________________________
>> >>> Mailing list: https://launchpad.net/~kicad-developers
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>> >>
>> >
>> >
>> > --
>> > Jean-Pierre CHARRAS
>> >
>> > _______________________________________________
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>>
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>
>