kicad-developers team mailing list archive

[Nick Østergaard <oe.nick@xxxxxxxxx>]

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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