kicad-developers team mailing list archive

[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.

Trapezoidal pads have a very specific purpose.
I am pretty sure a copper zone around tracks in a microwave design
breaks the 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