kicad-developers team mailing list archive

[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