kicad-developers team mailing list archive

[jp charras <jp.charras@xxxxxxxxxx>]

Le 27/11/2014 12:22, "Torsten Hüter" a écrit :
> Hi Jean-Pierre,
> 
> I agree that a the trapezoidal pad is seldom used for most circuits
> and this feature isn't important. However, commercial tools like
> Altium Designer or Mentor Expedition support custom pad shapes, there
> is a lot of freedom for the pad geometry (any polygonal shape). Have
> a look here, how Altium does this:
> 
> http://techdocs.altium.com/display/ADOH/Creating+a+Custom+Pad+Shape
> 
> For custom shapes, you have to define there polygon connection points
> - see the section "Thermal Connections for Custom Pads".

Generally speaking, using polygons on copper layers (such as polygonal
shapes attached to pads, which is roughly what Altium is doing, and also
the microwave tools in Pcbnew) need to take in account polygons in
DRC code.

Currently this in not the case in Pcbnew.
This is acceptable for microwave applications, which are very specific
(even DRC is specific in microwave applications, because traces are not
equipot)

But for usual applications DRC must take in account polygons.
Currently I do not know a way to do that with a calculation time
compatible with the on line DRC (calculating min dist between polygons
is not as fast as calculating a min dist between basic shapes.

Having said that, I am not opposed to add thermal reliefs to trapezoidal
pads.
I just said until now, it was not needed.
Obviously, if these pads are now used in usual boards ( I mean not
microwave applications) thermal reliefs are needed.

> 
> --
> 
> About the discontinuities: I've used a few years ago the RF package
> of Mentor Expedition, there you can create tapered striplines for
> these purposes. And of course the copper fill follows these shapes.
> 
> You can find on youtube a good video about a typical RF design
> process; have a look here (RF Design with Expedition PCB):
> 
> https://www.youtube.com/watch?v=qaeOii1rLN0
> 
> Bye, Torsten
> 

I am thinking you are not really talking about discontinuities, but
about using specific shapes: stubs, gaps, polygons and other geometric
shapes to create inductors, capacitors, filters, impedance adapters,
isolators and other microwave components (which are therefore "virtual"
components, because created by specific shapes on copper layers and are
not soldered components).

I am not a microwave specialist, but I worked with specialists (who
where widely using ADS from Agilent to calculate/simulate microwave
designs), when I wrote the pcb calculator and microwave tools in Pcbnew.

Because geometric shapes are used to create inductors, capacitors ...
non specialists can understand why discontinuities (and/or 90 deg track
segments) are bad: they add parasitic components to the path of a signal.

-- 
Jean-Pierre CHARRAS