kicad-developers team mailing list archive

["jean-pierre.charras@..." <jean-pierre.charras@...>]

Rok Markovic a écrit :
> Hi
>
> There are still some problems with thermals. One, that I encounter in my
> boards is when in close pitch components (VQFP, ... ) two neighbouring
> pads are on zone. When drawing thermal holes in such a situation, each
> neighbouring pad draws around itself a hole. This hole cuts the thermal
> connection to other pad. Please see atached pictures, I understand if my
> explanation is unclear.
>
> The only option I see is to add thermal connections after removing all
> pads from zones. I understand that this concept has problems (DRC), but
> I would like to ask if it CAN be done.
Removal all pads in zone is NOT the problem.
The problem is you have set parameters that cannot allow stubs.
You cannot want a minimun thickness copper zone bigger than max stubs 
width and expect to have subs.
You cannot want an antipad size bigger than pads gap and have copper 
between pads.

You cannot solve this by code modification, because this is not really a 
code problem.

One can want to specify specific thermal parameters for a givn footprint 
( or a given pad).
A possible approach is to allow to define parameters (when are not set 
to default) on a footprint and/or pad basis.
But obviously, minimun thickness copper zone must be bigger than max 
stubs width.

Advantage: handle very small pads ans special cases.
Drawback: more and more complex way to handle zones parameters, and in 
many cases not very easy to understand.
But this can be a solution in some cases and must be considered.

Many kicad users could be unable to set/choose good parameters.

the answer to your question is:
this can be done.
But this will creates some ugly code and problems:
- stubs must are tracks, not zone fill segments, because they will be 
outside filled areas, and must be considered in connection and DRC 
calculations
As a consequence, they are obstacle to create new tracks. Existing 
zones are never obstacles, because copper in areas is removed when 
calculating new filled ares in zones.
- stubs *must* be removed when a zone (or its filled areas) is removed.

So i am not well-disposed to this approach because this problem is only 
the result of an other problem, mainly a bad parameters choice.

--
Jean-Pierre CHARRAS

Maître de conférences
Directeur d'études 2ieme année.
Génie Electrique et Informatique Industrielle 2
Institut Universitaire de Technologie 1 de Grenoble
BP 67, 38402 St Martin d'Heres Cedex

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