kicad-developers team mailing list archive

[Dick Hollenbeck <dick@xxxxxxxxxxx>]

On 11/22/2011 02:44 PM, Brian F. G. Bidulock wrote:
> Dick,
>
>> Then why are you here?  What is your point?  Make the patch contribution, all fields if
>> you want, and I will personally give it extra consideration.
>>
>> If you are here to only create mischief and take shots, we can do without that.
>>
>> Contribute, do it like a team player, or go away please.
>>
>> This is your best chance, right here, right now, to be taken into this team or be shut out.
>>
> The changes are on my kicad-brian branch on launchpad
> from a year ago.  Pull away.
>
>
> I'll also take this opportunity to explain to you why the
> internal unit is a bug and increasing it is a bug fix and
> not a feature:
>
> When I was laying out CBGA fields with metric spacing in
> kicad, kicad moved every pad and via over to the next
> decimil grid position.  This causes several errors:
>
> 1. No pad is in it true position on a metric grid and is
>    no even in the correct position to a diagonal.
>
> 2. When placing vias between pads, each via was also off
>    the metric grid, sometimes adding in error to the pad
>    placement.
>
> 3. 45-degree dogbones between pads an vias could not make
>    a 45-degree angle (because pads and vias are not on the
>    diagonal, making a long dogbone and a little 1 mil jog
>    segment between the one end of the dogbone and the via
>    or pad.  Unlocking the 45-degree track does not solve
>    the problem because the round-off jogs the endpoint of
>    the track and the 1 mil fragment reappears.
>
> 4. Pads are misplaced with respect to their drill holes.
>
> 5. Pads and vias must be dropped from 12 mil to 11.8 mil to
>    avoid DRC errors.  Tracks must be dropped from 5 mil to
>    4.8 mil to avoid DRC errors.  (The DRC using integer math
>    rounds the other way from the grid error at points.)
>
> 6. Fabricator says we do 5 and 5 and to meet annular ring
>    requirements pads must be increased to 12 mil and tracks
>    increased to 5 mil; however, when that is done, they all
>    fail DRC on the fabricator's CAM tool.
>
> 7. The 5000 copper features on the board increase to about
>    7000 due to the little 1 mil segments that cannot be
>    gotten rid of.  Fabricator charges by number of copper
>    features (because the number increases the run time and
>    memory requirements of the CAM tool).  So I have 2000
>    features too many and have to pay for 4 and 4 instead
>    of 5 and 5.
>
> Please understand that the Gerbers given to a manufacturer
> represents design data and has nothing to do with
> fabrication limits.  Round-off errors in the design data
> simply add to the manufacturing tolerances making everthing
> worse.  CAM systems are quite accurate in their calculations
> of DRC on design data.  3.5 metric Gerber data (3.6 is
> better) is required to place everything in its true position
> on both an imperial and metric grid.  PCBNEW internal unit
> must be a nanometer so that vias in a metric BGA pad field
> are placed in their true design position.
>
> BTW, the 0.1-degree angle doesn't cut it either.
>
> This is why when I see someone take it upon themselves to
> change the internal value to nanometers and get jumped on
> for how the went about it rather disconcerting as a user.
> Because, from a user perspective, I don't care whether int
> was overloaded or macros are strewn everywhere:  without a
> precise internal unit, kicad is useful only for laying out
> dimmer switches.
>
> Make the unit a nanometer, or better.  Make the angle
> 1/1000th of a degree, or better.  Otherwise these same
> problems will result on some board.
>
> --brian


Thanks Brian.  That was helpful.

Keep the faith.  The internal units will get dealt with.

There will be some discussion, with the goal of reaching a consensus on strategy, and then
the changes will be made.

This has always been the plan.  What's different now is that man-hours are being committed
to it, from a resource allocation standpoint, and the concerned parties have agreed to
talk about it.

Jean-Pierre has asked me to work with Vladimir to get it done.  I had previously agreed to
volunteer this time, and working with Vladimir was one of the discussed options.

I will make a note to deal with the angle issue too, per your suggestion.

Unfortunately I don't think pulling from your tree is going to be practical however, and
this has to do with age and divergence. 

For now, I will begin to look over the internal units issues and then compare ideas with
Vladimir when he is available again.

Dick