Re: gEDA-user: pcb crooked traces

[Dave N6NZ <n6nz@xxxxxxxx>]

On Oct 7, 2010, at 7:50 AM, Stefan Salewski wrote:

> On Thu, 2010-10-07 at 22:29 +0800, Steven Michalske wrote:
>>>> I cannot get rid of the jagged diagonal lines on my design.  There's lots of them.  The picture shows a couple of examples.  I've tried different grid sizes, line widths, but nothing fixes the problem. Redrawing them in order to eliminate any sections does not help.  On PCB, it shows at some zoom levels but not others.  It is in the gerbers as well and it is in the photo-mode picture I attached.
>> 
>> 
>> Another thought,  When I am laying out mixed pitch mm vs mil parts, I
>> often leave the grid at a comfortable 10 or 25 mil setting. Turn on
>> snaps to pins and pads. Then I largly ignore the grid.  What I am
>> saying here is that I Use the grid as a guideline.
>> 
>> So to accomplish this I draw from the off grid pin out to the pcb and
>> let the 45degree tail end on the grid.  then off to the rest of the
>> layout, on grid.
>> 
>> When that tail is not quite correct, while drawing I use the u key to
>> undo the 45 degree tail,  this leaves the off grid stub that i can
>> continue drawing from.
>> 
>> Having a small grid usuially allows me to make a messier layout.
>> 
> 
> Fine description, maybe such a text should be part of a beginner
> tutorial.
> 
>> 
>> If these things don't help then we have a bug.....
>> 
> 
> Sure, we had bugs, and maybe some are still alive. 8 mil traces with 8
> mil clearance can be a problem due to arithmetic errors, 8 may be
> rounded up to next grid position, which is 9 with 1 mil grid. (I would
> use 8 mil traces, 8 mil grid and 7.9mil clearance to prevent problems)
> And we had the problem of 0.01 mil traces due to arithmetic errors when
> mm units are used. I guess the step to nm base units in PCB is still on
> the todo list.
> 
> 

I've had perfectly explainable jaggies that occur when I am routing parallel traces.  The 2nd through Nth traces of a parallel group can be pushed up against the previous traces as close as min-space, and therefore end up off-grid.  This is great for routing density, but leads to a little weirdness when breaking them out again.  One sources of  jaggies occurs when I form a straight track with two or more segments, one that is off-grid and the new one on.  Also "snap to center of pad" is often off-grid for TQFP's, etc, so that is another source of geometric oddities.

I've never had a jaggie that wasn't a PEBKAC, or that couldn't be fixed by a little bit of careful editing.

-dave


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