gEDA-user: Newbie PCB DRC questions

[Vaughn Treude <vltreude@xxxxxxxx>]

Hello everyone:
I've been checking my board layout with the Design Rule Checker command
in PCB.  I was encountering some mysterious behavior and wondering if
anybody could explain this a little.

1. The default minimum spacing is 10 mils, yet DRC flags everything that
is exactly 10 mils. This is a problem because the auto-router put traces
10 mils apart in many places.  I tried changing the minimum spacing to
9.9  or 9, but apparently that's not valid because it does not retain
that value.  (In fact, the preferences dialog experiences an error if I
do this, and refuses to close the second time I bring it up.)  So I set
the min-spacing to 5 mils and DRC found a few problems in the lines I'd
added manually, which I was able to correct.  Does this mean the actual
minimum spacing should be 15 mils or something like that, so that
auto-routed traces will pass the DRC 10 mil guideline?

2. I've been seeing "potential for broken trace" error a lot.  In some
cases I can see that a line has some unnecessary jags in it which I've
then straightened out.  In other cases the only problem seems to be that
two connecting lines that go in the same direction have for some reason
not been merged into a single line.  It's my understanding that if the
trace _looks_ continuous (at a pretty high zoom) it _is_ continuous.  Is
DRC flagging nonexistent errors here or is my understanding incorrect?

3. Sometimes when DRC reports "copper areas too close", I go to the
coordinates specified in the message and I cannot for the life of me
find anything closer than 10 mils. (And I still have it checking for 5
mil spacings.) Does DRC sometimes get fooled into thinking that
connected lines should be separated?  Or am I misinterpreting the
errors?

Thanks!
Vaughn T





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