DRC and split planes

Peter · 2021-01-05T16:50:26+00:00

Hi All, I am using Protel PCB 2.8. Yes it is ancient (1995) but it works, does all I need, and I know how to use it :) Also I often need to revisit very old projects - anything up to 20 years old. It runs fine in a winXP VM (VMWARE). I also have Protel 99SE which opens the v2.8 files apparently ok but so far have not felt the need to use it. I even found out how to generate gerbers for JLCPCB, who famously state they cannot read English and never read instructions on the layers, and who want apertures embedded within the gerber files. However v2.8 can sometimes generate a lot of mysterious DRC errors. Some of these I have not solved and just leave them. Some are e.g. vias within SMT pads; it doesn't like that. But others relate to "broken nets" where a plane has been split with a track, to get correct grounding routes etc. I don't like to ignore DRC errors; it is like ignoring compiler warnings. Protel PCB requires any such breaks to be done with a polygon (a specific feature), not with just a normal track. But even when I do this correctly, it still reports some plane segments are being unconnected. This appears to be related to splits which have tracks at an angle, not 90 degrees, leading me to suspect that they use some sort of geometric algorithm to work out the connection topology and this breaks with polygons which have say 45 degree tracks. The user manual is silent on this. OTOH I would have thought that algorithms for working out if you are "inside" a shape, for any arbitrary shape, have been thoroughly worked out in the 1960s, so why these issues in the 1990s? I wonder if any modern PCB software does this sort of thing absolutely correctly?

Jan 05, 2021 21 Replies

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keith 5 years ago

On Friday, 8 January 2021 at 09:57:03 UTC-8, John Larkin wrote: ...

...

They are useful in some scenarios:

I had one design with 34 closely packed through hole-DIMM connectors using

4mil traces (needed to route the ~4000 nets on the backplane). We were plag ued with open traces. The traces were cracking adjacent to the connector. A fter much trial and error we ultimately added teardrops at the connectors t o cured the problem.

Where I am currently the design rules for flex-PCBs require teardrops and c urvy traces to avoid cracking or trace separation.

We do have extremely high volumes in the hundreds of millions for each prod uct so the DFM group is very particular based on experience.

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jlarkin 5 years ago

Yeah, flex could be very different. I have an idea for a flex thing that I have to get around to one day soon, sort of a cheap active scope probe.

John Larkin Highland Technology, Inc The best designs are necessarily accidental.

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