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> > It's definitely NOT an RS-274X limitation and I can say that with 100%
> > certainty. I have a colleague who uses a cheap CAD tool which allows the
> > thermal reliefs to be controlled minutely on plane layers and it
> > produces (274X) gerbers with no problems at all.
> >
> > Douglas McDonald
> Geoff,
> I am not sure I buy into your explanation either.  I will disqualify
> myself by admitting I have little to no programming experience and
> even less knowledge of  Aperature generation,  but I bet it can be
> fixed. And if it can be fixed then it must be broke.
> Mike Reagan

I think that this is a bug in Protel, and that this *can*, and *should*, be
fixed; the way to do that is for thermal relief patterns having just two
openings to be *"drawn"* (rather than "flashed") within Gerber files (and
regardless of whether thermal relief patterns having four openings are
"drawn" or "flashed" in these files). (If the PCB designer was prepared to
provide an aperture list file and RS274D format Gerber files, perhaps those
patterns could be "flashed" instead in those circumstances, but the onus
would then be on the PCB manufacturer (and the PCB designer (to the extent
of specifically bringing such apertures to the PCB manufacturer's
attention)) to ensure that the PCB is still manufactured satisfactorily.)

What I was saying previously was that the RS274X standard does not support
"flashing" thermal relief patterns having just two openings. Given that
situation, the associated arcs (of these patterns) should (normally) be
"drawn" instead.

I have yet to have cause to design any PCB using such thermal relief
patterns, but given my understanding of the situation, if I ever did have to
design such a PCB, I would figure out some way of avoiding the problem (if
necessary, generating RS274D format Gerber files, and then converting these
to RS274X format using a Perl script). However, it definitely is a trap for
those who are unaware of the situation, so I fully agree that this is a bug,
and that it should be fixed.

Geoff Harland.
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