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Re: where footprints come from (was Re: Re: Internal


Manveru wrote:
> (probably) open standard *IPC-2581B*:* *http://webstds.ipc.org/2581/2581.htm

Thanks ! The preamble leaves the openness undefined. It doesn't
mention any specific restrictions or prohibitions (except for
the copyright) but has the general warning that there may be
patents, implicitly including patents held by members.

So it could be a dangerous standard to adopt until ~2017 without
first clarifying the patent situation.

The SPECCTRA Design Language Reference I found states the
information it contains is proprietary, confidential, and only
for Cadence customers. I think it's safe to obtain possession of
the document in most jurisdictions, but it may not be safe to
redistribute it or perform an act deemed equivalent, such as
posting a URL to a site illegally hosting it.

There is no information on patents covering the SPECCTRA DSN
format. The document warns that SPECCTRA is a trademark, so it
wouldn't be safe to use that name in a product without

I don't see a problem with just using the SPECCTRA syntax, which
are basically S-expressions with a LISP-ish flavour - a format
as old as time :-)

Now, regarding the content, IPC-2581 doesn't seem to differ much
from SPECCTRA DSN in terms of how it expresses locations. I.e.,
they are numeric literals defining offsets to a given reference,
and the hierarchy of references is of finite and actually quite
shallow depth.

There are no variables or analytical ways to express dimensions,
beyond the offsets mentioned above, so the capabilities for
constructive geometry are very limited.

There is measurement information (DfxMeasurement) that contains
both the measured value and references of the things being
measured. So this could be used for automatic measurements.

There is some room for annotations and comments.

So I would say that this not a format suitable for constructive
geometry. It should be adequate for carrying an unstructured
description of the origin of a footprint, but that's a fairly
trivial requirement. The measurement capability looks as if it
would be useful also for the design process.

- Werner