-- [ From: Doug Jeffery * EMC.Ver #2.5.1 ] --

Dear Designers

We have been using embbeded aperture Gerber formats for 5 years and have
not had a problem with either the RS274x or the MDA versions.  We also
have been reading in aperture tables from 12 different design systems. 
Many of the gerber editing software packages have supported aperture
table read in for years...However....The problem becomes that we still
get files that are not consistent with their original output.  We get
aperture files (dos text files) that are manually edited making it
impossible for the read in scripts to do a correct job, or are renamed
so that the standard file extention is changed or are read into a word
processing software and written off in a format that is not recognisable
.  If the design output, no matter what system, was true to it's form
each time (consistently the same), then we would be able to "autoload"
the apetures.   We(fabricators) do not want to type in your dcode
assignments. The only problems we have seen with RS274x or MDA is file
to file editing that may cause a dcode to have two different values..but
most editing systems will seperate these at readin and reassign one
dcode so the conflict is resolved.

Today both MDA and RS274x support compound apetures or "specials" and
the data accuracy can be improved by the use of more flashed features.  

One more problem that comes up constantly is the decimal format..We
today still get gerber in 2.3 format and drill data in 2.4 format for
designs that are not on grid...this means we end up "snapping" the
gerber to match the drill...(When you are fighting for registration
tolerance every .1 mills helps..).  Have you ever seen the results of a
.0197 pitch QFP written off in 2.3 format..where the soldermask round to
the left and the circuit layer rounds to the right..great for those LPI
registration problems...

And while I am on my soap box .... What happened to mechanical prints..I
am getting concerned when a design for a $100,000 order comes in and no
one can provide the board size or shape other than an "outline" they
slapped together when laying out the board?  Should fabricators be
making prints from board outlines? 

Douglas Jeffery
Electrotek, Inc.
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