Dear Mark,

IPC-D-350  is a standard that was written in the early 70's to address the need to have intelligent information about a printed board.  The idea was to develop something like Gerber machine code , but a format that had meaning.  The committee used numbers since computer storage at the time was expensive. A 1 was a line draw; a 3 was a flash, a 2 was a subroutine, and a 5 was text.  We used 80 column records based on the IBM card and were able to describe plated through holes, subroutines for special shapes, all conductor routing, differences between ground and voltage planes etc.

Delivering data to the government required the D-350 format.  I worked for Philco until 1974 when I joined the IPC staff.  The contracts that we had required the format to be extracted from our home brewed design system.  We sent many files to NSA for contracts that we had with them and also the Navy.

When commercial CAD systems became available the tool suppliers felt that having a neutral format was a threat to their hold on their customers.  They charged a great deal ($25K and $15 maintanance) for a D-350 output, so although board manufacturers offered discounts for anyone providing D-350 instead of Gerber no one who used commercial CAD could comply.  Computer Vision and Applicon had a D-350 output but it wasn't written real well.  Today the D-356 is still in use for describing bare board test requirements.

The D-350 to D-356 standards are still in effect at IPC even though we have moved to the GenCAM format.  It is a good format, and can still be used  to describe a printed board.  The D-350 has an international equivalent in IEC  61188-1.  They are identical.

Go to the GenCAM home page <gencam.org>. and click on the new CD that we sent to many people.  Go to the folder on presentations and find one called "GenCAM Roots"  It may take a while to open however it tells you all about the D-350 and its siblings.

Probably more than you wanted to know.

Dieter