All,

Having been task group chariman of the IPC-ML-950, IPC-RB-276 and IPC-6012, I
have found that even we so called experts never completely agreed on the what
the requirements should be.  So the specifications are a consensus of what
most of us thought the requirement should read.  We encouaged people to add
exceptions to the specifications by adding to their drawings or in-house
documents to make it just like they want it.

I find that many companies can write an easily maintained procurement document
with a company number of "XXX22YY" , or whatever, that is 1 to 5 pages long
that tell what department to contact in case of conflicts, who is the
qualifyiing department and the "exceptions, deviations, additons etc." to the
IPC standards.

 An example, after the company boiler plate, is that one of the headingx would
be  :
"XX. FABRICATIONS REQUIREMENTS: The boards shall be fabricated to meet
requirements of IPC-6012 Class 3 with the followiing exceptions:
   1. The minimum conductor width listed on the fabrication drawing is the
minimum acceptable conductor width and includes all variations such as nicks,
voids, and other  conductor reduction allowances.
   2.  The minimum copper plating thickness in the hole including thin areas
shall be 25 microns (0.001) inch

Usually the exceptions number less than 5, and if the IPC document changes and
you do not agree you merely put through a change notice with another exception
to the IPC Standard and you are done.

On the drawing you state: Fabricate to Whatever Tech Co Specification XXX22YY
and send it out with the PR.

Do not write a 30 page document that is a copy of an existing standard with a
couple of exceptions somewhere in the text.  This costs you megabucks to
maintain and the supplier many bucks to read and find your deviations.  They
tend to fill up file cabinets at both ends..

Unless you are firmly in bed with your supplier and can read his
specifrication with  considerable knowledge, do not buy to his specification.

The worst thing to do is to put no requirement or standards on your drawing
and buy based on some salesmans statement that, "We are certified to IPC", "We
fabricate to IPC-A-600", "We are a qualified source".  You may not be buy good
boards and you will have a very difficult time proving that you were wronged.

Phil HInton

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