Michael:
- Most folks with whom I have worked tend to use the 3,000 ppm (0.3%) which is
specified by ANSI/IPC-J-STD-001B.  The same number was previously used by the
military in Mil-Std-2000 and represents a 6-sigma spread.
- I should add that some companies, in an effort to assure that 3000ppm is not
sent to their customers, use more stringent limits (2000ppm or less).  Also,
as an aid to upstream feedback, it is normally desirable to differentiate
between assembly defects and soldering defects.
- You might check IPC-PC-90, General Requirements for Implementation of
Statistical Process Control, for additional thoughts on applications which you
might elect to use in-house.
- Also, I think the IPC is contemplating (or may have already set about)
starting a task group to develop "standard method" of identifying and
classifying defective parts per million opportunities (at the moment there is
not a level playing field so such data cannot be accurately compared between
competing companies).
Regards, Jim Moffitt, Moffitt Enterprises Consulting

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