The simple version of a formula is this:

 [(number of defects) / (number of opportunities for a defect)] X 1000000

If you count a defect for each lead that is off of the pad, then count an
opportunity for each lead.  If you have a QFP that is off of the pads and
you count that as one defect for a misaligned component, then only
count the component as one opportunity.  Don't cheat yourself in either
direction.   If you count every pad in your opportunity number then count
every lead overhang in your defect number.

Jon Moore
TRW

>>> <[log in to unmask]> 04/28/98 04:41am >>>
Dear colleagues

We have some argues regarding PPM calculations, For an example: for
placement station of automatic SMT components, do we have to count
the
soldering pads  or only the components.
If only the components its not the same level of difficult for capacitor
and fine pitch.
The same question is for dispensing machine of SMT glue.
Please E Mail me the general formula for PPM calculation.

Thanks and Best Regards

Rokah  Reuven

IPC Member

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