PPM Calculation

Guest

Hello,

Can anyone help me with the following:

1) When calculating outgoing PPM from QC sample testing, should I use the number of QC sample tested or entire sample size for given lots? We only QC test 135 pcs from a given lot but lot size is ~2k pcs. So, should I be using only the QC samples or entire lot populations for outgoing PPM calculation as the number of parts?

2) What is the best way to represent weekly outgoing PPM? Currently my company uses one PPM number for all products? Shouldn't the PPM be presented for each product or at least product family?

Thanks for your help.

Guest

Guest

For straight-forward process ppm computation, you can just use this simple formula: ppm= (total # of rejects/total tested SS) *1000000. So the answer to your first question is you have to use the total tested SS for all sampled lots as the denominator.

There's nothing wrong with having a single outgoing ppm number for all your products, especially if your ppm # is low. But there can also be an issue with this if the ppm is not yet good, and some product groups are really worse than others. In this case, it's probably better to report different ppm #'s for different product groups like you said.

By the way, you must have separate ppm #'s for electrical and visual-mechanical OQA.

QA 4ever