PPM Calculation & Lot Acceptance Rate (LAR)

Guest

Hi,

Could you please explain what is Lot Acceptance Rate (LAR) that is used in PPM calculation? i.e.

PPM= {(n * LAR)/N}*10E6

where, n= number of failure
N= total number tetsed,

Why LAR is used to calculate the PPM?

Thanks,
Guest

Guest

Greetings,

Your ppm computation is based on (but not exactly the same as) EIA's formula for computing ppm. EIA's point of interest is in the ppm received by the customer, and not the process ppm generated by the manufacturer. If you reject a lot in your factory, this lot no longer reaches the customer, and will no longer contribute to the ppm 'felt' by the customer.

Thus, the customer ppm is always lower than the process ppm at your factory. That's what the LAR is for - it removes the ppm contributed by rejected lots from the customer ppm. Of course, for this to be true, you must really prevent rejected lots from being shipped to your customers.

Dayo