DPU or First Pass Yield

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    Which metrics is better to use in a process?
    DPU or First Pass Yield



    Both.  Use FPY to understand how much is being rejected and put into the “hidden factory”.  Then you can use DPU to drill down to the root causes of the defects.
    For instance I’ve rejected  10 out of 100 units for a FPY of 90%, but what were the failure modes or defects.  You may have many defects per unit so you need to understand how many and what are they.  Once you know this you can implement improvements for an increased FPY.


    Mike Carnell

    It depends on what you want to know and how you put the data together.
    DPU is the metric most use for projects. If you want this to mean something you need to collect data throughout the entire line.
    FPY is a relatively dumb metric – it is like an attribute control chart – you still need to investigate. I am assuming it is being measured at the end of the line. It is going to tell you how well you screened and reworked everything through the line but that is about all it is good for. It could be construed to be what your customer will see – assuming you have reproducibility with their incoming test.
    The thing you have to watch is the test parameters. If you run a tighter test at EOL you will get rejects. If it is looser you won’t see anything. If you test to equal parameters you will get rejects that are probably a function of your R&R (if you have trouble making a measurement in line – poor R&R – you should expect to see rejects around that same measurement at EOL.
    Good luck.

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