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Multiple questions

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  • #38511

    marzuki
    Participant

    Hello guys,
    I’m coming from PCBA industry and some PCBs comes in panel form (4-8 individual PCBs in a single panel) and we did have SPC monitoring (Xbar R chart), however I have some concerns that need help from you guys.1. Let’s say the 4 individual PCBs coming in one panel and we measure the solder paste height for each PCB. We took 4 solder paste height readings and it’s total up to 16 readings. We did this in shiftly basis. Is the n is equal to 16 or 4 in the subgrouping? 2. If n=16 then should we use the Xbar S chart instead?3. We have the CpK computed for each time the solder paste height is taken, is it OK? As for this case the CpK computed after 16 readings collected.4. I did encounter that sometimes the CpK exceeds 2, is this OK or we should revise the USL/LSL in order to have more realistic CpK (0 to 2)?5. I plan to have GR&R for the solder paste measurement process but the problem is the source (uncooked printed PCB). I already identify the technicians and the measuring machines but I don’t have the fixed sample for the PCB since the printings having variation based on the height tolerence spelled out in the USL and LSL. Do we need to have fixed sample such as fixed height model so that we can check the machine repeatability and human reproducibility?Thank you so much for your feedback!-marzuki-

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    #115219

    Thaly
    Member

    Your n is 4 and you’d have 4 different control charts for each of your PCBs. (This is if you are treating the individual PCBs as separate entities.)
    You do not have to compute the CPk each time, because you are already using a control chart, and if the points stay within the limits, you already know your process is in control.
    I think you probably’d be better off getting yourself a good primer on GR&R before attempting to do an actual study. We do need random samples to do a GRR. There is no such thing called “fixed samples” and human reproducibility is an entirely different topic!!

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    #115220

    marzuki
    Participant

    Thaly,
    Thanks for your feedback and clear up my confusions regarding the GR&R. Basically my intention is to identify whether our set of technicians or machines or both of them working well so that I’ll get correct paste height readings, if one of them is problematic, I might end up having incorrect data and lead to wrong decision making.
    What I mean for fixed samples is like a measurement and calibration concept whereby we are having master item or reference item prior to making a single measurement so that we can cal the respective equipment based on the reference item. Do correct me if I’m wrong.Thanks Thaly!

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    #115221

    marzuki
    Participant

    Thaly,
    Thanks for your feedback and clear up my confusions regarding the GR&R. Basically my intention is to identify whether our set of technicians or machines or both of them working well so that I’ll get correct paste height readings, if one of them is problematic, I might end up having incorrect data and lead to wrong decision making.
    What I mean for fixed samples is like a measurement and calibration concept whereby we are having master item or reference item prior to making a single measurement so that we can cal the respective equipment based on the reference item. Do correct me if I’m wrong.Thanks Thaly!

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    #115222

    marzuki
    Participant

    Thaly,
    Thanks for your feedback and clear up my confusions regarding the GR&R. Basically my intention is to identify whether our set of technicians or machines or both of them working well so that I’ll get correct paste height readings, if one of them is problematic, I might end up having incorrect data and lead to wrong decision making.
    What I mean for fixed samples is like a measurement and calibration concept whereby we are having master item or reference item prior to making a single measurement so that we can cal the respective equipment based on the reference item. Do correct me if I’m wrong.Thanks Thaly!

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    #115225

    Thaly
    Member

    Marzuki,
    I mistook your talking about Gage Master to be GRR. What you say about masters is right. Yes, your master sample must be fixed and you should know the dimensions of the master(or atleast the ones you are interested in), so that you could offset your gage by the specified value everytime. (If you are using a transducer equipped digital gage, you’d calibrate for the resolution first and then set the offset). Masters do not help to improve your GRR. All they do is tell your gage where the reference point is. But, if you are interested in knowing the accuracy of the gage, you’d ve to do a R&R study.
    Hope this helps.

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