Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


how to achieve 500ppm?

peter ng

#34927

how to achieve 500ppm? | 13 June, 2005

Dear all, We faced some major issue in setting our company target to 500 points per million at machine throw rate.It might be caused by human error,machine,feeder,environment or other factor.We need some opition and advise on how to achieve this target consistansis.Meanwhile,how to perform 500ppm if the frequency of model convention is too high?Thanks.

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peter ng

#34928

how to achieve 500ppm? | 13 June, 2005

Dear all, We faced some major issue in setting our company target to 500 points per million at machine throw rate.It might be caused by human error,machine,feeder,environment or other factor.We need some opition and advise on how to achieve this target consistansis.Meanwhile,how to perform 500ppm if the frequency of model convention is too high?Thanks.

reply »

Stefan

#34944

how to achieve 500ppm? | 14 June, 2005

500 rejected (?) per million placed components is a very good rate, considered that it would be better than 4 Sigma if you name it defects on the board. Or do I incorrectly convert ppm to dpm?

* 3 Sigma 66,800 defects per one million opportunities. * 4 Sigma 6,210 defects per one million opportunities. * 5 Sigma 233 defects per one million opportunities * 6 Sigma 3.4 defects per one million opportunities

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pr

#34948

how to achieve 500ppm? | 14 June, 2005

Sounds a little tough to achieve. Math isn't my strongsuit but...If you run a million parts through the machine, you will have 200 feeder exhaust's (assuming 5000 per reel). So if you have your machine error out after 3 attempts/misspicks you will have 600 defects, If the machine ran perfectly!

good luck with that, pr

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#34956

how to achieve 500ppm? | 14 June, 2005

In that the machine times out and waits for a feeder refill and doesn't just skip that part and leave the space empty, it's not a defect.

I have found 500ppm *fairly* easily attained in SMT depending on the board mix and how you define (1) a defect, and (2), a defect opportunity. If you make every pad, component, and board one opportunity it's quite do-able.

My focal point is continuous improvement, so how I arrive at my ppm numbers is less important than reducing them consistantly, at least until the low fruit has been plucked.

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pr

#34959

how to achieve 500ppm? | 14 June, 2005

My chipshooter will not "Time out", it will try to pick 3x and then alert the operator. Which would be 3 misses per empty reel. Unless I misread his post, he said 500 ppm at the placement machine. That makes a big difference.

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#34960

how to achieve 500ppm? | 14 June, 2005

You may be right. I may have read something into his post that wasn't there....

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FD

#34971

how to achieve 500ppm? | 15 June, 2005

From my understanding: Sigma is the same as one standard deviation. So 3 sigma is the same as 3 standard deviations. It all boils down to how repeatable your machine is. Another way to look at it is the probability (or confidence) that the machine will actually place within its specs. 1 sigma is equivalent to 68.2%. This means if you said your machines are rated to +/- 0.1mm at 1 sigma, you only expect 68.2% to actually be +/- 0.1mm. The other 31.8% could be worse. 3 sigma is 99.73% and 4 sigma is 99.99%. I know of some machines (Siemens and Universal) who rate at 4 sigma, but I think most others either don't say or use 3 sigma. So the lower the sigma, the lower the probability (or confidence) that the machine will work within specs. I'm not sure where you got the numbers per million above...

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