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DPMO as a metic to qualify a CEM as World Class

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DPMO as a metic to qualify a CEM as World Class | 17 January, 2007

I have been using overall combined DPMO of SMT PCBAs as a performance metric. All defects are recorded down to component location and defect category. The resultant defect data table is analyzed with detailed pivot tables, defect type and defect location paretos. The top (3) defects are selected. Using 6-Sigma techniques the defect root cause is determined and corrective actions are implemented. I have been able to reduce DPMO of all boards made in a tier 1 CEM from 950 to 198 over a couple year period. As most know, a CEM will build all types of PCBAs, short runs and high volume builds.

My question to all is what DPMO number would indicate I have reached 'World Class Manufacturing'?

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DPMO as a metic to qualify a CEM as World Class | 17 January, 2007

i would say that you are there already. with 10,000 DPM0 you have a 1% fallout, you are at 99.9 basically. 1 out of a 1000 boards will fail?

of course one thing we need to know is how many opportunitites do you count for a chip resistor for example? 1? 5? (2 joints, 1 value, 1 registration in X, 1 registration in Y axis)just an example, one must be very careful when playing with statistics. What number do you want to see? hahaha

what is your first pass yield at test? This is what is important to customers and your factory as well.

World class mfg in my understanding is a first pass product yield of 99.87 % I do not know where that number came from or why. this number does not include assignable causes.


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John S.


DPMO as a metic to qualify a CEM as World Class | 17 January, 2007

We use a fairly simple system. IPC put out standards 7912A and 9261A to define opportunities. Basicly the "number of components" + "number of solder joints" = "number of opportunities." Some six sigma benchmarking studies indicated "Sigma Level" = "0.8406 + sqrt(29.37-2.221 * ln(dpmo))." That let's us compare product to product in terms of sigma level and helps compensate for complexity. Applied this way, we've found Six Sigma to be a challenging target, though we press on. 3.4 dpmo would be 6 sigma in the above calculation.

To Russ's point, we find yield has more impact on operators and customers. We define yield by including ALL defects: minor touch up, AOI, ICT, functional test, everything. This drives your costs and reflects your field issues better; however,it doesn't give you credit on a more complicated part vs. a less complicated part.

Hope that helps, John S.

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DPMO as a metic to qualify a CEM as World Class | 29 January, 2007

Thanks Russ and John,

To clarify defects when manufacturing a PCBA, I use (2) groups of defect categories, one for components and one for solder joints. These can be calculated separately or combined

A component defect could be: Missing, Miss-aligned, damaged, wrong, polarity, Etc.

A Solder joint defect could be: bridge, open, insufficient, excessive, etc.

For overall combined DPMO I simply sum the component and solder joint counts, the combined sum would be the opportunities.

DPMO is calculated by (sum of defects / sum of Ops)*1,000,000 = DPMO. This can be performed by PCBA, all the boards in a product, or all boards built in the factory

This DPMO number shows me general factory health trend, high hit PCBAs or the product with the highest defect rate.

I have several ways to drill to the hit defect hits by category and by reference designator. By working on the root cause of the top defect hitters, DPMO is continually driven down.

I am looking for a reasonable Overall Combined DPMO Number in which would deem my factory 'world class' (any ideas, someone toss me a number?

As DPMO rates improve, so do your yields, DPMO is a normalized quality indicator, yield is not.


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