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DPMO calculation and OMI calculations



DPMO calc and Overall Manufacturing Index (OMI) calculations | 27 August, 2001

It has been mentioned that DPMO offers large advantages over First Pass yield calculations for measuring process performance!!regarding the same I have a few queries: What are the benchmarks for using DPMO as measures of process performance? How is DPMO being employed in improving process performance? Besides the IPC 7912 is any other approach being followed for estimating DPMO levels. What opportunities (Component, Placement, Termination) exist at each stage of process, as Stencil printing, Placement and post reflow?? How is OMI interpreted as a measure of process performance?? What are the benchmark values used for the same?

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Michael Parker


DPMO calc and Overall Manufacturing Index (OMI) calculations | 28 August, 2001

The advantage of DPMO is that the numbers used are PPM, (Part Per Million), rather than percentage. Percentage can distort, depending on volume. For instance, 100 units processed, 25 defects found = 75 percent yield. 4 units processed, 1 defect found = 75 percent yield. Which is better? 1 defect or 25 defects? the yields are the same (75 percent). Calculating PPM evens out the distortion and gives a true picture.

To answer all of your othere questions, I suggest you obtain a copy of IPC 7912. It gives a clear, detailed, easy to understand example. After you get the standard, contact me for help on setting up spreadsheets to track and calculate your data. I have implemented PPM and abandoned percent recently, I could give you guidance to get started.

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DPMO calc and Overall Manufacturing Index (OMI) calculations | 28 August, 2001

To be honest with you, it doesn't really matter how you present the data, as long as you understand what the problems are. Bottom line is who cares what the numbers are unless you are doing something about it.

Are you able to track the individual defects, i.e. solder bridges, tombstoned, skewed, missing, etc. Can you track improvements? Whether you track by first pass yield (FPY) or DPMO, as long as you have a good handle on process improvement, you can use either method. I actually do both.

One thing to keep in mind though is that if you track FPY, it only takes one part defect to count a board failure. DPMO takes into account the total number of "opportunities". If a board has 1000 components, one part defect means DPMO is 0.001. This is still better than 3 sigma, but your FPY will suck if you have one part defect on every board.

FPY is a good indication of how many boards are needing rework, DPMO is a good indication of how good the overall process is.

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Michael Parker


DPMO calc and Overall Manufacturing Index (OMI) calculations | 28 August, 2001

To clarify on "Opportunities"-

With 1000 components, the opportunities are far greater than 1000. You have 1 opportunity per component for a component defect i.e. bent lead, damaged part, tested bad, etc. You have a second opportunity per component for placement defects i.e. missing, misaligned, reversed, tombstone, etc. You have multiple opportunities per component for each termination (solder joint, etc.)

The sum total of all opportunites is the basis for calculating PPM.


1000 components 999 placements (the PCB is not counted for a placement) 9001 terminations

11000 opportunities for the assembly

Steve is right in saying that examining the defect type and doing something positive about it is the real goal.

By using the PPM method and categorizing the defect types you will quickly see where you should spend your efforts in trouble shooting the process.

I have some assembles that have most defects in the terminations - I then trouble shoot the paste print, and wave solder processes.

Others are more heavily placement defects - which focuses on Pick and Place, through hole placement, 2nd ops assemblers errors.

If you have a good Incoming Inspection, component defects are usually the last thing to worry about.

I only use First Pass Yields in percentage for Test, but all defects found in test are also included into the daily PPM calculation per assembly.

One last comment - OMI calculations are good for examining the quality of a single assembly produced at multiple sites. An OEM would use this calculation to examine various suppliers. Since my company is a CM, I don't bother with OMI, that's for my customers to implement if they are concerned about multiple manufacturing sites.

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DPMO calc and Overall Manufacturing Index (OMI) calculations | 28 August, 2001

Several points are: * Some may argue that DPMO is peculiar and specific. That�s why IPC-7912 states �Users of this document are cautioned when comparing one manufacturer�s indices to one another due to differences in assembly complexity and the amount of data that may have been used in a computation.� [Er, words to that effect.] * And some might argue that maybe sigma levels are more accessible to benchmarking between companies. Currently Motorola and Sony are running 5.8 sigma. Honeywell is running 4 sigma. * Overall Manufacture Index [OMI] is an alternative [to the DPMO Index] measure that probably needs more explanation of its worth than its value. Maybe some of those black belt types can contribute here. * Ceeris periodically publishes electronic board assembly benchmarks [] that may be similar to those you seek. * IPC 7912 is used to calculate DPMO and other indices for end products. It states that it is not aimed at process measurement. It could be that you need IPC-9261. As is often the case, that document is not available. But as a bonus for you and you alone, check-out a working version at Be sure to use the secret SMTnet password.

Finally, aren't you supposed to base line your process; get it in control and keep it there; determine if it's capable; and if so, use it and improve it; or if not, fix it or replace it? None of that has anything to do with what someone else is getting from their process.

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Brian W.


DPMO calc and Overall Manufacturing Index (OMI) calculations | 4 September, 2001

IPC7912 deals with the end result, ie an OEM getting boards from a contract manufacturer. I have a friend who is sitting on these committees. He tells me there is a new standard due out for actually doing in-process DPMO.

From a process standpoint, DPMO (or ppm) is much more sensitive to variattions in the process. It also allows you to compare your boards. FPY does not take into account board complexities. For example: I have two different boards. The first has 2500 oportunities for error. It is a fairly complex board. FPY is about 80%. PPM is less than 150. My second board is very simple, 57 oppotunities. It has a 95% FPY, but a ppm level of 700. Hmmm which do I work on first? Looking at FPY would lead you to look at the more complex board, while PPM says check the simpler board. I normally find that the board with the higher ppm is the one to attack first.


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Michael Parker


DPMO calc and Overall Manufacturing Index (OMI) calculations | 4 September, 2001

Brian - do you have any more info regarding the in-process DPMO? Is there a working standard number to reference? What commitee is working on this?

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DPMO calc and Overall Manufacturing Index (OMI) calculations | 5 September, 2001

Jack Crawford, IPC Director of Assembly Standards and Technology says "IPC-7912 is used for end-item DPMO calculation; one gathering of DPMO data at the end of the entire assembly process. IPC-9261 will be used throughout the manufacturing process so users can determine DPMO/Yield on printing, placement or whereever they wish to track.

IPC-9261 for In-Process DPMO is on ballot now. To receive a review copy (and a ballot you are welcome to return) send a message to: and in the subject line put exactly this character string (it's not case sensitive): request IPC-9261

You don't need to put anything in the body but if you include your contact info it's easier for me to sory out mail delivery problems."

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Michael Parker


DPMO calc and Overall Manufacturing Index (OMI) calculations | 5 September, 2001

thanx mucho

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DPMO calc and Overall Manufacturing Index (OMI) calculations | 12 September, 2001

Look at "DPMO: A Tool For Achieving World-Class Process Quality" Charles-Henri Mangin, SMT magazine, 8/00, p 77-78

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Michael Parker


DPMO calc and Overall Manufacturing Index (OMI) calculations | 13 September, 2001

Dave et al,

I just print out and read a copy of the aforementioned recommended article. Mr. Mangin gives a clear picture of why DPMO is to be considered a more pure data than First Pass Yield (FPY).

However, I must note that his interpretation of how to formulate DPMO is not entirely in line with the IPC 7912. It may be that his article is outdated in that respect and it may be that his current opinion would be changed to more closely follow IPC.

I have also solicited and received a draft of IPC 9261 for In-Process DPMO. It is a straight forward and precise data collection and calculation method that should produce the desired results. It does require a dedication to detail and is a complex system that strict discipline for data collection must be followed to achieve meaningful results.

What is still missing from all information I have perused is the target values and ranges, Best In Class, for DPMO. It could be premature to expect this data but I would still like to hear from the community at large what their experiences may be and collectively we may come up with recommendations that all can follow to achieve the goal of Zero (or significantly reduced) defects.

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