From a 1999 response: The best method of reporting defects is to calculate the ratio of "errors per possible errors", hopefully expressed in parts per million (ppm). So when you are placing parts, it is "placement errors per total number of placements". Or if you are printing solder paste it can be the "number of print errors per number of apertures". When you start using "number of boards with any error per total number of boards" it becomes impossible to compare results. Very simple boards with a low defect ratio does not mean you are performing well, and neither does a higher defect ratio for very complex board indicate that you are out of control. The "First Pass Yield" number that some people use (number of correct boards per total number of boards) has the same problem: you cannot compare a line that makes very simple boards to a line that makes very complex boards. But if you use ppm for all your work, any board can be compared to any other board and the data can even be combined for a complete plant. Have fun, In addition: If you are a customer you don't really care how complicated a board is, if it has one error the product you just bought does not work. Therefore "First Pass Yield" (good boards per batch) is great to make your customers feel good, it is a Marketing tool. On the other hand, "DPMO" is the number you need to show how good your assembly process is, or how much you need to improve it; it is a Manufacturing tool. Regards, Ahne Oosterhof, GM A-Laser, Inc. 503-641-9428 Beaverton, OR, USA -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Blair K. Hogg Sent: Thursday, October 02, 2003 05:17 To: [log in to unmask] Subject: Re: [TN] DPU and PPM We use DPMO / PPM at our inspection step, and %yield at test. We're not following 7912 exactly, but pretty close. I don't think it is really important how you get the measures, but how you use them. When looking for improvement opportunities, we look at essentially defects per board as opposed to PPM. This is because a small run of a low volume product with a few defects would have a high PPM, but our high volume boards could have more defects and more opportunities even though they have a lower PPM. Blair Hogg QA Manager GAI-Tronics >>> [log in to unmask] 10/01/03 05:22PM >>> Hi everyone, The upper management team here uses a DPU metric for our board shop, for what reason I am trying to comprehend. Basically, one solder joint defect on a board equates to the whole board counting as a defect. The opportunities are irrelevant - every board gets one opportunity. When the "PPM" numbers are published, which is what they call them, they are outrageously high. My questions are: Does anyone use Defects per Unit at the board level? If so, what kind of numbers are you seeing.? I am pursuing a change to use real DPMO metrics, but so far I've been unsuccessful. I even presented IPC-7912, but it was ignored. Thanks in advance for the help. Howard Watson SMT Manufacturing Engineer AMETEK/Dixson Grand Junction, CO ********************************************************************** This email and any files transmitted with it are confidential and intended solely for the use of the individual or entity to whom they are addressed. If you have received this email in error please notify the system manager. 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