DPMO is defects per million opportunities. Lets say that 97
boards were fully assembled. Each board has 2875 opportunities. It makes a
total of 278875 opportunities for all the boards. All the defects were added
and they were 349.
278875 times 3.5858 is one million. Multiply 349 times the previous
number and it results is 1251 DPMO.
The opportunities can be obtained from the cad data and
there are software that can compute, graph, plot per type of board,
operation, shift, and so on. Also there are books that explain this more in
detail. Took a course long time ago and got used to the software do all the
work. What I explained is an abbreviated form of how it works.
Regards,
Ramon
> -----Original Message-----
> From: Eric Laroche [SMTP:[log in to unmask]]
> Sent: Thursday, October 02, 2003 9:34 AM
> To: [log in to unmask]
> Subject: [TN] RE : [TN] DPU and PPM
>
> Ramon,
>
> Can you expand a little on DPMO? What is measure and how is it
> calculated?
>
> Thanks
>
> Eric
>
> -----Message d'origine-----
> De : TechNet [mailto:[log in to unmask]] De la part de Dehoyos, Ramon
> Envoyé : 2 octobre, 2003 09:17
> À : [log in to unmask]
> Objet : Re: [TN] DPU and PPM
>
> Howard:
> It depends on the complexity of the board. It could be
> 0.7,
> 1.9 or 3.5. One board can have two defects others can have 7 defects
> and
> some none. DPU is a defect average of many boards of the same type.
> DPUs
> can be compared with other groups of boards of the same type. Gauging
> the
> whole shop for quality, a better method can be used, which is DPMO.
> Using
> DPMO all the boards can be put in the metric. Every part that gets
> placed
> by the chip shooter or the pick and place, every solder joint are
> opportunities. A DPMO of under 1000 is a good number in my point of
> view.
> Under 500 is great.
> Regards,
> Ramon
>
>
> > -----Original Message-----
> > From: Howard Watson [SMTP:[log in to unmask]]
> > Sent: Wednesday, October 01, 2003 5:22 PM
> > To: [log in to unmask]
> > Subject: [TN] DPU and PPM
> >
> >
> > 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
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