Hello there,

We are in the middle of  studying how to implement PPM in our
organisation and are looking for all information which can help us to
build a good system for defect counting.
So please keep me posted about all reply's you get. All other
information would also be welcome.

Thanx,


Jos Aarninkhof
SPA Nedworks Almelo bv
NetherlandsVickie Chapman wrote:
> 
> Rick --
> 
> Great question! I wish the industry as a whole would standardize on this! I
> would be very interested in hearing what other replies you get back.
> 
> We count defects basically the same way you do,  but with some variations
> depending on the defects were tracking:
> 
> Solder defect rate:
> 
>         # of defective solder joints / total # of solder joints
> 
> Placement defect rate or defective component defect rate:
>         # of defective placements or defective components / total # of
> components
> 
> Total process-related defect rate:
> 
>         (# of defective solder joints + # of placement defects) / (total # of
> solder joints + total # of components)
> 
> Over-all defect rate:
>         (# of defective solder joints + # of placement defects + # of defective
> components) / (total # of solder joints + 2*(# of components))
> 
>  Since the "over-all" defect rate includes electrically defective components,
> each component has an additional opportunity to be defective.
> 
> # of defective solder joints = the number of pins affected. If one whole side of
> a 60-pin QFP is shorted together, that's 15 defective solder joints.
> 
>  The exception is that if just two pins are shorted together, I suspect this
> just gets counted as 1 defect most of the time.
> 
> If the QFP is misclocked, that's one defective placement.
> 
> If the QFP has an internal defect, that's one defective component.
> 
> -- Vickie Chapman
> 
> 
> 
> On Wed, 9 Jul 1997 10:33:41 -0700 RICK VERNON wrote:
> 
> > From: RICK VERNON <[log in to unmask]>
> > Date: Wed, 9 Jul 1997 10:33:41 -0700
> > Subject: PPM Defect Counting
> > To: [log in to unmask]
> >
> > We count our defect opportunities as follows: one per component plus
> > one per solder joint. A resistor would be three defect opportunities, a 144
> > pin QFP would be 145 defect opportunities.
> >
> > We count actual defects as follows: Tombstone part is one defect.
> > Insufficient solder on one pad is one defect. Solder short between three
> > legs of an SOIC is one defect. Skewed SOIC is one defect.
> >
> > I have concerns that we are presenting an artificially low PPM rate by
> > counting defects this way. Others have concern that if we count defects
> > the same way we create opportunities, the PPM numbers will be inflated.
> >
> > I'm looking for info on how others in the industry count actual defects that
> > affect more than one opportunity.
> >
> > Thanks.  Rick Vernon, QA Manager   [log in to unmask]
> >
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