Marti, interesting question you have brought up. I've been telling people that inspection is like an insurance policy: you pay a price, and get protection from disaster. And I ask "what fraction nonconforming are you willing to live with and what fraction nonconforming are you definitely unable to tolerate?" (May also ask "what producer's and consumer's risk values do you want", but that sometimes makes things more confusing for them than they can handle, even when I couch these questions in "layman's" terms, which I like to do, being a layman myself.)
So what is the 500 your customer wants, where does it fit in the spectrum ranging from intolerable, don't care, tolerable? By "don't care", I mean a nonconforming fraction for which producer and consumer risk are each 0.5.
You can squeeze more information from your historic and current inspection data if you adopt a Bayesian approach, if your customer is really interested. American Society for Quality has a slim book, volume 7 in the How-to series from the Statistics Division, "How and When to Perform Bayesian Acceptance Sampling", by Thomas Calvin.
Lou Hart
Quality Assurance Manager
Compunetix
412-858-6184
----------
From: Marti Tully[SMTP:[log in to unmask]]
Sent: Monday, September 18, 2000 8:06 PM
To: [log in to unmask]
Subject: [TN] FW: Sampling Plans
> > Subject: Sampling Plans
> >
> > I have a customer who insists that the AQL sampling plans in IPC 6012 are
> not sufficient to guarantee his desired dppm and he is right. His product
> is class 2 and we, in general, follow a 2.5 AQL in final inspection for
> external defects. This customer wants a dppm of 500. I know of no cost
> effective sampling plan that can guarantee this. Only maintaining rigorous
> process control can meet this requirement.
> >
> > I, however, promised to survey the industry for their thoughts ... here I
> am ... comments?
> >
> >
> > Marti Tully, Quality Manager
> > Sanmina Phoenix
> > Office 602-824-8497
> > Cell 602-549-4535
> >
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