Thank you for the reference Daan. We have compared inspection operator to
operator with the aforementioned variation in results.
Another interesting site, for anyone interested, is the American Society for
Quality Control at www.asq.org.
Thanks again,
Jana Carraway
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of d. terstegge
Sent: Friday, January 04, 2002 8:36 AM
To: [log in to unmask]
Subject: Re: [TN] Final Audit/Inspection
Hi Jana,
Couldn't find anything detailed about the efficiency of visual inspection,
although the article at
http://www.circuitsassembly.com/online/2001/08/0108msl.htm refers to such
studies. A few lines copied from this article:
"Human inspection's greatest drawback lies in the inspectors themselves.
Studies have shown the inability of people to consistently and
objectively apply an inspection criterion over time. In one study, the
same set of boards was passed in front of the same operators multiple
times; the operators' results agreed with their own previous results
only 20 to 30 percent of the time. Variation in results between
operators was even greater."
I guess it's the kind of study that's not too difficult to setup for your
own process.
Daan Terstegge
SMT Centre
Thales Communications
Unclassified mail
Personal Website: http://www.smtinfo.net
>>> Jana Carraway <[log in to unmask]> 01/03 6:51 pm >>>
Daan or others,
Could anyone refer me to articles, studies, etc. that demonstrate the
inefficiency of visual inspection and, if I remember correctly, the drop in
efficiency over time? I'm working on incoming inspection of bare
substrates - possibly an AQL type sampling, but have many concerns regarding
supplier lot quality, visual inspection efficiency, and product quality
requirements. Earl and I have been chatting about this for a bit now.
Another question, since I have your rapt attention... is it possible to
statistically equate lot quality (yield) to outgoing quality (yield)? In
other words, the supplier would have to produce product at xx% yield to meet
incoming requirement of yy% yield?
Best of the New Year to you all,
Jana Carraway
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of d. terstegge
Sent: Thursday, January 03, 2002 7:22 AM
To: [log in to unmask]
Subject: Re: [TN] Final Audit/Inspection
Hi Olivia,
You should be very happy if your inspection people catch more than 50% of
the defects. The remainder will simply be overlooked. This is not an
opinion, but it's a proven fact !!
It is just not possible to inspect quality into the product, instead you
should focus on the assembly process.
B.T.W. on my website I have some nice software available (it's a free beta
version) that may be helpfull for you with the inspection of the pcb's after
pick&place machine. The URL is
http://www.smtinfo.net/smtmaestro/smtmaestro.html
Daan Terstegge
SMT Centre
Thales Communications
Unclassified mail
>>> Olivia Mc Dermott <[log in to unmask]> 01/03 4:01 pm >>>
We do have inspection points throughout the process. The problem is they are
also missing defects and letting them through to final inspection.I wondered
if there is a direct instruction on inspecting.
1. you do this
2. you do this.
>From: Kathy Kuhlow <[log in to unmask]>
>Reply-To: "TechNet E-Mail Forum." <[log in to unmask]>
>To: [log in to unmask]
>Subject: Re: [TN] Final Audit/Inspection
>Date: Thu, 3 Jan 2002 08:49:32 -0600
>
>I would first start with some in-process sampling so you can pinpoint what
>types of defects the process is currently producing. Do you see more
>missing components from surface mount or do you have a problem withe solder
>shorts on the solder side because of wave issues or snapping problems.
>All to many organizations use a final inspection as a safety net. In my
>dream world I would have no one doing final inspection but bring it back to
>the process and do the inspection at the process through auditing by both
>production and quality personnel so immediate feedback can be accomplished.
> Otherwise you get data that is out of date and you can't really take
>effective corrective actions, especially if your world is as a CM or small
>run lots.
>
>If you must do a final inspection then we typically start with a complete
>part verification (value, polarity, AVL check) than solder (quality,
>quantity, lead placement) and finally any specific customer
>instructions(labeling, rev add, etc).
>
>Kathy
><< TEXT.htm >>
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