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December 2004

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Subject:
From:
Judy Rae Brown <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, [log in to unmask]
Date:
Wed, 8 Dec 2004 17:25:40 -0800
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Where do I find the dimension for the spacing between a press fit connector
and other components?

-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Steve Mikell
Sent: Friday, November 05, 2004 12:04 AM
To: [log in to unmask]
Subject: Re: [TN] Process Indicators...


-Steve Gregory wrote

I look at Process Indicators as a "Flag" to investigate whether or not the
issues can be addressed and resolved properly, if they can't be resolved,
then it's not a defect. Am I wrong about this?


Steve, Wrong is not the best choice of words for a situation like this,
IMHO.

We need to reflect on PIs from a couple of different philosophical angles.
The original use of PIs also required the complimentary use of a process
control plan that was preventing things from running amuk. The PIs provided
a degree of relief in exchange for better process control.. and added this
third level of quality (accept, PI, reject). As we have all noticed, most of
the people raised in the "before world" of black and white have trouble
understanding gray.

What we engineers forgot was the original dynamic on the production floor. I
experienced this dynamic in a dramatic fashion when I arrived at a factory
in 1988, just after they converted from hand solder to wave solder. Because
the wave solder joints were not as beautiful as hand solder joints, many
operators touched-up 100% of the joints. The major impediment to shipping
was massive amounts of lifted pads from excessive rework! The dynamic in
play here was caused by the operator's supervision. If you sent boards to
inspection, and they came back, you got a visit from your supervisor asking
what your problem was.

So there we have it. Two requirements, one measureable, one not. If I rework
a gray area or minimum solder joint, nobody ever knows but me. If I let it
go, and the next guy rejects it, I get a board returned, my department gets
dinged, the event is recorded in the data that goes to the quality round
table, the plant manager can ask who the defective people are that are
letting these defects slip through, and I can get canned. I think I'll just
sit here and do some mighty fine solder sculpting until everything is
beautiful, in it's own way (thank you, Ray Stevens).

No wonder we have a hard time getting people to understand PIs. They don't
want to cut their own throats.

One solution is to have inspection preceed touch-up, create a sheet showing
all the defects and PIs, and then reinspect the boards after touch-up\2nd
hand solder operations for reworked joints and added parts.......
That worked until some bright manager decided that the NVA (that's Non-Value
Added) headcount ratio in our factory was too high according to the latest
MBA theories. Then we made the inspection function a line operation and went
to sampling (this also increased inspection from "100%", to "100% plus
sampling", which has to be cheaper!!). Then they started inspecting their
own work. Then we were back to our pre-wave solder days. Nobody wanted their
lots rejected at sampling, or pre-ship lot sample.

The PI was, and is, still a potential ally in this mess. I tried to get
operators, inspectors and QE's to use the PI as an indication that they saw
the condition, determined that it was sufficient, and moved on. It was not a
"missed" defect. If the inspector disagreed with the PI call, it required a
QE referree decision. This made people think before they just got obtuse and
started rejecting stuff.

This then changed the nature of my job as a process engineer. No longer
could I simply stop when my process created an accaptable product, but I
needed to create a process that produced product that was clearly acceptable
(zero PIs). Inspection, test, rework, handling, are all wasted money, and my
job is to create the process that minimizes their impact on company profits.
It also raises the quality, reliability, on-time delivery and customer
satisfaction.

PIs can work. They work best when a seperate inspection preceeds the
touch-up. They work best when the buy-off department also does the first
inspection. It also works better if line supervision, middle and upper
management are "informed" of the concept, buy into it, and don't beat-up the
operators.

Oh, one last thing. Sorry Jack, but fewer PIs is not better. Every defect
(almost) should have a PI. The PI should replace the referree decision. Any
condition that can cause two people to disagree, should be called a draw,
marked a PI, and everybody move on. I will then take the data, distill it to
find workable issues, and make every effort to have the next batch free of
these minimal accaptables.

ok, gotta stop now, hand cramps, gotta breathe now.....

Thanks for reading this far...  good luck!

Oh, one last thing. I started with PIs when life was still mostly thru-hole.
The circuit board protected the components from rework damage, for the most
part. PWB damage could often be repaired. Now that the world is mostly SMT,
this is far more important. Now the soldering iron is in direct contact with
the component, and the chance of doing something bad is much greater. Then
there is also the unreated no-clean flux residue issue as well. My lack of
warm fuzzies is really putting a drag on my karma.

Steve Mikell
[log in to unmask]


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