-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
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