I once worked for Burr-Brown in the function modules group. We made the weird stuff: square and square root, vector adders, log amplifiers, and the like.
Mostly I worked on computing RMS modules. These designs were all based on monolithic pairs of transistors, and the same were used as the input stage of operational amplifiers. They were made by gluing a pair of transistors in a ceramic cup and bonding gold wires out to six leads. Then a dot of very hard epoxy protected the bonding wires. We sorted out the incoming parts for the ones with the best-matched characteristics for multipliers, so the function modules got the newest parts.
One day a line tech came by and gave me a box of expensive multipliers that had failed after potting. Normal loss was a percent or so -- this time about 40 percent failed. I don't remember exactly why I suspected the dual transistors, but after grinding down half a dozen modules, I found that the leads were open on one or more of the dual transistors. Snapping off the potting plastic let me read the date code on the edge of the cups. Three date codes had failures.
Eventually this was traced to a materials mixup where the hard epoxy had been replaced by a soft epoxy that moved under the stress of potting -- enough to shear off the gold leads.
It never occurred to me that I should ask before shutting down production to get the bad parts out of the flow. Months later, at a performance review, I found this was a strike against me.
Not long after that review, I moved on to a job at the long-defunct Arizona Gear and Manufacturing Co. There I was dismissed for refusing to certify thermocouple isolation amplifiers for 250,000 MTBF. There were parts in the modules stressed to where they would be lucky to last 2,000 hours (400mW on a 250mW resistor as I remember).
The timing was wrong (1972) for these modules to have contributed to the Fermi-1 reactor meltdown (1966). However, the failure of similar thermocouples on the top of the reactor core made it hard to see the blocking effects on the sodium coolant of a loose plate of zirconium.
This entry was submitted by Keith Henson and edited by Rob Spiegel.
Keith Henson is electrical engineer, a proto-transhumanist, and a writer on life extension, cryonics, memetics, and evolutionary psychology. He has published a Web-book, Standard Gauge, which takes the reader on an exploratory journey into the post-singularity, near-future technology of an artificial intelligence directed clinic in Africa.
Tell us your experience in solving a knotty engineering problem. Send stories to Rob Spiegel for Sherlock Ohms.
It happens sometimes! Even if we have a good knowledge about something but sometimes we miss something that make the whole module unsuccessful and we are not able to detect it for long time!
You're right, ClarkSammy, one small materials swap/SNAFU and everything quits working right. Like most Sherlock Ohms blogs, this is a difficult problem to detect.
So you are telling us that you were criticised first for stopping a line with bad product, then for failing to certify a bad product?
That has a LOT in common with all the Made-by-Monkeys tales about modern product reliability. This story says bad products may be more due to managment than engineering.
Good point Roddalitz. Makes one curious about how common a situation likes this is. From the description, management didn't seem too concerned about the product failing in use. I may have been pressure to make quota. Or it could have been management not understanding the potential repercussions of bad product going out the door.
At some companies, the pressure to get parts out the door can be intense. At one company I worked at, engineers had the power to sign off non-conforming parts as "ok to use," or to tell manufacturing to sort the parts on the line.
One day I was surprised to learn that an MIT-educated engineer had signed "sort on line" for some parts which I was sure couldn't be sorted. Measuring to find the non-conformance involved a destructive test. If you checked 100% of them, you wouldn't have any parts left to build with! What genius solution had he come up with?
"Oh, I don't know. I hadn't thought of that," he said. "Anyway, it's manufacturing's job to figure out how to sort the parts, not mine."
"Do you even know what the non-conformance you just signed off on was?" I asked him.
"No, I just sign these things when purchasing tells me to sign them," he said. "They told me production needed the parts, so I released them."
While this might seem like a gross abdication of professional responsibility -- what would have happened if purchasing told him to sign off 'use as is'? -- I couldn't totally blame the engineer in question. The processes which the company had in place, and the underlying corporate culture, promoted this kind of carelessness at every level. Everything was always someone else's problem, and nobody really thought very much about the consequences of their actions.
It was a little like the TV show "The Office," except instead of making paper products, the company made safety-critical vehicle components.
In my short time at the company in question, I was able to institute new quality procedures which improved the handling of non-conforming material, and also cut down on the amount of non-conforming material coming in the door. But changing the underlying culture would have been a Herculean task. And, unfortunately, I suspect that this culture is not confined to just one company.
I'm curious as to whether you received blowback from customers due to the sloppy quality control. Did any of the parts go out into the world and fail -- or at least fail to do what the part was expected to do?
@Rob: Yes, there were examples of parts failing in the field. Fortunately, they were less common than you might expect -- and even more fortunately, none of them (that I know of, while I was there) resulted in people getting hurt. This might be an example of the saying, "Fortune favors the foolish."
I'd rather not give any details of the failures for now, since it would be difficult to do so without giving away identifying information about the company.
I will, however, give one example of a quality system failure. Manufacturing was allowed to build assemblies using non-inspected components, provided that the assemblies were marked with pink tags which said "QUALITY INSPECTION IN PROGRESS - DO NOT SHIP." The assemblies were to be held at shipping until the component inspections were complete. If the components were found to be non-conforming, the assemblies would have to be taken apart. If the components were found to be okay, the quality department would remove the tags and release the assemblies to be shipped.
Inevitably, however, after completing the inspection, the quality inspectors would go to shipping and find nothing but a pink tag lying on the floor. The parts would have already been shipped.
At least once, the shippers didn't even bother to take the tags off, so assemblies were shipped to a customer with the "DO NOT SHIP" tags still on them. I'm still not quite sure how the sales team was able to explain that one.
That's funny about the tags, Dave. Ultimately, though, I would guess that parts failing in the field would be more costly than the cost of shutting down the line and restarting or having a shipment go late because parts had to be re-run to get them right.
Worst part is, this type of situation arises far too often. And it's usually frowned upon to inform management that if you choose to use this you will have a high number of service calls. And it's frowned upon to stop the line. And it's frowned upon to say this part won't work for this design. What is an engineer to do? thanks for doing the right thing. No matter what management thinks.
Sometimes it isn't a matter of doing the right thing. If the engineer does not have the power to stop the line or call for a re-design then doing the right thing may not be an option.
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