Its 3:55 p.m., and I'm just a few seconds away from turning off the O-scope, detaching my ESD strap, and hanging up the alligator clips. Suddenly, the door to the electronics lab opens, and who do I have the pleasure of seeing, standing in the only doorway in and out of the lab? It's the boss. Not just any boss, but a boss holding a drink in his hand getting ready to leave and to tell me to stay just a tad bit longer. A boss who is asking me to stay because someone needs just one more prototype built to show the customer the next morning.
Now, any electrical engineer knows that the typical boss with no knowledge of electronics believes creating a hand-built circuit board can be done with the wave of a soldering iron. Ha. How many times have we created the perfect circuit that still didn't work? One hour to everyone else is five hours in EE terms.
I flip the scope back on, heat up the soldering iron, and lay out the components. I hear all my coworkers leaving, lights being switched off, and my stomach growling as I get hungrier. I begin to build. This time, it isn't quite as bad as it is sometimes. This particular circuit has only 22 parts, the largest and most complicated being a quad op amp. The night is still young, and there is still hope for a nice dinner.
Well, as most of us EEs know (and as I previously hinted), nothing ever goes right the first time around. Remember, one hour to everyone else is five hours to an EE.
A couple of hours pass, and the last leg on the op amp is soldered down. All components are double checked, and the layout is compared to the schematic. All looks good. The three-foot power cord with alligator clips is connected, and power is applied. The circuit is working -- 120Vac in, 12Vdc out. There's the 5V signal, and the lights are working. It's time to wrap it up.
Just as I'm getting up to stretch and clear the solder fumes from my head, something tragic happens. Remember the drink the boss had in his hand? Well, it's sitting on the top shelf of the lab bench. The drink gets bumped by the three-foot power cord, and, in what seems to be slow motion, I see the drink gracefully fall over and pour its contents on the only spot on the workbench where it's not welcome. It pours on the freshly built circuit board, which is still warm from the half roll of solder used.
After a few words that would not be recommended for saying during normal business hours, I grab the circuit and begin blowing off the drink. Now, in a twist of fate that shows the universe has a sense of humor, this drink is an RC soda. This is not the RC I prefer to have next to my op amp.
After several minutes of drying off the circuit, I notice that, though seemingly dry, it is still sticky. Worried that the sticky soda deposits may be conductive and damage the circuit, I apply a little water to a cloth and pat down the circuit. After drying the circuit with a fan, I hesitantly repower the circuit while holding my breath and crossing my fingers. Nothing blows up. All the voltages are just right. The sensor is working, and the lights are on. Tragedy has been sidestepped. Or has it?
The next morning, I immediately go to the lab to check on the circuit. I look it over and power it up again. Oh, no. It's not working. The power supply is working mostly. The 12Vdc is there, but no 5Vdc. What is going on?
After pondering a bit and testing the op amp, I determine that it's not functioning. It has small white deposits on the black epoxy housing and possibly some hard water stains on the leads. I replace it and catch a break. Everything seems to be back on track. It now works. So why did the op amp work last night after the tragic RC spilling, but it did not not work after sitting overnight? Is it possible the minerals in the dried water created a short? Is it possible mold grew in the tiny pores of the op amp device and short circuited it? What made the op amp go bad?
Here is the twist: It isn't long before I notice several of our sensors using the same op amp on other boards are either not working or working incorrectly. I didn't dump RC on every board we received, so that wasn't the problem. After a couple of weeks of testing and tracking date codes and lot numbers, and multiple overnight teleconferences and meetings, I come to the conclusion that we received a bad batch of op amps. They aren't just bad -- they're counterfeit.
With my trusty $2 magnifying loupe, I find some slight font differences on the manufacturing markings between a known good op amp and the bad op amps. I take a trip to the local hospital to do an X-ray on the good and bad op amps, and I find they were constructed totally differently. The bad ones had several large voids inside.
Did the RC or the water cause a failure? Nope, that was just a coincidence. And we know that correlation does not imply causation. It was actually due to fake parts. Since it focused my attention, in the end, perhaps putting an RC in front of the op amp was a good thing. Ha.