Photos of contaminated printed circuit boards
Late last month we posted Michelle Woolley’s article Gross causes of PCB failures, complete with pictures of ants and mosquitos in the most unfortunate places.
I asked for readers to send in their own stories/pictures. Here are the first few that have come in. Feel free to keep sending them and I’ll add them here.
Fuzz and Dust
Systems engineer Dean Severns sent in a picture of a failed power module that was returned from the field. It had been used in a mobile cart-based system. He reports that basic vacuuming returned it to operation. (The fan is actually outflow and not an inlet.)
Sloppy Workmanship
Benjamin Ford, a consultant for Sentry Group shared this story:
“One day a co-worker told me of his frustration with one of his automotive remote door lock fobs. After several years of use, it had started draining the button cell batteries in about three days, but it still functioned normally otherwise. He had appealed to the car dealer for help, to no avail. I offered to take a look, guessing that there must be a defective component or some other conductive path causing the problem. Fortunately, I had use of a USB microscope camera, and took pictures of the only anomaly I found on the circuit board – some white greasy goo smeared on and between a capacitor and a resistor. I cleaned the board up with some alcohol and an acid brush, and the fob has been working fine on the same set of batteries for the past two years!
“I don’t know what the substance was, but my guess would be some sort of contamination left over from manufacturing, as it was only found in that one area. It reminded me of conductive grease, but I’ll never know for sure. I see a lot of circuit boards in new products, especially from Asia, literally coated with a film of dirt and detritus because they couldn’t take the extra time for a proper cleaning. The long-term cost of cheap electronics is the loss of reliability, but we all are betting that this type of failure won’t occur before the warranty expires! After that, sadly, the product is disposable.”
Moon Mission Hoax?
Mike Hanchett shared some photos of the inside of a computer that was used in an auto-body shop. The first is the before, the second is the after, and the third is some fun Mike had with the image on Photoshop, suggesting that the computer had been used to perpetrate a hoax of a moon walk.
(Note the astronauts in the top right corner of the image.)
Avoiding “Bugs”
On a more serious note, Rob Putala, senior systems engineer at Bloomy Controls Inc., shared this observation for a way to avoid contamination problems at the door: “At a previous company, yields were improved by re-implementing ROSE testing – Resistivity of Solvent Extract at incoming inspection. Some critical PCBAs used by that company had very-high-gain circuits which would oscillate or show other odd behavior due to insufficient cleaning of flux. The amount of flux residue needed to affect a high gain circuit operation is surprisingly small – as measured by a ROSE test. Perhaps humidity increased the affect of the slight flux residue. All I am sure of is that some PCBAs were completely cured of their ills after a ROSE test, which washes the assembly thoroughly. Tracking of suppliers’ products cleanliness improved first pass yields on many products.”
