ZAP! Another ESD Casualty

DN Staff

June 5, 2013

3 Min Read
ZAP! Another ESD Casualty

Early in my career as an electrical engineer, I became very familiar with the Electro-Static Discharge (ESD) bugaboo. I was testing a 64K x 64-bit DRAM circuit card in the test lab. I had the card on an extender, standing it up out of the metal chassis. When I reached over to probe the board with an oscilloscope probe, I felt the uncomfortable zap of a static discharge. When I again ran the memory test, one of the bits was stuck high.

This was in the days before ESD control wrist straps, ESD control mats, etc. The lab had a waxed linoleum floor and the workbenches were steel, covered with Formica. By the technology of the day, one would think the chances of static discharge were minimal. It was winter, and I was wearing a light sweater. Also, most commercial buildings of this type have electric strip heat and no humidification, so it really was a perfect storm scenario for ESD.

Since this failure was for a military application, our reliability team got involved. We changed the affected DRAM chip. It was easy to locate, as it was the one I touched when I felt the zap and the reliability team absconded with it. They had it embedded in epoxy, sawed the lid off, and readied it for analysis. When it was inspected under a microscope, there was the telltale indicator of ESD. Envision, if you will, the famous meteor crater in Arizona. That is exactly what ESD damage to an IC substrate looks like under a microscope.

I guess I had the dubious honor of being the cause of my company adopting rigorous ESD controls. All work areas were covered with ESD control mats, and they were grounded. All circuit cards were bagged in those smelly, pink plastic bags. Everyone was required to wear wrist straps. We were even given funny light blue lab coats to wear. Also, the wrist straps were required to be tested every three months.

Fast forward to 2013. My sons and I were participating in the Easter play at my church. On the night of the last performance, I brought my camera (one of those $100 video/still cameras with the fold-out LCD screen). Our costumes were of synthetic materials and the relative humidity in the building was in the 30 percent range (as it was rather cold outside). I set up the camera, and when my son reached over to grab it, I felt a zap!

He took a picture and then he said, "Dad, look at this!" With a sinking feeling in my stomach, I looked at the camera display as it began to pixelate, turn white, and then go blank. The flash worked for a couple more shots and then it, too, stopped. I haven't tried it for a couple weeks, but more functions may have died in the interim. At the very least, it will be very difficult to page through all of the settings in my mind, since the display is dead. Time to get a new camera, I guess.

This entry was submitted by Dwight Bues and edited by Rob Spiegel.

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