Fun with ESD! - show 178

Gomer_X · Post by **Gomer_X** » Thu Feb 08, 2007 11:01 am

On last night's show there was a short discussion of Electrostatic Discharge (ESD) and safety precautions (around the hour mark). I did a science fair project in High School on ESD damage to CMOS circuits (this was in the early 80s). At that time not much research had been done, but I can share what I know (I've read up some since then).

Static electric discharge has very high voltage, but very little amperage. The voltage of a discharge varies with the distance. It takes more and more voltage to jump the gap as the gap increases. I had a formula that gave the charge in volts per inch in gap, but I can't remember it. I accidentally took a 3 inch zap to my hand once and figured this was around 100 Kilivolts! One of the books I read said if you can actually feel a zap, it's at least 2000 volts.

I never determined accurately how much voltage it takes to do damage to CMOS, but the number is fairly small. It's possible to zap a chip and not feel it. It's also possible to do damage that is not apparent immediately. I had chips that worked fine, but generated a lot of heat after zapped. You can do little bits of damage here and there that add up and eventually result in a "mysterious" hardware failure down the road.

As big of a pain in the ass as it is, I bought a wrist strap ($7 at Radio Shack) and use it whenever possible. Keeping the box plugged in and touching the case is better than nothing, but you CAN do damage and not know it.

snarkout · Post by **snarkout** » Thu Feb 08, 2007 11:42 am

The problem is those radio shack straps are basically worthless if you don't have a ground source for them. Clipping them onto a case provides almost no protection for your computer, and does provide a nice path to ground for anything you might happen to discharge while dicking around in your box - through your heart. Now, obviously that's not a large risk these days, what with new power supplies requiring a crowbar and a sledgehammer to get into, but if you're working on an old crapbox like it seems a lot of folks around here manage to scrounge up somehow, you never know.

That said, I haven't even started the show yet - I'm still on last week's.

adam · Post by **adam** » Thu Feb 08, 2007 4:55 pm

haha, I opened this topic thinking, "How could the Enlightement Sound Daemon be fun?"

Vogateer · Post by **Vogateer** » Thu Feb 08, 2007 5:37 pm

And I thought I was the only one.

Gomer_X · Post by **Gomer_X** » Mon Feb 12, 2007 1:19 pm

Snarkout wrote:The problem is those radio shack straps are basically worthless if you don't have a ground source for them. Clipping them onto a case provides almost no protection for your computer, and does provide a nice path to ground for anything you might happen to discharge while dicking around in your box - through your heart.

Well, pretty much anything isn't going to work if you don't use it the way it was designed. I leave the box plugged in and clip the strap to the case.
The most voltage you're going to see inside the PC is 12 volts DC (as long as you stay out of the PSU). Anyone poking around inside the box should definitely know where the high voltage lines are and how to avoid them.