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"The Shocking Truth", Apple's internal video about electrostatic discharge damage

I've just started to learn about electrophysics in school, so this thread came in with about the right timing.

Here in Norway we got quite humid air, and I have found that it reduces the risk of building up charge. However, I didn't know some components were that sensitive. In fact, I blew a transistor on a "MHz display" (from a pentium machine) not too long ago problably because of something like this. Perhaps this can be related to the EEPROM failures some of the XTIDE owners experiences?

I have not experienced zapping any chips before, but one factor may be that I'm usually working with my early IBM PC's, and old TTL chips seems to be more tolerant.
 
Ok I don't want to sound like an idiot, but what did he mean by "electrically float"? Did he just mean without contact with a conductor or ground?
 
So, if open air circulation itself, can create enough static to be harmful, was constructing this parts storage cabinet a bad idea? The goal here was to reduce humidity and avoid corrosion. Unfortunately, the only area I have available to use for parts storage can be extremely humid in the summer months.
 
I keep my parts in a tower of plastic drawers 9 high, in which the cards lay on top of one another unprotected and I've not had any immediate problems from this.. the video scared me, however. :/

I used to keep them alllll together in a pile.

We do keep our house at a neutral humidity though... perhaps that helps?
 
Raven said:
Ok I don't want to sound like an idiot, but what did he mean by "electrically float"? Did he just mean without contact with a conductor or ground?
Click to expand...

That's what it sounds like. I got this from Wikipedia, but that's no guarantee that it supports the "common sense" meaning of the phrase:

"A system where the system ground is not actually connected to another circuit or to earth (though there may still be AC coupling) is often referred to as a floating ground."

Sean
 
Electrically floating means it's not tied to anything electrically--there's an insulator between it and what's around it, whether air or bare fibreglass at the edges of the board.

So, here's what's happening in that situation. The board is generally at some fairly fixed level of potential. The novice carefully picks it up by the edges, to avoid a shock to the board. The are at a different potential to the board already, and haven't equalized themselves with the board. They then carefully hold the board out from their body and begin moving. Friction between the floor and their feet, and the air and their body, builds a static charge. Because their hand is stuck out from their body, the charge will be greatest between there and their feet across their body. The hand that's holding the board will be at some high level of potential, their feet the opposite, like a cap.

If they then discharge to the board, eitheer by now touching a conductive element or because the potential difference between them and the board is enough to bridge the gap of the insulating material, it'll be about as big a charge as they can get into the board. Say goodbye to FETs, A-series CMOS, and a lot of NMOS and PMOS.

If, instead, they had started out by first discharging themselves in the board's area to get close to its potential and discharge any big charges they may have built up getting there, brush their hand down themselves firmly to get rid of local charges on the hand, then firmly grasped the board by a ground trace, then spread their grip to an entire edge connector before lifting it, tucking it under their arm against their body and walking with it that way, the chances of a deadly charge are far less, and won't be made worse as they move.

Oh, and since the most common black dyes are carbon based, black clothes are good for more than looking cool. They'll keep the charges equalized across you like a resistive strap. Just keep your ankle strap on...and leave the circuits alone on cold windy days. ;)
 
Thanks for posting a link to those videos. Very educational. I can now understand why my PS/2 board stopped working when I washed it. It was probably the way I handled the board.

I will be a lot more careful in the future.

Tez
 
Raven said:
Ok I don't want to sound like an idiot, but what did he mean by "electrically float"? Did he just mean without contact with a conductor or ground?
Click to expand...

Hi
Yes, not connected.
The safe process of handling a board is:
1 . While holding a common grounded surface ( something electrically connected to the board )
2. Pick up the board, making sure that you are electrically connected to traces on the board
( best is power and ground )
3. Hold the board close to your body, not at arms length ( charges like pointy things like lightning rods
and out stretched arms ).
4. Put your other hand on the electrical surface of the destination of the board
5. While still in contact with the surface, put the board there.

A floating board is subject to induced charges but a board that is in contact with
a large body ( yours ) can't take on a charge relative to that body.
By touching the final surface, you drain off your bodies charge safely away from the
board.
If you want to make some good static cloths the where, take some cotton cloths
and don't put it through the rinse. The detergent will make it slightly conductive.
Dwight
 
I learned a few things from that, such as the pink anti static bags not shielding things from externally generated ESD.

I'm more amazed at how often poor handling doesn't result in failure. I often see boards and chips on ebay that are photographed while sitting on carpet. Even when I ask them to use an anti-static bag, they often ship it in peanuts, or regular bubble wrap.
 
Practice safe SEX (Static Electricity eXit).

Note that anti-static grounding leads have 1 MegaOhm or so of resistance built into them.
That's done for safety purposes. Not safety of the equipment, but safety of you.

Still, if I'm working on a live power supply or a live VDU, I won't wear an anti-static wrist strap (to protect what chips there are).
In that scenario, there is no way that I want to be grounded, or connected to a return path, even if there is 1 MegaOhm in the lead.
 
Yeah, 25kV isn't something you want a path to.

Once I was checking out a color monitor power supply. My benchtop housekeeping was a little lax that day. I'd left a roll of solder midships with the end of the solder pulled out and trailing over the edge of the bench. I powered up the supply, saw a good 25kV on it open-circuit, then reached over and hit the switch on my load box to test its regulation under load. As I did so, the anode cap popped off the fixture. The stiffness of the anode cable pulled it right into the roll of solder.

Guess where the end of the solder was hanging...

It hit me on the left thigh, I jumped left. Then it hit the right side. I jumped again. After 2 or 3 iterations I collected myself enough to switch off my low voltage DC supply.

I caught my breath about half an hour later, and ever since my "situational awareness" of my benchtop has been significantly enhanced.
 
andy said:
I learned a few things from that, such as the pink anti static bags not shielding things from externally generated ESD.

I'm more amazed at how often poor handling doesn't result in failure. I often see boards and chips on ebay that are photographed while sitting on carpet. Even when I ask them to use an anti-static bag, they often ship it in peanuts, or regular bubble wrap.
Click to expand...

I also read that the silver bags are the ones we want. I can't remember who in this thread keeps telling to walk with smelly boards under our armpits, but I think that's not good enough. My understanding is that the proper way to transport computer electronics with semiconductors is to remove them from a grounded computer (plugged in, turned off) while wearing a ground strap, put them into a protective bag, move or store them, then reverse the process as needed. If you're replacing bad chips, the board also needs to be on a grounded work station mat.

On a side note, I had the happy discovery that my EGA cards were actually stored away from the TV and in bags. Although I've got some memory boards that have been sitting next to the TV for a long time. It will be interesting to see if they work.

Sean
 
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