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Electrostatic Discharge

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January 11, 2008 2:06:32 AM

i took out the power supply from my computer and left it on a floor with no carpet. the computer with a hole in the case, also is on the floor. i've brushed both with my pants and socks a couple times while walking around my room. did i do any damage, even if not noticeable, to either? thanks.
January 11, 2008 2:43:22 AM

......Uhm, turn it on?
a b ) Power supply
January 11, 2008 3:00:52 AM

I'm 99% sure you didn't do any damage. In fact, touching the case is a good way to protect the parts from electrostatic discharges.
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January 11, 2008 3:09:51 AM

ESD is the most over hyped piece of bunk out there. The chance of an actual discharge is very small. The chance a discharge that actually does damage is even smaller. I've worked for several years in pc hardware (actually worked, as in 40 hours a week fulltime employment, not just as a hobby) and I've never seen an ESD that caused damage. For one the parts that would actually be affected by a discharge (CPU pins, memory and expansion card contacts) should not be being touched in the first place. Most the time that an ESD occurs it's either going to a part that is grounded like the case or to something that can easily handle the voltage without harm. Having your PC like that is more risky in that you could trip on the PSU or it's cables and fall on your computer or knock it over. Or in my case with my PC open there's a much greater risk that my dog will stick her face in and start chewing on something. But like jbj said, just turn it on.
January 11, 2008 3:38:28 AM

purplerat said:
ESD is the most over hyped piece of bunk out there.


I think not. I worked at a contract electronics manufacturing facility where they assembled printed circuit boards and computer assemblies. They went to considerable expense to train everyone about ESD - even office staff that might be in the manufacturing area - and proper handling techniques. I doubt they would make such a big deal of it and incur the expense if it were all hype.

When you are outside the case or handling devices like PSU, the risk is nil. But when handing pc boards with exposed circuitry there is a real risk. Much of it can be minimized by working on the proper surface and with proper handling techniques; then I don't think it something to worry about. But get sloppy and you could have a problem. Even with a small risk, why take an unnecessary chance of needlessly damaging components? The worst situation could be damaging a component without knowing it and then spending hours - or days - trying to diagnose the problem.
January 11, 2008 10:26:12 AM

Although I work in IT and have done for 10 years I do not regularly mess about inside PCs, rather it is something I do from time to time.

I have seen ESD killing components before. One time I even saw the blue spark pass between a friend's finger and circuit board. I've just built myself a brand new PC and I can tell you I made damn sure I was wearing an anti-static wrist strap when handling hundreds of pounds of my own components.

Thing is most of the time you likely won't see or hear ESD if it does occur, you'll just witnessing a dead component and assuming it was dead on arrival or something like that.
January 11, 2008 10:52:00 AM

Hi all!!

Although input CMOS transistors usually have some ESD protection this will undoubtedly not be present throughout a circuit (the protection will provide a way for the gate to discharge when at too high a potential).

CMOS transistors have a very high gate input resistance and a relatively high (parasitic) capacitance on the gate as well. When you run your hand along the carpet/cat whatever (I don't want to know :pt1cable:  ) and accidentally brush against a gold finger on a card or a solder joint on a MB you instantly raise transistors connected to that joint to 10,000's volts (by charging the parasitic capacitance) this can easily blow the transistor before the charge will leak from the gate. By grounding yourself you ensure that you are not going to being carrying any charge on the surface of your skin!!

Anyone commenting on this subject saying that 'ESD protection doesn't matter when handling £100.00's worth of home PC equipment' is talking bullshit... Especially if they have not done a proper Electronics course or degree (like myself)!! Why do you think all PC components come in special anti-static bags!! :hello:  A basic wrist strap is only going to set you back £5.00....

Bob
January 11, 2008 11:25:53 AM

ESD is a major problem cross the electronic equipment field since the componment get smaller, it may not kill it right way , but it can causes some serious damage, the pc may develop some random problems, and worse all is you may never found out.
January 11, 2008 1:42:26 PM

Why ESD damages/kills electronics:

(DISCLAIMER: this explanation is not intended to be taken as gospel truth - I am qualified in the electronic engineering field, quite highly in fact, but almost all of my electronics experience is in the heavy industrial field, particularly automation, where ESD isn't much of a concern due to the components used being of the Extra Heavy Duty variety)

Let us assume we're dealing with a single BGA chip from a stick of DDR2 SDRAM. Inside this chip is a tiny fragment of silicon with delicate little paths etched into it. The chip is connected to the pins using little wires that are somewhat thinner than a hair.

Electric current such as these components normally deal with is 1.8V (approx) in a steady stream for the power carriers and in short pulses for the data carriers. These short pulses come in through heavily filtered power supply circuitry, so the transitions tend to be fairly smooth.

A static discharge is similar, only instead of a pulse measuring just under two volts, it's a pulse of a few thousand volts plus. (NOTE: the most instantly recognisable form of ESD would be lightning, well known as a weather condition)

There are several electronic equations dealing with the above - we're mainly concerned with V=IR and P=IV.

V = Volts (voltage). I = Amps (current). R = Ohms (resistance). P = Watts (power). (NOTE: most numerical values assigned to variables are not verified)

Now, you have 1.8V = .05A x R. Solve for R. Our resistance on one of these tiny conductive paths and/or wires would then be 36 ohms.
The amount of power going through this path would then be:
P = IV; P = 0.05 x 1.8; P = .09W, most of which is lost in the form of heat.

Now let us assume that we've got a static discharge thundering through that same BGA chip: using V = IR and arbitrarily assigning 2,500V to V (which is a very conservative estimate) we end up with 2,500 = I x 36, so we've got about 70 amps (69.4 recurring to be precise) thundering through a path designed for no more than 0.05A. Using the P=IV equation we get a total of 173,611.11W - admittedly for an infinitesimal fraction of a second, but still long enough to inflict severe-to-fatal harm on any microcircuitry it passes through.

To condense most of the above: When ESD hits RAM, the circuit paths and/or connector wires inside the chips melt.

ESD is not bunk. It doesn't always happen due to the conditions required for it to happen being pretty specific, so some people are just incredibly lucky. Often it will happen, but the voltages generated are usually too small to do any damage. The zap you get when you touch a doorknob, for example, might weigh in from a fraction of a volt to anything up to about 15,000V+.

The scary part is that I had to look none of this up.

Hope this helps...
!