ESD: Truths, myths, and flat out lies

Ockie said:
Laying your motherboard down on a AS baggie wouldn't do it any harm from coming into contact with the surface below, however, it doesn't act as any grounding agent if you are working on it. Perhaps clarify this sentence a bit more so people know. Putting your board on a ESD bag is a much more sound practice than not using any at all.QUOTE]

If you take a metalized ESD bag apart you will find the metal film layer is inside, or is sandwiched between two layers. Therefore setting your board on top of an ESD bag does nothing to protect it from static.
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Let me rephrase this in an even simpler to follow way:

The only time an ESD bag works, is if the item being protected is completely wrapped inside the bag. The bag acts as a cage to prevent ESD from entering the item.

Setting a component ON TOP of a bag does it no good in any way shape or form. It is no better than setting your parts right on top of the carpet. ESD can and WILL go right around the bag to the components. You MUST have the parts INSIDE the bag.
 
Here's a PDF file about ESD bags. Don't really understand everything that's in there, but they say shielded bags are the ones best used.

If you look at figure 7, it says that metal-in shielded bags have an anti static coating on top. Shouldn't that be a good thing for when you put something on top of it?

Construction: Static Shielding bags consist of several layers. From the interior to the exterior the layers are: dissipative poly laminated (glued) to metalized polyester. The outside polyester has an antistat coating. The metal is vapor deposited in a vacuum chamber. Aluminum is the metal most used in this process, with nickel and copper also being used.

This structure of a shield bag, with the metal between two layers of plastic, is called "buried metal" or "metal-in".

In a "surface metal" or "metal-out" structure, the poly is laminated to the polyester with the metal on top. There is an abrasion coating on the metal. The metal generally used is nickel and it is sputtered instead of vapor deposited. See figures 7 and 8.

An antistat is a chemical that makes a surface able to resist charging. Most antistats, when applied to plastic, attract water (humidity) from the air creating a moisture layer on the surface of the plastic that can conduct electricity. Some more modern antistats contain different chemical arrangements that carry their own water with them. A combination of these chemical antistats is also used.
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An anti-static coating just prevents static from buiding up on it. It does not prevent a static charge from going through it, for example from your bed to the component.

Let me say this AGAIN. In order for an ESD bag to work, the parts must be INSIDE the bag. Also, the bag mnust be sealed.
 
So even though it's anti static, the ESD gets conducted through that top layer, right to the device?

edit: Okay, it seems you replied while I was busy typing mine. Thanks!
 
What about my comment on packaging materials and peanuts?

Also, I still don't believe putting your board on the baggie vs putting it on anything else is as bad as you are claiming it to be as at some point you have to put the board down on some surface..., you can't exactly work on your board when it's sealed inside of the baggie. In this case, what surface would you recomend to place your board on if you can't place it on the baggie even?
 
Ockie, I think you need an ESD bench mat for it. I too am not sure how to use these things properly, that's why I made a thread about it. :)
 
Question: How safe is to put a PC on carpet while its case is closed and it has no wires connected to it (including no grounding)?

Someone did this with one of my older desktops, and now I'm a bit concerned. Its bottom is made out of metal, the rest plastic.

:(
 
By the likelyhood that some electronic equipment inside the case can be damaged by ESD?
 
The foam mat the MB comes on should be safe. I've been using that for years and never had a problem. But I absolutely never put my motherboard or any other hardware right on something that I know has a static charge, carpet, bed, etc.
 
mikeblas said:
As a ratio, then?
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4 in 20 ;)

btw, regarding the bag thing, esd protection materials also work by keeping everything at a common potential. Chips placed in esd protective foam work this way. So it's not all about keeping esd out so much as it is keeping everything inside the same... A subtle but important point...

And you may have seen my post in the long winded thread showing my esd defying wall mount pc, still going strong after all these zaps...
 
I don't get it. :eek: Let me rephrase: can putting a PC with its case closed on carpet cause ESD damage to its internal components?

Come to think of it, I've done this a couple of times in the past. Not components though, only cases (with components in them).
 
If the case is plugged in (grounded through the 3rd prong on your power cord) then there is a place for the ESD to travel to. The metal shell of the case acts as the cage around the components. That's why each and every standoff has a grounding point on the motherboard, and why there are so many black wires on a power supply. There's approximately 1 ground for every power wire (+ or - a few), and why each device has at least 2 grounds (floppy, CD, hard drive, USB, SATA, etc....)
 
And what if the PC isn't grounded?

You know, for a subject that everyone who swaps hardware or builds PCs should be aware of, it's really difficult to find useful information about that I can actually understand. I've spent hours and hours searching and reading about ESD and I've only still learned a handful of things. On top of that, basic ESD protection equipment seems hard to come by where I live (Europe).
 
Perhaps you're thinking of it the wrong way, TomMe. You shouldn't be trying to analyze how likely damage is. Either damage is very unlikely -- when you've taken appropriate ESD precautions; or, it's likely -- when you're not.

If the PC isn't grounded, then I'd say it's at risk. If you're not following ESD precautions while handling components, you're putting them at risk.

That's really all you need to know.
 
I'm just trying to analyze to get a better understanding of what I can do to minimize ESD. So far I get the basics, but the details are still elusive.

Btw, I don't think that just knowing something is at risk by not taking appropriate precautions is really helpful if you don't know what those precautions are. :p But I'm sure you didn't mean it that way.
 
TomMe said:
I'm just trying to analyze to get a better understanding of what I can do to minimize ESD. So far I get the basics, but the details are still elusive.

Btw, I don't think that just knowing something is at risk by not taking appropriate precautions is really helpful if you don't know what those precautions are. :p But I'm sure you didn't mean it that way.
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my PC has been on carpet for the past 5 years.. no problems..
 
Essentially, if your PC is not grounded, and you place it on carpet, then there is a chance that ESD can occur and can possibly damage your components. It would be highly unlikely.

Most of your components are designed so that current flows toward the ground direction. The case is one of the last layers between your circuitry and the ground. Applying electrons to the case would be unlikely to damage circuitry as it seems the case itself would be at a lower potential than the circuits. As such, the flow of current would be from the carpet to the case, and no further.

I'm not an EE though, so if I'm wrong about this, let me know.
 
Here are some quotes from page 1:

gee said:
EE here :D earth ground is ideal, but in situations where earth ground isn't available the goal is to get everything at the same potential so current from ESD can't flow where it shouldn't.

Grounding yourself to your case without an earth ground still puts you and your computer case at close to the same potential, and that's what matters. An earth ground is better (especially when you're touching other stuff) but it's not absolutely crucial.
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Ice Czar said:
and religously touch a bare metal surface in the case to ground yourself when swapping componets (this is very typical in here with enthusiasts)
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So if I combine these 2, then touching the case would be a decent precaution. Even when I'm carrying a couple of 1000 volts compared to the case? If so, then what is the difference with putting the case on a piece of carpet? The carpet (perhaps) holds a charge, but doesn't even conduct (I think).. What am I missing here?
 
MjrStryker said:
Essentially, if your PC is not grounded, and you place it on carpet, then there is a chance that ESD can occur and can possibly damage your components. It would be highly unlikely.

Most of your components are designed so that current flows toward the ground direction. The case is one of the last layers between your circuitry and the ground. Applying electrons to the case would be unlikely to damage circuitry as it seems the case itself would be at a lower potential than the circuits. As such, the flow of current would be from the carpet to the case, and no further.

I'm not an EE though, so if I'm wrong about this, let me know.
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the point of grounding a case is so that the case is always at a known potential... if it weren't grounded.. then the case is free to pick up charge relative to ground, and discharge somewhere (possibly causing damage)

grounding doesn't gaurantee ESD protection though.. but i'm sure most of you know that.. if you pick up a chage relative to ground.. and you touch your grounded case. there will still be discharge between you and the case... just hopfully not as much
 
RancidWAnnaRIot said:
grounding doesn't gaurantee ESD protection though.. but i'm sure most of you know that.. if you pick up a chage relative to ground.. and you touch your grounded case. there will still be discharge between you and the case... just hopfully not as much
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And the ground gives the excess voltage a safe place to go. Voltage is like water. It looks for the place with least resistance.
 
And now with the inductive logic founded on an irrelevant assumption. It's uphill both ways, in some of these threads.

TomMe said:
But I'm sure you didn't mean it that way.
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I don't know what you do or don't know. Your original question was about the odds of damage occurring, which are very hard to set.

Earlier in this thread, I linked to the ESDA. On their site, the Basics of Electrostatic Discharge article provides an approachable overview about ESD management. It's aimed at manufacturers, so a few sections won't apply to computer hobbyists.

Device manufacturers will provide instructions, as well. Intersil's are getting old, but are quite easy to understand.
 
It is not the ESD in itself that is going to affect your circuitry but the rate of discharge. Most electronic chip makers suggest that you ground your system through a resistance so the built up charge dissipates at a slow enough rate & does not cause sparking or undesirably high level of current. You may have noticed sparks when touching a door knob after walking on a synthetic fiber carpet during dry winters.

Your best bet would be to work bare feet in the basement without any carpet (stone floor) & place your work on well grounded medium conductivity workbench.
 
pmshah said:
It is not the ESD in itself that is going to affect your circuitry but the rate of discharge. Most electronic chip makers suggest that you ground your system through a resistance so the built up charge dissipates at a slow enough rate & does not cause sparking or undesirably high level of current. You may have noticed sparks when touching a door knob after walking on a synthetic fiber carpet during dry winters.

Your best bet would be to work bare feet in the basement without any carpet (stone floor) & place your work on well grounded medium conductivity workbench.
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Such as an ESD mat. Rubber, cardboard, and other insulators will not work. Metal and other conductors will not work. It must be a semiconductor material.

This is why tying a wire around your wrist and sticking in a grounded outlet will not work. It also poses a HUGE electrocution hazard. The ESD wrist straps have a resistor inside them that turns them into a semiconductor, as well as acting as a fuse in case of malfunction.
 
SarverSystems said:
The ESD wrist straps have a resistor inside them that turns them into a semiconductor, as well as acting as a fuse in case of malfunction.
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A resistor that turns into a semiconductor, huh? What makes it magically turn into a "semiconductor"? Does it ever turn back into a plain old resistor? How long does that take?

A fuse? With what approximate rating?

SarverSystems said:
It must be a semiconductor material.
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What must be? The mat? What kind of semiconductor material would you recommend? Gemanium? Silicon? Gallium arsenide? Aren't they all too brittle to make a mat?
 
mikeblas said:
A resistor that turns into a semiconductor, huh? What makes it magically turn into a "semiconductor"? Does it ever turn back into a plain old resistor? How long does that take?

A fuse? With what approximate rating?
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LOL!! i'm glad you posted.. cause i was like WTF?!

lol a wrist strap just keeps you at the same potential as teh case.. it doesn't aloow a charge different to occur between you and the case... i know you know that mike, i'm just saying this in general...

you can't go wrong with a wrist strap though.
 
Wrist straps (and heel clips, and good mats, and so on) do have a resistor. It's just a resistor. Directly grounding one's self gives a direct path through the body to ground. That means if you come in contact with a high voltage, current will flow through the body to the grounding point on a path with no resistance.

Professional static dissipation equipment uses a very large resistor; usually, one-megohm or so. This severely limits the amount of current that will flow. The idea is to let any static charge dissipate, bringing the user to the same potential as ground safely. And that also means you have to wait a few seconds before handling components after putting on your strap. But it also offers a very high resistance, practically eliminating the possibility that a high voltage source will generate enough current through the body to be harmful on its way to ground.

But SarverSystems apparently knows differently, and I'm very eager to hear his explanation of this magic, sometimes-semiconductor, sometimes-fuse, usually resistor, component. Where can I buy a box of 'em, and how much do they cost?
 
mikeblas said:
But SarverSystems apparently knows differently, and I'm very eager to hear his explanation of this magic, sometimes-semiconductor, sometimes-fuse, usually resistor, component. Where can I buy a box of 'em, and how much do they cost?
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they're very expensive i'm sure :D
 
mikeblas said:
Wrist straps (and heel clips, and good mats, and so on) do have a resistor. It's just a resistor. Directly grounding one's self gives a direct path through the body to ground. That means if you come in contact with a high voltage, current will flow through the body to the grounding point on a path with no resistance.

Professional static dissipation equipment uses a very large resistor; usually, one-megohm or so. This severely limits the amount of current that will flow. The idea is to let any static charge dissipate, bringing the user to the same potential as ground safely. And that also means you have to wait a few seconds before handling components after putting on your strap. But it also offers a very high resistance, practically eliminating the possibility that a high voltage source will generate enough current through the body to be harmful on its way to ground.

But SarverSystems apparently knows differently, and I'm very eager to hear his explanation of this magic, sometimes-semiconductor, sometimes-fuse, usually resistor, component. Where can I buy a box of 'em, and how much do they cost?
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A resistor is a semiconductor, is it not? I might be using the incorrect terminology, but the principle is the same. I am stating exactly the same things you guys are saying.
 
SarverSystems said:
So if I apply 110VAC at 10A to an 1/8 watt resistor, it's not gonna blow?
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I'm not sure how that's relevant; has ESD measured at 110 VAC at ten amps? I don't think it has, and wonder why your quesiton is relevant to this discussion.

But let's analyze your hypothetical. To get anywhere, we have to figure out what your scenario is really about. Since you don't tell us the value of your resistor, we can't guess if it is conducting enough current to exceed its ratings. A one meghom resistor with 110 volts through it is only seeing a tenth of a milliamp of current, and only dissipating 11 milliwatts -- safely less than its 125 milliwatt rating.

So we have to assume that you're thinking of an eleven ohm resistor, which would allow approximately 10 amps of current to flow when connected across a 110 VAC supply. 10 amps at 110 volts is 1100 watts, vastly exceeding the eighth-watt limit of your resistor.

How is this current applied to the resistor? Continuously and immediately? For a few minutes? Seconds? Microseconds? Gradually, or suddenly?

Will it blow? Nobody knows, since your hypothetical question is missing some parameters. So let's further assume that you meant this large current was sudden and continuous. Given that, I'm sure the device will eventually fail.

But how will it specifically do so? Vendors don't intend resistors for use as circuit protection devices. Since the device's failure mode can't be predicted, a competent and responsible engineer doesn't use them where they want to have something that opens the circuit in response to a higher-than-expected current.

Instead, a competent and responsible engineer uses a fuse or a circuit breaker. These devices are designed, tested, and certified for such applications. They interrupt the circuit in a predictable amount of time without catching fire, damaging the surrounding components, emitting fumes or shrapnel, and so on.

A resistor offers no such predictability. It might fail and leave an open circuit, but not quickly enough to protect the device or circuit. Or too quickly, causing the device to fail in response to brief, transient currents. It might fail and catch fire, damaging other components or the hurting the user or its environment. It might leave a closed circuit and operate intermittently or eratically.

I hope that answers your question--though I'm not sure what you're asking about. Do you think that a fuse is a semiconductor because in one state it does conduct electricity, and in another state it doesn't? And you thought a resistor was a semiconductor because it could sometimes act like a fuse, "blowing" if it was subject to too much current for too long, and therefore was also a semiconductor?

How did you get from that to thinking ESD mats are semiconductors?
 
mikeblas said:
I'm not sure how that's relevant; has ESD measured at 110 VAC at ten amps? I don't think it has, and wonder why your quesiton is relevant to this discussion.

But let's analyze your hypothetical. To get anywhere, we have to figure out what your scenario is really about. Since you don't tell us the value of your resistor, we can't guess if it is conducting enough current to exceed its ratings. A one meghom resistor with 110 volts through it is only seeing a tenth of a milliamp of current, and only dissipating 11 milliwatts -- safely less than its 125 milliwatt rating.

So we have to assume that you're thinking of an eleven ohm resistor, which would allow approximately 10 amps of current to flow when connected across a 110 VAC supply. 10 amps at 110 volts is 1100 watts, vastly exceeding the eighth-watt limit of your resistor.

How is this current applied to the resistor? Continuously and immediately? For a few minutes? Seconds? Microseconds? Gradually, or suddenly?

Will it blow? Nobody knows, since your hypothetical question is missing some parameters. So let's further assume that you meant this large current was sudden and continuous. Given that, I'm sure the device will eventually fail.

But how will it specifically do so? Vendors don't intend resistors for use as circuit protection devices. Since the device's failure mode can't be predicted, a competent and responsible engineer doesn't use them where they want to have something that opens the circuit in response to a higher-than-expected current.

Instead, a competent and responsible engineer uses a fuse or a circuit breaker. These devices are designed, tested, and certified for such applications. They interrupt the circuit in a predictable amount of time without catching fire, damaging the surrounding components, emitting fumes or shrapnel, and so on.

A resistor offers no such predictability. It might fail and leave an open circuit, but not quickly enough to protect the device or circuit. Or too quickly, causing the device to fail in response to brief, transient currents. It might fail and catch fire, damaging other components or the hurting the user or its environment. It might leave a closed circuit and operate intermittently or eratically.

I hope that answers your question--though I'm not sure what you're asking about. Do you think that a fuse is a semiconductor because in one state it does conduct electricity, and in another state it doesn't? And you thought a resistor was a semiconductor because it could sometimes act like a fuse, "blowing" if it was subject to too much current for too long, and therefore was also a semiconductor?

How did you get from that to thinking ESD mats are semiconductors?
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you can also use diodes for circuit protection.. but they're not use to limit circuit.. in the case you want to limit voltage
 
SarverSystems said:
So if I apply 110VAC at 10A to an 1/8 watt resistor, it's not gonna blow?
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I believe ESD is more commonly in the thousands of volts but at very low amperage. 110VAC at 10A is more like house current, and I seriously doubt your body could discharge current of that magnitude without physically damaging your skin.

The resistor in ESD mats and grounding straps is there just to dissipate the voltage slowly instead of all at once. For an analogy, think of a bullet. Fire one bullet from a gun and it can penetrate concrete, and perhaps even steel. No matter how many you throw by hand, though, you're not likely to break through a concrete wall in any significant amount of time.
 
MjrStryker said:
The resistor in ESD mats and grounding straps is there just to dissipate the voltage slowly instead of all at once.
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Or, to prevent it from building up in the first place while keeping the wearer safe from electrocution.
 
I was told by our ESD representative that the wrist straps contained a resistor so that if you came into contact with a dangerous level of electricity, such as 110VAC, the resistor would blow, preventing you from getting electrocuted.

I assumed the ESD mats were semiconductors, because we need special metering equipment to test the mats to make sure they are still working. A thin layer of dust can throw off the readings.

Apparently my understanding of a resistor is wrong. The way I understodd it was a resistor allowed a certain percentage of electricity through (resisting the rest), therefor not conducting the full amount, therefor acting a semiconductor.
 
SarverSystems said:
I was told by our ESD representative that the wrist straps contained a resistor so that if you came into contact with a dangerous level of electricity, such as 110VAC, the resistor would blow, preventing you from getting electrocuted.
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His understanding is incorrect. A resistor limits the amount of current that can flow by providing resistance to that current. The higher the resistance, the less current flows. If you know the voltage and the resistance, you can predict how much current will flow.

If the resistor is not there, there's zero resistance; zero ohms. That means there's no resistance to the current, and as much flows as the source can provide. If that current is going through someone's body into the wrist strap, it is bad news.

If the resistor is there, and presents a resistance that's low enough to bleed off static charge, but high enough to prevent shock from common 110 or 240 voltage sources, then we win.

Resistors are not semiconductors, nor are ESD mats.
 
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