When I'm working on computers, I want to avoid eletrostatic discharge. I have a wristband, but I'm not sure that I'm attaching it to the right thing. Usually, I'll clip it to the case of the computer. However, there are two cases in which I'm not quite sure what the proper procedure is. First, sometimes laptops seem to have a all plastic case until you take them apart enough. Second, things like harddrives are ESD sensitive, but when you get them they aren't in any computer, so what should you attach to? That got me to wondering if it would work for it to be attached to a ground (like the third prong in a US outlet, which is attached to a grounding rod or water pipe). Could someone clear up for me what will work to avoid ESD and what will not?
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\$\begingroup\$ @LeonHeller Is there a better stack exchange site to ask about this on? \$\endgroup\$– AzendaleCommented Nov 19, 2011 at 17:29
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3\$\begingroup\$ I think this is relevant to electronic design and a valid question. \$\endgroup\$– Olin LathropCommented Nov 19, 2011 at 18:45
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1\$\begingroup\$ @stevenvh, I know those that work on these things, and they type of ESD protection they use is very different from what someone building boards uses. I think the user may be better served by asking on superuser, as they are working on computers and probably would prefer know standard IT methods. Using a floor mat and such is over the top for a computer repair. \$\endgroup\$– KortukCommented Nov 19, 2011 at 20:20
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\$\begingroup\$ @Leon: Nothing to do with electronic design ??? Are you kidding me? \$\endgroup\$– RocketmagnetCommented Nov 20, 2011 at 14:50
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\$\begingroup\$ @Kortuk - You're right when you're talking about connecting a hard disk, but for playing with DRAM modules I take the Usual Precautions. \$\endgroup\$– stevenvhCommented Nov 21, 2011 at 7:48
2 Answers
When I'm working on computers, I want to avoid electrostatic discharge. I have a wristband, but I'm not sure that I'm attaching it to the right thing.
ESD rule number 1 - The aim is to have all objects being worked on at the SAME potential.
If this is ground potential, so much the better.
Computer ground and wrist-strap clip should be connected.
Connecting both to ground is a desirable bonus.
The aim is to have you and it at the same voltage.
- Usually, I'll clip it to the case of the computer. However, there are two cases in which I'm not quite sure what the proper procedure is.
As above. The aim is to get you and ALL the electronics that you are working on at the same "potential". This should ideally be ground potential - but it is more important that you and the work be at the dame voltage than that you be at ground. In fact, if you are at ground and the circuit you are working on is not, you MAY do more damage by having the earth strap than by not having it. May.
If there are two cases, ground or connect them both in some way.
- First, sometimes laptops seem to have a all plastic case until you take them apart enough.
They will often have a ground connection or a jack etc that has "grounded" metal. If none of these then see below.
- Second, things like harddrives are ESD sensitive, but when you get them they aren't in any computer, so what should you attach to? That got me to wondering if it would work for it to be attached to a ground (like the third prong in a US outlet, which is attached to a grounding rod or water pipe). Could someone clear up for me what will work to avoid ESD and what will not?
You need an "ESD safe" work area. Typically this is a grounded work surface that is mildly conductive. An ideal material is "butyl rubber" which is used for roofing and waterproofing. This has carbon black included in it which is what makes it conductive.
Price is reasonable compared to almost any alternative. You can sometimes get scrap roll ends or sheet covers used to cover bales which are even cheaper.
Ideally avoid a high conductivity surface such as a metal sheet if you are going to work there with circuits with power on (magic smoke happens) and if you have a PCB with makns or high voltage on even butyl rubber sheet may end up smoking if you apply enough voltage :-(.
A common metal sheet is better than nothing at all - just keep ALL power away from it.
ESD will discharge to ground quit quickly via a 1 megohm resistor. Connecting one og these in the wriststrap gound is wise - unless there is one there already.
You connect your wrist strap via a resistor to the earth pin of your wall outlet. The resistor value is typically in the 1M\$\Omega\$ range. Be sure to also use an antistatic mat, also connected via a resistor to earth to be sure everything you work is safe.
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\$\begingroup\$ Do note that there are antistatic mats and straps that already have a resistor included in the cable. \$\endgroup\$ Commented Nov 19, 2011 at 17:56