I'm having trouble understanding ESD protection. I hope somebody can help. Should an anti-static mat on a lab bench be connected directly to ground or connected to ground through a 1Mohm resistor? What is an anti-static mat made out of? Is it conductive? If so then why don't I measure any resistance if I poke ohmmeter probes into two spots on the mat? Do I need to have an anti-static mat on the floor around my lab bench? If I have a charge on me do I have to touch a circuit board to damage it or can the charge jump through the air? How do I safely move a circuit board from one lab bench to another lab bench? (I see people carrying circuit boards around my lab by the edges of the board with their bare hands and they think by not touching any IC's with their hands that the board is safe.) I'm often out in the field working on electronics and I have no ground strap. Should I touch a ground point on a metal object first before handling a circuit board, to remove any charge on myself? Thanks for any help.
The mat does not have to be electrically conductive to dissipate a electrostatic charge. I conductive mat can cause problems with a circuit board under test on the bench if the components are shorted out or the resistance between two nodes are changed necessitation a piece of non-conductive mat on top of the conductive one.
The mat should be diretly connected to earth. Your wrist strap needa
1Megohm or greater so if you touch someting high voltage with respect to earth ground the current is limited below the lethal level.
Antostatic floor mats are nice for when the boss walks in and starts poking around the board without a wrist strap. Generally if you use a wrist strap and bench mat you don't need a floor mat to unless you are working with some very delicate stuff. (IMHO)
If you are charged up pretty good you will cause a noticable and audible zap. Often times the "zap" is unnoticed but one port pin or logic IC start acting funny on you. In generalt its best to put on the wrist strap before touching the board.
Moving a board from one bench to another requires putting the board in an ESD safe metalized bag or box. Esd pretetion bags are silver or black in color. The pink one on do not generate static when rubbed together but toe do not protect the board for a static hit.
there is almost always a ground point around. Any metal the goes into the ground (plumbing is good) can be use to ground your wrist strap. They sell ones with a alligator clip on the end for this purpose.
Walking around with a board held by the edge is a last option only proposition. when you get to the other side you should discharge yourself to the other bench with the opposite hand then place the board down.
The mat direct to ground is fine as the mat has an inherently higher resistance. It is your wrist strap cord that usually has one integrated into it.
Many times, a carbon impregnated material. These days there are several types, and most are multi-laminar in nature.
Yes... well... it has a high resistance, so it conducts "slowly".
Because the resistance is so high, you need a larger surface area of contact than the probe tips provide. A couple of 3 inch foil patches should allow you to see some motion (get a reading).
It is not required. If you are doing High Voltage work, it is not recommended at all.
When you are in an elevated condition, you also carry a field. That is why we wear smocks. They contain any field you would otherwise radiate. I ALWAYS touch grounded structures before I touch a PCB or approach an ESD work station with open assemblies on it.
In an ESD shielded container, such as a metallized or carbon black dissipative bag WITH the top folded over. This can also be toted around inside an ESD tote box with a lid on it, especially for longer hauls.
If you were talking about power supplies, I'd say the parts are pretty hardy.
Since you are likely referring to delicate digital circuit assemblies, I would be sure that everyone involved takes every precaution possible. Such failures do not immediately show themselves. Sometimes they take time to propagate a failure mode.
With a PC as an example, I would:
Keep the chassis plugged in, as this keeps things grounded, and gives you a place to be grounded as well.
Touch the chassis to equalize you body charge to the chassis. This should also be ground, but equality is more important. NOW you are able to touch circuit assemblies, etc.
Yes. If you use the chassis for the device in question, you bring yourself to its level, regardless of where ground is, though the two are typically equal.
You're an idiot.
Conductor: WILL dissipate a electrostatic charge.
Insulator: Will NOT dissipate an electrostatic charge.
You were saying?
Only if one intends to energize circuit card assemblies at their ESD safe workstation. It also depends greatly on the voltage in question. Low voltage DC circuits have no problem with ESD mats.
That is not the reason for it. It is there so that a charge does not get dissipated to fast, which can cause damage to a circuit element as well.
It doesn't mean a damned thing if he does not have on a heel strap. Anyone around and ESD workstation should ALSO have an ESD smock on as well.
Three minimums for an ESD workstation.
Bench mat.
ESD Smock,
and to be grounded.
The best smocks have the cord integrated into them, and you ground that, and there is no wrist strap.
Recommended:
Ionizer.
If you are causing zaps, you shouldn't be anywhere near an electronics lab, and said lab should look into the humidity conditions.
I am done teaching... You're a goddamned retard!
No shit.
Pink are useless completely in low humidity.
Nice logic, but flawed... kind of like the old "duck and cover" instruction for what to do if you see a nuclear blast.
So the 1Mohm resistor is only for protection against me getting shocked? If there is no dangerous voltage around me or I'm just working with 5V electronics then I can be connected directly to ground?
When I'm carrying a board in an antistatic bag does it matter if the bag is open, or does the bag need to be closed?
If I step on a grounded mat, any charge on me will flow through the rubber soles of my shoes? Isn't rubber very resistive?
The mats, straps, smocks, etc and the instructions governing their installation and use are designed to protect the electronics equipment and personnel from damage, even if the people don't why they are doing it. For people that do know why, they eliminate the need to think about it.
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