# Wood workbench as ESD protection?

ESD protection are really expensive for hobbyist like me.

I have a grounded wrist strap but do you think a simple non-treated wood workbench surface can replace a really expensive ESD tabletop ?

• Consider anti-static mats like this one. – Nick Alexeev Dec 11 '13 at 5:16
• Wood may not build much of a static charge (afaik - pretty sure not though, particularly if it's got some moisture in it) but it's not conductive either. A conductive bench acts to draw off any static charge on anything placed on it, making them safer for ESD work. Consider a steel or aluminium bench... or just cover your wooden bench in aluminium foil... and don't forget to earth it. – markt Dec 11 '13 at 6:06
• I used to be able to get a 7mm-10mm arc by standing up from my chair and gradually lowering a paperclip to the metal frame of my desk. Repeatably, every single time. I would routinely tap a metal utensil on my desk to ground myself before I got to the door handle until a colleague pointed out that I could just touch the wooden door frame, without the utensil, to ground myself gently (and quietly). Wood (dried and polished) definitely dissipates at least some charge. If it's truly inadequate I would love to see the reason explained. – sh1 Oct 12 '16 at 18:53

A good part of ESD safety is dissipating the charge in a controlled manner. If the wood acts as a very high impedance surface, you get no dissipation, and that allows static energy to build up and possibly cause problems. You really should go with a mat that has a ground lug (or buy a ground lug punch/crimper) on top of it.

Bare wood is a reasonably good "antistatic" surface.
I'd expect it to probably be safe but characteristics will change somewhat with timber type, degree of dryness etc.

For added confidence and/or a perhaps 'flasher' look, you can use butyl-rubber sheet (BRS). BRS is used for roofing and tank construction and various impermeable barrier applications and is relatively cheap. When shipped to larger resellers they may use BRS out packing around the whole bale and they generally sell that at a much lower price than the 1st grade product. I have used BRS bale outer wrappers as anti-static surfaces for many years. outer

BRS is bulk conductive due to the embedded carbon black which is used to colour it. You can probably rely on it being antistatic without testing but a test can be carried out by:

• Set multimeter to a 1 Megohm or more Ohms range.

• Press two probes into the rubber so that they deeply indent or penetrate the surface.

• Have probe tip spacing as small as possible without probes touching.

If you get ANY conduction at all the BRS will work as an anti-static surface. You can apply a ground clip to a corner or edge, but just laying on a wooden bench top should work well enough.

Note that if you use equipment with high voltage between terminals which both touch the sheet you may get conduction and bad things happening. Ground leads whether for the BRS or user ground straps or other ground anti-ESD connections should use say 1 megOhm series resistors to prevent high-current flows in case of accident. If you use a hard grounded wriststrap and touch live mains then it is easier to die than if you are not hard grounded.

• – JonRB Mar 10 '15 at 1:15
• @JonRB: That table states that BRS is conductive. You need that characteristic for a ESD surface. – Ignacio Vazquez-Abrams Mar 10 '15 at 1:18
• I was refering to using wood. That is bad. – JonRB Mar 10 '15 at 1:33
• @JonRB Apologies - you DID provide a reference which for reasons obscure (or worse) I did not note. What you meant would be useful expanding on. | That is an excellent reference that you cite. However, they suggest that pine wood is about 2 x worse in +ve charge generation than nitrile rubber - and they say in an example that nitrile rubber (+3) is far better than Butyl Rubber (-35). ie wood would rate far better than butyl rubber on that basis.| In addition to tribolectric affect, A major factor is conductivity, and wood floored buildings are by experience far safer ESD wise than eg concrete. – Russell McMahon Mar 10 '15 at 4:08
• yes my mistake, this is burnt into me due to every 2 years I have to have "ESD training" so it was a naive assumption everyone in electronics not only appreciates ESD, knows the damage it can do BUT also the Triboelectric series. I am planning a post but expect it to get "downvoted" :) – JonRB Mar 10 '15 at 8:38

Two concerns here

1. ESD (Electro Static Discharge)
2. EPA ( ESD Protected Area )

Now the question at hand has already identified the need for an EPA but is questioning how cheap? To determine that a bit more on ESD is needed

ESD is the sudden transfer of charge from one object to another

Two objects of dissimilar material when brought into contact with each other will experience a charge transfer, even if the two objects are metal. This is known as the Triboelectric effect

Materials close together on the series may not experience any charge transfer if simply touched (add friction into it however...) while materials further apart will.

What this also means is two materials that were initially GROUNDED that are then placed in contact with each other & then ungrounded will experience a charge transfer over time.

The rule of thumb is the better the insulator, the great the affinity for charge (there are obviously exceptions - see the chart). Walking on a carpet will generate 35kV of static, sliding down a fibreglass slide will generate 50kV etc...

If you were to come along and touch one of these two materials there would be a sudden transfer of charge, even if you were wearing an ESD strap & earthed (there would be an initial charge transfer & that would slowly normalise on you)

This is why components are stored in dissipative bags or trays and your wristband will terminate via 1MR to EARTH - to assist bleeding the charge away at a controlled rate.

Whenever you feel that zap when you touch something that is ESD, but here is the thing... The minimum discharge you can feel is 3kV while devices can be damage with as little as 50V. Basically you will not be able to tell if you are damaging a device.

So what can occur?

Instantaneous Damage the ESD has significantly damage the device and it no longer functions

Latent Damage damage has occurred BUT it isn't complete and the device still functions but is either significantly aged, weakened, significant device characteristic changes.

## How to manage it?

Profession EPA's use quite a few levels of protection

1. employee's have dissipative shoes
2. employee's have dissipative wristbands
3. employee's wear dissipative labcoats, closed all the time
4. The EPA is junctioned such that they need to check their ESD equipment before entering
5. the floor is dissipative
6. the benchtop is dissipative
7. there are earth bonding points for dissipative wristbands

8. electronics (assemblies or parts) are moved around in conductive bags & conductive boxes

9. ONLY removed at the designated workstation

Thing is this costs thousands to setup but results in zero ESD related returns

## How can this be done as a hobbyist.

1. dissipative wristband http://uk.farnell.com/multicomp/066-0055/set-esd-wristband-10mm-1meg/dp/1503191 ( £5 )
2. dissipative work surface via a mat: http://uk.farnell.com/multicomp/082-0002f2/black-conductive-bench-mat-0-7x0/dp/1687898 (£15)
3. dissapative box to store the work in http://uk.farnell.com/multicomp/025-0051/conductive-polyprop-box-230x130x42mm/dp/1687884 ( n x £5 )

£30 + depending on how many storage boxes and bags you want.

## References.

http://parts.jpl.nasa.gov/cots/external/ESDL_2_presentation.pdf

http://www.electrostatics.net/library/articles/ESD_damage.htm

http://www.sematech.org/meetings/archives/esd/20001019/steinman.pdf

• In no way does this answer the question. Your "answer", to this more than year old question, only describes the problem and verifies what he already does and already knows. – Rob Mar 10 '15 at 12:42
• Actually it does because wood is bad and as I posted, a mat is what is needed and they are cheep. Just because a question is over a year old doesn't automatically make what was posted correct, a lot that was posted here was factually wrong when it comes to ESD. That is a Historian's fallacy. To understand why it is bad and what you need todo there needs to be an understanding of ESD – JonRB Mar 10 '15 at 12:53
• How and why is wood bad? Your answer doesn't seem to mention wood except in one chart that puts it closer to zero than normal anti-static mats without telling us the significance of its position. What's bad about where it is? – sh1 Oct 12 '16 at 19:17
• its bad because it can still accumulate charge & it cannot dissipate it (because it is an insulator). "being close to zero" isn't important, it's the relative distance between materials that is as this provides an indication of the charge transfer between the objects EVEN if both were initially charge-neutral before being brought into contact. – JonRB Oct 12 '16 at 19:58
• You could say that in your answer so as to address the original question, but I haven't found it to be such an insulator when I've earthed myself through it. Certainly it had more resistivity than a metal door handle, but also much less than my shoes. There may well be something wrong with wood, but I haven't found out what. Perhaps, for example, it's less effective at lower voltages -- leaving behind enough potential to harm electronics but not enough to feel it. – sh1 Oct 12 '16 at 21:26

You have to remember that an ESD discharge into a component may not render a device useless, but can cause 'pits' in the silicon and can cause the device to prematurely fail. If you are a hobbyist and are willing to take the risk of ESD damage than it is your choice, but in the professional field you don't want to do that. It is a good way to have warranty issues and it isn't a good practice at all. You want to minimize damage as much as possible. ESD discharging can also cause intermittent failures on devices, especially microprocessors that have billions of transistors. Just because a device was hit by ESD doesn't mean it won't function at all, it means that the part is no longer reliable and should not be used in a unit that you plan on using in a production atmosphere. One example of a device is an amplifier. Op amps can get very expensive depending on your power demands, bandwidth, common mode rejection, and distortion ratings. ESD damage can cause an expensive amplifier to inject unwanted noise into a signal and cause distortion (in audio) or power loss (on power units).

If you are going to be working on more expensive items, such as computers, which deal with microprocessors, or DSP (digital signal processors), then I suggest you take the hit and get an ESD mat. I know they are expensive, but the last thing you want to do is cause damage to a $100.00 or$250.00 device. You will thank yourself, and so will your pocket book.

• butyl rubber sheeting works well in practice (see my answer) and is far cheaper than formal ESD mats. . When they ship it they bale it and may wrap the whole bundle in an outer of the same material. Here that outer is sometimes available at an extremely good price. Better again than BR 's normal pricing. – Russell McMahon Mar 10 '15 at 13:56

You could paint the surface with Total Ground conductive paint made just for this purpose. "Its primary application is to ground working surfaces to avoid static." Available from Amazon for $19. According to one of the comments, one can will cover about nine square feet with two coats. What I like about, is unlike mats (which I have used), the work surface is not going to move around. I've designed and built electronics professionally since 1964 and never used any ESD protection. The last time I worked for someone else, we had wood benches but, frighteningly enough, carpet on the floor. I've worked with CMOS and FETs and all kinds of sensitive devices and have never, ever had any of them ever fail on me. That said, I would just be careful. Don't have carpet on the floor and don't use a plastic table top. Mats and wriststraps are nice cause they give you some confidence in your handling of devices but, in my experience, it's never been an issue. • VERY BAD justification. I have never caught an STD, must be ok... trifield.com/content/tribo-electric-series – JonRB Mar 10 '15 at 1:17 • @JonRB The original question is trying to find out if the hobbyist can get by without an expensive ESD tabletop. 50 years of experience shows the answer to be true but I said he should still be careful such as how you are about STDs and the skanks you are with. – Rob Mar 10 '15 at 1:45 • No, it is very bad advice to peddle your anecdotal evidence that it is ok to "never use any ESD protection". "50 years of experience" equally does justify that because I can counter that with$50,000 worth of damage (proven when an IC was sent back to Infineon) due to ESD was not properly adhered to on the shop floor where I worked 15years ago. – JonRB Mar 10 '15 at 1:54
• @JonRB Then your anecdote is better than mine and every bedroom hobbyist needs to rush out to buy such a table to protect themselves cause every bedroom hobbyist has \$50K or more invested in their hobby circuits and needs equal protection. – Rob Mar 10 '15 at 11:15
• non-sequitur and is missing the point. – JonRB Mar 10 '15 at 12:22