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Workbench surface
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Steve
There was a discussion regarding workbenches on this reflector back in October and I'd like to ask for some follow up advice.
I'm planning to replace an old workbench. Is there a top I can put on my new workbench that is ESD safe? Right now I have an ESD mat that I place on the workbench surface when appropriate. Inasmuch as I'm going to be more or less starting from scratch, I thought I'd at least ask the question about an ESD-safe work surface. Thoughts or advice out there? Thanks. Steve K8JQ |
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have been through this a couple of times in last 20 years,
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a. Using a static mat from 3M or one of the top companies that supply to HP and others is the best recommendation, those mats allow static discharge at the best rate. Dont use an aluminium sheet to ground as some people have tried. b. If you have overhead fluoros then might need to reduce the mats 1M to 100K, in my case the 1M meant the mat wasnt draining the field from the fluoro and we blew many mosfet gates (the ones without protection zeners). If you are not going to be handling anything without protection zeners then dont bother. c. Have a region of interface between the static mat region and where you walk from so some static can dissipate before you get to the mat. Like a 3m area which is floor treated, floor mat is ideal but I find that carpet is ok if its treated twice a year with some spray on static treatment. d. If you are handling a lot of very sensitive devices in most other places in the lab where they might be stored but not worked on then a static controlled fan might be helpful, cant recall the name but it has a ion source either mildly radioactive or a power operated type. I dont use one myself but depends what you are handling, others might comment on that. cheers mike At 11:50 AM 3/12/06, you wrote:
There was a discussion regarding workbenches on this reflector back in |
have been through this a couple of times in last 20 years,That was all very interesting - particularly that a 1M-ohm mat was susceptible to fluorescent light e-m. Two points that are worth making to clarify: 1. The reason that Al foil is bad is that any static charge on a device comes out instantly - and the high peak current that flows (even from a few pF on the gate of a FET) is so high that thermal damage occurs. A resistive mat is essential to make sure that charge bleeds out slowly enough to prevent this. 2. It is possible to subtly damage devices without destroying them totally - leading to change in characteristics, noise and/or lifetime. The only solution is to follow a good protocol. I put that in place after I destroyed a rare double FET while repairing a 'scope. Craig |
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Rasputin Novgorod
The only solution is to follow a good protocol. I put that in placeAfter several careless incidents with soldering irons, I started using fireproof table tops (with static mats on top). It was some kind of laboratory table-top, a mix of asbestos and resin, that was made locally when I lived in New England. I've had them for 20 years. I remember the factory cutting room was clouded with airborne asbestos and cement dust; nobody wearing masks. The safety inspectors wound have had fits... /b ____________________________________________________________________________________ Have a burning question? Go to www.Answers.yahoo.com and get answers from real people who know. |
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Steve
Thanks Mike and others for the advice, it's most helpful and educational.
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I didn't realize that fluorescent lighting could be a problem. In any event, I'm not using that kind of lighting. I will take a look at 3M and other mats, both for the floor and the bench top. 73, Steve K8JQ Mike wrote: have been through this a couple of times in last 20 years, |
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At 10:30 AM 6/12/06, you wrote:
I didn't realize that fluorescent lighting could be a problem. In anyI forgot to mention that it was only a real problem because it was quite low over the bench and the cables to the lights wound around the back and side of the bench, plus they were the old inductor type ballast and the large metal housing might not have been well grounded. When a 20v max mosfet gate regularly gets 27v at 50hz it doesnt last long but all other ICs were ok, a drop in the mat resistor to 100k didnt upset any other handling and dropped the field voltage from 27 to around 2.5 I will take a look at 3M and other mats, both for the floor and theAh - I just checked my post, the '3m' later on referred to a 3 metre area of transition (miniumu) from an unsafe to the fully safe area. For me this did not need a 3M mat just an ordinary wool/cotton carpet which was treated with the same chemical women use when ironing to stop their dresses sticking to their panty hoses - it was *much* cheaper than the 3M or any other chemicals, I actually still have a Bokhara Afghan rug, cost about $600 in the olde days when these were being sold as "investments", still in one piece must have had it for over 20years now, more utilitarian than worth hanging on the wall for a seance ;) From what I recall, the chemical is just some ionic salt, perhaps even MgSO4 or maybe some mix which was very slightly hygroscopic, or at least had some lower resistance when dry at low humidity levels cant recall exactly. I dont use it anymore as my smallest lab is for my use only and if I ever have any very badly static sensitive devices on that 3M bench then my whole demeanor changes dramatically :P Cheers Mike 73, |
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Hi Steve,
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To see what you are dealing with, turn on your oscilloscope, set its sweep speed to 10ms/dividion, set its vertical deflection to 0.5 V/division, and with one hand, grab the tip of your scope probe. That signal on your screen is real, and has enough current to drive a 10 meg to ground load. Now, imagine what that signal would be if your load was 100 meg, or 1000 meg to ground. Oh, and it doesn't matter what kind of lighting you are using, this is stray coupling to the power line. If you use mains electricity, it is there. -Chuck Harris Steve wrote: Thanks Mike and others for the advice, it's most helpful and educational. |
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