anti static issues

Discussion in 'General Electronics Chat' started by Neil Groves, Oct 16, 2013.

  1. Neil Groves

    Thread Starter Member

    Sep 14, 2011
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    Last night I rolled my chair back under the bench and noticed in the low light a bright spark jump from the chair to the metal leg of the bench :eek:

    Sooo.....do I use an antistatic strap on my wrist connected to the ground skt on my oscilloscope, or do I need to go to the trouble of buying a grounding mat for my bench and connect THAT to my grounding peg?

    Neil.
     
  2. JohnInTX

    Moderator

    Jun 26, 2012
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    1,029
    I do both. I have stat-mats on all the benchtops but don't always bother with a strap since leaning on the mat will keep me discharged, but a strap is best - I just get lazy.

    If you don't like a wrist strap, tuck the strap snap inside your belt against your skin.

    Consider a floor mat as well if you tend to shuffle your feet - me again.

    The benefits of a good anti-static station go beyond not zapping parts.. you get fewer transients that false trigger your scope when you touch things etc. No more painful zaps either.
     
  3. ian field

    Distinguished Member

    Oct 27, 2012
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    Humidity is your friend - The mental case in the flat above constantly damages the water pipes and causes flooding, I have crippling rheumatism and terrible allergies to the mould spores - but I can throw P-MOS around like it was DTL (actually DTL isn't all *THAT* hardy - you can destroy the input diodes with the high Ohms range of an analogue meter).

    Alternatively you could boil a kettle from time to time next to your bench.

    The main cause of damage is not the charge itself so much as charging/discharging of such charges as occur, Your antistatic workstation could be floating at 100kV and all the parts are fine - until you touch one and the charge cracks over.

    It doesn't hurt to earth your antistatic area (but not a low resistance path that could carry lethal current if anything became live!) - the important thing is to equalise any charges between anywhere parts get handed over to. You need to ground yourself to your antistatic mat before touching the parts on it, and you need to link the mat to the ground plane of the PCB you're putting the parts into.

    When you take a MOS chip from its packaging, hold it by its plastic/ceramic and breath on it (just like people do when they polish their spectacles) the moisture in your breath dissipates any charge in a safe manner, plant your left hand on the anti-static mat before putting down the chip with your right hand.
     
    Neil Groves and PackratKing like this.
  4. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    5,435
    1,305
    The humidity meter is your friend. It's 50% here today. Not a static day. :)
     
  5. Neil Groves

    Thread Starter Member

    Sep 14, 2011
    125
    3
    Thanks guys, i'm going with the anti static strap on my wrist to just keep my carcass grounded.

    Neil.
     
  6. ian field

    Distinguished Member

    Oct 27, 2012
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    As the previous poster suggested - a RH meter is well worth having, you can have unusually dry weather that means you have to work very carefully even if you're doing anti-static procedures by the book!

    Anything over about 50% and you can relax a little.

    Also bear in mind; ESD damaged parts don't always fail immediately, degraded gate insulation can fail weeks - even months after going into service.
     
  7. Wendy

    Moderator

    Mar 24, 2008
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  8. Duane P Wetick

    Active Member

    Apr 23, 2009
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    This issue was a large part of my daily bread in my avocation (E.E.), so I will share some facts with you. First the issue of humidity is a valid one, but difficult to control. Static electricity cannot hold for long in a humid atmosphere.
    In the range of 0 to 10(9th) ohms, static electricity will not be supported on such a surface. In the range of 10(10th) TO 10(12th) ohms, static electricity will be dissipated to ground. In the range of 10(16th) and beyond, static electricity will be supported. In the first case, metal is the surface. In the second case, Micarta, Resistop., certain urethanes (dissipative) & Velostat are examples. In the last case, UHMW, Teflon, Polycarbonates, Styrene are examples. The best cure, however is to avoid generating static in the first place. There are static dissipative sprays on the market, but they must be renewed from time to time. If you can see a spark jump from your chair to a ground, the chip you are handling probably has been destroyed. By the way, your skin can hold a static charge.

    Cheers, DPW [Everything has limitations...and I hate limitations.]
     
  9. ian field

    Distinguished Member

    Oct 27, 2012
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    Just a general comment about (anti-static) sprays, and sprays in general - check very carefully whether any such sprays contain hydrocarbon solvents. Many components/assemblies in electronics these days have ABS (polycarbonate) parts - years ago while trouble shooting a VCR, I sprayed switch cleaner on the mode switch, it literally disintegrated into granules before my eyes!!!

    Speaking of sprays - I've heard rumours that freezer spray (for diagnosing thermal faults) in its new CFC free incarnation, can cause the buildup of static charges.
     
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