Static: what to do about it?

Discussion in 'The Projects Forum' started by nofiller, Mar 30, 2010.

  1. nofiller

    Thread Starter New Member

    Mar 30, 2010
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    I don't have much experience with electronics but I make simple projects here and there when I need to. My current project is a timing light that I want to house in a plastic pencil case. The pencil case is absolutely perfect, except that the plastic it's made from collects static.

    I've heard that IC's can be wrecked by static and want to protect them in some way. My instinct is to just wrap my circuit in aluminum foil, with maybe some cardboard or electrical tape preventing any shorts. Researching online all I can find is that static is scary, but no one says what to do about it.

    Please share your wisdom. Is this a valid concern? Will it work? How much aluminum foil should i use?

    Also, how would I know if static has affected my components, do they just die?
     
  2. Wendy

    Moderator

    Mar 24, 2008
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    Simple distance will go a long way toward isolation from static electricity. Just have only one pole of the battery touching the case

    Show us your schematic.

    Then describe how you would like to mount it (ignore the foil for the moment). A picture of the box and the board would be helpful.

    Also, this might give you some insight.

    http://www.allaboutcircuits.com/vol_3/chpt_9/1.html
     
  3. nofiller

    Thread Starter New Member

    Mar 30, 2010
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    Thanks for the quick reply Bill.

    I don't have a finished schematic because I'm still debugging, but I'll probably be using a 4071, two 4013s, about 15 LEDs, three transistors, a bunch of resistors, four push buttons for inputs, and two AA's for power (I can provide more detail about how it's all connected if it is relevant). Probably solder everything to a protoboard, but I've been know to just jam everything onto the ICs.

    Here's a sketch of what I want to end up with http://yfrog.com/0gtiminglight2p (not sure why it won't imbed). I was planning on just sort of taping and hot gluing everything in place, but it sounds like maybe putting it in a little cardboard box would be a good idea?
    [​IMG]

    That article was very interesting, but it only talks about what precautions to take while assembling not what to do with the finished project. I haven't been taking any of those precautions either, maybe it's too late! *sigh*
    [​IMG]
     
  4. nofiller

    Thread Starter New Member

    Mar 30, 2010
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    Oh, I can attach things. Here's that sketch again a different way.
     
  5. Wendy

    Moderator

    Mar 24, 2008
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    You would be better off keeping the case close, if possible. Move the buttons to the edge.

    I've had static jump from the bottom of the joystick to my C64 computer. This will likely not be a problem with portable equipment though.

    It is the act of opening the case that concerns me.

    The other side of this is, try it and see if you are wanting to do it your way. Just use sockets for the chips.
     
  6. nofiller

    Thread Starter New Member

    Mar 30, 2010
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    Hmm, I was worried that would be the case. I really want to use the design as is because of the mechanical protection that it provides.

    How about this plan:
    Put the circuit in a cardboard box. Then line the bottom and lid of the pencil case in aluminum foil which is attached to ground (negative side of the battery).

    Please elaborate on why using sockets would help. If that's all I have to do then no problem, I was probably going to do that anyway.

    Thanks,
     
  7. steveb

    Senior Member

    Jul 3, 2008
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    This is probably not the best choice for a case. You can use a metal case, or a plasitic case designed to be dissipative. Some standards plastics don't seem to induce much static charge. However, if you have a plastic case that is clearly collecting static charge, then it's best to avoid it.

    Usually, static damage occurs in assembly. Once the circuit is built and protected in a housing, the risk is reduced, but not eliminated.

    Simple steps can really help in assembly. Use a static mat on the floor and on the bench. Use a wrist strap grounded through a 0.5 Mohm resistor. Keep humidity above 40 %. Keep paper and other static generating materials away from your bench. Use a grounded soldering iron. Wear a static-resistance lab-coat. Pick up circuit boards by the edges only. Try to touch component leads a little as possible.



    This is tricky. Sometimes they die instantly, which is less of a problem. It is annoying and sometimes costly, but at least you know the component is damaged and you can fix it right away. The big problem is that often static damage does not instantly destroy the device. In some cases static damages the component and drastically reduces it's lifetime. The component then fails in the field prematurely. This is even more costly and leads the customer to question quality of the product.
     
  8. nofiller

    Thread Starter New Member

    Mar 30, 2010
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    Here's what I like about the pencil case:
    - closes and latches to protect everything
    - lid is attached and is a convenient display for the LEDs
    - opens to allow access to buttons and change batteries
    - clear so LEDs can be mounted inside, saves me the trouble of drilling holes
    - already made, sturdy and costs only $3

    The only problem is this static issue. So if I can get away with a little tin foil and cardboard that'd be great, however I realize that making something that's just going to break eventually is a waste of time.

    On a scale from probably fine to inevitable failure how big a risk would I be taking in using this case?



    ...anyone seen metal pencil cases for sale?
     
  9. steveb

    Senior Member

    Jul 3, 2008
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    It's really hard to answer that. Personally, I rarely see static damage on circuits that are installed in an enclosure, but it can happen. It might be fine once the board is installed and grounded. Realistically, static is always around anyway.

    The other day, I was sitting at my computer and I had a air purifier running with the ionizer on. The moving ionized air was charging me with static electricity in a way I've never experienced before. I kept feeling very strong static shocks going from my fingers into the grounded keyboard with aluminum shell. These were strong shocks occuring every 2 seconds, and I kept experimenting with this since it fascinated me. When I moved my hands aways, the time between zaps increased and the zap got stronger. It was really cool. After more than 100 zaps, my computer still works fine.

    However, if you blow a part, don't blame me. :p
     
  10. retched

    AAC Fanatic!

    Dec 5, 2009
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    Thats where I remember you from steveb! The sadist convention in DC last year! ;)

    Ah-hem

    The plastic box can end up working as a capacitor of types, charging the innards as the outside is continually handled.
     
  11. Bychon

    Member

    Mar 12, 2010
    469
    41
    After the components are installed in the circuit board, the parts connected often provide some static protection. For instance, a resistor from gate to ground on a MOSFET, which you would normally install as part of the circuit, helps protect the MOSFET.

    Here is a completely different idea: I bought a can of spray graphite for lubricating locks, a couple of weeks ago. I sprayed some in the kitchen sink, just to see what the spray pattern was, and it took days for the graphite to come loose from the stainless steel. Does that make the light bulb in your head sparkle? On the other hand, "the box is clear". This might turn out to be way too ugly to suit you. The graphite spray is black and can almost pass as an intentional paint job.

    So, I just now did the research. Here's how it works Go to Home Depot and buy a can of Jig-a-loo brand "quick-dry graphite lubricant" in the tool section. (Why not in the aisle with the door locks?) Shake well and spray the plastic. Wait for it to dry and then wash it with Crud Cutter, also from Home Depot. 409 might work. Common dishwashing detergent might work. The point is to get the oil component out of the graphite. Do not use a scratchy pad to wash the graphite coating. Be gentle of you will scratch right through the coating. After I did this, on my first try, without making any effort to make a thick or uniform coating, the plastic measured 21 megohms across one inch distance.

    This is incredibly good results! Megs per inch is exactly what you need. I also measured a conductive plastic bag that RAM boards came in. I couldn't get a reading, no matter how close I put the probes to each other, and I was using a Fluke 27 on the nano-siemens scale.

    I think this is a real breakthrough in home made static protection :)
     
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