ESD Foam vs ESD Shielded Bag

Discussion in 'General Electronics Chat' started by van53, Mar 29, 2015.

  1. van53

    Thread Starter Member

    Nov 27, 2011
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    I read in another post that using ESD foam (in the context of protecting ICs from ESD) is "Not as good as a Faraday cage, but it will reduce the possibility of damage."
    http://forum.allaboutcircuits.com/t...-for-logic-and-other-esd-sensitive-ics.57154/

    If one has an IC inserted in ESD foam and a static event occurs (e.g. the ungrounded person touches a pin on the IC directly and zaps it), how does the ESD foam reduce the possibility of damage when compared to a ESD shielded bag (i.e. a Faraday cage) ?
     
  2. Papabravo

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    Feb 24, 2006
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    The foam attempts(?) to keep all pins at the same potential. So no current will flow into or out of the IC if all pins are at ground or all pins are at +1000 VDC. I've seen 4000 series CMOS parts used in an oscilloscope where the GND pin was at -810V and VCC was at -800V
     
  3. #12

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    Nov 30, 2010
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    It's still a bit of a brain warp for me to think of how you zap a chip by touching one pin. There must be some other current path that is difficult for me to imagine. The foam (supposedly) provides conductivity to and from all pins so the chip fits my mental model of all pins being at the same potential, no matter whether that is ground potential or a thousand volts above ground. Still, the foam is NOT zero ohms per millimeter and neither are the, "conductive" bags.

    I think it's time for Google. Somebody that makes this stuff should know why they are in business.
     
  4. van53

    Thread Starter Member

    Nov 27, 2011
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    Thank you. So if I understand correctly, the foam (I would think in this case it would be conductive foam), would keep all the pins at the same voltage, so the ESD event in this case would not allow some pins to be at a higher potential than others and this would prevent the IC from be damaged?

    This would be a concern if only some of the pins were at a higher potential than others, correct?

    What about other types of foam such as anti-static (the non conductive type) ? I would think in the case of using this foam, all pins may not be at the same potential and an external ESD event would have a more likely chance of damaging the IC?
     
  5. Papabravo

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    Yes, damage may occur when some pins are at a higher or lower potential than others.

    I'm not sure I've ever encountered the non-conductive type of anti-static foam.
     
  6. #12

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    I think non-conductive anti-static is impossible, but then, I learn something almost every day.
     
  7. van53

    Thread Starter Member

    Nov 27, 2011
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    Above my bench I have several plastic drawers that slide out (no lid). Since my mat and myself are grounded, I would think that lining the bottom of the drawers with the conductive foam should be sufficient in this case. As I will be removing a drawer while being grounded and placing it on the grounded bench I wouldn't need to go as far as storing the ICs in zip lock anti static bags?
     
  8. Papabravo

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    Make sure the foam is thick enough to prevent the pins from touching the plastic drawer.
     
  9. van53

    Thread Starter Member

    Nov 27, 2011
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    I was reading the following here: http://electronics.stackexchange.com/questions/103797/anti-static-vs-conductive-vs-dissipative-foam
    Where there was mention of three types, conductive, anti-static, and dissipative.

    I *think* the anti-static (non-conductive?) foam is the one shown in this video (after Dave first demonstrates the conductive foam):

    see 11:40 to 12:45 where Dave shows conductive foam and then shows the anti-static type. To my understanding, anti-static would be able to prevent a static charge from building up on the material, however it would not prevent a static charge from passing through it.
     
  10. van53

    Thread Starter Member

    Nov 27, 2011
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  11. Papabravo

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    Check the lead length on a DIP IC. It should be about 0.145" to .170" from the bottom of the package.
     
  12. crutschow

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    Mar 14, 2008
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    The main function of anti-static materials (foam or bag) is to not build up a charge on the surface as standard plastics can do and dissipate any static charges that are generated. Thus touching the anti-static plastic before you touch the semiconductor in the plastic will equalize any charge difference between you and the plastic/part so that the part isn't damaged when you remove it from the foam/bag. (The anti-static material has a low enough resistance so that any typical static charge amounts are dissipated in a short time.)
    Similarly, you should touch your grounded bench mat (or be wearing a static wrist band connected to the bench pad) so that there are no differences in potential when you move the part from the anti-static foam/bag to the bench.

    I don't see how a material can be non-conductive and anti-static. That would appear to be a contradiction in terms.
     
    Papabravo likes this.
  13. van53

    Thread Starter Member

    Nov 27, 2011
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    Watching the video (2:05-4:50 and 15:30- 16:35) that I linked earlier, Dave shows how the anti static bags such as the ones that are commonly pink (however they can be clear) do not build up a charge on the surface. However a static charge can pass through such a bag and can destroy an ESD sensitive component within. He mentions that bags such as static shielded or conductive bags protect the devices within from being harmed by static charges from the outside.

    At around 3:00 he mentioned how the pink anti-static bags are also known as static-dissipative however in the comments some have indicated there is a difference between anti-static and static dissipative.

    Wikipedia indicates:
    ESD materials are generally subdivided into categories with related properties: Anti-Static, Conductive, and Dissipative
    ....
    ....
    Anti-Static[edit]
    Anti-static materials are generally referred to as any material which inhibits triboelectric charging. This kind of charging is the buildup of an electric charge by the rubbing or contact with another material. One type of anti-static packaging material is commonly referred to as Pink Poly. It is a clear pink (hot pink) polyethylenethat is available as a film for bags, bubble pack, or foam.

    Dissipative[edit]
    Dissipative materials allow the charges to flow to ground more slowly in a more controlled manner than with conductive materials.

    Conductive[edit]
    Conductive materials have a low electrical resistance, thus electrons flow easily across the surface or through these materials. Charges go to ground or to another conductive object that the material contacts.
    http://en.wikipedia.org/wiki/Electrostatic_discharge_materials#cite_note-1
     
    Last edited: Mar 29, 2015
  14. MCU88

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    Mar 12, 2015
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    Yeah bunch of BS. I just throw everything into an common plastic bag. Never had any problems.
     
  15. crutschow

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    You're lucky. :rolleyes:
    Static discharge damaging sensitive components is not BS.
     
  16. Papabravo

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    I guess I have seen the pink poly bags. I was unaware that they were different than the grey or silver poly bags.
     
  17. MrChips

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    Oct 2, 2009
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    There is a difference between anti-static and conductive foam.

    Conductive foam is built with carbon to provide electrical conductivity.

    Antistatic (pink) foam for all intents and purposes is non-conducting but contains an anti-static agent that suppresses the build up of static electricity.
     
  18. MCU88

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    You don't consider TTL parts to be a likely victim of static discharge do you?
     
  19. crutschow

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    I believe it has to be slightly conductive to do that, even if the conductance is very low.
     
  20. MrChips

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    Oct 2, 2009
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    True. The resistance is 10^9 to 10^12 ohms/square which is practically insulating.
     
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