Proper Storage for Logic and other ESD Sensitive IC's

Discussion in 'General Electronics Chat' started by Stuntman, Jul 19, 2011.

  1. Stuntman

    Thread Starter Active Member

    Mar 28, 2011
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    Hello,
    I have acquired a fairly comprehensive set of 7400 (BJT and CMOS) and CD4000 logic. The chips have been stored loose in plastic Akro Mils storage cabinets (non ESD safe plastic) in a non-temperature controlled warehouse. I would estimate many chips date back over 20 years, so I assume a majority have been in storage at least that long.

    I would like to reorganize these devices and make them usable for a prototyping at work and home. However, I realize that the storage conditions of these chips are far less than optimal. Which brings me to my questions:

    1. How likely is it that storage has damaged these ICs? I just don't know how these devices fare over such a long time in a warehouse that I'm sure reaches over 100F degrees in the summer, but probably not under 40F during the winter. As well as being stored in non-ESD safe containers.

    2. How should I approach storage now to avoid damage in the future. I know the optimal solution would be purchase ESD safe bins. However, the costs are on me personally, and ESD equipment is a very costly endeavor. Are the old hard plastic drawers prone to actually failing chips? On the work intensive side, I had considered cutting ESD foam and lining the storage bins in layers, pressing the chip leads into the foam. But I want to know I'm being realistic about the necessity of such steps.

    3. Still yet, I have access to metal cabinets and drawers. Are those a better choice (than plastic) for storage/use, I see opinions both ways on this. I simply don't know the precise details about static generative materials. For instance, is it ok to store IC's in statically generative plastic if you use proper ESD dissipation when removing them from the container?

    Any insight into this issue is much appreciated, I'd just like some realistic options on keeping these parts safe.


    Thanks in advance.
     
  2. Sparky49

    Active Member

    Jul 16, 2011
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    I'd be tempted to line the containers with the ESD foam. I simply have all my ICs stuck into the stuff and I haven't had a problem with ESD.

    As for how well they have been stored, I suggest making some sort of testing circuit.

    Make a simple circuit with a DIL socket. If you place an IC in the socket, turn the circuit on and an LED lights up, then you know that that one works. By going through them like this, you can be sure of the ones which work, and those which don't. It makes sense to ensure they work - otherwise you might be spening a load of money when only 3 out of 100 ICs work.
     
  3. Wendy

    Moderator

    Mar 24, 2008
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    I use squares of ESD foam with my chips inserted into them in project boxes. Aluminum foil is also your friend.
     
  4. Stuntman

    Thread Starter Active Member

    Mar 28, 2011
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    Thanks for the input thus far, let me narrow my questions a bit.

    I cannot test all these chips due to the sheer varieties I have, but I have been randomly sampling them to determine if I have an excessively high failure rate.

    So I want to ask, is ESD foam set in a statically generative drawer OK? I have access to metal drawers, but the plastic would be much more convenient. Do I have to be careful about leads sticking through the material and touching the plastic? Again, I realize this sounds obsessive, but I simply don't know the material characteristics regarding ESD.

    In the past, I have had problems with some ESD foam holding moisture against pins causing corrosion. I have read in my recent research that this was an artifact of the old black ESD foam, not the new "pink" foam. Any merit to this?

    Thanks for the responses so far.
     
  5. Sparky49

    Active Member

    Jul 16, 2011
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    I'll have to keep this short, as I'm on a 'phone, so forgive me of this sounds abrupt.:)

    I still use the black was foam, and I still use it in conventional plastic drawers. Like you say they are convenient and cheap. Personally I have never had any problems with esd to my ics. If you find that they are rusting, then I would look at the humidity of your storage room.

    All the best.
     
  6. MrChips

    Moderator

    Oct 2, 2009
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    I am just going to summarize what others have already said.
    1. The probability of failure at this point is low.
    2. Corrosion is a bigger problem if you have high humidity.
    I would not use the black foam. As Bill Marsden suggests, aluminum foil is your cheapest solution. Just bunch the chips of each drawer into one bundle of aluminum foil.
    Try to reduce the humidity by maybe using a dehumidifier.
     
    Last edited: Jul 21, 2011
  7. Stuntman

    Thread Starter Active Member

    Mar 28, 2011
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    What about the pink foam. I actually have access to some of that. Anyone tried this stuff for long term storage?

    In terms of the plastic storage, I do have some metal cabinets that could be used for these components. Is this a superior solution? I'm assuming I would need foam even if I went with the metal drawers.

    Finally, do you guys suggest grounding out storage shelves, ESD mats, etc, to the mains earth ground? I worry a little that a surge, lighting strike, etc, may load up an insufficient earth ground, making me want to install a dedicated stake. Opinions here?
     
  8. Wendy

    Moderator

    Mar 24, 2008
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    Main thing is a Faraday cage. The aluminum wrapping will make one. The static foam connects all the pins together, where they are at the same potential. Not as good as a Faraday cage, but it will reduce the possibility of damage. The main thing is to keep the pins at the same potential, it is when they conduct a surge that damage occurs. A static bag is also a Faraday cage. As long as they are enclosed you do not need to worry about a ground at that moment.

    Grounding the storage containers doesn't do much good if you have a static charge when you get the parts. The goal is to create a static neutral environment where you work, and a protection system for when you aren't using the parts.

    I don't like the pink stuff myself. There is a lot of counterfeit material that it isn't conductive. Some of it they mix soap in to make it conductive. It wears out. Not the best approach, IMO.

    The concern about using ground from electrical outlet is valid. Personally I would not use it in bad weather. It would suffice for most other cases, but if it is something you really worry about you can make your own ground by driving a metal stake into the ground.

    I go over a lot of the details in my article, ElectroStatic Discharge. I'm not an expert, but I've done the research, and have to follow the protocols at work. Been doing it for most of my working career, around 30 year or so.
     
  9. MrChips

    Moderator

    Oct 2, 2009
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    The older black sponge-like foam caused corrosion on the pins. The newer type has been improved and would be ok. I would not trust the pink foam.

    As an alternative I sometimes use white foam and wrap the foam with aluminum foil. Then I stick the DIP IC pins into this aluminum cushion.

    Now, most of my SMD and discretes I leave in the anti-static bags or chip rails. I save all the silica gel packets that come with the parts and keep them in the original bags in "shoe boxes". You can rejuvenate the silica gel by putting in an oven for 2 hours at 250F.

    I have lost more parts to corrosion than to ESD.
     
    Last edited: Jul 21, 2011
  10. KJ6EAD

    Senior Member

    Apr 30, 2011
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    You are more likely to cause ESD damage to the devices by all the handling and repackaging than any of the previous or future storage has or will, so take precautions to ground yourself when handling them.

    If I came into a bunch of chips, I'd just bag them by type in pink ESD bags, stick a label on the bags and line them up in a big bin like files. It saves space and makes them easy to find. If the bin is big enough to have a lid on top it keeps the dust off the bags. You might have to straighten a pin now and then when you go to use them.
     
  11. Wendy

    Moderator

    Mar 24, 2008
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    The silver gray static bags are common, you can buy them at most electronics retailers, and are much better than pink bags. They are coated with a thin layer of metal, giving them that gray appearance. As I've mentioned, the pink stuff has too many other problems.

    Can't argue with the rest, I think my article even makes the same point. If you want to put them in plastic bins just wrap them in a layer of foil.
     
  12. KJ6EAD

    Senior Member

    Apr 30, 2011
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    The silver bags are great for new or expensive parts but cost 7-8 times as much as the pink bags.
     
  13. Wendy

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    Mar 24, 2008
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    I'd rather have something that I knew worked. I wasn't kidding about the quality of the pink bags, long term they wear out and the numbers counterfeits are huge, not to mention how do you establish whether it worn out? Given you get a silver static bag from almost anything computer related. My cost is under 10¢ typically, though I have spent more. I just did a google search, 15¢ is typical.
     
  14. Stuntman

    Thread Starter Active Member

    Mar 28, 2011
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    So what if I had the resources to put all the static sensitive IC's in a painted metal drawer/cabinet and leave the plastic for passive components (I'm assuming plastic is ok for resistors and caps ??).

    Something along the lines of these:
    [​IMG]

    I could ground each steel shelving cabinet with a dedicated stake. How would this compare to the plastic, and would the ESD foam still be a necessity? I could also put the metal cabinets in a grounded metal shelving unit I have.
     
    Last edited: Jul 24, 2011
  15. Wendy

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    Mar 24, 2008
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    <sigh> I said this before, it doesn't matter if the storage is grounded.

    All that matters is if you are, and the container is. I use kit boxes, made from plastic (lousy antistatic properties). I take the foam holding the chips out and remove the chip with nominal static protections. If the chips are wrapped in aluminum foil, or are stored in static bags, or are in static foam they are protected.

    If you are not grounded when you pull a chip out of these drawers then you could zap them. If you are not grounded and the chips are stored in static proof containers it won't matter.

    What matters is the static proof work station.

    If these boxes are grounded, and are part of the static proof workstation then so much the better. I would still recommend static proof storage, such as the aluminum foil, as an extra precaution.

    ElectroStatic Discharge
     
  16. MrChips

    Moderator

    Oct 2, 2009
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    I agree with Bill Marsden. It is not the drawers that matters. What matters most is are YOU grounded? Are the parts at the same GROUND potential when you pick them up and take them out of the anti-static bags? Are all of the pins on the IC at the same GROUND potential while being handled? If I have to hold a bare chip in my hand I make sure that all the pins are in contact with my hand or between my fingers. It would be better to transport them on antistatic foam, rails, bags or aluminum foil.

    [​IMG]

    This is our electronics storage bins. Even though these are plastic drawers, ICs are kept in antistatic bags, foam or aluminum foil. Hobbyists, don't be intimidated. This is a major university electronics laboratory.
     
    Last edited: Jul 24, 2011
  17. Wendy

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    Mar 24, 2008
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    I had forgotten rails, they also protect the pins nicely as well as provide good ESD protection. I'll put a picture of one up when I have more time (right now getting ready for work).
     
  18. Stuntman

    Thread Starter Active Member

    Mar 28, 2011
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    Perhaps I'm not explaining my thoughts and plan well which is causing the aggravation. I just want to make sure I cover all bases before I set all my storage up. I simply have not done a thorough job of this in the past and want to do this without regrets.

    So I consider that two different scenario's can happen. Either the parts accumulate charge, or I accumulate charge, allowing myself and the parts to be at differing potentials. Therefore, necessitating that both be brought to earth ground before any interaction.

    If I use the steel drawer cabinets, and ground each on in a steel shelving unit. Would that not keep the parts in inside from collecting charge (being in a conductive drawer with a 10Mohm drain to ground). (These are painted/finished, so I really don't know if this works at all).

    In addition, my workstation (which has an ESD mat) is located away from the parts storage, so I could develop charge just in walking over the carpet to the parts bin. However, by touching the grounded shelves/cabinets, etc, I should discharge my body and be in good shape to pick up the part until I can take it to the ESD mat to install.

    I still don't understand some of the philosophy behind protecting these chips

    AFAIK, static safe foam, rails, bags, etc, simply put a slightly conducive path between pins of the chip, making them all reach the same potential. However, this potential could still be high voltage, no? Also, wrapping the pieces in aluminum, doesn't necessarily contact all the pins, so some pins could still float high no? Still yet, Mr. Chips talks about contacting all pins at the same time with his finger. This makes no sense to me. If some of the pins have floated high, and you happen to contact a "ground" pin before the others, why wouldn't the current dissipate through the chip and zap it? Or are you assuming you have the proper 10Mohm resistance to ground?

    What I'm gathering is there really isn't a safe way to store these chips WITHOUT buying a ton of ESD bags, ESD foam, etc., or wrapping them in foil? Assuming I do the foil, I should technically grab the whole bag of foil, take it to the ESD workstation, then open it and take the part I need?
     
  19. Wendy

    Moderator

    Mar 24, 2008
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    Thing is, we've addressed the scenarios. If you have an Faraday cage (in the form of aluminum foil, static bag, or some other ESD safe container) static is not reaching the part. When you put the container down on the grounded station with ESD protections the charge bleeds away very quickly, typically less than 5 seconds.

    There are two parts to this, protect the parts in their own individual containers when in storage. The odds are when you need them you will have to carry them to the workstation, so the need for individual protection is not eliminated.

    When you are at the ESD safe workstation then remove the parts from their protections. This is pretty much the industry standard. If you need to carry them away from the workstation put them back into a ESD safe container.

    You are over complicating this by quite a bit.

    You can not eliminate the individual parts storage (again, aluminum foil, static bag, or other ESD package). Paint is an ESD generator, but it should not matter if you have followed the storage protocols. For the same reasons it doesn't matter about the shelves, whether they be metal, wood, or plastic.

    There is nothing that says you can't have a bunch of parts in a ESD safe container. You just open and close this container at the ESD safe workstation.

    It doesn't matter if the aluminum foil is touching all the pins. All that matters is it is a solid ball or wall of metal. That is all a Faraday cage is, a metal enclosure. If the chips are bouncing inside a metal can they are still safe from static, though the mechanical shock is another issue.

    http://en.wikipedia.org/wiki/Faraday_Cage
     
    Last edited: Jul 25, 2011
  20. Stuntman

    Thread Starter Active Member

    Mar 28, 2011
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    But I see a disconnect between the methods. I'm not trying to test your patience, but i do want to know how to address this issue.

    First, I understand where you are going with the Faraday cage. It makes sense, but still requires I removed not just a lined drawer, but a complete foil "baggy" from the storage unit, to the ESD station. A bit inconvenient, but fair enough and inexpensive.

    But I do question this about ESD foam also shielding the part from static. The foam is simply moderately conductive right. So would not the whole piece of foam (and IC's attached) accumulate charge? Now, if I were to set the foam on an ESD mat, this charge should dissipate safely right?

    My thoughts at this point are to line the parts with foil bags in metal shelving until I can get enough esd foam to make layers of foam and parts. (by the way, I notice there is conductive polyurethane and conductive polyethylene. Any idea which is better and why?)

    I plan on keeping all my passive components in the plastic containers if this is acceptable.

    Thanks again
     
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