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Si9410BDY mosfets - are they particularly ESD sensitive?

Discussion in 'Electronic Design' started by Den, Aug 12, 2008.

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  1. Den

    Den Guest

    I'm having some probs repairing some gear with Si9410BDY SO-8 pkg mosfets in
    them.

    The FET will appear to be faulty - replaced it - still no go......replace it
    again - it works - WTF!

    It's happened too many times to be finger trouble or gremlins. I thought
    maybe it was ESD - even though I'm working on a grounded mat with a grounded
    iron. Are they particularly sensitive??


    Data sheet: http://www.vishay.com/docs/72269/72269.pdf


    cheers.
    D.
     
  2. MooseFET

    MooseFET Guest

    The faster and smaller the MOSFET the more static sensitive it will be
    but I don't think that that is your problem.

    Try putting your DVM on both AC and DC between various "ground"
    connections on your bench. Any reading over 0.1V is cause for
    concern.
     

  3. The very word MOSFET alone should say to anyone in the industry "very
    ESD susceptible". Remember folks, it boils down to the potential
    required to breach a single pn junction. These features are pretty
    damned small.

    ESD is now, has been for decades, and should be, a major part of the
    electronics industry, and I find it ludicrous that some engineers
    downplay susceptibilities. I have seen the micrographs.. parts that
    didn't even fail... right away. It looked like an Iraqi roadway.

    Proper ESD workstations and handling procedures should always be
    followed... as a rule... not merely when handling known to be
    susceptible devices. Even fields can cause failures on parts that haven't
    been placed yet. Even non volatile parts can build up and keep a charge,
    and discharge into a susceptible part, so proper procedures should be
    used at all times to ensure that every step possible was taken to keep
    all parts at as close as can be to a net zero stored electrostatic
    charge.

    Such tiny stored charges can be all the energy it takes to kill a pin on
    a sensitive device.
     
  4. HarryD

    HarryD Guest

    Hey Arch, your living in the dark ages, BGW. You are correct about some
    MOSFET devices will blow if you just get near them, especially if they have
    unprotected inputs. The gate on a MOSFET is the most sensitive pin and on
    these larger devices they look like 10nF to the other nodes. They are rated
    at +/-20V but can withstand >40V. So your 100pF body must be charged to >3KV
    to blow the junction. The OP sounds very careful so I am betting, like most
    others that ESD is not the problem.
    Cheers,

    Harry
     
  5. Joerg

    Joerg Guest


    However, those are pretty fat devices. Ok, tennis shoes and non-treated
    tile could still do ESD damage.

    SD5400 and similar low capacitance devices are another matter. I had a
    tech almost throw his coffee mug at me when he swapped a SD5400 four
    times and I told him it's still damaged. He was sure it was my design
    until I sat down, soldered one in and everything worked.

    What really helps is to make sure that the air in the room doesn't
    become bone dry. I always make sure I wear natural fiber clothing,
    cotton and stuff, nothing with mixed in acrylic fibers etc.
     
  6. "your"? "BGW"? Bwuahahahahah!

    As little as 20V electrostatic charge on a person can blow just about
    any modern chip made these days. 3kV WILL blow anything. The chip makers
    that tout resistance to such voltages refer to parts IN CIRCUIT, wired in
    a specific manner. This discussion is about raw parts, as assemblies
    are being populated, etc.

    Even a "High Voltage Diode" is actually a STACK of pn junctions. A
    single one of those pn pairs would be susceptible. Being in a stack is
    what makes it an HV Diode.

    In a chip, however, the features are very, very tiny and very, very
    frail. Far more so than they were back at the advent of CMOS and ESD
    concerns.

    Also, before an FET goes in, especially with a high sensitivity device,
    merely touching the pins with fingers, grounded or not, and solder iron
    tips can blow them.

    If his iron is not a modern, ESD compliant type, there is no way to
    know if it is grounded at the tip or carrying a floating AC potential. If
    he grounds the tip, is he also incorporating the 1 MegOhm series limiter?

    We had some transducers that were FET included that had the leads wired
    together for handling prior to installation, and installation required a
    specific procedure. Yes, many blew before we decided that indeed, it IS a
    concern.
     

  7. OK big parts? Then they are a bit more hardy, but I would still not
    stress any segment of one.
    Even though it is the best choice, cotton and especially the
    artificial fibers can hold a charge. Cotton simply is not a great
    generator, whereas the synthetics are huge generators.

    When a body is electrostatically charged, the electrons sit on the
    surface of the insulator. A conducting body, like a person's hand,can
    build up charge by peeling electrons off of charged bodies. This is all
    with respect to the "ground" one's ESD workbench and hopefully, the bulk
    remainder of one's assembly and parts sits at.

    One does not have to actually see (read witness) a direct failure off
    the line to have ESD damage cause a failure later on when the product is
    in
    service.

    Yes, cotton, and at least 50% RH. Our lab hovers around 60% actually.
    Smocks abate one's field however, and should also be considered when
    sensitive devices are utilized. Our smocks have ground leads to the
    bench, and our smock sleeves connect to our body and that drains us. So
    we do not need wrist straps, and even our smocks are grounded.
     
  8. qrk

    qrk Guest

    Going barefoot really helps to reduce the ESD issue. In the previous
    company I worked for, we had a charge meter. It was interesting
    looking at different things like people and plastic bags. Found a
    batch of pink poly bags that had static cling.
     
  9. Den

    Den Guest


    they'd be high heels of course. :)
     
  10. Den

    Den Guest

    Thanks for the many replies guys. I have no control over the design (which
    seems reliable in service), the faults I've got at the moment are the down
    side of production yeild.

    My ESD procedures are reasonable but I'll take a bit more care with the
    handling and see if that makes any difference. I might make a few
    measurments as well and see if there are any stray potentials "floating"
    around.


    thanks.
    D.
     
  11. Joerg

    Joerg Guest


    And watch the shoes. I found that some brands of sneakers can cause a
    lot of ESD grief so we had straps that go over the heel and bleed charge
    off into the (treated) VCT floor. Didn't work too well but at least it
    helped.
     
  12. Den

    Den Guest


    And those track pants made from parachute type material that young guys like
    to wear.....
    Spraying chair squabs / backs with a squirt bottle mix of water & fabric
    softener every now and again seems to help as well.
     

  13. Pink poly only works in properly humidified environments. In dry air, it
    will not generate a charge, but it doesn't dissipate one either.

    They are pretty useless (especially for circuitry) other than that the
    alternative is the bad poly, so I guess they have their place. I prefer
    black, dissipative media, or the metallized bags with the bubble linings.

    With the new carbon nano-tube technologies being what they are, I am
    surprised we do not have perfect packaging films and table top mats, etc.
    for this industry. The old, powder form carbonized media is past its
    prime.
     
  14. Joerg

    Joerg Guest

    I prefer parachutes above my head, plus one spare just in case :)
     
  15. neon

    neon

    1,325
    0
    Oct 21, 2006
    what is that going to do to the ESD? The problem is that when you get to the bench you must ground yourself to it before you do any measuraments. and voltage of 1.v is not going to blow anything but a ESD of a couple of kv will. FETS are hi inpedance devices.
     
    Last edited: Aug 14, 2008
  16. Joerg

    Joerg Guest

    I found that most FETs die from "ballistic activity". A loud bang,
    followed by little chunks of plastic flying about, smoke wafting through
    the room and so on :)

    The best ones are those which blow part of their TO220 package off and
    still somehow work.

    [...]
     
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