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1G ohm resistor

Discussion in 'Electronic Design' started by Arch, Jul 17, 2006.

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  1. Arch

    Arch Guest

    Hi,
    Can someone help me to find 1G ohm resistor - surface mount, for low
    noise application. I saw vishay-dale has CRHV series but all the
    distributors are selling 1000 min pieces.
     
  2. Bob

    Bob Guest

    Digikey is your friend.

    Bob
     
  3. Phil Allison

    Phil Allison Guest

  4. Barry Lennox

    Barry Lennox Guest

    I got a couple of 91M (IIRC) from Vishay as samples a few years back;
    it's worth a try if you only want a few. The worst that can happen is
    they say no.

    Barry Lennox
     
  5. It takes over ten of those in series to even approach 1GigOhm.
     
  6. Guest

    I don't know if this is still true, but you used to be able to get
    Newark stuff via Farnell, and Farnell stuff via Newark - delivery times
    were a couple of days, because the parts came from stocks held on the
    wrong side of the Atlantic, but here wasn't any problen about ordering
    small number of parts.
     
  7. Guest

    In general, yes, but are they in this case? I looked, and found
    high-value resistors, but none in surface mount.

    Cheers,
    James Arthur
     
  8. Guest

    When I looked in May, Bill & Phil's present suggestion of Farnell
    looked best. Here's a cut-n-paste of my notes regarding manufacturers
    & suppliers I found:

    Farnell stocks a number of high-value resistors.
    Farnell #9236473, 235052110476 by PHYCOMP (47M 5% 0805) is £0.099.

    RH73H2A50MKTN is 0805, 50M, for £0.58, mfr = MEGGITT
    (http://www.meggitt.com/)
    RH73H2A100MKTN, 100M, for £0.50
    The series includes values of 1,5,10,20, and 50G, with values over
    500M going for ~£1.14.

    Notes: Meggitt owns Piher, Ohmite owns Victoreen.

    http://www.resistor.com/p_hvalue.htm
    http://www.ohmcraft.com/ohmcraft/datasheets/

    Stackpole Electronics:
    http://www.seielect.com/products/productsearch.asp?SelFamilyID=1
    Series HMC: General Purpose High Value Chip Resistor, Sizes 0603 thru
    1206, 47M to 4.7G.
    Series HVC: High Voltage Chip Resistor, Sizes 0402 to 3512,
    tolerances down to 0.1% and TCR's to 25ppm. Values up to 1T with
    extended voltage handling to 2500 volts.

    HTH,
    James Arthur
     
  9. Arch

    Arch Guest

    Thank You everyone,
    I have requested ohmcraft and Stackpole people to send me a quote for
    resistors - 10Qty. Also asked Vishay if they can give me samples. Let
    me see if i can get them.
    Also Farnell has given me the quote. In the end of the day, i'll see
    which one is the best offer and buy. Thanks the replies helped a lot.
     
  10. Guest


    http://www.resistor.com/pthick_hval.htm (17-Jul-06)
    High-value chips resistors (hvchips.pdf): 12-200volts, 0502 case
    100M to 10G, other sizes to 100G.

    http://www.ohmcraft.com/Products/ResistorProducts.aspx (7/17/06)
    Series SM: ultra-high stability, TCR to 10ppm/C, tolerances to
    0.1%, values to 2T.
    Series HVC: ultra-high stability, TCR to 10ppm/C, tolerances to
    0.1%, values to 2T.
    0402 values 1K-20G, 0603 from 1-300G, 0805 from 1K-350G.

    Hmm, I see some of the links I supplied have already gone stale.
    Updated above.

    James
     
  11. Sjouke Burry

    Sjouke Burry Guest

    Maybe because a surface mount resistor will
    be degraded to much by leakage of the board/
    dirt film/moisture,in other words those resistors
    might have to be bigger,to be mounted with standoffs,
    and not touch anything in their neighborhood,
    protected by guard rings etc.
    Your surface mount resistor might surprise you
    unfavorably.
     
  12. Guest

    Those things can happen, but they don't explain DigiKey's
    lack of the parts. Several vendors offer surface mount
    resistors, with values up to 2T (2x10^12) ohms.
    Of course, it has to be clean.

    James
     
  13. Ken Smith

    Ken Smith Guest

    If your quantities are low, you can buy the through hole part and form the
    leads to surface mount it. This could save you if you have a mechanical
    reason to not use through hole.

    I think Newark stocks IRC's 330M and 250M resistors. You could string a
    few in series.

    www.resistor.com has them (or at least claims to). You can try them if
    you don't mind paying 10 times as much and waiting 10 times as long.
     
  14. What kind of surface are you going to mount a 1G resistor to without
    trashing its impedance?



    --
    Many thanks,

    Don Lancaster voice phone: (928)428-4073
    Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
    rss: http://www.tinaja.com/whtnu.xml email:

    Please visit my GURU's LAIR web site at http://www.tinaja.com
     
  15. Typically SMD stops at one or max 2 MegOhms. A 1GigOhm SMD is
    actually hard to make reliably (read repeatably). The most common
    type is called a "flatso" package, and they come bare or epoxy coated.
    The leads can be formed such that surface mounting is possible (though
    slightly elevated).

    Another thing about resistors that high in value. One MUST never
    touch them without gloves on, and one MUST get the area under the
    mount location VERY clean. Leakage is tantamount to not having the
    resistor value one thought one had. Even breathing coffee breath on
    them changes their value. The bare models are hygroscopic as is the
    epoxy to a slight degree (enough at these values). I would also
    recommend encapsulation after assembly as the environment will also
    change the value in fairly short order.
    A single fingerprint can lower the value several percentage points.
    At least enough to throw the tolerance out the window, and make the
    device function in an entirely unpredictable manner.
     
  16. If the application is a divider for HV, I would seriously recommend
    against using small SMD packages if you want reliably circuit
    operation. If the SMD must be used, the full encapsulation or
    conformal coating at the very least, would be a requisite procedure.

    I have seen what appears to be a 100% clean installation fail.
    Hot solvent bath, and a good 0.5 hr bake at 60C made the problem go
    away. In a humid environ, however, it rears its ugly head again quite
    rapidly. Within a couple days easily, and I am in a dry climate.

    The first thing we always did with a failure mode was ensure that
    the assembly is VERY clean, and well baked dry.

    Also, if it is HV, I would recommend that no mask be applied in the
    HV component section(s), as it tends to delaminate from encapsulants,
    which is a bad thing. At that point, it is as if there is no
    encapsulant at all.
     
  17. See my post regarding this, and why I declared "flatso" packages and
    encapsulation to be the current "best practice".

    Oh, and one cannot touch these devices either. They will suck it up,
    and NOT be of the same value any longer, and will be very
    unpredictable in behavior.
     
  18. John - KD5YI

    John - KD5YI Guest

    One with a slot milled between the pads?
     
  19. That's nuts. Cite?
     
  20. It has to be BEYOND clean. It has to be clean AND dry. Just for
    starters. It only takes a few picofarads of associated capacitance to
    cause problems as well.
     
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