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Soldering surface mount components

Discussion in 'Electronic Basics' started by Daniel Kelly \(AKA Jack\), Jun 8, 2004.

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  1. Ok, I am going to have to take a more nuanced position here.

    You and I were addressing two different phenomena.

    Your issue is with capacitors which have, in fact, developed a
    piezoelectric characteristic. (Not terribly surprising since high
    K capacitors are made of materials similar to those use for
    piezoelectric tranducers.)

    My issue is with incorrectly calling any instance of mechanical
    transduction in a capacitor "piezoelectric". As my point about
    vacuum should make clear, that usage is sloppy and at odds
    with the accepted definition. (Of course, with enough usage,
    sloppier definitions become accepted. Such is language.)
    I might squirm out here by insisting that your capacitor was in fact
    biased, even if you could not measure DCV at its terminals. That
    would be a fair description of the condition of a poled PZT, (from
    which your capacitor was likely made). But that would not be an
    out, because my original position, "[C]ommon ceramic capacitors
    are not actually piezoelectric.", is not quite right, as your experience
    shows. So I will grant your point without negating the essential
    truth of what I was stating.

    Your poor microphone, at some time during its life, transitioned
    from being a mere capacitor into a piezoelectric device. This
    most likely occured when it was held under bias for a long
    period of time. (It could occur in a short time at a temperature
    higher than most electronics see.) It became poled, probably
    not very well since it was inadvertant. You may have seen or
    heard of dielectric absorption. High K capacitors are also
    subject to it, and until their internal and only slowly available
    charge is gone, they will be slightly piezoelectric, as your poor
    microphone undoubtedly was.

    You may also have heard biased capacitors, when subject to
    AC currents having components in the audio range, make a
    sound. In all likelyhood, that sound is not due to piezoelectric
    effect. (A very small fraction of it could be, but not enough
    to reach audibility.) It is due to simple compression of the
    dielectric, by opposing charges, which varies in degree as
    the AC occurs.

    At any rate, under your relentless, pinpoint attack, I must
    alter my position: Common ceramic capacitors are not
    piezoelectric simply because they are made from materials
    used for their ablity to be made piezoelectric. They may
    become slightly piezoelectric for that reason, but without
    being poled either above their Curie temperature or for a
    long time, they cannot exhibit strong piezoelectric effects.
    Nevertheless, weak piezoelectric effect is a hazard to be
    aware of with all capacitors and especially high K ones.
    How about not sufficiently nuanced?
     
  2. Why not use a bigger capacitor to AC couple the
    capacitor under test? Then you could use a large
    resistor to enforce (nearly) 0 VDC bias.

    I question what your setup can show. New ceramic caps
    are very unlikely to exhibit a piezoelectric effect. But high
    K caps that have been biased may be slightly poled and
    respond to a "thump". Please see my response to Mr.
    Smith where I had to back off my initial position a tad.
     
  3. Terry Given

    Terry Given Guest

    I'm a bit out of my depth here (but still floating), but this sounds
    very similar to the ageing effect discussed by TDK in this paper:

    http://www.component.tdk.com/components/whatisthecapofthiscap.pdf

    "over time the internal molecular structure changes in such a way as to
    create an alignment of electrical dipoles. This alignment results in a
    structure that can hold less electrical charge than when the molecules
    are in a totally random state, such as at the time of heating or
    mounting on a printed circuit board"

    and

    "heating the capacitor above its curie temperature causes the
    crystalline structure to return to its optimal unaligned configuration,
    resulting in maximum capacitance. TDK recommends 150C/1 hour for
    de-aging" which alas is far too long to assert that soldering actually
    REDUCES the piezoelectric effect - just as well really, considering this
    thread.

    I had a quick squiz thru "surface wave filters", Mathews, John Wiley &
    Sons, but no real info on the piezoelectric materials themselves. I
    probably have the info kicking around (50 years of UFFC publications on
    20 CDROMs) but digging it out looks time consuming.

    It sounds like some sort of "forming" process is required for
    piezoelectric devices - is that what you are referring to when you say
    "poled" Larry? Care to describe the process a bit please?
    I would reason that electrolytics would be worse in this regard, as the
    dielectric is not a solid.
    Thanks guys, this is fascinating.

    Cheers
    Terry
     
  4. Terry Given

    Terry Given Guest

    If I have 2 caps, how do I tell which caused the signal?
    I question my setup too. The X7Rs I have have all been biased to 50%
    rated voltage for weeks. The pie was very nice, but I got sidetracked.
    Bac to the soldering iron...

    Cheers
    Terry
     
  5. Thump just one? Acousticly isolate the one with 4 mV
    on it, and use a modern low Eios opamp. Maybe thump
    both caps to bound the confounding factor.
    Are you attempting to see how good a microphone an
    unbiased capacitor can be? That would require some
    selection of capacitors with various histories. Are you
    attempting to show that not all ceramic capacitors are
    piezoelectric? That would require new parts, maybe
    even a few that were baked above the Currie point.
    Regards,
     
  6. Those considerations arise for the same underlying reasons
    that some materials become piezoelectric when poled.
    Google for "PZT" and "poling". That should keep you busy
    for quite awhile. This subject is not treated much in usual
    electronics related publications. The usual assumption is
    that a cap is a cap and if not, it's the engineer's problem,
    not the theortician's.
    Poling is a process where a tranducer (to be) has a voltage
    applied for awhile when above the Curie temparature. The
    voltage is typically also applied as the device cools. This
    leaves a (more or less) permanent shift of certain polarized
    molecules within the crystalline structure.
    For the gaseous electrolytics, I would expect the same
    due to higher compressiblity. For tantylum electrolytics,
    I could not venture a guess without some research.
     
  7. Terry Given

    Terry Given Guest

    Bounded confounding. I like it :)
    Just interested to look at an npo vs an x7r cap, of roughly the same
    size, to see what effect is due to the dielectric alone, for a range of
    uncalibrated thumps.

    Cheers
    Terry
     
  8. I read in sci.electronics.design that Larry Brasfield <donotspam_larry_b
    > wrote (in <BESsd.32$>)
    about 'Piezoelectric caps [was: Soldering surface mount components]', on
    Sun, 5 Dec 2004:
    Korma or vindaloo?
     
  9. Clarence

    Clarence Guest

    Had nothing of value to add!


    Plonk
     
  10. Bob Masta

    Bob Masta Guest

    When I was in engineering school, everyone took pretty much
    the same core curriculum for the first 2 years. Then you got
    to select whether you were going to be an EE, ME, or IE
    (Industrial Engineer). The administration tried to steer you
    into one of these based on your grade average: EE if you got
    good grades, ME if mediocre, else IE. (With my average, I
    had to *fight* for an EE slot!)

    Best regards,




    Bob Masta
    dqatechATdaqartaDOTcom

    D A Q A R T A
    Data AcQuisition And Real-Time Analysis
    www.daqarta.com
     
  11. Ken Smith

    Ken Smith Guest

    Yes, it appears so.
    Yes, sloppy language can lead to all sorts of curious statements and odd
    misunderstandings.

    [...]

    Actually it got pulses in one direction. The pulse was on the order of
    0.1 seconds and about 5V. It had been unbiased for many seconds when I
    did the test. Since it was in parallel with an inductor, any voltage on
    it at that time would have been very small.


    [...]
    I think I have to disagree with you on this. It takes very little actual
    energy to be heard so very little piezoelectric effect is needed.

    Imagine a circuit like this:


    --------------- +30V
    ! !
    O S1 O S2
    / /
    ! ! 3 x 2.2uF
    ! +-------!!----------
    ! ! \
    ! ! /
    ! ! \ 12R
    ! ! /
    +---------- ! -----------------
    ! !
    O O
    / S3 / S4
    ! !
    -------------- GND


    If the H bridge is driven at 50-50 duty cycle, the net bias on the
    capacitor is small or perhaps zero. If the bridge rests in one state, the
    capacitor will have a constant bias on it during the rest state. This
    will give the material lots of time to get poled.

    BTW: This is a simplified version of the actual circuit.

    Agreed
     
  12. Ken Smith

    Ken Smith Guest

    I would reason that electrolytics would be worse in this regard, as the
    dielectric is not a solid.[/QUOTE]

    I would argue that one electrode is the metal, the other is the liquid and
    that the dielectric is the thin layer on the surface of the metal. This
    layer is solid. I would expect less microphonics in a electrolytic
    capacitor.
     
  13. Terry Given

    Terry Given Guest

    And the mech guys drank the most booze, by far. Honestly, I was
    seriously impressed by the guys at Penn State, they were easily the
    smartest bunch of people I have met. And man did they do some cool
    stuff. I especially liked the sterling cycle engine powered by a block
    of burning lithium (in a seriously strong room with a Cu powder fire
    extinguisher handy).

    Cheers
    Terry
     
  14. keith

    keith Guest

    WIWIES, people were accepted into the cirriculum they wanted, up front.
    It *may* have been easier to get accepted into ME than EE, and ChemE than
    ME, but the selection was on entrance. Once one was *in* one could
    transfer, but that took grades. Transferring in from another college was
    almost impossible (it did happen, though only a few percent a year).

    Once one was an EE, one could further specialize into
    power/RF/microwave/digital/analog/computers/whatever. There were
    advantages to having a large class (~450 EEs, IIRC). Even in the first
    two years EEs took quite different courses than the rest.
     
  15. Paul Burke

    Paul Burke Guest

    Edwina. A major, eggsistential mistake.

    Paul Burke
     
  16. Hi there all!

    Just a quick message to say thanks a lot for your help and advice - my phone
    is now up and running again, plus I've got a brand new fine-tip soldering
    iron and all the other goodies for about £30 or so. So I've managed to fix
    my phone, PLUS buy some new toys in the process.

    The biggest help was probably the whole blue-tac thing. That resolved the
    biggest issue I was having - namely stopping the tiny chip from running
    around all over the place. I als found that having a reel of soldamop made
    a big difference - much easier to clean up mis-solders than with desoldering
    irons. Plus, I can't imagine using a soldering iron with such small
    components and gaps.

    Thanks a million, guys!

    Cheers,
    - Steve "once-again a happy nokia owner"
     
  17. I meant "desoldering iron", not "soldering iron".

    - Steve.
     
  18. dd

    dd Guest

    2 further items to assist a good light source and a magnifierliquid flux
    helps too
     
  19. Rich Grise

    Rich Grise Guest

    I once actually found a use for liquid rosin - I used it to make my
    hands sticky so I could get a grip on some cable-bundling tape in a
    piece of equipment that was all covered with hydraulic fluid.
    All I've ever been able to accomplish with it in electronics is gum
    up the board and make it harder to clean.

    But I do recommend a good magnifier, and a good source of light.

    Good Luck!
    Rich
     
  20. Hmmm...the solid stuff is put to good use by violinists, and baseball
    pitchers use the powdered version. I wonder how much stickier liquid
    rosin is than pine tar, or is it?

    Tom
     
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