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Breaking the epoxy bond under SMD ?

Discussion in 'Electronic Repair' started by N_Cook, Jun 28, 2012.

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  1. N_Cook

    N_Cook Guest

    Transistors , in this case 1-amp-continuous "size" whatever the SO
    designation of that is.
    If I've not used hot air then a scalpel tip or needle point, as used here,
    wedged under , soldering iron melt solder a touch leting the pins relieve
    themselves away from the lands , repeat wedging/desolder until fully free.
    But this time the epoxy was more structural than just for placement.
    I ended up breaking up the transistor body and the epoxy stayed resolute.
    Any advice for next time ? if relevant red colour and more than a micro-dot
    must have been under it as traces splurged out all around the body.
  2. "In this case, the SMD was a one-ampere-capacity transistor.

    "I wedged a scalpel tip (a needle point might work, too) under the device. I
    then touched a soldering iron to the pins, expecting that unsoldering them
    would allow the chip to pop loose. Apparently, though, the epoxy had been
    applied to keep the transistor forever in place, rather than just long
    enough for the initial soldering. I ended up breaking the transistor, while
    the epoxy remained intact.

    "Any advice for next time?"

    I'm biting my tongue.

    "if relevant red colour and more than a micro-dot must have been under it as
    traces splurged out all around the body."

    I can only make the vaguest of guesses as to what Mr Cook was trying to get
  3. N_Cook

    N_Cook Guest

    then applying a bit of heat to the transistor itself with a little prying
    with a screwdriver. The heat helps loosen the epoxy a bit allowing the
    Your mention of screwdriver - I'd forgotten about my jeweller's finest
    screwdriver with the blade I'd ground angles, either side , to
    give close to a point. Insert under and twist 1/4 of a turn. I'd only used
    it under ICs before, where there is a bit more space , out to the pins.
    to check my drawer of ancillary "tools & kit" to check its still there and
    more importantly remember to try it next time
  4. Hey William, I've found something that I think is just for you.
    I'm trying to help the guy. You're tolerating his lack of skill. Who's doing
    "something ... worthwhile"?
  5. Paul Drahn

    Paul Drahn Guest

    One watt is a lot of power to be dissipating without a heat sink. May I
    suggest the epoxy is a heat conducting formula and was there to conduct
    the heat to the circuit board material.

    Current designs use a device with a metal back side soldered to a large
    pad on the circuit board.

  6. I'm trying to help the guy. You're tolerating his lack
    You're absolutely right. If someone has a problem, they ought to work to
    overcome it.

    If you'd like to take this off line, I'd be happy to continue the
    discussion, in a friendly, constructive manner.
  7. Mr.Cooks original post was a little confusing, not like
    The issue is not whether I'm a bad person (I am), but whether anyone should
    publicly criticize someone who writes so poorly. I think they should,
    especially when a counter-example is provided.
  8. Jamie

    Jamie Guest

    a little LN usually works :)

  9. Why are you having to guess at anything, William?

    You were apply my final remark to the whole post, rather than to the text
    that immediately preceded it. If you look at my rewrite, it's obvious that I
    understood /exactly/ what I was trying to do.
  10. I'm still trying to figure out why epoxy was used to
    That must be it, because it would have been "overkill" simply to hold it in
    place during the intial soldering.
  11. N_Cook

    N_Cook Guest

    Belt and braces , to take the mechanical strain off the solder? To scrape
    back the epoxy to a clean board , the action of a soldering iron tip on it,
    was like the normal reaction of solder-iron heat to epoxy, goes powdery .
    Perhaps its bright red as a warning
  12. N_Cook

    N_Cook Guest

    The device was FZT949 (yes, revised, 5 or 6 amp rating/size) , the glue
    cleared away with soldering iron tip , in the manner of epoxy , with no
    smell of cyanoacrylate
  13. As ever, you've lost me there.

    Yeah, everyone else got it. I understand why you misunderstood -- you
    misread the context of the last statement.

    I might say to all the professionals in this group -- how can you work and
    respond to postings at the same time?
  14. N_Cook

    N_Cook Guest

    Crumble without clumping or sticking and without a change of colour and no
    observed smell given off.
  15. I might say to all the professionals in this group --
    I'm currently editing articles for "Electronic Design". The writing quality
    varies from barely acceptable to horrible. I have to guess at a lot of
    things -- such as what the writer /thought/ he was writing about, or what a
    particular sentence Really Means. I often refer to Wikipedia or search the
    Web, but sometimes it's a guessing game.

    Do any of you know what an IBC is? I didn't, and couldn't find the answer
  16. I'm currently editing articles for "Electronic Design".
    Thank you. Did you like "Did you buffer the buffered buffer?". That was one
    of my edits.

    I'm not the only editor, of course. They have full-time writers and editors
    who do a very good job.

    That suggests the original had significant problems. (I don't /know/, of
    course.) I have carte blanche to completely rewrite articles if I think it
    necessary. Many go through an extremely heavy edit -- and sometimes major
    rearrangement -- which the authors generally tolerate. (I would /like/ to
    think they look at the edited piece and accept it as a significant
    improvement. The late Bob Pease didn't. He told me my edits didn't
    contribute anything. That's about what Beethoven said about Haydn.)

    In some cases I'm asked not to disturb the original style too much. I just
    finished editing a piece about the advantages of custom analog ASICs, for
    the purpose of not only cutting costs, but avoiding counterfeit devices. The
    author had a fun, engaging style, which I didn't have to alter in the
    process of cleaning up his writing (mostly correcting grammar errors and
    tersifying here and there). Indeed, my edits actually pushed the piece
    /closer/ to the original style.
    There are articles so bad I feel my skull is about to explode. (In one case,
    the article was so awful and required so much time that I asked for a bit
    extra, which I got.) But I keep telling myself that, if engineers could
    write, I wouldn't have this job.

    That's not it. Not anything like it. Though it /is/ used in telecom systems,
    on the block diagram an IBC is some type of regulator/isolator.
  17. Does Penton seperate the technical editing from
    Not as far as I know. But my boss was surprised at how heavily I edited one
    piece, as it had been past another editor previously.
    Apparently they do. One didn't understand why I had so heavily edited his
    work, and I had to justify it. The article was published as I had edited it.

    Bob's writing was readable and understandable, but it certainly isn't what I
    would consider first-rate technical writing.
    Bingo! I was just saying that to my boss. You want to write so that people
    who are simply /curious/ about the material can read and understand it.
    That's exactly what I do. Poorly written jargon discourages readership --
    and thus subscribership.

    No, he's a major engineer of such. His name is Frosthold, and I wanted to
    add this to his bio: "He has two brothers, Fasoldt and Fafner Frosthold, who
    design and build custom homes."


    That's it! Thanks! (I'll get my boss to add a cross-reference.)

    By the way, it's rather wordy. It could stand another editing pass.

    PS: I'm typing this on a Unicomp buckling-spring keyboard. It's the only way
    to type.
  18. PS: I'm typing this on a Unicomp buckling-spring keyboard. It's the only
    way to type.

    I learned to type in high school on an Olympia manual. I typed at home on a
    Smith-Corona electric. Both have excellent, though quite different,

    In 1980, I was introduced to the pleasures of an IBM buckling-spring
    keyboard. That was it. In the intervening 30+ years, nothing has ever come
    remotely close. Tens of thousands of male typists will agree. It is in a
    class by itself.
  19. I'll admit that I rather liked the way these keyboards
    As Captain Redbeard Rum (Tom Baker) says in the "Potato" episode of "The
    Black Adder" -- "You have a woman's hands!"
    Absolutely. For most men, a short-stroke keyboad -- the IBM's Selectric
    being the notorious example -- is anathema. (It took 20 years of random
    exposure to the Selectric for me to gain some degree of comfort with it.)

    The Smith-Corona electric portables had a similarly long stroke that
    appealed to make typists. When Consumer Reports tested typewriters 50 years
    ago (I'm old, I'm old!), the panel strongly preferred the Olympia manual and
    the Smith-Corona electric portable -- my preferences, exactly.

    For those out there wondering what this is all about... The preference for
    the IBM Model M and its ilk among male typists is /almost/ universal. It is
    "Das Klavier". I used to work with Charles Frankston (Bob's brother) who was
    also an M freak. He had a drawer full of them, and would sometimes wave one
    in my face: "Look what I have, and you don't!"

    A short, easy throw does not a good keyboard make. The Model M's long stroke
    and non-linear relationship between force and displacement provide
    mechanical feedback that makes it posible to type faster and with fewer
    errors. Most users notice this immediately.

    I don't play a musical instrument. But I once compared a Steinway with the
    Baldwin SD-10. The keyboard action was completely different. This might have
    been what ultimately drove Baldwin out of business.
  20. I appreciate the compliments, Arfa.

    I'm an aggressive editor, and really "lay into" a piece if I think it needs
    it. (Most do.) My experience has been that most editors are "wussy", and
    don't begin to do what's needed to improve.

    When Jacqueline Kennedy was alive, "Esquire" (a porno-free men's magazine
    that predates "Playboy" by 20 years) poked merciless fun at Ms Bouvier's
    stint as an editor at a major publisher. "Mr Pynchon, I found a period in
    the wrong place on page 275, and there's a semicolon on page 681 that I'm
    not sure of, but otherwise, I don't see anything wrong." (Thomas Pynchon
    writes immense novels, such as "Gravity's Rainbow".)

    I do not, however, change anything for the sake of changing it. I can defend
    every change I make, though the author might not always agree. My goals are
    simplicity and clarity -- especially for readers not familiar with the
    material at hand.

    Most writers (myself included) overwrite, using too many words and
    pointlessly repeating ideas (while omitting important material). One of the
    effects of "paring down" the writing is that the piece becomes easier to
    read and understand. I also change words for a more-exact or vivid ones. I
    try to make the piece engaging, something that a reader will want to read,
    and enjoy reading.

    I was not generally happy with the editing my work received at "Stereophile"
    and "The Audio Amateur". Ed Dell, publisher of the latter, apologized,
    saying that he couldn't find really good people. Not surprisingly, the
    magazine couldn't afford to hire good editors.

    I'm a degreed EE, so I'm not working from a position of total ignorance. If
    I don't know something, I check Wikipedia (which has lots of technical
    articles, of widely varying usefulness) and the Web. I high whatever points
    of confusion remain, so my boss can fix them (if he chooses).

    One of /the/ great pieces of technical writing is Philbrick's book on op
    amps. It's nearly 50 years old, but still has all sorts of useful
    information, with the most-amazing indexing and cross-referencing you will
    ever see in a book. Your jaw will drop. It's also a "good read". I cut my
    op-amp teeth on it 40 years ago, and several years back an engineer in a
    UseNet group (perhaps this one) sent me a copy. I treasure it.

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