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Preventing Pad Lifts

Discussion in 'Electronic Repair' started by Rob, May 22, 2007.

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  1. Rob

    Rob Guest

    What are some good techniques for preventing pad lifts, particularly
    on cheaply made modern electronics? Is it better to have high
    temperature with quick soldering or lower temperature and working a
    bit slower? A suggested basic temperature setpoint for these types of
    boards?
     
  2. N Cook

    N Cook Guest

    I'm only coming at this from repair soldering rather than production and
    assuming you are referring to hand soldering.
    I would suggest the wrong soldering technique may be being used.

    With a conical tip then the very tip on the pad and the bulkier part of the
    cone to the, in comparison, more massive pin. More heat to the more
    massive/heatsinky part of a joint and the rest tends to take care of itself
     
  3. GregS

    GregS Guest

    Stay under 625 F. I seem to need at least that most of the time. use liquid flux,
    and only use higher heat on the larger pads. Cut off any parts before removing,
    and use some solder braid.

    greg
     
  4. bz

    bz Guest

    Very dependent upon the type of solder used, and what kind of components and
    what type of boards you are working with.

    By the way, there are printed circuit board repair kits. Google for them.





    --
    bz 73 de N5BZ k

    please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
    infinite set.

    remove ch100-5 to avoid spam trap
     
  5. Ken G.

    Ken G. Guest

    In the cheap electronics i dont think you can do much . I work on the
    cheaper stuff , basically brand new store returned items such as small
    stereos & such .
    Sometimes foils lift just by handling the board and pushing or tapping
    lightly on parts .
    I would say keep your soldering tips in good clean condition and dont
    heat anything very long . If you can get hold of the part first and pull
    on it while quickly heating the pads the part will pop out then very
    quicky use de-solder braid to clear the hole .
    Use lower heat irons . High heat can very quickly fry whatever holds the
    pads on .
     
  6. Golf

    Golf Guest

    I can only tell you from my experience (been there, done that), that
    too much heat for too long causes this especially when the iron tip is
    in contact with the pad. Heat the component pin first, then slide the
    tip to the pad to finish removal of solder. This seems to work best
    for me. Good luck.
     
  7. N Cook

    N Cook Guest

    I tend to only heat the pin with the iron and introduce the solder wire
    between the soldering iron and the pad so the melting solder,only, heats the
    pad.
    Unless it is a large ground pad or wide strip rather than a pad, ie
    substantial heatsinking.
     
  8. bz

    bz Guest

    (Ken G.) wrote in 3237.bay.webtv.net:
    An iron with a built in 'solder sucker' helps a lot.

    Radio shack has an el-cheapo with a red rubber bulb that works well, or one
    can buy an expensive vacuum equipped desoldering station (with temperature
    controlled iron).



    --
    bz 73 de N5BZ k

    please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
    infinite set.

    remove ch100-5 to avoid spam trap
     
  9. Jim Yanik

    Jim Yanik Guest

    (Ken G.) wrote in 3237.bay.webtv.net:
    My soldering training said that use of solder braid gets more heat applied
    to the PCB for a longer time,making pad lifts occur more.
    Same for SoldaPults.
    They specified the use of a temp controlled vacuum desoldering iron.
     
  10. Charles

    Charles Guest

    1/ Use some good liquid flux before you heat the joint.
    2/ Generally, a temperature controlled iron is best.
    3/ Lacking a temperature controlled iron, use an 18-W element with a small
    conical tip.
    4/ Tin the tip and wipe immediately before desoldering.
    5/ Sometimes it pays to add fresh solder to the joint before desoldering ...
    seems strange but it really works.
    6/ Some boards are so crappy that nothing will prevent the pads from
    lifting.
     
  11. Yes. And everything clean and a good flux.
    Never. Speed is the key.
     
  12. bz

    bz Guest

    Not strange. The original solder could be 95/5 or 60/40 or 50/50 even.
    adding some good eutectic solder will make the old solder melt faster and
    stay liquid longer.




    --
    bz 73 de N5BZ k

    please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
    infinite set.

    remove ch100-5 to avoid spam trap
     
  13. Jim Yanik

    Jim Yanik Guest


    For that matter,you could use ChipQuick,and desolder at VERY low temps.
    ChipQuick solder melts at 160degF,IIRC,so the combined melt point is
    IIRC,<250DegF. You could use a heat gun.
     
  14. Smitty Two

    Smitty Two Guest

    I'm going to agree with some of what's been said, and disagree with some
    of it. I always solder and desolder everything at 800 deg. F. The faster
    you can do it, the less chance of damage. And you can work ten times as
    fast at 800 as you can at 600. And I always use liquid flux. Always use
    liquid flux. And, make sure to use liquid flux, always. Yes, it's true,
    I'm the s.e.r. liquid flux police.

    The main reason pads lift, I think, is too much physical pressure. Don't
    push down on the board with anything more than the weight of the
    handpiece. Too many people think that pushing down on the joint will
    make the solder melt faster. Nuts. Just use some liquid flux, and crank
    that temp dial all the way up.

    Also, with a conical tip, do NOT use the point. It hasn't enough thermal
    mass to do anything. Try this. Put your left index finger on the desk in
    front of you, pointing straight down into the desk. Now take a sharp
    pencil in your right hand. The pencil is the soldering iron. The desk is
    the pad. The index finger is the component lead (aka leg.)

    Hold the pencil at a shallow angle to the desk, so that one portion of
    the tip taper, wood part, not graphite, lays flat on the desk. Now slide
    the pencil up against your finger. The point touches neither pad nor
    lead, but extends beyond them. Maximum possible heat transfer to pad and
    lead, simultaneously.

    For wicking, just put the wick between the iron and the solder joint,
    but use the same technique, and still use flux. It makes solder melt and
    flow.
     
  15. Yes. You should almost 'paint' the solder on.
     

  16. All of the paste solder we used in our reflow ovens was 80/20.


    --
    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
     

  17. Also, leave a 1/8" to 1/4" of used wick at the end to quickly
    transfer the heat into the joint. Put the solid spot on the joint, and
    apply the iron. When it stops its capillary action clip it back, and
    continue. A small bottle of liquid flux to dip it in, between uses is
    also handy if you don't have a squeeze bottle with a large bore
    hypodermic needle to dispense the liquid flux.

    Now that I have a decent digital camera, I will see about making a
    short video to show the techniques I used in manufacturing to rework
    boards on the module test line. In four years I only damaged a couple
    pads, and most of them were caused by the company's refusal to let me
    put the stereo microscope on a bench, instead of a cart.

    I could desolder and reuse 144 legged ICs. i agree with the liquid
    flux, I prefer Kester industrial RMA flux. i think the last bottle was
    type 1544 RMA.

    I used 750 to 825 degrees on my three different irons. They were
    calibrated every three months, and checked daily for high resistance
    between he ground pin and the tip. Anything above three ohms required
    the tip to be removed, and the shank cleaned with a soft brass brush to
    bring the resistance back down. Once an iron reached three ohms, it
    could go quite high and cause ESD damage.


    --
    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
     
  18. Smitty Two

    Smitty Two Guest

    That's the good shit, Maynard.
     
  19. Guest

     
  20. Guest

    Depending on what type of component you are removing the heat, time
    and tools are all important. The general rulle its least amount or
    heat in the least amount of time with no downward pressure and lots of
    patience, thats what I preach to my students. As with all processes
    the tools need to do the work and not be used improperly, which in
    soldering means avoid at all cost pressure, soldering should not be
    pressure activated. Pressure is what gets us in trouble when using
    poor maintained equipment or improper techniques.

    For most lead bearing solders, which is most likely what you are
    dealing with, you should always start with a temp around 600 f and
    modifiy from there. If its lead free you will need to up that
    slightly, but not dramatically.

    If you just do a lot of repair on the cheaper boards, I would suggest
    looking into the circuit repairkits/techniques, some of the kits will
    be better than the original when used correctly and again good well
    maintianed tips and tools are key.

    Anyway thats my 2cents email if you have questions or specifics of the
    application you would like help with.

    Ruffin Blackard
    IPC Instructor
    http://www.circuittechnology.com
     
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