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lead free soldering

Discussion in 'Electronic Components' started by R.Lewis, Oct 30, 2003.

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  1. R.Lewis

    R.Lewis Guest

    What do I need to change to lead free hand soldering pcb's (about 15 seats)?

    Any advice gratefully received.
     
  2. R.Lewis

    R.Lewis Guest

    For 15 seats read 15 people hand soldering components into pcb's (Yes we
    also use flow soldering ).
    We need to change from SnPb solders because of customer demand at this time,
    and because by July 2006 we will have no choice.
    ..
     
  3. Baphomet

    Baphomet Guest

    I'm not sure why you would want to. Lead free will probably raise the
    melting point and to compensate, you would either have to use lighter guage
    or flatten it with a hammer before soldering. Since it doesn't sound like
    you have much soldering to do, I wouldn't worry about it unless you are lead
    allergic.
     
  4. Glen Walpert

    Glen Walpert Guest

    On Thu, 30 Oct 2003 19:13:19 -0000, "R.Lewis" <h.lewis-not this
    Almost all of what I have seen published on lead-free soldering has
    been for automated soldering only (reflow and wave primarily).
    Likewise, most of the new lead free alloys seem to be availible in
    paste or bar only. It is not just the solder that is important but
    also the flux, and most of the lead free fluxes for automated
    soldering are synthetic rather than rosin based (no-clean or water
    clean) and are not well suited to manual soldering.

    My only suggestion would be to contact Kester and other solder
    manufacturers for recommendations and give them a try. Sn/Ag,
    Sn/Ag/Cu or Sn/Ag/Bi/Cu solders may prove most suitable based on what
    is most commonly used in automated processes. Avoid anything with
    Antimony.

    I have manually soldered a few boards with Sn97/Ag3 rosin core solder,
    and found that melting temp differences compared to tin lead are
    insignificant, the grainy appearance looking a bit like a cold
    tin-lead joint is easy to adjust to, and soldering clean parts &
    boards with a freshly cleaned tip is as easy as with tin-lead. The
    main problem is that the lead-free solders oxidise on the iron *much*
    faster than tin-lead; while I might solder 20 or 30 leads between tip
    cleanings with tin-lead I found myself cleaning the tip every 2 or 3
    joints with lead-free. Furthermore the lead-free dissolves the iron
    coating on soldering iron tips much faster than tin-lead, so you will
    probably get significantly shortened tip life. I am hoping that as
    lead-free becomes more common better fluxes and tip coatings will
    alleviate these problems, but AFIK this has not happened yet. Spray
    or other liquid fluxes pre-applied to the boards can help make the
    soldering easier at the cost of more difficult cleaning.

    BTW "no-clean" fluxes are NOT no-clean when used with manual
    soldering; these fluxes depend on a precise heating profile to
    completely deactivate them during soldering which cannot be insured
    with any form of manual process; they can be used for manual soldering
    but must be cleaned.

    I would love to hear how you make out with your conversion.

    Regards,
    Glen
     
  5. ddwyer

    ddwyer Guest

    A US defence contractor has informed suppliers that lead free
    soldering will be unacceptable .
    They are particularly concerned about the possibility of tin whiskers
    forming. Any knowledge out there.
     
  6. Glen Walpert

    Glen Walpert Guest

  7. Baphomet

    Baphomet Guest

    I think the O.P. was from Great Britain. Google Tin whiskers soldering
    http://www.turi.org/PDF/TI_Tin_Whiskers_and_Pb_Free_Finish_Evaluations.pdf
     
  8. Baphomet

    Baphomet Guest

    And yet another http://nepp.nasa.gov/whisker/anecdote/20year/
     
  9. I read in sci.electronics.design that Glen Walpert <>
    For defence and automotive applications, the behaviour of the solders at
    temperatures below about -20 C need to be investigated. At -23 C, pure
    tin undergoes a phase-change, to an at best semi-metallic form. The
    alloying elements no doubt affect this, possibly quite a lot, but one
    needs to know!
     
  10. Baphomet

    Baphomet Guest

    Apparently not if the government defense industry is currently proposing
    banning lead free soldering because of tin whiskers. I really don't know
    first hand because I have been out of the military industrial complex since
    about '77. Back then, lead free wasn't even a consideration in the mind's
    eye of the most politically correct ideologue.
     
  11. Jim Adney

    Jim Adney Guest

    We're now using a lead free alloy from Kester in our lab where all the
    soldering is by hand. It's in wire form on rolls that look just like
    the stuff we're all used to for the past 70 years.

    It seems to work well enough, but I remain skeptical....

    -
     
  12. Glen Walpert

    Glen Walpert Guest

    Where did you hear about this supposed ban on lead-free solder? Any
    reference for either the ban or evidence of tin whiskere from any
    current lead-free solder? I for one have not seen either, and I read
    all articles on lead-free in the major trade rags.

    A ban due to evidence of tin-whiskers would be big news these days,
    news I probably would have heard. Quite different would be waiting to
    approve lead-free for reliability-critical applications until there
    were enough years of trouble-free use in other applications, which is
    rather more likely, entirely reasonable, and not in any way indicative
    of known problems with lead-free.

    Regards,
    Glen
     
  13. I don't understand why you think the melting point would rise.
     
  14. A few years ago, there was a lot of information on the "Indium
    Corporation of America" web site on lead free solders. These often
    employ tin, indium, gallium(?) and bismuth. They also make "pre
    forms" that have just the right amount of solder in just the right
    places, in case you are making a lot of some board.

    I have worked with Indium / Gallium / Bismuth at different times. The
    Indium+Gallium eutectic is liquid at room temperature, and has an
    appearance very similar to mercury. It has the suprising property
    that it (appears to) dissolve aluminum, which ultimately deposits as a
    soot-black powder on the surface. I speculate that this is finely
    dispersed sapphire, but haven't run any analysis. Indium alloys also
    "wet" glass.

    I do have an alloy from the hobby shop that melts in warm water, but I
    am pretty sure that it contains antimony, cadmium, or both. I thought
    that it would be interesting on a project to electroplate an alloy
    that will melt in boiling water, and then use steam on an open stove
    to "wave solder" the board. I believe that there is a "green patent"
    in that idea.

    I am not aware of health concerns with Indium or Gallium. Bismuth is
    very inert, and possibly the least toxic of the metals. This is
    suprising with respect to its location in the periodic table, but I
    believe that this is a soluability issue. It precipitates from
    aqueous solutions that are more basic than about pH of 1.5 or 2 and is
    probably cubic in hydroxide concentration, so there may be a 10^15
    concentration differential from pH 2 to 7. One of the patents in the
    last 5 years mention that several bismuth salts kill harmful bacteris
    (e. choli I think) in seconds in simulated gastric juice, but are
    essentially not harmful to them at neutral pH.

    Copper is only sparingly soluble in bismuth. I would anticipate that
    a solder intended for hand soldering would be compounded so that it is
    saturated with copper, but that is pure speculation from me. I
    haven't seen the phase diagrams for copper+indium or copper+gallium.

    Bismuth does not tarnish quickly in air at office temperatures. Some
    of my ingots are several years old, and still have a "shiny"
    appearance. I don't have any tin side by side with the same storage
    history, but my gut feeling is that bismuth tarnishes more slowly than
    tin. However, in sulfur containing environments I expect bismuth to
    form a black sulfide very quickly.

    Bismuth has the property that it expands on freezing, so that the
    crystals float on the melt. It is possible to compound alloys that
    don't appreciably change volume on freezing. These materials are
    useful for high detail metal castings.

    Bismuth also "flows" pretty much as a liquid under high pressure (high
    shear?). I made some pellets of different thickness in a 13mm IR
    press (20 ton press) and the bismuth flows up the space between the
    piston and cylinder. This is especially suprising because of its
    brittleness at ambient conditions. It also takes excellent detail
    from the surface, and I am going to try to press holograms into it
    whenever I get around to making a master.

    Pure indium is very malleable. A person can leave a thumb print in an
    ingot of pure indium. I don't know the behavior under pressure, but
    it seems worth investigating whether it would stand up to vibration,
    or whether mechanical engineering practices could exploite its
    softness to make self-healing joints.
     
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