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Discussion in 'Electronic Design' started by Scott, Feb 6, 2009.

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  1. Scott

    Scott Guest

    I'm working on small project using some prototype circuit boards (8mil
    traces with 8mil gaps, no solder mask, mostly through-hole) and had a
    little difficulty with the soldering. Maybe my eyesight isn't as good
    as it used to be, or maybe the tip on my soldering iron is a bit worn
    out (it's a good temperate-controlled fine-tip soldering iron, but
    almost two decades old), or maybe it's the solder itself.

    Anyhow, I was using 0.031 solder for this job. I'm wondering if that's
    typical, or if I should find something finer? Where should I shop? I'm
    surprised to see solder is now very expensive via mail order ($20-$60
    per spool?).

    Also, I had a bit of trouble with the solder riding up on the tip,
    rather than onto the pin and pad. Yes, I did make sure to heat the pin
    and pad, and apply the solder to the joint.

    Thankfully I didn't bridge any of these microscopically-small 8mil
    gaps, but it was a bit of a slow and tedious process.
  2. Rich Webb

    Rich Webb Guest

    Pick up an Optivisor. It really helps.

    Might look at the pads, too. (no pun intended) If you're using round
    pads, try switching to elliptical pads for more contact area with the
    iron's tip.
    0.031" should be just fine for through hole (and much surface mount
    stuff). 63/37 or 60/40?
    Try fluxing the joint just a little before applying the iron. Kester
    paste flux (the kind in the flat little tubs) is fine; you can dab some
    flux on the joint with a toothpick. Or splurge and get a syringe of
    liquid flux. I prefer "regular" (not no-cleanup) but YMMV.
  3. tomrei

    tomrei Guest

    is it the IC that you are trying to soldering on to the board?

    from my experience i would suggest using solder paste and heat gun.
    using toothpick to apply small amount of paste on top of pads, use the
    heat gun to melt it, they will become hard solder and stick with the
    metal pad.
    then clean the rest of the paste off. place your IC on top of the
    pads, pins above the solder that's already there. carefully use
    tweezer to hold it there. then use the heat gun again, once the solder
    melted, the IC will drop on to the pad perfectly.

    it require some practice, but i find this is the best way of solder
    small foot print ICs, instead of solder each pin at a time.....
    beware of the heat gun, especially if you haven't use one before, if
    not careful you can burn the board or melt some other parts close by.

    hope it helps.

  4. Guest

    Is the solder you purchased new? It might be RoHS solder, it contains
    no lead and needs a higher temperature. It also doesn't wet as well.
  5. Rich Webb

    Rich Webb Guest

    Well, that doesn't have quite the primitive ambience as does a hunk of
    resinous goo on the end of a wooden stick but... probably a lot more
    practical. ;-)
  6. IanM

    IanM Guest

    You want primitive? Try a lump of real Rosin, straight from a third
    world market stall, beaten to a powder and a shot glass of the local
    clear unsweetened distilled rotgut to moisten the toothpick . . . .
    If the rotgut is over 90% alcohol, you can dissolve the rosin powder in
    it and use a brush!
  7. The flux that comes in a package like a Sharpie/Magic Marker is nice
    for SMT parts.
  8. qrk

    qrk Guest

    You don't say what brand solder you're using. There are brands of
    solder which use very poor grade fluxes, Globe being the worst I've
    ever seen. Quality of flux in the solder makes a big difference. I
    prefer Multicore or Kester 60/40 or 63/37, good old RMA flux, around
    0.020 to 0.025" diameter for most through hole. Your 0.031 dia solder
    should be OK. The newer no-clean fluxes are OK if parts are clean, but
    not as good as RMA.

    Solder riding up on the tip means that your tip is dirty. The tip is
    so dirty, it's solder repelant and needs to be scraped clean.
    Multicore makes a tip cleaner with pumice in it which cleans, tins,
    and fluxes the tip. The old, and unavailable except through E-Bay,
    TTC-1 tip cleaner is really good. They have a newer version out which
    is lead-free and works OK. This usually gets tips working like new. If
    tip cleaner doesn't work, you need a new tip.

    If all else fails, use liquid flux. Again, I like RMA. Your joints
    will come out looking very pretty with good flow. You can use alcohol
    to clean the board, but it will usually leave behind some residue
    unless you wash it a couple times then do a quick final rinse in
    running hot water.

    Newark is a good source for soldering supplies. Digi-Key and Mouser's
    lines are too limited these days.
  9. Ben Jackson

    Ben Jackson Guest

    If those are just bare copper (not HASL or otherwise plated) then you
    will need to flux the pads before you get nice flow on them like you
    might be used to with more finished PC boards.
  10. Jasen Betts

    Jasen Betts Guest

    0.71mm seems to be the smallest common solder size. (I figure that's 28 mils)

    at that price it sounds like you're talking 1kg (2.2Lb) spools.
    OTOH there may not be much demand for finer solder.
    ( will send you a 1kg spool of 0.71mm solder for 30 bucks inc. surface postage)

    0.56mm solder is less common and more expensive.
    try a flux pen.
    why no solder mask?
  11. Guest

    Very Low cost hot air reflow/rework gun and and paste dispensing
    available from China complete kit built up for £200 I also use 150C
    hotplate for single sided. Results quite professional
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