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Can this PCB section be salvaged? Beginner struggling...thanks

Discussion in 'General Electronics Discussion' started by yul, Feb 18, 2018.

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  1. yul

    yul

    12
    0
    Nov 11, 2017
    Hello!! I am simply trying to change a resistor on this PCB but for some reason things got nasty.

    I believe my iron tip is possibly too big for the task...


    Looking at the PCB section where the piece should go, is this still a workable scenario?

    It looks quite burned where there is the missing piece and the track seems to be quite far away.

    Any suggestions on what to do moving forward please? Is there a specific tip I should be using here? Also will I need a magnifier?

    Why is everything so black? I barely touched in that area, only for a few second in trying to get the old one out.


    Thanks in advance!
     

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    Last edited: Feb 18, 2018
  2. davenn

    davenn Moderator

    14,003
    2,025
    Sep 5, 2009
    when you put the resistor lead through the hole bend it over and cut it to length so that there is enough lead to solder to that remaining end of track

    you may have to scrape off a bit of green varnish on the end of the track so you can solder to it
     
  3. yul

    yul

    12
    0
    Nov 11, 2017
    Thanks a lot!! I will try that. Did I burn that section or is this normal for replacement work?

    I am trying to better understand.

    Should I use a smaller tip? I can't seem to be able to reach in between without touching the joints on each sides.
     
    Last edited: Feb 18, 2018
  4. davenn

    davenn Moderator

    14,003
    2,025
    Sep 5, 2009
    yes, you have applied too much heat and it has lifted the track up of the board and then it got torn off

    not knowing what size tip you are currently using ?? but it sounds as if it is too big

    I use a needle nose sized tip on my variable temp soldering station

    T2417.jpg

    http://www.altronics.com.au/p/t2417-micron-lead-free-soldering-station-60w/

    these are an awesome soldering station.
    I have one in my workshop at home and two in my workshop for my day job

    you can see it is quite a fine pencil tip ~ 1 mm

    Dave
     
  5. yul

    yul

    12
    0
    Nov 11, 2017
    OK got it much appreciated!! I will review my setup.
     
  6. duke37

    duke37

    5,364
    772
    Jan 9, 2011
    I use a broad tip to get plenty of heat from a simple Weller iron. Tip it on its side if too large.
     
  7. Cannonball

    Cannonball

    193
    53
    May 6, 2017
    I would recommend getting an old board and a smaller tip and practice soldering. It is fun and your soldering skills will improve.
     
  8. FuZZ1L0G1C

    FuZZ1L0G1C

    366
    118
    Mar 25, 2014
    Generally, an iron of 30-60W should be suitable for most medium work, 25W for light work, and 100W for heavy duty.
    I have various sizes to suit whatever project I am busy with.
    The 100 Watt monster was used to strip old components from an obsolete motherboard.
    As long as you solder / de-solder very briefly, a bigger iron can be used, but there is a risk of lifting the track foils.
    Burnt paxolin - scrape carefully between tracks using the point of a craft-knife or similar until the beige shows through, carbon removed.
    Lifted tracks - a very thin bead of superglue GEL - not liquid, is run under the track route, then pressed down with a ball of aluminium kitchen foil until set.
    Place a small sample drop of GEL elsewhere to monitor setting time.
    Cleaning brush: If you can get hold of a 'Suede' cleaning brush, this tool has become a handy addition to my workshop.
    The fine brass bristles are less harsh than steel wire, while the nylon fiber bristles help to brush away any dust / swarf.
     
  9. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,505
    2,853
    Jan 21, 2010
    I'd really like to emphasise that while there is equipment better suited to some tasks, there is nothing that replaces skill.

    I always recommend a double flat tip (like a screwdriver) over a conical tip.

    My party trick (and you haven't lived until you've been to one of my parties) is to hand solder an 0805 resistor using a 250W soldering iron having a tip about half an inch wide.

    If you're ever removing pads or traces then you're doing something wrong -- however it still happens from time to time. I had some prototype board (from China) that would shed pads if you looked at it sideways. Be aware, take more care, and everything is fine (but I didn't buy any more of it).

    There are many things that can cause a track to lift, and knowing them may help you avoid them:
    • "Digging" with the soldering iron. You place the soldering iron on the joint and remove it, you don't scrape it back and forth or use it to dig into the solder.
    • Overheating a joint. There is glue holding the copper to the substrate. To much heat will affect the bond and it will come off. Smaller pads and thinner traces are easier to overheat. This is a temperature and time thing, don't leave the iron on the joint too long.
    • Mechanical stress. Placing stress on the joint in the direction that pulls the copper away from the board is bad. Again, small pass and this traces are most succeptible.
    • Iron too cold or with insufficient thermal mass. A nasty trick is placing a hot iron on a joint, the solder partially melts, then the joint removed heat from the iron faster than it can be replaced causing the solder to solidify any the tip to stick to the joint. Trying to pull the iron away can rip off a pad. This usually affects you if the tip temperature is only just above the melting point of the solder and you're using a small tip. If you're expecting leaded solder and the board happens to use a higher melting point lead free solder, this can catch you out too. Make sure your iron is hot enough and test on something "safe". Pads connected to internal ground planes can be hidden traps -- they're harder to spot than a joint in the middle of a large area of copper on an outside layer.
     
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