Need help/advice on solder paste for cell phone PCB

Discussion in 'General Electronics Chat' started by Brap Brap, Apr 7, 2016.

  1. Brap Brap

    Thread Starter New Member

    Apr 7, 2016
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    Hi guys, I'm trying to see if i can get some help/advice on some soldering work on PCB, mainly to replace a charging port. I have watched alot of videos and I think soldering paste seems to work the best,

    I was watching this video, and it it showed that he used a soldering paste, but he used a stencil to apply the paste, then i watched

    and he didn't use a stencil. In the 2nd video the paste automatically attached itself to the wires. Is it because its a different kind of paste than the one used in the first video? I've looked at some paste and some say no clean while others are just soldering paste. I have also noticed that the 2nd video he mentions that its a 63/37 paste, what exactly does that mean? is the paste in the first video not a 63/37 paste?

    lastly my 2nd question is, i have a Metcal SP200 soldering machine, I would like to get a scapal like in the first video for my machine, how do i go about finding that? how do i know what pen fits my machine? currently i have a tip that is labled 9357LF SSC-722A.

    I really appreciate everyone that read through this and can give me some advice.

    thanks
     
  2. dl324

    Distinguished Member

    Mar 30, 2015
    3,211
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    Welcome to AAC!

    Soldering surface mount devices is usually easier with solder paste, but solder wire can also be used. Using a stencil makes applying paste easier, but the dab method can also work. If you don't apply too much solder, you don't need to worry about solder bridges.

    Lead free solder, and it's associated problems, was brought to us by misguided intentions of the European Union. You'll find lead solder easier to work with.

    You can use the "drag" method with a soldering iron using either solder paste or wire.
     
  3. Brap Brap

    Thread Starter New Member

    Apr 7, 2016
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    0
    so what you're saying is, if i just run a thin line of solder paste across all the connector like in the 2nd video then i dont have to worry about solder bridges correct?

    when i'm looking for solder paste, there are so many different kinds, besides lead free, what else do i need to look for? just 63/37?

    as far as the soldering on the 4 holes on the charging port, since the hole is a bit bigger, should i buy a different paste for that and not use the syringe? It seems like the syringe style cost more and the one in the tub cost less. I was thinking of using a paste with a syringe with the mini connectors while getting paste that comes in a tub to do the 4 bigger holes that hold the charging port in place. Do you think this is wise?

    thank you for your reply
     
  4. dl324

    Distinguished Member

    Mar 30, 2015
    3,211
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    The key is to get the line of paste thin enough. If there's too much solder, you can get shorts between pins. When that happens, you can use solder wick to remove the excess.
    You should use solder wire for through hole components.
    Solder in syringes might be smaller particles and has more flux in it to make it flow through a small opening. I prefer to use the thicker paste and water it down with more flux when I need a runnier consistency. Consistency is more important when you're using stencils.

    Solder paste has a shelf life (don't store it in a refrigerator/cooler that's used for food). I've used solder years past it's expiration date and haven't had problems; but my work doesn't need any certification. When it dries out, I just add more flux to rehydrate.
     
  5. KeepItSimpleStupid

    Well-Known Member

    Mar 4, 2014
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    63/37 is a lead solder that's easy to work with and solidifies instantly.

    A lot of the lead free stuff is essentially Sn96 (+other stuff), Rather high temperature and pretty strong, I hate the stuff.

    Some of the Bi (Bismuth) alloys are lower temperature and much easier to work with. Check out www.Chipquick.com

    Mixing solders can have some unintended consequences. It's sometimes done intentionally to facilitate removal.
     
  6. MrSoftware

    Member

    Oct 29, 2013
    497
    122
    This guy makes it look way too easy, but it's a great tutorial:

     
  7. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    4,769
    969
    63/37 is the percentage of tin to lead.. There are 63 parts of tin for 37 parts of lead.
    This is just about "obsolete" now as all exemptions for ROHS pertaining to solder are set to expire in July 2016.. (Exemption 7 I believe still allowed it for "critical" systems because the long term joint integrity of leadfree solder was still an unknown)

    Typically now many are using K100LD or similar.. Which is lead free tin based with 99.3% tin/.7% copper plus a dash of bismuth and nickel added to increase wetting,etc... This is also cost comparable with 63/37 but not nearly as costly as SAC solder which was supposed to be the replacement for tin/lead solder until people started complaining about the cost of it,etc...

    For DIY SMT use (without a stencil), a solder paste from Chipquik that comes in a small syringe is the best to use.. Just squeeze a small..small bit onto the pad to be soldered. It should have some flux in it too so that it cleans the contacts a bit before the solder is heated/solidifies..
    Some has a "tacky" flux which helps to ensure parts stay where they were placed during the reflow/soldering process..

    Solder also exhibits capillary action and will be "attracted" to metal so it "flows" together and pulls parts or itself into place..

    In general solder paste is for SMT parts and solder wire is for through hole parts..
    Solder paste can also be used with the "pin in paste" method for through hole parts when used with mixed boards of through hole and smt parts or the through hole parts are soldered on after the SMT parts via wave soldering or selective soldering methods..

    Oh and avoid trying the drag or long line of paste across all pads until you are skilled enough to do so.. Walk first.. then run..
     
  8. KeepItSimpleStupid

    Well-Known Member

    Mar 4, 2014
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    200
    With 63/37 it's soooooo easy to do the drag method. Not sure about anything else. My very first desolder(actually cut) and resolder was a CPU in a car radio.

    But then again I can solder pipe, electronics, braze/silver solder, weld (mig/tig/stick) and do some rudimentary glass blowing with quartz and pyrex.
     
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