Soldering 12 gauge solid wire to copper PC board

Discussion in 'Homebrew and Kit Projects' started by KG4GUF, Dec 3, 2010.

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  1. KG4GUF

    KG4GUF Ham Member QRZ Page

    I've been working on a DC distributor inspired by and having some real problems soldering the solid 12 gauge copper wire I have to the PC board. No matter how long I hold the 40 watt soldering pencil at the board and wire, I can't get the wire hot enough to melt solder. I always end up with a blob with a hole in it surrounding the copper and the hole. I've tried applying rosin flux to the wire and board, but that just creates a sticky mess so far. Any tips for this type of soldering? Do I just need a large iron/gun/torch for this thing?
    Thanks for any help,
  2. KF5FEI

    KF5FEI Ham Member QRZ Page

    You need a bigger iron. We regularly solder #14 and #18 stranded wire at work, and we use a commercial soldering station and a large tip -- on some boards we have to crank the heat up a bit to make it work. For the larger stuff I would use a Weller gun.
  3. WA4OTD

    WA4OTD XML Subscriber QRZ Page

    Yes large iron. and as always depending on how often you will do this you can get cheap "stick" or expensive iron where you can change out the tips and adjust the temperature.

    Wire like this will just sink away the heat.
  4. W9GB

    W9GB Ham Member QRZ Page

    Matt -

    A. Use a Temperature Controlled soldering iron (or station) to achieve repeatable results!
    Cheap line voltage irons bought at local hardware store or Radio Shack -- terrible tools for learning proper soldering techniques.

    B. Use a Quality Tin/Lead solder, such as Kester "44".

    C. Your work metals need to be CLEAN and free of oils or coatings -- before soldering.

    Proper soldering requires making 3 proper decisions for your work.

    1. Proper TEMPERATURE for your solder.
    This is 650 to 750 degrees for 60/40 or 63/37 Tin/Lead solder. NEVER "dial up" an adjustable station past 750 degrees for Tin/Lead solders -- that is why I refer to it as the Idiot Knob !

    2. Proper PROFILE.
    USE a Chisel or Screwdriver tip. Cheap soldering irons are sold with Conical tips -- a Conical tip is the WRONG profile for a majority of amateur radio soldering.

    3. Proper MASS.
    MATCH the SIZE of the tip to the MASS of the soldering work. You do not cook soup in a metal pot with a lighter or a match !!

    In your specific case, I would recommend a 1/8" or 3/16" Screwdriver tip.
    1/8 inch Screwdriver tips: Weller ETC for Weller "EC" series; WES51, or WESD1. Weller PTC-7 for the Weller TCP series.
    3/16 inch Screwdriver tips: Weller ETD for Weller "EC" series; WES51, or WESD1. Weller PTD-7 for the Weller TCP series.

    Last edited: Dec 3, 2010
  5. VK2TIL

    VK2TIL Ham Member QRZ Page

    As the others have said, a large tip is required; I think that even 'GBs spec for tip size is minimal.

    You are not heating just a little of the 12g wire; being copper, it's transferring heat along its length as fast as you can pour it in at the joint.

    A fair mass of copper is being heated and that calls for a large tip.

    A tip is like a bucket full of heat; you have to have enough in the bucket to fill the work with heat quickly.

    Extra temperature is of little use if the tip is undersize.

    In the job you are doing, the holes are not strictly necessary; you could just lay the wires flat on the PCB and solder. But the holes will help hold the wires steady so are a good idea. They will also hold the wire if the PCB copper starts to peel-away so that makes them an even better idea. :)

    If you use the holes, pass the wire through in a Z-form so the joint lies flat against the PCB copper.

    Technique; first thoroughly "tin" the wire; get as much solder as will stick on the part to be joined before it's laid flat against the PCB.

    Also tin the PCB at the joint.

    Now lay the wire on the joint and heat by placing the flat of the tip on top of the wire and pressing down; if the tip is large enough, heat will flow into the joint through the wire and it will all suddenly melt together.

    Since there is now a lot of heat in the wire, the solder will take some time to solidify; do not move anything until it does so.

    Some kind of clamping or holding helps a lot. A weight on the PCB and another weight on the wire(s) would be simple; to avoid burning the benchtop, I use a square of glass with rubber feet glued to the underside. I had a tile once as a heat-protector but I lost it. :)

    Once you have mastered this job you can begin to call yourself a solderer; as in welding, joining a thin part to a thick part is one of the most difficult tasks because of the different heat requirements of each part.
  6. VK2TIL

    VK2TIL Ham Member QRZ Page

    I usually try to "answer the question" instead of trying to re-design a poster's project but I have had a look at the web page you posted.

    Some of the designs might be marginal as far as current-carrying capacity is concerned if large currents are contemplated.

    This depends on copper thickness (usually one-ounce in commonly-available material), trace width and acceptable temperature rise so there is no "fixed" answer.

    Google "pcb current capacity" to find information and calculators.

    If in doubt, solder some wire along the tracks; this will further enhance your soldering skills. :)
  7. WA7PRC

    WA7PRC Ham Member QRZ Page

    Hi Matt,

    Copper, aside from being a good conductor of electrons, is also a very good thermal conductor. All that copper is wicking the heat right out of your 40W iron. As was mentioned, you don't have nearly enough "horsepower" in your iron. For a job like this, I'd use at least 100W of power and/or an iron with a tip that has a lot of mass. I use a Weller 8200 solder gun (100W/140W) for things like this.

    This type of gun is nothing more than a step-down transformer with a 1 turn secondary. It passes a large current thru a copper wire tip. When the tip opens on Sunday night and I don't want to wait 'til Monday morning to buy a new one, I just form one out of 12 ga solid house wire. ;)

    Ace Hardware has the 8200 for $34.
  8. VK2TIL

    VK2TIL Ham Member QRZ Page

    The Scope range of soldering irons has been made in Australia for a very long time; they were common when I began soldering more than 50 years ago.

    I don't think that they are available in the US; perhaps they were, years ago.

    The principle is simple; there is a carbon cylinder (something like a carbon motor brush) in the barrel behind the tip.

    There is a trigger arrangement that, when pressed, pushes this carbon against the bottom of the copper tip; this completes a circuit and very heavy current flows through the carbon and the tip to ground.

    This heats things very quickly; leave the trigger "on" for a few seconds too long and the tip, the carbon and the end of the barrel glow bright orange!

    I have a Scope transformer (3.3v @ about 30+A I think) and two irons; 70w (baby) and 100w "standard".

    The "baby" has a better trigger mechanism; it's possible to do large soldering jobs (UHF connectors, brass RF-shield cases) by just "tapping" the trigger to feed-in more heat as required.

    Not ideal for SMD :) but great for other jobs.

    But I think that our OP would be best-served by a basic iron of about 40-60w with a tip of, perhaps, 1/4" - 3/8" diameter.

    Wattage is important but it's secondary to a good-sized lump of copper in the tip.
  9. AI3V

    AI3V Ham Member QRZ Page

    A Star Trek tribute play by AI3V:

    (Bridge of Enterprise, in background general quarters alarm is going off)

    Sulu: Captian, Klingon ship dead ahead.

    Spock: They are firing torpedos.

    (strange space torpedo sound)

    Spock: Hit on starboard shields, shields down to 16%

    Captian Kirk: Scotty, I need mor heat.

    Scotty: I'm giving it all she's got captain, 2 dylithium crystals are shot, and the third one has a hairline fracture.

    Captian Kirk: Scotty, I...Need...Mor...Heat...

    (sound of bulkhead falling on bridge as klingon torpedo detonates)




    I have 7 or 8 soldering devices, from a 20 watt pencil, to a propane torch heated copper slug the size of your thumb.

    Just a note,IMHO the temperature of the iron is not as important as the thermal mass of the tip.

  10. KG4GUF

    KG4GUF Ham Member QRZ Page

    Thanks for all the replies!
    I'm not sure if Radioshack sells chisel bits for my current pencil, but if they do, I might try that seeing as they shouldn't be much more than $2. If not, then I'm looking for something inexpensive that I can go pickup in the store.
    Homedepot and Lowes both sell this Weller 40 watt kit
    for a decent price and it looks like it includes a chisel tip. The Atlanta Ham Radio Outlet also has their grand re-opening tomorrow and hopefully some good deals so I'll look there.
    Also, I didn't even think about the current capacity of the PCB. My SEC-1223 can have a draw of 23 amps and while I certainly wouldn't want to draw that for extended periods, I'd rather not start a fire on top of my desk. I have some brass strips from a previous project, 1/8" thick. I'm assuming it'd be much harder to solder these?
    Thanks for all the help.
  11. WN2SQC

    WN2SQC Ham Member QRZ Page

    Try yard sales, I picked up a 400 watt iron for $1, works fine and solders anything you
    want. It also works fine for desoldering components quickly. When the tip of my soldering gun splits I spread the tips about 1/8" or so and use it for resistance soldering. Talk about heat, but remember there's a lot of current going through whatever you're soldering, not recommended for solid state equipment.
  12. VK2TIL

    VK2TIL Ham Member QRZ Page

    I have the same model Weller; SP-40. Mine must be 30 or more years old!

    At under $20 you should add one to your tool collection; you will find plenty of uses for it in the future.

    As Rege noted, most serious workers have several soldering irons; I didn't realise I had so many until I thought about it. :)

    I have;

    • A 40w station with a range of tips;
    • The Weller SP-40;
    • One "standard" Scope and two "mini" Scopes and
    • A gas soldering-pencil kit.
    The Weller will do what you want with the 1/4" MT10 tip; it will solder your wires and also solder your brass strip to the PCB.

    Soldering the brass strip will be less-demanding; the strip will only be a few inches long and it will heat quickly as the heat has no-where to go, unlike the 12g wire where it "escapes" along the wire.

    Use the same technique; tin the brass and the PCB, hold the brass on the PCB and press down on it with the face of the tip. Hold the brass steady with pliers or similar and don't move it for a while (perhaps 10-20 seconds) after the solder has flowed.

    The essence of all good soldering is to get-in & get-out in an instant; that requires sufficient heat capacity in the tip for the particular job.

    If the solder doesn't flow in a second or two, never keep the tip on the job in an attempt to put more heat in; that melts insulation, lifts PCB tracks and damages components.

    Pull back and get a larger tip or iron.

    Have fun!
  13. WA7PRC

    WA7PRC Ham Member QRZ Page

    Your current 40W pencil isn't working. A different 40W pencil will be no better. You need either a humongous tip to store heat energy (much like a flywheel) or/and you need more "horsepower" behind the tip. Your description of your results w/ 40W and my experience tells me you need more horsepower.

    Brass is also a good thermal conductor. Soldering to it is almost as difficult as the same amount of copper. You'll still need lots of power (≥ 100W) to keep the tip hot.
  14. AI3V

    AI3V Ham Member QRZ Page

    One tecnique for soldering , say, a brass plate when your iron just isn't quite enough is to use a hotplate.

    Place the item(s) to be soldered on the hotplate and get them allmost hot enough to melt the solder, then come in with the small iron and finish up.

    This is paticuarly usefull for heavy metal work like bussbars, radial plates, or working with waveguide.

    Kitchen stove works great. CAUTION - AI3V is a batchelor, this stove advice may be null and void if a XYL is involved.:p

  15. WA7PRC

    WA7PRC Ham Member QRZ Page

    Yep! I have a small homebrew hotplate and a large commercially-made hotplate. But, if the work is too unwieldy to use a hotplate (or the XYL nixes the idea), you can use a heat gun or handheld hair dryer to preheat the item.
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