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Thread: Soldering tricks

  1. #1
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    Default Soldering tricks

    Was wondering what soldering tricks exist; I recently had to replace a small surface mount capacitor (3mm in length)

    Tricks I know so far

    * Use a low melting point alloy to remove the component without over-heating the board
    * Use lots of flux and copper braid to clean off the old solder
    * Use traditional leaded solder on the replacement to keep soldering temperatures down

    was hoping to learn some more tricks for next time.
    Last edited by ashiekh; 05-18-2019 at 04:53 PM.

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    You could use a desoldering gun. Even with desoldering gun, ADD solder to the joints. Then apply desoldering gun, and wiggle the tip (make circles around the lead) until the solder is melted and suck the solder while you're wiggling the lead - this way the lead has less chances of sticking to the side of the hole and the solder can be sucked from the hole.

    Motherboards or boards with leds often have lots of copper which act as heatsinks, making desoldering hard. You can pre-heat the circuit board to 60-80 degrees Celsius using infrared heater, or using a hair dryer a few cm away from the area, or a paint stripping gun some distance away from the board.

    Use LIQUID flux on the terminals because it helps to break the oxide layer over the metal, which helps transfers heat from iron tip into the joints faster.
    ADD solder to the joints that you want to desolder. Even regular leaded solder will have lower melting point (180-183 degrees Celsius) compared to the common lead free solder with higher melting point (~217 degrees C). So by adding some solder over the joints, you're lowering the overall melting temperature.
    You can ADD solder over both joints and then lay the soldering iron tip flat over both joints to have them warm up at same time and then pull the capacitor out.

    If there's solder in the holes and you can't get it out, ADD solder and while the solder is kept warm by the iron tip, carefully insert a stainless steel needle from the other side into the hole. Solder won't stick to stainless steel, so once you insert the needle, you can move the iron tip away and then carefully pull out the needle.
    The needle must be thinner than the hole, you have to be careful not to scrape or break the inner ring of metal inside the hole ... some boards have multiple layers and if you break the inner metal you may break connections within a middle layer.

    LIQUID FLUX is like liquid gold. When in doubt, pour a few drops of liquid flux on the joint. Even if your quality solder wire has 2-3% flux, you can't go wrong adding flux.

    I'm not a big fan of desoldering wick but mostly wasn't a fan because I used to buy cheap solder wicks with shitty flux. FLUX is critical for a desoldering wick.
    If you're not pleased with the wick, pour liquid flux on it, let the wick absorb flux.

    I buy cheap flux from TME.eu (distributor of electronic components like digikey.com or newark.com/farnell.com or mouser.com), they distribute stuff from a Polish company that makes rosin based and no-clean liquid flux and sells it in bottles up to 5 liters (500ml or 1 liter bottles for something like 10-20$) ... as cheap as single 10ml flux pens.

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    ashiekh (05-22-2019)

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    Default

    Much appreciated, many a useful suggestion.

    Perhaps it is time for me to invest in a de-soldering gun.

    Adding solder and flux is already on my list, but still appreciated, and I have a set of stainless needles for through-hole work. I also use cheap copper braid, adding liquid flux (Kester 186) before I use it. I tend to clean the flux off, even if it is no-clean, perhaps just to have nice looking work (isopropyl alcohol seems to work just fine for this).

    Not sure I need 500 mL of flux, my 1.25 oz bottle of Kester 186 seems to be lasting (and has a 2 year shelf life).
    Last edited by ashiekh; 05-18-2019 at 07:22 PM.

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    Quote Originally Posted by ashiekh View Post
    Was wondering what soldering tricks exist; I recently had to replace a small surface mount capacitor (3mm in length)

    Tricks I know so far

    * Use a low melting point alloy to remove the component without over-heating the board
    * Use lots of flux and copper braid to clean off the old solder
    * Use traditional leaded solder on the replacement to keep soldering temperatures down

    was hoping to learn some more tricks for next time.
    As noted by others: spare the flux, spoil the joint. For SMT, I will often pre-tin one of the pads while leaving the others clean and use some down pressure with the iron for that joint. Then you can go to work laying in a proper fillet for everything else. Magnification is also very important for SMT, so keep your eyes open for a good binocular microscope with 10x magnification (20x for 1005 parts and similar which are like grains of sand).

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    ashiekh (05-22-2019)

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    A binocular microscope sounds very useful.

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