Soldering Micro LEDs

ajkochev Jan 15, 2021

  1. ajkochev

    ajkochev TrainBoard Member

    I just got some 603 SMD LEDs and I'm intimidated by the size a bit. Looking for advise on the best way to solder wires to them. I have 42 and 40 AWG wire and 38 is on the way. I'd especially like advise on soldering bi color leds as one side has two positives and I want a separate wire for each.
  2. RBrodzinsky

    RBrodzinsky Staff Member TrainBoard Supporter

    Make sure you have a very fine tip soldering iron. I use a 1/64" conical tip on my PACE ADS200. With the proper sized tip, you can keep it hot enough to act quickly, while also ensuring you aren't pouring heat into the device.

    For 0402 and 0603 devices, I like to use the LED/Wire Holding tool from Also, I find Tim's Intelligent LED tester (on the same page) invaluable. For the bi-color 0603s, I just use the holder, and carefully ensure I am soldering to just the correct corner of the device.

    I simply use 38awg magnet wire for all my devices, works just fine. Oh, and I always wear an optivisor with the #7 lens when doing these.
  3. rray

    rray Staff Member

    Get some Blu Tack Putty, put the SMD face down, place the pre tinned and clipped wires using the putty to hold in place while soldering.
    blu tack.jpg
    Kez likes this.
  4. Sumner

    Sumner TrainBoard Member

    Agreed, the holding tool is well worth the money. Haven't tried the tester but live with the optivisor on,

  5. ajkochev

    ajkochev TrainBoard Member

    Thanks everyone. I was able to develop a workflow and got several wired.

    I need more LED help thought. I got my 603 LEDs soldered but need to know how to wire them is special circumstances. I have a bi-color Red-Green LED. The Red side is 2.2v and the Green is 3v I cannot get both red and green to light at the same time but I'm only using one tester. I'm assuming it is the voltage difference between the two. I need to know how best to wire these and what resistors to use so they can both be on at the same time and I get yellow.

  6. Sepp K

    Sepp K TrainBoard Member

    Usually Red is one polarity of DC, Green is the other polarity, and Yellow is AC. I've never worked with bi-color SMD's, though.
  7. RBrodzinsky

    RBrodzinsky Staff Member TrainBoard Supporter

    You have to plan your resistors accordingly. Really depends on the voltage source, but, from your first post, what you want is to have two wires going to the positive with a common wire coming from the negative. Then, hook two resistors on the positive wires and feed into the resistors from your positive DC. Start with the resistors the same (but don't feed from the same), and see how the color is. Then adjust one resistor up/down until you get the color you want.

    Since we know nothing about your LEDs (wavelengths, etc) (except possibly the forward voltage from the text I quoted) or your input voltage, it is impossible to give any additional guidance (and even then, what "yellow" do you want?).
  8. brendanf

    brendanf TrainBoard Member

    Honestly I tired that before and it is very hard to do. You can actually buy those leds with wires pre-soldered on them from some of the chinese wholesale sites. save yourself the aggrevation.

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