Soldering SMD LEDs




Introduction: Soldering SMD LEDs

SMD, (Surface Mounted Devices) LEDs, love these little suckers, working with them, not so much. The good thing is that the price has come down and the brightness has gone up as compared to the recent past. The ones that I’ve ordered are only a buck and a half each and rated over 100 lumens.

Step 1: Commercially Available LED Bulbs

One day, I just felt like replacing some incandescent 194 bulbs with LED bulbs for my car. The picture shows 2 different commercially available ones. Both have decent light outputs, appears to be sufficient for side markers, license plate illuminators, and so forth. The flat one is cheap, just a couple of bucks works great in my license plate lights even though it doesn’t point directly down on my plates . Actually, it worked a little too well for my taste. I’m not exactly a fan of having attention grabbing illumination for my plates. The one on the right is a well designed replacement for the 194 bulb. The light distribution is probably the closest possible for any array of LEDs to approximate an incandescent 194 bulb. From what I was told, it’s made in Japan and soldiered by robot into these neat little buggers.

Anyway, with these commercially available ones that I already have, why bother putting together one from scratch. Well, I simply didn’t like the color. Yes, there are some offered in different color temperatures of white, but why not, I already mentioned they are cheap. I can sleep well experimenting with cheap stuff!

Step 2: What Was Used

There are great LED current calculators and theories on the web, so I’m not going to go into details on how to properly power these LEDs. Just know that you’ll need to feed them the right amount of electrical volt/current and to make sure they don’t overheat or else they will fry.

Here's what I've needed used:

SMD LED emitters
Solder (rosin core) for electrical applications, soldering iron. Temperature controllable iron really helps or if you’re cheap like me, the Home Depot light dimmer special will work just fine.
Double stick foam tape, and regular tape
Magnifying glass, helpful to be able to see these suckers.
Flux, in case need to re-solder anything that didn't turn out well the first time.
Copper Wires, I've used cat 3 solid core, these are rigid enough to hold its shape and thin enough so I can bend it easily into a tight configuration.
High Pressure Laminate (samples)

Step 3: Here We Go

First of all, I did some measurements of a 194 bulb, and did some sketches to approximate where and how to arrange the emitters. From those sketches, figured out the approximation of where the wires and the rest of the components need to be.

  First was to tin the copper wires, this is easily done by holding the iron to the soldering wire and running the copper wire back and forth on the iron.  This coats the wire with a layer of solder and primes it for easier assembly.

Now for tinning the LEDs, I smashed a portion of the soldering wire flat, careful to not smash it too much because there is rosin flux in the wire. Then used an xacto knife, cutting little squares, probably no more than 1/2 a millimeter long. To hold the LEDs in place, cut a piece of double stick foam tape and just stuck it to down to something that wont move. The double stick foam tape does an adequate job on holding the LEDs temporarily free my hands from having to hold the piece down. Now here is the part where having a steady hand helps. I was able to pickup a piece of the precut soldering wire with a sewing needle and accurately align and deposited it on the contacts. A light prick, just enough pressure to indent into the surface will allow the small piece of soldier to be lifted. A gentle wiggle when in position will dropped it in place. A light touch of the tip of the soldering iron and presto, nice microscopic balls of tinned contacts.

Next, holding the tinned wires over the contacts, or just tape the wire over the contacts, any way  to make sure the wire will only move either up and down and not side to side will help. Again, tapped the iron on top of the wires and once you hear the sound of the solder fizzing, found I have tiny LEDs soldered to a thin wire.  Looking at it with a magnifying glass showed how well formed the soldering worked, and considering how small things are, it’s really impressive. The key was to be able to control the amount of solder that ends up on the final product. Cutting little bits of solder prior to heating things up gave me precise control. Tinning each sides of the object I’m trying to solder allowed the separate pieces to bite on to each other as the temperature hit the melting point of the solder.

Of course, just the nature of doing things by hand, there’s bound to be mistakes, de-soldering is way easier to do. To re-solder just dab the area with a little flux on the end of a needle and press with the iron until results are to your liking. For the most part, I got away without de-soldering anything while using the tinning method, but trying to de-soldering parts (that went crooked) needed to have a heat sink to keep pieces that was good from also coming off.  As described on my materials list, my soldering iron is not connected directly to a wall outlet, but goes through a metal J-box consisting of a duplex outlet hooked up to a slide dimmer. The soldering iron by itself is actually too hot for such small pieces, having the ability to limit the heat coming off the iron gives a little more time to keep things from getting out of hand.

Step 4: Not Quit As Planned

Testing, it lit up, as expected, but had no idea how well it will keep working. Right away, there was a problem. The resistor got scorching hot hot. Not good, resistor are supposed to get hot, bringing down current by converting it to heat, but it was so hot, that I was afraid it will melt the solder, and fry the LEDs no less. Well my goal was to be able to keep all this in a tight configuration (and not change the wiring /sockets) to my car, the only thing I could think of doing was to add some length of wire between the resistor and the LEDs. I managed to spiral 2” of extra wire between the resistor and the first LEDs in the series just so there is at least some buffer from the heat conducting to the LEDs.  At this point, I’m just decided to put it together and just go with it. I couldn't think of any other ways to dissipate the heat since I can't fit a heat sink into the lens assembly of the car.  Plus, anything else I add will either block the light or show up as noticeable junk, my side markers are clear lens.

To make the interface between the socket and the LEDs, I got a hold of some counter laminate samples, cut them to a square shapes that will slide into the sockets and used epoxy to form the base of the array. The two long wires protruding forward is from the soldiering of the heat sinks. It helps stabilize the array and shed a little heat.  Figured it wont really be visible once in the diffuser housing so just left it long.

Step 5: Update - Bummer, Sort Of

Well, the LEDs been in the car over 5 months and to my disappointment, at least 1 of the 3 emitters, has died. This happened on both sides. I'm not totally surprised about that. But I am surprised that part of the array is still working, I expected the whole thing to black out since all the LEDs are placed in series. For now, I'm just waiting to see when the entire thing will fails, for now, it’s still plenty bright. I suppose trying to make a 300+ lumen array this size is a little on the wishful thinking side without proper heat management. But hey, it was educational and I discovered some useful techniques I’m sure will come in handy for future projects.

Anybody got any ideas or suggestions on what else I could have done to make this work within this size and output let me know, ‘cause one day, just maybe, I might even try to replace the halogen headlights with LED(s).

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    8 Discussions


    4 years ago

    Planning on a similar project, with Warm Whites, wanted to look for tips on not over hea the LEDs when soldering. Planning on using a dot perf. board with big solder lines as a heat sink, and will run them lower than the rated current.


    Reply 4 years ago

    old post i know, but i liked it :) had to comment

    Doktor Jones
    Doktor Jones

    6 years ago on Step 5

    You probably needed higher-power resistors, I'd imagine that's why they got too hot. Also if just one of the LEDs fried, it may be operating as a short-circuit, which will cause the others to fail soon.

    In the future, I might suggest building a small buck converter as a current regulator to install behind the lamp assembly (so it's neatly tucked away inside the car). I actually intend to do something similar for my truck's dome light, so if that works well I'll try to remember to follow up and let you know :)


    Reply 6 years ago on Introduction

    Had a feeling it would eventually give, actually surprised how long it lasted considering I knew it was really hot to the touch. Anyway, found warm whites for a couple of dollars, so probably not worth making your own these day. Exited on these new COB LEDs, these are definitely bright enough to replace my low beam head lights. Maybe eventually take a stab on converting these. displacing heat would definitely be the biggest challenge. Anyway, good luck with your project.


    6 years ago on Introduction

    When making gizmos for a car you have to make sure vibration will not destroy your handiwork. All components should be tight down onto the PCB, avoid long component leads and it is recommended the finished product should be potted.
    If you pot ( cast in resin) the PCB do not use a resin that sets rock hard and shrinks when cured as this can also break components or connections.

    From your photos it looks like the whole job was a recipe for disaster. Sorry about my negative comments but vibration and water are two big contributors to failed electrics in a car.



    Reply 6 years ago on Introduction

    It's all good, no need to be sorry for offering your thoughts, and yes, did consider the vibration issue. As I saw it, there's 2 was to handle it. One way is to arrest it and design it so that the force of the vibration cannot overcome it, or just make sure it can vibrate without coming apart. Basically it was meant to act like a spring and absorb the vibrations.

    Guess This is a good time for an update. I have since took it out, one side started to blink. The heat killed it since it didn't have enough surface area to dissipate heat quickly enough. I knew this would be a problem, it got scorching hot when I lit it up on the bench. I wasn't able to keep my fingers on it after 20 seconds. That twisty spring thing was a result of that, but it had by no mean the necessary surface area to be effective enough.

    Anyway, I thought the way I was able to cleanly and precisely soldier such small items might be useful to someone else. The project overall was a good experiment. I wanted to achieve a minimum of 300 lumen otherwise if it wasn't as bright as the incandescent, then there wouldn't be a strong reason for me to try this. There were no LED replacement with that sort of output (at that time) for this size bulb. I presently using a pair of china made 3500k LEDs with an output of about 300 lumens. Except it's huge and use a dozen emitters to my original that uses only 3 emitter. I missed having the 4000k neutral white, planning to eventually try this again since I still have enough pieces from my original make. Definitely will need to design a real heatsink this time, just need to figure out how to fit it through that small hole in the housing.


    8 years ago on Introduction

    Those Specific LED's Need to be heat sinked better. 5 Months isnt a long time, their supposed to operate way beyond that. The Center thing is for a heatsink. Ive actually used the same ones you did, and despite what the data sheet says, dont run them at 150mA! 125 ma Is just as fine :)