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Soldering millimeter components (Cree LEDs)

Soldering millimeter components (Cree LEDs)

Soldering millimeter components (Cree LEDs)

Hi Guys,

I recently bought myself some Cree LEDs ( XL-M 3 RGB + White ). I am planning on using a micro-controller to generate a light(colour) profile.
These lights are normally used with the four LEDs connected in series (with pre-fitting PCBs), however I require each of these to be individually set.
I have a relatively narrow soldering iron tip (& station). I have already spent hours frustrating away trying to solder leads, along with solid connectors.
I have managed to solder onto some of the legs, but it really isn't pretty. There is a largish copper heatsink inside the centre of the LEDs which needs to be flat (Adhesive heatsink).

Is there a better way to approach this situation ? I only have about 5 millimetres to solder 4 pins. Should I be trying different hookup wire ? Using a hot air gun ?

Thanks in advance (Soldering these devices is not recommended by the manufacturer - However I don't have any other method available)


RE: Soldering millimeter components (Cree LEDs)

Surface mount using solder paste and a hot air gun? You should be able to control paste application using a syringe and large bore needle.

Ideally you want to get some preheat into the PCB using a hotplate, or even a chunk of metal heated in an oven, if you possibly can. You need the pre-heat to reduce thermal shock and take the mechanical stress out of the joint, and most of the fluxes work better with some preheat to help activate them, but for prototyping I guess you could forego long term reliability for ease.

RE: Soldering millimeter components (Cree LEDs)

To avoid damaging LEDs, you really need to be using a reflow oven with the manufacturers heat profiles plugged in... the days of two-lead, 10mA LEDs are long gone.

Dan - Owner

RE: Soldering millimeter components (Cree LEDs)

"...about 5 millimetres to solder 4 pins."

That's tiny and beyond anything I've ever done by hand. A binocular microscope or head-mounted magnifiers would be mandatory. You'd need a pick to hold down the components, otherwise the surface tension of the molten solder will have them sticking to the iron. Obviously steady hands and skill.

I doubt the hand soldering technique would work at this scale. It's too small by about 2:1 ratio.

RE: Soldering millimeter components (Cree LEDs)


Nah, I do that scale every day (and smaller). The eyesight started really going south once I hit 40, but I can still do 1mm pitch components by naked eye... but I routinely do 0.5mm pitch and smaller using a microscope and a fine-tip iron. For one-off and repair work it's done every day in shops all over the world, but production-level work would obviously never stand a chance.

Dan - Owner

RE: Soldering millimeter components (Cree LEDs)

Do you mean the XM-L series? It's definitely possible with a bit of patience. I recommend that in addition to your narrow tip (hopefully a needle point not a spade tip) you have either head-mounted magnifying glasses and a lamp or a magnifying lamp, plus a hot air gun, a hobby knife and a pair of tweezers. The hot air gun is not necessary if you're just fabbing a few up, but it definitely helps to get things started.

I gather you're attaching flying leads to the pads on the underside of the LED, and gluing the heatsink on? If so, remember to tin the pads and your wires first - put a dab of solder on the wire and each of the pads before trying to bring them together. If the solder ends up bridging some of the pads, cut the intersection away with the knife. Then bring the wire to the pad while you heat the pad. Most importantly: as soon as the solder runs together, take the iron away and hold the wire in place - don't try to overdo the iron work. Get in, get it soft, then get out. You can always trim up any messy bits with the knife afterwards.

RE: Soldering millimeter components (Cree LEDs)

Those LEDs have only 9mil between their pads... You will not be successful using wires. The only way to hand solder those is to solder it all and then wick the inter-pad bridges away with solder wick. That method ONLY works on board traces since the wicking process would release all the non-rigid wires. The smallest solder only comes as 15mil diameter.

Second problem is that those LEDs dump boo-koo heat and if you don't have the large pad correctly soldered to heat-sinking the LED will self-immolate promptly anyway. You cannot get that package thermally connected with wires soldered under it. No sticky tape heat pad will not work against the LED's base.

You need a star board that accepts that LED. Have you looked for one?
Your 'tape' thermal tape will work under a star board.

Keith Cress
kcress - http://www.flaminsystems.com

RE: Soldering millimeter components (Cree LEDs)

If you think you would like to be able to solder small smd parts into the future, invest in a stereo microscope with a sturdy boom arm. It doesn't have to be high power. With a set up like this, I've been able to solder leads onto parts like you've got with a fine tip soldering iron.

Next step up is to use a toaster oven on a custom pcb. Get your pcb cheap (if it is small) thru OSHPark. About $10 total (including shipping) for a batch of 3 if they are about 1" square. Watch how to do the toaster oven soldering on YouTube. You can manually place the solder paste using the stereo microscope.

As a side benefit, if you ever get a splinter or glass shard deep in your hand or finger, you can use the stereo microscope to find and pull that puppy right out in no time flat.

RE: Soldering millimeter components (Cree LEDs)

We work with the same Cree LEDs and it is very difficult to solder to the leads. Why not use regular axial (leaded) LEDs until you are through with prototyping? There are lots of tricolor and white LEDs out there in larger packages and you could get close enough by matching wavelengths. If you are at the point where the exact lighting characteristics are a concern, maybe it is time to build a PCB? If you absolutely must do it with only the tools you have, try using small gauge magnet wire (enamel coat keeps the insulation from being a space factor) and microscope. Solder a bit of wire to the heatsink part of the LED too.

44AWG enamel coated wire:

Some inspiration:

RE: Soldering millimeter components (Cree LEDs)

There are numerous "star" or other shaped metal clad PCB's available unpopulated for those particular led.
Then its simply a oven reflow or hot air gun process to attach the LEDs to the PCB's.. Then you can solder wire to those or TE has quite a few "solderless" LED holders/mounts to choose from.
There is no need to use a hand soldering iron and you really won't be successful with them.
Heck you can even reflow in a frying pan.

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