soldering crees are a @#$%! [pics]

I've bought a few XR-E emitters and first thing I noticed was the smallness of the solder tabs...and whats worse? the emitter ring is conductive
I drilled a hole near the diameter of the ring on a scrap 2x4, tuck the emitter down and proceeded to sand the bottom contacts off....fired up the dremel and

lets just say the rectangle base of the first LED turned into a square almost immediately, theres not much material to sand off:shrug:
heres the pic of a slightly sanded 2nd LED, its supposed to look like the PCB color right?


I made the mistake of putting solder on the ring....so I had to wick it off and all the heating and cooling I saw a fine whiff of smoke and there goes my first CREE...nothing looks amiss but doesn't light up

the second one was success...well sort of [I apologize for the pics, I can't seem to take shots any closer than this]


the red wires contacting the emitter ring, theres a tab of solder on the ring above the green, but *whew* a cold solder joint, from a magnifying glass the two beads are touching but I guess theres rosin between, bucause it registers as a short when I clip my AMM [analog multimeter] to the green and the ring and it registered an open circuit [resistance at infinity]

will a magnifier help any? I'm soldering this with only a spotlight and a standard weller 75 watt "chisel" tip sanded down by me into a "pencil" tip and retinned...and the soldering job is not pretty.

can anyone give tips to soldering cree emitters or do I have to buy a star for it and toss it into the oven?

two other emitters that completed their transplant on to DOA DX seoul stars today....ones from a magLED and the other bare emitters from somewhere:thinking:

Re: soldering crees are a @#$%!

I think 75w is a bit overkill for delicate tasks like this. Haven't tried a LED yet but for switch and wires a 25w iron is plenty.

Re: soldering crees are a @#$%!

I only have two solder units, 75W iron and 200 watt gun
someone told me way back when I was starting with luxeon Is that 25 watts too weak for soldering...so I bought the 75 and used it for years

the CREE XR-E data sheet spoke of 3.3V at 350ma to be a recommended driving spec...I'm thinking of mounting it on a heatsink and connect it directly onto to a Nokia 3.7V 340ma AC-DC step down

from the closeups you can see the domes been damaged, but as an area light I don't think theres going to be a problem

Re: soldering crees are a @#$%!

EDIT: Ok, I saw the pics, use a pen knife and cut off the solder to the ring. Solder is very soft and easy to work with.

I don't understand how you can have problem with soldering CREE when you can solder SMT LEDs.

Yes the emitter ring is aluminium and is conductive but it is not connected to neither the + or -. Normal 40/60 solder will not stick to it, if it does you can use your fingernail and pry it off easily. It's the flux that sticks. If your solder sticks to the ring, you are probably using the wrong type of solder.

The pads are very small, there is no point of using lots of solder. Buy some high temperature real Kapton tape. Wrap it around the emitter ring, like a tube. This way you won't have to worry about solder touching the ring.

Tin the pads with very little solder if there's a lump wick it off, tin the wire. Place the wire on top of the pad, then use your new chisel tip and touch the wire with slight pressure. When the solder starts to melt, lift the iron. Finally, remove the kapton tape barrier.

This method will only works on a wooden surface. Make sure your surface is not sucking away the heat.

Re: soldering crees are a @#$%!

koala said:

I don't understand how you can have problem with soldering CREE when you can solder SMT LEDs.

Yes the emitter ring is aluminium and is conductive but it is not connected to neither the + or -. Normal 40/60 solder will not stick to it, if it does you can use your fingernail and pry it off easily. It's the flux that sticks. If your solder sticks to the ring, you are probably using the wrong type of solder.

The pads are very small, there is no point of using lots of solder. Buy some high temperature real Kapton tape. Wrap it around the emitter ring, like a tube. This way you won't have to worry about solder touching the ring.

Tin the pads with very little solder if there's a lump wick it off, tin the wire. Place the wire on top of the pad, then use your new chisel tip and touch the wire with slight pressure. When the solder starts to melt, lift the iron. Finally, remove the kapton tape barrier.
T
his method will only works on a wooden surface. Make sure your surface is not sucking away the heat.

Click to expand...

:wow:, I screwed up big time eh
my SMT LED soldering experience came from PCB kits all that was necessary was to presolder the contacts, place the led above the pads and heat both sides for a second or so...I dunno if its possible for me to solder wires onto SMT leds

I'm using the .022 rosin core from radioshack...dunno whether its 60/40 but it helps with avoiding putting in too much solder. and I have the tip cleaner/tinner but no standalone tinner

can I buy such Kapton tape from general hardware stores?

and finally...to ensure I dont overheat the LED...I clamped the emitter to a heatsink during the soldering process, which [now I know why it] took 30 minutes despite I preheated the iron for an hour to burn off the spider webs and what not that accumulated on my iron for a good half a year

I stole your pic and edit I hope you don't mind.

The green arrows is pointing to little holes called the through-hole-via. They are surprisingly small, probably laser drilled.

Again I stole the pic from somewhere to show you how it works...



So what you need to do now, is to dremel off the 4 bottom corners of the CREE to remove the connection, it's very easy and quick!

Judging from you photos, It seems like you are using Wires with very thick copper strands with thick pvc insulations ( this makes your soldering job on delicate components very tough and messy).

You should get wire with only a few thin strands of copper wire that is tin plated with Teflon insulation. ( We are after all working with only small voltages and low currents on led here ).

:laughing:

Re: soldering crees are a @#$%!

Illum_the_nation said:

can I buy such Kapton tape from general hardware stores?

Click to expand...

This one is fake(called Koptan instead of Kapton) actually works VERY WELL. I have tested it, I stick the tape to a plastic card, then proceed to melt the tape, the plastic card melted but the tape on top stayed perfectly fine except a bit of solder stuck on the surface, it didn't penetrate the tape, I could just wipe the solder off..

http://www.dealextreme.com/details.dx/sku.5101

The real Kaptop tape can probably withstand higher temperatures. Kapton is used in various applications and devices. APPLE like to use a lot of these tapes in their laptop, same with other manufacturers. Some dumba$$ in the Apple forum who crack open the laptop thinks that the manufacture is using cheap(NOT at $15 a small roll) tape.

I think there are a lot of members who bought the Koptan tape, you only need a bit, you can ask them to mail you some. Otherwise just use a pen knife and scrape the solder off the ring, it's soft it's easy. Paper tube around the ring will also work as a barrier as long as you don't heat it up too much. You don't need the Koptan tape but it will come in handy in the future, for more CREE adventures.

DOH!

IsaacHayes [where I bought the LEDs from] referred to trimming the "sides" if I wasn't going to use a star, I just remembered that....
I couldn't figure out what hes talking about, cuz when I saw the LED I thought "doesn't clipping the side [contacts] remove the solder spots also?"
I tried to imitate 3rd_shifts 3c Cree XRE Maglite modding method [PICS REHOSTED W/O PERMISSION]

still trying to figure out how he did it so cleanly, I used a sand grinding stone instead of what he used and I grinded through the PCB on the first try

richdsu, only wire I had with me are 22 gauge hookups from the shack, I couldn't find anything thinner except to resort to ripping out datelines from scrap LAN cables

and no problem on modifying the pics, they are all free for anyone who wants them

Re: soldering crees are a @#$%!

Illum_the_nation said:

I only have two solder guns, 75W and 200 watt

Click to expand...

You're soldering LEDs with soldering guns? Are you insane?
Get a cheapie soldering iron, or better yet a soldering station (check my thread about one somewhere in this forum).

Illum_the_nation said:

DOH!

IsaacHayes [where I bought the LEDs from] referred to trimming the "sides" if I wasn't going to use a star, I just remembered that....
I couldn't figure out what hes talking about, cuz when I saw the LED I thought "doesn't clipping the side [contacts] remove the solder spots also?"
I tried to imitate 3rd_shifts 3c Cree XRE Maglite modding method [PICS REHOSTED W/O PERMISSION]

still trying to figure out how he did it so cleanly, I used a sand grinding stone instead of what he used and I grinded through the PCB on the first try

richdsu, only wire I had with me are 22 gauge hookups from the shack, I couldn't find anything thinner except to resort to ripping out datelines from scrap LAN cables

and no problem on modifying the pics, they are all free for anyone who wants them

Click to expand...

Here's how you do it:

1) Use a fine tip grinding bit. The one that's about 4mm at the base and 1-2mm at the tip. It should be the green colored one, not the orange colored one (finer grit)
2) Use very slow speed (setting 1 or 2 on your dremel)
3) Go very slow. Apply light pressure and use a very steady hand. It took me about 5 minutes per side (10 minutes total) to grind off the contacts in the proper spots on my XR-E. You only need to grind at the corners where the vias are at.
4) Use a sanding disk to clean things up - this will clean up any burrs that the grinding bit created. Just apply lightly to the area that you ground off. You're just trying to clean up the grinding residue from the ceramic substrate, and clean up the edges of the copper layer.

You should end up with something like this:



Edit:

Here's another XR-E I did:

Re: soldering crees are a @#$%!

Fallingwater said:

You're soldering LEDs with soldering guns? Are you insane?
Get a cheapie soldering iron, or better yet a soldering station (check my thread about one somewhere in this forum).

Click to expand...

lol, the 75 is an iron, the nose [contact metal] of the 200/250 watts the size of the cree itself
I've mounted todays on a heatsink already...with plenty of AA epoxy underneath, I made sure not to press fit the cree close to the heatsink which minimizes a short

Evan, my dremels ....lets just say I need to buy that head first, I know which part your talking about, for I have a catalog of all the goodies [a couple hundred headsoo:]

I'd have to say too much overkill and not enough delicate prep is the "problem" here.

A dremel to take out the bottom pads? An exacto knife of rubbing it on sandpaper for a bit will do it.

Flux and pre-tinning is your best bet with the crees. You gotta prep your wire well and pre-tin it to keep it manageable. Pre-tin the pads on the Cree. Pre-tin the tip place the wire on the pad touch and bam.

I've done this about 10 times with the Cree and that's how I solder all my jobs. Haven't killed a thing yet.

My problem is in the de-soldering depo, old wicks and crappy pumps. I can't usually get this new solder to melt enough for a good clean up either leaving me with a high percentage of cold joints. Fresh jobs are easy.