Cree XR-E Thermal Concerns
- Thread starter cmacclel
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ViReN
Flashlight Enthusiast
One more reason NOT to buy mounted Cree XR-E
chimo
Flashlight Enthusiast
Here's another reason not to buy a mounted emitter. This is a 1W Cree emitter from an earlier group buy (It is NOT an XR-E). It is mounted on an ETG heatsink. I removed the emitter from the board today. That little dab of solder is certainly not the best method for transferring heat!
Paul
Paul
NewBie
*Retired*
cmacclel said:Yup it was an IR thermometerHey I tried
Mac
Well, hey, thanks a bunch for trying!
If you go up a few posts, up to my IR pictures, you will note the one that is on the ETGTech MCPCB. Note that the hotspots on the LED body are about 13C above the MCPCB temperature. So for surface temp, it basically agrees nicely with the IR camera. Also notice, how you see the surface temperature of the lens, and not the die, you can't even make it out...
IsaacHayes
Flashlight Enthusiast
Chimo, wow!!! crazy, even looks like air bubbles under the solder. How did you pop it off?
ViReN
Flashlight Enthusiast
the best I would suggest is file off the base contacts (not to remove the base Heat sink contact) and then directly epoxy it (with a very thin layer) over the copper heat sink (for those who do not have expertise on direct soldering to copper plate). this should give much better results.
oh use upper contacts
oh use upper contacts
IsaacHayes
Flashlight Enthusiast
or clip the corners then the bottom are no longer connected! too easy.
NewBie
*Retired*
chimo said:Here's another reason not to buy a mounted emitter. This is a 1W Cree emitter from an earlier group buy (It is NOT an XR-E). It is mounted on an ETG heatsink. I removed the emitter from the board today. That little dab of solder is certainly not the best method for transferring heat!
Paul
I've seen some really **** poor soldering in my days, but dang ETGTech did a really poor job on those.
Definitely click on the picture link, it tells a thousand words...
Outstanding find chimo!
chimo
Flashlight Enthusiast
IsaacHayes said:
- Held it vertically in a vise
- Applied heat with a mini-torch on the back of the heatsink
- Grasped the sides of the emitter with pliers and pulled gently until the solder was soft enough to release the emitter
Paul
Kryosphinx
Enlightened
You don't even need a mini-torch. Any ordinary lighter is hot enough to do it. The only problem is that it can leave a black film on the bottome of whatever you're heating up.
45/70
Flashlight Enthusiast
I have a "what if" idea.
What if you unsolder the emitter, as chimo did. Take an exacto knife, cut around the thermal "pad" (not the elecrtical contacts!) on the board and peel this section up and remove it. Clean up the heatsink that is now exposed. Then, either of two things,
Put solder paste on the MCPCB electrical contacts. Put thermal epoxy in the area you cut out, where the thermal pad goes. Mount the emitter and clamp it together, untill the epoxy sets. Then, heat the assembly up to reflow the solder at the electrical contacts.
OR,
Same as above but, cut a piece of thin copper sheet to the dimensions of the cut out area. Place thermal epoxy in the cutout area, place the copper sheet on the board and clamp it in a jig to assure flatness, untill the epoxy sets up. Then, apply solder paste to the electrical contacts and, the thermal pad area. Heat the the assembly up to reflow the solder.
Most of you guys know a lot more about all this than I do but, I thought I wouild present my idea for comment.
Dave
What if you unsolder the emitter, as chimo did. Take an exacto knife, cut around the thermal "pad" (not the elecrtical contacts!) on the board and peel this section up and remove it. Clean up the heatsink that is now exposed. Then, either of two things,
Put solder paste on the MCPCB electrical contacts. Put thermal epoxy in the area you cut out, where the thermal pad goes. Mount the emitter and clamp it together, untill the epoxy sets. Then, heat the assembly up to reflow the solder at the electrical contacts.
OR,
Same as above but, cut a piece of thin copper sheet to the dimensions of the cut out area. Place thermal epoxy in the cutout area, place the copper sheet on the board and clamp it in a jig to assure flatness, untill the epoxy sets up. Then, apply solder paste to the electrical contacts and, the thermal pad area. Heat the the assembly up to reflow the solder.
Most of you guys know a lot more about all this than I do but, I thought I wouild present my idea for comment.
Dave
NewBie
*Retired*
Sounds like a lot of work to fix these MCPCB.
chimo said:
That does look like a bunk solder job but can we be certain that's what it looked like before you softened the solder and had it reflow to some extent? The solder under the LED leads is nice and rounded and full making me think that it had reflowed and reformed after you removed the LED. :thinking:
I am no expert at all but I have reflowed some of these LED's and watched the process. I have also dabbled a bit with jewlery soldering and learned to use the heat to pull the solder towards it. It would be interesting to take a component that you know has been flowed properly and see what you get when you remove it in the manner this was done.
I guess I don't know enough to make a judgement on this solder job so I defer to others.
chimo
Flashlight Enthusiast
Don,
It appears that was as far as the solder paste reflowed under the emitter body.
If you will note the emitter, you can see that a significant portion of the center pad never had any solder - the same is true for the heatsink. I was applying tension to the emitter while I was heating the underside of the heatsink.
Pretty well all the solder came off with the emitter. Perhaps that's because of the heat transfer direction - the solder touching the heatsink would have softened before the solder at the emitter interface, so it would have released first (especially while tugging on the emitter).
An explaination for the anode/cathode contacts having better reflow would be that they would have heated first and would have been at reflow temperature for a longer period. This one just may not have been in the oven long enough. It seems like the most likely explaination.
Paul
It appears that was as far as the solder paste reflowed under the emitter body.
If you will note the emitter, you can see that a significant portion of the center pad never had any solder - the same is true for the heatsink. I was applying tension to the emitter while I was heating the underside of the heatsink.
Pretty well all the solder came off with the emitter. Perhaps that's because of the heat transfer direction - the solder touching the heatsink would have softened before the solder at the emitter interface, so it would have released first (especially while tugging on the emitter).
An explaination for the anode/cathode contacts having better reflow would be that they would have heated first and would have been at reflow temperature for a longer period. This one just may not have been in the oven long enough. It seems like the most likely explaination.
Paul
McGizmo said:That does look like a bunk solder job but can we be certain that's what it looked like before you softened the solder and had it reflow to some extent? The solder under the LED leads is nice and rounded and full making me think that it had reflowed and reformed after you removed the LED. :thinking:
I am no expert at all but I have reflowed some of these LED's and watched the process. I have also dabbled a bit with jewlery soldering and learned to use the heat to pull the solder towards it. It would be interesting to take a component that you know has been flowed properly and see what you get when you remove it in the manner this was done.
I guess I don't know enough to make a judgement on this solder job so I defer to others.
Paul,
I agree with the appearance as you have stated it. From watching the parts I reflowed and using some solder paste myself, I would say it looks like the solder never really flowed in the first place. It doesn't look like the part snugged down to the MCPCB. As you suggest, it doesn't look like the center pad ever had a complete film of solder on it. :shrug: Havingnever removed parts in this manner, I won't pretend to know what it should look like but I agree that this sample doesn't look right!
I agree with the appearance as you have stated it. From watching the parts I reflowed and using some solder paste myself, I would say it looks like the solder never really flowed in the first place. It doesn't look like the part snugged down to the MCPCB. As you suggest, it doesn't look like the center pad ever had a complete film of solder on it. :shrug: Havingnever removed parts in this manner, I won't pretend to know what it should look like but I agree that this sample doesn't look right!
IsaacHayes
Flashlight Enthusiast
yup, looks like the surface tension never was broke and the solder never spread out and covered everything. Once it does, it's near impossible to have the tension rise up and the solder come cleanly off of something like that from my experience. It won't want to ball up after it's been spread and contacted everything.
45/70
Flashlight Enthusiast
Yeah, well, I need to use a star for my application. I don't have my Q2 bins yet, as they won't be coming for a few weeks.NewBie said:
Whether or not the reflow job is good (my impression of chimo's example is, it obviously wasn't hot enough), if NASA/JPL oversaw the reflow process and it was perfect, these MCPCB's still wouldn't be worth a crap anyway. Just trying to find a solution.
Dave
45/70 said:.......... if NASA/JPL oversaw the reflow process and it was perfect, these MCPCB's still wouldn't be worth a crap anyway. Just trying to find a solution.
Dave
I am not sure why these MCPCB's aren't worth crap but like you, I too need a solution. My present one is using these MCPCB's.
So far, they seem to work fine so I am really feeling stupid here! :green:
According to ETG and a spec sheet they provided me, the isolation layer used on the MCPCB's is rated at less than .6 C/W resistance. Now the whole LED package is bonded to the MCPCB with this isolation layer and this means that the area under the LED lead pads as well have this thermal connection. From messing with these LED's, it is clear to me that this LED package has great heat transfer throughout and this includes the lead "wings". I like the idea of the center pad and the two lead pads all solder flowed to copper which then has this isolation barrier of reasonable thermal resistance and then on to the core of the MCPCB. In a more perfect world, the MCPCB would be silver and the center portion would be somehow raised up directly to the plane of the center pad of the LED and only the lead pads would have an electrical isolation layer and perhaps only the positive pad for that matter. Well If such a board is available or any board with marked improvement over the ETG board, sign me up.
In the mean time, I will stick with the crap I have available and the crap that seems to work pretty well to me.
NewBie
*Retired*
Well, something is quite wrong with their spec, to say the least, unless you are driving the A19 at 20 Watts?
It is extremely clear the package does not have good thermal spreading in it, and something is wrong with the ETGTech board.
Possibly their process is partially to blame. I took Chimo's picture of the ETGTech MCPCB and blew it up, to look at things closer. Notice how the solder didn't flow, as well as the grain of the CREE surface in the solder area:
It is extremely clear the package does not have good thermal spreading in it, and something is wrong with the ETGTech board.
Possibly their process is partially to blame. I took Chimo's picture of the ETGTech MCPCB and blew it up, to look at things closer. Notice how the solder didn't flow, as well as the grain of the CREE surface in the solder area:
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