XP-E2 color LED with cracked die

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Flashy Mike
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XP-E2 color LED with cracked die

I have several XP-E2 color LEDs (green and royal blue) with a crack in the middle of the die. The crack divides the die into 2 rectangles. The LEDs have been reflowed with the well known careful tap to the top of the dome so I first considered this tap as the cause of the crack. But now I found a LED – which has been ok after reflow – with this same crack. The LED was mounted with a carclo 4x lens (http://budgetlightforum.com/comment/1257195#comment-1257195). Due to the lens some force to the dome might have happened, but the LED was also overdriven with a maximum of 1.4 Amps quite often.
Apart from one, the damaged LEDs are still working, but with a higher forward current (I guess, since I can’t light up the LEDs with my multimeter in diode test mode anymore).

Does anybody know more about the cause of the crack?

Edited by: Flashy Mike on 01/10/2018 - 04:49
The_Driver
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How do you reflow?
Where did you buy the LEDs?

Flashy Mike
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Hotplate, only roughly temperature controlled. Bought at Kaidomain.
Never noticed this with other LEDs. I’ve the impression the green and royal blue LEDs are notably more sensitive.

koef3
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Can you make some pics?
Would be interesting for me to see it in detail.

My theory is that the LED chip itself (the semiconductor which ‘produces’ the light) is not mounted correctly to the LED substrate in production process so thermal hot spots could occur in operation which causes cracks due to the high temperature differences in the semiconductor material. If so, this would be also independent from the reflow on the LED board.

Since the Anode (positive) is ensured by the two bonding wires on the edges and cathode is loocated underneath the chip, the LED might be still working, like in your case. But that this affect so many LEDs at same time is strange, though…

My LED tests: Cree SC5 based LEDs (WIP!)  ---  Nichia 319AT 83 CRI - Optisolis (3000/5000 K) - Lumileds Luxeon LXML-PWD9 - Luxeon MZ 5700 K (90 CRI, 3 V) - Luxeon V (CSP) 4000 K 70CRI - Luminus SST-40-W (+ dedomed) - Cree XP-L2 (+ High CRI variant) - XHP35 HI - XHP70.2 - CXA1304 COB - OSRAM OSLON Black Flat HWQP - SYNIOS DMLQ31.SGLE UW Q8WP - unknown 5050 LED ---- finished: JAXMAN M8 (Mini C8) HighCRI Triple

Flashy Mike
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Sorry, can’t make pics, don’t have the means for closeups currently. It’s even difficult to see through my mini microscope. It’s a crack in parallel to the side where the bond wires sit, straight through the middle of the die, from one side to the other. One LED even has 2 cracks in parallel. It’s not too many damaged LEDs, just 2 green and 1 royal blue up to now. The LEDs are overdriven at about 1.4 Amps and my reflow capabilities are mediocre so it can easily be my fault. Have more LEDs on order and just want to avoid this in future.

koef3
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I reflowed many color / white XP-E2 by hotplate and soldering iron by myself.
I never discover such phenomena like you, all the LEDs are still working fine. Overall, Cree LEDs are really tough in case of reflowing, including the newest generation.

Maybe the LED chip itself isn’t broken, but the ‘phosphor’ layer which can be seen with the eyes. If you are not sure about the reflowing you might reflow with the lowest temperature possible (but enough to melt the solder) and ensure that there are no strong or sudden temperature changes of the LED after reflow procedure.

My LED tests: Cree SC5 based LEDs (WIP!)  ---  Nichia 319AT 83 CRI - Optisolis (3000/5000 K) - Lumileds Luxeon LXML-PWD9 - Luxeon MZ 5700 K (90 CRI, 3 V) - Luxeon V (CSP) 4000 K 70CRI - Luminus SST-40-W (+ dedomed) - Cree XP-L2 (+ High CRI variant) - XHP35 HI - XHP70.2 - CXA1304 COB - OSRAM OSLON Black Flat HWQP - SYNIOS DMLQ31.SGLE UW Q8WP - unknown 5050 LED ---- finished: JAXMAN M8 (Mini C8) HighCRI Triple

Flashy Mike
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Yeah, perhaps it’s only the phosphor since 2 of 3 LEDs are still working, don’t see a visual impact but will do a lumen measurement later (if I find my my notation of the last measurement when the LED was not broken). Thanks.

Lexel
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colored LEDs have no phosphor they you see the semiconductor

Lightbringer
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Lexel wrote:
colored LEDs have no phosphor they you see the semiconductor

Except PCA. Big Smile

09 F9 11 02 9D 74 E3 5B D8 41 56 C5 63 56 88 C0

koef3
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And Phosphor converted green. Some manufacturers sold them in newer time, in most cases Low- and Mid-power LEDs.
But in general I’m sure that there is a sort of layer on the chip which might be cracked here especially the crack cannot be really seen with the eyes.

Without pictures it is difficult to make clear statements on this problem…

My LED tests: Cree SC5 based LEDs (WIP!)  ---  Nichia 319AT 83 CRI - Optisolis (3000/5000 K) - Lumileds Luxeon LXML-PWD9 - Luxeon MZ 5700 K (90 CRI, 3 V) - Luxeon V (CSP) 4000 K 70CRI - Luminus SST-40-W (+ dedomed) - Cree XP-L2 (+ High CRI variant) - XHP35 HI - XHP70.2 - CXA1304 COB - OSRAM OSLON Black Flat HWQP - SYNIOS DMLQ31.SGLE UW Q8WP - unknown 5050 LED ---- finished: JAXMAN M8 (Mini C8) HighCRI Triple