Cree XM-L T6 - bad contact INSIDE?

hi, im doing my own lights for a while, but today i was ready to make another one, and in a purchase of 10 XM-L T6, 3 of them where not working.

i tested all of them in the DMM (diode test) 7 light up, 3 do not. then connected in a proper led driver for XM-L (3.3v, 1A) no light.

then i tried to find where was the problem, the soldering on the base perhaps? nope, all was ok, but no light.

tried even the contacts over the led (there 2 square on the side) and the led didn't light up. so, i was sure the led was the problem itself. then i tried heat up the soldering, and during that, i pushed a bit the "silicon" covering of the led to the side, and BAM, the led light up. "wiggling" a bit, the led now works fine, but if i put some pressure over the silicone lens, it stop working.

anyone had problem like this? is the internal soldering perhaps?

It sounds like these may have experienced too much shear force.

A note on the square top-side pads: they are covered with silicone, you'll need to cut with hobby knife if you want to use those for electrical contacts.

Were these LEDs purchased on stars or were they still in the reel tape? If they were on stars, you may be right in that they might not have been reflowed properly, and that the wiggling is allowing the pad on the star to connect with the pad on the bottom of the LED to make it light up, when these pads should be soldered together anyways.

I've seen pictures of some QC issues with XM-L, but haven't heard of improperly bonded internal bond wires yet.

yes, i cut the silicone over the contacts to test there.

they where purchased on stars (from focalprice.com) but they do not work also connecting on these pads on the led. the connection between the led and the star is ok, no bad contact there.

pressing the led on the star do not change anything, only pressing the silicone lens on the led itself that made it light up;

How were they shipped to you? If the LED domes were not isolated from pressure during shipping and/or handling, they can be ruined. Cree has documentation on handling their LEDs. Many suppliers do not follow the handling recommendations.

On a side note, the silicone domes used over LEDs can absorb various chemicals which adversely influence lumen maintenance. Cree provides a long list of various chemicals that can be a problem when used around the LEDs such as adhesives. Just a heads up to builders and modders.

each led was in a mini ziplock bag, and the leds in a bubble-bag envelope. no extra protection.

i will talk with focalprice support about this, so they can ship properly...

i will make 200W leds arrays, as they are in parallel/series, one of them cannot fail, or the current would overload the working series of leds

i talked about it to focalprice, and they said the problem was passed to the department, and assured next shipments will have better packaging to avoid damage to the leds

let's see on my next purchage...