LED failures - Car #194/T10 style LED lamps

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prairiemystic

Joined Jun 5, 2018
191
I replaced #194/T10 incandescent lamps in my car with LEDs. But the LED's last only about 1 year and then start blinking, strobing and cutting out. I've seen this before as a bad connection - bonding wire or die-attach adhesive failure.
Here (pics) I see some strange black regions first around the die then spreading out on the lead frame - so I think this is the problem but not sure what it is. These are in a sealed light fixture with no corrosion anywhere.

Normally there are five SMD5050 LED's that each have three dies inside, in series. The five LED's are in parallel with a 62 ohm resistor feeding it. I removed two LED's (so total of three, for a bit brighter) and measure total 75mA at 14V, giving 25mA per LED die, they don''t run hot.

Just wondering what is this black plague on (Chinese) LEDs, it seems to give them a short lifetime.
 

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BillB3857

Joined Feb 28, 2009
2,546
I hope there is an answer to this question since I have exactly the same problem. Two of the lamps are on the lights inside the door that come on when the door opens, so water contamination is obviously not the problem.
 

MrSoftware

Joined Oct 29, 2013
2,015
My guess is they're poor quality LEDs and they are configured for too much current for long life. Also even though they might not feel warm, temperature at the LED itself might still be a problem. If there is insufficient heat transfer between the LED and heat sink, the LED itself can get very hot while the heatsink stays relatively cool. It might be worth disassembling one of the dead ones to see what, if any connection exists between the LED body itself and the heatsink. Did they use a thermal solder pad, heatsink compound, etc? If not, then maybe build one good one from your dead ones and see if you can get something like heatsink compound in there and see if that helps.
 

MisterBill2

Joined Jan 23, 2018
9,495
I have dealt with similar failures of similar looking LEDs in much larger lights. These are 4 foot 96 LED florescent substitutes that have 4 parallel strings of 24 LEDs in series on an aluminum backing with a clear plastic snap on cover. The failure mode is similar in that it varies between going dim and then starting to flash and then failing completely. Identical units installed inside the building have lasted almost 3 years, while those outside have failed within the first year. They are all protected from the weather, and the replacement devices have not yet started to fail. My guess is that it is indeed a very large poor quality production run of some Chinese LED maker that has caused so many failures. The deffective ones do not survive the larger temperature swings, it seems.
 
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