Hi guys,
recently I have many problems with SMD LEDs. The most common problem is some kind of leakage in silicone encapsulation. It might be air but I have no idea, what is the root cause of it. Do you have any idea? Is it dangerous? What can be done to prevent it? Is it encapsulation process fault?
LED after putting into tester first shines few times, than start to work normally. After about month they become damaged permanently.
Here are some photos of good and bad one.

 

Can we see a data sheet on the LED....and the circuit that it's in?

 

Sure. Here is electric scheme in attachment.
These are simple switch circuits. It looks like LEDs are well protected with Zener diode inside, capacitance and resistance outside hmmm...

What about datasheet, I am not sure. I attach also a picture of SMD package. I could not find on Internet exactly my type. I think it is PLCC 2, color: blue or yellow, does not matter.

 

I have not seen that before.......but the environment looked good. I'm not a LED expert.

What do you mean when you say " LED after putting into tester "? What is a "tester"?

 

My guess is that they are overheating.
What is their current draw?

 

It is a connector under small voltage to test if LEDs are ok. Also it checks resistances of PCBs between pins.
Before posting here I also checked many websites about LED failures and noone is similar to mine problem.

Current draw is 20 mA.

 

The most common cause of LED failure in products is improper reflow temperature profile.

Read the data sheet for the LED- make sure the reflow process matches the recommended profile!
It's easy to think this doesn't matter much anymore- but it does! Many thousands down the toilet because of this simple stupid problem.

 

Yes, I think you are right. How do you think - what is it? Air, moisture from silicone or other substance?
I am not sure also why air influence gold wire in such strange way. Can you get such a bubble after LED is produced?
This is really weird problem...

 

LEDs are sensitive, I suggest to operate that below but not too below to the actual operating voltage or current or try to enlarge the value of the protecting circuit base on datasheet. If none, try experimenting what values it will lit and reduce the values for the range of tolerance.