I need some advice about a problem that happened in a SMT LED:
The failure symphoms of this SMT LEDs is that the LED body itself seemed to be functional, but when soldering on the products, it showed good wetting and soldering, LEDs are bright and light up as normal. However, after 48 hours of storage, some of the LEDs did not light up in the products, some of them became very dim or blinking when used. When we checked these problematic LEDs by multimeter, they were still bright as good LEDs.
we had done some experiment and examination and reaching a conclusion that the poor SMT surface was cause by Gold plating contaminated, and Nickel exposed to the plating surface.
My question is 1. whether this is named Pososity. 2. What lead to such contamination. 3. How it will affect the finished products after soldering 4. Can such contamination be cleaned? 5. If it can be cleaned, what chemical shall be used.