Due to the nature of the problem, I've decided to post this on chemistry.stackexchange and not electronics.stackexchange, since I believe that the problem is chemical in nature.

Long story short - we have an electronic product that is submerged in fuels (kerosene being one of them) and uses an RGB LED (click here for datasheet). Due to a sealing problem in the enclosure, fuel has managed to get in and cover the PCBs. What's interesting is the effect that has had on the PCB. The PCBs functionality has been completely unaffected, apart from the fact that the red LED in the RGB LED module has completely stopped working. We've replicated this ourselves manually by submerging 2 new PCBs in kerosene for a day and then taking them out and powering them up and seeing that the red LED stops working entirely. The green and blue LEDs continue to work just fine.

Examination of the failed boards shows that there are no other electrical faults. It is just the red LED that completely stops illuminating.

Looking at the last page on the datasheet, the LED material is listed as AlGaInP / GaAs. Is there any obvious reaction between kerosene and these materials that would explain why just the red LED stops working?

Update After leaving the PCBs to dry, the red LED starts working again! So the problem is not permanent.

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    $\begingroup$ The issue probably isn't dependent on the diode material itself but on what the diode material is packed in. Typically diodes are encapsulated in some sort of resin (possibly a transparent epoxy or something like that). If kerosene penetrates that, it could damage the functionality. Moreover, the encapsulation material might differ for other LEDs (some might require higher standards of protection from air or light degradation than red LEDs). $\endgroup$ – matt_black Aug 2 '16 at 9:23
  • $\begingroup$ @matt_black What confuses me is that the LEDs are all packed in the same package. If you have a look at the product page (uk.farnell.com/multicomp/703-1028/led-rgb-3528-plcc/dp/2112143) or the datasheet, the LEDs are all housed in the same package. I wouldn't have expected them to have different housing arrangements. $\endgroup$ – Amr Bekhit Aug 2 '16 at 9:49
  • $\begingroup$ The device is probably not meant to be submerged in kerosene ;) Nevertheless, as the respective R,G,B LEDs are arranged in one part and have different semiconductor as support. I'd guess that they are "glued" on some support (silicon, ceramics) and connected with wires. Could you inspect under microscope, if the part did not mechanically decomposed? In all cases, I'd suggest to place some drop of epoxy or other resin on top of the PCB as a protection. Asphalt-like stuff is commonly used, but not transparent enough for LEDs ;) $\endgroup$ – ssavec Aug 2 '16 at 10:05
  • $\begingroup$ @AmrBekhit You may still have 2 different types of packaging: the overall encapsulation is one but, if the device is made by assembling different individual diodes into a single device, each diode may have a different encapsulation on the original component. $\endgroup$ – matt_black Aug 2 '16 at 10:13
  • $\begingroup$ @matt_black After drying out the PCBs, the red LED has started working again! So clearly the problem is not permanent. $\endgroup$ – Amr Bekhit Aug 2 '16 at 13:53

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