TM4C1294KCPDT: problems with conformal coating

Hi Holger,

  I have no knowledge on your question about conformal coating. I'm asking internally and will get back. 

Hello Charles,
I asked them further questions on this issue. They saw that the RTC was not working after the coating.

1. There is no physical failure; all other functionality is working except RTC ( which worked before coating); after coating if they put battery it’s voltage is going down to 0V from 3V.
   Presently as they are using this board in system without RTC function.
2. What coating material are you using?
   - SCC3 conformal coating and DCT thinner mix up ratio 2:1  ( Conformal coating material: SCC3 Conformal coating from electro lube, Thinner: DCT thinner from electro lube)
   
   
3. Have you check the pins and soldering? Did you x-ray the board?
   – Checked all the pins on magnifier lens; It’s found that TM4C pins rusted in 1 board; they have cleaned & did re-soldering on those pins. Then tested & gave for coating.
   after that it worked again?  - Yes it’s started working .
   
   
4. e.g. In 1 board, RTC section is not working;
   is it always the RTC section or also other error? – only RTC (as mentioned in above sl. No. 1)
   if it is RTC does the failure vanish by reprogramming? – No (we have reprogrammed & also changed battery, still same issue)
   
   
5. > Is there any standard to follow for coating of TM4C, please update.
   I will check this – Please update (is there any particular time duration for coating after TM4C soldered on board as we are doing coating on the boards which was 1 to 2 years old )

Regards, Holger

Hi Holger,

  I'm still waiting for our expert in this topic to comment. In the meantime, can  you find out if the conformal coating is applied to the entire PCB or only a subarea of the PCB or just the MCU? I have no understanding how conformal coating works and can't really relate how it can impact RTC. RTC runs off of  the external 32.768kHz crystal. Is it possible the crystal is damaged or if the battery is damaged. Can you ask the customer to do a ABA swap test. Swap out the suspected MCU to a good known board and is RTC functioning or not functioning?