nRF52840 Lead Finish of the BGA Balls

[John]

We are having a very difficult time soldering the nRF52840 to the PCB. Our Operations Department is asking what the lead finish of the BGA balls is. Would be great to get on the phone with you guys to discuss all the things we have tried. You might have some ideas. Thank you!

[John]

Hi Kaja,

We are still trying to resolve why our nRF52840 design is having some resets when we run the baord at -20C. For a long time we thought we were having a soldering issue with the BGA, but now we are not sure. If we run 50 boards in our environmental chamber at -20C, after two days about 1/2 of the PCBs will have experienced a reset. The reset reason reported by the nRF52840 is a power on reset. We have been monitoring the 3.3V supply and the 1.3V supply and we don't see them ever going away.

Typically, our design utilizes low power mode so we can get the longest battery life. We tried a test where we switched to constant latency mode, and now we never see a reset on any PCB! We can't ship out product with constant latency turned on because that increases our power consumption too much, but perhaps this is a clue to what is going on. As I mentioned above, we only see this problem when we soak the PCBs at -20C or lower. Does the 32MHz crystal stay on at all times in constant latency mode? If the 32MHz crystal is taking a little longer to start up at -20C, could that cause a reset? Typically, our device is in low power mode 99.9% of the time. We do wake up every second to do some housekeeping tasks. 

Thank you,

John Araujo