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,

Is there any chance we could have a conference call with your package expert for the nRF52840? Our process people have done everything they can but we are still seeing many PCBs where the nRF52840 is resetting. We are temperature cycling the PCBs in our environmental chamber from +70C to -30C. All resets are occuring very close to when the chamber gets to -30C. We've never seen a reset at any other temperature. We also noticed that the reels have an expiration date. We've made a lot of these boards with ICs that are a few months past the expiration date. Not sure if this is an issue because we had some newer reels, made some PCBs from those parts and we are still seeing the problem. We could send some of these ICs back to you for your inspection. We don't believe the reset issue is due to the power circuitry, but we will tripple check this. We operate the PCB from two AAA alkaline batteries and VCC is generated from an external boost supply with a 3.3V output. We use the nRF52840's internal buck regulator to generate 1.3V for the core. There are many DECn pins on this processor and the product spec doesn't get into a lot of details on their function. Our circuit is basically a copy of Reference Circuit 5 shown in Figure 212 of the product spec. If we short out any of the DEC caps, the processor resets.  Thank you!