Problem
We have manufactured a custom board using the nRF9151 and we ran into some manufacturing QA/QC issues. The reserved pins of the SiP are very close to ground pads on the bottom -- 30% of the manufactured boards in 110 units run potentially are shorted.
Analysis
This section details the analysis of the problem identified; it's effects and causes.
Programming
There were two issues with programming --
1. SWD is not detected by J-Link -- cannot program neither main app nor modem
2. SWD is detected and can program main app but cannot program the modem
Power Consumption
I observed very high consumption on a board that cannot be programmed, below is the plot -- it was averaging around 100 mA suggesting the pins were shorted. I tried to apply heat with hot air gun a handful of times and tried to program & see consumption, but it has not helped.
So, I popped the SiP to confirm my theory (I can't see underneath, so I was only speculating at this point), and it looked like below.
And the consumption dropped to sub milli-amp with the SiP removed
More Power consumption numbers
As there are 9 large ground pads, any combination could've been shorted on the malfunctioned boards and below are some behaviours.
First normal base current - 3.5 mA 
High base current - 16 mA
Even higher base current - 24 mA
These above two boards with higher-than-normal base current were programmable, and functional but not ideal consumption numbers.
Question
Are these reserved pins connected to somewhere and can anyone confirm this is correct -- "The reserved pins shorts to GND pads can be fatal" and above behaviors are caused by this. Before I pop all these boards, I thought I better ask the Nordic hardware team.
Also, a suggestion to the SiP design team to not put them very close to large GND pads unless they need to be -- it is challenging to manufacture with mid or even higher-level PCB fab houses
ps: Was so consumed with RF readiness for PTCRB levels and totally did not see this coming -- small but a headscratcher so thought I would share :)
