Studies of the CBC3.1 readout ASIC for CMS 2S-modules

The CBC3.1 is the final version of the CMS Binary Chip for readout of the outer radial region of the upgraded CMS Tracker at the High Luminosity LHC. The CBC development was completed with an engineering run in 2018 and two pre-production lots delivered in 2019. Large scale manufacture began in May 2021. Issues were raised when some wafers were tested at low temperature (-30\,$^{\circ}$C) and probing was suspended for investigation. After studies, some additional tests were added to reject affected chips and we show that the impact of the low temperature issues is expected to be very small.