The testing and performance of the ETROC2 for CMS MTD Endcap Timing Layer (ETL) upgrade

The Endcap Timing Readout Chip (ETROC) is designed to process LGAD signals with time resolution down to $\sim 40-50$ ps per hit. The ETROC2 is the first full-size prototype design fully compatible with the final chip specifications for CMS ETL. The ETROC2 chips have been extensively tested over the past year since May 2023, with laser, hadron beam at CERN, and electron beam at DESY, with temperature vs voltage vs TID scan, with proton beam and heavy ion beams for SEU and wafer probe testing and stress testing using charge injections. Overall, the performance of ETROC2 is satisfying, the time resolution performance meets the ETL design specification (<50 ps per hit), TID has passed 400 MRad even though the specification is 100MRad, and the yield is very high reaching 97% based on wafer probe testing studies. So far, only few relatively minor issues identified, and all have been fixed with the ETROC2 wafers on hold. The ETROC2 design, test results, and design improvements using wafers on hold will be presented.