Speaker
Description
The High-Luminosity upgrade of the Large Hadron Collider (HL-LHC) will push the performance of tracking detectors to unprecedented levels, with instantaneous luminosities reaching up to $7.5 \times 10^{34}\,\mathrm{cm}^{-2}\,\mathrm{s}^{-1}$. To operate under these extreme conditions, the CMS experiment will replace its current tracking system during Long Shutdown~3 with a new Inner Tracker (IT) designed to sustain high radiation levels, accommodate increased particle fluxes, and support high-rate data readout.
At the core of the IT are hybrid pixel modules combining n-in-p silicon sensors with a pixel pitch of $25 \times 100\,\mu\mathrm{m}^2$ and a $65\,$nm CMOS readout ASIC developed by the RD53 collaboration, interconnected via bump bonding. The assembly is mounted on a high-density interconnect (HDI), which distributes power and signals, and is wire-bonded to the readout chip. The Phase-2 IT comprises three subsystems and extends the tracking coverage to $|\eta| = 4$. In the innermost barrel layers, where radiation levels are highest, single-chip modules equipped with 3D silicon sensors will be employed, while the outer barrel layers and endcaps will use dual-chip and quad-chip modules. To minimise the material budget and power losses, the modules operate within a serial powering scheme. As the project transitions from preproduction to large-scale production, ensuring uniform performance and long-term reliability across thousands of modules becomes a central challenge.
To address this, a comprehensive Quality Control (QC) program has been developed and deployed across production sites. The QC procedures cover all stages of module qualification, including electrical characterisation, verification of powering and readout functionality, threshold tuning, and detailed assessment of pixel response uniformity and noise performance. Dedicated tests are also implemented to evaluate the integrity of the sensor--ASIC interconnection and to identify defective channels that could degrade position resolution.
Stress tests and irradiation campaigns are used to validate module performance under conditions representative of the detector lifetime. This contribution presents the QC strategy for the CMS IT pixel modules, highlighting the test methodology, automation, and grading criteria used during production to ensure that only fully compliant modules are integrated into the final detector. First results from pre-production and early production modules are discussed, demonstrating the robustness of the QC workflow and its role in preserving the tracking performance required for HL-LHC operation.