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Description
To fully exploit the increased luminosity of the HL-LHC, the CMS Inner Tracker is undergoing a major upgrade to withstand extreme radiation levels of 1.2 Grad and hit rates of 3.2 GHz/ $cm^{2}$ while maintaining a reduced material budget and improved granularity. The detector modules feature thin 3D and planar silicon pixel sensors with a pixel size of 25x100 µm, bump bonded to a new ASIC, called CROC (CMS Readout chip), designed in 65 nm CMOS technology and powered by a novel serial scheme. Modules are tested for functionality, noise, and bump bonding quality to meet stringent performance specifications. The bump bonding tests are essential for evaluating the integrity of the bump bonds, which connect the pixel sensors to the readout electronics. Accurate assessment of these connections ensures that the modules can withstand operational stresses and maintain high efficiency. Different methods have been developed to determine the bump bonding yield with electrical measurements. This work describes the various bump bonding test methods and presents results from the prototype modules, highlighting their performance and reliability under operational conditions.
