Qualification of Bump Bonding in CMS Inner Tracker Pixel Modules for the Phase-2 Upgrade

TL;DR

This paper discusses the qualification procedures for bump bonding in CMS Inner Tracker modules, crucial for detector performance in the HL-LHC upgrade, using various testing methods to ensure quality and reliability.

Contribution

It introduces comprehensive qualification procedures and compares multiple test methods for detecting defective bumps in the upgraded pixel modules.

Findings

Multiple test methods effectively identify missing or defective bumps.

X-ray and beta source imaging provide detailed defect localization.

Qualification procedures improve bump bonding reliability for HL-LHC upgrades.

Abstract

To fully exploit the increased luminosity of the HL-LHC, the CMS Inner Tracker is undergoing a major upgrade to withstand extreme radiation levels and data rates, while improving granularity and reducing material budget. The upgraded modules employ thin planar and 3D silicon pixel sensors, bump bonded to a new radiation-hard readout chip, the CROC, designed in 65 nm CMOS technology and powered via a serial scheme. Ensuring the quality of bump bonding between sensors and readout chips is critical for efficient detector operation. This work presents the qualification procedures developed to identify missing or defective bumps using multiple test methods, including crosstalk analysis, reverse/forward bias testing, and X-ray or beta source imaging. Results from prototype modules are presented, and advantages and limitations of each method are discussed.