Speaker
Description
The upgrade of the ATLAS Inner Tracker for the High-Luminosity LHC faced a critical challenge: thermal cycling from +20°C to -35°C induced cracks in silicon sensor modules due to coefficient of thermal expansion (CTE) mismatches between sensor materials and hybrid components. Finite element analyses revealed that the combination of stiff (TrueBlue) and soft (SE4445) adhesives exacerbated stress concentrations at sensor edges, leading to structural failures.
To mitigate this, an interposer-based decoupling strategy was developed using a Kapton foil as a mechanical buffer between sensors and hybrid/power boards. The interposer, bonded with SE4445 adhesive (containing glass beads for controlled thickness), effectively reduced stress transmission while maintaining electrical insulation. Validation tests on production-scale petals demonstrated crack prevention in interposer-equipped modules across multiple temperature cycles (-55°C), compared to consistent failures in non-interposed samples.
The solution was scaled through a semi-automated production tool with workflows, enabling consistent quality and a throughput of 4 hybrid arrays in one go. Collaboration with industry partner further accelerated production. This approach not only resolved the immediate reliability issue but also established a reproducible manufacturing process.
The tool’s design prioritized scalability for industrial production, featuring:
• Modular stencil systems for controlled glue coverage and thickness.
• Vacuum plates for accurate component positioning, reducing manual errors.
• Optimized Kapton cutting via pattern cutter to streamline integration into existing workflows.
By outsourcing the production to an industry partner after developing the tool enabled a ramp-up of hybrid arrays significantly, meeting the project’s throughput requirements.