Flexible front-end hybrids for the CMS outer tracker upgrade

Abstract

The upgrade of the CMS tracker for the HL-LHC is based on a binary readout scheme using the CMS Binary Chip (CBC2). The connectivity requirements of this flip-chip ASIC requires the use of high density interconnecting hybrids. Module integration studies indicated that a foldable flexible hybrid circuit results in an optimal module arrangement. A full module size HDI flexible hybrid was designed, integrating eight CBC2 ASICs. The hybrid is fitted with carbon fiber stiffeners and a sharp folding allows connecting the two strip sensor wirebond arrays. The front end circuit development was focused on the 2 Strip (2S) module electronics. This paper will present the implementation of the 2S front end electronics on a flexible substrate covering the mechanical and electrical properties of the assembly.

Front-end hybrid designs for the CMS Phase-2 Upgrade towards the production phase

“…In this case, a flexible adhesive was applied in order to relax the stress caused by the CTE mismatch between the flex circuit and CF stiffener. A few pieces were successfully produced of this circuit called 8CBC2 [2].…”

HDI flexible front-end hybrid prototype for the PS module of the CMS tracker upgrade

“…The stiffeners improve the thermal properties of the hybrid, while preserving the low mass of the assembly. The PS hybrid is using HDI circuit technology to accommodate all the required features in a very small circuit area [7]. …”

“…In order to fulfil this requirement, the hybrid is built on a four layer polyimide substrate, featuring HDI technology [7]. Seven dummy flip-chips, two active CMS Binary Chip second prototype (CBC2) [8] chips, several passive components and connectors are assembled on the circuit.…”

“…Figure 11. External antenna circuit with metal frame, designed for testing a 2S front-end hybrid prototype [7].…”

“…Flexible HDI substrate circuits using flip-chip bumped ASICs were recently introduced to the High Energy Physics (HEP) community [7] and limited information is available on the reliability, yield, cost and other parameters of these circuits. Therefore, the hybrid development requires several -2 -…”