Development of novel single-die hybridisation processes for small-pitch pixel detectors

Hybrid pixel detectors require a reliable and cost-effective interconnect technology adapted to the pitch and die sizes of the respective applications. During the ASIC and sensor R & D phase, especially for small-scale applications, such interconnect technologies need to be suitable for the assembly of single dies, typically available from Multi-Project-Wafer submissions. Within the CERN EP R & D programme and the AIDAinnova collaboration, innovative hybridisation concepts targeting vertex-detector applications at future colliders are under development. Recent results of two novel interconnect methods for pixel pitches of 25 mu m and 55 mu m are presented in this contribution - an industrial fine-pitch SnAg solder bump-bonding process adapted to single-die processing using support wafers, as well as a newly developed in-house single-die interconnection process based on Anisotropic Conductive Film (ACF). The fine-pitch bump-bonding process is qualified with hybrid assemblies from a recent bonding campaign at Frauenhofer IZM. Individual CLICpix2 ASICs with 25 mu m pixel pitch were bump-bonded to active-edge silicon sensors with thicknesses ranging from 50 mu m to 130 mu m. The device characterisation was conducted in the laboratory as well as during a beam test campaign at the CERN SPS beam-line, demonstrating an interconnect yield of about 99.7%. The ACF interconnect technology replaces the solder bumps by conductive micro-particles embedded in an epoxy film. The electro-mechanical connection between the sensor and ASIC is achieved via thermocompression of the ACF using a flip-chip device bonder. The required pixel pad topology is achieved with an in-house Electroless Nickel Immersion Gold (ENIG) plating process. This newly developed ACF hybridisation process is first qualified with the Timepix3 ASICs and sensors with 55 mu m pixel pitch. The technology can be also used for ASIC-PCB/FPC integration, replacing wire bonding or large-pitch solder bumping techniques. This contribution introduces the two interconnect processes and presents preliminary hybridisation results with CLICpix2 and Timepix3 sensors and ASICs.