Validation of ACF for large and small pitch assemblies

A flexible, reliable and cost-effective interconnect technology is required for the development of hybrid pixel detectors, which is suitable for in-house single-die hybridisation performed during the R&D phase. Within WP6, an in-house single-die interconnect process based on Anisotropic Conductive Adhesives (ACA) has been developed and validated with dedicated interconnect test structures and a variety of different ASICs and sensors. The ACA interconnect technology replaces solder bumps with conductive micro-particles embedded in an epoxy layer applied as either film (ACF) or paste (ACP). The electro-mechanical connection between the sensor and ASIC is achieved via thermocompression of the ACA using a flip-chip device bonder. The ACA technology requires metal pads with a vertical extension above the passivation layer, which is achieved using a newly developed in-house single-die Electroless Nickel Immersion Gold (ENIG) bump-deposition process.  This document reports on the achieved validation of the developed plating and interconnect processes for pad diameters ranging from 12 μm to 140 μm and pitches between 20 μm and 1.3 mm.