ABSTRACT

In contrast, ACAs, which are the subject of this paper, only conduct normal to the surface bond-pad. ACAs are composed of spherical conducting particles dispersed throughout the polymer matrix, as shown schematically in Fig. 1. The conducting particles can be hard or soft, and provide electrical paths between mating gold bumps on the flip-chip die and gold-plated copper tracks on the flex substrate. The coplanarity requirement for these bond-pads is not very stringent because compliant conducting particles compensate for any dimensional variations in pad height. ACAs can be applied under the entire flip-chip die because they do not create lateral conductive paths (shorts) between neighboring contacts [1].