Flow-induced spatial non-uniformity and anisotropy in electrically conductive adhesives

Electrically conductive adhesives (ECA) are popular solutions for joining relatively large (> 500 mum) electrical interfaces or when lower-temperature requirements preclude soldering or brazing. When assembled by squeezing between two flat, rectangular surfaces, the flow dynamics of the conductive filler and matrix can induce variations in local electrical conductance. This becomes significant as the area of the interface (bond pad) becomes comparable to the bondline thickness (BLT) of the adhesive. We observe order-of-magnitude local variations in electrical conductance and strong anisotropy in the direction of flow in ECAs with silver (Ag) flakes. We discuss the influence of these electrical results on heat diffusion across the interface and consider how fabricating microchannels in the interface could reduce the non-uniformities. Both electrical and thermal aspects are analyzed in light of ever-shrinking dimensions and 3-D stacking trends in thermally-critical electronics packages.