Selective Deposition of Conductive Particles for Anisotropic Conductive Adhesive Interconnects

A new concept for anisotropic conductive adhesive (ACA) based on a predefined number of electrically conductive particles captured at individual interconnects is introduced. Capillary assembly method is applied to deposit conductive particles on a patterned polydimethylsiloxane (PDMS) carrier. These particles are transferred to electrical pads on a substrate whose surface is laminated with a non-conductive adhesive film. A die is then aligned and thermocompression bonded to the substrate. A yield as high as 97.8% is obtained for the particle deposition process while the yield of transferring particle process is almost 100%. Bonded samples achieve 63% of interconnects having the exact predefined number of conductive particles. The measurements of electrical resistance and contact area between particles and substrate indicate the formation of electrical paths between the electrical pads and conductive particles. This work has demonstrated the feasibility of ACA interconnects with conductive particles localized only between mating electrical pads on the die and substrate, but not outside these desired locations. Such interconnection approach minimizes the risk of short-circuit and open-circuit failures in fine-pitch applications.