Assembly and packaging of functional heterogeneous microsystems by directed three-dimensional self-assembly

In this work, we present a fluidic self-assembly technique which uses the surface tension to enable the fabrication of functional heterogeneous systems that carry devices out of different materials. The self-assembly process combines solder based surface tension driven self-assembly with geometrical shape recognition and sequential self-assembly. We have demonstrated the self-assembly of two-component, three-component, and four-component heterogeneous microsystems. In further process development, we also have demonstrated the ability to control angular orientation and contact pad registration during the self-assembly process. The key building blocks of our self-assembly process that enable assembly of standard die forms with single angular orientation and contact pad registration are "two-element docking sites" on the substrate that contain alignment pedestals and solder-coated areas. Combinatorial methods that combine geometrical shape recognition, surface tension, sequential self-assembly, and angular orientation control are necessary to achieve the required flexibility in the design of heterogeneous systems on both the micro and nanometer length scale with minimal defects. Finally, we have investigated how the surface energy and surface tension forces scale with the size. We have demonstrated the self-assembly of 20 microm sized components onto solder coated receptor assays through the liquid/liquid interface. The scaling law and the preliminary results show that surface tension is an enabling technique to be applied to 1∼20 microm and even smaller scale components and systems.