1.14 – Self-Assembly

Self-assembly, a process typically based on interfacial energy minimization, enables rapid fabrication and packaging of microdevices. Microcomponents pose significant challenges for traditional handling techniques such as robotic pick and place because adhesion forces (electrostatic, capillary, and van der Waals interactions) dominate over gravitational forces in microdomains. This chapter reviews virtually all the published self-assembly methods that deal with sticky microcomponents. These self-assembly methods can be classified into four major categories: electrostatic-, magnetic-, inertial-, and capillary force-driven self-assembly. Electrostatic attraction can assemble neutrally charged and electrically polarizable microcomponents on an array of charged sites or holes with fringing electric fields; electrostatic repulsion, due to the similar charges on microcomponents and a carrier substrate, can construct 3D microstructures. Magnetic forces, short-range interactions, can attach microcomponents to magnetized sites on a substrate and can build 3D microstructures by varying the driving magnetic fields and by employing locking features. Inertial forces successfully applied to self-assembly are gravitational and centrifugal forces: gravitational forces anchor microcomponents to recessed sites on a horizontal substrate and centrifugal forces flip the hinged microplates to form 3D structures. Capillary forces from droplets on a substrate attract and anchor microcomponents in flat or 3D tilted poses. Employing two or more different self-assembly mechanisms in sequence can achieve an assembly of microcomponents to satisfy more stringent requirements such as unique face and in-plane orientations of microcomponents. At the end of this chapter, a physical model for developing a theoretical understanding of the self-assembly processes as well as for designing tools to optimize the processes and to establish the theoretical and practical bounds on their performance is given.