Self-Assembly of Microscale Parts through Magnetic and Capillary Interactions

Abstract

Self-assembly is a promising technique to overcome fundamental limitations with integrating, packaging, and general handling of individual electronic-related components with characteristic lengths significantly smaller than 1 mm. Here we describe the use of magnetic and capillary forces to self-assemble 280 µm sized silicon building blocks into interconnected structures which approach a three-dimensional crystalline configuration. Integrated permanent magnet microstructures provided magnetic forces, while a low-melting-point solder alloy provided capillary forces. A finite element model of forces between the magnetic features demonstrated the utility of magnetic forces at this size scale. Despite a slight departure from designed dimensions in the actual fabricated parts, the combination of magnetic and capillary forces improved the assembly yield to 8%, over approximately 0.1% achieved previously with capillary forces alone.

A review of micro-devices assembly techniques and technology

“…External fields were used to manipulate ferromagnetic parts [58][59][60] as well. As underscored in [61], the underlying principle involving the use of magnetic forces for selfassembly was due to the expected 1/r 4 force law, where r represents the distance between two identical magnetic dipoles. Thus, at large separation distances, magnetic forces were negligible.…”

“…Thus, at large separation distances, magnetic forces were negligible. Consequently, when the separation distance decreases, these magnetic forces had a dominant role to play along with surface tension [61].…”

“…A drawback with capillary forces was that they have a dominant effect only over very short distances; consequently, for capillary forces to produce the desired assembly, a micro-device must be in contact with its target binding/ destination site. In Morris [61], the self-assembly of micron-sized parts (280 μm) into interconnected structures was described which involved the use of capillary and magnetic forces. The capillary forces were provided using low meting point solder alloys while the magnetic forces were generated using magnetic microstructures.…”

“…Iwase [60], Wang [61], Grzybowski (2010) • External magnetic fields • Manipulation of ferromagnetic parts Saeedi et al [52] • Discussion of fundamental aspects of self-assembly process • Discussion of selection of appropriate alloy…”

Magnetic self-assembly with unique rotational alignment for thin chips

“…Micro-manipulation of small-scale parts with magnetic forces is an extensively used approach, i.e magnetic micro-robots [7] and 3D assembly of complex structures [8][9][10]. As in other methods, the friction between the parts and the substrate should be eliminated or decreased that the parts become free to move in the surrounding force field.…”