Microsolidics: Fabrication of Three‐Dimensional Metallic Microstructures in Poly(dimethylsiloxane)

This Communication describes a method of fabricating complex metallic microstructures in 3D by injecting liquid solder into microfluidic channels, and allowing the solder to cool and solidify; after fabrication, the metallic structures can be flexed, bent, or twisted. This method of fabrication—which we call microsolidics—takes advantage of the techniques that were developed for fabricating microfluidic channels in poly(dimethylsiloxane) (PDMS) in 2D and 3D, uses surface chemistry to control the interfacial free energy of the metal– PDMS interface, and uses techniques based on microfluidics, but ultimately generates solid metal structures. This approach makes it possible to build flexible electronic circuits or connections between circuits, complex embedded or freestanding 3D metal microstructures, 3D electronic components, and hybrid electronic–microfluidic devices. There are several techniques for making metal microstructures in 3D. Electroplating and electroless deposition are routinely used to construct microstructures with metallic layers several nanometers to several microns thick in 2D or 3D. [1–11] To generate solid replicas of 3D objects, several groups have developed a technique, referred to as “microcasting”, to form metals in order to fabricate microparts (e.g., posts and gears) with features as small as 10 lm and aspect ratios as high as 10 from steel, zirconia, and alumina. [12,13] Techniques based on LIGA (Lithographie, Galvanoformung, und Abformung) produce even more complicated metallic objects by depositing a metal onto a molded polymer template that is subsequently removed to yield an open structure (such as a honeycomb arrangement of cells). [14,15] In principle, these approaches can be used to pattern metals of any thickness to produce features with an aspect ratio that is larger than that produced using electroplating.