Fig. (12).

A schematic of the basic steps involved in the fabrication of hollow, patterned cubic containers. (A, B) First, a silicon wafer is spin-coated with PMMA, which acts as a sacrificial layer. This is followed by evaporation of Cr and Cu. Cr promotes the adhesion of Cu, while Cu acts as a conductive seed layer for electrodeposition. (C) Photolithography and Ni electrodeposition are then used to produce the 2D frames of the containers. (D) A second round of photolithography patterns the hinges of the frames. Regions of the Cu and Cr layers that are exposed at the hinges are selectively etched. (E) Solder is then electroplated at the hinges. (F) The remaining photoresist is stripped with acetone. Then, the Cu and Cr layers are selectively etched, except for the regions directly under the frames. (G) The sacrificial layer is subsequently dissolved with N-methyl-2-pyrrolidone to release the frames from the wafer substrate. (H) Heating the frames in flux above the melting point of solder cause the frames to fold into a cube, due to the force exerted on the frame from the minimization of the surface area of the molten solder. Reproduced with permission from ref. [35].