Forming Electrical Networks in Three Dimensions by Self-Assembly
10.1126/science.289.5482.1170
Crossref journal-article
American Association for the Advancement of Science (AAAS)
Science (221)
Abstract

Self-assembly of millimeter-scale polyhedra, with surfaces patterned with solder dots, wires, and light-emitting diodes, generated electrically functional, three-dimensional networks. The patterns of dots and wires controlled the structure of the networks formed; both parallel and serial connections were generated.

Bibliography

Gracias, D. H., Tien, J., Breen, T. L., Hsu, C., & Whitesides, G. M. (2000). Forming Electrical Networks in Three Dimensions by Self-Assembly. Science, 289(5482), 1170–1172.

Authors 5
  1. David H. Gracias (first)
  2. Joe Tien (additional)
  3. Tricia L. Breen (additional)
  4. Carey Hsu (additional)
  5. George M. Whitesides (additional)
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  12. Masters for forming the polyhedra were machined out of aluminum and molds were made from these masters using poly(dimethyl siloxane) (PDMS Sylgard 184 Dow Corning). Polymeric polyhedra were then cast in these molds using a photocurable polymer (NOA 73 Norland). A sheet of flexible copper-polyimide composite (Pyralux LF 9110 DuPont) was coated with a photoresist (Microposit 1813 Shipley) using hexamethyldimethylsiloxane (HMDS) as a primer. Both were spun on at 4000 rpm. After a soft-bake at 115°C for 5 min this sheet was exposed to UV light through a negative mask containing an array of the pattern of connector dots contact pads and wires. The exposed photoresist was developed and the exposed copper was removed by etching with an aqueous ferric chloride solution (1.4 g of FeCl 3 per milliliter of H 2 O). Unexposed photoresist was removed with acetone. The basic pattern was then cut out manually and glued (Krazy Glue Elmer's Products) to the faces of the polyhedra. In the demonstrations of parallel and serial networks LEDs (BL-HS136 American Bright Optoelectronics) were manually soldered (Rosin Core Solder Radio Shack m.p. ∼185°C) onto the copper contact pads. These soldered regions were coated with a thin impervious layer of adhesive (CA-50 Gel 3M) to avoid wetting and cohesion of these regions during assembly. The adhesive was allowed to harden completely over 48 hours. The polyhedra were then immersed in a bismuth solder (117 Small Parts Inc. m.p. ∼47°C) which was melted in an aqueous solution of hydrochloric acid (pH ∼ 1). The acid dissolved the oxide layer on the copper and the solder. The solder coated only the exposed copper regions on the polyhedra (dots and wires) but did not wet the polymeric surfaces. The solder-coated polyhedra were allowed to self-assemble in an aqueous KBr solution [density of 1.1 to 1.4 g/cm 3 pH of 3 to 4 adjusted with acetic acid to dissolve oxides on the solder (a function similar to that of flux in conventional soldering) and ∼0.001% (v/v) of detergent (Triton X-100 Aldrich) to prevent the formation of bubbles at the surface of the polyhedra] in an indented round-bottomed flask heated above the melting point of the solder (∼70°C) in an oil bath. The flask was placed horizontally on a rotary evaporator that was rotated at 5 to 20 rpm. All self-assemblies were complete within 1 hour. The assemblies were rotated for an average of 15 min after they formed at which time the assembly was allowed to cool. We believe that the last 15 min may serve to anneal the structure to correct errors in the connections. On cooling the molten solder interconnections solidified and gave the aggregates sufficient strength so that they could be manipulated.
  13. Two electrically isolated wires connected the two sets. An LED was soldered on the contact pads between the wires using a polarity in which the cathode was connected to the wire between dots {2 5 8 and 11} and the anode was connected to the wire between dots {1} (Fig. 3A). The pattern was glued on the TO in such a way that the copper dots covered two opposite square faces while the two wires ran across the two hexagonal faces between them.
  14. In order to reduce the number of circuits that would be formed (and of LEDs required to check their electrical connectivity) and to minimize the geometrical problems of packing the LEDs in the arrays only four of the dots (we call these dots “active”) in the solder pattern ({3 9} and {7 13}) were wired to LEDs. The other four dots ({6 12} and {4 10}) in the pattern were connected to each other (we call these dots “passive”). A single TO contained eight LEDs one on each of the hexagonal faces with the square faces covered with the pattern of connector dots. The active and passive dots had twofold symmetry while the global pattern on individual connector dots on the assembling square faces had fourfold symmetry. This difference in symmetry resulted in the formation of a stochastic network upon self-assembly [if a deterministic network were required all the dots ({3 6 9 and 12} and {4 7 10 and 13}) would need to be connected to LEDs]. There are three types of connections which result from overlap of dots at each assembling face: (i) connections between LEDs on different TOs involving only active dots with a probability of one-fourth; (ii) connections between LEDs on the same TO involving both active and passive dots with a probability of one-half; and (iii) connections containing no LEDs involving only passive dots with a probability of one-fourth.
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  29. Supported by Defense Advanced Research Projects Agency/SPAWAR/AFRL and the NSF (CHE-9901358 and ECS-9729405). We thank S. Brittain for help with photography.
Dates
Type When
Created 23 years, 1 month ago (July 27, 2002, 5:50 a.m.)
Deposited 1 year, 7 months ago (Jan. 13, 2024, 4:36 a.m.)
Indexed 1 day, 21 hours ago (Aug. 28, 2025, 8:25 a.m.)
Issued 25 years ago (Aug. 18, 2000)
Published 25 years ago (Aug. 18, 2000)
Published Print 25 years ago (Aug. 18, 2000)
Funders 0

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@article{Gracias_2000, title={Forming Electrical Networks in Three Dimensions by Self-Assembly}, volume={289}, ISSN={1095-9203}, url={http://dx.doi.org/10.1126/science.289.5482.1170}, DOI={10.1126/science.289.5482.1170}, number={5482}, journal={Science}, publisher={American Association for the Advancement of Science (AAAS)}, author={Gracias, David H. and Tien, Joe and Breen, Tricia L. and Hsu, Carey and Whitesides, George M.}, year={2000}, month=aug, pages={1170–1172} }