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Micro Self Assembly - Controlled Multi-Batch Self-Assembly of Micro Devices

Team Members

Xiaorong Xiong, Yael Hanein, Jiandong Fang, Yanbing Wang, Karl F. Böhringer Weihua Wang, Daniel Schwartz (Chemical Engineering)

 

Summary

A technique is described for assembly of multiple batches of micro components onto a single substrate. The substrate is prepared with hydrophobic alkanethiol-coated gold binding sites. To perform assembly, a hydrocarbon oil, which is applied to the substrate, wets exclusively the hydrophobic binding sites in water. Micro components are then added to the water, and assembled on the oil-wetted binding sites. Moreover, assembly can be controlled to take place on desired binding sites by using an electrochemical method to deactivate specific substrate binding sites. By repeatedly applying this technique, different batches of micro components can be sequentially assembled to a single substrate. As a post assembly procedure, electroplating is incorporated into the technique to establish electrical connections for assembled components. Important issues presented are: substrate fabrication techniques, electrochemical modulation by using a suitable alkanethiol (dodecanethiol), electroplating of tin and lead alloy and binding site design simulations. Finally, we demonstrate a two-batch assembly of silicon square parts, and establishing electrical connectivity for assembled surface-mount light emitting diodes (LEDs) by electroplating.

 

Adsorption Desorption

Figure 1: Adsorption is done by soaking surfaces in ethanolic alkanethiol solution.

Figure 2: Reductive desorption of SAMs:
CH3(CH2)nS -Au + e– —> CH3(CH2)nS– + Au

Figure 3: Selective assembly process (the assembly was performed after selective desorbtion of the SAM from the gold sites at the left).

Figure 4: Two step assembly results. The parts were permanently bonded after each assembly step by curing the organic lubricant.

Videos

 

Selected Publications

A complete list of our publications (many of them available online) can be found here.

 

Acknowledgements

 

Micro Self Assembly - Modelling of Capillary Forces in Fluidic Self-Assembly

 

Team Members

Andreas Greiner, Jan Lienemann, Jan G. Korvink (Universität Freiburg, Germany) Xiaorong Xiong, Yael Hanein, Karl F. Böhringer

 

Summary

Parallel self-assembly in the fluidic phase is a promising alternative technique to conventional pick-and-place assembly. In this work the hydrophobic-hydrophilic material system between binding sites for microparts is simulated with respect to alignment precision. The results are compared with experimental findings and allow predictions for the optimization of the fluidic self assembly technique. volume.

 

Figure 1: Geometry: the part displacements, with respect to the substrate pad, are measured using a local coordinate frame. The shape of the liquid meniscus was computed numerically.

Figure 2: Saturating restoring force (left scale) and potential energy (right scale) as function of shift in part placement.

 

Selected Publications

A complete list of our publications (many of them available online) can be found here.

 

Micro Self Assembly - Designing the Binding Sites in Fluidic Self-Assembly

 

Team Members

Karl F. Böhringer, Uthara Srinivasan, Roger Howe (UC Berkeley)

 

Summary

Massively parallel self-assembly is emerging as an efficient, low-cost alternative to conventional pick-and-place assembly of microfabricated components. The fluidic self-assembly technique we have developed exploits hydrophobic-hydrophilic surface patterning and capillary forces of an adhesive liquid between binding sites to drive the assembly process. To achieve high alignment yield, the desired assembly configuration must be a (global) energy minimum, while other (local) energy minima corresponding to undesired configurations should be avoided. Thus, the design of an effective fluidic self-assembly system using this technique requires an understanding of the interfacial phenomena involved in capillary forces; improvement of its performance involves the global optimization of design parameters such as binding site shapes and surface chemistry.

This work presents a model and computational tools for the efficient analysis and simulation of fluidic self-assembly. The strong, close range attractive forces that govern our fluidic selfassembly technique are approximated by a purely geometric model, which allows the application of efficient algorithms to predict system behavior. Various binding site designs are analyzed, and the results are compared with experimental observations. For a given binding site design, the model predicts the outcome of the selfassembly process by determining minimum energy configurations and detecting unwanted local minima, thus estimating expected yield. These results can be employed toward the design of more efficient self-assembly systems.

 

Selected Publications

A complete list of our publications (many of them available online) can be found here.

 

Acknowledgements