Manipulating and assembling metallic beads with Optoelectronic Tweezers

Abstract

Optoelectronic tweezers (OET) or light-patterned dielectrophoresis (DEP) has been developed as a micromanipulation technology for controlling micro- and nano-particles with applications such as cell sorting and studying cell communications. Additionally, the capability of moving small objects accurately and assembling them into arbitrary 2D patterns also makes OET an attractive technology for microfabrication applications. In this work, we demonstrated the use of OET to manipulate conductive silver-coated Poly(methyl methacrylate) (PMMA) microspheres (50 μm diameter) into tailored patterns. It was found that the microspheres could be moved at a max velocity of 3200 μm/s, corresponding to 4.2 nano-newton (10−9 N) DEP force, and also could be positioned with high accuracy via this DEP force. The underlying mechanism for this strong DEP force is shown by our simulations to be caused by a significant increase of the electric field close to the particles, due to the interaction between the field and the silver shells coating the microspheres. The associated increase in electrical gradient causes DEP forces that are much stronger than any previously reported for an OET device, which facilitates manipulation of the metallic microspheres efficiently without compromise in positioning accuracy and is important for applications on electronic component assembling and circuit construction.

Assembly of Topographical Micropatterns with Optoelectronic Tweezers

“…In recognition of these limitations, a second category of "dry" cleanroom-free methods has been developed, including 3D printing, [8][9][10] laser machining, [11] and "pick-and-place" technologies. [26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41] The new method is a member of the wet cleanroom-free assembly techniques, but lacks many of the limitations indicated previously. [22][23][24][25] These techniques, in which patterns of 3D particles are assembled in a fluidic environment and are later dried for use in TMP applications, are creative and interesting, and preserve many of the advantages of the canonical methods while allowing for accessible, cleanroom-free operation.…”

“…[26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41] The new method is a member of the wet cleanroom-free assembly techniques, but lacks many of the limitations indicated previously. [26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41] The new method is a member of the wet cleanroom-free assembly techniques, but lacks many of the limitations indicated previously.…”

Use of optoelectronic tweezers in manufacturing—accurate solder bead positioning

“…To functionalize the OET device, a 15 kHz 25 V peak-to-peak AC voltage was applied, similar to the bias conditions used to manipulate other metallic particles in the OET device. 5,8 On applying the AC, the solder beads were attracted to the illumination region due to the positive DEP force, as shown in Figure 1(c). As provided by the company, the beads have a wide size range from 20 lm to 110 lm.…”

“…This result matches up with the previously reported results of moving silver-coated Polymethyl methacrylate (PMMA) beads in an OET system: the large metallic beads can experience a very high DEP force in the regime of several nano newtons (10 -9 N), which is due to the large size of the bead and the influence of its metal surface on the surrounding electric field. 8 The simulated trap profiles (solid lines) are also presented in Figure 2(e), which will be discussed later.…”

“…8,9 Due to the large size of the solder bead and the influence of its metallic surface on the electric field, the electrical potential (see Figure 4(a)) and electric field vary significantly across the solder bead, which makes the usual assumption that the field varies little over the particle inappropriate. 8 To solve this problem, a calculation method based on the integration of the Maxwell stress tensor over the surface of the bead was used, which takes the variation of electric field into account and has been proven to be successful for calculating the DEP force of large objects in varied electric field. 7 Shown in Figure 2(e) (solid lines) are the normalized simulation results of the trap profiles and the measured results (data points).…”