Dry self-alignment for discrete components: Exploiting combinations of electrostatic fields and mechanical features (original) (raw)
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Journal of Applied Physics, 2010
As the limits of Moore's law are approached, 3D integration appears as the key to advanced microelectronic systems. Die-to-wafer assembly appears to be an unavoidable step to reach full integration. While robotic methods experience difficulties to accommodate fabrication speed and alignment accuracy, self-assembly methods are promising due to their parallel aspect which overcomes the main difficulties of current techniques. The aim of this work is the understanding of the mechanisms of self-alignment with an evaporating droplet technique. Stable and unstable modes are examined. Causes for misalignments of chips on wafers and their evolution are investigated with the help of the Surface Evolver numerical software. Precautions for suitable alignment are proposed.
Precision Engineering
Self-assembly of components using liquid surface tension is an attractive alternative to traditional robotic pick-and-place as it offers high assembly accuracy for coarse initial part placement. One of the key requirements of this method is the containment of the liquid within a designated binding site. This paper looks to expand the applications of self-assembly and investigates the use of topographical structures applied to 3D printed micro components for self-assembly using liquid surface tension. An analysis of the effect of edge geometry on liquid contact angle was conducted. A range of binding sites were produced with varying edge geometries, 45-135°, and for a variety of site shapes and sizes, 0.4 - 1 mm in diameter, and 0.5 × 0.5–1 × 1 mm square. Liquid water droplets were applied to the structures and contact angles measured. Significant increases in contact angle were observed, up to 158°, compared to 70° for droplets on planar surfaces, demonstrating the ability of these ...
Precision passive mechanical alignment of wafers
IEEE/ASME Journal of Microelectromechanical Systems, 2003
A passive mechanical wafer alignment technique, capable of micron and better alignment accuracy, was developed, fabricated and tested. This technique is based on the principle of elastic averaging: It uses mating pyramid (convex) and groove (concave) elements, which have been previously patterned on the wafers, to passively align wafers to each other as they are stacked. The concave and convex elements were micro machined on 4-in (100) silicon wafers using wet anisotropic (KOH) etching and deep reactive ion etching. Submicron repeatability and accuracy on the order of one micron were shown through testing. Repeatability and accuracy were also measured as a function of the number of engaged elements. Submicrometer repeatability was achieved with as little as eight mating elements. Potential applications of this technique are precision alignment for bonding of multiwafer MEMS devices and three-dimensional (3-D) interconnect integrated circuits (ICs), as well as one-step alignment for simultaneous bonding of multiple wafer stacks. Future work will focus on minimizing the size of the elements.
Methods and Characterization of Pick and Place Microassembly
Microelectromechanical Systems, 2006
Microassembly of MEMS structures using serial pick-andplace has been demonstrated as a method for constructing complex three-dimensional microstructures. A new methodology to perform pick-and-place microassembly using a 3 DOF micromanipulator is demonstrated here. In this approach, the "pick" operation is performed on one chip, while the "place" operation is performed on a second chip mounted orthogonally to it under a microscope. This removes the need for the rotation of parts during assembly as required in previous works thus creating a significantly simpler assembly process. Also new in this work is the characterization of the contact resistance and the rigidity of assembled microstructures. The contact resistance of assembled microparts coated with 30nm of gold is measured to be approximately 12Ω using a four-point measurement. The force required to pull out a micropart from a socket (into which it is assembled) is characterized along all three axes and found to be over 5mN in each case. The relationship between the force taken to engage the sockets and the force to pull out a micropart is measured to be linear. An electrostatic inchworm motor with extended range and a vertical thermal actuator are demonstrated which are manufactured using microassembly. Thus this assembly process with mechanically rigid assemblies is shown to have a number of potential applications.
Electrostatic attraction and surface-tension-driven forces for accurate self-assembly of microparts
Microelectronic Engineering, 2010
Self-assembly is not widely used in industrial micro-fabrication, although it can potentially involve assembly processes that are considerably less complex. A variety of procedures for self-alignment of parts have been introduced and investigated lately. These procedures mainly utilise capillary, gravitational or electrostatic forces in the micro-scale. This paper investigates two different concepts for accurate selfassembly of parts. One is well described in the literature by third parties and involves the alignment of parts by utilising the surface tensions of micro-scaled adhesive films, which are selectively coated on hydrophobic alignment structures. In the present publication the influence of the dimensions of such structured alignment sites on the process flow is discussed. The second concept is a novel approach to accomplish self-alignment of micro-structures with electrostatic attraction. Several complementary and electrically conductive micro-structured patterns serve as binding sites for the alignment of parts in this approach. In order to obtain knowledge of how these two approaches operate, they have been modelled and simulated. Additionally, in order to analyse the feasibility of these procedures and to verify simulation results experiments have been performed on micro-structured parts and substrates. In particular, the layout of the alignment structures and the size of the parts were identical for both described concepts in the experimental work; therefore, these two methods were compared. With the self-assembly procedure that utilises electrostatic attraction, high alignment accuracies and forces, affecting the part over large distances, were observed. Finally, parts with micro-structured binding sites, which were as small as 10 Â 10 lm 2 , could accurately be self-aligned with electrostatic attraction.
Journal of Microelectromechanical Systems, 2007
This paper describes a packaging concept for precise hand-assembly of microelectromechanical systems (MEMS) subsystems that uses mesoscaled deep-reactive ion etching (DRIE) patterned passive deflection spring clusters. The method is intended for applications that require decoupling of subsystem process flows to simplify device fabrication in order to attain macro three-dimensionality, or for cases where the device requires spatially referenced macro-and microfeatures with good precision. The design considerations for the deflection springs are presented, and a simple reduced-order model of the expected elastic behavior is proposed. The assembly concept is demonstrated with an electrospray array test structure. This test structure assembles perpendicularly two wafer substrates. The performance of the test structure is benchmarked using finite-element simulations and by measurements of the misalignment introduced by the assembly. A floor for the ultimate alignment accuracy of the assembly concept is proposed. [1456] Index Terms-Deep-reactive ion etching (DRIE) patterned springs, low-pressure low-temperature die-level packaging, out-of-plane wafer assembly, passive deflection spring assembly, system integration. I. INTRODUCTION, GOAL, AND MOTIVATION M ICROELECTROMECHANICAL systems (MEMS) take advantage of the set of technologies developed by the semiconductor industry. In the majority of cases, these technologies imply the deposition or removal of layers of material where a planar layout is directly involved via a photolithographic process [1], [2]. The use of in-plane layouts to build structures restricts the range of geometries that can be implemented as part of a micromachine, in particular the aspect ratio and three-dimensionality of MEMS parts. Most of the efforts for photolithographic processes focus on reduction of Manuscript
Hybrid microassembly of chips on low precision patterns assisted by capillary self-alignment
Proceedings of the ... IEEE/RSJ International Conference on Intelligent Robots and Systems. IEEE/RSJ International Conference on Intelligent Robots and Systems
this paper discusses capillary self-alignment assisted hybrid microassembly of chips on low precision patterns, in both the precision of the dimension and the precision of the edge smoothness. Special segmented patterns having jagged edges have been purposely designed and fabricated to mimic some real-world RFID antennas. Experimental tests have been carried out to investigate influence of the dimension and the edge jaggedness on the yield and accuracy of the self-alignment, using 730 × 730 × 70 µm RFID chips as the test samples. The results show that the self- alignment occurs reliably with releasing bias less than 300 µm in both horizontal axes, despite the variation in size of the segmented pattern and edge jaggedness. However, both the dimension and the edge jaggedness affect the alignment accuracy.
Adhesive-based self-alignment mechanisms for modular stacked microsystems
The development of modularly designed systems could provide a cost-effective alternative to state-of-the-art manufactured microsystems. The purpose of this research was to develop a robust, cost-effective and low-temperature module assembly for the production of modular stacked systems with high positioning precision. To achieve this aim, a new alternative self-alignment process using the surface tension of a resin as a driving force was examined. This was then followed by characterization, simulation and optimization for self-assembly. The experimental results show that viscosity is the main parameter for the self-alignment capability of an adhesive. Furthermore, successful resin self-alignment requires both solid edge and edge treatment. Better results were achieved by dispensing the adhesive by the cross pattern then by the square pattern. In the two-dimensional simulation, it was shown that the self-alignment has a laminar aperiodic motion and the largest aligning forces occur a...
Self-alignment in the stacking of microchips with mist-induced water droplets
Journal of Micromechanics and Microengineering, 2011
This paper reports a novel and versatile water droplet self-alignment technique where the water is delivered in mist form onto the assembly site. The droplet forming process has been carefully investigated using machine vision, where each individual droplet on the microchip surface can be identified and the volume per surface area can be calibrated at a specific time. The result reveals that the volume of water droplets on the assembly surface grows linearly as a function of time. Self-alignment based on the mist-induced droplets has been studied, where a robotic microgripper is used to deliver the microchips on the assembly site. The paper also investigates the maximum tolerance of the initial placement error in stacking SU-8 chips 200 × 200 × 70 μm in size, and the possibility of stacking two SU-8 chips of different dimensions using the proposed self-alignment technique. Moreover, self-alignment of chips on hydrophilic/hydrophobic patterns covered by mist-induced water droplets has been studied. The experimental results indicate that this novel self-alignment technique is very promising. Furthermore, a statistical model has been used to validate the experimental results.