Shift Dynamics of Capillary Self-Alignment (original) (raw)
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Investigation of the capillary self-alignment of complex geometrical chips
Capillary self-alignment (CSA) of mesoscopic objects has emerged in the 2000s [1,2]. It has been recently widely investigated for applications such as 3D microelectronics [3] and assembly of optical components [4]. It is now thought that it could be a solution for packaging technologies [5] (Fig.1). For 3D microelectronics, it has been found to be an efficient technique if specific precautions are taken [6]. However, the case of the alignment of complicated plate shapes is still a challenge, even if encouraging first experiments have been recently performed [5], and a model for the shift-restoring force has been published [7]. In this text, we investigate re-alignment of several complex plate shapes used in microsystem packaging.
Self-alignment of silicon chips on wafers: A capillary approach
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.
Part tilting in capillary-based self-assembly: Modeling and correction methods
2008 IEEE 21st International Conference on Micro Electro Mechanical Systems, 2008
We present a model and experimental results on tilt angle of microparts in capillary-driven self-assembly. The assembly is carried out in an aqueous environment, using a heat curable adhesive for part-substrate lubrication and mechanical bonding. Silicon parts and substrate have matching hydrophobic binding sites, which drive the assembly by surface energy minimization. Force balance analysis of an assembled part leads to a model describing the dependence of tilt angle on assembly parameters such as adhesive volume and water-adhesive interfacial tension. The effect of adhesive volume on tilt angle is investigated experimentally. Tilt correction of the assembled parts is achieved by providing external energy to the system via vertical vibration.
Capillary self-alignment of mesoscopic foil components for sensor-systems-in-foil
Journal of Micromechanics and Microengineering, 2012
This paper reports on the effective use of capillary self-alignment for low-cost and time-efficient assembly of heterogeneous foil components into a smart electronic identification label. Particularly, we demonstrate the accurate (better than 50 μm) alignment of cm-sized functional foil dies. We investigated the role played by the assembly liquid, by the size and the weight of assembling dies and by their initial offsets in the self-alignment performance. It was shown that there is a definite range of initial offsets allowing dies to align with high accuracy and within approximately the same time window, irrespective of their initial offset.
Journal of Fluid Mechanics, 2021
In the fields of microgripping and microassembly, the self-alignment motion of a solid micro-object linked by a liquid meniscus to a substrate or a tool is an inexpensive way to overcome the current limitations of the assembly processes at microscale by getting rid of the positioning actuators. Original models providing a dynamical description of the capillary self-alignment of an L × D × d chip are reported, as well as experimental results as evidence of their validity. The first two models describe the liquid and the solid physics in two dimensions. Both include nonlinearities and describe the coupling between a laminar flow and a solid structure. The fluid-solid coupling is ensured by the boundary conditions at their surface of contact and by the forces the liquid and the solid apply on each other. Both models yield the shift, lift and tilt modes of deformation of the liquid meniscus. Equations are first numerically solved by using a finite element method (model 1). By approximating the menisci with spherical caps, a geometrical model is then presented (model 2). Next, for small oscillations and thin liquid layers, the equations are linearised. The solution to the semianalytical three degrees of freedom (3-DOF) modal analysis is thus obtained (model 3). Finally, a semianalytical 1-DOF model is presented and numerically solved by considering a one-dimensional motion for the solid object (model 4). Solutions for models 1, 3 and 4 are computed and show good agreement with the experimental measurements. Yet, the remaining deviations are investigated to identify their origin.
Self-assembly of microsystem components with micrometer gluing pads through capillary forces
Journal of Manufacturing Processes, 2020
The self-alignment of microparts based on capillary forces and micrometer adhesive pads was evaluated through experimental evidence, analytical modelling and simulation. The local deposition of adhesive pads in the range of 2000 to 20 μm was realized by photo-lithographical patterning of an acrylate adhesive interlayer, followed by the spontaneous assembly with glass counterfaces that have a complementary array of hydrophobically modified gold structures. The design rules for self-alignment of microparts were studied from calculations of the capillary force and displacement as a function of the adhesive pad dimensions, pad heights and offset length. In all cases, the self-alignment induced by capillary forces is driven by a minimization of the surface energy, leading to an equilibrium position. The analytical results provided good qualitative understanding of the alignment process: larger dimensions, smaller separation and higher offset values contributed to higher forces and fast alignment. The simulation experiments in Surface Evolver were based on calculated geometries of adhesive pad providing a minimum surface energy and also take into account the local deformation of the adhesive pad together with an additional degree of rotational freedom. Consequently, the latter results indicated a high degree of precision with good correlation to the experiments and analytical results.
Challenges for capillary self-assembly of microsystems
2011
Within the currently rising trend of heterogeneous microsystem integration and packaging, capillary self-assembly emerges as an innovative technique to enhance, complement and eventually replace pick-and-place assembly. Vast literature and experimental data support such claim. Still, the technique needs to overcome some important limitations in order to fully express its potential and earn wide industrial recognition. In this paper, we review and illustrate what are in our opinion the challenges ahead for making part-to-substrate capillary self-assembly reliable and seriously competitive with long-established assembly techniques. After setting self-assembly methods in the context of microsystem assembly and integration technologies, we focus on the standard embodiment of capillary self-assembly, and we describe in details the main, often novel technological steps required for its effective and reproducible performance. This preludes to an outline of what are presently, in our view, the major failure modes affecting the overall yield of the capillary self-assembly technique. Consequently, we propose solutions to face and overcome these challenges, which need to be met to foster the success of this technique.
Low-height sharp edged patterns for capillary self-alignment assisted hybrid microassembly
Journal of Micro-Bio Robotics, 2014
This paper studies the hybrid microassembly of 300 μm (L)×300 μm (W)×30 μm (H) microchips on sharp edged patterns with different edge heights. Hybrid microassembly combines the robotic pick-and-place technique and the droplet based surface tension driven selfassembly technique, where the robotic pick-and-place handling tool is used for coarse positioning and the droplet selfassembly technique is used for high-accuracy self-alignment. Spreading of the liquid outside the pattern leads to failure in self-alignment. Sharp edge on a solid surface is known for enabling contact line pinning according to Gibbs inequalities, which prohibits spreading of the liquid. Topological patterns featured with the sharp edge can be used as the receptor site for surface tension driven self-alignment. However, it is unclear how high the sharp edged pattern should be to achieve successful self-alignment in hybrid microassembly. In this paper, sharp edged topological patterns with five different edge heights: 70 nm, 140 nm, 280 nm, 540 nm and 1,050 nm, have been fabricated and tested with water to investigate the influence of the edge height on the hybrid microassembly. The experimental results indicate the edge height affects both the contact line pinning and the selfalignment process. Water droplet can successfully pin at the edge of patterns higher than 280 nm. Self-alignment can reach 100 % success rate on the patterns with edge height of 1 μm when the initial placement error is below 150 μm.
Foil-to-Foil System Integration Through Capillary Self-Alignment Directed by Laser Patterning
Journal of Microelectromechanical Systems, 2015
This paper introduces a new integration technology for cost-effective high-precision mechanical and electrical integration of mesoscopic functional foil components onto foil substrates. The foil-to-foil assembly process is based on topological surface structuring via laser patterning that enables accurate capillarity-driven self-alignment of foil dies. The concurrent establishment of high-yield electrical interconnections is obtained through conductive adhesives. The foil surface energy controls the acceptance window of initial offsets for optimal self-alignment performance. The proposed topological patterning and system design enable alignment accuracies for centimeter-sized foil dies as high as 15 µm, barely influenced by the evaporation of the assembly liquid and curing of the conductive paste. Full foil-tofoil system integration is demonstrated through the electrically functional assembly of an array of Au-sputtered capacitive humidity sensors onto a patterned base foil circuitry.