We demonstrate a novel parallel micro assembly process based on both shape recognition and capillary-driven self-assembly in an air environment. Mechanically diced 790 µm square silicon parts with flat or step edges were used for proof-of-concept demonstrations. Each part had only one hydrophobic 790 µm × 790 µm face and its other faces were hydrophilic. On a vibrating plate, tumbling parts were captured by cavities having an opening clearance that only admitted a single part standing vertically. The trapped parts were then transferred to a substrate having an array of receptor sites covered with water droplets. The flat-edge parts attached vertically to these sites and then capillary forces from water condensate turned them to face the substrate with their 790 µm × 790 µm hydrophilic faces. The step-edge parts attached at a tilted angle due to their featured edges and then a pressing plate laid them down. This process assembled micro parts to 1000 densely packed receptor sites in about 2 min with a defect rate of ∼1%. A single batch assembly process achieved 31% surface coverage, and a second batch doubled the ratio to 62%.
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.[839]
Abstract-A wafer-level packaging strategy for micro device chips based on uniquely orienting self-assembly is presented with the following steps: 1) bulk parts are uniquely face-oriented and spread in a single layer; 2) parts are palletized onto an alignment template having an array of receptor sites; 3) parts are anchored one-to-one to the receptor sites; 4) each anchored part is fixed to a unique in-plane orientation. We demonstrate all of these steps with two different self-organizing parallel assembly (SPASS) processes: a semidry uniquely orienting process (semi-DUO-SPASS) and a dry uniquely orienting (DUO-SPASS) process. The semidry process exploits: 1) an agitated air/water interface to uniquely face-orient bulk parts having a single hydrophobic face; 2) a hydrophobic carrier wafer to palletize the parts in an air environment; 3) orbital shaking to drive the parts until they are anchored to receptor sites; 4) gravity to uniquely align the parts. Experiments show that 2-mm square silicon parts are correctly registered on a 4-in alignment template having 164 receptor sites with a defect rate of 1% after 3 min orbital shaking. The dry process utilizes: 1) asymmetry in dynamic stability to uniquely face-orient bulk parts having protruding features on one face; 2) orbital shaking to drive the parts until they are first anchored to receptor sites and then fixed in well-defined in-plane orientations by two-stage shape recognition. In our experiments, 1-mm square silicon parts are assembled with a defect rate of 2% in 10 min on each of two 4-in alignment templates having, respectively, 397 and 720 receptor sites.[1490]Index Terms-Self-organizing parallel assembly (SPASS) process, two-stage shape recognition, uniquely orienting self-assembly, wafer-level packaging.
In this paper, we report a novel capillary-driven self-assembly technique which proceeds in an air environment and demonstrate it by assembling square piezoelectric transducer (PZT) actuators for 28 diffuser valve micropumps on a 4-inch pyrex/silicon substrate: on the substrate, binding sites are wells of 24 m in depth and the only hydrophilic areas; on the bonding face of the PZT actuator, the central hydrophilic area is a square identical in size to the binding site, and the rim is hydrophobic; acrylate-based adhesive liquid is dispensed across the substrate and wets only the binding sites; the hydrophilic areas on the introduced PZT actuators self-align with the binding sites to minimize interfacial energies by capillary forces from the adhesive droplets; the aligned PZT actuators are pressed to contact the gold coated substrate by their rims and the adhesive is polymerized by heating to 85 C for half an hour, so permanent mechanical and electrical connections are established, respectively, at the center and rim of each PZT actuator. These pumps perform with high uniformity, which is indicated by a small standard deviation of their resonant frequencies to pump ethanol: the average resonant frequency is 6.99 kHz and the standard deviation is 0.1 kHz. Compared with the conventional bonding process with highly viscous silver epoxy, this assembly method has several major advantages: highly accurate placement with self-alignment, controllable adhesive thickness, tilt free bonding, low process temperature and high process repeatability. [1491] Index Terms-Capillary-driven self-assembly, diffuser valve micropump, recessed binding site, interfacial energy minimization. I. INTRODUCTION P ZT actuators can convert electrical energy to mechanical energy with fast response and are widely used as driving elements for several types of microfluidics devices such as micropumps [1], micromixers [2], [3] and microdispensers [4], among others. Typically, piezoelectric transducer (PZT) actuators are manually mounted onto a silicon, glass, or polymer substrate with batch-fabricated microfluidic components using highly viscous silver epoxy, a slow serial process without good control of process parameters such as placement of PZT actuators, adhesive thickness and PZT actuator tilting; therefore this assembly process cannot achieve good repeatability and does not scale well to wafer level packaging. Capillary forces have been exploited to assemble microstructures in two or three dimensions by several research groups [5]-[9]. We previously reported capillary-driven self-assembly Manuscript
Abstract-Sobel algorithm is an important method of image edge detection. Comparing the Sobel operator with several other edge detection operators used frequently and making a further study on the classical Sobel operator, the advantages of Sobel operator are its fast detection speed, meanwhile , it has an effect on smoothing and suppressing noise. Also, Sobel operator has a good effect on edge detection. Although Sobel operator has advantages in many aspects, it exists some problems: the Sobel operator is a kind of edge detection in horizontal and vertical direction, so it neglects edge points in other directions. It can not achieve a true detection for the points on image edge. In this paper, the algorithm is based on the Sobel operator, an increase of 45 degrees and 135 degrees 2 direction template, while the main edge of the oblique, re-assigned the weight of the operator template. At the same time, in order to achieve an effect of detection, binarization method is used to make an edge thinning for detected image. According to simulation experiments, they show this method is simple and feasible, and the detective result is more concrete and abundant than traditional Sobel edge detection. Some problems are improved, such as traditional Sobel edge is rough and detection is incomplete.
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