Hybrid Microassembly with Surface Tension Driven Self-alignment: Handling Strategies and Micro-fabricated Patterns

Hybrid microassembly combines self-assembly technology with traditional robotic pick-and-place technology or other robotic feeding mechanics to construct microsystems. In a typical hybrid microassembly process, a micro part is brought adjacent to the assembly site by a robot handling tool at a high speed but with a relatively low precision, and liquid droplets dispensed by a dispenser at the assembly site align the part at a higher precision. By combing both the robotic pick-and-place technique and self-assembly technique, hybrid microassembly technique can achieve high speed and high precision simultaneously. This thesis explores the adaptability of hybrid microassembly technique by investigating different hybrid microassembly methods and different types of the patterns. Three hybrid microassembly approaches have been investigated: 1) droplet assisted hybrid microassembly, 2) water mist induced hybrid microassembly and 3) hybrid microassembly with forced wetting. The droplet assisted hybrid microassembly has been studied using patterns with segments and patterns with jagged edges. Parallel microassembly of microchips with water mist induced hybrid microassembly has also been explored. Hybrid microassembly on hydrophobic receptor site with super-hydrophobic substrate has been experimentally investigated with two forced wetting techniques. Four different types of patterns have been investigated for hybrid microassembly technique: (a) oleophilic/phobic patterns, (2) hydrophobic/super-hydrophobic patterns, (3) segmented patterns and (4) patterns with jagged edges. Hybrid microassembly has been studied on a new patterned oleophilic/oleophobic surface using adhesive droplet in ambient air environment. A patterned hydrophobic/super-hydrophobic surface has also been investigated and hybrid microassembly has been demonstrated with both water and adhesive. Application relevant patterns such as segmented patterns and patterns with jagged edges have been investigated. In summary, this thesis shows that hybrid microassembly can adapt to large varieties of patterns. Several new hybrid microassembly methods are developed and demonstrated. Such a wide adaptability and a variety of the processes indicate that hybrid microassembly can be a very promising approach for many potential applications, such as integration of surface emitting lasers, integration of small dies and 3D integration of chips with high density pin counts

Self-transport and self-alignment of microchips using microscopic rain

Alignment of microchips with receptors is an important process step in the construction of integrated micro- and nanosystems for emerging technologies, and facilitating alignment by spontaneous self-assembly processes is highly desired. Previously, capillary self-alignment of microchips driven by surface tension effects on patterned surfaces has been reported, where it was essential for microchips to have sufficient overlap with receptor sites. Here we demonstrate for the first time capillary self-transport and self-alignment of microchips, where microchips are initially placed outside the corresponding receptor sites and can be self-transported by capillary force to the receptor sites followed by self-alignment. The surface consists of hydrophilic silicon receptor sites surrounded by superhydrophobic black silicon. Rain-induced microscopic droplets are used to form the meniscus for the self-transport and self-alignment. The boundary conditions for the self-transport have been explored by modeling and confirmed experimentally. The maximum permitted gap between a microchip and a receptor site is determined by the volume of the liquid and by the wetting contrast between receptor site and substrate. Microscopic rain applied on hydrophilic-superhydrophobic patterned surfaces greatly improves the capability, reliability and error-tolerance of the process, avoiding the need for accurate initial placement of microchips, and thereby greatly simplifying the alignment process.Peer reviewe

Surface defect machining : a new approach for hard turning

Hard turning is emerging as a key technology to substitute conventional grinding processes, mainly on account of lower equipment cost, short setup time, and a reduced number of process steps. This is, however, being impeded by a number of challenges required to be resolved, including attainable surface roughness, surface deteriorations, surface residual stresses and metallurgical transformations on the machined steel surface (white layer). In this thesis, a novel approach named Surface Defect Machining (SDM) is proposed as a viable solution to resolve a large number of these issues and to improve surface finish and surface integrity. SDM is defined as a process of machining, where a workpiece is first subjected to surface defects creation at a depth less than the uncut chip thickness; either through mechanical and/or thermal means; then followed by a normal machining operation so as to reduce the cutting resistance. A comprehensive understanding of SDM is established theoretically using finite element method (FEM). Also, an experimental study has been carried out for extensive understanding of the new technique. A good agreement between theoretical and experimental investigations has been achieved. The results show very interesting salient features of SDM, providing favourable machining outcomes. These include: reduced shear plane angle, reduced machining forces, lower residual stresses on the machined surface, reduced tool-chip interface contact length and increased chip flow velocity, as well as reductions in overall temperature in the cutting zone and changing the mechanism of chip morphology from jagged to discontinuous. However, the most prominent outcome is the improved attainable surface roughness. Furthermore, SDM shows the ability to exceed the critical feed rate and achieve an optical surface finish upto 30 nm. A scientific explanation of the improved surface roughness suggests that during SDM, a combination of both the cutting action and the rough polishing action help to improve the machined surface. Based on these findings, it is anticipated that a component machined using the SDM method should exhibit improved quality of the machined surface, which is expected to provide tremendous commercial advantages in the time to come

Foil-to-Foil System Integration Through Capillary Self-Alignment Directed by Laser Patterning

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-to-foil system integration is demonstrated through the electrically functional assembly of an array of Au-sputtered capacitive humidity sensors onto a patterned base foil circuitry

Three-dimensional femtosecond laser processing for lab-on-a-chip applications

AbstractThe extremely high peak intensity associated with ultrashort pulse width of femtosecond laser allows us to induce nonlinear interaction such as multiphoton absorption and tunneling ionization with materials that are transparent to the laser wavelength. More importantly, focusing the femtosecond laser beam inside the transparent materials confines the nonlinear interaction only within the focal volume, enabling three-dimensional (3D) micro- and nanofabrication. This 3D capability offers three different schemes, which involve undeformative, subtractive, and additive processing. The undeformative processing preforms internal refractive index modification to construct optical microcomponents including optical waveguides. Subtractive processing can realize the direct fabrication of 3D microfluidics, micromechanics, microelectronics, and photonic microcomponents in glass. Additive processing represented by two-photon polymerization enables the fabrication of 3D polymer micro- and nanostructures for photonic and microfluidic devices. These different schemes can be integrated to realize more functional microdevices including lab-on-a-chip devices, which are miniaturized laboratories that can perform reaction, detection, analysis, separation, and synthesis of biochemical materials with high efficiency, high speed, high sensitivity, low reagent consumption, and low waste production. This review paper describes the principles and applications of femtosecond laser 3D micro- and nanofabrication for lab-on-a-chip applications. A hybrid technique that promises to enhance functionality of lab-on-a-chip devices is also introduced

BioMEMS

As technological advancements widen the scope of applications for biomicroelectromechanical systems (BioMEMS or biomicrosystems), the field continues to have an impact on many aspects of life science operations and functionalities. Because BioMEMS research and development require the input of experts who use different technical languages and come from varying disciplines and backgrounds, scientists and students can avoid potential difficulties in communication and understanding only if they possess a skill set and understanding that enables them to work at the interface of engineering and biosciences. Keeping this duality in mind throughout, BioMEMS: Science and Engineering Perspectives supports and expedites the multidisciplinary learning involved in the development of biomicrosystems. Divided into nine chapters, it starts with a balanced introduction of biological, engineering, application, and commercialization aspects of the field. With a focus on molecules of biological interest, the book explores the building blocks of cells and viruses, as well as molecules that form the self-assembled monolayers (SAMs), linkers, and hydrogels used for making different surfaces biocompatible through functionalization. The book also discusses: Different materials and platforms used to develop biomicrosystems Various biological entities and pathogens (in ascending order of complexity) The multidisciplinary aspects of engineering bioactive surfaces Engineering perspectives, including methods of manufacturing bioactive surfaces and devices Microfluidics modeling and experimentation Device level implementation of BioMEMS concepts for different applications. Because BioMEMS is an application-driven field, the book also highlights the concepts of lab-on-a-chip (LOC) and micro total analysis system (μTAS), along with their pertinence to the emerging point-of-care (POC) and point-of-need (PON) applications