Towards high throughput fabrication of 3D microscale parts using microscale selective laser sintering
Creators: name: Behera, Dipankar
Publisher: name: The University of Texas at Austin
Year: 2021
Subjects: Microscale fabrication
Additive manufacturing
Slot die coating
Multiphase simulation
Nanoparticle sintering
Microscale 3D printing

description: Microscale additive manufacturing (AM) technologies are rapidly gaining traction within the AM community as well as the micro/nanofabrication community. While there are several applications of these technologies in fabricating microelectronics, MEMS/NEMS devices, the development of a precision microscale AM framework is imperative for the meeting the growing needs in several other industries like aerospace structures, medical devices, metamaterials, and micro-optics, etc. Scalability challenges of existing microfabrication frameworks, high barriers to entry, lack of design freedom and complex miniaturization needs are primary driving factors for this shift towards AM approaches. However, microscale AM is still in its nascent stages, partially because of the inflexibility of the micro/nano-fabrication industry, but mainly because of the limitations to its fabrication capabilities. The most commercialized microscale AM approach is based on photopolymerization (microstereolithography), and therefore is limited to polymers. Metals play a crucial role in development of functional microdevices in several of the aforementioned devices, and currently there are several challenges associated with making small parts with AM techniques. Commercially available microscale AM machines are not capable of producing sub-100 µm features reliably in a production scale environment. Therefore, the microscale selective laser sintering process (µ-SLS) was developed at The University of Texas at Austin to address this problem. The primary applications of this tool are in fabricating interconnect structures for back-end-of-line of a semiconductor fab in a high throughput environment for up and coming chip integration strategies like 3D chip stacking. Previous work on this technology focused on developing the key aspects of the µ-SLS process and tool. The µ-SLS process is a layer-by-layer AM approach that uses metal nanoparticle inks (silver, as primarily used in this study) for fabricating multilayer sub-5 µm parts. However, there were several unknowns specifically related to layer-by-layer AM using this process including (but not limited to) - how to get multiple layers of ink and sintered parts stacked on top of each other, how does the heat spread on the nanoparticle bed, how to get near-net shaped parts and minimize/remove heat affected zones, how to remove excess ink, etc. This thesis furthers the development of the micro-SLS process by outlining the fundamental challenges associated with multilayer sintering, and presents computational and experimental investigation of several key steps towards it. More specifically, this study outlines the integration of the disaggregated parts of the µ-SLS system to develop the tool as designed, which is a pre-cursor to the multilayer sintering process. This µ-SLS tool is used to develop multilayer sintered parts, discuss challenges associated with fabricating these parts repeatably, and propose new approaches to improve the process. Along this path, this study explores the need to develop near-net shape parts and proposes methods to understand and mitigate the current limiting factors. Multilayer sintering results demonstrating fabricated 2.5/3D parts and their repeatability contributes to the development of this precise microscale AM techniques. Lastly, the next steps to continue the development of this process, optimizing the process parameters and integration within a high throughput environment are discussed in the future works sections.