Flexible electronic devices are of great interest due to the rapid expansion of wearable devices for health monitoring and the rise of the Internet-of-Things. One key factor limiting their development is the integration of diverse high-quality, silicon-based electrical components with flexible substrates. This integration is difficult because the small electrical connections needed to interface the silicon chips with flexible substrates cannot be fabricated using existing manufacturing processes. A new process called microscale selective laser sintering (microscale-SLS) has been developed which offers the potential to overcome this manufacturing limitation by successfully sintering (fusing) nanoscale particles to create complex, three-dimensional, metal parts with micron-scale resolution on almost any substrate. Currently the commercial viability of the process is limited by a lack of understanding of the underlying physics governing the sintering process, and an inability to accurately model the process outcomes. This Grant Opportunities for Academic Liaison with Industry (GOALI) research project will overcome this limitation by developing fundamental science regarding the impact of nanoscale physics on the mass and energy transfer within the microscale-SLS process, and ultimately the final part integrity. As this project is an industry-university collaborative effort between NXP USA and the University of Texas Austin (UTA), it will provide both educational experiences and industrial traineeships for graduate and undergraduate students. A particular focus on providing opportunities and training to students from underrepresented backgrounds in engineering will be pursued through senior design projects and the Nanomanufacturing Systems for Mobile Computing and Mobile Energy Technologies (NASCENT) Center's High School Fellows program.
The research objective of the project is to understand the fundamental science regarding mechanisms by which thin layers of nanoparticles (NPs) are selectively laser sintered to realize 3D structures with resolutions of around one micron. The central hypothesis is that nanoscale effects such as surface diffusion, near-field radiation, and light scattering dominate the part-formation process in microscale-SLS, and therefore must be considered to accurately model microscale-SLS part formation. The specific aims of this project are to determine the mechanisms for (1) NP reshaping during the microscale-SLS process, (2) light penetration/absorption in the NP powder bed, and (3) heat transfer within the NP powder bed, and (4) to determine the relationship between NP-level mechanisms and continuum-level parameters for modeling part formation. A multiscale computational modeling approach for the macroscale selective laser sintering process (MCM-SLS) will be leveraged to construct a model of the microscale-SLS part formation process. It is expected that the development of accurate models of the microscale-SLS process will have a positive impact on the manufacturing of three-dimensional microscale interconnect structures by (1) reducing the time required to determine the optimal process parameters for microscale-SLS parts, (2) improving the scientific understanding of how part design affects part quality/yield, and (3) allowing designers to estimate part quality (strength, shape, conductivity, etc.) before fabrication. The computational models will be validated in collaboration with NXP USA using a prototype microscale-SLS system at their facilities.
