Date of Award
Doctor of Philosophy
Material Science and Engineering
Ryan B. Wicker
The focus of this research was the development of a hybrid manufacturing system that integrates stereolithography (SL) and direct print (DP) technologies to fabricate three dimensional (3D) structural electronic devices within a single set-up. The capabilities of this new additive manufacturing (AM) technology was explored in the context of fabricating and prototyping complex electronic devices in which conformal shape, rugged and light-weight integration, and a natural resistance to reverse engineering are all of paramount importance. Consequently, electronic components can be tightly integrated together in a rugged, light-weight 3D structure of arbitrary form. This research is a continuing advancement of the Mesoscopic Integrated Conformal Electronics (MICE) program which was developed at the Defense Advanced Research Projects Agency (DARPA) with a primary goal to develop direct write (DW) electronics applications for advancing the traditional IC manufacturing. It was during the developments as part of the MICE program that the concepts for integration of AM and DP for producing functional, monolithic 3D structures with embedded electronics emerged. Several researchers have since explored a variety of AM and DP systems, including multi-material technologies for fabricating unique functional products including structural electronic devices. Early developments in this research included the fabrication of multilayer circuitry and a manufacturing process for fabricating 2D electronic devices using separate SL and DP systems. Due to significant improvements in both the SL/DP process in recent years an increased level of sophistication of the integrated electronics has been achieved. These developments have culminated into the current work that describes a fully integrated system and a corresponding process that enables fabrication of complex, 3D structural electronic devices within a single integrated manufacturing environment.
As a result, this dissertation broadly demonstrated what can be achieved by integrating multiple AM technologies together for fabricating unique devices. Specifically, a hybrid SL/DP machine that can produce 3D monolithic structures with embedded electronics and printed interconnects is demonstrated. Advancements in the development of a hybrid manufacturing system that integrates SL and DP technologies to fabricate 3D structural electronic circuits are described. These advancement lead to the development of the state-of-the-art hybrid SL/DP system which included a 3D Systems SL 250/50 machine and an nScrypt micro-dispensing pump integrated within the SL machine through orthogonally-aligned linear translation stages for accurate 3D material dispensing. The 3D micro-dispensing DP system provided control over conductive trace deposition and combined with the manufacturing flexibility of the SL machine enabled the fabrication of monolithic 3D electronic structures. A corresponding manufacturing process was also developed using this system to fabricate 3D monolithic structures with embedded electronic circuits without removal from the hybrid SL/DP machine during the process. The process required multiple starts and stops of the SL process, removal of uncured resin from the SL substrate, insertion of active and passive electronic components, DP, in situ UV laser curing of the conductive traces.
As a key enabler of 3D structural electronic device fabrication, in situ UV laser ink curing of particulate silver based conductive inks was investigated further. Various laser curing parameters, including laser power, scan speed and time of laser incidence, laser scanning location, and laser wavelength were investigated through a series of experiments. The trace resistances for each experiment were compared to determine the laser conditions that resulted in the most effective ink curing. As part of this research, the laser energy supplied by the 355nm SL laser was related to an effective steady-state curing temperature as determined by a commercially available thermistor. Scanning the laser on the edge of the ink channel gave the best ink curing, measured in terms of lowest trace resistance, but resulted in charring of the SL substrate. Alternatively, the laser condition at which the substrate did not char provided relatively less effective ink curing. Scanning the laser directly on the ink resulted in some discoloration, although SEM images revealed no structural changes. The effect of laser wavelength on trace resistance during repetitive laser curing was determined. Laser curing at 325 nm wavelength was found to be more effective than at 355 nm wavelength due to reduced reflectance of the silver particles at 325 nm wavelength. This research determined the experimental conditions for successful in situ UV laser curing of particulate silver-based inks in the context of fabricating 3D structural electronic devices using a hybrid SL/DP machine and advanced the capabilities of AM technologies. Opportunities exist for expanding the laser parameters to generalize the laser curing process for a variety of conductive inks. The electronic devices demonstrated as part of this research were simple 555 timer circuits designed and fabricated in 2D (single layer of routing) and 3D (multiple layers of routing and component placement).
In summary, a new methodology is presented for manufacturing non-traditional electronic systems in arbitrary form, while achieving miniaturization and enabling rugged structure and advanced applications are demonstrated using a semi-automated approach to SL/DP integration. Although the process does not require removal of the structure from the machine during fabrication, many of the current sub-processes are manual. As a result, further research should focus on the automation and development of many of the sub-processes to optimize the overall manufacturing process.
Received from ProQuest
Lopes, Amit, "Hybrid Manufacturing: Integrating Stereolithography and Direct Print Technologies" (2010). Open Access Theses & Dissertations. 2525.