Thesis Title: Process Monitoring, Modeling, and Quality Assessment for Printed Electronics with Aerosol Jet Printing Technology

Advisor: Dr. Ben Wang and Dr. Chuck Zhang

Committee members:

Dr. Kamran Paynabar

Dr. Jianjun Shi

Dr. Tequila Harris (George W. Woodruff School of Mechanical Engineering)

Date and Time: Friday, May 5th, 2017, at  10:00 am

Location: Manufacturing Research Institute Building (MARC) R114

Summary:

Printed electronics (PE) technology has attracted significant attention in recent years due to its potential to simplify process steps and reduce costs when compared to conventional photolithography. PE technology is a one-step deposition process with post-sintering (or baking) to activate printed ink functionality. Furthermore, PE technology can be readily scaled to large-area production with high throughput with roll-to-roll printing. These features can be applied in a way that lowers cost and offers flexibility for work in large areas. These features offer new ways to develop novel electronics and accelerate their use in other areas of research and production. Examples include rapid prototyping, pilot production, small lot size production, organic light emitting diodes, organic solar cells, thin-film transistors, logic circuits, radio frequency identification (RFID) tags, and sensors.

Aerosol jet printing (AJP) was developed in 2007 by Optomec, Inc., to fulfill the increasing demand for miniature and flexible electronics. Compared with other PE technologies, such as screen printing and inkjet printing, AJP has demonstrated superior capabilities, for example, having a smaller feature size, thinner layer deposition, a larger pool of available ink and substrate materials, non-planar printing capability, and a low processing temperature. There are some limitations however. AJP is limited by not having in situ monitoring or control capabilities, which leads to inconsistent performance in products. Up to today, most AJP systems are installed in laboratories or research centers for fundamental research, product design, and prototyping. In spite of the increasing maturity of lab-scale fabrication, the lack of quality control becomes a critical roadblock for this transformative technology to be a viable production process. Using AJP for industrial applications involves complex system interactions including printed materials, process parameters, environment, post treatment, and device characterization, all of which require an in-depth understanding of the science and engineering of AJP. The objective of this proposed research is to create a knowledge base and establish engineering methods and tools for AJP quality control by understanding the relationships between the AJP process, properties, structure, morphology and performance. This thesis covers three major aspect of AJP processes.

Chapter 4 presented two exploratory device applications that could benefit from AJP technologies, but they suffered from process variation. From the fabrication processes, we identified major issues of AJP. The atomization stability and lack of systematically study of the relationship between process parameters and printed line morphologies. In the following chapter (Chapter 5), we developed tools to address the observed issues using statistical process control methodologies. We observed around 20% variation reduction in resistance response and a 50% completion rate improvement in carbon nanotube gas sensor and 3D transmission line fabrication, respectively.

Chapter 5 focuses on developing monitoring methods for the AJP process includes a vibration-based wavelet method for atomization monitoring and image processing techniques for extracting quantitative printed line quality matrices. In the end of the chapter, a design of experiment model using central composite design (CDD) is conducted to create a process model and create printing optimization guidelines.

Chapter 6 demonstrated two novel manufacturing process that extend current AJP capabilities into 3D printing and the nanocomposite fabrication area. A facile method called print-stick-pee l (PSP) was developed for integrating printed sensors into 3D printed objects. This method overcomes several challenges in the integration of 3D printing and printed electronics such as surface roughness, surface mismatch, and temperature limitation. Another method developed is called dual material aerosol jet printing (DMAJP), which can mix polymer and conductive filler material in different ratios on the fly. This method can fabricate conductive tailorable nanocomposites in a single piece and machine setup, which has a potential impact on soft robotics and nano-actuator research.