06/13/2022
By Sokny Long

The Francis College of Engineering Department of Mechanical Engineering invites you to attend a Master’s thesis defense by Channing Favreau on “Resistance Prediction Method for Cyclically Strained Printed AgNP Traces.”

MSE Candidate: Channing Favreau
Defense Date: Monday, June 27, 2022
Time: 1 to 3 p.m. EST
Location: ETIC-445, 4th floor conference room and virtually via Zoom. Those interested in attending should contact channing_favreau@student.uml.edu and committee advisor, christopher_hansen@uml.edu, at least 24 hours prior to the defense to request Zoom access.

Committee Chair (Advisor): Christopher J. Hansen, PhD, Chair, Associate Professor, Mechanical Engineering, University of Massachusetts Lowell

Committee Members:

  • Alkim Akyurtlu, PhD, Professor, Associate Chair for Graduate Affairs, Co-Director Center for Photonics, Electronmagnetics and Nanoelectronics (CPEN) Doctoral Coordinator, Deputy Director for Printed Electronics Research Collaborative (PERC), Electrical & Computer Engineering, University of Massachusetts Lowell
  • Scott Stapleton, PhD, Associate Professor, Mechanical Engineering, University of Massachusetts Lowell


Brief Abstract:
Electronics are ubiquitous in the modern world, and with 6G, Internet of Things, self-driving cars, and wearable electronics on the horizon, the demand for more complex and dense electronics is growing. The heart of these electronics are printed circuit boards (PCBs) and integrated circuit (IC) components. The next generation of electronics will require agility, precision, and an increase in the design degrees of freedom, which is not easily met by traditional manufacturing approaches. Additive manufacture shows significant advantages over these traditional approaches in agility, precision, and design degrees of freedom for electronic applications. Despite these advantages, a continuing challenge with printed conductors – including silver nano-particle inks – is a behavior of resistance increase with cyclical strain. As most applications will experience some degree of strain over their lifetime, this results in drift in the resistance of the printed features that the electronic functionality depends upon.

The work in this thesis hypothesizes the resistance increase behavior is due to fatigue crack growth at nanopaticle necks. In this work, a resistance prediction method was developed, cases of applied strain analyzed, fusing current tests conducted, and small strain cycling performed. The resistance prediction method was developed using a resistance model for a representative microstructure; this model combined statistical parameters taken from an SEM microsection of the trace, and fatigue crack growth theory to predict resistance at each cycle of strain, and which was verified using Ansys Maxwell. Conformal, flexible, and printed interconnection applications were analyzed using Ansys Mechanical to determine strains; the strains were then used to predict resistance as a function of cycles using the aforementioned resistance prediction method. Fusing current testing was performed on several traces to better understand sintering criticality using a 4 wire test. Lastly, a 4 wire cyclical strain test was performed on 2 printed traces using a DMA to cycle at strains less than .1%.
The resistance prediction method predicted the general behavior of resistance increase as a function of cyclical strain seen in the literature. This method does not predict under-sintered traces well due to the absence of contact resistance in the method. The flexible and interconnect applications analyzed show significant strain and resistance increase over cycling, while thermally loaded conformed applications show small strains and small resistance increases. The fusing current showed the lowest initial resistance traces was reached with well-sintered traces, and forcing too much current can lead to over-sintering and brittle traces. Lastly, the small strain cycling testing shows this resistance increase behavior is seen even at strains less than 0.1%. Further work is needed to investigate direct correlations between tested and predicted results for cyclically strained samples, as well as temperature effects to determine its impact on resistance increases during cyclical strain.

All interested students and faculty members are invited to attend the defense via remote access or in-person.