Georgia Institute of Technology

Conductive Anodic Filament (CAF) Formation: A Potential Reliability Problem for Fine-Line Circuits

Mar 16, 2023 | Laura J. Turbini, W. Jud Ready & Brian A. Smith

Outline * Introduction & Background * Factors Affecting CAF Formation * CAF Formation ** Catastrophic Field Failure of Military Hardware ** Laboratory Experiments * Conclusion...

Conductive Anodic Filament Failure: A Materials Perspective

Mar 16, 2023 | Laura J. Turbini and W. Jud Ready

Conductive anodic filament (CAF) formation was first reported in 1976.1 This electrochemical failure mode of electronic substrates involves the growth of a copper containing filament subsurface along the epoxy-glass interface, from anode to cathode. Despite the projected lifetime reduction due to CAF, field failures were not identified in the 1980s. Recently, however, field failures of critical equipment have been reported.2 A thorough understanding of the nature of CAF is needed in order to prevent this catastrophic failure from affecting electronic assemblies in the future. Such an understanding requires a comprehensive evaluation of the factors that enhance CAF formation. These factors can be grouped into two types: (1) internal variables and (2) external influences. Internal variables include the composition of the circuit board material, and the conductor metallization and configuration (i.e. via to via, via to surface conductor or surface conductors to surface conductors). External influences can be due to (1) production and (2) storage and use. During production, the flux or hot air solder leveling (HASL) fluid choice, number and severity of temperature cycles, and the method of cleaning may influence CAF resistance. During storage and use, the principal concern is moisture uptake resulting from the ambient humidity. This paper will report on the relationship between these various factors and the formation of CAF. Specifically, we will explore the influences of printed wiring board (PWB) substrate choice as well as the influence of the soldering flux and HASL fluid choices. Due to the ever-increasing circuit density of electronic assemblies, CAF field failures are expected to increase unless careful attention is focused on material and processing choices....

Printed Electronics: Manufacturing Technologies and Applications

Mar 13, 2023 | Chuck Zhang

Translational Research in Additive Manufacturing at GTMI * Additive manufacturing/3D printing process and equipment development (e.g., metal, polymer and composites part manufacturing) * Computational modeling and simulation of additive manufacturing/printed electronics processes * Advanced materials development for additive manufacturing/printed electronics * Application development and demonstration of additive manufacturing/printed electronics...

Modeling Resistance Increase In A Composite Ink Under Cyclic Loading

Mar 13, 2023 | Q Li, E Chung, A Antoniou and O Pierron

The electrical performance of stretchable electronic inks degrades as they undergo cyclic deformation during use, posing a major challenge to their reliability. The experimental characterization of ink fatigue behavior can be a time-consuming process, and models allowing accurate resistance evolution and life estimates are needed. Here, a model is proposed for determining the electrical resistance evolution during cyclic loading of a screen-printed composite conductive ink. The model relies on two input specimen-characteristic curves, assumes a constant rate of normalized resistance increase for a given strain amplitude, and incorporates the effects of both mean strain and strain amplitude. The model predicts the normalized resistance evolution of a cyclic test with reasonable accuracy. The mean strain effects are secondary compared to strain amplitude, except for large strain amplitudes (>10%) and mean strains (>30%). A trace width effect is found for the fatigue behavior of 1 mm vs 2 mm wide specimens. The input specimen-characteristic curves are trace-width dependent, and the model predicts a decrease in Nf by a factor of up to 2 for the narrower trace width, in agreement with the experimental results. Two different methods are investigated to generate the rate of normalized resistance increase curves: uninterrupted fatigue tests (requiring ∼6–7 cyclic tests), and a single interrupted cyclic test (requiring only one specimen tested at progressively higher strain amplitude values). The results suggest that the initial decrease in normalized resistance rate only occurs for specimens with no prior loading. The minimum-rate curve is therefore recommended for more accurate fatigue estimates....

Additively Manufactured mm-Wave Multichip Modules With Fully Printed "Smart" Encapsulation Structures

Feb 09, 2022 | Xuanke He, Bijan K. Tehrani, Ryan Bahr, Wenjing Su, and Manos M. Tentzeris

This article presents the first time that an millimeter-wave (mm-wave) multichip module (MCM) with on-demand "smart" encapsulation has been fabricated utilizing additive manufacturing technologies. RF and dc interconnects were fabricated using inkjet printing, while the encapsulation was realized using 3-D printing. Inkjet-printed interconnects feature superior RF performance, better mechanical reliability, and on-demand, low-cost fabrication process....

All-in-One, Wireless, Stretchable Hybrid Electronics for Smart, Connected, and Ambulatory Physiological Monitoring

Aug 19, 2020 | Yun-Soung Kim, Musa Mahmood, Yongkuk Lee, Nam Kyun Kim, Shinjae Kwon, Robert Herbert, Donghyun Kim, Hee Cheol Cho,* and Woon-Hong Yeo*

Commercially available health monitors rely on rigid electronic housing coupled with aggressive adhesives and conductive gels, causing discomfort and inducing skin damage. Also, research-level skin-wearable devices, while excelling in some aspects, fall short as concept-only presentations due to the fundamental challenges of active wireless communication and integration as a single device platform. Here, an all-in-one, wireless, stretchable hybrid electronics with key capabilities for real-time physiological monitoring, automatic detection of signal abnormality via deep-learning, and a long-range wireless connectivity (up to 15 m) is introduced. The strategic integration of thin-film electronic layers with hyperelastic elastomers allows the overall device to adhere and deform naturally with the human body while maintaining the functionalities of the on-board electronics. The stretchable electrodes with optimized structures for intimate skin contact are capable of generating clinical-grade electrocardiograms and accurate analysis of heart and respiratory rates while the motion sensor assesses physical activities. Implementation of convolutional neural networks for real-time physiological classifications demonstrates the feasibility of multifaceted analysis with a high clinical relevance. Finally, in vivo demonstrations with animals and human subjects in various scenarios reveal the versatility of the device as both a health monitor and a viable research tool....

Additive Manufacturing for Next Generation Microwave Electronics and Antennas

Aug 13, 2020 | Xuanke He, Bijan K. Tehrani, Ryan A. Bahr, Manos Tentzeris

The paper will discuss the integration of 3D printing and inkjet printing fabrication technologies for microwave and millimeter-wave applications. With the recent advancements in 3D and inkjet printing technology, achieving resolution down to 50 um, it is feasible to fabricate electronic components and antennas operating in the millimeter-wave regime. The nature of additive manufacturing allows designers to create custom components and devices for specialized applications and provides an excellent and inexpensive way of prototyping electronic designs. The combination of multiple printable materials enables the vertical integration of conductive, dielectric, and semi-conductive materials which are the fundamental components of passive and active circuit elements such as inductors, capacitors, diodes, and transistors. Also, the on-demand manner of printing can eliminate the use of subtractive fabrication processes, which are necessary for conventional microfabrication processes such as photolithography, and drastically reduce the cost and material waste of fabrication....

Soft, Wireless Periocular Wearable Electronics For Real-Time Detection Of Eye Vergence In A Virtual Reality Toward Mobile Eye Therapies

Jul 22, 2020 | Saswat Mishra et al

Recent advancements in electronic packaging and image processing techniques have opened the possibility for optics-based portable eye tracking approaches, but technical and safety hurdles limit safe implementation toward wearable applications. Here, we introduce a fully wearable, wireless soft electronic system that offers a portable, highly sensitive tracking of eye movements (vergence) via the combination of skin-conformal sensors and a virtual reality system. Advancement of material processing and printing technologies based on aerosol jet printing enables reliable manufacturing of skin-like sensors, while the flexible hybrid circuit based on elastomer and chip integration allows comfortable integration with a user's head. Analytical and computational study of a data classification algorithm provides a highly accurate tool for real-time detection and classification of ocular motions. In vivo demonstration with 14 human subjects captures the potential of the wearable electronics as a portable therapy system, whose minimized form factor facilitates seamless interplay with traditional wearable hardware....

Smart and Connected Bioelectronics for Seamless Health Monitoring and Persistent Human-Machine Interfaces

Jun 10, 2020 | Yun-Soung Kim and Woon-Hong Yeo

Recent advancement of flexible wearable electronics allows significant enhancement of portable, continuous health monitoring and persistent human-machine interfaces. Enabled by flexible electronic systems, smart and connected bioelectronics are accelerating the integration of innovative information science and engineering strategies, ultimately driving the rapid transformation of healthcare and medicine. Recent progress in the development and engineering of soft materials has provided various opportunities to design different types of mechanically deformable systems towards smart and connected bioelectronics....

High Frequency Electrical Performance and Thermo-Mechanical Reliability of Fine-Pitch, Copper - Metallized Through-Package-Vias (TPVs) in Ultra - thin Glass Interposers

Aug 10, 2017 | Sukhadha Viswanathan, Tomonori Ogawa, Kaya Demir, Timothy B. Huang, P. Markondeya Raj, Fuhan Liu, Venky Sundaram, Rao Tummala

This paper demonstrates the high frequency performance and thermo-mechanical reliability of through vias with 25 μm diameter at 50 μm pitch in 100 μm thin glass substrates. Scaling of through via interconnect diameter and pitch has several electrical performance advantages for high bandwidth 2.5D interposers as well as mm-wave components for 5G modules....