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Low-Cost Manufacturing of Flexible Functionalities

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By Ed Korczynski, Sr. Technical Editor

SEMICON West includes many business and technology workshops and forums for attendees.  On Wednesday morning July 15, attendees packed the TechXPOT in the South Hall of Moscone Center to hear updates on the status of flexible hybrid electronics manufacturing.

M-H. Huang of Corning showed the surprising properties of “Corning Willow Glass: Substrates for flexible electronic devices.” Willow Glass is created in a fusion-forming process similar to that used to create Gorilla Glass, though with thickness <=200 microns to allow for flexibility. “A key advantage is hermeticity compared to plastic substrates,” reminded Huang. Thin bare glass without any edge or surface coatings can be repeatably bent and twisted without cracking. The minimum bending radius for roll-to-roll (R2R) processing is limited by coating layer delamination:  12.5mm for bare glass, 25mm for AZO-coated glass, and 50mm radius for CZTS cells on glass all passing 500 bending cycles at 60 cycles per minute. Working with the State University of New York at Binghamton Center for Advanced Microelectronic Manufacturing (CAMM), Corning has demonstrated R2R sputtering of Al, Cr/Cu, ITO, SiO2, and IGZO films. Collaborating with ITRI in Taiwan using tools designed specifically for processing flexible glass, Corning demonstrated R2R gravure-offset printing of metal mesh structures silver ink that can be used for 7” touch-panels. Working with both CAMM and ITRI has led to R&D fabrication of a touch sensor with 90% device yield.

Thomas Lantzer, of DuPont Electronic Materials, discussed the “Materials Supplier Perspective on Flexible Hybrid Electronics.” Since the overarching goal of flexible electronics is not just mass and volume reduction but a huge reduction in manufacturing cost, it is axiomatic that fabrication must evolving toward the use of traditional printing methods and flexible substrates.

“There are many printing techniques,” explained Lantzer, “So there are building blocks out there today that we feel will lead to an explosion of fabrication capabilities in the future.” DuPont has been actively involve in flexible materials and electronics for decades, supplying screen printed conductive pastes, resistor pastes for automotive defoggers, flexible films, and flexible materials for copper circuitry.

Mark Poliks, Professor at the State University of New York at Binghamton and Director of the Center for Advanced Microelectronic Manufacturing (CAMM), provided a comprehensive overview of “Materials, Processes & Tools for Fabrication of Flexible Hybrid Electronics.” Working with partners in the Nano-Bio Manufacturing Consortium since 2013, CAMM researchers are developing a wearable disposable sensor system with a target price of $2 to measure human performance parameters. The device including sensors, processor, battery, and wireless communications blocks will be built with copper (Cu) connections on flexible substrates such as polyimide. Initial functionalities will include biometric parameters such as electro-cardio-gram (ECG) signals and skin temperature. First prototypes of ECG sensors on 12.5 micron thin polyimide have been completed, which demonstrate output wave forms with equal or better signal extraction compared to industry standard silver/silver-chloride (Ag/AgCl) electrodes. This new printed sensor and breadboard electronics can be flexed over 200 times and retain the same signal quality and heart-beat extraction. The flexible substrate can accommodate assembly processes for flip-chip (FC) ASIC dice having micro-bumps on a 70 micron pitch, using die-placement accuracy of 9 microns (3 sigma). For flexible hybrid applications, dual-sided placement of components along with printed circuitry reduces the real estate of the final packaged device.



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