NDLI: Foldable substrates for wearable electronics

Content Provider	IEEE Xplore Digital Library
Author	Pun, K. Islam, M.N. Tin Wing Ng
Copyright Year	2014
Description	Author affiliation: Compass Technol. Co., Ltd., Hong Kong, China (Pun, K.; Islam, M.N.; Tin Wing Ng)
Abstract	The personal electronics market is experiencing rapid growth where smaller electronics carrying more functionality is required. Increasingly, small electronic devices are expected to be incorporated into personal accessories and clothing to make them wearable. This raises great challenges to the substrate technology and related assembly technologies in electronic packaging for high density, small feature size, and high performance. The requirement on foldable substrate, especially, is intensive for smaller device foot print and system on flex (SOF), where the chip size is reduced and its pin count is increased. Thus, the formation of highly reliable foldable flex has become an important factor in increasing the functionality of future devices. In this paper, a 2 metal layer flexible substrate was assembled with different active and passive components to form a multichip module (MCM). This is achieved by building 30 μm fine pitch circuitry upon a thin, flexible substrate. The flex have sufficient area to carry all the components and able to fold in an S-shape, which gives its characteristics to reduce the overall device footprint, thus enhancing the portability and functionality, making it suitable for wearable applications. Several base film substrates have been assessed by means of restoring force test which revealed that lower base film thickness is beneficial for folding with minimum spring back. Also, LCP material is identified to be a good candidate for foldable substrates especially for good electrical reliability requirement. To minimize package size, assembly was carried out on both sides of the flex including Cu pillar reflow, die attach, wire bond and SMTs. Cu pillar flip chip of low die thickness (approximately 500um) is made achievable reliably by applying OSP coating on the bond pads before multiple reflow soldering. The assembled flex is then folded several times into a septum to form a completed module with the body size of 6mm × 4mm × 2.6mm. Such compact modules are demonstrated to function reliably in temperature cycling, high temperature storage and temperature and humidity storage tests. Accelerated high temperature storage test indicate that Cu from the substrate are gradually consumed to form IMCs with the Sn in the solder joint at increasing storage time. It is estimated that the module could survive at least 5 reflow cycles without demonstrating detrimental degradation. As a result, the foldable flex with its unique assembly process is an attractive solution to a wide range applications that satisfy demands for small, multi-functional applications at potentially low cost such as that for wearable electronics.
Starting Page	74
Ending Page	79
File Size	780980
Page Count	6
File Format	PDF
ISBN	9781479947072
DOI	10.1109/ICEPT.2014.6922600
Language	English
Publisher	Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Publisher Date	2014-08-12
Publisher Place	China
Access Restriction	Subscribed
Rights Holder	Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Subject Keyword	Soldering Substrates Flexible printed circuits Films Reliability Bonding C2 Flip Chip Wearable electronics Flex Flexible substrates System on Flex (SOF) MCM Cu Pillar
Content Type	Text
Resource Type	Article

Sl.	Authority	Responsibilities	Communication Details
1	Ministry of Education (GoI), Department of Higher Education	Sanctioning Authority	https://www.education.gov.in/ict-initiatives
2	Indian Institute of Technology Kharagpur	Host Institute of the Project: The host institute of the project is responsible for providing infrastructure support and hosting the project	https://www.iitkgp.ac.in
3	National Digital Library of India Office, Indian Institute of Technology Kharagpur	The administrative and infrastructural headquarters of the project	Dr. B. Sutradhar bsutra@ndl.gov.in
4	Project PI / Joint PI	Principal Investigator and Joint Principal Investigators of the project	Dr. B. Sutradhar bsutra@ndl.gov.in Prof. Saswat Chakrabarti will be added soon
5	Website/Portal (Helpdesk)	Queries regarding NDLI and its services	support@ndl.gov.in
6	Contents and Copyright Issues	Queries related to content curation and copyright issues	content@ndl.gov.in
7	National Digital Library of India Club (NDLI Club)	Queries related to NDLI Club formation, support, user awareness program, seminar/symposium, collaboration, social media, promotion, and outreach	clubsupport@ndl.gov.in
8	Digital Preservation Centre (DPC)	Assistance with digitizing and archiving copyright-free printed books	dpc@ndl.gov.in
9	IDR Setup or Support	Queries related to establishment and support of Institutional Digital Repository (IDR) and IDR workshops	idr@ndl.gov.in

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