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Mechanical Testing for Stretchable Electronics

[+] Author and Article Information
Steven A. Klein

Intel Corporation,
5000 W Chandler Boulevard,
Chandler, AZ 85226
e-mail: steven.a.klein@intel.com

Aleksandar Aleksov

Intel Corporation,
5000 W Chandler Boulevard,
Chandler, AZ 85226
e-mail: aleksandar.aleksov@intel.com

Vijay Subramanian

Intel Corporation,
5000 W Chandler Boulevard,
Chandler, AZ 85226
e-mail: vijay.subramanian@intel.com

Pramod Malatkar

Intel Corporation,
5000 W Chandler Boulevard,
Chandler, AZ 85226
e-mail: pramod.malatkar@intel.com

Ravi Mahajan

Intel Corporation,
5000 W Chandler Boulevard,
Chandler, AZ 85226
e-mail: ravi.v.mahajan@intel.com

1Corresponding author.

Contributed by the Electronic and Photonic Packaging Division of ASME for publication in the JOURNAL OF ELECTRONIC PACKAGING. Manuscript received December 26, 2016; final manuscript received April 3, 2017; published online April 28, 2017. Assoc. Editor: S. Ravi Annapragada.

J. Electron. Packag 139(2), 020905 (Apr 28, 2017) (7 pages) Paper No: EP-16-1147; doi: 10.1115/1.4036389 History: Received December 26, 2016; Revised April 03, 2017

Stretchable electronics have been a subject of increased research over the past decade (Lacour, S., et al., 2006, “Mechanisms of Reversible Stretchability of Thin Metal Films on Elastomeric Substrates,” Appl. Phys. Lett., 88(20), p. 204103; Lacour, S., et al., 2004, “Design and Performance of Thin Metal Film Interconnects for Skin-Like Electronic Circuits,” IEEE Electron Device Lett., 25(4), pp. 179–181; and Maghribi, M., et al., 2005, “Stretchable Micro-Electrode Array,” International IEEE-EMBS Conference on Microtechnologies in Medicine and Biology, pp. 80–83.). Although stretchable electronic devices are a relatively new area for the semiconductor/electronics industries, recent market research indicates that the market could be worth more than $900 million by 2023 (PR Newswire, 2015, “Stretchable Electronics Market Worth $911.37 Million by 2023,” PR Newswire, Albuquerque, NM.). This paper investigates mechanical testing methods designed to test the stretching capabilities of potential products across the electronics industry to help quantify and understand the mechanical integrity, response, and the reliability of these devices. Typically, the devices consist of stiff modules connected by stretchable traces (Loher, T., et al., 2006, “Stretchable Electronic Systems,” Electronics Packaging Technology Conference (EPTC '06), pp. 271–276.). They require electrical and mechanical connectivity between the modules to function. In some cases, these devices will be subject to biaxial and/or cyclic mechanical strain, especially for wearable applications. The ability to replicate these mechanical strains and understand their effect on the function of the devices is critical to meet performance, process, and reliability requirements. In this paper, methods for simulating biaxial and out-of-plane strains similar to what may occur in a wearable device on the human body are proposed. Electrical and/or optical monitoring (among other methods) can be used to determine cycles to failure depending on expected failure modes. Failure modes can include trace damage in stretchable regions, trace damage in functional component regions, or bulk stretchable material damage, among others. Three different methods of applying mechanical strain are described, including a stretchable air bladder method, membrane test method, and lateral expansion method.

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References

Lacour, S. P. , Chan, D. , Wagner, S. , Li, T. , and Suo, Z. , 2006, “ Mechanisms of Reversible Stretchability of Thin Metal Films on Elastomeric Substrates,” Appl. Phys. Lett., 88(20), p. 204103. [CrossRef]
Lacour, S. P. , Jones, J. , Suo, Z. , and Wagner, S. , 2004, “ Design and Performance of Thin Metal Film Interconnects for Skin-Like Electronic Circuits,” IEEE Electron Device Lett., 25(4), pp. 179–181. [CrossRef]
Maghribi, M. , Hamilton, J. , Polla, D. , Rose, K. , Wilson, T. , and Krulevitch, P. , 2002, “ Stretchable Micro-Electrode Array [for retinal prosthesis],” 2nd Annual International IEEE-EMB Special Topic Conference on Microtechnologies in Medicine and Biology, Madison, WI, May 2–4, pp. 80–83.
MARKETSANDMARKETS, 2015, “ Stretchable Electronics Market by Component (Battery, Conductor, Circuit, Electroactive Polymer and Others), Application (Health Care, Consumer Electronics, Automotive Electronics, Textile, Aerospace & Defense And Others), Geography - Trends & Forecast to 2015-2023,” PR Newswire, Seattle, WA, Report No. SE 3498.
Perry, T. S., 2016, “ Stretchable Electronics Have Their Coming Out Party at CES,” IEEE Spectrum, New York, accessed Apr. 13, 2017, http://spectrum.ieee.org/view-from-the-valley/biomedical/devices/stretchable-electronics-have-their-coming-out-party-at-ces
Loher, T. , Manessis, D. , Heinrich, R. , Schmied, B. , Vanfleteren, J. , Debaets, J. , Ostmann, A. , and Reichl, H. , 2006, “ Stretchable Electronic Systems,” 8th Electronics Packaging Technology Conference (EPTC '06), Singapore, Dec. 6–8, pp. 271–276.
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Figures

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Fig. 1

Depiction of band-type stretchable electronic device during typical operation showing (a) radial strain normal to device and (b) hoop strain in the direction of band

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Fig. 2

Depiction of patch-type stretchable electronic device during typical operation showing (a) radial strain normal to device and (b) hoop strain in biaxial tension

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Fig. 3

Experimental setup for method #1 (bladder tester). Directional control valve solenoid allows for bleeding, holding, or increasing pressure to the bladder system.

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Fig. 4

(a) Patches would typically be attached on four edges, (b) bands are typically attached on two edges, and (c) and (d) show the radial normal stresses in both cases. The attach type should relate to the product mode of operation which would impact the results of the testing. Other methods than adhesive can be used to attach the sample or clamp it in place.

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Fig. 5

Method #2—membrane test for stretchable electronics experimental setup. Directional control valve solenoid allows for bleeding, holding, or increasing pressure to the DUT membrane.

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Fig. 6

Depiction of membrane expansion method: (a) and (b) the method can be unidirectional or bidirectional and (c) detailed view showing how the DUT is clamped (similar to bulge tester)

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Fig. 7

Method #3—lateral expansion method. As the rubber is compressed, it expands laterally and stretches the DUT. As the DUT stretches, it will see strain field as shown in Fig. 1.

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Fig. 8

Schematic of uniaxial tension system with in situ microscope inspection

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Fig. 9

Trace crack with varying strain in uniaxial tension tester. Initial strain level is set in (a), which is then reduced to half the strain in (b), and finally 0% strain in (c).

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Fig. 10

Electrical open detection system. The failure shown will cause an electrical open detectable by measuring resistance across the trace with an ohmmeter or similar device.

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Fig. 11

Process for evaluating stretchable devices

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Fig. 12

Failures observed after cyclic testing with uniaxial tension tester

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Fig. 13

Failures observed after cyclic testing with bladder tester both with and without adhesive along the long dimension of the device

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Fig. 14

Failures observed after cyclic testing with bladder tester at 3× the strain value in the previous test

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