Geers, M.G.D.

Hoefnagels, J.P.M.

Neggers, J.

English

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 Interface roughness improves stretchable electronics reliabilityCitation for published version (APA):Neggers, J., Hoefnagels, J. P. M., & Geers, M. G. D. (2012). Interface roughness improves stretchableelectronics reliability. Poster session presented at Mate Poster Award 2012 : 17th Annual Poster Contest.Document status and date:Published: 01/01/2012Document Version:Accepted manuscript including changes made at the peer-review stagePlease check the document version of this publication:• A submitted manuscript is the version of the article upon submission and before peer-review. There can beimportant differences between the submitted version and the official published version of record. Peopleinterested in the research are advised to contact the author for the final version of the publication, or visit theDOI to the publisher's website.• The final author version and the galley proof are versions of the publication after peer review.• The final published version features the final layout of the paper including the volume, issue and pagenumbers.Link to publicationGeneral rightsCopyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright ownersand it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.            • Users may download and print one copy of any publication from the public portal for the purpose of private study or research.            • You may not further distribute the material or use it for any profit-making activity or commercial gain            • You may freely distribute the URL identifying the publication in the public portal.If the publication is distributed under the terms of Article 25fa of the Dutch Copyright Act, indicated by the “Taverne” license above, pleasefollow below link for the End User Agreement:www.tue.nl/taverneTake down policyIf you believe that this document breaches copyright please contact us at:openaccess@tue.nlproviding details and we will investigate your claim.Download date: 08. Feb. 2024Interface roughness improvesstretchable electronics reliabilityJan Neggers, Johan Hoefnagels and Marc Geers/ department of Mechanical Engineering / Mechanics of MaterialsIntroductionStretchable electronic devices enable a range of futuristic bio-compatible applications (Fig. 1-2). The designs of these devicesusually consist of off-the-shelf electronic components, intercon-nected with metal lines made stretchable by design, (Fig. 3a)embedded in a stretchable (rubber) matrix material.Figure 1: Hart ablation catheter Figure 2: Smart skinMany design solutions can be found in literature, one of whichis the horseshoe shape interconnect. However, interface delami-nation is a common precursor to failure in all designs (Fig. 3c).Figure 3: (a) Horseshoe shaped interconnect sample, (b) uni-axiallystretched under a microscope, (c) showing fibrillation at the interfacefailure position, when imaging in-situ in an ESEM.GoalUnderstanding the delamination micro-mechanics responsible forthe interface toughness. This knowledge can be applied to allinterconnect designs to increase their stretchability.ExperimentsFour types of peel-test experiments are performed to investigatethe characteristics of interfaces, i.e., two types of roughness intwo opening modes. Moreover, the delamination front is visual-ized with in-situ ESEM imaging.F FαCuPDMS(a) (b) (c)Figure 4: (a) Schematic of a 90◦peel-test (b) 90◦peel-test samplemounted in a tensile-stage, (c) which is mounted in the ESEM,Figure 5 shows that the roughness morphology dictates the shapeof the fibrils. Moreover, the interface of the rougher sample ismore tough, this is due to the extra energy dissipation in thelonger fibrils.RoughExtraRoughFigure 5: in-situ visualisation of the delamination micro-mechanics,i.e. the forming, stretching and ultimately rupture of fibrils.Figure 6 shows that the area fraction of rubber left behind on thenew metal surface is greater for the rougher sample indicatingan increase in rubber fracture, again showing that the roughersample is more tough.RoughExtraRoughFigure 6: The new metal surfaces for both roughness types, for a90◦peel test, i.e. crack opening mode.Figure 7 shows an increase in rubber fracture for the less roughsample, showing some sensitivity to the crack opening mode.Yet, the rougher sample shows no mode dependency.RoughExtraRoughFigure 7: The new metal surfaces for both roughnesses, for a 0◦peeltest, i.e. crack shearing mode.Conclusions• In-situ ESEM imaging revealed a complex mechanism,which is the dominating dissipation mechanism• The roughness initiates and controls the fibrillation process• The fibrils and large surface roughness cause these inter-faces to be insensitive to the crack opening mode, due tothe “local” mode-mixity in the roughness morphology andthe orientational freedom of the fibrils• Future designs of stretchable electronic devices should aimto initiate the fibril process, with an artificial “tailored”roughness

Interface roughness improves stretchable electronics reliability

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Interface roughness improves stretchable electronics reliability

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