Bond Strength and Failure Mechanisms of Nonconductive Adhesives for Stretchable Electronics

Salo, Teemu; Halme, Aki; Kanerva, Mikko; Vanhala, Jukka

doi:10.1109/tcpmt.2020.2980121

Cited by 3 publications

(3 citation statements)

References 24 publications

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“…The majority of adhesives form a polymeric composition after curing [18]. Different kinds of adhesives have been studied for use in stretchable electronics joints, and the durable bonding of rigid and highly pliant substrates has been found challenging [19]. The removal of the requirement for adhesive is a major benefit of the direct 3D-printing method, which considerably simplifies the fabrication process and improves the stretchability of the system.…”

Section: Peel Testsmentioning

confidence: 99%

Enhanced stretchable electronics made by fused-filament fabrication

Salo

Halme

Lahtinen

et al. 2020

Flex. Print. Electron.

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3D printing is widely used for manufacturing complex non-functional parts, and recently, the fabrication of electronics has also attracted research attention. The commercialized process of fused-filament fabrication (FFF), which is still evolving,has been used in the preparation of basic electronic conductors and sensors but only a few studies of more complex structures with integrated circuits and passive components have been reported. Notably, the usage of FFF in wearable stretchable electronics has not been studied previously. We demonstrate that the combination of FFF printing and commonly used stretchable electronics materials and methods enables new wearable stretchable electronics. In this study, thermoplastics were extruded directly onto a stretchable substrate and their adhesion was measured using T-peel tests. The test results were further used in the fabrication of supports for meander-shaped screen-printed interconnects. The elongation of the interconnects with the supports were studied by tensile tests with simultaneous measurements of the electrical conductivity. The results were good, and the adhesion exceeded the constitution of the substrate when the filament and the substrate were of the same material type. The average bond strength was ∼2 N mm−1. Support structures placed close to the meander-shaped interconnects changed the interconnects’ deformation under elongation. The average maximum elongation of the interconnects was improved by ∼27% when the supports directed stresses away from the interconnects’ weak areas. Conversely, the results were ∼21% lower when the supports directed stresses towards the weak areas. This study demonstrates that it is possible to use direct 3D printing onto highly stretchable substrates. Currently, commercial FFF materials and methods can be used to manufacture supports, frames and other non-functional parts on wearable electronics substrates in a single process step. We believe that in the future, FFF will become a valuable tool in the manufacture of inexpensive and reliable wearable electronics.

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Section: Peel Testsmentioning

confidence: 99%

Enhanced stretchable electronics made by fused-filament fabrication

Salo

Halme

Lahtinen

et al. 2020

Flex. Print. Electron.

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“…The adhesive strength of the stretchable substrate of a serpentine metal conductor to form a sticker-type stretchable conductor surface for electrical and mechanical connections is carefully controlled. It is expected that the sticker-type stretchable conductor surface should overcome current problems including connections of rigid electronics and multimodules. − It is highly expected that no other contact forming methods, including the use of soldering, conductive adhesives, metal wiring, or a mechanical clamper, should not be needed. ,− …”

Section: Introductionmentioning

confidence: 99%

Dual-Functional Self-Attachable and Stretchable Interface for Universal Three-Dimensional Modular Electronics

Hwang

Yang

et al. 2022

ACS Appl. Mater. Interfaces

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Stretchable electronics have become essential for custom-built electronics, self-assembling robotics, and wearable devices. Although many stretchable electronics contain integrated systems, they still limit bulky connection systems. We introduce a new dual-functioned self-attachable and stretchable interface (SASI), allowing a direct and instant interconnection between rigid and soft electronics. The SASI consists of a sticky and stretchable substrate and surface-embedded serpentine conductors with the single-sided polyimide fabricated using the embedded transfer process. The adhesion property of the SASI is controlled by the mixed elastomer ratio. The resulting sticky and conductive SASI can instantly adhere to a metal surface and create conductive paths. The SASI serpentine conductors exhibit high stretchability (∼290%) and provide self-attachable, re-attachable, and low-resistant electrical contacts (0.85 ohms in 0.25 mm2) between interfaces without pressure, heat, or extra solder. In addition, three-dimensional curved and modular electronics can be formed with the SASI by compiling functional blocks. SASI provides a novel strategy for assembling functional chips or modules for stretchable electronics, opening a path to onboard integrated electronics that are customizable by users for real-world stretchable electronics.

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“…In addition, in some cases, stretchable circuit lines should be connected to other stretchable circuit lines. The direct integration on a stretchable substrate and the stretchable-stretchable interfacing require large mechanical toughness and the stable adhesion force of the adhesion layer to prevent mechanical failure under a large strain ( 29 , 44 , 45 ). Toughness of the commercial adhesives that are used in the conventional ACFs are not large enough to endure the large strains (ε ≥ 50%): acryl (1 to 4 MPa/m 2 ), epoxy (0.5 to 2 MPa/m 2 ), and silicone rubbers (0.02 to 0.5 MPa/m 2 ) ( 46 ).…”

Section: Introductionmentioning

confidence: 99%

Stretchable anisotropic conductive film (S-ACF) for electrical interfacing in high-resolution stretchable circuits

et al. 2021

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In stretchable electronics, high-resolution stretchable interfacing at a mild temperature is considered as a great challenge and has not been achieved yet. This study presents a stretchable anisotropic conductive film (S-ACF) that can electrically connect high-resolution stretchable circuit lines to other electrodes whether they are rigid, flexible, or stretchable. The key concepts of this study are (i) high-resolution (~50 μm) but low–contact resistance (0.2 ohm in 0.25 mm2) interfacing by periodically embedding conductive microparticles in thermoplastic film, (ii) low-temperature interfacing through the formation of chemical bonds between the S-ACF and the substrates, (iii) economical interfacing by selectively patterning the S-ACF, and (iv) direct interfacing of chips by using the adhesion of the thermoplastic matrix. We integrate light-emitting diodes on the patterned S-ACF and demonstrate stable light operation at large biaxial areal stretching (εxy = 70%).

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Bond Strength and Failure Mechanisms of Nonconductive Adhesives for Stretchable Electronics

Cited by 3 publications

References 24 publications

Enhanced stretchable electronics made by fused-filament fabrication

Enhanced stretchable electronics made by fused-filament fabrication

Dual-Functional Self-Attachable and Stretchable Interface for Universal Three-Dimensional Modular Electronics

Stretchable anisotropic conductive film (S-ACF) for electrical interfacing in high-resolution stretchable circuits

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