Stretchable electronic systems: Realization and applications

Abstract

Commonplace electronic appliances for consumer or industrial use are still mostly rigid or at maximum flexible entities. The flexibility of foldable units like laptops or cell phones is usually realized through flexible circuit board (FCB) interconnectors. Although flexibility allows for considerably enhanced degrees of freedom in design, it is not compatible with more complex three dimensional curvatures and dynamics thereof. In the past years a number or approaches to realize stretchable electronic circuits in order to reach beyond unidirectional bending or folding of electronics have been reported. In the frame of the European Project STELLA a particular fabrication technology for stretchable electronic systems has been developed at Technische Universitaet Berlin. This technology, termed "stretchable circuit board" (SCB) technology, is derived from conventional printed circuit board manufacturing. Stretchability of the boards is enabled by (i) using polyurethane inst ead of FR4 or polyimide as a carrier material of the copper structures and (ii) a meandering design of the Cu interconnects between commercial (rigid) electronic components. Such boards can be (once) extended by up to 300 % before fracture of the Cu interconnections. For repeated elongation/relaxation cycles elongations with a few percent are allowable in order reach high cycle numbers. Electronic components are assembled after local application of a solder mask and surface finish for solderability. The electronic interconnection is established using a low temperature solder alloy (SnBi, Tm=142 °C). For protection and enhanced system robustness all components are subsequently encapsulated within a polyurethane capping. Systems thus realized can be readily attached to different kinds of surfaces. Most interesting for various application cases is the easy attachment to textile substrates by a simple lamination process. The field use case studies of stretchable systems in the frame of the STELLA are m

Impact of geometry on stretchable meandered interconnect uniaxial tensile extension fatigue reliability

“…Only structured metals (meanders [11][12][13][14], meshes [15], yarns or buckled films [16]), forming a stretchable interconnect exhibit electro-mechanical properties that can fulfill the above mentioned requirements. In particular, in-plane meandered interconnect ( Fig.…”

Crack-Configuration Analysis of Metal Conductive Track Embedded in Stretchable Elastomer

“…Of late, many research groups have been developing flexible or stretchable electronic devices [ 1 , 2 , 3 ], such as stretchable displays [ 4 , 5 ], devices fixed to the human skin [ 6 , 7 , 8 , 9 , 10 , 11 ], and neural interfaces devices that are embedded in animals [ 12 ]. As metal conductive tracks are one of the critical components for achieving device flexibility or stretchability, various types of metal tracks, such as straight-shaped metal tracks with microcracks [ 13 , 14 , 15 , 16 ], straight-shaped metal tracks on a wavy surface [ 17 , 18 ], and wave-shaped metal tracks [ 19 , 20 , 21 , 22 ], have been researched. Straight-shaped tracks with microcracks are stretchable and conductive with randomly distributed tribranched microcracks on the tracks; the track thickness is several tens or hundreds of nanometers, and the metal track layer is directly deposited on a stretchable elastomer substrate by thermal or electron-beam deposition [ 12 ].…”

“…Wave-shaped metal tracks can be stretched by the deformation of the wave-shape. The thickness of the metal layer is serval micrometers, and it is fabricated by plating or laminating a metal foil and a stretchable elastomer sheet [ 19 , 22 ].…”

Lifetime aspects of wearable electronics

“…Quite understandably, initially research and development organizations have spent most effort to the study and development of the application areas and the technologies. As for stretchable substrates with conducting tracks and components, the first investigations are from Princeton University, Lawrence Livermore National Laboratories, and John Hopkins University (see references in [1]). Here, we refer to the European project STELLA * where three technologies were investigated and demonstrator products were made [1,2,3].…”