Stretchable electronics: near-term commercial success stories

Stretchable electronics is a diverse umbrella term including numerous technologies, each targeting a different market, each having different technology readiness level and each facing a different market prospect.

In the IDTechEx report ‘Stretchable and Conformal Electronics 2017–2027’, we offer a comprehensive assessment of the emerging industry. In this article we highlight one stretchable electronics technology with the potential to become a near-term success story: interconnects.

Stretchable interconnects

Connectors are a simple essential component in all electronic systems. Their simplicity means that they can be made stretchable. This is in contrast to complex multilayer interfacial devices like transistors whose stretchable versions are commercially years away despite numerous laboratory proof-of-concept results or prototypes. Indeed, they can even be the only stretchable component in stretchable systems made using the rigid island-stretchable interconnect approach.

A variety of approaches have been developed to produce stretchable interconnects. In one approach, PCBs are made stretchable. Here, ICs and other rigid electronic components are mounded on a standard PCB ‘island’. These islands are then interconnected using thinned meandering PCB lines, introducing stretchability. This technique is not yet easy to scale with good yields, but is serving high-value low-volume applications.

In another approach, cables are arranged in a specific way to impart stretchability. Here, stretching does not change the total length of the wire and thus causes no resistance change. Note that this approach often requires introducing a separate distinct cable onto the e-textile systems, and while robust it is not structurally embedded. Note that conductive cables are themselves not intrinsically stretchable. Many approaches are, however, being developed, most at the early-stage prototyping level, to create truly stretchable conductive fibres/yarns.

Conductive inks

Yet another approach is based on stretchable conductive inks. This approach enables the use of post-production processes steps such as transfer or screen printing to introduce the stretchable interconnect onto the textile. It therefore requires no alternation to standard textile production lines. It can also be used in stretchable circuits, particularly acting as stretchable interconnects on long stretchable substrates for use in, for example, medical electronics.

This approach is trendy all around the world: while only three years ago only two or three companies offered such inks, now most players have either launched a product or demonstrated capability. The application pipeline is also gathering momentum with many products in late-stage prototyping phases and some even in the early commercial phase sales.

Stretchable conductive inks are still a young technology. Indeed, performance progress is highly visible when tracking the last few generations of inks launched by any given company in quick succession. Stretchable inks today can tolerate higher elongation levels and suffer less resistance change. These improvements have been achieved thanks to changes in resins, binders and even at times filler size distribution.

There is still a long way to go though. Currently, the printed lines are encapsulated using a material such as TPU. This is not an elegant solution and the encapsulant is not ideal, suffering issues with comfort, breathability, etc. Direct on-textile printing remains a long-term challenge as numerous textile substrates exist, each with different properties and almost none offering a good printing surface.

Critically, the market requirements are yet fully known, and may even remain diverse and fragmented. For example, today suppliers receive enquiries for conductivity and stretchability levels at opposite ends of the performance spectrum. This is an opportunity for competent suppliers to offer customised solutions before slightly more standard product groups emerge. In fact, the ability to address varying cost-performance needs represents an opportunity for the entire category of ink-based stretchable interconnects compared to its rivals.

In-mould electronics

In addition to wearable and medical application, in-mould electronics (IME) applications are also emerging as a market for stretchable conductive inks. IME has previously got off to a false start, but we believe that its time has come.

In IME, functional and graphical inks are printed on a flat sheet then formed into a 3D shape. Consequently, the inks will have to withstand a one-off elongation event (30–50% original length). While similar to the previously discussed stretchable inks, IME inks have different requirements: (a) they experience a one-off elongation, (b) they need to adhere well to the substrates used (eg, polycarbonate) and (c) they must be compatible with the stack of other materials used in IME, eg, layers graphical, insulating, transparent conducting and other inks.

Here, too, the industry has responded. Today, most suppliers have launched products or demonstrated capability. Today, many are engaged with major end users in either the automotive or appliance industries. The trend is reflected in the increasing number of prototypes launched on the market. In our 10-year market forecasts in Stretchable and Conformal Electronics 2017–2027, we expect success stories in the next two years.

Image credit: ©stock.adobe.com/au/Alexander Vasilyev

Originally published here.