a flexible film with a matrix of illuminated color LEDs being stretched

Truly Flexible Circuits Are A Bit Of A Stretch

Flexible PCBs have become increasingly common in both commercial devices and DIY projects, but Panasonic’s new stretchable, clear substrate for electrical circuits called Beyolex takes things a step further. The material is superior to existing stretchable films like silicone, TPU, or PDMS due to its high heat tolerance (over 160° C) for the purposes of sintering printable circuit traces.

But, a flexible substrate isn’t very useful for electronics without some conductive traces. Copper and silver inks make for good electrical circuits on stretchable films, and are even solderable, but increase resistance each time they are stretched. Recently, a team out of the University of Coimbra in Portugal has developed a liquid metal ink that can stretch without the resistance issues of existing inks, making it a promising pair with Panasonic’s substrate. There’s also certain environmental benefits of printing circuits in this manner over traditional etching and even milling, as you’re only putting conductive materials where needed.

a flexible film with a strip of LEDs connected by a novel liquid metal ink circuit

After the break, check out Panasonic’s earlier videos showing some of their demo circuits that include a stretchable NFC antenna harvesting electricity even while submerged in water and an LED matrix performing while being, bent, rolled, and stretched. We’re excited to see where this technology leads and when we hackers will be able to create our own stretchable projects.

A great many flexible PCB projects have graced Hackaday, from early experiments to sophisticated flexible PCB projects. Heck, we had a whole Flexible PCB Contest with some awesome flexible projects.

Continue reading “Truly Flexible Circuits Are A Bit Of A Stretch”

Silicone Devices: DIY Stretchable Circuits

Flexible circuits built on polyimide film are now commonplace, you can prototype with them at multiple factories, at a cost that is almost acceptable to your average hacker. Polyimide film is pretty tough for something so thin, but eventually it will tear, and with larger components, bend radii are quite restricted. But what about stretchable circuits, as in circuits you can flex, twist and stretch? Let us introduce silicone devices. A research group from Hasselt University, Belgium, have been prototyping making truly flexible, silicone-based circuit substrates, managing to integrate a wide range of SMT component types with a dual layer interconnect, with vias and external contacts.

It should be possible to reproduce the process using nothing more special than your average Makerspace CO2 laser cutter, and a couple of special tools that can be easily made — a guide for that is promised — it is purely a matter of gathering a few special materials, and using off-cuts you have lying around for the rest. The interconnect uses Galinstan, which is a low melting point alloy of gallium, indium, and tin. Unfortunately, this material is fairly expensive and cannot be shipped by air due to the gallium content, without specialised handling, at considerable expense. But that aside, other than some acrylic sheets, some vinyl, copper foil and a few sprays, nothing is beyond reach.

The construction process is reverse to what we normally see, with the components and copper contact plates placed first, on to a primed vinyl sheet. This sheet is laser marked with the component outlines to enable them to be corrected placed. Yes, that’s right, they’re using a laser cutter to mark vinyl, a chlorine-containing plastic. Hold on to that thought for a bit.

Insulating layers and substrate layers are constructed by blade-coating with a layer of clear silicone. Interconnect layers are formed by sticking a fresh vinyl sheet onto the exposed contacts and laser cutting just though it to expose the pads and the interconnect traces. Next the fancy Galinstan is applied by brush and the vinyl stencil removed. Rinse and repeat for the next layer of insulating silicone, more circuit traces, then use the laser cutter to precisely etch through the via regions to allow more metalisation to be added. Finally a coating of silicone is applied over the whole assembly, the laser is again used to etch the silicone away from the contact pads, and with a little solder tinning of these, you’re done. Simple, if only our Makerspaces didn’t have rules against laser cutting vinyl.

This was clearly a very brief overview, here is a very detailed instructables guide ready for you, as well as a formal research paper, detailing why this came about and why you might want to try this yourself.

If you’re into custom wearables, you might remember this earlier piece about silicone circuits, and this one weird organic-looking thing from the same time-frame.

Continue reading “Silicone Devices: DIY Stretchable Circuits”

Stretchable Traces For Flexible Circuits

Electronic components are getting smaller and smaller, but the printed circuit boards we usually mount them on haven’t changed much. Stiff glass-epoxy boards can be a limiting factor in designing for environments where flexibility is a requirement, but a new elastic substrate with stretchable conductive traces might be a game changer for wearable and even implantable circuits.

qxMo1DResearchers at the Center for Neuroprosthetics at the École Polytechnique Fédérale de Lausanne are in the business of engineering the interface between electronics and the human nervous system, and so have to overcome the mismatch between the hardware and wetware. To that end, [Prof. Dr. Stéphanie P. Lacour]’s lab has developed a way to apply a liquid metal to polymer substrates, with the resulting traces capable of stretching up to four times in length without cracking or breaking. They describe the metal as a partially liquid and partially solid alloy of gallium, with a gold added to prevent the alloy from beading up on the substrate. The applications are endless – wearable circuits, sensors, implantable electrostimulation, even microactuators.

Looks like progress with flexibles is starting to pick up, what with the conductive silicone and flexible phototransistors we’ve covered recently. We’re excited to see where work like this leads.

Continue reading “Stretchable Traces For Flexible Circuits”