Printed Electronics Applications and Innovations

The use of printed electronics is on the rise, and Chris Hunrath from Insulectro is here to talk about how to design for it. Learn about the different applications and design possibilities that are available to PCB designers. The proliferation of more advanced printed electronics materials from polyester film, polycarbonate, to transfer film for fabric and flexible circuitry have enabled interesting new applications for printed electronics. Listen in to learn the latest from Chris Hunrath, an expert in material supplies for circuit board design.

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Show Highlights:

• Insulectro has seen a significant growth in sales of printed electronics products, this is an area of massive growth.
• Printed Electronics have traditionally been used in RFID along with metal foils such as anti-theft devices and security access cards - items with conductive inks and membrane touch switches, for example: coffee makers, dishwashers, rear window defoggers, etc.
• Interesting new applications include: glucose test strips, wearables - sensors of all kinds, automotive, and self darkening windows.
• Self darkening windows are used in skyscrapers and airplanes, silver conductive ink, placing current on the window, giving the user control and saving energy.
• Printed Electronics is a high-growth area: business doubled every year in the past five years, doing very well in both substrates and inks.
• Predominant applications driving this uptick in usage: Capacitive Touch switching, in general it saves costs, lighter in weight and has no moving (i.e. car dashboards: a lot of work being done on it today) makes it more reliable.
• The molded structure: print the matte side and ink moves with plastic when molding, circuitry is totally encapsulated in the injection molding process.
• Ink technology: silver  is used and is cheaper than gold and more conductive; silver flake or conductive particles make it possible to have the ink move with the plastic.
• Insulectro offers materials for Printed Electronics, some examples: polyester film - trade name Mylar and other brands, polycarbonate, transfer film for fabric and flexible circuitry in wearables.
• What’s the difference between conventional and printed electronics? Conductivity, and Resistance - know the sheet resistance and use a comparable copper thickness and width.
• Altium 19 and Tactotek, who do in-mold structural electronics are working on relative design features in Altium.
• Printed Electronics whiteboard video
• There are inks that can sense chemistry and can be ion selective i.e. blood glucose, natural gas, carbon monoxide and so forth,
• Applications in wearables: Neural bypass, can pick up nerve impulses, movement sensors, chemistry sensors and more, and can withstand several washings.
• Higher silver loading inks can be used in many different applications.
• Chris shows an example of printed antenna that uses silver inks.
• Can be used in materials that you couldn’t use in a traditional PCB process.  
• Conductive ink kits for children - you can draw conductive inks with a pen.
• Chris shows an example of substrate with high temperature ink, that has a 500-degree operating temperature.
• Events where you can see examples at the Insulectro booth: IPC Apex in San Diego, DesignCon in Santa Clara and Insulectro typically at IT TechEX.
• Conductive adhesive is more ideal for components, soldering to printed electronics is very delicate.
• Screen printing is the main way to print and is very scalable.
• Printed electronics is easier and cheaper to get started and environmentally more friendly.
• Stay posted for more developments in this exciting field!

Links and Resources:

Tactotek IMSE / Printed Electronics Podcast

Altium Printed Electronics whiteboard video

IT TechEX

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Transcript:

Hi, everyone it's Judy. Welcome back to the OnTrack Podcast. Today I'll be talking with Chris Hunrath of Insulectro. He'll be talking about the explosive growth of printed electronics as well as how to design for it, and he'll cover the vast array of possibilities that this opens up for designers. If you have the chance to catch this episode on YouTube, I encourage you to do that because he's had a great session of show and tell of some of these technologies. So lean in and enjoy - I’ll see you on the other side. 

Welcome to Altium’s OnTrack Podcast, where we talk to leaders about PCB design, tackling subjects ranging from schematic capture all the way to the manufacturing floor. I'm your host, Judy Warner. Please listen in every week and subscribe on iTunes, Stitcher and all your favorite podcast apps, and be sure to check out the show notes at Altium.com. where you can find great resources and multiple ways to connect with us on social media. 

Well Chris, welcome back we're glad to have you again.

Thank you Judy.

We were talking recently and we were discussing printed electronics and you told me that Insulectro, over the last four to five years has seen a significant growth in the selling of these products that you carry. So, why don't we jump in right there and just talk about what kind of growth you're seeing in the printed electronics market?

Yes. So, traditionally, printed electronics has been used in RFID along with metal foils. If you've ever seen anti-theft devices, they're typically little RF devices that are either aluminum foil or some sort of conductive ink. But they're also used in security access cards and things like that. And then of course, membrane touch switch. So, coffee makers dishwashers, washing machines–all those things have memory touch switch–very often printed electronics in combination with some mechanical parts as well; those were kind of the mainstays. Oh, and rear window defoggers in cars - that's conductive inks also, that's printed electronics. That's in a different category than the thick foam polymers, but the same kind of technology. What we're seeing now is a lot of growth, yes, but we're also seeing a lot of interesting new applications. New glucose test strips, same technology–conductive inks. That's a little different and we'll talk about that later, but then we're also seeing a lot of new applications on the wearable side, sensors of all kinds, heater sensors, wearable electronics, but also electronics in cars. Lots of new applications–one of our largest customers does the self darkening windows–so they use the conductive…

That’s cool, I didn’t know about that, but I've seen the LCD. Have you ever seen those where you can flip the switch and the LCD opaques the glass? It's really cool.

Yeah. So this is really more for both energy and privacy. But you can make the windows dark, and this is used on skyscrapers and very large windows. You could make the windows darker or lighter, at the touch of a button. Different than the phototropic systems, where you add something to the glass to make it light or darker based on the light, this gives you control. So, the conductive ink, in this case silver, is used as the busbar to put the current on the window and change its lightness or darkness. It's being used in planes because it saves weight over the shades - the pull down shades, but in high rises it has a lot of potential to save energy in those kinds of applications. So, that's a big expanding area for us as well and we've seen growth in a lot of new areas. And as you know, electronics is going into everything now so there's a lot of different technologies. Touch screens have always used printed electronics to some degree, typically again, used as the busbar on the ITO coatings. But yeah, we're seeing a lot of new applications and drug delivery systems, again heaters, wearables, all that kind of stuff.

So, what kind of percentage of growth are you seeing?

We've been traditionally a supplier in printed circuit board materials; rigid printed circuit boards, FR4, polyimide, in the last ten years, the low loss materials; copper foils and the like. We thought printed electronics was a good fit for our business, because we're good at handling sheeted goods, we understand conductors. We did sell some inks in the industry already so we thought it was a good fit for us. And as we get more involved, it's been growing very nicely. So, I would say in the last five years, business has close to doubled every previous year. It was relatively small, but then it's going pretty good. I think we're on track to do twelve million in the next year - printed electronics - both in substrates and in inks. But who knows? One big application and that could really, really take off. So, it's a smaller part of our business today, but we think it's here to stay and expand a lot of different areas. A lot of it's... the material science drives a lot of it, and what you could do. We talked a little bit before about the in-mold. We'll talk about that. But yeah, lots of good applications.

So is there a predominant area - I think we had discussed medical. We all know that automotive, being able to put printed goods say, inside of a console or a card door or a bumper or dashboard - that those kind of things have exploded. Are there predominant applications that are sort of driving this spike?

So capacitive touch switching is nice because it saves cost, weight and there's no moving parts, so it's very reliable, relatively new to cars in terms of car dashboards. So there is... I'm not gonna say reluctance, but it needs to prove out. But I think it makes a ton of sense, and I think a lot of the automakers agree with that. I mean, there's a lot of work being done on that today, and then I have corpus - I have got that sample. Actually, this is a good time [shows sample]. So, this is a sample of in-mold, and I know some of your other podcast guests have talked about injection molding, and this is the step before injection molding. So what you would do is this; this polycarbonate sheet would be flat, and I don’t know if you can tell from the video, but just to describe for the listeners, one side's matt, and one side's shiny right?

Yeah, I can see that it’s shiny.

Typically, you print the matt side and there's different ways to make print treatment, and we'll talk about that a little bit later, but basically you print it flat; screen print it, and then you thermal form it and the ink, this particular ink is designed to move with the plastic, so it still makes the connection. You do have a change in resistance, but it's relatively small. And then you would injection mold this and the circuitry, along with any components, are totally encapsulated. So again, there's no moving parts. If this were a switch, you would just run your finger up and down, you could control a fan, for instance, or a dimmer switch for a light. It could be any number of devices, but this would be encapsulated in an injection molding process. And of course, you could add decorative parts to the plastic and so on and so forth. And then it's sealed, and then there's nothing to tarnish, nothing to wear, it should last a very long time. Again it also saves weight. So, you could literally have a molded dashboard with all the electronics inside it, and you're done.

That's so cool. So what is in the properties of the ink that allows it to move like that, in a molded structure?

So, that gets into some interesting ink technology questions. So typically conductive inks use silver. They use silver metal because silver oxide’s more conductive than other metal oxides. Gold is a good choice, too, but it's very expensive. Silver's quite a bit cheaper than gold, so the particles in the inks are typically silver flake, so the flake particles overlap, like pieces of slate, and that gives you good connection. So what happens is, if you have a binder system and that's the other part of a conductive ink, you have two main components. You've got a binder system of some sort, and then you have the conductive particles, in this case, silver flake,  and what happens is, if the binder system's flexible, it stretches and the particles can slide over each other when it gets thermal formed. But they still make connection.

I see.

And of course, a lot of the performance characteristics of the inks are determined by the size and shape of the silver flake and the chemistry of the binder system. And there's different categories to the binder systems. And, I know your other guests have talked about, like a hundred to one comparison between conductive inks and copper of a similar size a hundred to one difference in resistance. And really there are so many different inks, it probably ranges more like from, fifty to one to a few thousand to one, depending on the type of ink. And they all have their applications. They all have their pluses and minuses whether it's cost, flexibility, it's rheology when you print it. So inks have been used on solar panels. You want an ink that stays put so you maximize the amount of area that can see the sunlight. So you want an ink that's more vertical than horizontal, right? So that ink’s formulated for that application. You also formulate it to stick to the silicon or whatever semiconductor material you’re using for the solar panels. So again, there's all kinds of inks for all different applications and that's where we come in, we try and help customers find the right ink for the right application.

So, I think you mentioned something else about what else besides inks does Insulectro carry relative to printed electronics.

Well, the predominant substrate is polyester film, which we sell, it's a PET film - most of your listeners will recognize the trade name Mylar but we sell polyester film from a number of suppliers. Mylar is one of them, it comes with codings and treatments for adhesion. Sometimes we sell polyester film that's treated to make it hydrophilic and for medical applications, that's very important you want it to wet out with whatever you're testing. So on medical applications, you would want a hydrophilic  treatment on the polyester. So it comes in a lot of different ways, and again, that's where we help customers. Of course polycarbonate for in-mold, that's another kind of substrate. And then we have the thermal plastic polyurethane transfer film for wearables. So this has got a temporary carrier on it, and you would print this flat and then you would transfer it to a fabric and then it would heat transfer, remove the carrier, and now you've got flexible circuitry that could be put in clothing.

So for those of you that are listening to the podcast, if you have a chance to hop over, Chris has been doing a little show and tell here, and he's demonstrating some of the fabrics and things. So if you have the opportunity to go over and check out the video, you can see that. But we will also share – Chris will give us some things that we can share in pdf format and whatever so you can see these things visually because if you're like me, I need pictures, I need to see it visually to help really get my mind around it. So, again we're talking to designers and engineers here. What's the comparison in regards to designing with printed electronics as opposed to traditional printed circuit boards, what are the differences?

Obviously conductivity is a big difference between the silver and copper foil. The advantage of the conductive inks, and I really shouldn't say just silver, because there are carbon inks and there's silver coated copper and so on and so forth. But really, the comparison is in the resistance. So really, what you would need to know is what kind of circuit you are looking to use for your application, and then you could use some of the Altium Designer^® tools, that are based on copper, as long as you know the comparison between the resistance of the ink and the resistance of the copper. So for example, if I was going to make an eight mil wide conductive ink trace, and I knew the sheet resistance - I would just use a comparable copper thickness and copper width to give me the same information, and I could use that in the design, and that's something I think that we probably need to collaborate on in the future. Let's make it even better for the customers designing printed electronics.

Well, we just stuck our toe in the waters here on Altium Designer 19^®, and you had mentioned - I will also share the link for those of you that haven't had a chance to see. We did do one, we have a partner called TactoTek that does the in-mold structural electronics, and so we interviewed them. But they actually partnered with us to put some design features relative to printed electronics. Now they're not super fancy, doesn't have all the bells and whistles we’re just, like I said, sticking our toes in the water but you heard Chris Hunrath say it here; maybe we'll put our heads together and make it a little bit better so the design tools could do some of that, the calculating and it is a little bit of a different animal.

It's because there's so many different inks for so many applications and that doesn't even get into the inks that consents chemistry. There's a technology with a silver chloride ink that with the right additional chemistries, can be ion selective, so you could detect things like blood glucose, you can detect things like natural gas, carbon monoxide. I mean, there's all kinds of things. And actually for the pyrodynamics, that's the basis of technology that's used for O2 sensors. So, you could, and that's an area I think we'll see some activity in, is you could use conductive inks and traditional PCB. Let's say you want to put a heater in a printed circuit board. I mean, it has been done before for embedded passives, but for things like heaters or chemical sensors, you could actually print them directly on a PCB. So there's a lot of opportunity and really, there's no limit to how you could put some of these things together.

It's very exciting because I know we've both been around a long time and the idea that you could do printed electronics that, just X amount of years ago, was like boy, we all wished we could but... I feel like a little bit of science fiction become reality - for me anyways - that we can do these things, so it's pretty exciting.

The wearables are actually interesting. I mean, they could be used for everything from what they call a neural bypass. So in other words, you could pick up nerve impulses from one area–it could be any number of areas on the body–there are some great videos too where they pick up nerve impulses from one part of the body, or even the brain, and transmit it to another part of the body. That has a lot of applications for people that have nerve injuries. There's four sensors, movement sensors, chemistry sensors; there's all kinds of applications in wearables for printed electronics and a lot of the inks for the wearables, if you use the right substrate, the right fabric and the right encapsulant it would withstand anywhere from twenty to one hundred washings, and they're still fully functional. Again, as the material science gets better that'll get extended even further. But just going back to the inks, for example, some of the higher silver-loading inks are 5 milliohms per square, per mil of thickness, and some of them, let's just say, in staying with the silver inks, they may be 150 milliohms per square. Of course, the carbonate, maybe 20 ohms per square - but you want that resistivity in that case. So, there again, many different inks with different applications, and this is what your customers would need to know, or designers. We need to know to design some of the circuitry depending on their application. I just have another sample here. This is a printed antenna. In fact, some of the antennas, the TV antennas that you could stick in your window, to  get local broadcasts - that uses print electronics–silver inks. So again, a lot of different applications, and you could put them anywhere and you could put them on materials that you couldn't use in a traditional PCB process.

That's the exciting part to me; is what you can print on. We’re kind of being freed from the planer FR4. We're able to take that circuitry off those traditional flat surfaces and also off a traditional PCB where we’re constrained by materials. So it's pretty exciting.

You can buy kits for children that you can draw conductive inks with a pen.

Oh, I've seen those actually.

The conductivity is not real high. It's just a way to get people interested in that kind of technology, and they can actually build things that work - that's conductive.

That's neat. I'd forgotten about those, I saw that at a Maker’s fair.

Yeah, there was a company that crowdsourced that kind of device some years ago, and that was kind of interesting, but going back to the actual design part. So, one of the things and again, I know the listeners can't see this, but you would start with a substrate of some sort–could be polyester–could even be kapton. I have some of the high temperature ink; this is kind of interesting. This is a polyamide binder system with silver flake - this has a 500 degree operating temperature.

Wow! 

So it's not just for low tech applications. But anyway, traditionally, you would have a polyester substrate and you would apply your conductors and then you would apply your dielectric and then you could apply more conductors, and you could literally make a multi-layer by alternating the conductor and dielectric layers. And wherever you want to make an interconnect in the Z axis, you would simply leave an opening in the dielectric. So you could make a multilayer printed electronics board. Typically, though, the applications don't require that; I typically see two layers of conductors. I don't see any more than that, but that doesn't mean that's the way things will stay, as the applications get more complex.

Yeah, so we've got a couple big shows coming up; we've got IPC Apex in San Diego and Design Con in Santa Clara, both in California. And I know you're right up there by the Santa Clara Convention Center. So what is the presence of Insulectro going to be, so if some of our listeners are in that area, they can maybe stop by and see some samples?

Okay, yes so, Design Con. We're not exhibiting, we're going to be down at IPC. So, your listeners are certainly welcome to contact us, and we could get them technical information. We typically exhibit at the big print electronics show IDTechX. It’s in the same location as Design Con. It's in the Santa Clara Convention Center, typically November so we just had that show this year - we exhibited. Great turnout response.

Yeah, so since you're seeing a growth in that. How was the traffic in that show as opposed to other years? Do you see that also growing?

It's growing - the previous - let's say five, six, seven years ago... a lot more flashy stuff, lights - the electroluminescent lighting and things, which is another print electronics technology which used to be used in cell phones. Now we're seeing a lot more wearable applications. A lot more serious applications. It really is changing - a lot more technical applications, a lot of printed heaters. DuPont has their RD center here in Sunnyvale, and they have a lot of printed electronic demonstration samples. They have a corian countertop that they actually embedded, using printed electronics, they embedded cell phone charging places.

Oh, that'd be so great.

So you just put your phone on a certain [place] and what happens is, it lights up when you're in line with the charging, so it lights up so you know you’re in the right spot and they can also play music through the tabletop and it's all done with printed electronics.

Wow - I want that counter top. [laughter]

That's with the DuPont RD facility in Sunnyvale but also, they display. Some wearable technology stuff was used for the heated jackets at the Olympics - this previous Winter Olympics - the US team had heated jackets with printed electronics heaters built into it. So, yeah, I think you'll see more and more of that kind of technology and things.

Will you share? I'm assuming that DuPont then has a place on their website that has some of that information as well?

Yeah, I could share that with you. I did want to mention one thing; for components for printed electronics, typically conductive adhesive is used because soldering to printed electronics is very delicate, to put it mildly. It can be done with the right inks and the right substrates, but it is a very, very delicate process. So typically, connections done for heaters are done with either slide-on connectors or rivets and for components you use conductive adhesive. So, for example, and I know the listeners can't see this, but there are some components on this sample. These LEDs here in this test sample, they’re mounted with conductive adhesive, so the adhesives, both mechanically join and electrically connect to the circuit and then this is a near-field connector coil. And again, it has a component, a little microchip, and it's done with conductive adhesives.

I didn't think to ask you that. Yeah, you're not going to solder on a piece of plastic basically, so that makes sense that it would be a conductive adhesive.

There are some soldering machines that can do it. What they do is they heat the ink just enough to get the solder to form the inner metallic. It's better with silver plated copper flake, because copper does not dissolve as readily a silver and into solder; so it can be done, but that's again, that's where we would encourage customers to contact us, and we could help point them in the right direction with the right materials and so on and so forth.

All right Chris, well send me all the goodies, and we'll make sure that we get that in the hands of our listeners. So anything else we need to cover? That was kind of a lot in a short period of time. Sounds like a very exciting area of growth, right?

Yeah. There are so many different ways this could go and I think you'll see all of it, and as for  materials, DuPont has a lot of R&D. They're working on an inkjet version and again, pluses and minuses to inkjetting but I did want to mention that primarily screen printing is the main way to apply the inks and dielectrics and it's done in sheet form. There are revere systems; for people who aren't familiar with revere, basically, it's a drum that's etched in a pattern and then you bring the substrate through as a roll, almost like, reel processing or actually it is reel processing. The downside of that is the upfront cost; tooling cost, is very high so, it's only good for very high volume. 

I see. 

And we're talking like, not tens of thousands of parts, like hundreds of thousands of parts where it makes it cost effective to do that kind of technology. Where screen printing is nice, screen printing is very scalable, too, so you could do small quantities, unlike a PCB shop. I do want to mention this. Unlike a PCB shop, the cost of entry into printed electronics is somewhat lower. You don't have to worry about all the laser drilling, the plating, all the chemistries, environmentally it's a lot simpler to do printed electronics. So there's some advantages there as well.

And the supply chain - is it a traditional board shop that would do these or... it doesn't seem like you’d be constrained by that?

You wouldn't be and some of our board shop customers are dabbling in it, but it's not... I wouldn't say it's an area that they're focusing on. It’s other companies that seem to be getting more into it; some of the nameplate companies and things that have done screen printing, they’re branching out into electronics. So, and those are the ones that have traditionally done membrane touch switch, which is an early application for this. 

Wild. So, okay, keep us posted because I'm sure this is going to be a changing landscape, and I'll be sure to share everything that we talked about in the show notes below to our audience. Chris, thanks for joining us again and to our audience - thank you for joining us again and I hope you enjoyed learning a little bit about printed electronics and we'll give you all we can in the show notes below. So we look forward to being with you next time. Until then, remember to always stay on track.