Tour of Latest Innovations in Printed, Flexible, InMold Electronics by TechBlick

Updated: Mar 14

Low temperature soldering

The first topic is low temperature soldering. And if you think about flexible PCBs, you will notice that many of the flexible PCBs are actually based on a substrate. And part of the reason for this is that people can tolerate a relatively high temperature allowing automated reflow process of soldering.

This is part of the reason, of course, one can still solder on, but usually this is done manually. And the reason is that when it is done manually, one can much better control the temperature profile of the soldering process, making sure that it does not exceed the constraints of PET.

However, now there is some very, very interesting approaches that allow one to solder on substrates such as PET. one of the interesting approaches is by our gold sponsor, NovaCentrex. And what they do is they are bringing their pulsed lighting system into soldering so you can expose the joints to a high dose of light, and that the pulse light will form the joint without the actual substrate experiencing a high temperature.

And what is even more interesting is that this process can happen, if the sintering profile is optimized, can take place on a matter of milliseconds. So it means that you can really solder roll to roll at high throughput on substrates such as PET.

Another very interesting innovation here is shown in the middle of this slide, and this one is interesting because it is from the same you know, it comes from the birthplace of SAC305 solder: Iowa State University.

The company commercializing this is a startup called Safi-Tech. And what they are developing is a SAC305 microcapsules solder that can be applied on PET at just 120 degrees Celsius.

So it is really interesting because it means that you can combine the properties of solder, including that automatic self alignment, which eases the burden on pick in place as it doesn't have to be as accurate with a low temperature substrate.

And all of this means that flexible hybrid electronics becomes closer to reality because you can roll to roll metalize, you can roll to roll pick and place and also you can solder at fairly good speeds, but more importantly, at low temperatures.

But conductive adhesives are also experiencing many interesting trends. And one that I like to highlight here is by CondAlign. CongAlign has a very interesting process. What they do is they use electric fields to vertically align, or form chains, of the fillers inside of the host. So the key benefit of that is that one can achieve an anisotropic conductive thermal or electric conductance without needing as much filler content. And it is often the filler that is the expensive part in these kinds of conductive adhesives. So one can cut down the filler amount by as much as, let's say, 80 to 90 percent.

So here you can see an example on the on the right hand side. On the top side, you can see the particles which are in the host dispersed at random. And in the second image on the right in the middle, you can see that the particles have been aligned vertically under an electric field. So as to reduce the amount needed for the same or better performance.

And as you can see in the image below, this can come in the form of sheets. This is now done roll to roll. The thickness of the sheet can be variable per customer request. And also the pitch density is now excellent and the process is now being scaled up.

So I think it is something also to look into because I think it's an interesting innovation that can help really drive down costs while exceeding or at least matching the performance of existing options.

Printed Electronics in Large Area Lighting

Another interesting trend is in printed electronics in large area LED lighting. And I think, of course, for quite some time, printed electronic or printed circuitry or metallization has been applied to LED lighting.

And one of the key advantages, as you can see on the left, and this is by a company called Kundisch, is that one can achieve customized patterns on the surface and then apply the LEDs on that customised patterns. So what it means is that one can have the shape or the geometry or the design that one desires using the printed circuit on the on the flexible substrate or on the larger your substrate.

Another interesting trend that this has been around for some time. There are companies that started commercializing this maybe four or five years ago at least, but now it is gathering steam and momentum is doing everything roll to roll.

So here you can roll to roll prins, the metallizations and also the component attached materials, and also roll to roll assemble the LEDs onto your flexible conformable substrate, allowing one to have excellent throughput. This can be an excellent production process for creating flexible conformable LED foils.

And so I think this is again, an interesting area that one should keep an eye out. And this particular example that I've highlighted here is by Holst Center in the Netherlands.

Printed Electronics in microLED displays

But while we are on the topic of LEDs, I think one of the hot trends in the display industry, is, of course, microLED.

They are fantastic, but they're hard to manufacture. As you can see on the right hand side, they come in many, many different forms and they can be put to use in different kinds of displays from small size displays, micro displays, all the way to very, very large area displays. And there are many methods of transferring the inks, transferring to the LEDs and so on.

One point that is often neglected is that how do you metalize the actual substrate? So once the LEDs have been created, these have to be placed or transferred onto your mother substrate, there has to be some metallization on the substrate and this can be done by PVD. Then you have to create a connection between the front side of the of the substrate, typically glass, to the back side by creating a via and filling that via.

However, now companies are proposing that this metallization and also the connection from the front side to the back side be done using screen printing.

And this is an example by Applied Materials. This comes out of their Italy group. And what you can see is that the printing screen printing electrodes that wrap around the edge of the glass connecting the front to the back side, and they're achieving a linewidth to spacing ratio of around 60 to 40 micrometers.

And clearly the advantage here is that you don't need vias and you are doing additive printing. So I think a very interesting approach, and this is an engineering problem that is not, let's say, as sexy as the transfer problem. So it receives less attention but is equally important. And I think printed printing can play an interesting role here.

Transfer challenge in microLED

But of course, transfer is a big, big problem when it comes to making microLEDs.

On the left hand side, you can see that micro LEDs are very small. This chart shows you a comparison in size with, let's say, hair, which is relatively big actually compared to microLEDs, and with dust and viruses. And note that the x axis is actually logarithmic.

And the chart on the right shows you the number of failed dies for a given yield at different resolutions and the inset is kind of a blowed up or a zoomed version of this.

And basically, to achieve very few failed dies, the yield of the process has to be very, very high. And this is, of course, extremely challenging when one aggregates the yield across the whole process, including metallization, transfer, bonding and so on and so forth.

Digital printing in display repair

So there is a need to repair. And one opportunity that again printed electronics offers is precision digital printing on 3D surfaces.

Here, I want to highlight this very interesting company out of Poland. And what they do is they have a digital printer that can achieve using their own viscous silver nanoparticle things, very, very fine line.

So here on the top left hand side, you can see examples where they have printed, let's say, a 3.2 micron line with a spacing of just 0.7

If you look at the bottom left hand side, you can see examples of this technology being applied to enable open defect repair in high resolution displays.

Of course, this could be applied to microLED, but also other types of displays. This is really interesting because it shows how the resolution of printing processes are dramatically improving.

Here on the right, you can see a benchmarking of this process against some other kinds of additive processes, including inkjet and aerosol and so on. And what is interesting is that here you can achieve very good feature sizes, very small feature sizes and also have a good ink viscosity.

So this is a process that, of course, is not just applicable to a defect repair in high resolution displays, but could be used in security, in prototyping redistribution layers, in electronic packages and in many, many other applications.

High resolution and high speed R2R printing

But I think the trend towards better resolution is not just limited to digital printing, and I want to highlight here that also roll to roll printing is achieving resolutions which were not customary in the early days of printed electronics.

I remember when I entered into this field about 10 years ago, one of my first exposures was to a company that was doing cutting edge R2R printing, achieving a linewidth resolution of around 18 micrometers.

Now, here is an example by Kodak, again, showing that one can do roll to roll flexo printing, achieving a linewidth resolution of five micron meters while running the process as fast as 100 meters per minute.

And this is very interesting. And of course, as you can see on the bottom right hand side, some of the innovation has to do with the way they form their master templates. And one of the key points here is that the way they manufactured the dots to have a flat top.

Transparent antennas

And one of the applications is in transparent antennas. And here actually this is not a fully direct, additive printed approach. It is a hybrid approach. And you can see this in the bottom left hand side. It is hybrid because it involves ink patterning with flexographic printing R2R printing, and then the process goes through a roll to roll electroplating to metalize it further.

But if you look at the table on the bottom right hand side, you can see some very interesting parameters. So they are getting a metal mesh with a line with of seven to eight micrometers with a sheet resistance of just point six, ohms per square and very good transparency of about 90.5 percent and green at 550 nanometres.

And the application you are targeting is a transparent, printed, transparent antenna, which the design of which can be customized to meet different requirements, including GPS LTE and Wi-Fi and so on and so forth.

Skin patches and medica electronics

A hot area in printed flexible electronics is in medical electrodes and there are many applications.

One of the development frontiers has been in the use of electronic skin patches for continuous health care monitoring. And of course, this area has become extremely hot as we transitioned from, or as we are transitioning from, a standard glucose sampling to continuous glucose sampling and also all types of continuous heart rate monitoring, which are multibillion dollar businesses today.

And printing can really play a role here. The example I want to highlight here is the development by Holst Center and they've developed a full solution. This is a clinical grade disposable patch with a reusable electronics, with dry electrode, etc. And the dry electrode includes printed metallization. And that allows one to measure EKG and respiration and temperature. And it is useful for seven days continuous monitoring. So the full solution from the adhesive to the printed lines to the rigid electronics and so on. And I think. It shows you what is possible with printed electronics.

The example on the right hand side are from another company, a Screentec Oy. And what you find here is that the on the top right side, the kind of the purple red picture, what you see is a medical electrode with integrated surface metal devices on the top. And the bottom right picture is an example of a screen printed sensor which can detect skeletal muscle activities. So you can see that all kinds of electrodes can actually be printed.

Stretchable conductive inks for e-textiles

And while we are on the topic of skin patches, a lot of discussion has also been on electronic textiles. And one overlap between electronic textiles and the printed electronics is often the printing of the interconnects or the printing of the stretch sensors.

In the early days, maybe four or five years ago, companies started to bring out the first generation of conductive stretchable inks.

And what has happened in the last, let's say, two years or so is that companies are not just offering stretchable conductive inks, but they are offering the full portfolio of stretchable inks needed to create your electronic textiles. And this includes, of course, the silver inks, but also the carbon inks, the dielectric ink, the conductive adhesive.

The example I've picked here is from Nagase. So you can see they've got a silver ink that can be stretched by 100 percent. They've got a carbon ink and they've got even a very good adhesive.

And in the chart in the middle shows you the properties of the adhesive, it can be stretched up to 30 percent with very little hysteresis. And also it can be cured at 180 degrees Celsius. And I think the adhesives are very, very important in the full system.

And the chart on the bottom right hand side, I've picked this because it shows you that if you only had a silver printed lines, the resistivity would be lower compared to when you had a stack printed, a stack composed of silver, carbon, and dielectrics. But when you have a stack, you are making it more washable. And in this case, you can see that after experiencing 100 washing cycles, the material or the stack of materials has performed better. It has experienced a smaller amount of change in the overall resistance.

Medical Electronics: R2R volume screen printing

So back to this topic of electrodes, actually, and what I want to highlight here is that this is a fairly big, big business. Just by showing you one example, this is from Mekprint out of Denmark.

The example you see on the right hand side is a roll to roll screen printed ECG electrodes. And this application has a volume sales of more than one hundred million units per year.

And the example I'm showing on the left hand side is an incontinence sensor. It is again roll to roll screen printed. And the reason this is interesting is that here conductive cable lines are actually roll to roll printed on a stretchable non-woven material. And again, this is a commercial application and that the printed sensor is part of a full solution, including the rigid electronics, the communications and so on and so forth.

R2R printed displays

So when we are talking about rotary printing, I just want to highlight this example of electrochromic displays.

Electrochromic displays have been around for quite some time, actually, and in the early days, the production was manual and it was very slow. But now the company, Ynvisible, has made the process roll to roll.

So here you can see an example of the roll to roll machine and the whole process is roll to roll. So the printing, the conversion, the testing, everything can happen on the roll to roll machines.

And of course, this is helping bring down the costs, meeting volume demands.

And one recent application, which was announced just a few months ago, is the application shown here in the middle where the electrochromic displays are attached to the package to enable one to continuously monitor the conditions of the minced meat as it goes through the value chain.

Actually Ynvisible is now able to take customers from the R&D, the design phase, all the way to pilot and volume production as a single one-stop-shop supplier.

Innovations in printed secondary batteries

So while I was talking about electrochromic displays, I came to this in progress in printed batteries. And the reason I chose this is because of the example on the bottom right hand side.

So if you look at this example, you've got an NFC charger on the left side. You've got an electrochromic display on the top side and in the middle you've got a printed, fully printed battery, secondary battery.

In a few seconds, you can charge it up and then use it to drive your electrochromic display. Very interesting innovation, in my view, because it is a unique, durable polymeric solid-state battery.

The company supplying is Evonik

you can screen print the slurries as part of your own production process to meet your own design and geometry requirements. There are no toxicants involved and it is a secondary battery. So I think it is solving some of the key pain points in our industry.

And of course, we all know that the industry has been using coin sales even though printed batteries have been available ( of course, some very good exceptions. Printed batteries are commercialized, have been commercialized).

I think this is really an interesting development in the in the industry.

Full line R2R process interation

I want to show you an example of a full inline integrated roll to roll system integrating both digital and analog processes. This one is by Coatema, and it's really interesting because it has everything in one machine from unwinders to dryers to laser patterning, to rotary screen printers, to inkjet, to inline inspection, to cooling.

So you can see that one can have almost a roll to roll foundry in a box system.

on the right hand side you can see kind of examples of the different elements of the machines used at different stages.

Coatema is a fantastic company with many, many years of experience in the field. And they allow you to do prototyping and testing of inks and concepts on their machines. And they have to have a deep and long standing experience in the field.

Printed Organic and Perovskite Photovoltaics

At the start, I mentioned that printed electronics and photovoltaics are, of course, very closely linked. We know that printed bus bars are used in solar cells and this is already a huge application.

And, you know, people tried to also print organic photovoltaics for many years. And the peak, the honeymoon, was when Konarka was around.

Some of you guys may remember Konarka, the American company, they raised well over a hundred million dollars. And in the end, they failed. They hyped up the industry dramatically. They overpromised. And after the failure of Konarka, the industry went into this long period of just wilderness. It was lost.

And, you know, it kind of lost the attention to perovskites because perovskites were demonstrating a very, very fast growing efficiency.

But I think OPV are again on the cards. They are on the agenda and they are suddenly showing rapid improvements in efficiency.

So the chart here was supplied to us by Brilliant Materials out of Canada, and it shows you the materials that are being developed to further improve the efficiency of the OPV.

Also, there is a shift in the from fullerene to non- fullerene based accepters, which is accelerating this trend.

There is a lot more production knowhow now in the in the field. So companies are transitioning to wider format printing, faster printing, and they're much better able to control the morphology of the printed acceptor donor mixture on the substrate.

What is also very interesting, in my view, is the example on the right hand side. This is from EMS, whom I think came out of Kodak .

What they are doing is they are trying to scale up the roll to roll production of perovskites. They are printing on a flexible 100 micrometer glass.

So the picture in the middle is showing you ow they are printing the metal mesh on a hundred micrometer flexible glass. In this example, they were able to run at up to 60 meters per second. But of course, the whole process is a little bit slower.

As you can see on the right hand side, they are going from a pilot role to a pilot down to a very large scale machine.

And the idea here is that they want to do it on a 1.5 meter web with a targeted web speed of 30 meters per second. And if everything goes well, this could be a big application for flexible glass. A big success story for R2R printing, creating a 4GW roll roll printed or coated perovskites factory.

Of course, there is a lot of development to be done. But nonetheless, this shows you the kind of the intent and how far these companies have come.

3D Printed Electronics: Bringing intelligence to 3D surfaces

So now let's talk a little bit about a printed 3D printed electronics. This is also a very interesting area. And I think, roughly speaking, one can divide it into two directions. One is metallising an already 3D shaped substrates.

So the top row shows you examples of this. Here you can see a metallization ofof an antenna on a 3D shape substrates. You can see examples in the automotive, in a heater, and also in a medical device. And there are many other applications. Of course, the antenna printing was the biggest one. But now I think more are coming.

And the row at the bottom shows you examples of actually 3D printed electronics, where printed electronics is being combined with classic 3D printing to create circuits and sometimes surface mounted devices inside and outside of a 3D printed object with a very complex shape

Here you can see examples where the parts have been integrated into a into a kind of a device or they've been integrated into an egg shape.

It allows one to really bring intelligence to 3D printing. So instead of just creating dump mechanical objects, one could integrate also the electronics inside the 3D printed object. And if one has a seamless design to production process, it could open up many fantastic opportunities.

And one good example here is a company, Neotech AMT, from Nuremberg in Germany, and they have some of the best machines in the field.

Printing of PCBs on all manners of substrates

Of course, PCBs are etched, they are not printed, but one trend that started maybe, again, four or five years ago and is now beginning to mature is actually printing the PCBs.

And one example is the company from Canada, Volterra. They have a desktop printer that allows you to print the conductive lines. So you supply the machine with a Gerba file and it prints the metallization lines. It can create the vias, it can deposit the solders or conductive adhesives, and it can also go through the reflow process.

This is an interesting desktop, all in one turnkey solution with many applications in prototyping for all new research centers, for groups trying to design various kinds of circuits and trying it out. And also, of course, for universities.

InMold Electronics: Taking off

IME is another trend that should be watched as it is beginning to mature. This has been a story of start and stop and start and stop, I think the big story many years ago was that Ford accepted the overhead console made using in-mold electronics, but then had to recall the product because there were defects.

But the development continued behind the scenes. And then a few years ago, applications, small sized, in wearables and consumer devices appeared.

Then we had applications ics for creating heaters embedded through the cover glass of LED lights for cars so to accelerate the defrosting.

And now I think we've reached a point where we can expect very soon applications in the interior of cars being made using in-mold electronics.

So this process has come a long way from developing the entire materials to developing the very complex processes, which has had a very steep learning curve for the industry, printing all the layers needed, reforming and curing it.

It's a fairly complex process. But now there is a built up experience in the industry. The industry is able to handle a complex design, integrated lighting, integrate various functionalities in the small electronics.

So I think this is a trend that is really taking off. But I want to show that 3D shaping and stretching and kind of applying functional layers is not just in electronics. A very good example is by Kimoto.

They have created these three formable diffusion films. You can see this on the right hand side. The idea is that you have this film, as you can see at the bottom right, which can be stretched up to 200 percent into an arbitrary shape that you want.

This is a light diffuser film and the purpose is shown on the top right. So instead of having discreet LED lights, it looks more like continues lighting. Therefore, by applying these 3D formable diffusion films, one can achieve excellent distribution of light.

And also the film is able to dissipate heat well, and so to hide a lot of the heat hot spots.

Printed Transparent Heater in Auto

Printed transparent heaters, you know, excuse the pun, are really a hot area, because there are not so many good solutions out there for printing transparent heaters and a lot of the solutions that are emerging involve printing.

One approach is to embed a very, very fine trenches inside of the substrate, print the seed layer and then electroplate so that you end up with very fine but deep embedded copper lines, highly conductive, into a substrate and achieve excellent over large areas with very fine metal mesh features. So having both very low connectivity and very high transparency

Another approach is by a company Chasm out of Massachusetts, and they have their own material, which I believe is a combination of silver nanowires and carbon nanotubes, which can be screen printed.

And when you screen print it onto a film, as you can see in the example at the bottom, you can create a heater that goes to, I believe, 120 degrees Celsius or beyond.

You can see an example on the right hand side where this film has been applied to a front headline of a car. And you can see how the temperature profile has actually increased.

Copper inks: have the challenges been overcome?

Of course, the story of printed electronics and conductive inks are intertwined. And for many years, people have tried to create copper rings to replace the expensive silver without so much success.

There have been two major problems. One of them has been the curing without oxidization. So a special equipment or special conditions were required, often adding expenses and additional equipment, and also making copper NOT a drop in replacement.

And another problem has been the copper ink wasn't conductive enough. So you would end up printing such a thick layer that you would make your cost benefits disappear.

Now, there are some copper is appearing on the market, which seem very promising. And what one example I want to highlight is by a company out of Israel, Copprint.

You can see their own benchmarking here. This is a benchmarking done by the company itself. But you can see here an example of conductivity versus sintering time of their copper in comparison to a range of nanoparticle and other types of inks. It is a process that you print, dry, and then you do a very rapid sintering to achieve very high conductivity.

The sintering is usually higher than 200C. But they also have a process which allows one to sinter at 160C o so, so compatible with, let's say, y heat stabilized PET.

Ag nanoparticle inks: higher performance at lower curing temperatures

Progress the story of development is not limited to copper, also silver nanoparticles.

Ag nanoparticles are not a new technology. They have been around for well over a decade, if not much longer. They are now a technology in the phase of incremental improvements, but those incremental improvements are nonetheless very important.

And I want to highlight one example by AGFA which actually also acquired recently the assets of Clariant’s Ag nanoparticle business. So now they have both organic and water based silver nanoparticle inks in their portfolio.

These examples shows you that for a given curing temperature, the achieved conductivity has dramatically improved. So in particular, look at the case when the curing is just 110 degrees Celsius, you can see that the latest generation of inks are achieving much better conductivity.

This is an important development because it pushes silver nanoparticles towards low temperature processing. It widens the scope of available substrates. And for a long time, people were complaining that when you have a sort of annealing temperature constraint and your substrate cannot handle the temperature, the challenge is that you don't get enough conductivity. So these developments are really trying to address that.

Even HMI not standing still

Printed electronics for a long, long time, for decades, was about membrane switches and human machine interfaces and capacitive switches. I just want to quickly highlight that even in these areas, the industry is not staying stationary, is not at a standstill and is making really good progress.

So here are three examples. On the left, you can see just a customized membrane switch keyboard with integrated USB. In the middle is a capacitive keyboard with an integrated controller, and on the right is an integrated tight sensor with a display driver.

Basically, the message here is that companies making atomize memory switches and capacitive switches are trying to integrate more higher value and complex steps into the printing process, or they're integrating a USB system into the membrane switch and so on

The idea is to migrate towards higher value add as the membrane switch itself becomes, as it has been, a highly commoditized business.

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