Alun Morgan on Thermal Management and LEDs in Automotive
Guest Editor Judy Warner met with Alun Morgan, technology ambassador for Ventec International Group, to discuss topics addressed at the Automotive Executive Forum that took place at IPC APEX EXPO 2019. Morgan describes his presentation and findings centered around thermal management in automotive, specifically LEDs, as well as the unique set of growing thermal management challenges Tier 1 (T1) suppliers are now facing in the automotive sector.
Judy Warner: Welcome, Alun. I wanted to talk to you a little bit about the presentation you did at the Automotive Executive Forum. Could you tell us a little bit about what you presented on and what came out of that?
Alun Morgan: It was a very interesting forum. We had speakers from across the whole automotive sector, including OEMs, Tier 1 suppliers, and test houses. The idea was to look at the implications of electronics in automotive. The particular topic I focused on was thermal management. We heard about how we integrate electrical properties with mechanical properties, which is a big topic for automotive. Rather than just thinking about the circuit just as an interconnect, there’s a mechanical component as well. I tried to explain that having the electrical properties is a given, but on top of that, there’s also thermal management that we can build into the substrate.
Specifically, I discussed LED lighting, which has become very popular in vehicles. It started as cabin illumination or sometimes daylight running lights or indicators, but now it’s mainstream in headlamps. These are pretty high-powered devices. And even though LEDs are pretty efficient, at the most, they only run approximately 40% of the output power that is turned to light—the other 60% is heat. In some cases, 85% is heat, and you have to manage that.
So, you have this very intense device at the front of a headlamp cluster, generating a lot of heat, and it’s turned on in an instant, of course, so the heat comes straight away; that must be managed. If you don’t, there are issues of reliability, the device can fail, and these are designed for the life of the vehicle. You don’t want to have to change these at any point in the life of the vehicle. If the temperature changes, you also change the color of the light, which is also unacceptable for the automotive sector.
Thus, the whole concept is that we build a substrate that is fairly thin to build the circuitry on. The back of that has an aluminium layer, and then the back of that has a radiative layer applied. The heat generated by the device can be spread and dissipated, and then it can be dispersed into the environment behind the cluster. We call this an insulated metal substrate (IMS) material, and it has become a go-to device for automotive headlamps. Without that, you’re talking about a lot of mechanical structures and old, ribbed heat sinks and massive devices with forced air cooling that we used to see.
However, the problem with that is there’s no space. Secondly, they’re very expensive. IMS materials are a great solution to bring into the automotive sector, so that has been the trend for a while. Ventec has a number of products that fit into that space, which was the basis of the discussion. There was some talk around how heat flows, from where, and how we have to manage that, which is an interesting background story for people.
It all sounds very easy and straightforward, but there can be issues as well. Sometimes a design is made, and we do the calculations, so we know from the OEM what space they have, the size they have for the circuitry, the temperature they want to run at, and the dissipation in the heat of the device. We can calculate from that what’s required to make that heat dissipate. This process works very well. There are usually two components: a convective and a radiative component.
Traditionally, the convective component is the biggest one so that we remove most heat by convection. The cold air in the radiator heats up, rises, and more cold air is replaced. You have a constant stream of new, cold air running around. However, the radiation side is also very important. And because we now have a patented process for treatment on the back layer of the aluminium, we can radiate a lot more energy than we could in the past. Now, 50% of the heat we can radiate or eliminate is by radiation. We’ve managed to improve the radiation properties significantly of that radiator. That’s the way we built it from the design brief; generally, it works, but it occasionally goes wrong.
Warner: Like all things in electronics tend to do.
Morgan: Right. So the OEMs or T1 suppliers have test regimes. These are quite onerous, so we’re talking -40°C to +105°C or 150°C, for example, and pretty quick cycles; talk about going from low to high temperatures in the space of a few seconds. Imagine a vehicle in Finland. You go out in the morning and turn on the engine. The headlamps immediately power up, giving 12–20 watts of power in the space of one-millimeter square, and you’ve gone from -30°C to +80°C in a matter of seconds, and you do that over and over. You drive around, park the car, it cools down, and you do it again and again.
Typically, cycles of testing run up to 3,000 times on that range. We found that with a traditional solution, two OEMs came in with issues. One was a failure in the interconnect between the device, which was in a ceramic package and the solder joints, that were failing completely. We looked at it and wondered what could be the cause. At the same time, another issue came in with again another traditional solution where the circuit traces were cracking and fracturing underneath the solder joints. We call these no-light failures, and when it comes to a headlamp, that’s about as bad as it gets.
Warner: What was causing it, and were you able to troubleshoot?
Morgan: We came to the coefficient of thermal expansion (CTE). These devices are built with a ceramic package that has around a 10 ppm per degree Celsius (°C) expansion rate. This is then mounted on copper which has around a 16 ppm per °C expansion rate. Then, we had the dielectric, which is pretty thin. Under that, aluminium was expanding and contracting at around 23 ppm per °C. So, you go from 10 to 16 to 23, and because this aluminium block is pretty big, the force of expansion was running right through the dielectric, through the copper, and fracturing the solder joints.
That was the case on one occasion. The other case was also related to CTE. That time, there was a fracture in the copper rather than the solder, but it was the same issue—23 ppm against 16 ppm cycled over and over from cold to hot. The modular expansion was enough to cause that failure. In the end, the solution was the same for both, which was great. We redesigned the dielectric to where the dielectric had a much lower modulus.
Elastic modulus is how much it moves for the stress you apply to it. So, a very stiff material has a high modulus. If you apply a large stress to this material, it doesn’t move very much. In that case, all of the energy from the expansion of the aluminium is passed straight through the dielectric, because it’s stiff, to the solder. You could lower the modulus by making it softer; then, you can make sure some energy is absorbed in the dielectric layer. The aluminium still expands, but all of that energy is not being passed anymore because this layer acts as a buffer between the aluminium and the next copper.
First, we softened the material and made it have a lower modulus. Second, we looked at the aluminium. As we don’t use pure aluminium you can have different alloys of aluminium. We took the 23 ppm that we’re used to running with and took it down to 19. So, we dropped from 23 to 19, copper 16, the package was 10, and the dielectric allowed this softer lower modulus so that we could absorb some there. That reached the point where we could pass 3,000 cycles.
Warner: Interesting. So when you were adjusting the modulus, were you trying to match among the materials so that they would move more or expand and contract at the same rate?
Morgan: Not so much match, but more try to avoid transferring that big expansion to the next material and try to use a buffer layer. Imagine putting a layer of rubber somewhere that can absorb stress, stretch, and move around. Or imagine having a layer of glass that can’t move or absorb stress. If you hit a piece of glass with a hammer, it shatters. When you hit a piece of rubber with a hammer, it just absorbs it and can take that bit of stress and dissipate it. That’s more or less the condition we had and the two things that were required.
So, we had to change the modulus of the dielectric, which is unreinforced; there’s no glass in there. It’s very thin, so we have very high heat transfer rates, which is also required. And to manage the CTE of the aluminium, those two things gave us that 3,000-cycle window the OEM needed. Also, this took a while to do because there are also qualification cycles; for example, 3,000 cycles from -40°C to +150°C doesn’t happen in any time less than 3,000 cycles. We had to do this on a number of test coupons and the original cycles. And not everything failed. We were talking around 20–30% fails of 3,000, so it wasn’t everything, but it was marginal, and we don’t talk about marginal with automotive; it has to be zero defect, and we have to pass.
A big test program was required to do this, which took some time. But having done that, the solution was then made available to the OEM through the T1 supplier worldwide. That is an important point of the Ventec supply chain; it means making the solution. We didn’t make it for only one person; it was for anyone who encountered that kind of issue, which is many. There are many global suppliers in the automotive sector with the same application areas, and we gave them all the solution. That was the critical part of Ventec’s global presence that played into the equation. Sometimes, there can be a solution found that’s very unique and specific.
Warner: For one OEM or supplier.
Morgan: Right, but normally, they don’t like that. The T1 supplier may propose it, but the OEM says, “What happens if you stop doing that and then I don’t have a supply chain?” Typically, they require a couple of sources, which is important for us to recognize. We wanted to make the solution available to all, and that was a primary driver. Having developed it, we made it available to all T1 suppliers around the world.
Warner: When you presented on this topic, what response did you receive?
Morgan: The response was positive and there were good questions too. I talked a bit about the science behind it, but I think the case studies were useful because everyone understands test cycles and how things need to be qualified for automotive. Some of the audience hadn’t considered using the PCB as the thermal interconnect. Many of them use thermal interface materials and heat sinks. That’s their standard thinking, so we deal with the electrical interconnect; then, after having done that, we deal with thermal management.
It was a great theme because the guys from MacDermid Alpha Electronics Solutions started with the same theme as well. They said, “Here, we have an electrical interconnect. We also have a mechanical structure required.” From the beginning, they showed how these two came together. Then, I added the thermals, which is also a mechanical property to the electricals. I showed that all of these things should come together, and that interconnect of the PCB can serve multiple purposes.
Warner: What were one or two memorable questions that came up that you had not anticipated?
Morgan: The first question was, “How much better is the treatment on the radiative side of the aluminium?” We can improve the performance overall of the system by around 15%, so that was one question I hadn’t expected.
Warner: Now that you’ve developed the solution and have test cycling, we all know that automotive has the most stringent requirements, such as zero defect, as you mentioned. How do you supply the solution to these T1s in a scalable way?
Morgan: Each of the T1 suppliers has their own test cycles, so you need to do this one by one. We’ve done this with two of them, and they’ve both qualified it through their own test program that is unique to them. They’re not the same; for example, there are different dwell times and numbers of cycles, but that’s the way it runs. We took the most stringent of these tests that we knew of and built to that. Now, those two T1 suppliers have that solution at all of their sites worldwide and are using it; it’s in production.
Warner: Congratulations on that. That seems like a big win for Ventec.
Morgan: Yes, and thermal management is something that has become very important now.
Warner: It sure has.
Morgan: Right from the outset of the talk, we discussed areas of the vehicle where thermal management has become critical again. In the past, with internal combustion engines, there was a different regime with that kind of system. There are areas where you have high heat dissipating devices, and LEDs would be one of them. Just imagine the engine management systems now with all of the converters, inverters, and power required on an electric vehicle. I found around 20 areas on the vehicle that are issues for thermal management that all use thermal interface materials, so they need to connect and couple heat-diffusing devices to something else.
I also talked about LEDs, which is just one of those 20 areas, and some of the solutions require additional material to be bolted on afterward. Others can have an integrated solution; for example, the inverters can have an integrated solution as well. Traditionally, it would have a big heat sink on the back, but it doesn’t need to be that way. So, it opens up a whole world of new possibilities that wasn’t around before electromobility was around. We have inverters, power converters, and a lot of power in these vehicles that have 100-kilowatt hours in the batteries. We have power trains that take a huge current. What are we going to do with that heat? It’s not something that we can get away from.
I also mentioned the energy available in an electromotive solution, so in a battery-powered vehicle, only around 55% is used for motion and 45% is used for other things. Motion is just about half of it, and the rest of it is used for other stuff—heating, cooling, electrical systems, headlamps, and all of the other stuff. There’s a whole world of power out there you have to deal with.
Warner: With all of the unique challenges, I imagine.
Morgan: Absolutely. Some challenges are in the transmission system, fluid, or the air. The battery is also a big issue and needs to be warmed up because it won’t work at -40°C. Then, it needs to be cooled because it must generate energy and heat, which it must then cool down. A lithium battery running too hot is not a good thing to have around. They must manage both the heating and cooling in the vehicle, so there’s a whole world there. It’s going to be a fascinating area as we move forward. This energy has to be managed somehow, and we talked about just one little solution.
Ventec is well positioned, and I don’t think we’d thought about the future potential for this. LED lighting is what started everything. We were talking about lighting in homes, stadiums, and on streets, so that’s an area we’re very familiar with. But automotive comes along with a unique set of new challenges and testing regimes—a lot of which are mission critical. If you’re driving your vehicle late at night at 80 miles per hour and all the lights fail, that is not safe and cannot be allowed to happen. We must have things in place to avoid that.
Meanwhile, it’s very different if a light in your home, on the street, or in a stadium goes out. Who cares? In those cases, there’s usually another light, but automotive is significantly different, and we have to understand that. That’s why we have complicated, comprehensive qualification cycles—to make sure the solution we provide is one that will give the satisfaction to the producer for the life of the vehicle and won’t fail.
Warner: Ventec is a global provider of laminates, so where are you seeing the most immediate interest and engagement when you’re talking to T1s?
Morgan: Well, everywhere because although the designs are largely made in Europe and North America for automotive, that’s where the design base sits. The manufacturing system sits in China, so China’s volume of IMS is huge. Volume in Europe and North America is there, but it’s often for prototyping and proof of concept, and then the volume moves to China. We’re certainly a Chinese producer and have production in China and Taiwan, and that’s where the use of our materials is, which helps us. But it’s also important that we can have suppliers in Europe and North America as well. Unless we finish the qualifications in these two regions, we don’t get the volume anyway, so we need that.
And there are special solutions too. I’ve talked a lot about automotive, but there are other areas where the solutions can be on much smaller scales. For example, I talked to a company in Norway called TactoTek that makes printed electronics for automotive interiors. They’re producing these on plastic, printing electronics, and then encapsulating and molding them into shape.
Warner: I know them, and I know where you met them (laughs).
Morgan: We met them at AltiumLive and I was fascinated when I talked to them. It was good to meet them here as well.
Warner: That’s great!
Morgan: They have devices generating small amounts of heat but for a long time—the life of the vehicle. If the heat is concentrated in one place, then there is a potential risk over time of degradation of the plastic surround, discoloration, or other cosmetic things. We’ve talked to companies like that about using thermal-dissipating materials to bolt on the back and spread the heat out to act as a spreader and take away the hot spots.
Again, that was another application area we hadn’t thought about. But when you have a solution, it’s a bit like the laser. When lasers were invented, they were a solution looking for a problem. Now, they’re ubiquitous; they’re everywhere. And I must admit, I thought that LED lighting substrates to manage the heat would be something you’d do a little bit; you’d replace all the lights, and then it would be done because they last forever, so there would be a limited business opportunity. But that’s not true at all. There are new applications coming all the time. And I think the move toward automotive was a massive change because we’re talking about dozens of LEDs in vehicles. Vehicles are being produced at the rate of 70–80 million per year, and life cycles of vehicles are becoming shorter for vehicles as well, so there’s a massive market there for this.
And when I think about the possibility of going not only for the LED but also for the other 20 areas where thermal management is needed in the vehicle, there’s a whole massive area of growth. The positioning and agility of Ventec has been very good in this area because it was possible to create a new solution fairly quickly. We had the requirement, we knew we had to do something different, and it was possible to build it. Now, the product data sheets and product offerings can be expanded to customizable solutions for individual users that will then be used across the supply base.
Warner: It sounds like a wonderful opportunity.
Morgan: Yes, I’m excited about it. I spend most of my time in low-loss and high thermal reliability solutions, which means thermal endurance. But now thermal management is another area to think about.
Warner: Which is why we love this industry—we never stand still, do we? And you have to do very rigorous testing, so do you do that in one or multiple locations?
Morgan: It’s normally the T1 suppliers. They have their own approved laboratories. We share in the cost of doing the testing, but most people need to do their own testing to be sure. Some test labs, such as Bob Neves from Microtek who was at the seminar, are very familiar with this. Bob is an approver for many of these T1 suppliers, and they would go to him trusting his methods and techniques. We do internal testing, but that wouldn’t be enough to qualify the product. It needs to be done in an external lab either in their own laboratories or at a third party, such as Microtek, for example.
Warner: Well, this has been a fantastic conversation. I’m excited to see where you go from here. Good luck!
Morgan: Thank you, Judy.
Warner: It was great to talk to you, Alun.
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