Aismalibar: Cooling Off With Thermal Interface Materials

Estimated reading time: 10 minutes

Pete Starkey stops by the Aismalibar booth at electronica to hear from Uwe Lemke about how evolving e-mobility constraints have propelled a growing demand for materials that can address electrical isolation and thermal conductivity concerns in high voltage battery systems and the company’s plans to further expand its footprint into the Chinese PCB market. As always, Aismalibar is up to the task, having developed a new thin fluid coating technology called AirGapFiller that boosts the performance and reliability of any interface using the same foil-based TIM technology that has long defined its impressive line of product offerings.

Pete Starkey: Good morning, Uwe, it’s a great pleasure to meet you and thank you for taking the time to talk with us.

Uwe Lemke: Welcome to the booth of Aismalibar.

Pete Starkey: Thank you very much. This is a very impressive booth. I’ve overheard several people here at electronica saying what a pleasure it is to have a real show again, with real people and real exhibits. It’s like we’re finally getting back to normal, isn’t it?

Uwe Lemke: Yes, we have been having some shows already this year here in Germany, and everywhere it’s the same general feeling. People are hungry. They want to meet people, to talk, touch things, and do all the kinds of things we used to do. We are very happy that we can be here in, if a not totally normal atmosphere, a kind of back-to-normal atmosphere. We had good discussions yesterday on the first day of the show, which is normally a pretty quiet day; things are continuing to recover, and we’ve been enjoying today so far.

Starkey: Aismalibar has been associated with thermal management for many years. You’re the specialists in this area, and I think you yourself are a specialist in thermal interface materials. Can you give us a little bit of background on thermal interface materials?

Lemke: What we like to highlight on this topic is that Aismalibar is one of the few European companies developing and producing these kinds of high-tech materials for thermal interface and heat management in electronics. For the last 20 years, it has been Aismalibar’s duty to reduce the heat of the components through the PCB. All this requires different technology steps. Everything in terms of R&D and production is Spain-centric right now. The headquarters for this area are in Spain. Aismalibar is intending to expand with a second production facility in China to serve the local Chinese PCB market. Eighty percent of the PCB market is in China, and to have equal competition conditions, we need to be there locally to serve Chinese PCB shops. This does not mean, however, that we are intending to import thermal interface materials or laminates from China into Europe.

Starkey: So, you’ll be in China to service the Chinese market while servicing the European and Western world markets from the facilities in Spain.

Lemke: Absolutely. Having a second factory of the same standard on a different continent is interesting especially for automotive customers because our competitors tend to have a single operation either in the U.S., China, or Europe. But in the future Aismalibar can offer this kind of dual fab concept in case something happens with the manufacturing and/or the supply chain. This will go into operation around the middle of next year. We will not be manufacturing the latest technologies at first but will instead be focusing on other mass market technological needs.

Starkey: You mentioned automotive; is that a principal area of application for these materials?

Lemke: Yes, for Aismalibar, automotive currently represents a major share of all our laminate-related business. With the new focus on thermal interface materials, and with the changes in e-mobility we’ve seen in Europe these last two years, there are tremendous efforts and investments right now in the e-mobility sector. The model of e-mobility is more power from less space; more electrical power always means more heat, but when we’re talking about the low charging time for e-cars in relation to the distances they need to travel, that’s a challenge. This means that the demand for electric power is constantly rising, but the space available for electronic applications is shrinking. Getting rid of that excess heat is a challenge, and this is where thermal base materials come into the game in different application areas in automotive.

One classic example has been inverters for the powertrain, but now we see a lot of effort in onboard chargers—not only the infrastructure for charging, but the onboard chargers in the car. In talking to OEMs, as well as to Tier 1 customers, we’re seeing the most momentum in the battery sector. The battery sector is the main differentiator in e-cars, in addition to the thermal interface materials in both aspects. Electrically isolating or optimizing a battery for thermal conductivity depends on where in the battery the TIM is being used, like whether it requires electrical isolation for touch sensitive housings. We have a certain portfolio covering this area, but we’re also focusing on what’s going on inside the battery to bring the cells to the same temperature level with low/no electrical isolation needs. We’ve developed solutions for this through our TIMs.

Starkey: TIMs—is this your name for your proprietary thermal interface materials?

Lemke: TIMs stands for thermal interface materials, and at Aismalibar, we’ve built our promotional materials around this term because this is the brand name for our thermal management technologies. These thermal interface materials are focused on either electrical isolation or thermal conductivity/resistance because that’s what’s on our customers’ minds right now. Everyone is trying to optimize their future high voltage battery systems—we are talking about 800, 1,000, even up to 1,200-volt batteries. To optimize this in a different way, there are OEMs interested in isolating the modules inside the batteries. There are other OEMs and Tier 1 customers who are counting on the full isolation of the entire battery system. There is no mainstream solution right now; everyone is trying to find their best solution, but there will eventually be a general approach for these high voltage batteries in the future.

Starkey: In principle, how are these materials formulated? What do they consist of and how do they work?

Lemke: Everything we do in terms of thermal interface materials is foil-based. If you run into us at a show—not specifically here at electronica, but in general—we have some specific options for batteries this year. There are other thermal interface materials in the market like thermal paste, thermal grease, liquid, solid—all these options are possible, but our approach to thermal interface materials is foil-based. The reason we’ve chosen foil is because it’s thin and easy to handle in the customer’s production process. With foil, you can just put it into the application, and you can work on this in the power module manufacturing; it’s also easy to use.

Starkey: So, the foil is something that you would actually incorporate in the stackup of the printed circuit board?

Lemke: We are offering different foil technologies depending on those two differentiators, because the question for customers is always: What is your focus? Is your focus electrical isolation, or is your focus thermal conductivity? We have different solutions depending on the answer to that question, because you can’t mix and match these parameters. You must focus on one or the other, not both simultaneously, and find the best compromise for your project needs. For somebody focusing on dielectric isolation, we have a fiberglass-based foil of 70, 80, or 100 microns, depending on your isolation requirements. In the area of thermal optimized foils, we are using a carrier of copper foil at 35 or 70 microns. The new thing we are promoting here at electronica is a special coating that we can apply to both technologies. This coating can be applied to both the high-dielectric isolating foil and the very thin copper foil. This special coating is called AirGapFiller, and its purpose is to close all the micro air gaps between the two surfaces being connected, such as between a heatsink and a power device. To optimize the thermal interface here, there is foil in between. When it’s the thermally optimized technology COPPERFILLER, you can see a little shadow of the copper color. These are the two options we have if you want to have something electrically isolated or thermally optimized. The AirGapFiller is new. It should close all the micro voids you always find in this kind of interface; the AirGapFiller can prevent any hindering of the temperature flow as it comes into the heatsink.

You may remember earlier technologies like thermal paste. Thermal paste is very effective, cheap, and widely available, but it’s very difficult to manage in production because of the thickness of the material, which makes coating materials very, very difficult. There is no easy recycling possible either. This AirGapFiller technology, which we can put on both types of carrier material (fibre glass foil with mineral fillers or copper foil), solves this issue by closing those micro airgaps; it’s also easy to manufacture because this material isn’t sticky at room temperature.

Starkey: With this material, you’ve nailed down some of the most important aspects in manufacturing new technologies of this kind: repeatability, consistency, and reliability.

Lemke: You bring up a very good point, because I haven’t touched on reliability yet. Thermal paste does a good job when it’s mounted on an electronic power module. But how will that thermal paste perform in 10 years? After thousands of temperature cycles, there is evidence that thermal paste has two major drawbacks; one is the “pump-out” effect, and the other is the “dry-out.” Pump-out means that, over time, the thermal paste tends to move away from the thermal hot spots toward the edges of the module, where no heat transfer is necessary. The second effect is the dry-out effect, which is when the material dries out and loses its thermal transfer capabilities. These two major reliability disadvantages of thermal paste are covered by the AirGapFiller. It reliably moves heat along by filling up any air gaps and staying there forever. There’s no movement or crystallization; it’s already a 100% cured material. We’ve performed long-term reliability tests together with OEMs to verify how this material behaves. Another plus compared to thermal paste is that once you remove these power module mounting screws, you can easily rebuild the power module if something fails. The recyclability of the AirGapFiller material has important implications in automotive.

Starkey: You’ve clearly cultivated some very close applications engineering relationships with your OEM customers.

Lemke: We are working on this together. For us, these thermal interface materials are a new area, especially in the battery sector. We’ve all heard reports about the risk of high voltage batteries, e.g.  touching the chassis in a car. Can high voltage batteries give you strokes? A lot of articles have been written about how these new high voltage batteries bring in new safety aspects compared to the 12 volts or 24 volts of the past. In automotive, we see a clear trend toward prioritizing safety in high voltage environments, and TIMs can help with that—that’s their purpose. Thermal conductivity performance comes second. Safety is also an important consideration because it defines the longevity and performance of the battery itself, and here we have technologies offering this high dielectric isolation.

We can offer these materials to our OEMs and say, “Use this as a basis,” use the thin coating of this AirGapFiller  to make, thanks to the high dielectric foil, a dielectrically high-performance system. Plus, replacing the thermal paste with this AirGapFiller is easy. The dielectric has been proven for years, but this coating brings the thermal performance to a higher level, regardless of whether you’re using the high isolation foil or the copper foil.

Starkey: Uwe, thank you for such a thorough explanation of these new technologies. I’ve learned a lot in these few minutes of talking with you. Thank you very much indeed.

Lemke: Thank you very much.