Isola Releases IS550H Material: Interview with Experts

Interview by Nolan Johnson

Nolan Johnson speaks with Michael Gay of Isola and Chris Hunrath of Insulectro about the release of their new halogen-free, high-thermal reliability material, which they hope fills the gap in the market between epoxies and polyimides.

Nolan Johnson: I understand there’s something new on the market for us to talk about. Why don’t you tell us what it is and what the application is?

Michael Gay: Quite a few years ago, the automotive industry OEMs were looking for an alternative to ceramic-based materials for high temperature applications. They wanted something that was less costly. They wanted something that would fill the gap in between typical FR-4 applications and ceramics. A consortium called The Help Project was developed with several large OEMs and other industry participants in the automotive sector who wanted to work together and develop this material. We started with about a half-dozen different candidates and then whittled it down, making comparison to products like 370HR, which is a typical FR-4 lead-free compatible material. We started doing evaluations and we came up with the product we now call IS550H.

Johnson: And this is a new product?

Gay: Yes, it’s brand new. We launched this product about four or five weeks ago. The product is manufactured at Asia. It’s really directed toward the automotive industry, but because of the properties of the material, it can actually be applied to other industries where high temperatures and high voltage CAF performances are required.

Johnson: From the automotive application perspective, how is this a response to the demands of OEMs?

Chris Hunrath: High-speed charging is an obvious area of concern, and one of the ways you accomplish that is using higher voltage. You need something with very good bioelectric properties. Epoxy is good, but this material is better. Rapid charging drives this heavy copper as well as the ability to make circuits and embed them in the dielectric material rather than thick coppers. With thermal performance, in the organic substrates, it has always been the domain of polyimide, with epoxies, multifunctional epoxies, and some materials in between. But there was a space between polyimide and epoxy, and we knew that polyimide doesn’t do certain things very well. It absorbs moisture, but it gets brittle as cures. It is very decomposition resistant, but it does have some other drawbacks.

As Michael mentioned, ceramics are very good in certain applications for high temperature, but you can’t do everything you want to do in circuitry in ceramics that you can easily do with a PCB material or organic PCB material. This just gives the engineers and designers a whole lot of options when they’re designing circuits. The resin chemistry (and I don’t believe it’s proprietary), but the base chemistry is something called benzoxazine, and it’s a newer resin system. It’s been around for a long time, but it’s newer than epoxy. The way it cross-links and the way it behaves in high temperature applications is different. It’s actually been used in aircraft bodies. You’ve heard the airline industry is moving away from aluminum parts to composite parts. Well, this is the resins that is being used. Resin has to be able to flow and fill very well large features, but it also has to withstand temperature variations. Think of an aircraft on the runway vs. an aircraft in the upper atmosphere—we see some pretty wide temperature changes. This resin chemistry does all those things very well.

Johnson: If it’s being used for exterior aircraft parts, that indicates it is resistant to UV. Plus, it’s good with rapid temperature variations. It’s good with humidity issues.

Hunrath: It’s good with fracture toughness.

Gay: Yes, fracture toughness is a big deal.

Johnson: Right. And that fits with what the automotive industry has been asking for. You can’t necessarily put standard FR-4 into a vehicle that might go to either an Arctic region or a tropical region.

Hunrath: Yes, and this is intended for the electronics, the battery structure, the charging systems, and those types of things.

Johnson: How appropriate is benzoxazine for miniaturization? Does it play well on the sensor side, or is this primarily the powertrain?

Gay: It’s primarily designed for power distribution and the systems that connect the automobile to the charging stations and then distribution within the automobile. In the charging arena, we’re going from lower voltages to much higher voltages. The material has to be able to withstand those voltages across tight spacing. You have the hole wall to hole wall spacing, and it needs to be able to manage both that and Z-axis spacing. You can’t build a board that’s two inches thick; you have to build a thin board, so Z-axis capability on thin dielectric is really important. This is where this particular material excels.

Johnson: Do you see IS550H having application in the infrastructure and charging distribution portion of the network?

Gay: Yes, there’s definitely opportunities in the distribution network. We’ve seen applications that are ripe for this type of material where voltages are up in the 20K to 160K range. There are many applications where very high voltage are applied. We see that as an adjacent market we need to look at as well and see how that works. As for automotive—for example, the wall charging systems, the trailered battery systems—those types of systems all need to be managed. Distributing that energy in the heat-generated as well must be managed through that material. An advantage of this material is that it has a much higher thermal conductivity than a typical FR-4. Typical FR-4 will be about 0.35 to 0.4, whereas this material is 0.7 W/mK. This gives it a much better current carrying capacity and heat dissipation capability, so that when you do have those high voltages and high currents, you’re not damaging the material and causing premature failure.

Johnson: You mentioned that there were some other applications outside of automotive that seemed to be well suited for this material.

Hunrath: The material comes in the regular building blocks that people are familiar with for multilayers. There are many other applications, everything from the ATE and burn-in boards to even some down-hole applications. There are plenty of applications where you need higher thermal performance, but you don’t want to do something more with a more exotic material.

Gay: Adding to that, for example, polyimides have always been used as the primary high temperature material. The problem with that material is the polyimides are fairly brittle and this material is just the opposite. It’s got the high temperature capability, but it’s not brittle. It’s got a very high TG because it’s halogen-free, and it gives you very good temperature management while maintaining its structural integrity when you apply vibration to it, or you apply various structures within the material, copper for heat dissipation such as embedded heat sinks or coins or things like that. With polyimide, you may have a hard time doing that because it creates stress risers and those stress risers crack during thermal cycling; this material is a solid material for those types of applications.

Johnson: So how does this material behave during fabrication?

Hunrath: We have some experience with BZ-based materials and they drill and they smear and plate pretty conventionally. That’s another nice thing about this material—when you try and form circuits on ceramics, it’s a whole different, more complicated and specialized technology. There will be applications where there are certain sensors in the exhaust system that must be ceramic based. Of course, that’s not an electric vehicle; that’s a combustion engine. But this material can be dropped into a PCB fabricator. And that’s really the point—you can use conventional building blocks in terms of the prepregs and cores. It also goes through the shop, drills normally, plates, and all that.

Johnson: Fabricators can anticipate it behaving a lot like FR-4?

Gay: Yes, FR-4 processing ease.

Johnson: That certainly plugs a hole in the spectrum of materials, doesn’t it?

Hunrath: There has been a need for something that has the performance advantages of polyimide without some of the drawbacks. When I saw the data from Isola on this material, I was really impressed with its CAF performance.

Gay: We’ve actually had four different OEM tests that have been run all the way up into the 1500-volt DC range. You’re looking at both hole wall to hole wall at various spacings and then also Z-axis spacing. We’ve seen that at 1500 volts, you can run the material up to 2,000 to 3,000 hours in an accelerated life test. Now with the voltages increasing, we will have to go higher than that, maybe up to 3,000 volts or possibly higher, but when you do an accelerated life test, you’re trying to test multiples of the actual operating voltage. For example, 460 VDC might be a pretty common voltage for some of these supercharging stations to operate. Those inverters that are in the car get very hot, very easily. This type of material is going to be a solution for those specific boards within the interconnection of the car and the charging station.

Hunrath: If you put that into perspective, 100-volt CAF test, passing that at 1,000 hours is considered very good. To do 1,500 volts for 3,000 hours is of off the chart.

Johnson: It would seem this is a good response to some of the automotive industry requirements regarding charging and battery management.

Gay: What’s interesting is that the construction set in those tests has included 7628 glass and automotive folks want the least cost option to build the boards out of it. Just a couple of these tests are using 7628 and the hole-wall to hole-wall performance performs great at these very high voltages at tight spacing. It’s pretty interesting chemistry that allows you to do that with 7628 glass.

Hunrath: I would think that probably comes from a combination of the fracture toughness and the resin’s ability to bond to the glass fabric.

Gay: Yes, definitely.

Johnson: Did you say that you’ve had three or four OEMs working with you or working with this material?

Gay: Yes, several automotive OEMs have done tests, but we’re also looking at applications outside the automotive segment. They are looking for the attributes like burn-in board or ATE type applications where you’re seeing repeated thermal cycling; that repeated thermal cycling in a typical burn-in board has numerous slots on a given board and that’s going through four or five cycles for that chip set so that they can test it. It’s loaded again, put back on the oven and thermal cycled again, then they take it out and load more chips. This happens repeatedly. As the number of sockets is reduced in that test board it reduces the amount of throughput. When you get to a certain number of sockets that are defective or not functioning, then you have to pull that board out and replace it with another board. This type of material would give the test equipment the ability to run more cycles and last longer in their test system, thus reducing the overall cost.

Hunrath: There are probably applications for this material in aerospace, outer space, where we need that extra reliability combined with fracture toughness—extra thermal reliability combined with fracture toughness. There’s probably a lot more applications for this material.

Gay: Yes, exactly.

Johnson: You’re manufacturing it in one facility right now?

Gay: We developed the material in Düren, Germany, and that facility can run the material, but because most of the automotive work is done in Asia, we’ve set up the facility for building our material. It is where most of the material will be manufactured. We have inventory in place, so the necessary materials will be readily available for customers that want to do testing, UL qualifications, process evaluations, and so forth.

Johnson: Finally, let’s talk about pricing for this new material.

Hunrath: From a material cost standpoint, this will be a premium over epoxy, but less than polyimide. It fits that in-between space. As Michael pointed out, automotive applications are very cost sensitive. Both the material costs and some of the building blocks are such that you should be able to make a whole lot of those applications, and that’s another good thing about this. I think there’s some aerospace applications that have historically been polyimide. I think that this material in some of those applications could outperform polyimide. Polyimide is still very composition resistant, but it does get brittle as it sees heat.

Johnson: Which limits its lifetime.

Gay: Exactly.

Hunrath: That is a drawback. Anything that sees break shock and vibration or copper structures, this material could be a good fit.

Gay: Thinking about that from an automotive perspective, your automobile is going to see a lot of vibration over the lifetime of the car. It’s also going to see thermal cycling. You’ve got cars that are up north, you’ve got cars that are down south. You’ve got cars that are operating in dry desert environments like Arizona, and ones that are operating in wet environments like Seattle, Washington. You need a material that withstands those environments very solidly and performs well for long lifetime. You don’t want to have to be replacing circuit boards in these electric vehicles every few years.

Hunrath: I think its price point puts it in a place where it’s actually more economical than the alternatives, and that’s an important attribute. We’re talking about a new resin technology that allows you to do more with organic PCB materials rather than using something like ceramic. This extends the range of what organic can do. Michael, do you know why you couldn’t use this in some of the BT applications?

Gay: Oh, I think it might fit in that category just fine.

Hunrath: BT resins were a popular choice for organic chip substrates, and it’s been hard to get for a long time. The supply chain is not great on that material. So, if I look at the numbers, this material outperforms BT (bismaleimide triazine).

Gay: And it’s also a very moisture resistant type of material as well, which is one of the things the BT is tested to using JEDECstandards.

Johnson: I think you’re onto that. This is one of those situations where the overall cost is lower for the OEM than the price of the material because of the durability, reliability, and manufacturability, they’re going to get out of this material. It may be at a premium for price, but all in it’s going to be cheaper in the long haul.

Hunrath: And it’s not that much of a premium; it’s not like some of the more exotic materials out there on, but because of its standard building blocks, you can also broaden its applications, especially if you need high reliability. I mean, it doesn’t just have to be the power network in a vehicle, it could be the motherboard in an electric vehicle where you want that extra reliability.

Johnson: Where you’re seeing the heat and the humidity, nonetheless.

Hunrath: Right. You may not have some of the other challenges, but you want to get some more reliability without going to a polyimide or ceramic. This is an option.

Johnson: That’s part of the challenge for the automotive industry in that you need to be able to handle all conditions. In automotive, reliability is so important. I know this product is relatively new, but do you have any hints or indication on how it’s doing for overall reliability?

Gay: As far as reliability is concerned, we’ve done a lot of accelerated life testing, but as far as applications are concerned, since we just launched the product, there’s not a lot of infield type of reliability data that we can cite at this point in time. We’ve done some cycling tests from -40°C all the way up to 175°C, and that cycling, I think, was in the neighborhood of 2,000 or 3,000 cycles. There was some additional testing where we heated up the material from room temperature to 200, then 225 and 250; we did this in 500-hour increments. This material just does not degrade over time. It maintains its integrity, even though it’s been through a lot of environmental conditions. We see this as the type of material that can really prove itself in the field. With the data that’s used in the industry to understand material performance, the indicators are that this material will perform very well in the field.

Hunrath: It should outperform phenol cured epoxies.

Gay: Most definitely.

Hunrath: It is also halogen-free and V zero. It’s got those boxes checked off as well. But based on the nature of the resin chemistry and its history in aerospace composites, it should outperform epoxy in really every attribute.

Figure 1: Cross-section figure with white highlighted cracks.

Gay: Yes. In this image (Figure 1), you can see the white lines are just where the cracks we’re seeing there. It’s obviously drawn over the top of the cracks vs. actually showing the cracks because they’re hard to see in the materials.

Hunrath: Right. You’d see in the microscope the cracks would be a dark line or you’d see the fracture on the resin.

Gay: Probably one of the standout features of the material is the fracture toughness. When you look at it from that perspective and the vibration that the product’s going to see in during its life cycle, I think that’s pretty important. But you know, even maybe under the hood applications on fuel powered cars as well.

Hunrath: This just shows the thermal conductivity. Resins are not only electrical insulators, they’re also thermal insulators. But this resin chemistry has a better ability to dissipate heat.

Gay: Yes. It certainly increases the current carrying capacity of the circuitry. And that means you’re going to be able to increase how much power you’ve pushed through the system into the vehicle’s battery. This kind of attribute is one of the attributes they were looking for during the development process.

Johnson: Gentlemen, thank you for such a detailed discussion today.

Gay: I appreciate the opportunity to talk with you. It’s really great to do that. And having Chris on this call makes me feel a lot more comfortable because he’s a very knowledgeable applications expert.

Hunrath: Thanks.

28 April 2021