Meeting Current and Future Requirements of the Automotive Industry
While at electronica in Munich recently, I spent time in Electrolube's booth with Phil Kinner, technical director of the company's Coatings Division. As the resident expert on conformal coatings, Kinner explained the role of conformal coatings in various applications of the automotive industry.
Starkey: Phil, thank you for inviting me to sit down with you today. We recognize you as the expert on conformal coating. And the automotive industry is very high profile, particularly in Europe, and in Germany. What sorts of things are the automotive industry demanding of you, the solutions people, in terms of the right conformal coatings for the right applications?
Kinner: That's an interesting question, the way that you phrased that. The right product is always a compromise. The requirements on the conformal coating are so many and so varied that probably the right product doesn't exist. Historically, automotive manufacturers may have used multiple coatings for different applications, but increasingly what we're seeing is a standardization on one or two coatings to cover all of the different applications.
What that really translates into for us is increased performance requirements from the coating because they're looking for the same level of protection ultimately in the cabin as they would for an under-hood or exterior kind of application. We're seeing a lot more challenges and a lot tougher performance requirements than we've ever seen, so it's a challenging time for us, but it's what we thrive on.
Starkey: What sort of materials are you formulating for these certain applications, without giving away too many trade secrets?
Kinner: Increasingly, the solvents emissions directive from 1999 is starting to become more of an issue.
Starkey: Right, so you're making solvent-free or aqueous based products?
Kinner: Solvent-free coatings yes; aqueous based, not so much, but mostly solvent-free. It definitely is the way the industry's looking to go. For us, we have a variety of different solutions from UV curable polyurethanes through to two-component polyurethane solvent-free coatings. What we've seen is that those materials in particular are giving us some outstanding properties and outstanding protection, and helping us to really be able to meet and more than meet and to really exceed the requirements of those automotive manufacturers.
Starkey: What sort of coating methods are they typically using?
Kinner: Increasingly we see selective coating being the primary application method, which is no real surprise. It's automated, it's repeatable, and the machine doesn't get tired. It doesn't generally have bad Monday mornings or lackadaisical Friday afternoons. It just does the same thing time after time, which is what the automotive industry's looking for. Then depending on the design of the part, we still see dip coating, but I think that's going to become more of a challenge with solvent-free materials. It's going to become more and more difficult, so I think selective coating is going to become more and more preferable.
Starkey: Would you effectively tune the formulation to suit the coating method?
Kinner: Absolutely. One of the key requirements really is that the material works in the equipment to give optimum results in the user’s process: defect-free, bubble-free, void-free, perfectly wetted and perfectly uniform. We've invested in buying coating equipment ourselves, so that we have it in our labs, and it's a key part of our development process to make sure that whatever we make is highly suitable for volume production.
Starkey: And do you form close working relationships with the manufacturers of the coating equipment?
Kinner: Absolutely. You can't separate one from the other. It's a bad material or a bad machine. Ultimately it's a bad process, so, for us, the focus is really having a good process. We do a lot of work, ourselves, then once we've got something we're happy with, we work very closely with the equipment guys to make sure that they can polish it and make it perfect.
Starkey: How do you see the requirements progressing into the future, and what sort of demands do you anticipate being expected to resolve for the future?
Kinner: I think traditionally thermal shock has been one of the hardest tests. In the past, with a coated assembly, it's a destructive test intended to find out weak points in design. That's really been our focus in making sure we can pass a thousand thermal shocks. I think we're now seeing 2,000, 3,000, 4,000 thermal shock cycles becoming normal requirements.
Starkey: When you say "thermal shock," can you put some numbers on that thermal shock?
Kinner: I guess the most recent one I've looked at was -40° to +140°C with a rate of change of greater than 30° per minute, so I guess it's designed to simulate a car that's been parked in North America somewhere during the winter. So the circuit was cold, and as soon as the car fires up, everything warms up and it hits its operating temperatures. Definitely a challenge. Like I said, we've just seen more and more cycles with harder and harder acceptance criteria, and then the temperature range. Not so long ago 105° was really the top end, now 140°C is normal for pretty much everything.
Starkey: I've heard people talking about 180°C this week.
Kinner: 180°C is next, and I don't think it getting any lower, and that's really where we see the two-component technology becoming more and more applicable because that's really exceeding the capabilities of single-component organic-based materials. Two-component materials enable us to achieve a much broader range of properties. The other thing that we're seeing a lot of is condensation testing.
Starkey: I know that you've been working very closely with the people at National Physical Lab on condensation testing. Can you bring us up to speed on that?
Kinner: Sure. Historically, one of the hardest things has actually been doing repeatable condensation tests because the chambers are designed to maintain a standard, or whatever conditions you set them to. So if you set it to run at 40°C/93% RH and you try and trick it to create condensation, the machine is saying, "Whoa, something's not right here! We'll take out extra humidity.” Or, “I need to put more in to keep the conditions standard.” So really what the NPL and we have been focused on is developing a test method where we're changing the temperature of the substrate, so that the chamber conditions remain constant and we're creating a micro-climate on the circuit board itself.
A lot of the automotive guys have these tests as part of their performance specification. Depending on who did it, what chamber, and what day of the month it was or how the stars were aligned, maybe you'd pass maybe you wouldn't pass. So the NPL's goal is to create a more repeatable, standardized test method. For us it's been a great opportunity to understand what material challenges there are, and what creates a great result in condensation testing.
Starkey: Do you find in the automotive industry that they're looking for internationally accepted specifications? Or do the individual OEMs like to be in control and set their own in-house specs?
Kinner: I think a little bit of both, but more the latter. They mostly have their own specs and they're all kind of the same, but a little bit different. For us, if there was an international standard it would be great. I think having a standardized methodology, regardless of the pass-fail criteria, the standardized methodology is the important part so that we can all be certain if we put the material into a test, we're going to get a result that's A, representative of real life performance, and B, repeatable and reliable.
Starkey: Is there going to be some sort of agreed standard coming out of the work you've done with NPL?
Kinner: I think that's the goal. There's a lot of automotive Tier-one suppliers involved in that project, so I'm hoping that there will be a standardized test that everyone says, "Yes, that's what we're going to use." But like I say, establishing the methodology is a key part of the process. As long as that's the central part of the test, then I expect the OEMs and Tier 1 suppliers will tailor it to their own requirements—that's normal. For us, it's been a fantastic opportunity to see what makes a great coating in a condensing environment, and we've published quite a few papers jointly with NPL, and on our own, where the real advantages of two-component materials become clear. They have inherently better barrier properties, but also they've been formulated to be applied more thickly, and encapsulate devices better, to get better coverage, and obviously survive the thermal shock cycling requirements of the industry. It's been a really great process for us to really show that the technology is performing the way that we think it should.
Starkey: Is there anything else you think we ought to talk about while we're here?
Kinner: Yeah, we could talk about corrosion. Following on from the last point where we were talking about the improved barrier properties and the improved thickness and edge coverage, nearly every paper I've ever written, and nearly every paper I've ever seen about conformal coatings in corrosive environments, the conclusion basically is if the coating isn't there then it's not going to give any protection. So for us, it’s the ability to encapsulate leads and guarantee that we're getting good coverage of all the vulnerable parts.
The same is with the condensation, with salt spray, with corrosive gases; we're just seeing an entirely different world of protection much closer to what we can achieve from potting than we can from traditional thin conformal coatings. So it's an opportunity for you to improve the protection, but also there's a case where maybe conformal coating wasn't enough, but potting was overkill. So, having somewhere in the middle, that's an interesting space where people have the opportunity to reduce the weight, reduce the thermal insulation characteristics of their material, and reduce some of the stress on their assemblies.
Starkey: Once you've got the formulation, it's all about the interactive applications engineering. Not just in the sense of “applications” in terms of putting coatings down, but “applications” in finding the right material for the right purpose.
Kinner: That's it, and kind of formulating, tailoring, and really understanding what people are trying to achieve so that you can give them something, they put it in the machine, and it just works, so there's not really too much effort required by the user to make it perfect.
Starkey: And again, as Electrolube, you have definitely this reputation of rather than just offering a standard product and saying, "That's it, take it or leave it." You can customize the product to make it suit the requirement.
Kinner: Certainly that is our aim and our ambition, and we get it right most of the time. Just one last thing, it's sort of out of sequence, but tin whisker mitigation is another issue related to the coverage. Conformal coating is the proven mitigation strategy for tin whiskers, and again the improved coverage, the improved thickness of the two component materials again have shown a big advantage in mitigating against tin whiskers, so it's ticking a lot of the right boxes.
Starkey: That's great. Phil, we could ramble on all day, but I think that it's been really, really interesting to talk to you, thanks very much.
Kinner: Likewise, Pete. Thank you.
Starkey: Have a good day. Thank you.