Indium's Karthik Vijay Talks Engineering for Automotive Applications
As head of Indium Corporation’s application support team in Europe, Karthik Vijay is at the center of the complex material challenges faced by the world’s biggest automotive manufacturers in their creation of PCBs and power modules. Barry Matties met with Karthik at last year's productronica, where everything from stencils and laser cutting to flux technology and jetting were discussed. If you want to know about where material technology currently stands in the automotive landscape, you’ll want to read on.
Barry Matties: Karthik, why don't you just tell me a little bit about yourself.
Karthik Vijay: Sure. In my current role, I'm responsible for the application support team in Europe, and we are responsible for supporting customers by providing technical knowledge, helping them with evaluations, and ongoing product assistance. I’ve been with Indium Corporation for close to 14 years.
Matties: You're in a unique position as an application engineer. You must get to see a lot of the different projects and challenges out there. What are some of the most interesting ones you've come across so far?
Vijay: I'd say automotive. Three to five years ago, it wasn’t considered as exciting; however, this is a good time to be in automotive electronics. We are seeing multiple technology drivers. For instance, there are different levels of autonomy leading eventually to the fully autonomous vehicle, more electrification of normal cars, as well as semi-hybrids and hybrids. Then there are driverless systems that are going to become mandatory because they're safety related with a lot of sensors.
There is 48-volt technology that basically helps reduce even further CO2 emissions. With all this, it throws up some very unique challenges and obvious opportunities, because in the automotive industry, the mindset has always been, "Once you're in, you're in." It becomes difficult to break in, but because of all the challenges, the automotive industry has opened up like no time before. With the level of miniaturization that we’re seeing and being in sync with, say, mobile technology in terms of miniaturization and the complexity, the industry is catching up really fast.
Matties: So that's a general overview of the challenges, but what are some of the specific challenges that your customers are facing?
Vijay: Again, in the context of the technology drivers and the autonomous vehicles, the challenges are from a materials standpoint. If you look at fluxes in the past, they needed to be rated from an electrical reliability standpoint. At minimum, I'll say a value of 100 megaohms needed to be measured over 168 hours, or seven days, for a voltage of five volts and a pitch of 0.5 millimeter. Today, customers are asking for 5,000 megaohms for 1,000 hours with a voltage of 10 to 50 volts, and a pitch of 0.2 to 0.3 millimeters—so a world of difference. Additionally, if you look at mechanical thermal cycling reliability, what was rated for 1,000 cycles before now needs to be rated to 3,000 to 6,000 cycles, and surface temperature has increased from 125°C to 150°C. At that temperature, traditional alloys don’t perform as well because the delta between the melting point of the alloy and the surface temperature has now decreased significantly. That means there's a higher chance of failure during thermal cycling.
Alloy selection must take into consideration not only mechanical rigidity or hardness, but with increased surface temperature, you've got exponentially different CTE mismatches which means you've got to have ductility as well. Hitting that sweet spot between hardness and ductility is key to withstanding more stringent performance requirements at increased surface temperatures with enhanced reliability. In addition, we need to eliminate head-in-pillow and graping, so it's not an either/or. It's got to check all these boxes. That's where material technology becomes very important.
Matties: Because it's all mission-critical in automobiles, right? Especially the autonomous.
Matties: When you start looking at the autonomous vehicles, how great of a challenge is that in the engineering phase or what do you see has the greatest challenge in the autonomous?
Vijay: There are five levels of autonomy. It is estimated to be 20-30 years for autonomous vehicles to become mainstream technology. Having said that, if you are looking at the various levels of semi-autonomy, which it's going to come to, that is imminent. In the next 24 months to the next five years, where qualifications are going on as we speak, for it to be fully functional for production validation (PV) and start of production (SOP) builds, say in the next two to three years. Because it's safety related, a lot of work goes into it. The challenges tie in with what I mentioned earlier. As an example, with autonomous or semi-autonomous vehicles, in addition to camera and vision systems, and radar and lidar, there are now sensors.
For all of this, there’s active and passive safety. Passive safety is an example of a camera sending an image and then the driver decides to react. Active safety is the camera seeing something, sending a message, and telling the car to do something specific. The requirements and challenges of active safety from a complexity standpoint are monumentally different compared to passive safety. Now you've got temperature-sensitive components, and the temperature-sensitive components have, for example, a vision system that can only see up to 240°C. A traditional SAC alloy becomes a challenge because your peak temperature, dealing with the reflow profile, can be anywhere in the region of 235–255°C. That means a need for lower melting point alloys.
Matties: So it's at risk for failure.
Vijay: Exactly. But if you look at lower melting point alloys, they have not yet really been proven for these stringent reliability requirements. It is a challenge, but again, it becomes an opportunity as well.
Matties: Are there new standards being created as we talk for this application?
Vijay: Oh, yes.
Matties: Are you a part of that process?
Vijay: Yes. The automotive industry is involved both with the end customers as well as their tier one suppliers. They are also involved as a supplier because it goes down the supply chain. We are all involved in this discussion especially in safety systems.
Matties: Is there a lot of alignment in these discussions? Because you have so many different viewpoints and approaches, how does that process work?
Vijay: I think it depends. For instance, for safety critical requirements, there's a lot of alignment. On the other side, look at something like solder voiding. The end customers want very low voiding, which is not a problem. But when building these devices, achieving those levels of voiding are sometimes difficult, but it can be achieved with capital equipment and flux technologies.
Matties: Why is it difficult? Just because of the equipment?
Vijay: Because there are certain limitations today. It can be solved, but then the question arises, what is the benefit because these are not necessarily safety related. Now the question is “what is your cost benefit analysis and what advantage do you derive from a reliability standpoint versus potentially a feel-good standpoint?
Matties: So there's a balance there for sure?
Matties: You mentioned Avoid the Void®. I see you have a plus. Talk a little bit about your plus.
Vijay: Avoid the Void®+ is our way of telling the industry that not only do we have materials that achieve very low voiding, but our materials also excel in other areas of performance. Specific to a flux technology, even prior to Avoid the Void®, there were certain characteristics that were pretty important to the automotive customer, but they have just become vastly more important. It's talking about enhanced electrical reliability, so it is purely boiling down to what you do with the flux chemistry to make sure that it's rated now to a minimum value of 5,000 megaohms.
By the same token, if I needed to be really electrically safe, I need to make sure that my activators in the flux package are not over the limit because when I put in a lot of activators my electrical reliability drops. It will still pass, but will take a wee bit of a hit. If I'm going to take a hit on the activity level, that could affect my head-in-pillow and wetting. My customer is not going to accept either/or. It's got to check the box of enhanced electrical reliability, good wetting, eliminating head-in-pillow, eliminating graping, and getting good pin-in-paste soldering, as well as fantastic print transfer.
I was talking about miniaturization. In the past, talking about automotive PCBA, they have never even have worked with a BGA. It was so easy to print that printing was never an issue. Today, you're looking at big boards with 0201s as well as big components. Then you've got heavy thermal mass in a reflow profile in air with a six-minute profile. That's a huge challenge for the flux and that's where the flux chemistry really becomes the secret sauce.
Matties: For all in the flux.
Matties: Then I see response to pause, stability, HIP.
Vijay: That's the head-in-pillow in-circuit testing. That's to make sure that before the product goes out of the door, you're checking for electrical and product functionality. When you’re printing 24/7, machines may break down. Let's say you got three or four hours idle. Afterwards, you'll want the paste to take off from where you left it, where you don't need dummy prints because all of that is a problem that's going to affect throughput. You need a paste with great response-to-pause.
Matties: From a customer's point of view, when they're looking at this process, what are the most important considerations?
Vijay: In selecting the right flux?
Vijay: What we're saying, again, in automotive, it's basically spilling over to the other more advanced reliability applications that involve industrial products as well. It’s enhanced electrical reliability, low voiding, head-in-pillow elimination, not just minimization, as well as the ability to get very good print transfer efficiencies with excellent response-to-pause performance.
Matties: But it's all part of the process or you've got to have the right equipment, the right process, the right people, the right training, the right product. There's a lot of variables to success. What sort of level of success or yields do people typically get in this?
Vijay: In the automotive world, we are looking at 99+%. It's more in the region of 99.8%. In my past life, I worked in PCB assembly. My belief is the material should fit the process, not the other way around. I should not be band-aiding the process to fit the material. From a material standpoint, it's our job to make sure that the solder paste has the widest possible process window to account for other tolerances and stack-ups, or issues with old equipment or outdated processes. If the material could check these boxes from a process window, then you get the lowest cost of ownership.
Matties: When you talk about solder paste, I see a lot of jetting and people moving into the jetting. What's your thought around jetting? It seems like it's more controlled and perhaps a better end product.
Vijay: Jetting has certainly got its place. In the context of zero PPM defects, where there is a complete hands-off on depositing solder paste on the board, jetting certainly has an advantage because with a stencil printing process, you've got to change the stencil at some point. All other aspects are automated because you could automatically deposit your solder paste, your cleaning frequency, but even on the wipes, that's something where you do have the variables. The downside with jetting is if I grab 10,000 pads, I cannot do everything in one shot, so throughput is a problem. At the end of the day, that balance has got to be considered on what you want to achieve.
Matties: You can get quality out of both, but it seems like you have a lot more control over the jet process.
Vijay: Right. In jetting where you've got safe cavity applications, where you can't print, jetting certainly makes a lot of sense.
Matties: Are you seeing your customers with a higher level of interest in jetting?
Vijay: I'd say it's been a buzzword for the last two or three years. There's a lot of interest. Has it taken off in huge volumes replacing stencil printing? Probably not. I think there's many more ways to go in that direction for something like that to happen.
Matties: In terms of stencils, what advice do you give your customers around that?
Vijay: Well, stencil technology was an art. It's way more of a science today, especially when you're talking about miniaturization and step stencil technology. The levels in the stencils are so many, like standard stainless steel with laser cut. But even with laser cut, the amount of polish on apertures, the grain of cut, all of this makes a statistically significant difference in the level of print transfer, especially with smaller ratios and smaller apertures. Then there’s nanocoatings and electroform stencils. Again, in terms of advice, we try to cater to the worst-case scenario. If you can cover the worst-case scenario, everything else is going to be a lot better.
When you're looking at a standard stainless steel stencil with standard laser cutting, which can get damaged over time, we try to make sure that you get the maximum transfer. The same with step stencils. But again, if you look at the automotive world, the insurance they build in from a reliability standpoint is, you could say, after 30,000 strokes, I'll replace the stencil no matter what. The bells and whistles in terms of the nanocoatings and then the grain of cut, the electroform stencils; all of this further enhances the process window and repeatability.
Matties: There's a lot of different variations in recipe with the solder paste itself. What do your customers require or ask about that?
Vijay: There are many requirements. But normally there are the top four or five, which you're not going to be able to compromise on. As an example, for an automotive platform, in-circuit testing (ICT) might not be really important. Whereas for a base station or a networking platform, ICT could be really important, but they may not have a problem with voiding; however, somebody else may have a problem with voiding. That's where some of the customization comes in, where we've got a base platform that's got to check off core requirements, so there's no compromising on that. The electrical reliability, the head-in-pillow, the good wetting, the great print transfer, the low voiding, so over and beyond that, you could have certain tweaks to make the flux more compliant for a probe technology for ICT, the color of the residue, or the ease of cleanliness - things like that.
Matties: Is there anything that we haven't talked about in this that you feel like we should also include?
Vijay: I would say a lot of what we've spoken about is automotive PCBA—printed circuit board assembly. But when I spoke about the technology drivers – the 48 volts, electrification, electric vehicles, semi-autonomous, autonomous vehicles, power modules – that have become equally important to IGBT power modules, and we're having more and more of that in automotive. Their reliability is even more important because here we are talking about voltages of, let's say, 600 to 1,000 volts. Double-sided cooling modules are putting out a lot of power.
Thermal management becomes key. You also have your IGBT module and your bond line control or co-planarity between your DBC or substrate to the baseplate. They've come up with pretty innovative solutions to achieve a lower cost of ownership compared to some of the traditional techniques. Today, a wire bond is stitched and trimmed. Then a solder preform is placed in reflow versus having something like an InFORM®, which is a composite fabrication consisting of solder and a reinforcing matrix. That is a drop-in for the standard solder preform technology eliminating the extra steps. But what we have also learned while working with customers is that it enhances the reliability by a factor of two to three, which was not our original intention when we started out. But again, that's because of the way the reinforced matrix is designed that has helped achieve this reliability.
When you've got challenges, you've got opportunities as well. When you've got higher surface temperature and the increased reliability requirements, something like an InFORM makes perfect sense in not only achieving the lowest cost of ownership, but also enhancing reliability.
Matties: How do people go about measuring this?
Vijay: Yields and failures. Hoping they don't have failures.
Matties: I guess you don't know until you buy it is what you're saying?
Vijay: Well, as a material vendor it is up to us to provide a pretty extensive and in-depth data pack on what we believe is important to the customer, which has come over years of listening to and working with customers. A lot of these traits in terms of what the material needs to deliver are common across customers in the high-rel verticals anyways. With that, obviously they are in a much better position to judge if it checks their boxes.
Matties: And you have performance data is what you're saying?
Vijay: Correct. Then, obviously, to make sure that it's doing what we say. It is evaluating.
Matties: Compatible with their process. Because every process is slightly different.
Vijay: Exactly. Then we also collaborate with them on both processes as well as reliability requirements.
Matties: If a customer is interested in becoming a customer, what's the typical cycle time for them just to knock on your door and then ultimately become a customer?
Vijay: Again, I think it depends on the vertical. If you are looking at automotive, PCBA, and power modules, they've got a very structured approach to qualifications. They've got design validation, production validation, and then start of production. But even before the DV, all the nitty gritty, which is not only the material, but the material has got to tie in with every other component where you've got the conformal coating, the plastics, and then the overall reliability rather than just volt level reliability. When you factor all of this to get qualified, it could take anywhere between 12 and 18 months. Then your volume runs on DV, PV, and then SOP.
Matties: So to win over a customer, it seems to me that they must be having some problem first because why else would they change?
Vijay: From a technology standpoint, yes.
Matties: Because if they have a proven reliable process, that's got to be a difficult challenge for you in the selling process, yes?
Vijay: Perhaps, but it might not necessarily be a problem they're facing today versus what the environment outside is dictating in terms of the future challenges for which they've got to start getting ready today, because their qualification could take another 24 months. The current material might not be giving them actual problems for their products today, but they know that the same product has got to be rated for more reliability.
Matties: But having a crystal ball that looks out two years is…
Vijay: Not in automotive.
Vijay: For instance, they are looking at surface temperatures for plus 150°C today, and they have started qualifications knowing full well that they're going to hit a wall in the next two to three years. Because they've got to get the other aspects of their material sets, but they've got so many other variables also.
Matties: You're a wealth of knowledge, and I could talk to you for much longer. Do you have any other thoughts that you'd like to share with the industry?
Vijay: Thank you, and you’re right. I’m sure we could keep talking, but let’s save that for another time.
Matties: Good. Well, thank you very much.