Indium's Karthik Vijay Talks Engineering for Automotive Applications

Estimated reading time: 16 minutes

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.

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