Indium's Karthik Vijay Talks Engineering for Automotive Applications

Estimated reading time: 16 minutes

Matties:

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?

Vijay: Yes.

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.

Vijay: Absolutely.

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?

Matties: Yes.

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.

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