Focusing on Surface Sensitivity for Reliability

Estimated reading time: 3 minutes

During the IPC High-Reliability Forum and Microvia Summit, I spoke with Customer Applications Scientist Elizabeth Kidd and Sales Engineer Alex Bien, both of BTG Labs, about their presentation on the challenges of working with highly sensitive surfaces, such as the risk of contamination. We also discussed the various surface characterization techniques that BTG Labs uses to identify such contaminants, and some PCB design strategies for creating a better surface—and a more reliable board.

Andy Shaughnessy: Elizabeth, it’s nice to meet you. I know you’re giving a presentation in a few days, but tell us about the company, and then we’ll talk about your presentation.

Elizabeth Kidd: Sure. BTG labs is a materials science company specializing in surface science and adhesion technologies. We have our roots in being a research and development lab and scoping root cause analyses for people who are scratching their heads at these industrial adhesion problems. From there, we develop the technology to make manufacturing floor inspections of materials as they go through their critical surface process points.

Alex Bien: We help folks to hone in on one area—the surface—that they’ve never had eyes on nor had a way to quickly evaluate surface chemistry in a fast, point-and-shoot manner. Our opening speaker today is addressing this lack of insight into the three nanometers that we need to control to create reliable adhesion. Thus, our focus is putting that technology to the floor in the hands of people who are making dollars-and-cents decisions every day.

Kidd: And taking the high sensitivity of R&D techniques—such as XPS, X-ray photoelectron spectroscopy, and FTIR, which is Fourier transform infrared spectroscopy—that have their eyes on the top molecular layer of a surface, and being able to scale that to a method or technique that can be taken onto the manufacturing floor.

Shaughnessy: Can you also tell us about your presentation?

Kidd: The presentation addressed what we just mentioned—controlling your surface process to better your wire bonding, die pad bonding, laminate coating adhesion, and all of those things. We even have some applications for the coupling agents that we were speaking of known as a conversion coating, and other industries use those organosilanes to increase adhesion between organic material and inorganic material.

Shaughnessy: Are you talking about copper, FR-4, and any sort of surface?

Kidd: Yes. We’ll have some applications in metallics, polymers, and in composites as well.

Bien: That’s a good point, though. It’s particularly difficult to control surface chemistry and match surface chemistry between dissimilar materials. It’s very easy to bond metal to metal, and it’s pretty easy to bond composite to composite, but metal to polymer, glass to polymer, and those material interfaces are more challenging to create to promote adhesion.

Shaughnessy: What are the biggest takeaways from your talk?

Kidd: Namely, the sensitivity of this surface. As Alex mentioned, we have a monomolecular layer that we’re trying to control, and that layer is highly sensitive to contamination events. Contact contaminants from the manufacturing process—things like upstream process aids from stamping or anything left over from any wash process from a chemical etch bath—have a huge impact. Or perhaps you’ve had a change in your supply chain where supplier X used chemical X, and now supplier Y is using chemical Y, and all of a sudden, you have more random failures or successes, and you don’t know why.

It’s drawing attention to those small changes in a process that can affect that monolayer that we’re trying to adhere to. We’ll mainly be talking about contamination, how to look for it, how to characterize that, using various surface characterization techniques—such as FTIR, XPS, and contact angle measurements—and surface activation and detection of coatings. The main takeaway is to increase the awareness of the sensitivity and how you can change—negatively or positively—that surface, even unknowingly.

Shaughnessy: With one small thing having a large influence on the process.

Bien: A small change in the process creates a snowball effect downstream.

Kidd: Exactly. Think about a fingerprint. If you put a fingerprint on the surface, that’s 1,000–10,000 molecules thick. If you try to stick something to it now, you’re not sticking to the surface; you’re sticking to the chemicals and the oil from that person’s fingers. That kind of sensitivity is important.

To read the full article, which appeared in the July 2019 issue of PCB007 Magazine, click here.