A Visit With ‘Flexperts’ Mark Finstad and Nick Koop

Estimated reading time: 7 minutes

Mark Finstad, director of application engineering at Flexible Circuit Technologies, and Nick Koop, director of flex technology at TTM Technologies, are seasoned experts who have been teaching lessons learned and how to successfully navigate the “seas” of flexible circuits to help their students avoid the hazards that have taken down many of their predecessors in the past.

At IPC APEX EXPO 2025, I chatted with Mark and Nick about their roles as leading educators and in the realm of standards development for this increasingly indispensable electronic interconnection technology. They’ve cleverly named this partnership in writing and live instruction as “Ask the Flexperts.”

Thank you for taking the time to share some of your experiences and knowledge about flexible circuits. When and how did you find your way into the flex circuit industry?

Nick Koop: I was a college intern when I started. I knew nothing about flex circuits before I started. I found it very interesting—so many different processes and technologies are used to build circuits.  There has never been a dull moment. 

Mark Finstad: I was taking classes at a local community college and met a guy who worked for a flex manufacturing company. I asked him if his company was hiring and the rest is history. Like Nick, I had no prior knowledge of flex circuits.

When did you first meet?

Koop: Mark and I met in 1985 at Minco Products (a flex circuit manufacturer). We worked together for over 25 years.

When did you start teaching together as the Flexperts? It’s a very clever name, by the way.

Finstad: Nick and I were having a couple of beers one night on the roof of the Standard Hotel in LA, the year that APEX EXPO was held at the LA Convention Center.  Chris Jorgensen, the editor of Circuitree Magazine at that time, was at our table and I asked him what he thought about a “Dear Abby” type of column for flex circuits. He pitched the title “Ask the Flexperts.” He liked the idea, so we started this as a bi-monthly column where we took turns answering all of those pressing flex circuit questions that inquiring minds what to know. A couple years later, Nick and I took the show on the road and we have been speaking at PCB West, IPC APEX EXPO, and other events ever since.

Do your students ever get back to you with follow up questions?  How often and what is/are the most common question?

Koop: We often get follow up questions, some immediately after the session, others months or years later. We are always happy to answer a question once an actual situation arises.

Finstad: I agree. We tell our classes at the very beginning that we hope to give them some important tips on flex circuit design, but at the end of the day, there will be only two people walking out of the room as flex circuit design experts: Nick and me (and you of course when you were in attendance). But, we will leave each of them with an important tool, which is our business card containing our contact info, and we encourage them to reach out with any questions that they may have in the future. 

What are some of the biggest or most common challenges facing designers today based on your interactions with your students? 

Finstad: The biggest challenges seem to be how to make their flex circuits smaller (think earbuds) or bigger (think EV battery monitoring, drones, etc.). Going to the extreme in either direction can cause headaches for flex suppliers. 

What are some of the most common mistakes made by new flex designers?

Koop: Some common mistakes include:

1. Over dimensioning and/or tight tolerances. We are using flex materials, which permit looser tolerances and building in stress relief. These materials move with temperature and humidity.
2. Selectively removing layers from certain sections in an attempt to save money. In fact, it is the opposite.
3. Not using thick enough adhesive to fully encapsulate the copper features.

Do most designers avail themselves of and study IPC standards before beginning their designs? 

Finstad: Most seem to have some level of familiarity with the main specs like IPC-6013, IPC-2223, IPC 6011, etc. We reference the IPC standards often during our presentations and encourage our classes to procure these standards so that they can use them during the design process.

Do you think the use of Gerber files or the term Gerber will ever exit industry data packages or lexicon?

Koop: While the use of Gerber data will fade away, I don’t think the term will go away. It is kind of like “Kleenex.” I still hear some use the term “tape out” when referring to completing a design, which has not been done for forty years. Old habits die hard.

Finstad: The majority of data that I see coming from customers is Gerber and ODB++. Most zip files I receive contain both. I don’t see it going away anytime soon.  

What properties would you most like to see in next generation flex materials?

Finstad: While the mainstay flex materials (copper clad PI, and PI covers with thermoset adhesive) have not changed appreciably over the last few decades, they still make a pretty good circuit when properly designed. The newer releases of low loss thermoset adhesives have been very well received and are easy for the manufacturers to use. I personally would like to see flex materials that are significantly less hygroscopic. Absorbed moisture still causes a lot of problems for customers that are not aware of the requirement for pre-conditioning flex circuits prior to processes using elevated temps like solder reflow.

Based on your experience, roughly what percentage of flex designs are “flex to fit” as opposed to dynamic/active applications?

Koop: I would say that easily 95% of the flex designs are flex to fit. Dynamic applications are not that common. That said, vibration and G forces in flex to fit applications can present stresses equally as challenging as dynamic applications do.

You both have manufacturing experience, which is very important to your customers. I am confident we can certainly agree on that. What manufacturing equipment or equipment improvements would you most like to see to improve capabilities or yield? 

Finstad: The limiting factor for feature sizes is mainly imaging through etching processes. While the imaging equipment has really improved with the widespread use of laser direct imaging (LDI), the wet processing equipment has had only slight improvements over the last few decades (vacuum etching, etc). In order for improvements to have a significant impact, they have to be a joint effort between the etch resist manufacturers and the processing equipment suppliers. 

I greatly appreciate this discussion, and we can all agree we have just scratched the surface of flexible circuit technology. Is there anything else you’d like to mention?

Koop: I would recommend reaching out for help when working a new design. A second set of eyes is always useful and can help avoid a complete restart. I can be reached at nick.koop@ttmtech.com.

Finstad: Absolutely agree. A quick 5-10 minute call can set designers on the right path. I like to say, “We may not be able to tell you everything that can work, but with our four decades of flex circuit designs each, we can tell you pretty much everything that won’t work. By avoiding these pitfalls, you greatly increase your chance of creating a reliable flex design. You can reach me at mark.finstad@flexiblecircuit.com.

Conclusion
Many thanks to Mark and Nick for the important educational services they have been providing the industry for all these many years, and I trust for many more yet to come. I’m sure they are inspiring some young engineers to follow in their footsteps as they new professionals work up through the ranks to become educators one day.

By the way, Nick Koop is presenting an online class titled Flex and Rigid-Flex Design for Manufacturability starting May 12. To enroll today, click here.

Joe Fjelstad is an I-Connect007 columnist and founder and CEO of Verdant Electronics and an international authority and innovator in the field of electronic interconnection and packaging technologies with more than 185 patents issued or pending. To read past columns or contact Fjelstad, click here. 

Download your free copy of Fjelstad’s book Flexible Circuit Technology, 4th Edition, and watch his in-depth workshop series “Flexible Circuit Technology.”