Flex Cost Drivers and Next Gen Technologists, a conversation with Tara Dunn from OMNI PCB

Judy Warner
|  Created: February 20, 2018  |  Updated: February 5, 2021

PCB Design Podcast Announcement by Altium

More than ever, people design with Flex and Rigid Flex for the very first time as industries drive for smaller, more user-friendly devices. Join Altium's Judy Warner and OmniPCB CEO, Tara Dunn for a conversation on industry trends and cost drivers.

Listen to the Podcast:

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Show Highlights:

  • What is driving growth in the market? Space, weight, packaging.
  • Flex is everywhere especially handhelds and medical devices, uptick in flex and rigid flex PCB across every industry.
  • Three main cost drivers for Flex and Rigid Flex: Materials selection, Panel utilization and Technology.
  • And a fourth consideration - understanding your fabricator capabilities and making sure you’re matching your design to their capabilities.
  • Most materials: copper and polyimide.

Links and Resources:

OmniPCB Company website

Tara Dunn’s AltiumLive presentation


PCB Advisor site

Flex Talk

FlexFactor by NextFlex

Jabil’s Blue Sky facility in San Jose

Trade In Your Outdated PCB Design Tool & Unlock 45% OFF Altium today!


Hi everyone, this is Judy Warner with Altium's OnTrack podcast. Welcome back, if this is your first time we're glad to have you. Before we get going today I've got a great guest for you, but before we get going I wanted to remind you to please subscribe to this podcast, and you can follow us on iTunes, on your favorite RSS feed, or wherever, whatever app you like to use for your podcasts.

Today I have with me Tara, oh before I get going on Tara I wanted to also say, please follow me on LinkedIn and also on Twitter, I'm at Altium Judy, and Altium you can also follow us on Facebook, Twitter, and LinkedIn. Okay, Tara, hi my friend, so good to see you, welcome to La Jolla, California.

Thank you.

So, Tara was a recent, is a dear, dear friend of mine in the industry. There's not many of us women that have actually been in the printed circuit board business and understand how circuit boards are made, but we do indeed know how that's done, and Tara owns OmniPCB. She's based in the Minneapolis area, and she is a real flex expert, and we've been friends for, how long has it been now?

I don't know, what six or seven, eight years? Probably something like that. Anyways, Tara and I met at a trade show and instantly started introducing each other to our friends and colleagues and next thing you know, we just created this energy, and we both have written columns for iConnect 007. Tara has an event in Minnesota called Geekapalooza.

Which Judy helped bring out to California. California, so I brought it out here to Irvine, and then we brought it together to Boston, so we've had lots of professional adventures together, so it's my joy to have you and for us to

learn more about your expertise in flex. So, how are you liking La Jolla?

I know you're here for a few weeks, I bet you're glad to get out of the snow.

Oh yeah, it's no hardship to leave Minnesota winter this time of year.

I'm loving the sun and the beach, so like- What was the temperature when you left?

Minus five, something like that, and slippery roads and cars were going into ditches, we're driving to the airport I'm like "just please make it there so I don't miss my flight"-

Oh my gosh. -and I landed here, it was sunny and beautiful.

Right? I know.

I know, that's why we like it here. It's expensive to live here, but we love it.

So, welcome to the La Jolla office, anyways. So we want to talk today about your deep knowledge on flex circuits, which are becoming more and more commonplace, right?

You and I started out in our careers really focusing on Rigid FR-4, very standard boards, but it's really evolved now. Oh yeah, flex is a significantly growing portion of the market.

And what do you think's driving that?

Space, weight, packaging. You know, it's small it can be smaller, lighter, folded, it's really perfect for all of those electronics, the handheld electronics, medical devices.

Right. So what would you say, give us an overview, you just said medical devices, what other things are you seeing an uptick in the flex market?

You know, really across the board. Across all industries.


Absolutely. You know, we've got companies that have been working with flex that are developing maybe more complex flex or rigid flex and, you know, easily once a week somebody's contacting me brand new, just trying to figure out how to work with flex and how to design flex and what's different, what do I need to know. So a lot of new applications cropping up are people that are just trying it for the first time.

Well, that's why we invited Tara to be our flex expert at this year's Altium Live, and we'll share the link below but there's a really great presentation that Tara gave at Altium Live, and we have the video and her slide deck, so we'll share that at the bottom here so you can check into that later.

So, let's talk a little bit about that presentation. That was speaking a lot about cost drivers. So, for the designers and engineers listening, what are some of the just overview, basic overview, of what cost drivers are for flex and rigid flex?

Okay, so we often talk about three primary cost drivers, materials selection, panel utilization, and technology. I kind of like to throw, a little bit tongue-in-cheek but not really, a fourth one in there, which is understanding your fabricators capabilities and making sure that you're matching their capabilities with your design. Yeah. That's not just true in flex, by the way.

True, it's across the industry. It's across the board.

Yes. [laughter]

So, start with materials. How does that affect cost? Okay, so there are just so many materials you can choose from with flex, so, but just for this quick discussion let's focus on the most common which is copper and polyimide.

So, even focusing just on that segment, your fabricators are going to purchase laminates. They come in generally three different types which would be, two of them are adhesive-based, one with a standard acrylic adhesive, one with a flame retardant version of that adhesive, and then adhesive-less materials.

So, all of those types come in a range. Typically your copper thickness is going to be a quarter, or a half ounce to two ounces. It doesn't mean you can't get a flex circuit greater than two ounces, it just means that your fabricator has to create the material themselves.


And polyimide thicknesses are generally between half mil and six mil.

When you said your fabricator has to create that, does that mean they actually take the material and plate it up in their tanks, or you're buying a specialized material from the materials supplier?

Right, you would buy the polyimide, the adhesive and the copper and the thicknesses that you need.

So, like I said, huge range of options that you have when selecting materials for flex. So cost drivers, keeping that in mind, you know, why would you choose one over another or how does that progression go?

Typically, the adhesive-based options are going to be a little bit less expensive.

Okay. Okay, and they are typically used in single- sided, double- sided, maybe three or four layer flex is where you'll see those applications.

As you go into higher layer count, or rigid flex, the adhesive-less material becomes necessary. Highly recommended for rigid flex.

There's a z-axis mismatch between the FR-4 material and that acrylic adhesive, so you don't want to introduce the acrylic adhesive into the FR-4 stack-up.

So that's why, you know, your fabricators are always going to recommend adhesive-less materials.

All right, that makes sense. Mhmm. So, it's kind of like cost versus function-


-at certain point-


-that you need to keep in mind.

Right. So, other than materials, I know, what are other things that help drive the cost? I mean I think that's what people are afraid of, right? They think "oh flex is too expensive, I can't go that way" but they really need to go that way, route, for functionality, and I think really what you taught us at AltiumLive was it's not that cut-and-dry, right? If you evaluate all these different things then it may not be as expensive as you think.

Exactly, and as you decide to move to flex, you know, working with your fabricator on the materials side specifically can really help drive out cost.

Is it looking at just the raw material? You know, you're generally going to be FR, flame-retardant, material, LF adhesive, and adhesive-less, but if your fabricator is building a lot of rigid flex they're gonna stock more adhesive-less materials, and your adhesive-less material is gonna be probably less expensive-

Because they're buying more of it, they have it in stock you don't have to worry about minimum.

Make that match, and so finding someone that does a lot of flex and rigid flex is going to help you right off the bat. Exactly, and understanding the material sets that they're using, and you know a great way to do that is to ask their field applications engineering group to help you with a stack-up.

'Cause if you're not directing them in a certain direction they will default to the material that they're using most commonly.

So it's a really good way to make sure you're fitting that gap. Right. So what are some of the other cost drivers?

You know, we look at different types of coverlay. Coverlay kind of follows a progression.

So like, explain what coverlay is. So, with flexible circuits there's two types of coverlay.

There's a flexible solder mask, which is very similar to our board type solder mask other than formulated to be flexible but applied the same way.

It's a good option for circuits that might be single sided, double sided or less than two ounces of copper. Okay.

Tends to be a little bit less expensive. I see.

It does have a limitation in flexibility. It is flexible, but if you're having a highly dynamically flexing application it's probably not your best choice.

Right. But another advantage is it does allow you to form those nice 90-degree angles on your surface mount pads.

Of course. But when you need to, when you're concerned about reliability for flex life, the polyimide cover length, so it would be the polyimide that's the same as your base material and a layer of adhesive.

That would be the next option that you would want to go to. The limitations on that tend to be, you know, because you're drilling or routing that coverlay, you're gonna have a round or an oval opening.

Oh, okay. So as your circuits get more and more dense, it gets more and more difficult. We jokingly call it the Swiss cheese effect-

Right, you drill it and you take off the back route entry and there's not enough material there to even hold it together. You know, it looks great on the screen when it's this big but when the part's little. So your fabricator will watch out for that if you're doing a design. We all do try to minimize that impact.

The circuit board designer may be asked to gang open or, you know, make a larger opening over several pads to kind of alleviate that problem. And then continuing on that cost spectrum if you need the polyimide coverlay and you need that individual pad coverage, laser-cut coverlay would be the next option.

Okay. So that allows you to get the nice 90 degree angles for the surface mount pad, much tighter registration.

I would think from a cost standpoint too, in this case like laser cut, again a fabricator that doesn't do a lot of production of these kind of circuits may not have that equipment, may have to send it out, which drives the price up.

Exactly, exactly.

So, you know, I could see, that would be another benefit to making sure you're finding a fabricator that's really good at this technology.


Okay. Are there other areas or did we did exhaust that one?

I think on the materials, yeah I think that those are the two primary things to look at, is the base material and the coverlay.


So, it's always easy to kind of relate to that if we can hear a case study or an example that you've had, you know in your career, is there a couple stories you could tell us?

Sure, sure. So, there is a medical application, for example, and trying to reduce the material cost it was designed as a three layer rigid flex and flex being on the outer layer in that case.

Oh on the outer layer, okay.

Because of the three layers, okay?

So, but then in this case that required the flex to be button plated to maintain the flexibility and it required the circuit to have to be sent out to laser-cut for the coverlay to maintain the surface mount pads. So those two together required it to be done on a smaller manufacturing panel for the tighter registration.

So, very expensive circuit and very difficult to manufacture. After a review with a fabricator, they decided to go to a four layer rigid flex, more standard construction. So the material costs are higher but it eliminated the need for the laser cut of the coverlay, it eliminated the need for the button plating and it was processed more standard. So although the material costs were higher the overall cost of that flex circuit dropped dramatically. So it's not always about look at the material cost and run, right, it really is about collaboration, which you and I both over the course of our careers have sang that song, you know, in a variety of circuits right? It's not, but I can see how in the case of flex and rigid flex it's even more important, right, because there's all these variables.

Exactly, and that tends, flex and rigid flex tends to be a product that people are a little less sure of themselves when they're designing, have a lot more questions, so my advice is always to identify a few fabricators that you think will be good partners and then involve your fabricators early in the design. You know, because they're doing flex and rigid flex all day.


They've learned a lot of lessons so we all might as well take advantage of those lessons. Yes, absolutely, and that reminds me, another plug for Miss Tara is that she writes a column for the PCB 007 magazine monthly?

Yes. Monthly, specifically about flex- Yep, it's called Flex Talk.

Flex Talk, there you go.

So there's another resource that, and she usually covers a lot of these in that magazine and I always, I always look forward to reading your columns. So another case study?

Okay. A second case study I can think of is a military application.

The product was, I would say having probably 90% failure in the field after assembly. So, very very expensive after a fully populated board and what happened was it's a rigid flex and it was being bent and it was cracking.

So back to the drawing board, what can we learn from that?

Turns out, simply re-did the stack up and went from adhesive based materials to adhesive-less materials.

Oh wow.

So it eliminated only three mils thickness in the overall stack up but it was a thickness, and the bend radius was causing that cracking. So by making that one simple change in that stack up, you know they've had 300 assemblies completed now with no cracking at all.

And there's the expertise, right? Like who would know that three mils could fix that problem. I would have never guessed that in-

Yeah, it seems insignificant, especially when we're used to looking at thick rigid boards 3 doesn't seem like anything at all. It doesn't seem like anything at all.

That's so cool.

Well, thank you. Those are great stories.

You know, since you and I started in this industry, there were, I'm kind of shifting subjects now, a little bit and I wanted to talk to you a little bit about women in our industry. So, there are far more women in this industry now than there used to be. There still isn't that many of us who actually are on the front lines of sales and marketing that kind of thing. How did, I know I didn't end up in this industry on purpose. I love it and I love the industry, so how did you find your way, and I don't think I've ever asked you this?

I'm here completely by accident. See? We didn't do this on purpose.

No, my first job out of college was in the accounting department of a flexible circuit manufacturer. Okay, what was your major?

Economics and industrial relations. Well, there you go.

I didn't know what a flex circuit was when I started there. Right.

Because of that, they required me to work out on their manufacturing floor and learn how to build a circuit, so I was out on that manufacturing floor for a few months.

No way, I did the same thing but- Really?

Yes, yes I-

I'm so sorry to interrupt you, but the first circuit boards shop I worked at, and they had this whole language, these terms and things I'd never heard, you know what is SMOBC and I'm like, I don't know, solder mask over bare copper, and so I asked a production manager

I'm going to come in on Saturdays and he's like, I'll put you in every department.

That was like the best education ever, wouldn't you agree?

I agree and I totally didn't appreciate it at the time.


But looking back I would have never learned the process as well, because I was running equipment and, I'm really terrible at registering coverlay. I've learned this. It's not something I should do. I don't have that hand-eye coordination, but it was it was a good thing to learn.

Yeah, absolutely. That's so funny, I never knew that about you.

So, what do you think we can do to sort of encourage, I mean we're doing a lot to encourage women in STEM and encourage them to become exposed to these types of careers. What do you think would be a good way, or how are some ways that you've seen, oh I know one thing you're going to tell me about right!

Okay the Flex Factor program, Flex Factor, put on by NextFlex, so centered around flexible hybrid electronics, they have a program that reaches out to high school kids and it's an entrepreneurship program that ties in advanced manufacturing.

So they go to Jabil, they get to see all the cool things, it's a month-long program.

And this is in the middle of Silicon Valley?


So fun.

And I believe it's expanding beyond that.


I was lucky enough to be on the judging panel at the end of one of their last ones.

So much fun, but what it does is -  it takes students who may or may not be interested in a technical field, they might be interested in marketing or entrepreneurship, and it is a month program.

First week they kind of get the charter and you have to develop, it's about product development, what kind of need do you see around Health and Human Services and what how could you solve it using a product that's using advanced manufacturing?


And then they get to go into the fancy Jabil building and see all the really cool things that they do there. They tie that into the next step, is entrepreneurship at a community college, and the students are actually given credit, college credit for this program, and then the fourth and final week they need to pitch kind of shark tank style to a panel and go through the whole product development process, profit and loss, and I mean it's just it's an amazing program, and it's so fun to watch kids you know who, I talked to one girl

Jordan and she had really no interest in manufacturing or advanced manufacturing until, she wasn't exposed to it until this program, and now she's got a lot of ideas.

Which is so great! I don't know how kids otherwise would get exposed to manufacturing, and when you go into a facility like Jabil or TTM or some of these big facilities, you know I think kids think manufacturing is like a dark, dank building with, you know, I don't know, something awful and you go in and there's robotics and chip shooters and all this amazing high-tech equipment and these clean rooms and you have to wear the whole bunny suit and the glasses and you go in and you're like wow this was not what I was expecting and that's so great. I forgot that you told me about that program and the whole shark tank, which makes it so- oh it was so much fun.

-so what did the students pitch? Or like what are a couple things that the students pitched?

You know there was all kinds of different things. They tended to kind of centre around babies or athletes.


Well, different injuries that you might have as a student-athlete and how to rehab those injuries.

Oh, okay.

Or baby monitoring devices.

Oh that kind of, okay.


So, what was the winner? Was there, is there a clear winner, do you remember?

I don't remember who won for the panel I was on because they didn't announce it the day that I was there.

All right. And so you're continuing now, right? To be involved with this initiative, and is this gonna be each year, or how often do they offer it?

They do it throughout, throughout the year. I think they just had another round that went through so, and I might mix up the numbers slightly, but I think that the first program that they did which would have been the fall of 2016. I think they had eight students participate and its teams of four. So now they are up to thousands of students participating in this program. It's just growing and growing so fast.

We're going to make sure that we put that website, so you have to make sure and share that, the URL, so people that are listening can look into that. Such an exciting program and I, you know, here at Altium we're doing so much with the universities and stuff and I love to see it happening, and it's so fun when you see the light bulbs go on and, you know, we love our industry and we want to keep it vitalized.

Yes, yes. I think this is a great tool for generating some excitement. I know, I love it.

I want a program for people our age to go back and do that.

Right? Wouldn't that be fun?

Yeah. What would we call it?

I don't know, we'll have to think about that later.

So okay, here's a really wonky question I think I already know the answer but I'm asking anyway. Are you a nerd or a geek?


I asked the woman who runs Geekapalooza, that was a really easy answer.

I know, okay but why do you think a geek? Why is it not Nerdapalooza?

Like, why do you think you're a geek and not a nerd?

That is an excellent question.

Other than geek sounds better than nerd. See, I know, well- It's the general excitement over something that other people-

Right, like geeking out over something right? Geek Squad.

It's become cooler.

I think geeks are cooler than nerds still, like just generally. I think that's the consensus. And my other wonky question is, on a scale from one to ten how weird are you? Well, pretty high up there, yeah.

So like, what are some wonky things that make you weird?

You know, I -

Well first of all you're in this industry.

First of all it's the industry right? I laugh because I'll go out to have lunch, a work lunch, and sometimes I think if anybody is listening to our conversations, we're talking about impedance control and stack-ups and EMI and I'm like, what are they talking about over lunch?

I know I posted a video of me talking about fusion bonding on my personal Facebook page, and it blew up and people are like who are you? What are those words? They had no idea that I spoke this whole other tech language. And if you're out of the industry, you know, most of my friends, you know, my parents, my family, they don't know what I really do.

I know, I know. We're gonna put your podcast, this podcast.

We're gonna put this podcast on your- Can you cut that part out?

No we'll put it on this and see what they think of you on a podcast talking about coverlay. They'll be like what? And my final question would be, well, one thing I know about Tara Dunn is that you love the beach even though you live in the snowiest place in the country.

I live in a landlocked state.

Yeah, there's that. But I noticed that a lot of technical people have really interesting hobbies, so what kind of things you like to do with your family or places you like to vacation or things you like to do in you're very few off hours that you have Tara because you don't have a lot of off hours.

I don't, but with the job that I have it allows me to travel quite a bit because I can work pretty much remotely from anywhere and make that easy. So, yeah we love to travel.

Specifically the beach. It's one of my favorites or in the winter anywhere warm. Desert area, everything's great, and I don't know what happened this year but suddenly I've become a music buff.

Oh. I haven't been to a live concert in a few years and all of a sudden I think I have six or seven things booked so..

That's so funny.

I don't know why. It's because your son went to college and you have a little more free time. That could be it.

I don't know, I'm picking up new things now that my kids are out to college so that's probably the reason why.

Well Tara, thanks.

It's always a blast to hang out with you, and it's so fun to have you in California.

Thanks for having me here. Usually we're on the phone on conference calls and we actually get to see each other in person, it's fun.

So again we'll share lots of informative links for, that Tara has shared on this podcast and some that she didn't have time to talk about, we'll share them below so you can tap into all the interesting resources that Tara has, and I want to thank you again for what, for listening and or watching the OnTrack podcasts today. Please remember to subscribe at your favorite podcast app. Until then, always remember to stay OnTrack.

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About Author

About Author

Judy Warner has held a unique variety of roles in the electronics industry for over 25 years. She has a background in PCB Manufacturing, RF and Microwave PCBs and Contract Manufacturing, focusing on Mil/Aero applications. 

She has also been a writer, blogger, and journalist for several industry publications such as Microwave Journal, PCB007 Magazine, PCB Design007, PCD&F, and IEEE Microwave Magazine, and an active board member for PCEA (Printed Circuit Engineering Association). In 2017, Warner joined Altium as the Director of Community Engagement. In addition to hosting the OnTrack Podcast and creating the OnTrack Newsletter, she launched Altium's annual user conference, AltiumLive. Warner's passion is to provide resources, support, and advocate for PCB Design Engineers worldwide.

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