Flex, Rigid-flex, and Rigidized Flex: What’s Right for You?

Estimated reading time: 7 minutes

I recently spoke with Mike Morando, director of sales and marketing for PFC Flexible Circuits and a contributor for Flex007. I asked Mike to discuss the latest innovations at PFC, as well as some of the trends he’s seeing in flex and rigid-flex circuits now. Mike also discusses rigidized flex, a technology that is an alternative to rigid-flex circuits—one that can save customers up to 20% compared to rigid-flex. Innovation in the flex arena never seems to stop.

Andy Shaughnessy: How’s it going, Mike? Long time.

Mike Morando: I’m doing great today. Yourself, Andy?

Shaughnessy: Great to be here. For anybody who’s not familiar with PFC, give us a brief background on the company.

Morando: Sure. PFC Flexible Circuits has been in business since 1997, in Ontario, Canada. We were acquired in 2018 by a OSI Systems, a $1.2 billion NASDAQ company. We reside in the Electronics Division that also includes Altaflex in Santa Clara, which does quickturn prototypes of flex circuits and assembly. And then there are other OSI group companies in Southeast Asia that do Microelectronics and wire bonding, contract manufacturing, box builds, cable assemblies, displays etc. It’s been a real great upgrade for PFC, quite frankly.

Shaughnessy: Right. So, what’s your sweet spot?

Morando: A lot of our business seems to be medical products. There’s a lot of development going on, obviously, in the medical industry. There are all kinds of opportunities for flex circuits in the realm of longer flex, and assembled flex, and flex with cameras. We’re seeing all kinds of wearable medical devices with sensors that are worn with Bluetooth capabilities, enabling the transmission and the ability to transmit sensor data. We’ve seen a lot of medical business. Department of Defense and military type applications are also on the rise, and we’re seeing a lot of that too.

Shaughnessy: You all do a lot of rigid-flex too, don’t you?

Morando: Yes, we do a fair amount of rigid-flex. I would say somewhere in the range of 30-40% is rigid-flex. We try to steer our customers, quite frankly, towards more of a rigidized flex just because it’s less expensive. You use rigid-flex if you needed to put components on two sides of the circuit. But if you don’t, then it’s very easy to do a multilayer flex with some kind of stiffener behind it, and then you can assemble the circuit on one side. 

Shaughnessy: Is this for flex that doesn’t need to be quite as dynamic?

Morando: Well, it’s still dynamic. It’s still rigidized, like a rigid-flex, and just on one side. So underneath it’s just a piece of FR-4. We don’t need to do plated through-holes all the way through the circuit. We just do everything on one side, and it allows us to do a rigidized flex. We’re doing stuff that’s 12 layers now, for example. That’s a flex circuit that’s rigidized. It’s not “flexible,” but it’s still bendable enough to have a three-dimensional shape. Because it’s bendable, it can make turns and so forth.

Shaughnessy: That’s a great idea. Now, when you have a new customer, do they come to you knowing what they want? Or is flex a completely new concept for them?

Morando: It’s interesting. There are two types of customers. There’s the ones that have never done a flex before, but really needs it. And those customers, quite frankly, are great because we train them, we become their experts, and they come back to us. It’s a great partnership. The other type come to us with a finished design already, and they’re looking for price. And since we’re a North American manufacturer, price is not what we sell on. We sell on our capabilities. The fact that we can do fine-pitch, high layer counts, and assembly all under one roof—that’s what customers come to us for. We’re ISO-9001 and 13485 approved for medical devices.

Shaughnessy: Shifting gears a little, what are you seeing as you look out at the flex market right now?

Morando: One of our divisions in Southeast Asia is working on microelectronics. We’re seeing opportunities there for flex circuits to become integrated into wire bonded areas, and more small microelectronic devices and substitutions for hard-to-get semiconductors. We’re always seeing flex and rigid-flex applications. I think the great thing about flex circuits, quite frankly, is the fact that it’s a three-dimensional design, and there are always opportunities to add value to a current electronic design.

Shaughnessy: When I talk to designers, some of them say they’re being forced into flex because they needed higher reliability. One of our contributors was designing boards for headphones, and the rigid boards we’re cutting it, so they went to flex and that was the perfect solution for reliability.

Morando: If you think about headphones, for example, there’s a rigid board and some wires, and the wires are somehow soldered to the board or there’s a connector involved. A flex circuit can offer a one piece solution, right? Flex takes the place of connectors, the printed circuit board, the wires, and the assembly. It’s all designed into one piece with a couple of components on it, and you’re done. And it is repeatable. That’s how flex adds reliability, and can lower the cost of assembly as well. In addition using a flex will save real estate by eliminating the connector. Ultimately, the solution becomes more reliable and less costly for assembly. As everything’s getting smaller, flex circuits become the perfect solution.

Shaughnessy: How hard is it for a rigid PCB designer to move into flex design?   

Morando: Quite frankly, to go from a printed circuit board design to a flex circuit design is not a huge leap. There are some idiosyncrasies between the rigid PCB design and flex or rigid-flex design. But this is mainly related to the Manufacturing rules and the fact that flex can bend. Manufacturers should preview the design and provide a DFM report that will steer the designer to a buildable solution. if a rigid printed circuit board designer looks at flex circuits as a solution, it’s not a big leap. You don’t have to have special training. I think we’re seeing more and more designers using flex as a solution.

Shaughnessy: There’s a lot of interest in flex and rigid-flex, especially. Every time we run an article on rigid-flex, we get a lot of reads.

Morando: Rigid flex is the most expensive approach. And that’s what I was saying earlier. Rigid-flex is great in some solutions, but if a customer could do a rigidized flex, they could save some money. They might save somewhere in the area of 20% by using rigidized flex.

Shaughnessy: Do you think rigidized flex will ever become a separate segment? Or is it very niche?

Morando: That’s a really good question. I just think it’s more of a matter of designing it in that direction, versus thinking, “I need a rigid-flex,” and then you design it that way. I think manufacturers could help out a lot if they just promoted the fact that if you can get all the components on one side of the flex, you’re good. With a rigid-flex, you have to remember that we’re encapsulating a flex circuit inside of a rigid printed circuit board. The whole process has so many more steps. 

Another thing that we’re seeing now is blind and buried vias in flex. Before, we didn’t do them, but now everybody wants blind and buried vias on their flex circuits and rigid-flex. They have their own challenges; there are some things that can’t be done regarding via fill. If you put via fill on a flex circuit, you’re going to have issues with it because you want it to be able to bend it. And if it’s got fill in it, it could crack, right? 

And sometimes our team can help prevent that from happening, starting in the design cycle. So, there are some things that we can do regarding via fill in blind and buried vias. That is a trend that we’re seeing more of. It just adds a lot of cost, and a lot of flex circuit shops don’t have the capabilities in-house yet to do blind and buried vias on flex.

Shaughnessy: This has been really interesting. Thanks, Mike.

Morando: Thank you, Andy. Good to see you.