What Are Flex PCBs?

If you are familiar with the terms printed electronics, flexible electronics, or flexible circuits, you’ve probably heard Flexible Printed Circuit Board (Flex PCB) tossed around in the mix. Flex PCBs may also be called Flexible Printed Circuits—they are one and the same. The term has become more popular in recent years; thanks to the technology’s application in LCD TVs and bendable touchscreen smartphones. What exactly are they, though, and what capabilities can they add to our devices? We will answer all that and more, but let’s first define what it means for a circuit to be “flexible.”

Defining flexible circuits

According to PFC Flex, flex PCBs are thin and lightweight electrical circuits that can conform to small spaces. Flexible circuits usually consist of metal strips that are encased inside a material made from polyimide. The polyimide allows the circuit to be flexible in the first place and withstand damage, as well as hot temperatures. 

Flex PCBs often have one axis of flex at a time. This makes them different mechanically from e-textiles which often have multi-axis flex. They will also hold a bend if they are creased. Because of this, they often have some sort of bend radius limitation for use.  

Pros and cons of traditional flex PCBs 

Aside from their small size and light weight, there are many advantages to using flexible printed circuit boards. Here are just a few:

Pros

1. Ease of use

   Because of their printed circuity, flex PCBs are thin and can conform easily. Because they contain a flexible circuit, designers are able to experiment more freely. They can bend and move to meet specifications and can get creative with implementing them into projects.  Flex PCBs are produced using established processes, so they are also accessible.

2. Ease of integration

   This sort of goes along with our last point about ease of use, but flexible circuits can be integrated seamlessly. They can be added to everything; from something as basic as computer keyboards, to something as complex as solar satellites.    

3. Cost-effective 

   Flex PCBs are pretty cost effective, as well. Provided of course, they are made with stiffeners. Also, when compared with a rigid circuit board, they require less materials and manufacturing processes. It is important to note, however, that rigid-flex PCBs are an option and might even be a better one for certain applications.

Cons

1. Complex assembly 

   Flex PCBs are known to be a challenge to produce for two main reasons: Traditional components that are mounted to the circuit board must be able to withstand flexible movement, and making the circuits requires a great attention to detail which can make the production process time-consuming and less efficient.  

2. Mechanical limitations 

   Flex PCBs should not be creased and are generally meant to withstand a limited number of flexes. They also don’t have any elasticity, so they cannot conform to some surfaces that require tension for a good fit.   According to Machine Design, flexible circuits that are bent beyond 90 degrees are subject to more tension. Therefore, they will break more easily. In addition, if water or moisture enters the channels on a flexible PCB, the circuits will short and eventually fail. 

3. High initial cost  

   So, we may have said earlier that flex PCBs are cost effective in the long run, but that does not mean the cost to produce them can be high at the start. Often, flex PCBs require tooling that can cost thousands of dollars. 

Flexible PCBs vs. the LEL 

Drape comparison of the LEL (lower left hand corner) vs a flex PCB (center, bottom row)

There are several key differences between the LEL and a standard flex PCB. In fact, in many ways, they could not be more different. To refresh your memory, the LEL is a flexible soft circuit system (e-textile) that can provide lighting and heating capabilities to a wide variety of products. With that being said, here are some important distinguishing factors to note: 

• The LEL has a multi-axis flex, so it drapes easily. Whereas, the flex PCB is built to flex in one direction at a time.  

• The LEL is designed for large surface area applications, and the flex PCB is best when used in small areas.  

• The LEL has a natural give and elasticity, whereas the flex PCB does not.

Application Areas

Disk Drives

One widely used application of flexible PCBs is in hard disk drives. Way back in 2003, engineers at 3M integrated Electronic Design Automation (EDA) technology into an HDD flexible interconnect via Microflex circuits (Are you still with us? We know that’s some fancy language!). These thin, lightweight circuits allowed for a more compact disk drive.

Dashboard Systems

Another common application of flex PCBs is automotive dashboard systems and control panels. The great thing about flex PCBs is its removal of pesky wiring harnesses and ribbon connectors. So, not only is the labor greatly reduced, but the resistance on flex PCBs to vibration makes them ideal for use in vehicles.

Commercial electronics

Flexible PCBs are a great solution for designers of commercial electronics that want to increase the battery capacity, without increasing the bulkiness of say, a smartphone. Flexible PCBs have been utilized in the latest smartphones with bendable screens, such as the new Samsung Galaxy Z Flip and Motorola Razr.

The Loomia Electronic Layer (LEL)

Automotive Interiors

The LEL offers features in two main performance areas in automotive interiors: Seat and steering wheel heating and user interfaces. Each heating and user interface application can be custom-made to a product’s specifications to ensure seamless integration. The LEL can fit comfortably under textile surfaces (like steering wheel leather) for applications that require a tighter bend radius than a flex PCB can comfortably handle.

Medical Wearables

For medical and wellness applications, the LEL can provide wearables with high technical functionality. Our low resistance conductor makes for comfortable power and data cables that can be worked around the body.

Outdoor Goods

The LEL can provide outerwear and outdoor accessories (such as camping gear) with heating and lighting capabilities. The LEL is more fabric-like than most flex PCBs and can be easily integrated into products of varying sizes.  

Overall, flexible PCBs play a meaningful role in the electronics industry and they are even used within some LEL constructions for sensor, light, or vibration motor mounting. Aside from those listed above, flex PCBs have tight pitches for components. This means that they can fit in small spaces. At the end of the day, your decision to use these circuits really comes down to the project you are working on, and the needs of that project. We highly encourage you to do further research beyond this article to ensure you are choosing the best option that will result in optimal performance.  

Want to test the LEL’s capabilities before you decide? A sample is best way to do just that!