Flex-Rigid PCB – How to Make Your Product More Perfect

Printed circuit boards are the core of electronic devices and why customer electronics, smartphones, and many other products work like a charm.

Ordinary boards are useful, but there are situations when you need to utilize a restricted amount of space while optimizing performance. It is why you should consider a flex-rigid PCB, which is a mixture of standard and flexible boards.

Here is everything that you need to know about flex-rigid PCBs and their manufacturing technology!

1、Learn More About Flex-Rigid PCBs

It doesn’t take to be an industry expert to figure out what flex-rigid PCBs are. These boards use both worlds, and they mix flexible and rigid material during the manufacturing process.

If you isolate the board's rigid section, your PCB will look like any other ordinary board out there. It is a flexible part that makes this board unique.

You probably heard of flexible PCBs and their capability to bend and adjust the form to the application and space where you planned on fitting them. You also use these flexible materials in flex-rigid boards, and the only difference is that you mix them with “ordinary” materials. Thanks to that, you can get the best of both worlds, which should deliver the performance you were looking for in your application.

Image 1: Flexed printed circuit close up

2、Major Benefits of Using Flex-Rigid Technology

While ordinary PCBs can still be useful, the flexing capability revolutionized the market. Whether you choose a completely flexible board or start by trying a flex-rigid PCB, you can enjoy many benefits.

Here are some main advantages of utilizing flex-rigid technology:

• Choose the board's desired form–the benefit of flexibility gives you a lot of freedom when designing your PCB. You can take advantage of 3D space, which means there is no place where you can’t fir your board. That might lead to creative and unusual designs, but as long as you maintain optimal function and reliability, it is an approach you should consider.

• Reduced size and weight – the material used enables decreasing the overall size of the board and reducing its weight. The result is a compact and lightweight PCB that keeps the application light and small, which can be important for your needs or customer expectations.

• No solder joints – you don’t have to bother with additional connectors or solder joints because you put a flexible layer between rigid layers. That makes the manufacturing process easier and ensures improved reliability of the board.

Some other benefits include protection against chemical and UV exposure and using fewer materials, which should decrease the overall cost of your PCB.

Image 2: A flexible printed circuit

3、What Materials Should You Use for Flex-Rigid PCBs?

The key factor to consider when it comes to PCB performance is the material. Substrate materials should be your primary concern, and flex-rigid boards tend to combine flexible dielectric and adhesive films.

The most common choice in the category of flex materials is polyimide. However, you can also go with polyester if you are looking for an affordable solution, or PTFE (fluoropolymer) if your application is complex and advanced.

When it comes to the difference between the popular materials, we should consider the dielectric constant. Polyimide has the highest one, and it also can handle extreme temperatures while ensuring optimal mechanical and electrical characteristics. The downside of this material is that it has a high moisture absorption level, which is something you need to keep in mind.

Polyester is similar in relative dielectric constant and volume resistance, but it has better moisture absorption. However, it also has a limited heat resistance and doesn’t handle temperatures over 150C well (unlike polyimide, which can handle the heat of up to 400C).

PTFE is a costly material with incredibly low moisture absorption and solid heat resistance (up to 260C). While you can consider it for your application, and it is popular in aircraft and military industries. But the price is the reason why not many people use it these days.

The most common materials feature a mixture of epoxy, acrylic acid, and polyester when it comes to flexible adhesive films. The last two perform well in adhesion; they can handle heat and chemicals well and offer admirable flexibility. Keep in mind that you should keep the internal thickness at a maximum 0.05mm because of high thermal expansion potential.

Epoxy doesn’t have great adhesive properties, but you can use it on internal and stick covering layers. Its main benefit is resistance to thermal shock, which can come in handy during the manufacturing process.

Image 3: Electronic flexible circuit board

4、Flex-Rigid PCB Manufacturing Technology

Electronic devices remain the main application of printed circuit boards. It is why there is a need for excellent and consistent performance. That makes high-density interconnect (HDI) and embedded boards the most popular choice today.

Layer Stackup Manufacturing Method

The most common method of fabricating flex-rigid boards is via the layer stack method. Since these PCBs use a mixture of flexible and rigid layers, you stack the layers and use plated-through holes to connect them.

The structure involves a layer of flexible substrate material, covering film, prepreg, and rigid substrate material on top of it. You can choose between single and double-sided printed circuit boards, depending on your application.

The main benefit of this method is admirable reliability. Since connectors and harness can cause heat issues and other performance issues, flex-rigid PCBs resolve them and significantly improve devices’ reliability.

Although different manufacturing technologies have been used for decades, it seems that using FR4 as an external rigid layer and applying a solder mask to protect the circuit pattern is the best approach.

The experts recommend using polyimide as the substrate material for the flexible layer. But use copper to cover it, and acrylic/polyimide film for protection of the pattern. You should also laminate all the elements together.

Image 4: A flexible printed circuit

5、Embedded Flex Manufacturing Technology

If you want to use embedded technology to manufacture flex-rigid PCBs, you can do that, too. As the term suggests, you should embed flex circuits into rigid units and continue with the process of layering up your board.

In this case, you will use buried and blind vias for connecting the layers. You cannot use interconnections for rigid and flexible circuits in the same layer.

The benefits of using this approach include using fewer materials overall because you won’t waste a lot of substrate material. Additionally, you can reduce the overall size of the board while keeping a high level of performance. We should mention that it can also reduce the overall cost of your flex-rigid PCB.

Ultimately, whether you will go with the embedded technology or the standard layer stack up approach only depended on your applications and desired. It is vital to estimate which technology would work better for your needs. That includes cost, performance, and any other relevant considerations. Analyze all factors that will help you to make the right choice.

Image 5: A transparent flexible electronic circuit

6、The Most popular Industries for Using a Flex-Rigid PCB Design

We cannot neglect the increased popularity of flex-rigid PCBs throughout various industries. The demand for these boards pushes the industry experts to manufacture even better boards. These are the industries with the highest demand for flexible boards:

• Wearable technology – smartphones and tablets and smartwatches and fitness trackers all use boards with different flexibility. As we see new products with smart features every day, the use of these PCBs can only increase.

• Flexible displays – you may have had the chance to use a flexible PC monitor or a smartphone screen. These displays are the future, and we can thank printed circuit boards for that.

• Internet of Things (IoT) – things are still heating up, but there is no doubt that IoT will need many PCBs with the flexibility feature.

Image 6: A detail of a flexible printed circuit board connected to LCD

7、Reasons Why You Should Choose OurPCB for Your Flex-Rigid PCB Needs

Are you having problems choosing a manufacturer that can meet your flex-rigid PCB requirements? Not many companies can handle flex-rigid technology's specifics well and ensure the best results with every order.

One of the benefits of working with OurPCB is that you can rest assured our professional staff will follow your instructions to the smallest detail. That means you will get the board you wanted from the very start.

Check out some other reasons why you should stick to OurPCB:

1. State-of-the-art equipment – you need modern equipment to manufacture modern products, such as flex-rigid boards. That is why we have the latest machines and tools that enable us to meet even our users' most advanced demands.

2. Support throughout the entire process – are you in a dilemma which material would suit your board better? If you have any questions related to PCBs, we are at your service during the entire process!

3. Quick turnaround and delivery time – we care about doing things right, but we also want to do them quickly. We know you want your board as soon as possible, which is why we ensure swift order completion and shipping.

Image 7: PCB Processing on a CNC machine

8、Conclusion

We’ve reached the end of our article about the flex-rigid PCB manufacturing technology. There are many good reasons why you should go with this approach for your next application.

Flex-rigid designs are the latest technology available to users throughout the world. That is why you should consider using its advantages and improving your product!