Blog  /  Rigid Flexible Circuit – The Ultimate Guide to the Most Effective PCB

Rigid Flexible Circuit – The Ultimate Guide to the Most Effective PCB

Most hardware engineers and inventors know what a Rigid-Flex is. It is both the most frustrating part of a significant circuit and yet is, at the same time, the most valuable and essential part of the course.

Its layout and components give it an edge above the rest of the PCB at an average inventor's disposal. More importantly, thanks to the orientation of the Rigid-Flex PCB, a designer can maneuver it around different parts of the circuit and connect other parts of the course.

Various problems come with using such a peripheral as it is also one of the most complicated Printed Circuit Boards to integrate. This guide will go over a Rigid-flex circuit board's basics, layout, problems, and solutions.


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1、Rigid Flexible Circuit--What is a Rigid-Flex PCB?


A Rigid-Flex Printed Circuit Board combines various rigid and flexible technologies that tend to make up a very diverse and effective combination of the two.

Unlike most Printed circuit boards, a Rigid-Flex PCB has multiple different layers of both rigid and flexible technology so that it may function at an optimum level without the risk of breaking.

Contrary to popular belief, the rigid-flex is not fragile; instead, it is in a steady state of a curve.

The shape of the Rigid-flex is similar to a spring, where if you stretch or compress it, it will return to its original state.

It is also right about the rigid Flex, except you can bend it whichever way you please, but it will return to its original position.

However, that doesn't mean that all Flex PCBs have a constant shape; various devices have a somewhat flexible PCB that allows them to have no regular form.

An excellent example of such PCB is printers, as they boast a flexible tape that allows them to move back and forth without any restrictions. The Flex PCB is one of the essential parts of a printer, as the machine can't print otherwise.


Image 1: Rigid Flexible Circuit


2、Rigid Flex PCB Design


To say that the design for the Rigid-Flex PCB is complicated would be an understatement; not only is it one of the most hectic PCBs to craft, but it is also a PCB that requires meticulous design.

Due to the various layers in a Rigid-Flex PCB, a designer must give intense attention to each layer so that one may not be different from the other or intersect the other.

So to better understand how a Rigid-Flex PCB works, let's dive deeper into its design and the many different layers of such a PCB.

Before we move on to the proper design of such a PCB, you must also consider certain factors.

Technology is always changing and evolving as the years go by; this means that people come up with new designs and methods of creating a Rigid-Flex PCB are and will always be different, so there is no absolute way of making a rigid Flex PCB.

Moreover, depending on the application of the rigid Flex and its purpose, the design and layout can be very different from the standard format, so keep in mind that the purpose of the PCB can significantly affect the creation of the PCB.


Rigid Flexible CircuitImage 2: Rigid Flexible Circuit


The thickness of a Rigid-Flex PCB is very subjective, as depending on the purpose of the build, the difference can be minor or incredibly significant.

The average board thickness for a rigid Flex PCB can be somewhere between 0.2mm and 0.4mm. 0.2mm is the average thickness of a single-layer PCB circuit, and 0.4mm is the average thickness of a PCB with nearly four layers.


Rigid Flexible CircuitImage 3: Rigid Flexible Circuit




The materials used to construct a proper Rigid-Flex PCB are copper and the adhesive material used to join the rigid and Flex layers.

Although the choice of material for this is extraordinary, to say the least, this unique adhesive prevents the copper from cracking or breaking.


Rigid Flexible Circuit--PCB Assembly


Combining rigid Flex PCBs is also a daunting task because there are too many variables to consider, which means you can make many mistakes that, in turn, destroy the entire circuit and application.

There are many different PCB assembly types, including Flip Chip, Wire harness, Ultrasonic Welding, and in-circuit testing, to name a few.

These other assembly methods have their benefits, and each is complicated in its own right.

Some designers and manufacturers use several of these methods in conjunction with other ways to create a Rigid-Flex PCB that is both durable and flexible.

All of these methods combine to make an effective and efficient circuit board.


Rigid Flexible CircuitImage 4: Rigid Flexible Circuit


PCB Design Considerations


When you are crafting your Rigid-Flex Printed Circuit Board, there are certain things that you must first take into consideration, as they can significantly reflect on the overall outcome of the application.

The first thing that you must consider is the electromechanical factors.

Whenever you make a PCB circuit, you must always think about electromechanical factors and how they will affect the result of the application.

First, you must consider the bend-to-thickness ratio; the thicker the wire, the larger the curve. If your circuit happens to be very thick, it can increase the risk of failure and sabotage the entire course.

Another consideration that you must also make is the bend line of every Rigid-Flex PCB. Seeing how nearly all flexible circuits have bend lines that significantly affect their routine, you should be careful not to place any components on or around them.

Furthermore, it would be best not to repeatedly bend the flex circuits as it stresses the various surface-mount pads and holes.

There is a remedy for this: you can use hole plating to reduce stress and add additional padding to anchor the places.

When designing your trace routing, you should also consider some practices that will reduce the stress you might otherwise experience on your flex circuit.

Use curve traces instead of 90° or 45° angles, as they can carry more power without the risk of bending and breaking.

You can also use hatched polygons so that your circuit may carry a ground or power plane without compensating for the flexibility of your course.


Image 5: Rigid Flexible Circuit


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3、Rigid Flex PCB's Technology and Production Process


The technology that most manufacturers use on a PCB differs depending on the manufacturer, type of PCB, and the efficiency of the PCB.

The efficiency of the PCB is one of the unique attributes of a rigid-flex PCB, as depending on the task of the PCB, the technology that a designer uses can differ significantly.

An excellent example is a rigid-flex in a printer and a 3D printer.

While both machines are accomplishing the same task, bringing a soft copy into a hard copy, the technology is significantly different.

Seeing how the purpose of the PCB greatly influences the technology being used in it, it will undoubtedly also affect the PCB production process.

At this point, it is obvious what factors can influence the production process, so rather than talking about the factors that influence it, we will discuss the process itself.

The production process of every PCB starts with stacking various layers of metal and other circuit boards. This part of the process is called the stack-up.


Rigid Flexible Circuit--The Stack Up

The stack-up is placing the layers for the rigid Flex printed circuit board. Depending on the Rigid-flex circuit board, the stack-up can be of one, two, or four-layer(s), and layers increase by the object's application and use.

Think of these layers as ingredients to a recipe, they all might be completely different from the other, yet they all combine to make for a delicious recipe, with each component adding greatness to the dish in some way, shape, or form.

The process is straightforward, but it is quite challenging to explain without a visual aid, so to explain the process better, look at the following diagram.


Image 6: Rigid Flexible Circuit


As you can see in the diagram, each layer takes center stage, and you can see the difference between each one. Now that you know the significant differences between these PCBs, the next two diagrams will show you all the components that go into making a PCB.

Note that this is a generic view of the components that make a PCB and that these components can significantly differ depending on the type of PCB you intend to make and its purpose.


Rigid Flexible Circuit

Image 8: Rigid Flexible Circuit


4、 Benefits of Rigid-Flex PCBs


They are moving onto what is possibly the essential part of this guide, the benefits. Why do people use Rigid-flex PCBs? To say that because it is somewhat elastic is to do this magnificent work of engineering injustice.

The Rigid-Flex PCB has many benefits other than just reaching and connecting other circuits, making it possibly the most versatile type of PCB in the world.

The first of the many advantages of a Rigid-Flex PCB is its customizability.

Some of you might be thinking that all PCBs are customizable; this PCB is a little different regarding customizability. Unlike generic PCBs that shape how the device will be, a designer can customize the size and shape of the Rigid-Flex to fit the device.

In other words, if you make a design that you like, but are having trouble making a proper PCB for it, then you can craft a rigid-flex PCB to fit the system better.

Another one of the many benefits of the rigid-flex is its compact and flexible design.

Thanks to the compact and flexible design of these printed circuit boards, various accessories' sizes can be significantly reduced.

The compact design of a rigid-flex board always gives way for more portable accessories and equipment that do not compromise functionality for size.

Rigid Flexible Circuit

The rigid-flex design also allows for more components in a particular device, significantly improving the overall product.

Thanks to the flexible system, the manufacturer can make various advancements and modifications to their design to accommodate multiple changes that can improve the overall product.

Rigid-Flex PCB is a famous choice among various mobile phone manufacturers, as it gives them the liberty to make a PCB that caters to the design and specifications they have in mind.

As the name implies, Rigid-Flex technology allows for the best rigid and flexible circuitry in their boards. This means that a Rigid-Flex PCB can give you all of the benefits that come with a stiff and flexible circuit without having any of its disadvantages.

It is possibly the single most significant advantage of a Rigid-Flex PCB. It can give manufacturers all of the positives of these two individual circuit boards without many negatives.

Another benefit of rigid-flex is its exceptional heat absorption capability. Unlike the other two types of these circuits, a rigid-flex PCB can take a lot more heat thanks to the technology used in these circuits.

The addition of polyimide to Rigid-Flex PCB makes it exceptionally resistant to heat, UV rays, and radiation.

This feat is more impressive because Rigid-Flex PCB is much less thick than its other counterparts. With the maximum height of a 4-layered PCB going up to 0.4 cm, a rigid-flex PCB is extremely thin yet more functional than other PCB.


5、 Rigid-Flex PCB Applications


The rigid-flex PCB has various applications in different types of accessories and equipment that we use daily. One of its most apparent uses comes in a smartphone application.

Nowadays, smartphones have to be incredibly thin yet very functional, which can only be achieved using rigid-flex technology.

Another famous application of rigid-flex PCB comes in various computer electronics, all of which use rigid-flex PCB.

One of the many components that use rigid-flex technology is the hard drive; it keeps up with the ever-increasing write speeds of today's computers.

Using a rigid flex for a hard drive is excellent as it keeps the hard drive cool even when it is working at its peak.

Rigid-flex PCB is also used in the field of medicine. Most recently, the pill cam allows you to see the inside of a person's stomach to examine the internal damage. This pill is made of well-designed rigid-flex circuits that are very effective.


6、Rigid Flexible Circuit--Rigid-Flex PCB Cost


The cost of a rigid Flex PCB is very different depending on the type of rigid Flex you get and where you get it. A rigid-flex PCB can have between one to four layers of other materials to make up the PCB.

The prices of a Rigid-Flex PCB vary greatly depending on the type of PCB you want and the layers it will contain.

It means that the price will increase or decrease depending on the type of PCB you require.

Another factor that makes up for the cost of the PCB is the developer or manufacturer.

Depending on the manufacturer, the price can be reasonable or absurd. However, this high price is justified by the fantastic quality of the product and the immense attention to detail that the more expensive manufacturer will give to your work.


7、Rigid Flexible Circuit--Conclusion


Rigid-Flex PCBs are one of the most important and useful in the current market.

Not only can they absorb much heat, but they can also make for a tiny and compact circuit that can be as effective as bigger circuits. Finding the right manufacturer to give you a cheap service without compromising quality can be very hard.

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