Customized Rigid-Flex PCB: The Ultimate Guide

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Oakley Mae

Home » Blog » Rigid Flex PCB » Customized Rigid-Flex PCB: The Ultimate Guide

Very few people realize that customized rigid-flex PCB technology has existed for over forty years.

Nowadays, these circuit boards are in use in high-performance applications.

They involve integrating layers of flexible and rigid materials to form one complex PCB. 

And what’s more, copper-plated vias connect the flexible inner layers with the rigid outer layers.

Furthermore, designers prefer these circuit boards thanks to their high reliability and flexible design options. 

Surprisingly, there is more to customized rigid-flex PCB than you already know.

This article will help you understand the custom rigid-flex PCB limitations, benefits, design, types, and applications.

Table of Contents

What’s A Custom Rigid-Flex PCB

These circuit boards involve integrating flexible and rigid circuit boards to form more complex boards.

We use copper-plated vias to connect the flexible inner and rigid outer layers.

The flexible layers, in this case, penetrate through the rigid part and are buried in the circuit board. 

Therefore, rigid-flex PCB borrows the rigid nature of rigid circuit boards and the bending and folding characteristics of flexible PCBs.

Surprisingly, their manufacturing process differs from flexible and rigid circuit boards. 

Moreover, these circuit boards have the durability of rigid PCBs and are resistant to harsh conditions.

Consequently, you’ll find them in use in military and medical applications. 

Custom circuit boards present a higher component density and more quality control.

This and their high flexibility make them ideal for use in limited spaces and compact devices wearables.

We recommend them for designing electronic components’ secure connections and for providing contact stability and polarity.

Benefits of Custom Rigid-Flex PCB

A flexible PCB

(A flexible PCB)

You’ll get the following benefits if you use custom rigid-flex circuit boards

Connection Reliability

As highlighted, the foundation of rigid-flex circuit boards is in connecting rigid and flexible layers.

This eliminates the use of a wiring harness to connect rigid circuit boards. 

Lower Part Count

You’ll need fewer parts and interconnections on rigid-flex circuit boards than on traditional rigid PCBs.

We can attribute the reduction in parts and interconnections to the elimination of wire harnesses and board-to-board connections. 

Flexible Design Options

Combining rigid and flexible substrates to make rigid-flex PCBs makes it easy to meet unimaginable and highly complex configuration requirements.

Moreover, you can use rigid-flex PCBs to integrate the following: 

  • High layer count
  • High complex configurations
  • Controlled impedance
  • Reduce interconnections

High-Density Applications

Since rigid-circuit boards free up space by eliminating hardware interconnections, they enable greater connection density.

Surprisingly, you populate the high-density SMT devices on the rigid parts of the circuit.

Additionally, the flexible layers connect the rigid layers ensuring the circuit is in a 3-D shape

Weight Reduction

One downside of a rigid-flex circuit is that they’re heavy, thus limiting their application in compact devices and wearables.

Fortunately, rigid-flex PCBs are designed with flexible materials, making them thin.

Therefore, they offer a high connection density and lower overall circuit board weight. 

You can use this low weight to design devices that withstand extreme vibration and shock. 

Custom Rigid-Flex PCB Limitation

Despite all the positives of custom rigid-flex PCBs, some negatives are worth noting. Check them out below: 

  • Production is labor intensive: Manufacturing rigid-flex PCB is labor and material intensive.
  • We can attribute this to these antenna PCBs’ sensitive nature and variation. 
  • Elaborate manufacturing: Generally, custom rigid-flex circuit board fabrication requires you to integrate a rigid and flexible substrate layer. Therefore, you’ll spend more manufacturing these PCBs than traditional circuit boards. 
  • Complex fabrication process: Customized rigid-flex PCBs undergo a very complex manufacturing process. Surprisingly, you’ll have to use complex and highly effective software. All these factors point to a high-cost production process. 

Custom Rigid-Flex PCB Types

A flexible PCB connecting a hard drive

(A flexible PCB connecting a hard drive)

Below are three custom rigid-flex circuit board types: 

  • Single-sided circuit boards: These rigid-flex circuits have only a single conductive layer. You can integrate your electronic components on the other side of your circuit boards. Generally, a single rigid-flex circuit board is easier to fabricate than other options. 
  • Double-sided circuit board: This option comprises a single flexible substrate and another single rigid substrate layer. Surprisingly, the rigid layer offers compactness, while the flexible layer offers flexibility. Moreover, a double circuit board allows more routing traces. 
  • Multilayer circuit board: This rigid-flex PCB has more than three conductive flex and rigid substrates layers. 

Choosing The Right Custom Rigid-Flex PCB Manufacturer

Custom rigid-flex circuit boards are difficult to design and manufacture.

Therefore, you can only get a good custom rigid-flex PCB from a good manufacturer. However, selecting one might be difficult owing to the high number of manufacturers in the industry. 

Luckily, we have highlighted the below tips to make your selection easy:

  • The best manufacturer should have the required certifications and comply with industry standards. These include IPC, UL, and ISO standards
  • It would be best to consider a manufacturer with long-term experience developing rigid-flex circuit boards. 
  • The manufacturer should produce high-quality materials by employing the best manufacturing procedures and using quality materials. 
  • Customer support should be outstanding in helping you, especially when you encounter challenges using the PCB. 
  • They should have the right machinery and equipment. Also, the technology they use should be up to date. 
  • Consider the large volume scales and how fast the manufacturer can produce circuit boards in bulk. This means you’ll get your circuit board without delay. 
  • You should consider the manufacturer’s storage conditions. In most cases, circuit boards get destroyed by high temperatures and humidity. Ensure the manufacturer will deliver the circuit boards in vacuum seals. 
  • The manufacturer should have qualified and professional personnel. Most of the time, you’ll interact with their technicians, and it will be better if they’re hardworking, welcoming, and professional. 
  • Finally, the manufacturer you select should guarantee in-house inspection and testing. This way, you will get a circuit board without errors. 

Custom Rigid-Flex PCB Design

Engineers assembling PCBs

(Engineers assembling PCBs)

Let’s take you through the steps of designing rigid-flex circuit boards: 

Base Material Preparation

Before starting the fabrication process, you must laminate the base material thoroughly.

This involves dipping copper into an acidic solution. Alternatively, we recommend the spaying method.

Afterward, you can coat the coil extensively. 

Circuit Pattern Generation

This step entails developing the circuit pattern and using screen printing or photo imaging.

With screen printing, you can deposit on the substrate surface. However, photo imaging is the most common technique. 

Etching

This process entails dipping your substrate in an etch bath. Alternatively, you can spray the etchant on your substrate.

For the best results, etch on both sides. 

Drilling

Next, you should drill the pads, holes, and vias. However, the drilling tools should sustain high speed to achieve precise holes.

We recommend the use of drilling to create very small holes. 

Through-hole Plating

The manufacturers should take maximum precision and care during this step. After drilling the hole, the manufacturer should deposit copper inside. 

Covercoat or Coverlay Application

Finally, it would be best to protect your circuit’s top and bottom sides by applying a covercoat or overlay.

This protects your circuit board from solvents and hostile environments. 

Application of Customized Rigid-Flex PCB

(A person wearing a smartwatch)

Customized rigid-flex PCBs find application in several areas. However, the following two stands out: 

Automotive Industry

We all know the automotive industry is experiencing new developments and innovations, especially with the introduction of electric vehicles.

Surprisingly, these vehicles require a high quantity of electronic components.

Therefore, it would be inefficient to use automotive wiring harnesses due to their connection complexity.

And this is where rigid-flex boards come in. 

Rigid-flex is replacing traditional PCBs in automotive since they offer flexibility and still have the tolerance to dynamic bending without getting damaged.

These circuit boards also work well in extreme conditions like high temperatures. 

The specific areas you’ll find custom rigid-flex circuit boards include navigation, entertainment system, and car display. 

Medical Wearables

We have seen an increase in the use of wearables like fitness trackers, smart clothes, and smartwatches in the medical field.

Most of the time, we use these devices to track our health and general well-being.

And since these devices are compact and small enough to wear on your wrist, there is no longer a need to use traditional rigid boards.

For this reason, designers are turning to rigid-flex circuit boards thanks to their high reliability and ability to work under stress.

Nowadays, it’s almost impossible to come across wearables with traditional rigid circuit boards. 

FAQ

How thick is a rigid-flex PCB?

The rigid-flex circuit board thickness varies from 0.4mm to 3mm. Surprisingly, the circuit boards are flexible regardless of the thickness.  

What material makes rigid-flex PCB?

Rigid-flex circuit boards are designed with substrate adhesives and conductor material.

In most cases, the substrate we use is polyimide or polyester, and the conductive material is copper.

Moreover, we use adhesives to secure the conductor and substrate material connection. 

What are the custom rigid-flex PCB characteristics?

The main characteristics of rigid-flex PCB are that they’re flexible and rigid simultaneously.

They combine the features of flexible and rigid circuit boards. 

Conclusion

As highlighted, rigid-flex circuit boards involve integrating flexible and rigid circuit boards.

Therefore, they borrow the folding characteristics of flexible circuit boards and the rigid nature of rigid PCBs.

They are either single-sided, double-sided, or multilayer circuit boards. 

Surprisingly, these circuit boards are highly durable and resistant to harsh conditions.

Moreover, they find major applications in the medical wearables and the automotive industry.

And since they have a complex manufacturing process, you should follow our tips above to select the best manufacturer.