Understanding Rigid Flex PCB Stackup: A Deep Dive

Rigid flex PCBs  are becoming increasingly popular in the electronics industry due to their ability to combine the best features of both rigid and flexible PCBs. However, designing a rigid flex PCB stackup can be a complex process that requires careful consideration of the layer structure, material selection, and manufacturing constraints.

 In this article, we will take a deep dive into the world of rigid-flex PCB stackups, exploring the key factors that need to be taken into account to ensure a successful design. Whether you are a seasoned engineer or a newcomer to the field, this article will provide valuable insights into the world of rigid flex PCBs.

What is rigid-flex PCB stackup?

Rigid-flex PCB stackup is a type of printed circuit board (PCB) that combines both rigid and flexible PCBs into a single unit. This type of PCB is commonly used in electronic devices that require both flexibility and rigidity, such as medical devices, aerospace equipment, and military applications. Rigid-flex PCBs are designed to be compact, lightweight, and able to withstand high levels of stress and vibration.

The stackup of a rigid-flex PCB consists of multiple layers of rigid and flexible materials that are bonded together with adhesive layers. The rigid layers are made of fiberglass or other reinforced materials, while the flexible layers are made of polyimide or other flexible materials. The layers are then arranged in a specific order, with the rigid layers on the outside and the flexible layers on the inside. This stackup provides the necessary flexibility and rigidity in the appropriate areas of the PCB.

Flexible-PCB-Assembly_Noise-Remove-Quality-Enhance_x1 new
Rigid Flexible Circuit

What are the advantages of using a rigid flex PCB stackup?

A rigid-flex PCB stackup is an innovative solution that combines the benefits of both rigid and flexible PCBs. It is a highly valuable technology for manufacturers looking for a robust and dependable PCB design. Here are some of the advantages of using a rigid-flex PCB stackup:

  1. Reduced Assembly Time: Using a rigid-flex PCB stackup significantly reduces the assembly time, as it eliminates the need for multiple interconnects and connectors. With fewer interconnects, there are fewer chances of errors, and the overall assembly time is reduced.
  2. Improved Reliability: Rigid-flex PCBs are known for their excellent reliability. They are highly resistant to vibrations, shocks, and other environmental factors that can affect the performance of traditional PCBs. The rigid-flex technology also allows for a smaller form factor, making it ideal for devices with limited space.
  3. Enhanced Durability: Rigid-flex PCBs are highly durable and resistant to wear and tear. They are less prone to damage, breakage, and corrosion, making them ideal for high-stress applications.
  4. Higher Design Flexibility: Rigid-flex PCBs provide greater flexibility in design, as they can be customized to suit specific requirements. They allow designers to create complex designs in smaller form factors, making it ideal for applications where space is a constraint.
  5. Cost-Effective: Using a rigid-flex PCB stackup can be more cost-effective than using multiple PCBs and connectors. It reduces the number of components required for assembly, which ultimately reduces the overall cost of production. Additionally, since rigid-flex PCBs are more reliable and durable, they require less maintenance, resulting in cost savings in the long run.
​Rigid-flexible circuits can be designed and fabricated in two dimensions and assembled in three dimensions.

How many layers can a rigid-flex PCB stackup have?

A rigid-flex PCB stackup can have multiple layers, typically ranging from two to eight layers. The exact number of layers depends on the specific requirements and design of the circuit.

In a rigid-flex PCB, the circuit board consists of both rigid and flexible areas interconnected by plated through holes. The rigid areas provide stability and support for components while the flexible areas allow the board to bend and conform to the shape of the product it is being used in.

The number of layers in a rigid-flex PCB stackup is determined by several factors, including the complexity of the circuit, the size of the board, and the space available within the product. However, adding more layers can increase the cost of production and may not be necessary for every design.

It is important to note that the design of a rigid-flex PCB stackup should always be done with the help of an experienced PCB designer who can ensure the proper placement of components and the appropriate routing of traces. Proper planning and design can help prevent issues such as signal interference and electrical noise, ensuring the reliable performance of the circuit.

1 layer flex with optional fr4 stiffeners and PSA
2 Layer Flex Circuit with ZIF Contact Fingers
2 Layer Flex Circuit with ZIF Contact Fingers
4 Layer Rigid-Flex PCB (2 Flex Layers)
4 Layer Rigid-Flex PCB (2 Flex Layers)

What type of substrates are typically used in flex rigid PCB stackups?

Rigid-flex PCBs have a unique construction that is designed to provide both flexibility and rigidity to the circuit board. These boards are used in a variety of applications, including aerospace, medical, defense, and consumer electronics. The substrate materials used in a rigid-flex PCB stackup are carefully chosen to provide the necessary properties for the design.

The rigid portions of the board are typically made from a layered substrate material such as FR-4 or polyimide. These materials are chosen for their ability to provide structural support to the board while also allowing for the creation of complex circuitry. FR-4 is a popular choice for rigid portions of the board due to its high heat resistance and low cost. Polyimide, on the other hand, is a more expensive option but offers superior flexibility and heat resistance.

The flexible portions of a rigid-flex PCB are typically made from a polyimide material. Polyimide is a thin, flexible material that is able to withstand repeated bending and twisting without cracking or weakening. It is also highly resistant to heat and chemicals, making it an ideal choice for these applications.

In addition to these substrate materials, manufacturers may also use other materials such as copper and adhesive layers to create a complete rigid-flex PCB stackup. The adhesive layer is used to bond the rigid and flexible sections of the board together-

What is the best way to bond the layers in a flex rigid PCB stackup?

When it comes to bonding the layers in a rigid flex PCB stackup, there are a few different methods that can be used. Ultimately, the best approach will depend on the specific requirements of your project and the materials you are working with. Here are some of the most common options:

  1. Adhesive bonding: This involves using an adhesive material, such as epoxy or acrylic, to bond the layers together. Adhesive bonding can be a good choice for applications where there is a need for a strong, durable bond. However, it can also add weight and thickness to the PCB, which may not be desirable in all cases.
  2. Lamination: This involves using heat and pressure to bond the layers together. Lamination can be a good choice for applications where a thinner, lighter PCB is desired. However, it can also be more difficult to control the thickness of the layers with this method.
  3. Surface treatment: This involves treating the surfaces of the layers so that they bond together more effectively. This can be done through a variety of methods, such as plasma treatment, corona treatment, or chemical treatment. Surface treatment can be a good choice for applications where a strong bond is needed but weight and thickness must be minimized.
  4. Mechanical fasteners: This involves using screws, bolts, or other mechanical fasteners to hold the layers together. Mechanical fasteners can provide a very strong and durable bond, but they can also add cost and complexity to the PCB design.

How to Define a Layer Stackup for Rigid Flex Designs?

Creating a layer stackup for your rigid-flex and flex designs involves selecting the appropriate material, defining the number of layers, and determining the thickness of each layer. It also requires considering the bend radius and flexibility of the design. Here is a video about how to create a layer stackup for your rigid-flex and flex designs:

How does a rigid-flex PCB stackup differ from a standard PCB stackup?

A rigid flex PCB stackup differs from a standard PCB stackup in several ways, primarily due to its unique construction. A rigid flex PCB combines both rigid and flexible materials to create a single board, resulting in a more versatile and durable design.

In a traditional PCB stackup, the board consists of several layers of rigid substrate material, typically made of fiberglass or other reinforced plastics. These layers are laminated together using an adhesive material, with each layer containing traces and vias to create the necessary electrical connections.

In contrast, a rigid flex PCB stackup typically consists of alternating layers of flexible polyimide material and rigid substrate material. The flexible layers allow the board to bend and conform to a specific shape or design, while the rigid layers provide support and stability where needed.

The overall construction of a rigid flex PCB stackup can vary depending on the specific design requirements. For example, a board may consist of multiple rigid sections connected by flexible sections, or it may be a continuous flexible design with embedded rigid areas.

Another key difference between a rigid flex PCB stackup and a traditional PCB stackup is the use of different types of vias. In a rigid flex PCB, blind and buried vias are commonly used to connect the flexible and rigid layers, allowing for a more compact and efficient design.

What steps are involved in creating  rigid flex PCB?

Rigid flex PCBs are becoming increasingly popular in the electronics industry due to their unique design and versatility. However, creating a rigid flex PCB stackup requires specialized knowledge and attention to detail. In this blog post, we will outline the essential steps involved in creating a rigid flex PCB stackup.

  1. Design the Circuit: The first step in creating a rigid flex PCB stackup is to design the circuit using a PCB design software. The design should include all the necessary components, including resistors, capacitors, ICs, and connectors.
  2. Determine the Number of Layers: After designing the circuit, you need to determine the number of layers that will be required to accommodate the circuit. The number of layers will depend on the complexity of the circuit, the availability of space, and the flexing requirements.
  3. Choose the Right Materials: The choice of materials is critical in creating a rigid flex PCB stackup. You need to choose materials that can withstand bending and flexing without breaking. The materials should also be able to withstand high temperatures, humidity, and other environmental factors.
  4. Determine the Stackup Configuration: Once you have chosen the right materials, you need to determine the stackup configuration. The stackup configuration refers to the arrangement of the layers and the materials used for each layer.
  5. Plan the Copper Traces: The copper traces are an essential component of the rigid flex PCB stackup. You need to plan the copper traces carefully to ensure that they are aligned with the circuit design and can accommodate the flexing requirements.
  6. Design the Vias: As mentioned earlier, a rigid flex PCB stackup uses different types of vias to connect the flexible and rigid layers. You need to design the vias carefully to ensure that they are placed in the right location and can withstand the flexing requirements.
  7. Test and Verify: Once the rigid flex PCB stackup is designed, it needs to be tested and verified to ensure that it meets the design specifications and requirements. This may involve conducting various tests, such as thermal cycling, vibration testing, and flex testing.


Overall, designing a successful rigid flex PCB stackup requires a deep understanding of the materials, layer configurations, and flexing requirements. It is important to work with experienced and knowledgeable designers and manufacturers to ensure that the design meets the necessary standards and specifications. By taking the time to carefully design and test the rigid flex PCB stackup, it is possible to create a reliable and durable product that can meet the demands of today’s fast-paced technological landscape.


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