Rigid Flex PCB Design Guidelines: A Complete Beginner’s Guide

PCBs are the backbone of every circuit and electronic device. They are present in our daily appliances, which makes them very crucial for us. A significant component of these PCBs is rigid-flex PCBs. They are very useful as they have flexible circuit boards that can easily bend and take up less space. They can even fit into tight spaces without damage. Flexible circuits are also advantageous for design packages where space is an important concern.

In this blog, we will discuss all the necessary guidelines for building a rigid-flex PCB design as a beginner. This guide will help you understand the basics and learn how to design one yourself.

What is a Rigid Flex PCB?

This specific PCB is a combination of two key qualities required for efficiency: rigidity and flexibility. Both of these qualities combine to form a rigid flex circuit. A rigid-flex design is typically composed of two or more rigid areas interconnected by a flexible strip. This way, while all the important parts of the circuit remain rigid and almost unbreakable, the connecting part is flexible. 

A rigid flex PCB design eliminates the need for connectors and interconnecting cables. These circuits are also easier to install, as the entire design is manufactured on a single PCB. But they can be a bit more complex to design compared to a normal PCB. 

Rigid-Flex PCB Design Guidelines to Follow :

If you’re designing a rigid flex PCB by yourself, it can prove to be a difficult task as you have to ensure quite a few things. Beginners may not have access to every tool or material that is required. You can follow these guidelines to ensure both mechanical and flexible aspects of your circuit board:

Gathering the Right Material 

You first need to understand if you want a dynamic or stable circuit board. The dynamic circuit board will allow you to bend your circuit far more. However, it will also require additional materials. You should select a polyimide material with a dielectric capability of 3.2-3.4. After that, remember to opt for an adhesive-free substrate as it will allow more flexibility.

Plan the Stack Up 

A rigid-flex PCB combines rigid FR-4 layers with flexible polyimide layers. You would need to carefully plan out how many of these layers will be flexible and how many will be rigid. This will help to create a ratio. You should also:

1. Keep high-speed signals on the rigid planes.
2. Limit the number of copper layers to reduce stress in them. 
3. Place power and ground planes to maintain impedance control.

Define Bend Areas

You should mark all the areas that will be rigid or flexible. Also, the bend radius must be high enough to prevent any copper cracking or fatigue.  Out of all the rigid flex PCB design guidelines, this is the most important. You should also avoid placing vias and components in the flex areas. Moreover, you can follow the rule of thumb. It states that the bend radius should be 10 times the thickness of the flex material.

Routing the Traces

Routing in flexible areas will differ from that in rigid regions. This is because only simpler routings can be made through the flexible areas. You should:

• Run traces perpendicular to the bend whenever possible.
• Space traces are slightly farther apart to reduce stress.
• Use curved traces rather than sharp angles to improve durability.

Component Placement

Component placement is also an important part of design in flex circuits. Since most components should not be placed on flexible areas, careful placement is required. The flex areas are meant for interconnection, not for heavy component mounting:

• Place connectors, ICs, and heavy parts on rigid zones.
• Only allow lightweight SMDs on flex regions if absolutely required.

Use of Software Tools

Software tools can be of great help, especially for beginners. Rigid flex PCB design software like Altium Designer, KiCad, or Eagle can help you visualize rigid-flex designs. These tools will let you define flex and rigid zones, stack-ups, and bending simulations before manufacturing.

Prototype and Testing

Once a design is complete, the next step is to create a prototype and test the circuit. This testing is going to help  you verify:

1. Signal integrity across rigid and flex areas
   
2. Mechanical bending strength
3. Reliability of solder joints and interconnects.

Once everything is complete and connections are properly made, your design will be ready to use. By following this set of rigid flex PCB design guidelines, you can ensure they’re properly designed.

Conclusion 

Designing a rigid-flex PCB is not a particularly difficult task. If you keep a few things in mind and follow this guide, you can create your very own flexible circuit. These circuits are of great help in almost all types of electronics. They can fit into tight and small spaces. Therefore, learning how to build one is important in the field of electronics. You can easily learn how to create a rigid-flex PCB design and then experiment with its applications and implications. 

Ready to learn more about PCBs and their construction? Visit Insight PCB for expert solutions, reliable repairs, and top-notch PCB services.