How To Design 3D Rigid-Flex PCB

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There are three primary varieties of printed circuit boards that exist today—rigid, rigid-flex, and flex. They have different construction and design, yet, they serve the same purpose. For instance, flex PCBs can be bent and tailored to fit certain products or systems, but rigid boards cannot. On the other hand, a rigid-flex PCB is a combination of both, as the name suggests.

A rigid-flex circuit board is made by combining hardboard and flexible circuits. Although some layers in a rigid-flex PCB house flexible electrical components, the manufacturing process is similar to that of a conventional circuit board. The board manufacturer will only add plated through holes to join areas of a flexible circuit board with layers of a rigid circuit board.

flex-rigid pcb

These boards are suitable for dynamic flex applications, which involve continual bending. A rigid-flex board that has been properly built can sustain hundreds of thousands of flex cycles without breaking. With that out of the way, here are a few guidelines for designing 3D rigid-flex PCB.

Step-by-Step Guide For Designing 3D Ridig-Flex PCB

Consider The Electrical Parameters

Before doing anything else, You should learn the system's electrical specifications. These include:

  • Impedance properties
  • Capacitance restrictions
  • Voltages
  • Maximum current
  • Shielding
  • Schematic and wire listing
  • Location and type of connectors and components

Design The Schematic

Making a schematic, which refers to your circuit board's overall representation, shape, and design, is always one of the first steps in PCB design. At this stage, it's crucial to consider your PCB's flexibility. Do you have a static or dynamic board? Unlike a static board, which can only bend a few times until failing, a dynamic board must be able to withstand a lifetime of bending.

Create Your PCB Layout With Schematic Capture Software

The ideal layout supplier will collaborate with the key engineers to create a layout using a software program like Altium, Allegro, or Mentor® PADS. This software will demonstrate how components on your rigid-flex circuit board will be placed and how your PCB will look and function. After your layout is finalized, the mechanical engineer will load the PCB design file and decide how it will fit in a particular device.

That said, it is also critical to consider the material you will use in your 3D rigid-flex PCB. These boards typically have looser outline tolerances than other types of PCBs. Some of these materials include:

  • Cover layer and Insulator

The most commonly used Insulator and dielectric in rigid-flex PCBs is polyimide. It serves as the cover layer for the flex circuit, insulating the copper conduct.

  • Conductor

Because it is highly conductive, copper foil is commonly used in a 3D rigid-flex PCB. Furthermore, using little copper is sufficient for the PCB your rigid-flex board function. Additionally, it can be obtained in a low temperature or completely annealed form, improving its bendability.

Create Rigid-Flex PCB Stackup

The Stackup affects how the mechanical and electrical engineers design and place the PCB into an electronic device. However, the strains that a rigid-flex circuit board receives due to the bends and curves of the PCB are a crucial aspect to consider when creating a Stackup. So, here are four suggestions that will enable you to design a sturdy rigid-flex PCB Stackup.

  • Keep vias in stiff sections at least 50 millimeters apart from the flex board's edges when installing them. This is because the edge of the rigid-flex PCB is unstable. After the drilling operation is complete, the 50-millimeter gap guarantees higher material durability.
  • Teardrops should be used to route traces to the via, expanding the copper to create a stronger connection to the via itself. This will help you strengthen your board and decrease premature wear and tear.
  • Make sure vias don't become worn out or start to peel after prolonged usage. Use vias in the flex part at least ten millimeters in diameter. Furthermore, add another ten millimeters to the total diameter to create a broad anchoring point to the polyimide surface.
  • Place the flexible layer of your PCB in the center of your Stackup design to reduce the chances of breakage.

Consider PCB Design Regulations And Rules

The requirements and acceptance standards from IPC, the industry association for PCB and electronics manufacturing, essentially guide this stage of the rigid-flex circuit board design process. You can learn all you need to know about PCB manufacturing from these standards on their website. However, choose a PCB layout vendor that knows IPC rules and regulations to prevent extensive changes and project delays.

Place Electrical Componenets

When it comes to component placement, the client and PCB/layout supplier will frequently negotiate design and layout parameters. For instance, certain components may not be allowed to be positioned next to others according to rules because they induce electrical noise in the circuit.

Every component (usually connectors) has a datasheet, which you should use to create a component layout on your 3D rigid-flex PCB. If you're using a third-party vendor, they will help you decide which component placement is the best.

Add Drill Holes

The component and the connection type typically guide this step. As most PCBs available in the market are multi-sided circuit boards, there need to be drill holes forming connections between the layers. Discuss with a PCB layout designer to ensure you make correct connections for your components and layers.

Route Your Traces

After you've created drill holes and placed your desired components, the next step in the 3D flex-rigid circuit board design process is to route the traces. This is usually done to make connections between components and layers.

Any good PCB design software will allow you to route traces easily. If you don't know how to do this, a quick online tutorial will allow you to learn the trace routing process for your choice of PCB layout design software.

Create Layout/Design Files

The last step in the flex-rigid board design process is to save your project and generate layout/design files. These files contain information that the PCB manufacturer will utilize to design a physical rigid-flex PCB.

Benefits Of A 3D Rigid-Flex Circuit Board

Listed below are a few benefits of using a rigid-flexible circuit board:

  • High-temperature tolerance
  • High tolerance against environmental elements
  • Excellent reliability
  • Improved duty cycles
  • Space saving
  • Low noise
  • Low cost
  • High signal integrity

Wrapping Up

The benefits of using a rigid-flexible PCB over other circuit board types are endless. These tiny circuit boards are lightweight, space-saving, and reliable. As a result, these boards are used by several electronic companies worldwide in various gadgets and electronic products. So, if you're working on a project requiring printed circuit boards, then rigid-flex PCBs are the way to go.

Hopefully, the steps mentioned in this article will give you an excellent idea of designing a 3D rigid-flex PCB. If you want to learn more about what these PCBs are and various other circuit board design tips and tricks, visit Hemeixin today!

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