Configuring Flex and Rigid-Flex PCB Materials in Altium's Layer Stack Manager

Summary:

This tutorial provides a comprehensive guide on setting up materials and commands for rigid-flex PCB designs in Altium Designer. Key topics covered include:

Understanding different flex stack-up types, such as flex ribbons and stiffened flex designs, and how they differ from rigid-flex assemblies.
The essential workflow for configuring flex and rigid-flex PCB materials using Altium's Layer Stack Manager.
Step-by-step instructions on creating flex sub-stacks, assigning materials like polyimide cores, adhesive layers, and coverlay.
Details on adding and removing solder mask, and adjusting layer thicknesses for accurate design.
How to convert a basic flex design into a stiffened flex configuration within Altium.
Tips for reviewing the advanced view of the stack-up to ensure material compatibility and correct configuration.

Introduction to Flex and Rigid-Flex PCB Design [0:00]

Host Zach Peterson introduces the tutorial, focusing on setting up materials and commands for rigid-flex designs in Altium.
The video will clarify different stack-up types and how to properly control and configure layers within Altium's Rigid-Flex design tools.

Overview of Flex Stack-up Types [0:50]

Flex Ribbon:
- Consists of copper layers with dielectric polyimide layers in between.
- Features an adhesive layer bonding copper to polyimide.
- Includes a coverlay, which is the flexible analog of solder mask.
Stiffened Flex Design: [1:31]
- Involves adding a stiffener (prepreg) bonded to one side of the flex ribbon.
- Purpose of stiffener:
  - Provides mechanical fixation.
  - Reinforces areas for component placement to prevent bending.
  - Allows for drilling through the entire stack for mounting holes without fatiguing solder joints.
Rigid-Flex Stack-up Construction: [2:46]
- Integrates a flex ribbon into a rigid layer stack.
- Involves rigid sections (prepreg, copper, core) above and below the flexible section.
- Rigid sections behave like standard rigid PCBs, allowing for component mounting and through-hole vias.
- It is possible to integrate multiple flex ribbons in different sections of the rigid stack-up, even in "book-binder" designs where layers are separated by air.
- This tutorial will focus on rigid-flex with copper above and below the flex, and basic flex with a stiffener.

Getting Started in Altium [4:44]

Enabling Rigid-Flex Mode: [4:50]
- Navigate to the Layer Stack Manager.
- Select "Enable Rigid Flex" from the options.
- This defines the selected section of the stack-up as a flexible region, allowing addition of flex-specific materials like coverlays and adhesives.
Basic vs. Advanced View: [5:36]
- The basic view shows a simplified layer stack.
- The advanced view visualizes where different materials meet and interact across various sections of the PCB stack-up.
- The recommended workflow is to start in the basic view, build individual materials, then use the advanced view for visualization and review.

Creating Flex Sub-Stacks and Assigning Materials [7:08]

Initial Setup:
- Start with a default PCB stack-up in Altium.
- Delete the default solder mask layer, as it's not typically used in simple flex ribbons.
Configuring Polyamide and Adhesive Layers: [11:01]
- Right-click on a layer, select "Insert Layer Below/Above".
- Insert a "Coverlay" layer.
- Insert a "Prepreg" layer and define it as an "Adhesive".
- Set thicknesses, e.g., 1 mil thick adhesive, 2 mil thick polyimide dielectric.
- Configure dielectric properties (e.g., dielectric constant 3.4 for polyimide).

Setting Coverlay and Solder Mask Thickness [15:02]

For basic flex ribbons, only coverlay is typically needed, not solder mask.
Adjust coverlay thickness in the properties.
In cases where a solder mask is required for rigid sections, ensure it's added correctly and its thickness is specified (e.g., 0.4 or 0.5 mils).

Converting to a Stiffened Flex Design [16:02]

Adding a Stiffener: [16:02]
- Create a new layer stack (e.g., "FlexCableStack").
- Enable the "Is Flex" option for this stack.
- Add top and bottom polyimide layers and adhesive layers, setting appropriate thicknesses (e.g., 1 mil adhesive, 2 mil polyimide).
- Insert a prepreg layer and define it as a "Stiffener".
- Modify the "Stiffener" stack to include a prepreg layer, ensuring it's appropriately thick (e.g., 10 mil or 20 mil).
Integrating Rigid Sections (Rigid-Flex):
- Create additional layer stacks (e.g., "BoardStack") for the rigid sections.
- Disable the "Is Flex" option for these rigid stacks.
- Add copper, core, and prepreg layers as needed for the rigid structure.
- Re-add solder mask layers for the rigid sections, ensuring proper thickness.
- Important: Verify material consistency and layer definitions between flex and rigid sections, especially at interfaces, by checking warnings in the advanced view. Resolve any material mismatches (e.g., ensuring adhesive thickness is consistent across adjacent sections).

Final Review and Next Steps [18:15]

After defining all sub-stacks and materials, use the advanced view in Altium's Layer Stack Manager to visualize the complete rigid-flex assembly.
Ensure all warning messages related to material mismatches are reviewed and addressed if unintentional.
The tutorial concludes by directing viewers to other Altium Academy videos for drawing these stack-ups in the PCB layout and defining bending regions and radii for static or dynamic flexing.