BoardSurfers: The Power of Nesting Stackup Zones

In the world of PCB design, the term stackup refers to the arrangement of different layers of materials that make up the board. These layers include the conductive and insulating layers and other components, such as vias and planes. A stackup is an important consideration when designing a board because it determines the electrical and mechanical properties of the board.

A zone is a specific area of the PCB where specific layers of materials are placed and where specific electrical or mechanical properties are required. By defining multiple stackups and creating zones in the board layout, you can optimize the design for electrical performance and manufacturability. This is particularly important in rigid-flex designs where different layer stackups are required in different parts of the design.

In Allegro® PCB Editor, you use Cross Section Editor to define multiple stackups, such as STACKUP_1, STACKUP_2, and so on. These stackups can then be assigned to specific zones on the board layout. For instance, you can create a zone, ZONE_1 in the layout and assign STACKUP_2 to that zone.

There are certain rules that need to be followed when working with stackup zones. You can read more about creating stackup zones here.

Nested Zones

A nested stackup zone is useful when an area of the board requires special solder mask coating or specific plating requirements. The mask or plating materials can be specified in the zone stackup. With nested stackup zones, you can optimize the stackup for different areas of the board while ensuring that the design meets the required electrical and mechanical specifications.

To create a nested zone within an existing zone, start by creating a zone for the enclosing region that meets the required electrical and mechanical properties. Within that zone, create a second zone for the new region that requires a different set of properties.

The zone nesting functionality of PCB Editor facilitates mask layer differences between an inner zone and its enclosing zone but requires the etch layers to match. This feature is important as it enables you to create stackup zones with different properties for specific areas of the board.

Overlapping Restrictions

A zone can be nested within another. However, intersecting or overlapping zones are not supported in PCB Editor. If a new zone overlaps or intersects an existing zone, the new zone is automatically trimmed to the boundary of the existing zone. This restriction ensures that there are no overlapping zones or gaps in the stackup that can cause electrical connectivity issues or affect the mechanical integrity of the board. Automatic trimming of a zone guarantees a well-defined and optimized stackup that meets the required electrical and mechanical specifications.

Conclusion

Nesting zones is an effective way to optimize a PCB design. By creating multiple zones with different properties and nesting them within each other, you can achieve precise control over the electrical and mechanical performance of their designs, resulting in high-quality and reliable PCBs.

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About BoardSurfers

The BoardSurfers series provides solutions to the various tasks related to the creation and management of PCB design using the Allegro platform products. The name and logo of this series are designed to resonate with the vision of making the design and manufacturing tasks enjoyable, just like surfing the waves. Regular, new blog posts by experts cover every aspect of the PCB design process, such as library management, schematic design, constraint management, stackup design, placement, routing, artwork, verification, and much more.