Cadence PCB Best Practices

Allegro/OrCAD Rigid Flex Design Creation Best Practices _______________________________________________________________________ Learn more at Cadence Online Support - https://support.cadence.com Page 5 © 2016 Cadence Design Systems, Inc. All rights reserved worldwide. D efault RIG ID FL EX a nd SURFACE FIN ISHE S S ub classes When a user defines a rigid-flex, flex, or an inlay style design, placing user-defined subclasses into related classes helps to maintain a better organized design data. For rigid-flex, it is practical to place structural materials into the RIGID FLEX class. It might be more viable to place plating, coatings, or other non-structural materials into the SURFACE FINISHES class. Creating the Physical Outline The common practice of using the BOARD GEOMETRY/OUTLINE subclass has changed in 17.2. Even though this subclass remains, because of the way this layer has been used historically, its initial purpose has been altered making this subclass unreliable for identifying the true outline of the design. A new BOARD GEOMETRY/DESIGN_OUTLINE subclass has been created as the main source of identifying the boundary of the design. As PCB Editor continues to be enhanced, more features can leverage this geometry as the proper 2D profile of the design. When updating a design from earlier releases into the 17.2 release, the geometry on the OULTINE subclass that can be identified as the board outline and converted into a shape will be copied to the DESIGN_OUTLINE subclass. The geometries in the OUTLINE subclass found in the interior of the board boundary are copied to the CUTOUT subclass. The geometries on the OUTLINE subclass determined to be outside the board boundary are ignored. Other import/export tools that use the new DESIGN_OUTLINE and CUTOUT subclasses are IDF, IDX, Artwork, and IPC-2581. The artwork command displays a pop-up warning that the artwork layers contain the OUTLINE subclass and do not include the DESIGN_OUTLINE subclass when the situation arises. If the DESIGN_OUTLINE subclass does not exist, the other interfaces report that in the log files. For these export tools, it is strongly recommended that the DESIGN_OUTLINE subclass be used for outline creation. Using the DESIGN_OUTLINE subclass for rigid-flex designs enables other objects related to rigid flex design to behave more effectively, such as stackup zones that trim to the design outline. When multi- stackup zones are added within a design, if required, certain keepouts are generated that are also trimmed to the ZONE and DESIGN_OUTLINE definitions. The DESIGN_OUTLINE geometry comprises a single unfilled closed polygon or shape. Only one DESIGN_OUTLINE geometry is allowed in a layout drawing. When IDX or IDF ECAD/MCAD exchange formats are imported or exported in 17.2, only the DESIGN_OUTLINE geometry is used. Voids are not allowed in the DESIGN_OUTLINE geometry. Cutouts in the design are now represented by the new subclass BOARD_GEOMETRY/CUTOUT. You may add as many CUTOUTs as needed in the design, each being an unfilled shape. Without importing a mechanical interface (IDX, IDF, and so on) for outline creation, defining the outline using shape editing tools can often become a challenge. Defining a complex DESIGN_OUTLINE geometry can be done by creating the design profile using the BOARD_GEOMETRY or OUTLINE subclasses for the initial profile creation. Using the Compose Shape command, the board OUTLINE can be copied to the DESIGN_OUTLINE subclass. In the following example, a board outline with cutouts is created using the OUTLINE subclass:

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