BoardSurfers: Exploring the Dimensioning Environment

Dimensioning features specify the measurements of different design elements, such as the board outline, mounting holes, components, and so on. Adding dimensions to a PCB design is a crucial step in the design process for conveying the design intent during fabrication and assembly to ensure that the manufacturer meets all the requirements to produce a successful product. For instance, if your design has critical mounting holes for mechanical components or installation inside an enclosure, they need to be clearly dimensioned to ensure proper alignment during assembly. Not dimensioning these critical components might result in more cost-effective manufacturing but runs the risk of resulting in ill-fitting components and other manufacturing defects.

Setting Dimensioning Standards

With the Allegro® layout editors, such as Allegro PCB Editor, you can use one of the several industry standards to document the dimensions of your design, including American National Standards Institute (ANSI), British Standards Institute (BSI), and Deutsches Institut für Normung or German Industrial Normal (DIN), among others.

The layout editor matches the default parameter settings to the standard in which you document the design. By default, the drafting and dimensioning parameters conform to the ANSI specifications for Dimensioning and Tolerancing. The dimensioning parameters in your design can be displayed and even modified without interrupting the active command. Additionally, the layout editor enables you to modify these settings to accommodate your unique dimensioning style. For instance, if you specify AFNOR, the layout editor provides all dimensions in millimeters. You can later change the Units parameter from millimeters to any other required unit.

Dimensioning Environment

The Dimensioning Environment helps you create and edit various types of dimensions. Use the Manufacture – Dimension Environment menu command or type dimension edit in the Command Window to display all the available dimensioning commands, such as Linear dimension and Angular dimension. You can create multiple dimensions within each command until you terminate the command or switch to a new one.

For details on the standard dimensioning capabilities, see Dimensioning in Allegro PCB Editor.

Associative Dimensioning

Allegro PCB Editor provides the associative dimensioning feature that attaches dimensions to the elements that they are associated with during creation. Without associative dimensioning, when a dimension is defined using multiple elements in a design, it detaches itself from the elements. For example, the distance between two components on the board. If these components are moved or deleted, the dimension is not moved or deleted with them; instead, it stays in the design as an independent floating dimension.

          

With associative dimensioning, if an element with an associated dimension is moved or deleted, the dimension follows suit. For example, the dimension showing the distance between two elements dynamically updates when one of the elements is moved and even disappears if one or both elements are removed from the design.

Using Dimensions with Detailed Views

Detailed views are separate expanded views of a particular assembly or section of a design that displays the assembly or section in greater detail. A detailed view helps in highlighting intricate sections of a design and provides a clear view of the dimensions used. For example, in a section of a design containing several parts with small dimensions in proximity, the dimensions might appear too crowded and difficult to read in the default view. A detailed view can be beneficial in such cases as it provides an uncluttered view of the densely packed dimensions.

To create a detailed view, choose Manufacture – Drafting – Create Detail or type create detail in the Command window. There are two steps in creating a detailed view:

1. Selecting an area of the design to be enlarged.
2. Positioning the enlarged view in another section of the drawing.

The layout editor automatically copies the geometric information (electrical, logical, and property information is excluded) of all the visible elements in the selected area and enlarges them by a user-defined scale factor. By default, the scale factor is set to 2, which means the enlarged view is twice the size of the selected area. You can edit this value by changing the Scaling Factor setting in the Options panel of this command.

Conclusion

Well-defined dimensioning and drafting practices go a long way in making your designs cleaner and more organized. Dimensioning helps ensure adherence to industry standards which leads to greater accuracy and control over your manufacturing processes.

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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.