Implementing Complex Pad Shapes into Your PCB Designs
Table of Contents
Most component package types have consistent and straightforward rectangular or round pad shapes. Creating footprints for such packages, either manually or using an automated IPC footprint generator, is a simple process. However, component packages occasionally require complex pad shapes that can result in significant manual effort as well as additional time spent to get it just right. What if there was a way to quickly implement complex pad shapes into your printed circuit board designs to save you time and energy?
In some instances, geometrically complex or irregular shaped pads may be required in your designs. For example, LED lighting components can require uniquely shaped heat dissipating pads that include multiple inverse curves. Such curves are impossible to implement by combining multiple standard round/rectangular pads or by manually placing fills or solid regions. However, an often overlooked method exists whereby if the outline of the required shape can be placed (or imported) as a series of tracks and arcs forming a closed outline, then the outline itself can be easily converted within the PCB Editor to a precisely-shaped solid region defining the pad. Furthermore, solder and solder mask can be automatically controlled by DRC rules through a property setting of the region object. To better understand this method, the entire process can be explored by creating a PCB footprint for a Bourns SRR5028 series shielded SMD power inductor as described below. To get started, a datasheet for this example from the manufacturer’s website can be found here for part number SRR5028-101Y. Each pad of this two-pin device includes an inverse curve with a 2.2 mm radius. Now let’s explore how to define pad shape outlines using the example provided in the datasheet.
In the recommended PCB layout section of the SRR5028 series datasheet, the key dimensions of the component pads are illustrated relative to the component origin. Within the PCB Editor, six lines and one arc are placed on a mechanical layer to capture these critical dimensions of each pad relative to the component’s origin (see Figure 1). The precise size and placement of these lines and arcs are then verified to be exactly in accordance with the manufacturer's dimensions as shown in the datasheet. Setting the snap grid to 0.05 mm within the PCB Editor ensures the manufacturer's dimensions can be precisely replicated.
Now that the critical dimensions of the component pads have been placed and verified, any extraneous lines or arc segments can be sliced, resized or removed altogether so that the end result is just two closed outlines on a mechanical layer, where each represents a pad shape. In this example, the closed outlines were manually created and verified. Alternatively, you can import complex pad shape outlines from DXF/DWG format if such data happen to exist and are more practical to use.
Occasionally, some components will require complex or irregular shaped pads as per manufacturer’s recommended layout. Always remember that an easy and efficient solution exists to implement complex pad shapes quickly. By creating or importing a precise outline of the complex pad shape using tracks and arcs, the result can be converted to a solid region object.
Interested in learning more about the available methods for quickly implementing complex pad shapes in Altium? Download a free white paper Implementing Complex Pad Shapes for your circuit board today.