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76 DESIGN007 MAGAZINE I JULY 2022 Avoid Plated Through-holes on the Bending Areas Avoid placing pads and vias on the bending area of the flex part of a PCB. Areas near the bending line will deliver mechanical stress that could jeopardize the structure of the plated holes. Pads and vias can be placed on areas that are not subjected to bending, although it's not recommended. In such cases, use anchors to strengthen the plated holes. Additionally, use a teardrop to connect the trace to the plated hole for stronger joints. It's also a good prac- tice to use larger pads and vias. Pay Attention to Routing Across the Bending Area Traces across the bending line should be kept as straight, perpendicular lines. It's better to use narrower traces that are spread evenly across the flexible area. Adding in dummy traces can help to increase mechanical sturdi- ness that protects the traces from breaking. For a double layer design, traces should be routed alternately on both the top and bottom layer. Avoid making any corners with the traces on the bending area. If the traces need to change direction on a flex PCB, use curves rather than sharp 45° or 90° corners. Use a Cross-hatched Ground Plane If you're pouring the ground plane as a solid area of copper, you'll risk putting a huge amount of stress on it and reducing its flexibility. Instead, use a cross-hatched ground plane on the flex area of the PCB. It goes without saying that using a PCB design soware that supports rigid-flex PCB design guidelines helps in creating an error- free prototype. DESIGN007 Cody Stetzel is a lead techni- cal marketing engineer with Cadence Design Systems. This article originally appeared as a blog post on the Cadence Design Systems website. Figure 3: Use curved corners and teardrops for the flex area of a rigid-flex PCB.