At the core of the Cadence PCB design solution lies the PCB Editor, a powerful and user-friendly tool designed to streamline the creation and modification of printed circuit boards. This constraint-driven environment offers a wide range of features that help engineers tackle complex design and manufacturing challenges efficiently. Built on the Allegro platform, the PCB Editor provides advanced layout planning capabilities with synchronous design functions. Its intuitive interface reduces wiring time and accelerates time-to-market by offering real-time length and timing tolerance tracking, as well as dynamic copper plating and floor fill during placement and routing. The tool also supports full negative film processing, bare board assembly, and test output in multiple formats, including Gerber 274X, NC drill, and more.
**Cadence PCB Wiring**
**PCB Laminate Structure**
When designing a multi-layer PCB, the stack-up structure plays a critical role in ensuring signal integrity, power delivery, and electromagnetic compatibility. A well-considered cascading structure is essential. Key principles to follow include:
- Place a ground plane on the second layer beneath the component side to provide shielding and a reference for top-layer routing.
- Keep all signal layers as close as possible to the nearest ground plane.
- Avoid direct proximity between two signal layers to minimize crosstalk.
- Position the main power supply adjacent to its corresponding ground or power plane.
- Ensure symmetry in the laminated structure for balanced performance.
- Maintain complete ground planes on both the component and solder sides for effective shielding.
- Avoid having parallel wiring layers next to each other.
- Ensure that all signal layers are as close as possible to the ground plane.
- Place key signals adjacent to their respective reference planes without crossing partitions.
For a four-layer board, a recommended stack-up is: Signal – Ground – Power – Signal. For a six-layer board, an optimal configuration would be: Signal – Ground – Signal – Ground (or signal if needed) – Power – Signal. For an eight-layer board, two common options exist, with the second option being preferred when there are many power supplies.
The SMDK6410 core board, designed as an eight-layer PCB, uses a specific stack-up structure that includes rule settings and layout considerations. To set up the stack-up in the PCB Editor, open the program “Cadence SPB 16.5,†then load the PCB file. Click the “Cross-section†icon or navigate to Setup > Cross-section.
A dialog box appears where you can define the layer stack. Since this is a manually built board, only the Top and Bottom layers are initially present. You will need to manually add six additional layers and adjust the stack accordingly. Right-click on the serial number in the Subclass Name column to add or remove layers as needed. A dielectric layer should be placed between any trace layers.
Once the eight-layer stack is configured, the final structure is defined, with the second option often used for boards with multiple power supplies. The Subclass Name column defines the name of each layer, while the Type column specifies whether it's a conductor, plane, or dielectric. Additional parameters such as material, thickness, conductivity, dielectric constant, and loss tangent are set based on the manufacturer’s specifications. Some layers may require negative output, which can be specified in the Negative Artwork field.
**Wiring Rules**
Setting up proper wiring constraints is crucial for achieving high-quality PCB layouts. These rules directly impact signal integrity and design efficiency. Common constraints include differential pair rules, line width, equal length matching, via placement, and more. These rules are managed through the Constraint Manager.
To access the Constraint Manager, select Setup > Constraints > Constraint Manager from the menu, or click the corresponding icon on the toolbar. The interface consists of two workspaces: one for selecting constraint types and another for setting specific values. Typically, the first four worksheets—Electrical, Physical, Spacing, and Same Net Spacing—are most commonly used. These cover electrical rules, physical dimensions like line width, spacing between different nets, and spacing within the same net. Properly configuring these constraints ensures a reliable and efficient PCB design.
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