Summary of techniques for transferring PCB schematics to layout design

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Summary of techniques for transferring PCB schematics to layout design [Copy link]

PCB Best Practices: Six Things to Consider When Transferring a PCB Schematic to Layout. All examples in this article were developed using the Multisim design environment, but the same concepts apply when using different EDA tools. Initial Schematic Transfer The process of transferring the schematic to the layout environment via the netlist file also transfers the device information, netlist, layout information, and initial trace width settings. Here are some recommended steps to prepare for the layout design phase: 1. Set the grid and units to appropriate values. For finer control over the placement of components and traces, design the device grid, copper grid, via grid, and SMD grid to 1 mil. 2. Set the board outline blank area and vias to the required values. The PCB manufacturer may have specific minimum or nominal recommended values for blind and buried via settings. 3. Set the appropriate pad/via parameters based on the PCB manufacturer's capabilities. Most PCB manufacturers can support smaller vias with a drill diameter of 10 mil and a pad diameter of 20 mil. 4. Set the design rules as required. 5. Set custom shortcuts for frequently used layers so you can quickly switch layers (and create vias) while routing. Handling Errors During Schematic Transfer A common error during schematic transfer is non-existent or incorrect footprint assignments. It is important to note that: ● If there is a device in the schematic that does not have a footprint, a warning message will pop up indicating that the virtual component cannot be exported. In this case, no default footprint information is transferred to the layout and the component is simply deleted from the layout. ● If the footprint is transferred but does not correctly match a valid footprint shape, a warning message indicating the mismatch will also be generated during the transfer process. ● Correct the footprint assignment in the schematic, or create a valid footprint for any device. Once corrected, perform the forward annotation step to update and synchronize the design information. Updating the Design through Annotation Annotation is the process of transferring design changes from schematic to layout or from layout to schematic. Backward annotation (layout to schematic) and forward annotation (schematic to layout) are key to keeping your design accurate. To protect the work that has already been done, back up and archive the current versions of the schematic and layout files before any major forward or back annotation steps. Do not attempt to make changes in both the schematic and layout simultaneously. Make changes to only one part of the design (either the schematic or the layout), then perform the correct annotation steps to synchronize the design data. Renumbering Components Component renumbering is the function of renumbering the components on the PCB to a specific sequence. Reference designators should be ordered from top to bottom and from left to right on the PCB. This makes it easier to locate the component on the board during assembly, test, and troubleshooting. Dealing with Last-Minute Component or Netlist Changes Last-minute PCB component or netlist changes are undesirable, but sometimes they must be made due to component availability issues or the detection of a last-minute design error. If the component or netlist change needs to be made, it should be made in the schematic and then forward annotated to the layout tool. Here are some tips: 1. If you are adding a new device after layout design has begun (such as adding a pull-up resistor to an open-drain output), add the resistor and net to the design from the schematic. After forward annotation, the resistor will appear outside the board outline as an unplaced component with flying wires indicating the connecting net. Next, move the component inside the board outline and route it normally. 2. Backward annotation works well with reference designator changes, such as post-layout renumbering. Locate Devices by Highlighting Selection During the PCB layout process, one way to navigate to specific components or traces in the schematic is to use the 'Highlight Selection' feature. This feature allows you to select a component or trace (or multiple objects) and then see where they are located in the schematic. This feature is especially useful when matching bypass capacitors to their corresponding IC connections. Conversely, you can also locate specific components or traces in the layout while browsing the schematic.