Six Tips for Transferring PCB Schematics to Layout

　　PCB Best Practices: Six things to consider when transferring PCB schematics to layout design. All examples mentioned in this article were developed using the Multisim design environment, but the same concepts apply when using different EDA tools.

　　Initial Schematic Transfer

　　When transferring the schematic to the layout environment via the netlist file, the device information, netlist, layout information, and initial trace width settings are also transferred.

　　Here are some recommended steps to prepare for the layout phase:

　　1. Set the grid and unit to appropriate values. In order to achieve more precise layout control of components and traces, the device grid, copper grid, via grid, and SMD grid can be designed to 1mil.

　　2. Set the blank area and vias of the circuit board frame to the required values. The PCB manufacturer may have specific minimum values ​​or nominal recommended values ​​for blind and buried vias.

　　3. Set the appropriate pad/via parameters according to 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 design rules as per requirements.

　　5. Set custom shortcut keys for commonly used layers so that you can quickly switch layers (and create vias) when 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 has no footprint, a warning message will pop up indicating that the virtual component cannot be exported. In this case, no default footprint information will be passed to the layout and the component will simply be deleted from the layout.

　　●If the package is passed but does not correctly match the valid package shape, an alarm message indicating the mismatch will be generated during the transfer process.

　　●Correct the footprint assignment in the schematic, or create a valid footprint for any device. After correction, perform the forward annotation step to update and synchronize the design information.

　　Update designs with annotations

　　Annotation is the process of transferring design changes from schematic to layout or vice versa. Backward annotation (layout to schematic) and forward annotation (schematic to layout) are key to keeping your design accurate.

　　To protect the work already done, backup and archive the current version 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 at the same time. Make changes to only one portion of the design (either the schematic or the layout), and then perform the correct annotation steps to synchronize the design data.

　　Renumbering devices

　　Device renumbering is a function that renumbers the components on the PCB in a specific order. The reference numbers should be sorted from top to bottom and from left to right on the PCB. This makes it easier to locate the device position on the board during assembly, testing and troubleshooting.

　　Handling last-minute device or netlist changes

　　Last-minute PCB component or netlist changes are undesirable, but sometimes they have to be made due to component availability issues or the detection of a last-minute design error. If the component or netlist needs to be changed, it should be done in the schematic and then forward-annotated to the layout tool. Here are some tips:

　　1. If you add a new device after the layout design has begun (such as adding a pull-up resistor to an open-drain output), add the resistor and network to the design from the schematic. After forward annotation, the resistor will be displayed outside the board frame as an unplaced component, and the flying wires will be displayed to indicate the connecting network. Next, move the component inside the board frame and perform normal routing.

　　2. Backward annotation works well with reference number changes, such as back layout renumbering.

　　Locate device by highlighting

　　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 a trace (or multiple objects) and then see where they are located in the schematic.

　　This feature is particularly useful in matching bypass capacitors to their corresponding IC connections. Conversely, it can also be used to locate specific components or traces in the layout while browsing the schematic.