PCBgogo

When transitioning the PCB schematic to the distribution design, there are many things to consider. To sum up, it is basically the following six things. 

Initial schematic transition

Note: All the examples mentioned were developed with the MulTIsim design environment, but the same concepts apply when using different EDA tools.

I.Some Recommended Steps to Prepare for the Distribution Design Phase:

· Set raster and units to suitable values. To achieve finer distribution control over components and traces, the device grid, copper grid, via grid, and SMD grid can be designed to be 1 mil.

· Set the blank area and vias of the circuit board frame to the required values. PCB manufacturers may have specific minimum or nominal recommendations for blind and buried via settings.

· Set the corresponding pad/via parameters according to the capability of the PCB manufacturer. Most PCB manufacturers can support smaller vias with a drill diameter of 10mil and a pad diameter of 20mil.

· Set design rules as required.

· Set custom shortcut keys for commonly used layers to quickly switch layers (and create vias) when routing.

II. Handling Errors during Schematic Transfer

A common error during schematic transfer is a non-existent or incorrect package assignment.

It should be noted that if there is a device in the schematic that is not packaged, 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 distribution and the component will simply be removed from the distribution.

A warning message indicating a mismatch is also generated during the delivery if the package is passed but does not correctly match a valid package shape.

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

III.Update the design with callouts

Annotation is the process of passing design changes from schematic to distribution or from distribution to schematic. Back annotation (distribution to schematic) and forward annotation (schematic to distribution) are key to keeping your designs accurate.

To protect the work that has been done, a backup and archive of the current version of the schematic and distribution files is required before any important forward or reverse annotation steps.

Don't try to make changes in both schematic and distribution at the same time. Make changes to only one part of the design (either schematic or distribution), then perform the correct annotation steps to synchronize the design data.

IV. Renumber the Components

Components renumbering is a function of renumbering components on a PCB in a specific order.

Reference numbers should be ordered from top to bottom and left to right on the PCB.

This makes it easier to locate components on the board during assembly, test, and troubleshooting.

V. Handling Last-minute Components or Netlist Changes

Last-minute PCB components or netlist changes are not desirable, but are sometimes necessary due to device availability issues or detection of last-minute design errors. If what needs to be changed is a component or netlist, it should be done in the schematic and then forwarded to the distribution tool through forward annotation.

Here are some tips:

· If adding a new device (such as a pull-up resistor on an open-drain output) after the distribution has been started, add resistors and nets to the design from the schematic. After forward labeling, the resistor will appear outside the board frame as an unplaced component, with flying leads indicating the connection to the net. Next move the components inside the board frame and perform normal routing.

· Back callouts work well with reference number changes, such as post distribution renumbering.

VI. Positioning Components by Highlighting Selections

During the PCB distribution process, one way to browse 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 see where they are in the schematic.

This feature is especially useful when matching bypass capacitors to their corresponding IC connections. Conversely, you can locate specific components or traces in the distribution while browsing the schematic.