Graphical netlist comparison allows you to visually compare your design data against the original netlist. VisualCAM performs the comparison automatically, and all violations are stored internally like DRC/MRC and DFF violations. This means you can quickly scan through and fix connectivity issues.
As an aid to those who wish to compare a netlist created from Gerber data back to an ODB++ or PADS ASCII database netlist, the File|Import|Netlist|ODB++ and File|Import|Netlist|PADS ASCII commands import only the netlists from those databases. It is not necessary to use the File|Import|ODB++ or File|Import|PADS ASCII command to import the entire database, export an IPC-D-356 netlist, discard the database, load your Gerber data and import the IPC-D-356 netlist.
Tip: A VideoClip is available for this tutorial. (Internet access required.)
Use File|Import|Import Wizard to import your Gerber data or File|Open to a previously-created VisualCAM .vcam file.
Tip: If you are importing an ODB++ or PADS ASCII database for the purposes of verifying their netlists against the artwork (not Gerber data), you can automatically run a netlist comparison when importing those databases. See the File|Import|ODB++ and File|Import|PADS ASCII topics for details.
Using the Setup|Layers command or the Navigator, make sure that each layer is "tagged" with the correct layer type. This is required so that the system understands what each layer is.
Remove any extraneous data on your electrical layers that are outside the perimeter of the board, such as title blocks, targets, crop marks, etc.
Tip: We recommend that any documentation for the board be done on a separate Drawing layer. If you wish to keep the data, placing it on a drawing layer assures it will not interfere with any processing, such as netlist extraction.
If you have any drawn pads in your database, select one of the Tools|Convert|Drawn Pads commands to convert them to flashes.
Use the Analysis|DRC/MRC command to make sure your layers are properly aligned. If any layers are misaligned, you can use the Edit|Align Layers command to align them.
Use the Tools|Pad Removal|Stacked command to remove any redundant pads.
Select the Tools|Netlist|Generate command, or use the Navigator shortcut command, to extract a netlist from your data.
Import your CAD system (external) netlist using the File|Import|Netlist|IPC-D-356 command, File|Import|Netlist|ODB++ command, or File|Import|Netlist|PADS ASCII command, depending upon where your "golden" netlist resides.
After you import the netlist, a new External Net layer is created. Viewed by itself, this layer appears to contain no data. However, this layer contains the external netlist information, and links the external net points to the appropriate top/inner/bottom layer net test points. To view the points, turn on the associated top, bottom, and inner layers, and the external net layer. The net points are displayed in four ways for easy reference:
Select the Analysis|Netlist Compare command.
After performing the analysis, discrepancies are automatically displayed in the Navigator, which you may use to view the errors in the workspace and print reports.
Double-click on the error in the Navigator to view it in the workspace. The VisualCAM internal net in question highlighted, and zoomed to fit the screen. The external net points are shown in a unique color for each net.
Tip: The external net point graphic colors are arbitrary. If necessary, you can change the highlight, draw, and flash colors for the layers you are looking at for better contrast and easier visibility.
In the below example, a Net Short was detected. The blue net point symbols represent one external net (Net X), and the green net point symbols represent another (Net Y). Note that one of Net Y's points lies on the same VisualCAM net as Net X. A trace was mis-routed.
If the error is an open or a short, you can find the location of the error more quickly by right-clicking on the error in the Navigator, and selecting the Pin-Point Error command. The system then places a bounding-box around the area where the open or short is located.
You can now change the data as necessary. Once you have done so, you should then re-run the Netlist Compare command to verify that the fix was accurate. Once no more errors exist, you can use the Tools|Netlist|Apply ExternalNet Names command to apply the external net names to the database, if you wish.