Tips to Reduce the File Size of a Board Database

While working on a design, or a redesign, you may notice an increase in the file size of the board. This is particularly the case when you reuse old .brd files and rework them into the new design. A good rule of thumb is to create your design afresh, whenever possible. Setup files, such as the stack-up tech files, constraints, and even placements, can be transferred from a previous design and imported using the File > Import menu. If this is not possible, use the following pointers to reduce the size of the older database:

1. Shrink Board Design Extents
2. Remove Unused Layers/Classes
3. Purge Unused Padstacks
4. “Force Sector Tune” using DBDoctor.exe

Let us examine these in more detail:

1. Shrink Board Design Extents

If a design has large drawing extents but the actual PCB size is small, this can cause performance issues for PCB Editor. In such cases, DBDoctor optimizes the size of sectors within a database. While working on large designs, the database’s sector table is tuned, based on the size of drawing extent to help with speed and performance. Having oversized extents results in a larger database on the disk.

You can visually check for oversized extents. Start by making grids visible in PCB Editor using the following icon:

Here, you will see whether the total grid size is much larger than required for the PCB design. To safely reduce this, go to Setup > Design Parameters > Design (tab) and click the Shrink Extents to Design Contents button.

You can observe that the Extents values of the design have reduced significantly. If not, check for stray objects on all layers and delete them.

2. Remove Unused Layers/Classes

It is common for imported layers to reside in the database from a previous design. Imported artworks or plots, which are used for documentation purposes or redundant mechanical information in the form of DXF or IDX imports, can increase board file sizes significantly.

To resolve this, open the Display Color/Visibility Dialog window and make visible all nonstackup-related layers. Review and delete all shapes and objects that are surplus to requirements.

3. Purge Unused Padstacks

You can remove unused padstacks from the list available in the design. Purging unused padstacks increases the performance of the editor. This is because the program must load all padstacks whether used or unused. A few of them may contain remnant unwanted layers. To purge unused padstacks from the design, go to the Editor menu and select Tools > Padstacks > Modify Design Padstacks. Then, go to the Options tab and select the Purge button, choosing All.

You will be presented with a text list of padstacks that are not used in the current layout. On closing this, the system confirms whether you want to remove these padstacks from the database.

4. “Force Sector Tune” using DBDoctor

The DBDoctor.exe executable has many options that are not available in the user interface version of the tool. To see these additional options, enter the following command at the command prompt:

dbdoctor -help

This displays the following list of helpful arguments that can be used while running DBDoctor:

One such argument is -force_sector_tune, which is described below:

This feature is useful if you have deleted large symbols with high pin counts from the design.

A reused design that starts with a high pin count, which later reduces significantly, results in a database that is not in tune with the sector size needed. Reusing designs in such a way is not the expected flow. PCB designs are expected to grow larger during development. Therefore, database sectors are not tuned downwards automatically; this is to prevent negative performance impacts using the editor. It is considered better to have a large design than a slow design.

To tune the design and potentially reduce the file size, place a design in a folder of your choosing and enter the following command at the command prompt:

        dbdoctor -force_sector_tune C:\Folder\filename.brd

The modified design is written back to the same folder. The original design will be stored in the same folder under a new name: “filename.brd.orig”.

Note: For this tool to operate via the command prompt, the “path” of your tool should be set up correctly in your Windows-based environment variables.

If you have any questions or comments about the information contained here, please feel free to comment in the section provided below.