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For every PCB designer, adding correct footprints to the PCB is important. Also, sometimes when you are creating a new project, your client demands a new component to be added to the design for which you do not have a footprint. You need to quickly create a new footprint.
What is a designer supposed to do in such situations? Without the correct footprints in the CAD files, your PCB will not be assembled using the automatic assembly lines. At this point of time, you will have to create footprints on your own. Allegro® ECAD-MCAD Library Creator provides the options to create custom footprints with just a few clicks of the mouse.
We have talked about how you can create footprints using a STEP model in the past. In this blog, let us discuss how you can create a custom footprint using Allegro® Library Creator.
The very first step when creating a custom footprint is to select a package. Choose Tools – Templates – System - Packages from the menu and select a template from the available list.
A new instance can be created by editing the values in the parametric table as per your component’s data sheet and then clicking the New Instance button. The Package (3D) view displays the template that you have selected including the changes that you made to the template.
The next step is to edit the thermal pads.
In this step, you will move the existing thermal pad to a new location, create a copy of the existing thermal pad, change its height and move it to the desired location.
To move, you just have to right-click the thermal pad, choose Delta and enter the DX or DY values.
Next, you right-click the thermal pad and click Copy to create a replica of the existing one. Change the height of the copied thermal pad as per the datasheet by choosing Tools – Properties and again move the thermal pad to the desired location.
Now it’s time to change the shape of the first thermal so that it matches the H-shape. This can be done by adding reference dimensions that are used as aids in sketching the outline and then using the subtract shape tool of Library Creator. To change the shape, right-click the thermal pad and choose Selection Filter – Shapes.
Next, you need to set the vertical and horizontal dimensions using the Add a Vertical Symmetrical Dimension and the Add a horizontal relative dimension icons on the toolbar. Now, add a rectangle shape using the Add a new standard shape object icon at the top and bottom of the thermal pad.
Finally, you must click the Subtract one shape from another shape icon on the tool and click the two rectangles to give the thermal pad the required shape.
If you see the 3D image and spin it around to the backside, you will notice that only the contact has been updated to the H shape. The shape of the actual thermal pad on the 3D STEP model has not been updated. This step updates the actual thermal pad shape.
In the Explorer pane, right-click the thermal pads one by one under Flat Thermal and choose Extrude Contact. Click OK without editing the values.
This will match the underside of the 3D STEP model with the contacts.
Now that you have a complete package, it's time to save it to the Library Creator repository. This can be done by simply choosing File – Upload – Save New Version. You can also add notes in the Version Notes dialog box.
Once the package is saved to the repository, you can apply rules to the package to make it compliant with the industry standards. This can be done with just two mouse clicks. Click the Apply menu and select a rule.
Performing the steps mentioned above will allow you to create custom footprints. You can also verify the footprints by loading it in Allegro PCB Editor and launching the 3D Canvas. If you want to try these steps in detail, just check the Rapid Adoption Kit (RAK) on creating a custom footprint in Library Creator.
Note: The above link can only be accessed by Cadence customers who have a valid login ID for https://support.cadence.com.