IC Packagers: Understanding Stadium-Style Cavity Package Design

Design complexity and space constraints are pushing designers to innovative novel solutions. Placing a die inside a cavity is the most common and effective technique and you have most probably used it if you are designing an application for the automotive industry or the Microwave/Telecommunications domain. Allegro^® Package Designer Plus provides a complete range of toolset right from setting the design in the cavity to cavity-specific DRC checks to manufacturing. In this blog, we will discuss the steps to wire bond a design for an open stadium cavity style.

We will explain in detail the following design-flow steps for the wire bond stadium cavity:

1. Place the die in the stadium cavity
2. Define the bond fingers and wire bond the die
3. Set up the cavity assembly checks to check for assembly issues and review the DRCs
4. View 3D models and check DRCs

Place the Die in Stadium Cavity

Placing the die inside a cavity is an easy task using Die-stack Editor:

• Choose Edit – Die Stack to open the Die-Stack Editor.
• Select the layer from the Sits on layer drop-down list.
• Set the Cavity edge clearance and Expansion per layer values to create the stadium-style cavity.

Applying these changes creates the stadium cavity automatically in the design. It also creates the Route keepout on the layers where the cavity is created, and the Component keepout on the Top substrate layer.

The following image shows die placement in a cavity. The stadium cavity is created per the clearance and expansion values. The Report in the Die-stack Editor is also updated to show the cavity-related changes.

Wire Bonding the Die

To start wire bonding, first define the bond fingers in the cavity:

• Choose Route – Wire Bond – Settings.
• In the Wire Bond Settings dialog, select the Allow cavity placement option and click OK.
  This option lets you create bond fingers on the internal layers.
  
  

• To start wirebonding, choose Route – Wire Bond – Add.
• Click Add in the Options window pane when adding the wire bond to define a new finger padstack.
  The Bond Finger Padstack Information form opens. You can see the internal layers are now available in the drop-down list
  
  

• Select a different internal layer or to continue with the same Click OK in the Bond Finger Padstack Information form.
• Repeat the above steps to complete the bond finger placement.
  The following image shows the bond finger placement on the internal layers.
  
  

Set up Assembly Rules for Cavity

Multiple assembly rules are available for wire bond-specific cavity designs. To select and apply these rules, open Assembly Design Rules Checks dialog from Manufacture – Assembly Rules Checker. Enable the Bond Fingers to Cavity Spacing constraint under the Cavity category and click OK.

The batch DRC process runs and generates a report. You can see DRC markers in the design for any violation against those checks. Use the show element command and select a marker to view the constraint violation details.

There are more Assembly checks for the cavity-specific wire bond designs. These checks are available under the Wire Spacing Assembly rule selection.

View 3D Models and DRCs

3D Viewer supports cavity design. Run View ─ 3D Model to launch the Cadence 3D viewer. By setting up the 3D DRCs rules, you can verify DRCs in a design. The next image shows a die in the cavity with bond fingers on multiple layers.

Conclusion

Allegro Package Designer Plus provides a comprehensive set of functionalities to successfully create a design package with a cavity. I encourage you to design your next wire bond cavity package using this powerful set of functionalities. Do SUBSCRIBE to stay updated about upcoming blogs. If there is any topic you want us to cover or any feedback to share, write to us at pcbbloggers@cadence.com.