What is exact reason for different types of ENDCAP/BOUNDARY Cells is used for left and right side edges of macros and core area ?

Nice Question Ganesh!, I think the main reason we use different types of ENDCAP or boundary cells on the left and right sides of macros and the core area lies in the design and connectivity requirements of these edges. You see, the left and right sides of the macro might have different pin configurations, such as input or output pins, which require specialized boundary cells to ensure proper signal routing and electrical isolation.

We also need to consider the mismatch in design constraints like well-tap connections or the alignment of power rails. For example, the right edge might need cells optimized for connecting to a particular type of signal wire, while the left side could require cells with ESD protection or shielding features for sensitive signals.

When it comes to the top and bottom edges, we often see differences because of the power rail configurations. You might notice that VDD and VSS connections are handled differently at these edges, which dictates the choice of specific boundary cells. The same logic applies to the left and right sides, but the variations come from how the signal flows and how the standard cell rows are oriented. This is why we carefully select boundary cells to align with the physical design requirements while ensuring functionality and manufacturability.

I want to edit addition details related above question,

When it comes to the edges of macros or core areas in chip design, the use of different types of endcap or boundary cells on the left and right sides is essential. I’ve learned that these differences arise because each edge has unique physical and electrical requirements.

For example, the left and right sides may connect to different(potentioal) neighboring cells or macros, which means their alignment and spacing need to be handled differently. We also have to think about well continuity—ensuring that N-wells or P-wells are properly maintained—since the termination can vary between the left and right edges.

You might notice that the routing patterns or density at the edges differ too, which calls for specific cells to support those variations. On top of that, stress, lithography constraints, and design rule checks (DRC) all play a role in why the cells need to be distinct.

Ultimately, these specialized cells ensure everything stays aligned, functional, and compliant with foundry rules, making the design both robust and manufacturable.