VLSI Interview QA

Routing congestion in VLSI explained for physical design engineers: how global routers measure GCell capacity, demand and overflow, cell density vs pin density, global, local and layer congestion, floorplan, logic and placement causes, fixes with halos, partial blockages and cell padding, the timing impact, a debugging flowchart and interview Q&As.

Scan chain reordering in VLSI physical design explained: why synthesis scan order wastes wirelength, what the scan DEF (START/STOP, FLOATING, ORDERED, PARTITION, MAXBITS) allows, clock-domain, edge-order and lockup-latch rules, chain balancing, scan shift hold timing, verification and ATPG regeneration, with illustrative examples, a debugging flowchart and interview Q&As.

ECO (Engineering Change Order) in VLSI physical design explained: timing, DRV, noise, leakage and functional ECOs, pre-mask vs post-mask (metal-only) changes, spare cells, the sign-off STA to place-and-route ECO loop, what to re-verify after every ECO and how to debug an ECO that will not converge, with illustrative examples and interview Q&As.

Multicycle paths and false paths in STA explained for physical design and timing engineers: how set_multicycle_path moves setup and hold checks, why setup N needs hold N-1, -start vs -end across clocks, valid and dangerous false paths, clock groups, exception precedence and a debugging flow, with illustrative examples and interview Q&As.

The difference between a latch and a flip-flop explained for physical design and STA engineers: level vs edge triggering, master-slave structure, where setup and hold are checked, time borrowing, phase-dependent hold, ICG and lockup latches, and unintended RTL latches, with illustrative examples, a debug flowchart and interview Q&As.

What is routing? Creating physical connections to all the logical connections present in the design with the help of metal layers is known as routing. What are the types of routing? What are the pre routing checks? What are the goals of routing? What are the stages of routing?