Short answer
Front-end VLSI design covers logical design — writing and verifying the chip’s functional behavior — while back-end design covers the physical implementation, turning that logic into an actual manufacturable layout.
Chip design is generally divided into these two broad phases, often handled by different specialized engineers.
Front-end design
- Writing RTL (Register Transfer Level) code, typically in Verilog or VHDL
- Functional verification and simulation, to confirm the design behaves correctly
- Logic synthesis — converting RTL code into a gate-level netlist
Back-end design
- Floorplanning — deciding where major blocks physically sit on the chip
- Placement and routing — arranging and connecting the actual transistors and wires
- Static timing analysis, power analysis, and physical verification before manufacturing
The netlist produced at the end of front-end design is the handoff point into the back-end flow.