What are the design challenges in 3D IC integration?

3D IC stacks multiple dies or layers for increased functionality and reduced footprint. Challenges: TSV (Through-Silicon Via) design (TSV parasitics, keep-out zones, stress effects), Thermal management (power density, hot spots, limited heat paths), Power delivery (distributed PDN across tiers), Clock distribution (skew across dies), Testing (pre-bond, mid-bond, post-bond test strategies), Yield (compound yield of multiple dies), Design tools (3D-aware floor planning, thermal-aware placement), and Known-good-die selection. Benefits include: shorter interconnects, heterogeneous integration (logic + memory), and smaller form factor. Active area for research and advanced packaging development.