Wafer Thinning is mechanical removal of silicon from backside reducing total thickness for advanced packaging — enables short interconnects, thermal vias. Thickness Reduction standard ~750 μm → ~50-200 μm. Aggressive thinning challenging. Grinding diamond-wheel abrasion removes material. ~5000 rpm spindle, 10-50 μm/pass feed. Planarization grind entire backside flat (±5-10 μm runout). Polishing subsequent CMP smooths surface (Ra ~0.1-0.2 μm). Removes damage layer. Contamination silicon dust, slurry must be cleaned thoroughly. Bowing thin wafers bow under weight/heat. ~500 μm bow for 50 μm wafer. Limits subsequent processing. Support temporary carrier bonded to front protects during thinning. De-bonding heated to melt adhesive; carrier peels off. Residue chemically cleaned. TSV thinning enables short through-silicon vias (~50-100 μm). Backside Metallization after polish, deposit metal (Al, Cu, Ti) for contacts. Reliability thin wafers fragile. Mechanical care during assembly. Cost grinding equipment expensive; amortized over volume. Yield thinning introduces defects (cracks, warping). Yield lower; test coverage important. Inspection defects detected via etch-pit analysis, electrical testing. Thickness Uniformity ±5-10 μm variation controlled. Wafer thinning enables advanced 3D packaging reducing interconnect length.