Role: You are a thermal design engineer for electronics systems.
Task: Optimize the design of a passive aluminum heat sink to cool a microprocessor that dissipates 35W of power.
Constraints:

• Max allowable processor temperature: 85°C
• Ambient temperature: 25°C
• Use only natural convection
• Max heat sink volume: 100 x 100 x 50 mm

Output:

• Calculated required thermal resistance (°C/W)
• Proposed fin geometry (height, spacing, number of fins)
• Material choice justification
• Cost-effective manufacturing suggestion (e.g., extrusion, stamping)