Follow a systematic thermal design process:
- Define Parameters: Determine Power Dissipation (P), Max Component Temperature (T_jmax), Max Ambient Temperature (T_amb), and available space.
- Calculate Total System Thermal Resistance: Rθ_total = (T_jmax – T_amb) / P. This includes resistance from junction-to-case (Rθ_jc), case-to-sink (TIM, Rθ_cs), and sink-to-ambient (Rθ_sa).
- Isolate Heat Sink Requirement: Rθ_sa = Rθ_total – (Rθ_jc + Rθ_cs). This is the maximum allowable thermal resistance for your heat sink.
- Select from Datasheets: Consult manufacturer graphs that plot Rθ_sa vs. airflow for their heat sinks. Choose one that meets your Rθ_sa requirement at your expected airflow.
- Consider Derating: Add a 10-25% safety margin. For complex systems, use thermal simulation software or build a prototype for testing.