OpenSFF Management Module Specification

6. Airflow and Cooling

The Management Module (MM) relies on enclosure-provided front-to-back airflow for thermal management. A plastic shroud directs this airflow across the module’s thermal solution and out through perforations in the I/O shield. All major heat-generating components are passively cooled by the module’s thermal assembly, which MUST operate as part of the active cooling system supplied by the enclosure.

6.1 Requirements

The cooling system must manage thermal output across an inlet air temperature range of 10 °C to 35 °C. Junction or case temperatures of all critical components must remain within specified limits to prevent throttling or damage:

• Maximum Ambient / Intake Temperature:** **35 °C
• Maximum Junction Temperature (CPU): 85 °C
• Maximum Junction Temperature (Memory Modules): 85 °C
• Maximum VRM MOSFET Case Temperature: 120 °C

To ensure reliable operation, the cooling system must deliver sufficient airflow across the MM’s thermal interfaces:

• Minimum airflow requirement: 18.4 m³/h at the shroud inlet.
• Required static pressure: 1.06 mmH₂O at 18.4 m³/h, to overcome losses through heatsink fins, ducting, filters, and other chassis restrictions.

These figures are based on theoretical airflow calculations, adjusted upward (by about 200%) to align with empirical data from comparable systems and provide adequate margin.

The MM MUST integrate a thermal solution capable of maintaining all components within the limits defined above. Designs with very low power dissipation (e.g., components below 5W TDP) MAY omit a dedicated thermal assembly, including the shroud, if enclosure airflow alone maintains compliance.

6.2 Design Guidelines

• The MM’s thermal solution MUST support a maximum TDP of 50W, consistent with the overall power budget defined in Section 4.1.
• Thermal solutions SHOULD be optimized for the enclosure’s airflow path and pressure characteristics.
• Acceptable methods include heatsinks, vapor chambers, heatpipes, or equivalent thermal transfer assemblies.
• Where conduction to a cooling assembly is required, high-quality Thermal Interface Material (TIM) or equivalent MUST be used. The thermal solution MUST function in conjunction with enclosure airflow as specified above.
• Cutouts, pedestals, or similar features MAY be used to minimize TIM bond-line thickness.

6.3 The Shroud

A plastic shroud MUST be used to direct airflow across the MM’s thermal solution whenever the module includes a CPU or other components exceeding a thermal design power (TDP) of 5W per component. For modules below this threshold, including most Pass-through MMs, the shroud MAY be omitted provided that all temperature limits defined in Section 6.1 are satisfied.

• Maximum External Dimensions: 215 mm (L) × 104 mm (W) × 22.4 mm (H)
• The inlet section MUST extend 7 mm beyond PCB length (equal to connector plug length) to seal against the enclosure intake fan array.
• Shroud width and height MUST taper at the top corners to clear I/O shield mounting features (see Figure 3.4.2).
• Shroud Inlet: Minimum area of 22 mm (H) × 88 mm (W).
• Shroud Outlet:** **I/O shield perforations SHALL meet exhaust requirements while preserving I/O functionality and structural integrity.
• Design Features: Baffles or channels MAY be included to direct airflow over memory or VRMs. Curves and fillets MUST be incorporated where possible to reduce turbulence and flow separation.