NOCOLOK CAB Brazing: Flux-Free vs. External Flux Aluminum

For aluminum liquid cooling plates and plate-fin radiators, NOCOLOK controlled atmosphere brazing (CAB) commonly uses two material routes:

• Option A: Flux-free composite aluminum sheet with a pre-integrated NOCOLOK flux layer
• Option B: Standard 3003 aluminum sheet with externally sprayed NOCOLOK flux

The better choice depends on material cost, production volume, cleanliness requirements, and process stability.

1. Material Cost

Material cost is the biggest difference between the two options.

Standard 3003 + 4343 brazing sheet:
RMB 21.5–24/kg

Flux-free self-activating composite aluminum sheet:
RMB 26.0–30.0/kg

The flux-free material therefore carries a premium of approximately RMB 4.5–6.0/kg.

This premium comes from multi-layer rolling, pre-integrated flux coating, surface protection, higher MOQ, and longer delivery times. For production below 5 tons/month, the price difference can be more noticeable.

2. Production Process

With Option B, manufacturers need additional flux spraying and drying processes.

NOCOLOK flux loading is typically 4–6 g/m², followed by hot-air drying at 200–240°C.

This adds:

• Flux and water consumption
• Spraying equipment and maintenance
• Drying energy
• Labor and process inspection
• Wastewater and exhaust treatment

The additional spraying-route cost is approximately RMB 1.8–3.2/m², or about RMB 0.8–1.6/kg of sheet material for a typical stamped liquid cooling plate.

Option A eliminates external flux spraying and drying, shortening the production process and reducing related equipment and labor.

3. Quality and Cleaning

For closed liquid cooling plates, external flux spraying can create additional quality risks.

Uneven spraying may cause incomplete brazing or leakage, while excessive flux can leave residue inside channels. Incomplete drying can also increase the risk of corrosion and brazing defects, particularly in high-humidity conditions.

Flux-free composite aluminum can reduce these risks because there is no externally applied flux inside the production process. It can therefore be attractive for AI server cooling plates and energy-storage cooling plates with strict cleanliness requirements.

However, the active surface layer must be protected. Scratches or damage during stamping, handling, or laser cutting may affect local brazing performance.

For plate-fin radiators with open-flow structures, internal flux residue is generally less critical, so standard aluminum sheet with flux spraying remains widely applicable.

4. Which Option Is More Economical?

Small-Batch Production

For production below approximately 30,000 pieces/month, standard aluminum sheet + NOCOLOK flux spraying is generally more flexible.

Lower material cost, easier purchasing, and multi-product production can outweigh the additional process costs.

High-Volume Liquid Cooling

For production above 80,000 pieces/month, especially for high-cleanliness liquid cooling products, flux-free composite aluminum deserves a detailed cost evaluation.

The key comparison is:

RMB 4.5–6.0/kg material premium

versus savings from:

flux spraying + drying + cleaning + rework + scrap.

If these combined savings exceed the material premium, the flux-free solution can become economically attractive.

5. Practical Selection

A hybrid approach is also possible: flux-free material for the flow-channel plate and standard brazing sheet for the cover plate, balancing material cost and brazing performance.

Conclusion

The choice between flux-free composite aluminum and externally sprayed NOCOLOK flux should be based on total production cost rather than material price alone.

For flexible, small-batch production, standard aluminum sheet with flux spraying remains a practical solution. For high-volume, high-cleanliness liquid cooling applications, flux-free composite aluminum may provide advantages in process stability and post-brazing cleaning.

SUNHOPE supplies aluminum brazing furnaces and radiator and condenser manufacturing equipment for CAB brazing applications. The suitable equipment configuration can be selected according to product structure, material, production volume, and brazing requirements.