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Vacuum brazing technology of aluminum cold plate

Vacuum brazing technology
Vacuum brazing is a high-precision process for joining metal parts in a vacuum environment by heating and using a brazing material with a lower melting point than the base material. It is widely used in the manufacture of aluminum cold plates. The heating stage is a key step in the entire process, which directly affects the welding quality, part deformation and final performance.
Vacuum brazing is an advanced cold plate manufacturing technology, especially in the application of aluminum cold plates. The process ensures that the cold plate has excellent thermal conductivity and structural strength by welding aluminum with an internal microchannel structure in a vacuum environment, avoiding oxidation problems in traditional welding, making the cold plate surface flat and lowering the contact thermal resistance, thereby improving the heat transfer efficiency with the chip. In high-power devices, vacuum brazing aluminum cold plates can effectively cope with hundreds of watts of heat loads and ensure the efficiency and reliability of the heat dissipation system. In addition, the microchannel design can optimize the flow of coolant and further reduce thermal resistance.
The vacuum brazing heating rate is usually controlled at 1-3°C/minute to ensure uniform heating of the aluminum cold plate and reduce thermal stress. The heating process needs to be adjusted according to the size and complexity of the part, and may include a preheating stage to avoid deformation. Evidence suggests that ramp control is critical to weld quality and cold plate flatness, especially in high-precision applications.

Ramp rate control
The ramp phase of vacuum brazing is a critical step in ensuring the quality of aluminum cold plates. Studies suggest that the ramp rate is typically set at 1-3°C/minute, a range that helps parts heat evenly and prevents thermal stress or deformation caused by temperature gradients. For example, for large or complex assemblies, a slower ramp rate may be required to ensure that all parts reach the target temperature at the same time.

Process adjustments and equipment
The ramp process may include a preheating phase, especially when the parts are large or complex, to reduce the risk of thermal shock. Modern vacuum brazing furnaces are equipped with advanced temperature control systems that accurately maintain the ramp rate by monitoring and adjusting the heating elements to ensure process consistency.

Vacuum brazing insulation
The insulation phase is the core of vacuum brazing and directly affects weld strength and cold plate performance. After reaching the melting point of the brazing filler metal, it is necessary to maintain a constant temperature (usually between 590-610°C) for 10-30 minutes to allow the brazing filler metal to fully melt and penetrate into the aluminum joint. This process needs to be carried out in a high vacuum environment (usually 10-⁴ to 10-⁵Pa) to prevent oxidation and pore formation. The length of the insulation time depends on the size and complexity of the cold plate. Too short may lead to incomplete welding, while too long may cause coarse aluminum grains and reduce strength. The optimized insulation process can ensure the sealing and thermal conductivity of the microchannels inside the cold plate, providing solid support for efficient cooling.

Vacuum control
Precise control of vacuum is the key to successful vacuum brazing, which directly affects the welding quality and cold plate performance. During the brazing process of aluminum cold plates, the vacuum degree is usually maintained in the range of 10-4 to 10-⁵Pa. If the vacuum degree is insufficient (for example, higher than 10-³Pa), residual oxygen may react with aluminum to form an oxide layer, reduce the wettability and bonding strength of the brazing material, and even cause pore defects. On the contrary, although excessive vacuum requirements (such as less than 10-6Pa) can further reduce oxidation, it will significantly increase equipment costs and process complexity, affecting production efficiency. To this end, modern vacuum brazing furnaces are usually equipped with high-precision vacuum pumps and monitoring systems to ensure that the vacuum degree fluctuates stably within the process window (±5×10-5Pa), thereby achieving high-quality aluminum cold plate manufacturing.

Vacuum Brazing Furnace