Advantages of vacuum brazing for liquid cooling plates

Principles of Vacuum Brazing

Vacuum brazing is essentially a solid-phase joining process. It involves heating the material to a temperature above the melting point of the brazing filler metal but below that of the base metal. This allows the liquid brazing filler metal to flow and fill gaps in the base metal through capillary action, dissolving and diffusing with the base metal, thereby achieving a reliable connection between parts.
Vacuum welding and brazing join dissimilar materials, welding metal to metal and insulator to metal. The brazing flux must be resistant to high temperatures, suitable for use in a vacuum environment, and must not vaporize. The primary purpose of using a brazing flux is to remove residual oxides, reduce surface tension, and improve wettability of the weld.

Vacuum Brazing of Liquid Cold Plates

In a data center liquid cooling system, a typical cold plate system consists of a liquid cold plate, heat exchanger, piping, pump, coolant, and control system. The closer the component is to the heat source, the more technical and process-intensive it becomes. A liquid cold plate is not a flat “plate,” but rather a block-like object. Its structure includes a liquid inlet and outlet connectors, a cold plate base, a flow channel cover, and fluid channels. The cold plate base is the bottom component of the cold plate and directly contacts the heat-generating device through an interface material. The flow channel cover is the top component of the cold plate, sealed to the base plate to form a closed cavity. The cold plate is equipped with pre-recorded piping or connections, allowing coolant to flow through the fluid channels and achieve heat exchange through contact with the fluid channels.

Vacuum Brazing Characteristics

Vacuum brazing: This is the most widely used method. The workpieces are heated and brazed in a vacuum chamber. The vacuum environment effectively prevents oxidation of the base metal, eliminating the need for flux and avoiding corrosion problems caused by residual flux. It also produces clean, high-quality welds.
Shielded atmosphere brazing: For example, brazing under a nitrogen shield also prevents oxidation. Vacuum brazing is performed in a vacuum environment, avoiding oxidation, carburization, decarburization, and contamination and deterioration. The result is highly clean and strong weld joints. The process typically involves punching to form flow channels, rigorous cleaning, and flux application. After assembly, the workpieces are placed in a vacuum brazing furnace and heated at a specific temperature profile to melt the brazing filler metal and fill the weld, ultimately forming a strong metallurgical bond. It offers excellent corrosion resistance, lacks oxidation reactions, allows for design flexibility, and reduces equipment costs, but requires high workpiece surface finishes and minimizes thermal stress.

Vacuum Furnace Brazing

1. Operating Temperature: 300-1250°C (depending on the brazing material);
2. Vacuum Degree: 10-³~10-⁵Pa;
3. Advantages: Oxidation-free brazing, capable of brazing nickel-based high-temperature alloys, joint strength exceeding 90% of the parent material;
4. Typical Applications: Aerospace engine blades, spacecraft heat pipes, and liquid cooling plates.

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