What are the advantages of vacuum brazing of liquid cooling plates?

Vacuum brazing of liquid cooling plates is a key joining process used in the manufacture of liquid cooling systems. It is particularly widely used in the heat management of new energy vehicles, energy storage systems, data centers, and high-power electronic equipment. The following describes the vacuum brazing process principles, key technical features, primary materials, advantages and disadvantages, and typical applications.

1. Vacuum Brazing Process Principles and Main Forms
Vacuum brazing is essentially a solid-phase joining process. By heating the material to a temperature above the melting point of the brazing filler metal but below that of the base metal, the liquid brazing filler metal flows and fills the gaps between the base metals through capillary action, dissolving and diffusing with the base metal, thereby achieving a reliable connection between the parts. Common brazing fillers include silver, copper-phosphorus, and other materials.
Main Forms of Liquid-Cooled Plate Vacuum Brazing:
Vacuum brazing is currently 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 potential corrosion problems caused by flux residue. This results in clean, high-quality welds. Vacuum brazing is a process in which grooves and holes in the shape of water channels are first CNC-machined onto the substrate (aluminum or copper). Then, under vacuum conditions, a brazing filler metal with a melting point lower than that of the base material is used. At a temperature higher than the melting point of the filler metal, the liquid filler metal is used to wet, spread, and fill the surface of the base material, achieving connection between parts. Air brazing of water-cooled plates utilizes this principle to achieve a perfect connection between the aluminum base plate, composite brazing filler metal plate, and aluminum cover plate.

2. Vacuum Brazing Process and Key Steps
A complete liquid cold plate vacuum brazing process typically includes the following core steps:
Pretreatment: The liquid cold plate components to be welded undergo rigorous cleaning, such as ultrasonic cleaning and pickling, to remove oil and oxide films. This is essential for ensuring good brazing filler metal wetting and weld quality.
Assembly and Pre-positioning: The upper and lower plates, internal flow channels, fin structures, joints, and other components are precisely assembled. Spot welding is often used to pre-fix key areas, such as joints, to prevent them from shifting before entering the brazing furnace.
Vacuum Brazing: The assembled workpieces are placed in a vacuum brazing furnace (either a vacuum furnace or a continuous atmosphere brazing furnace). The heating profile (including the temperature and duration of the preheating, brazing holding, and cooling stages) is precisely controlled to ensure uniform melting, filling, and metallurgical bonding of the brazing filler metal.
Post-processing and Inspection: After welding, a leak-tightness test (such as a hydrostatic test) is performed to ensure leak-free flow channels. Surface treatment (such as polishing and insulating spraying) is also performed to meet end-use requirements.

3. Key Material Selection
Material selection directly impacts the performance, manufacturability, and cost of liquid cold plates. Vacuum brazed cold plates are typically made from metals with excellent thermal conductivity and mechanical strength. Aluminum and copper are the most common materials. Aluminum’s lightweight, cost-effectiveness, and good thermal conductivity make it a popular choice for many applications. Copper, on the other hand, offers excellent thermal conductivity, which is crucial for systems requiring maximum heat dissipation.

4. Advantages and Challenges of Vacuum Brazing
Brazing of liquid cold plates, particularly vacuum brazing, offers the following significant advantages:
(1. Design flexibility allows for the manufacture of liquid cold plates with complex internal flow channels and fin structures, optimizing heat dissipation performance.
(2. High-quality welds, aesthetically pleasing and clean, with joints offering excellent sealing and corrosion resistance.
(3. High efficiency, enabling the welding of multiple components or multiple welds in a single furnace load.
(4. Minimal deformation, uniform heating across the entire workpiece, reduced thermal stress, and better control of deformation.

At the same time, this process also faces several challenges, primarily:
(1. High process requirements: Stringent requirements for part machining accuracy, assembly clearances, and process parameter control are imposed, resulting in significant technical complexity.
(2. High cost: Equipment such as vacuum brazing furnaces require high investment, and production energy consumption is high.
(3. Potential strength issues: The strength of brazed joints is typically lower than that of the parent material, requiring special consideration for applications requiring extremely high strength.