liquid cold plate,Vacuum brazing liquid cooling plate,

Vacuum brazing liquid cold plate

liquid cold plate Vacuum brazed liquid cooling plate

Ⅰ)What is vacuum brazing liquid cold plate

Vacuum brazed liquid cooling plates are liquid cooling plates that are sealed by a vacuum brazing process. Compared to friction stir welding liquid cooling plates, vacuum brazed liquid cooling plates can be fitted with heat generators on both sides, creating internal features and fins by adding deflectors to the flow path or adding high performance corrugated aluminum sheets. Higher heat flow density can be addressed. Power electronics components require a cooling solution that is both effective and reliable. These cold plates are typically used in industries that require low thermal resistance and superior leak-free, high power, high heat flow density requirements (e.g., in the cooling of heat generating devices such as IGBTs, FBGAs, PAs, batteries, etc.). They provide designers with maximum flexibility to specify criteria such as thermal resistance, heat flow, pressure drop, pressure resistance, fluid path, size, shape, material hardness, surface geometry, and the ability to mount components on both sides of the board.

Ⅱ)Introduction and principle of vacuum brazing

Vacuum brazing refers to the filling of the metal (called solder or flux) with liquid solder to the base metal in a vacuum environment at a temperature lower than the melting point of the base metal and higher than the melting point of the solder. It is a welding method that wets and spreads the surface of the material, fills the gap of the parent material, and dissolves and diffuses with the parent material to achieve the connection between the parts. Since welding is performed in a vacuum environment with negative pressure, the air bubbles generated by the solder are sucked into the vacuum environment. This is a highly reliable joining technique that allows for extremely strong connections of parts without residual corrosive solder or porosity.













 

Ⅲ)History and application of vacuum brazing

Brazing was one of the earliest methods of joining materials used by mankind, and was used to join metals before mankind had even begun to use iron. Among the ancient artifacts excavated in Egypt, there are pipes brazed with silver and copper brazing materials and amulet boxes connected with gold brazing materials, which are proved to be items from 5,000 and nearly 4,000 years ago respectively. In the ruins of Pompeii, which was buried by a volcanic eruption in 79 A.D., remains of domestic brazed water pipes connected by brazing, using a brazing material with a composition ratio of Sn : Pb = 1:2, similar to the composition of brazing materials used in modern times. Despite the early appearance of brazing technology, it was not developed significantly for a long time. After the 20th century, its development also lagged far behind the fusion welding technology. Only in the 1930s, on the basis of the development of metallurgical and chemical technology, brazing technology developed faster and gradually became an independent industrial production technology. Especially after the Second World War, due to the development of new technologies such as aviation, aerospace, nuclear energy and electronics, the adoption of new materials and new structural forms put forward higher requirements for connection technology, and brazing technology was therefore given greater attention and developed rapidly, with many new brazing methods appearing and their applications becoming more and more widespread. Vacuum brazing technology has become a promising welding technology since the 1940s. It was first used in the electronics industry to braze copper and stainless steel parts, and later in the aviation and atomic energy industries, and in 1959 it was applied to the manufacture of stainless steel plate-fin heat exchangers. Nowadays, it is widely used in plate fin heat exchangers and coolers in industrial sectors such as air separation equipment, petrochemical equipment, engineering machinery, vehicles, ships and home appliances.
Since vacuum brazing technology has unparalleled advantages, it has been rapidly developed and widely used in industrial countries around the world.

1Application of vacuum brazing on aero engines

American Pratt & Whitney JT9D engine honeycomb seal ring, made of ring parts and honeycomb core with vacuum brazing; the engine fuel main pipe by the main and a number of branch pipes, nozzle with vacuum brazing; this engine stainless steel heat exchanger by more than 300 stainless steel tube, spacer, shell with vacuum brazing; JT8D engine 12, 13-stage compressor static sub ring by the inner and outer ring and dozens of blades with vacuum brazing made. The U.S. GE engine magazine is made of more than 240 0.25 ~ 0.7mm thick Inconel alloy parts vacuum brazed in three steps. In China, Shenyang Liming Engine Company and Chengdu Engine Company vacuum braze the static sub ring respectively, which is used on naval aircraft; Chengdu Engine Company vacuum brazes the fuel main pipe and passes the engine test. Vacuum brazing furnace is the main brazing equipment in the manufacture of aero-engines, and there are more than 200 vacuum brazing furnaces in the United States.

2Application of vacuum brazing on construction machinery

Vacuum brazed small and medium-sized brazing bits are an example and are widely used in metallurgy, geology, coal and carbon, water conservancy, railroad, military and other construction businesses. The small and medium brazing bits produced by vacuum brazing have drilled different types of ore rocks and withstood the test of hard granite, difficult to drill angular rocks and hard and abrasive massive magnetite sandwiched between silica rocks. The service life has been increased by 1 to 1.5 times compared with ordinary brazing bits, which has brought significant economic benefits to users.

3)Application of vacuum brazing in cars and ships

The vacuum brazed plate fin oil cooler is used in cars and boats. With high heat transfer efficiency, compact structure and light weight, the plate-fin oil cooler is a newer product of today's diesel engine coolers and is widely used in automobiles, tractors, marine diesel engines and other fields. At present, there are more than 20 parts with vacuum brazing on a car, which shows the great role, good effect and wide application of vacuum brazing technology.

4Application of vacuum brazing on air separation equipment

The plate fin heat exchanger used on air separation equipment is mainly used for the production of oxygen, nitrogen, argon and rare gases. In the past, the main use of salt bath impregnation brazing manufacturing plate fin heat exchanger, this process technology, not only energy consumption, the process is complex, but also corrosive, serious pollution of the environment, high production costs, low product life. Vacuum brazing than the salt bath brazing has many advantages, the British Marsden company has closed the salt bath brazing furnace at the end of 1983, and the use of the British Consac company produced FVB-114-120-240 large vacuum brazing furnace production of low-temperature heat exchanger.

5Vacuum brazed plate and fin heat exchanger in petrochemical applications

Vacuum brazing is widely used to manufacture floor fin heat exchangers in petrochemical industry, for example: (1) gas recovery in petrochemical refineries; (2) separation and recovery of natural gas and coke oven gas; (3) liquefaction of natural gas and LPG. Because the plate fin heat exchanger has the advantages of large processing capacity, good separation effect, low energy consumption, high purity. Therefore, countries around the world attach great importance to the development of vacuum brazed plate-fin heat exchanger technology.

6Vacuum brazing technology in other applications

Vacuum brazing technology is used for locomotive radiators, compressor intercoolers, Freon and alkane and olefin cooling systems, excavator oil coolers, gas turbine recuperators, high-power transformer radiators, liquid-cooled plates for high-precision medical equipment, liquid cold plate and heatsinks for military examination reliability requirements, and applications for household appliances, such as vacuum brazing of heat exchanger core strips for household air conditioners and various electric heaters.

Ⅳ)Advantages of vacuum brazing

1) Vacuum brazing without brazing flux significantly improves the corrosion resistance of the product, and does not require complex flux cleaning process, which reduces the production cost, eliminates various kinds of pollution, harmless processing equipment costs, and has good safety production conditions.

2 Vacuum brazing brazing material has good wetting and fluidity, and can weld more complex and narrow channel devices, and can braze multiple adjacent brazing seams at one time, or can braze multiple components in the same furnace according to the capacity of the furnace, vacuum brazing improves the yield of the product and obtains a solid and clean working surface.

3) Many materials suitable for vacuum brazing, such as: aluminum, aluminum alloys, copper, copper alloys, stainless steel, alloy steel, mild steel, titanium, nickel, composite materials, ceramics, graphite, glass, diamond, etc. can be brazed in the vacuum furnace, and the designer determines the required materials according to the purpose of the brazed device, with aluminum and aluminum alloys being the most widely used.

4) The benefits of vacuum brazing include uniform heating, tight temperature control, no post-cleaning process and process repeatability. Compared to other metal joining processes, brazing does not melt the base metal of the joint, allowing for more precise control of tolerances. Compared to partial joining processes, vacuum aluminum brazing also minimizes part distortion due to uniform heating and cooling. This type of brazing produces a continuous, sealed bond. Vacuum furnace brazing provides extremely repeatable results as critical furnace parameters, i.e. vacuum and temperature uniformity, are achieved with each load.

Ⅴ)Structure and Process Flow of Vacuum Brazed Liquid Cooling Plate

Vacuum brazing can weld aluminum, aluminum alloy, copper, copper alloy, stainless steel, alloy steel, low carbon steel, titanium, nickel, composite materials, ceramics, graphite, glass, diamond and many other materials, but in the radiator industry, based on economic and thermal conductivity, weight and other considerations, the material of liquid cooling plate mainly consists of stainless steel (SUS304, SUS316, SUS316L), aluminum ( AL1060, AL1100, AL3004, AL6063, AL6061), copper (C1020, C1100, etc.), vacuum brazing liquid cooling plate can be composed of a variety of materials, of which all-aluminum cooling plate due to the lighter density of aluminum, higher thermal conductivity, more cost-effective, the most widely used; all-copper cold plate is mainly used for very high heat density scenarios, Regis' extensive experience in the design and manufacture of vacuum brazed cooling plates allows us to achieve seamless, strong, corrosion-free products to guarantee perfect sealing reliability and excellent thermal and pressure drop performance.

                                         Fin chip structure

The structure form of vacuum brazing liquid cooling plate varies according to the usage, and the common structure forms are as follows.
The product consists of cover plate, base, middle frame, fins, between the cover plate, base and middle frame placed between the thickness of about 0. 3mm sheet brazing material, through the tool to fix each part of the cold plate and brazing material, and then put into the brazing furnace, closed brazing furnace, brazing furnace vacuum, and then by heating the product temperature higher than the melting point of brazing material, but lower than the melting point of each part of the product, insulation for a period of time after the end of brazing furnace heating temperature The temperature drops to the ambient temperature and the welding is completed. The specific product structure is shown in the figure below.


Regardless of how the structure of the vacuum brazed liquid cooling plate changes, its processing process is roughly as follows: machining of parts to finished size - cleaning (removal of oxide film on the surface of the parts) - vacuum brazing welding - ultrasonic detection of welding defects - leak testing - thermal resistance and pressure drop testing - flushing of flow channels - cleaning – packaging
 

Ⅵ)Thermal design difficulties of vacuum brazing liquid cold plate

1) Weight and cost constraints: need to optimize the product structure according to the product environment and use cheap and lightweight materials (e.g. aluminum) as much as possible while meeting the heat dissipation requirements.
2) Heat dissipation and mechanical constraints: the cold plate runner and flatness must be optimized to ensure perfect contact with the electronic equipment and maximum contact area; the need to meet the customer's needs for installation space to make the product as thin as possible.
(3) The pressure drop limit of the cold plate: the pressure drop has a direct impact on the energy efficiency of the system (pump consumption) and the cover thickness of the cold plate; a low pressure drop allows the use of smaller pumps and thinner cover plates.
4) Coolant and material compatibility restrictions: a high degree of compatibility between the material and coolant is essential.
(5) The above conditions limit the operation of liquid cooling systems are interrelated and need to be considered in the design process.


Ⅶ)Quality control of vacuum brazing liquid cooling plates
 

1) Product structure inspection. The mechanical dimensions of the cold plate are tested by height ruler and CMM equipment to ensure that they meet the customer's requirements.

                                              height gauge

2Welding defect detection: detect whether the cold plate has welding defects by ultrasonic detection machine and pick out the defective products.

Cross-section of welding effect detected by ultrasonic

3)  Heat dissipation performance test: the thermal resistance and pressure drop parameters of the cold plate are tested by the thermal resistance testing machine to ensure compliance with customer requirements.



4)  Leakage test: fill the closed cold plate with air, the pressure of filling air is 1.5-2 times the operating pressure of the cold plate liquid cooling system, put the cold plate into the water, observe whether there are bubbles coming out of the cold plate, there are bubbles coming out of the cold plate is defective, this is the most basic and important reliability test of the cold plate, need 100% testing.



5)  Helium mass spectrometer: Helium or hydrogen is used as leak detection gas, and helium is detected by gas analyzer for leak detection. Helium has a low background noise, low molecular weight and low viscosity coefficient, which makes it easy to pass through the leak hole and diffuse. The gas is sprayed onto a container connected to a gas analyzer (adjusted to react only to helium), and if there is a leak in the container, the analyzer reacts to it, so that it can know where the leak is and how much gas is leaking. This test is mainly used to detect micro-leaks in products.



6)  Visual inspection: Determine whether there are aluminum chips, dirt, impurities, etc. inside the liquid-cooled plate runner through industrial endoscope inspection

 

Services and Capabilities

Product Material Stainless SteelSUS304SUS316SUS316L
Aluminum (AL1060AL1100AL3004AL6063AL6061)
CuC1020C1100
Maximum product size 1800*800*800MM
Surface Clean, anodizing, powder coating, oil spraying, baking, plating, passivation
Flatness 0.01-0.05MM100*100MM
Roughness Ra0.8-3.2
Maximum working pressure 0.2-2.0Mpa
Coolant Ethylene glycol solution, propylene glycol solution, pure water
Flow 0.5-80L/MIN
Temperature difference between inlet and outlet coolant 0.5-8.5
Inlet and outlet pressure drop 0.001-0.05Mpa
Product surface temperature rise 5-20
Thermal resistance 0.003-0.01K/W
Power 0.1-50KW

Vacuum Brazing Liquid Cold Plate

In the fields of power electronic control, conversion, drive, signal transmission, and new energy fields (new energy vehicle power battery heat dissipation, UPS and energy storage system heat dissipation, large server heat dissipation, large photovoltaic inverter heat dissipation, SVG/SVC heat dissipation Etc.), in order to pursue high-efficiency, low-noise and low-temperature operation, and when space is limited, the heat dissipation problem becomes the biggest limit to the idealization of product development, and liquid cooling technology has become the preferred thermal management method.

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