A two-phase immersion liquid-cooled IGBT power module based on surface contact angle partitioning

Abstract

The application discloses a two-phase immersion liquid cooling IGBT power module based on surface contact angle partitioning, and belongs to the technical field of thermal management of wind power power electronic devices. The IGBT power module comprises a chip, a DBC substrate and a contact angle regulating area arranged on the lower surface of the lower copper layer. The contact angle regulating area comprises a hydrophilic area and a relatively hydrophobic area, and the static contact angle difference of the hydrophilic area is not less than 20°. The hydrophilic area covers the corresponding heat exchange area of the chip to enhance the cooling liquid supply, and the relatively hydrophobic area is arranged on the outside of the hydrophilic area or on the bubble discharge path to promote the separation of boiling bubbles. The hydrophilic area can have a gradient contact angle structure to enhance directional liquid supply, and the relatively hydrophobic area can have an asymmetric micro-ratchet array structure to enhance directional bubble discharge. The application can improve the stability of two-phase immersion boiling heat exchange and reduce the risk of local overheating.

Description

Technical Field

[0001] This invention relates to the field of thermal management technology for power electronic devices in wind power generation, specifically to a two-phase immersion liquid-cooled IGBT power module based on surface contact angle partitioning. Background Technology

[0002] IGBT (Insulated Gate Bipolar Transistor) power modules are commonly used in wind power converters, rail traction converters, industrial frequency converters, and grid-connected conversion devices for new energy sources. When a wind power converter is operating, the chips within the IGBT power module generate heat during turn-on, turn-off, and frequent switching. If this heat cannot be conducted to an external cooling medium in a timely manner, the chip junction temperature will rise, the module's equivalent thermal resistance will increase, and the solder or sintered connection layers will be more prone to thermal fatigue.

[0003] The heat load changes in wind power generation scenarios are not gradual. Wind speed fluctuations, gust disturbances, grid connection impacts, low voltage ride-throughs, and rapid adjustments in active and reactive power all subject IGBT power modules to steady-state heat loads, transient high heat flux impacts, and local hot spot migrations. The heat dissipation structure in these wind power generation scenarios not only needs high heat exchange capacity but also needs to maintain a relatively stable heat exchange state when heat flux density changes.

[0004] Common heat dissipation methods for IGBT power modules include air cooling, liquid cooling plates, heat pipes, vapor chambers, and external heat sinks. Air cooling is simple in structure, but its heat transfer capacity per unit volume is limited. Liquid cooling plates can improve heat transfer capacity, but require coordination of the cold plate, thermal interface material, pump, piping, and sealing structure, resulting in high system complexity. Heat pipes and vapor chambers can improve temperature uniformity, but thermal resistance still exists between the heat pipes / vapor chambers and the IGBT power module, which may lead to localized thermal hysteresis under transient thermal shock.

[0005] Two-phase immersion liquid cooling provides another thermal management method for high-power power electronic devices. In a two-phase immersion liquid cooling system, the IGBT power module is immersed in an electrically insulating coolant, with the heat exchange surface in direct contact with the two-phase immersion coolant. The heat generated by the chip is transferred to the heat exchange surface through the packaging structure, where the two-phase immersion coolant undergoes a phase change and boils, utilizing its latent heat of vaporization to dissipate the heat. Compared to air cooling or single-phase liquid cooling, two-phase immersion liquid cooling can achieve higher heat transfer intensity with a smaller temperature difference and also reduces the thermal resistance introduced by external cold plates and thermally conductive interface materials.

[0006] Two-phase submerged boiling heat transfer is affected by the wetting characteristics of the heat exchange surface. When the surface contact angle is small, the two-phase submerged coolant easily spreads on the heat exchange surface and forms a liquid film, resulting in good liquid replenishment and a relatively low probability of localized dry spots. If the entire heat exchange surface has strong hydrophilicity, the adhesion between boiling bubbles and the heat exchange surface may increase, the bubble detachment frequency decreases, and localized areas may be easily blocked by bubbles. When the surface contact angle is large, bubbles detach more easily from the heat exchange surface, but the replenishment capacity of the two-phase submerged coolant to the heat exchange surface is affected, and localized dry spots may appear in high heat flux density areas.

[0007] Existing IGBT power modules typically employ conventional metal processing, ordinary roughening, or uniform surface coatings on their outer surfaces. These surfaces generally possess singular wetting characteristics, making it difficult to spatially arrange them according to chip location, chip heat flux density distribution, and bubble removal requirements. For the same IGBT power module, the heat flux density is higher in the chip's projected area and surrounding heat diffusion region, requiring more two-phase immersion coolant replenishment. Areas between adjacent chips, the outer hydrophilic region, module edges, or bubble convergence areas require greater bubble detachment and removal. Conventional surface roughening techniques primarily rely on increasing surface area or nucleation points to enhance boiling, but roughened surfaces may not necessarily form stable liquid replenishment and bubble removal paths. Overall liquefaction treatment can improve liquid spreading ability, but bubble adhesion is easily restricted. Overall relative hydrophobic treatment can reduce bubble adhesion but weakens liquid replenishment capability. For IGBT power modules in wind power converters, heat flux density exhibits spatial and temporal variations, making it difficult to simultaneously meet the requirements of liquid replenishment and bubble removal in high heat flux areas with uniform wetting characteristics. Summary of the Invention

[0008] The purpose of this invention is to provide a two-phase immersion liquid-cooled IGBT power module based on surface contact angle partitioning, which improves the technical problem that a single contact angle surface is difficult to simultaneously handle the supply of two-phase immersion coolant and the removal of boiling bubbles.

[0009] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0010] A two-phase immersion liquid-cooled IGBT power module based on surface contact angle partitioning includes a chip, a DBC substrate, and a contact angle adjustment region;

[0011] The DBC substrate includes an upper copper foil layer, a ceramic insulating layer and a lower copper layer arranged sequentially from top to bottom. The chip is disposed on the upper copper foil layer. The lower surface of the lower copper layer is a heat exchange surface that is in direct contact with the two-phase immersion coolant, used to transfer the heat generated by the chip to the two-phase immersion coolant.

[0012] The contact angle adjustment region is disposed on the lower surface of the lower copper layer;

[0013] The contact angle control region includes at least one hydrophilic region and at least one relatively hydrophobic region, wherein the static contact angle of the hydrophilic region is smaller than that of the relatively hydrophobic region, and the difference in static contact angle between the hydrophilic region and the relatively hydrophobic region is not less than 20°.

[0014] The hydrophilic region covers at least a portion of the heat exchange area corresponding to the chip, and is used to enhance the two-phase immersion coolant supply to the heat exchange area corresponding to the chip; the relatively hydrophobic region is disposed outside the hydrophilic region, between adjacent heat exchange areas corresponding to the chip, at the edge of the contact angle control region, or on the bubble discharge path for boiling bubbles to be discharged, and is used to promote the detachment of boiling bubbles from the heat exchange surface.

[0015] The heat exchange area corresponding to the chip is the orthographic projection area of ​​the chip on the lower surface of the lower copper layer, and the peripheral heat diffusion area formed around the orthographic projection area.

[0016] Furthermore, the peripheral heat diffusion region is an area that extends outward from the projected region by 0.5 to 3 times the thickness of the ceramic insulating layer.

[0017] Furthermore, the static contact angle of the hydrophilic region is less than or equal to 50°, and the static contact angle of the relatively hydrophobic region is greater than or equal to 70°.

[0018] Furthermore, the static contact angle of the hydrophilic region is 10° to 45°, the static contact angle of the relatively hydrophobic region is 75° to 120°, and the difference in static contact angle between the hydrophilic region and the relatively hydrophobic region is not less than 30°.

[0019] Furthermore, the contact angle control region is composed of the hydrophilic region and the relatively hydrophobic region, wherein the area of ​​the hydrophilic region accounts for 40% to 80% of the total area of ​​the contact angle control region, and the area of ​​the relatively hydrophobic region accounts for 20% to 60% of the total area of ​​the contact angle control region.

[0020] Furthermore, the contact angle control area is a strip-shaped partition structure, a grid-shaped partition structure, an island-shaped partition structure, a surrounding partition structure, or a combined partition structure formed by combining two or more of the above structures.

[0021] In the surrounding partition structure, the hydrophilic region is located in the heat exchange region corresponding to the chip, and the relatively hydrophobic region is located around the outer periphery of the hydrophilic region.

[0022] The hydrophilic region includes at least one of the following: a hydrophilic metal oxide coating, a plasma-treated layer, a laser microtextured layer, a chemically oxidized layer, an electrochemically roughened layer, or a hydrophilic porous layer.

[0023] Furthermore, the hydrophilic metal oxide coating includes at least one of aluminum oxide, titanium oxide, silicon oxide, or zinc oxide.

[0024] Furthermore, the relatively hydrophobic region includes at least one of a fluoropolymer coating, a silane-modified layer, a low surface energy coating, a micro / nano composite structure, or a composite surface layer formed by the micro / nano composite structure and a low surface energy material.

[0025] Furthermore, after undergoing no less than 100 thermal cycles, the static contact angle of the hydrophilic region and the relatively hydrophobic region changes by no more than 15°; the thermal cycle is a cyclic change between a first temperature end in the range of 25°C to 40°C and a second temperature end in the range of 80°C to 120°C, with each temperature end maintained for 10 min to 30 min.

[0026] Furthermore, the two-phase immersion coolant is an electrically insulating coolant, which is a fluorinated liquid, a hydrofluoroether coolant, a fluoroketone coolant, or an electrically insulating dielectric coolant capable of undergoing phase change boiling within the operating temperature range of the IGBT power module.

[0027] The hydrophilic region has a static contact angle gradient distribution structure. From the outer periphery of the hydrophilic region towards the center of the corresponding heat exchange area of ​​the chip, the static contact angle decreases continuously or in a stepped manner, thereby forming a unit-width capillary driving force on the surface of the hydrophilic region pointing towards the center of the corresponding heat exchange area of ​​the chip. The unit-width capillary driving force is characterized by the following formula:

[0028]

[0029] in, The capillary driving force per unit width is expressed in N / m. The surface tension of the two-phase submerged coolant is expressed in N / m. The position of the hydrophilic zone along the wetting path length Local static contact angle at the location; The cosine value corresponding to the local static contact angle; The length of the wetting path from the outer periphery of the hydrophilic region to the center of the corresponding heat exchange region of the chip, in meters; The integral variable is along the length of the wetting path, in meters. For hydrophilic regions where the static contact angle decreases in a stepped manner, the difference in the cosine value of the local static contact angle between adjacent stepped regions is discretized and summed according to the wetting path length to obtain the equivalent value of the capillary driving force per unit width.

[0030] Furthermore, the relatively hydrophobic region is provided with an asymmetric micro-ratchet array structure, which includes micron-sized ratchet units periodically arranged along the bubble discharge path. Each micron-sized ratchet unit has a steep slope facing the hydrophilic region and a gentle slope facing downstream of the bubble discharge path. The angle between the steep slope and the reference horizontal plane is greater than the angle between the gentle slope and the reference horizontal plane, which is the average plane of the lower surface of the lower copper layer when the micron-sized ratchet units are not formed. The asymmetric micro-ratchet array structure is used to change the force balance of the solid-liquid-gas three-phase contact line during the expansion and detachment stages of boiling bubbles, and guides the detached boiling bubbles to unidirectionally transport along the bubble discharge path. The unidirectional net driving force on the boiling bubble on the asymmetric micro-ratchet array structure is characterized by the following formula:

[0031]

[0032] in, The net driving force in one direction is expressed in N. The surface tension of the two-phase submerged coolant is expressed in N / m. The length of the solid-liquid-gas three-phase contact line is in meters. The local retraction contact angle is the surface of the micron-scale ratchet unit, which is measured when the boiling bubble contact line retracts along the bubble discharge path direction; The local advancing contact angle is the surface of the micron-scale ratchet unit, which is measured when the boiling bubble contact line advances in the opposite direction of the bubble discharge path; The cosine value corresponding to the local retreat contact angle; The cosine value corresponding to the local forward contact angle.

[0033] The contact angle adjustment area is located on the heat dissipation surface of the IGBT power module housing or on the outer surface of the IGBT power module base plate.

[0034] The present invention also discloses a two-phase immersion liquid cooling system, including a cooling container, a two-phase immersion coolant, a condensation assembly, and the aforementioned two-phase immersion liquid-cooled IGBT power module based on surface contact angle partitioning;

[0035] The two-phase submerged liquid-cooled IGBT power module is submerged in the two-phase submerged coolant. The contact angle control area is in direct contact with the two-phase submerged coolant. The two-phase submerged coolant boils in the contact angle control area and generates boiling bubbles. The boiling bubbles leave the heat exchange surface through the bubble discharge path corresponding to the relatively hydrophobic area and enter the area where the condensation component is located.

[0036] Furthermore, this invention also discloses a method for fabricating a two-phase immersion liquid-cooled IGBT power module, used to fabricate a two-phase immersion liquid-cooled IGBT power module based on surface contact angle partitioning as described above. The fabrication method includes:

[0037] Determine the chip-corresponding heat exchange area on the heat exchange surface to be processed. The chip-corresponding heat exchange area is the orthographic projection area of ​​the chip on the heat exchange surface to be processed and the peripheral heat diffusion area formed around the orthographic projection area.

[0038] The location of the hydrophilic region is determined based on the heat exchange area corresponding to the chip, and the location of the relatively hydrophobic region is determined based on the relationship between the heat exchange areas of adjacent chips, the edge area of ​​the heat exchange surface to be processed, or the area where a bubble discharge path is expected to be formed.

[0039] A mask layer is formed on the heat exchange surface to be processed, so that the location where the hydrophilic region is to be formed or the location where the relatively hydrophobic region is to be formed is exposed.

[0040] The exposed areas are treated with either a hydrophilic or a relatively hydrophobic treatment to form the hydrophilic region and the relatively hydrophobic region;

[0041] Remove the mask layer; detect the static contact angle between the hydrophilic region and the relatively hydrophobic region; when the difference in static contact angle between the hydrophilic region and the relatively hydrophobic region is not less than 20°, a two-phase immersion liquid-cooled IGBT power module with a contact angle control region is obtained.

[0042] Furthermore, the hydrophilic treatment includes at least one of the following: depositing a hydrophilic metal oxide coating, plasma treatment, laser microtexturing, chemical oxidation, electrochemical roughening, or forming a hydrophilic porous layer; the relatively hydrophobic treatment includes at least one of the following: depositing a fluoropolymer coating, forming a silane-modified layer, depositing a low surface energy coating, or constructing a micro / nano composite structure; the static contact angle is detected by a contact angle meter, during which two-phase immersion coolant droplets with a volume of 2 μL to 5 μL are added to the surface to be tested, at least three measurement points are selected in the same area, and the average value of at least three measurement points is taken as the static contact angle of the corresponding area; when forming a static contact angle gradient distribution structure, the hydrophilic treatment includes scanning along the outer periphery of the hydrophilic region to the center of the corresponding heat exchange area of ​​the chip using a laser beam with continuously linearly increasing energy density, so as to form a static contact angle that decreases from the outer periphery of the hydrophilic region to the center of the corresponding heat exchange area of ​​the chip; When forming the asymmetric micro ratchet array structure, the relative hydrophobic treatment includes forming the asymmetric micro ratchet array structure along the bubble discharge path and forming a low surface energy coating on the surface of the micron-scale ratchet unit.

[0043] Compared with the prior art, the present invention has the following beneficial effects:

[0044] Compared with existing heat exchange surfaces that use a single wetting characteristic, the beneficial effects of this invention are as follows: by constructing a contact angle control zone composed of a hydrophilic region and a relatively hydrophobic region on the same heat exchange surface, the two functions of liquid supply and bubble removal are decoupled and spatially coordinated. The hydrophilic region corresponds to the chip and the heat exchange zone to enhance the spreading and supply of the two-phase immersed coolant, reducing the probability of local dry spots forming in high heat flux density areas. The relatively hydrophobic region is set outside the hydrophilic region or on the bubble discharge path to reduce the adhesion of boiling bubbles and promote their rapid removal, so that the contact angle control zone forms a stable liquid supply and bubble discharge state during the boiling heat exchange process.

[0045] By setting a static contact angle gradient distribution structure in the hydrophilic region, the static contact angle decreases from the outer periphery of the hydrophilic region towards the center of the corresponding heat exchange area of ​​the chip. This generates a capillary driving force per unit width pointing towards the center of high heat flux density, enhancing the directional liquid backfilling capability of the central region and effectively suppressing the drying tendency under high power density or transient thermal shock conditions. Conversely, by setting an asymmetric micro-ratchet array structure in the relatively hydrophobic region, the asymmetric geometry of the micron-level ratchet units alters the force balance of the solid-liquid-gas three-phase contact line, generating a unidirectional net driving force along the bubble discharge path. This guides the directional transport of boiling bubbles, shortens the residence time of bubbles on the heat exchange surface, and reduces the risk of bubble collision and merging to form a large-area gas film. When the static contact angle gradient distribution structure and the asymmetric micro-ratchet array structure are used in conjunction, the directional liquid replenishment and directional bubble removal capabilities are synergistically enhanced, significantly improving both the critical heat flux density and the maximum heat transfer coefficient, and significantly reducing the chip's maximum temperature under the same heat flux density conditions. Meanwhile, the contact angle control area of ​​the present invention is formed on the heat exchange surface of the module through surface engineering treatment, which does not require changing the internal chip circuit structure of the IGBT power module, nor does it require changing the main structure of the external two-phase immersion liquid cooling system. It is easy to implement in combination with existing module packaging technology and immersion cooling system, and has good engineering adaptability and industrial applicability. Attached Figure Description

[0046] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained from these drawings without creative effort.

[0047] Figure 1 This is a schematic diagram of the overall structure of the present invention.

[0048] Figure 2 For the present invention Figure 1 Side view.

[0049] Figure 3 This is a schematic diagram showing the relationship between the hydrophilic and hydrophobic regions of the present invention.

[0050] Figure 4 This is a schematic diagram of the surface wetting state of the hydrophilic region of the present invention.

[0051] Figure 5 This is a schematic diagram of the surface wetting state of the hydrophobic region of the present invention.

[0052] Figure label:

[0053] 101 Chip, 102 DBC substrate, 103 Contact angle control area, 104 Upper copper foil layer, 105 Ceramic insulating layer, 106 Lower copper layer, 107 Hydrophilic region, 108 Hydrophobic region. Detailed Implementation

[0054] In the following description, only certain exemplary embodiments are briefly described. As those skilled in the art will recognize, the described embodiments can be modified in various ways without departing from the spirit or scope of the embodiments of the invention. Therefore, the drawings and description are considered to be exemplary in nature and not restrictive.

[0055] The following is in conjunction with the appendix Figures 1-5 The embodiments of the present invention will be described in detail below.

[0056] Example 1: This example discloses a two-phase immersion liquid-cooled IGBT power module based on surface contact angle partitioning, including a chip 101, a DBC substrate 102, and a contact angle adjustment region 103. The DBC substrate 102 includes an upper copper foil layer 104, a ceramic insulating layer 105, and a lower copper layer 106 arranged sequentially from top to bottom. The chip 101 is fixed to the upper copper foil layer 104 through conventional thermally conductive connection structures such as solder layers and sintered silver layers. The packaging connection structure can be achieved using existing mature IGBT module packaging processes.

[0057] A ceramic insulating layer 105 is located between the upper copper foil layer 104 and the lower copper layer 106, and is used to provide electrical insulation and transfer heat. The ceramic insulating layer 105 is a commonly used insulating and thermally conductive ceramic material for the IGBT power module DBC substrate 102. For example, it can be an AlN layer, an Al2O3 layer, a Si3N4 layer, or other ceramic insulating layers 105 suitable for power module packaging.

[0058] The contact angle control region 103 is disposed on the outer surface of the two-phase immersion liquid-cooled IGBT power module that is in direct contact with the two-phase immersion coolant. For structures where the DBC substrate 102 directly participates in heat exchange, the contact angle control region 103 is preferably disposed on the lower surface of the lower copper layer 106. For two-phase immersion liquid-cooled IGBT power modules with a housing or base plate structure, the contact angle control region 103 can also be disposed on the heat dissipation surface of the housing or the outer surface of the base plate. The heat generated when the chip 101 is working is transferred to the contact angle control region 103 through the upper copper foil layer 104, the ceramic insulating layer 105, and the lower copper layer 106. The two-phase immersion coolant absorbs heat and undergoes phase change boiling in the contact angle control region 103.

[0059] The contact angle control region 103 includes a hydrophilic region 107 and a relatively hydrophobic region 108. The hydrophilic region 107 and the relatively hydrophobic region 108 have different static contact angles. The hydrophilic region 107 is used to improve the spreading and replenishment capability of the two-phase immersed coolant in the corresponding heat exchange zone of the chip 101. The relatively hydrophobic region 108 is used to reduce the adhesion of boiling bubbles to the heat exchange surface, making it easier for boiling bubbles to leave the heat exchange surface. The hydrophilic region 107 and the relatively hydrophobic region 108 form a spatially distributed wettability difference on the same heat exchange surface, thereby obtaining corresponding surface conditions for liquid replenishment and bubble detachment within the contact angle control region 103.

[0060] The heat transfer area corresponding to chip 101 is the orthographic projection area of ​​chip 101 on the lower surface of the lower copper layer 106, the heat dissipation surface of the outer casing, or the outer surface of the base plate, and the peripheral heat diffusion area formed around the orthographic projection area. When the heat generated by chip 101 is transferred downwards through the DBC substrate 102, it diffuses laterally. Therefore, the high heat flux density areas on the lower surface of the lower copper layer 106, the heat dissipation surface of the outer casing, or the outer surface of the base plate are typically larger than the geometric orthographic projection area of ​​chip 101. The peripheral heat diffusion area can be an area extending outwards from the orthographic projection area by 0.5 to 3 times the thickness of the ceramic insulating layer 105. Defining the heat transfer area corresponding to chip 101 as a combination of the orthographic projection area and the peripheral heat diffusion area allows the hydrophilic region 107 to cover areas with higher actual heat transfer loads.

[0061] The hydrophilic region 107 covers at least a portion of the heat exchange region corresponding to chip 101. This allows for better two-phase immersion coolant replenishment in the high heat flux density region. The relatively hydrophobic region 108 is located outside the hydrophilic region 107, between adjacent heat exchange regions of chip 101, at the edge of the contact angle control region 103, or in the region corresponding to the bubble discharge path. The bubble discharge path can be a path formed by the relatively hydrophobic region 108 continuously extending from the outside of the hydrophilic region 107 towards the edge of the contact angle control region 103, or it can be a continuous arrangement direction of the relatively hydrophobic regions 108 between adjacent heat exchange regions of chip 101.

[0062] The hydrophilic region 107 forms a preferred liquid replenishment location, while the relatively hydrophobic region 108 forms a preferred bubble detachment location. After boiling bubbles form near the hydrophilic region 107, they can migrate to the relatively hydrophobic region 108 under the influence of buoyancy, merging, or liquid disturbance, and detach from the heat exchange surface on the surface of the relatively hydrophobic region 108. The relatively hydrophobic region 108 is not intended to weaken the wettability of the entire heat exchange surface, but rather to arrange a sustainable bubble detachment path near the high heat flux density region, reducing the situation where boiling bubbles cover the corresponding heat exchange area of ​​chip 101 for extended periods.

[0063] When multiple chips 101 are arranged side by side, each chip 101 can be provided with a corresponding hydrophilic region 107. Multiple hydrophilic regions 107 can be connected by narrow strip-shaped hydrophilic connection regions to form a continuous liquid replenishment path. Relatively hydrophobic regions 108 can be provided between the heat exchange regions of adjacent chips 101, so that boiling bubbles are preferentially discharged from the gaps between chips 101, reducing the possibility of boiling bubbles merging between the heat exchange regions of each chip 101 to form a large-area gas film.

[0064] In a preferred embodiment, the static contact angle of the hydrophilic region 107 is less than or equal to 50°, more specifically, it can be from 10° to 45°; the static contact angle of the relatively hydrophobic region 108 is greater than or equal to 70°, more specifically, it can be from 75° to 120°. The difference in static contact angle between the hydrophilic region 107 and the relatively hydrophobic region 108 is not less than 20°, preferably not less than 30°.

[0065] In this invention, the static contact angle refers to the angle between the solid-liquid-gas three-phase contact line of a droplet, measured by a contact angle meter at room temperature using a two-phase submerged coolant as the test liquid. During testing, droplets of 2 μL to 5 μL of the two-phase submerged coolant are added to the surface to be tested. For the same area, at least three measurement points are selected, and the average value of these three points is taken as the static contact angle for the corresponding area. Since the surface tension of a two-phase submerged coolant is typically different from that of water, using a practically used two-phase submerged coolant as the test liquid is more conducive to ensuring that the test results reflect the actual boiling heat transfer state.

[0066] The contact angle control region 103 can adopt a strip-shaped partition structure, a grid-shaped partition structure, an island-shaped partition structure, a surrounding partition structure, or a combined partition structure. In the strip-shaped partition structure, the hydrophilic region 107 and the relatively hydrophobic region 108 are alternately arranged along the length or width direction of the contact angle control region 103. The strip-shaped hydrophilic region 107 forms a continuous liquid replenishment path, and the strip-shaped relatively hydrophobic region 108 forms a continuous bubble discharge path. When the chips 101 are arranged along the length of the module, or when the module mounting posture is relatively fixed and the boiling bubbles mainly rise in one direction, the strip-shaped partition structure is easier to match with the arrangement of the chips 101 and the bubble flow direction.

[0067] In the grid-like partitioned structure, hydrophilic regions 107 form an interconnected liquid replenishment network, while relatively hydrophobic regions 108 are located between the liquid replenishment networks. After the hydrophilic regions 107 form the liquid replenishment network, the two-phase immersed coolant can be replenished to the corresponding heat exchange area of ​​the chip 101 from multiple directions. The relatively hydrophobic regions 108, located between grid cells, can provide multiple detachment points for boiling bubbles. This structure is suitable for multi-chip 101 parallel packaging structures and large-area heat exchange surfaces.

[0068] In the island-shaped partition structure, the hydrophilic regions 107 are arranged in an island-like form corresponding to the heat exchange areas of the chip 101, while the relatively hydrophobic regions 108 are arranged around or distributed among the hydrophilic regions 107. When the chip 101 is relatively dispersed, each island-shaped hydrophilic region 107 can provide local liquid replenishment for the corresponding chip 101, while the relatively hydrophobic regions 108 form a bubble discharge path between multiple hydrophilic regions 107.

[0069] In the surrounding partitioned structure, a hydrophilic region 107 is disposed in the corresponding heat exchange region of chip 101, and a relatively hydrophobic region 108 is disposed around the outer periphery of the hydrophilic region 107. During operation, the hydrophilic region 107 maintains the liquid supply to the corresponding heat exchange region of chip 101, while the relatively hydrophobic region 108 guides boiling bubbles to migrate outward from the boundary of the hydrophilic region 107 and detach. This structure is suitable for module surfaces with relatively concentrated high heat flux densities.

[0070] In practical implementation, strip-shaped, grid-shaped, island-shaped, and surrounding structures can also be used in combination. For example, an island-shaped hydrophilic region 107 is provided in the heat exchange area corresponding to each chip 101, a strip-shaped relatively hydrophobic region 108 is provided between multiple island-shaped hydrophilic regions 107, and a surrounding relatively hydrophobic region 108 is provided around the contact angle control area 103.

[0071] The contact angle control region 103 consists of a hydrophilic region 107 and a relatively hydrophobic region 108. The area of ​​the hydrophilic region 107 can account for 40% to 80% of the total area of ​​the contact angle control region 103, and the area of ​​the relatively hydrophobic region 108 can account for 20% to 60% of the total area of ​​the contact angle control region 103. When the heat exchange area corresponding to the chip 101 is large or the heat flux density of the chip 101 is high, the area ratio of the hydrophilic region 107 can be set higher to enhance the supply capacity of the two-phase immersed coolant. When boiling bubbles tend to accumulate at the edge of the module, in the gap area of ​​the chip 101, or in the local recessed area of ​​the heat exchange surface, the area ratio of the relatively hydrophobic region 108 can be set higher to improve the bubble detachment capability.

[0072] The hydrophilic region 107 can be achieved by altering the surface chemical composition, increasing surface energy, constructing micro / nano structures that facilitate liquid spread, or forming a hydrophilic porous layer. A hydrophilic metal oxide coating can be deposited on the corresponding area of ​​the lower copper layer 106, the heat dissipation surface of the outer casing, or the outer surface of the base plate. The hydrophilic metal oxide coating can be at least one of aluminum oxide, titanium oxide, silicon oxide, or zinc oxide. After the hydrophilic metal oxide coating increases the surface energy, the two-phase immersed coolant spreads more easily in the hydrophilic region 107, and the static contact angle of the hydrophilic region 107 is correspondingly reduced.

[0073] The hydrophilic region 107 can also be formed through plasma treatment. Plasma treatment can clean the surface and introduce high surface energy groups, making the hydrophilic region 107 exhibit stronger wetting ability to the two-phase immersed coolant. The corresponding region can also undergo laser micro-texturing, chemical oxidation, or electrochemical roughening treatment to form grooves, pits, micron-level protrusions, nano-level rough structures, or multi-level rough structures. The above structures can provide capillary replenishment capability, making it easier for the two-phase immersed coolant to enter the hydrophilic region 107 and maintain the continuity of the liquid film.

[0074] When the heat flux density in the heat exchange zone corresponding to chip 101 is high and the local liquid replenishment demand is large, a hydrophilic porous layer can be formed in the corresponding area. The hydrophilic porous layer can be formed by sintering metal particles, depositing porous oxides, chemical etching, or electrochemical deposition. The hydrophilic porous layer utilizes capillary force to enhance the local liquid replenishment capacity, allowing the local area after boiling bubbles detach to be quickly refilled by the two-phase immersed coolant, thus shortening the duration of dry spots.

[0075] The relatively hydrophobic region 108 can be achieved by reducing surface energy, constructing micro / nano structures that reduce bubble adhesion, or a combination of both. A fluoropolymer coating, a silane-modified layer, or a low surface energy coating can be deposited in the corresponding region to increase the static contact angle of the two-phase immersed coolant on the relatively hydrophobic region 108. After the low surface energy coating reduces the adhesion between boiling bubbles and the heat exchange surface, the boiling bubbles are more easily detached from the relatively hydrophobic region 108.

[0076] The relatively hydrophobic region 108 can also have micron- or nano-scale protrusions, grooves, trenches, or composite micro / nano structures, and be combined with low surface energy materials to form a composite surface layer. The composite surface layer can reduce bubble adhesion and can also induce bubbles to converge, grow, and detach in the relatively hydrophobic region 108 through geometric boundaries. The relatively hydrophobic region 108 should not completely block the contact between the two-phase immersed coolant and the heat exchange surface. The relatively hydrophobic region 108 is preferably arranged adjacent to the hydrophilic region 107, allowing the two-phase immersed coolant to replenish the boundary of the relatively hydrophobic region 108 from the hydrophilic region 107, reducing the probability of long-term dry spots forming in the relatively hydrophobic region 108.

[0077] In one fabrication method, the contact angle control region 103 is formed using a mask partitioning process. During fabrication, the lower surface of the lower copper layer 106, the heat dissipation surface of the casing, or the outer surface of the base plate is first cleaned and pre-treated to remove oil, oxide contaminants, and particulate impurities. Then, a mask layer is applied to the surface to be treated. The mask layer can be a metal mask, a photoresist mask, an etch-resistant tape mask, or other process materials capable of defining the processing area. When a hydrophilic region 107 needs to be formed, the mask layer exposes the location where the hydrophilic region 107 will be formed and masks the location where the relatively hydrophobic region 108 will be formed. The exposed location undergoes hydrophilic treatment. Hydrophilic treatment can include depositing a hydrophilic metal oxide coating, plasma treatment, laser microtexturing, chemical oxidation, electrochemical roughening, or forming a hydrophilic porous layer. After the hydrophilic treatment is completed, the mask layer is removed or replaced.

[0078] When a relatively hydrophobic region 108 needs to be formed, a mask layer exposes the location where the relatively hydrophobic region 108 will be formed, while masking the already formed hydrophilic region 107. The exposed location undergoes a relatively hydrophobic treatment. This treatment can involve depositing a fluoropolymer coating, forming a silane-modified layer, depositing a low surface energy coating, or constructing a micro / nano composite structure. After the hydrophobic treatment is completed, the mask layer is removed and the surface is cleaned. After the hydrophilic region 107 and the relatively hydrophobic region 108 are prepared, the static contact angles of the hydrophilic region 107 and the relatively hydrophobic region 108 are measured using a contact angle meter. When the difference in static contact angle between the hydrophilic region 107 and the relatively hydrophobic region 108 is not less than 20°, the contact angle control region 103 meets the basic wetting difference requirements; if the difference in static contact angle is insufficient, supplementary treatment can be applied to either the hydrophilic region 107 or the relatively hydrophobic region 108.

[0079] The two-phase immersion coolant is an electrically insulating coolant, specifically a fluorinated liquid, hydrofluoroether coolant, fluoroketone coolant, or other dielectric coolant suitable for immersion cooling of power electronic devices. The two-phase immersion coolant should meet requirements for electrical insulation performance, chemical stability, material compatibility, and boiling point matching. The boiling point of the two-phase immersion coolant should match the allowable operating temperature range of the IGBT power module, enabling the two-phase immersion coolant to undergo phase change boiling in the contact angle control region 103 when the chip 101 generates a heat load, and to dissipate heat through the vaporization latent heat. The materials of the hydrophilic region 107 and the relatively hydrophobic region 108 should be compatible with the two-phase immersion coolant to reduce the possibility of coating swelling, peeling, or contact angle drift after long-term immersion.

[0080] When the IGBT power module is operating, the heat generated by the chip 101 is conducted sequentially through the upper copper foil layer 104, the ceramic insulating layer 105, and the lower copper layer 106 to the contact angle control region 103 on the lower surface of the lower copper layer 106, the heat dissipation surface of the casing, or the outer surface of the base plate. The two-phase immersed coolant absorbs heat and undergoes phase change boiling in the contact angle control region 103. In the hydrophilic region 107, the static contact angle of the two-phase immersed coolant is smaller, making it easier for the coolant to spread and maintain a liquid film on the heat exchange surface. When the hydrophilic region 107 corresponds to the heat exchange area of ​​the chip 101, the ability of the two-phase immersed coolant to replenish areas with high heat flux density is improved, and the probability of local dry spot formation is reduced. The hydrophilic region 107 can also form a capillary replenishment effect through micro / nano structures or hydrophilic porous layers, allowing the liquid to backfill onto the local heat exchange surface after boiling bubbles detach.

[0081] In the relatively hydrophobic region 108, the static contact angle of the two-phase immersed coolant is relatively large, and the adhesion between boiling bubbles and the heat exchange surface is weak, making it easier for boiling bubbles to detach from the heat exchange surface. When the relatively hydrophobic region 108 is located outside the hydrophilic region 107, between the corresponding heat exchange areas of adjacent chips 101, or at the edge of the contact angle control region 103, it can provide a preferential detachment position for boiling bubbles, reducing the prolonged residence of boiling bubbles in the corresponding heat exchange area of ​​chip 101. The hydrophilic region 107 is responsible for liquid supply, while the relatively hydrophobic region 108 is responsible for bubble detachment. With the cooperation of these two types of regions, the contact angle control region 103 can form a relatively stable liquid supply and bubble discharge state during the two-phase immersed boiling heat exchange process. Under the conditions of low voltage ride-through, load fluctuation, and transient thermal shock in wind power generation, the heat flux density of the IGBT power module changes rapidly. The contact angle control region 103 can regulate the coolant spreading and bubble detachment behavior by relying on a fixed wettability spatial distribution.

[0082] In one specific embodiment, the contact angle control region 103 is disposed on the lower surface of the lower copper layer 106 and is configured as a strip-shaped partition structure along the length of the IGBT power module. Multiple chips 101 are disposed on the upper copper foil layer 104, and the heat exchange areas corresponding to each chip 101 are located at different positions on the lower surface of the lower copper layer 106. Hydrophilic regions 107 are correspondingly disposed to the heat exchange areas of the chips 101, and relatively hydrophobic regions 108 are disposed between the heat exchange areas of adjacent chips 101 and at the edge of the contact angle control region 103. The hydrophilic region 107 can be formed by plasma treatment, resulting in a static contact angle of 10° to 45° for the two-phase immersed coolant on the hydrophilic region 107; the relatively hydrophobic region 108 can be formed by a fluoropolymer coating, resulting in a static contact angle of 75° to 120° for the two-phase immersed coolant on the relatively hydrophobic region 108. The difference in static contact angle between the hydrophilic region 107 and the relatively hydrophobic region 108 is not less than 30°. After the IGBT power module is installed in the two-phase immersion liquid cooling system, the hydrophilic region 107 supplies the two-phase immersion coolant to the heat exchange area corresponding to the chip 101, while the relatively hydrophobic region 108 promotes the detachment of boiling bubbles between adjacent chips 101 and in the edge area.

[0083] In another specific embodiment, the contact angle control region 103 is disposed on the heat dissipation surface of the IGBT power module's casing. Based on the projection position of the chip 101 on the heat dissipation surface, the heat exchange area corresponding to the chip 101 is configured as a hydrophilic region 107, and a relatively hydrophobic region 108 is disposed around the periphery of the hydrophilic region 107. The hydrophilic region 107 is formed by depositing a hydrophilic metal oxide coating of titanium dioxide or aluminum oxide, while the relatively hydrophobic region 108 is formed by a silane-modified layer or a low surface energy coating. During operation, the hydrophilic region 107 continuously introduces the two-phase immersion coolant into the high heat flux density region corresponding to the chip 101, while the relatively hydrophobic region 108 guides boiling bubbles to migrate outward from the boundary of the hydrophilic region 107 and detach. With the relatively hydrophobic region 108 surrounding the periphery of the hydrophilic region 107, boiling bubbles are more easily transferred from the boundary of the hydrophilic region 107 to the relatively hydrophobic region 108, thus reducing the probability of the central region of the hydrophilic region 107 being permanently blocked by bubbles.

[0084] In another specific embodiment, the contact angle control region 103 is disposed on the lower surface of the lower copper layer 106. Hydrophilic regions 107 form an interconnected mesh-like liquid replenishment network, and relatively hydrophobic regions 108 are disposed between the mesh units. The contact angle control region 103 consists of hydrophilic regions 107 and relatively hydrophobic regions 108. The area of ​​the hydrophilic regions 107 accounts for 40% to 80% of the total area of ​​the contact angle control region 103, and the area of ​​the relatively hydrophobic regions 108 accounts for 20% to 60% of the total area of ​​the contact angle control region 103. The hydrophilic regions 107 are formed by laser micro-texturing and a hydrophilic metal oxide coating, while the relatively hydrophobic regions 108 are formed by a micro / nano composite structure and modification with low surface energy materials. During operation, the mesh-like hydrophilic regions 107 provide two-phase immersion coolant replenishment to the heat exchange areas corresponding to multiple chips 101, and the relatively hydrophobic regions 108 provide multiple detachment points for boiling bubbles. When the number of bubbles increases in a local area, the surrounding hydrophilic zone 107 can still replenish liquid to the high heat flux density area, which helps to control the spread of local dry spots.

[0085] In a further specific embodiment, the contact angle control region 103 simultaneously includes a static contact angle gradient distribution structure within the hydrophilic region 107 and an asymmetric micro-ratchet array structure within the relatively hydrophobic region 108. This structure is suitable for two-phase immersed liquid-cooled IGBT power modules operating under high power density conditions or transient thermal shock conditions. Under these conditions, the local heat flux density in the central region of the heat exchange area corresponding to chip 101 is higher than that in the edge region. If the hydrophilic region 107 uses only a single static contact angle, the backfilling rate of the two-phase immersed coolant may be lower than the local liquid film evaporation rate, posing a risk of dry spots in the central region of the heat exchange area corresponding to chip 101. Simultaneously, when the relatively hydrophobic region 108 receives a large number of boiling bubbles, without physical directional guidance, the boiling bubbles are prone to collision and merging under the influence of buoyancy and local flow field disturbances, increasing the residence time of the boiling bubbles in the contact angle control region 103. The static contact angle gradient distribution structure is used to improve the directional replenishment capability of the two-phase submerged coolant, and the asymmetric micro ratchet array structure is used to improve the directional discharge capability of boiling bubbles.

[0086] A static contact angle gradient distribution structure is set within the hydrophilic region 107. At the center of the orthographic projection area of ​​the heat exchange zone corresponding to chip 101, the static contact angle is set to its minimum value within the hydrophilic region 107. The center of the heat exchange zone corresponding to chip 101 can be the geometric center of the orthographic projection area of ​​chip 101 on the lower surface of the lower copper layer 106, the heat dissipation surface of the casing, or the outer surface of the base plate, or it can be the center position corresponding to the location of maximum heat flux density. From the outer periphery of the hydrophilic region 107 towards the center of the heat exchange zone corresponding to chip 101, the static contact angle decreases continuously or in a step-like manner. The outer periphery of the hydrophilic region 107 refers to the boundary region of the hydrophilic region 107 near the relatively hydrophobic region 108 or near the edge of the contact angle control region 103.

[0087] From the center of the heat exchange zone corresponding to chip 101 towards the outer periphery of the hydrophilic zone 107, the static contact angle increases continuously or in a stepwise manner. The static contact angle at the outer periphery of the hydrophilic zone 107 is relatively large, while the static contact angle at the center of the hydrophilic zone 107 is relatively small. Under the influence of surface tension imbalance, the two-phase immersed coolant exhibits a tendency to replenish towards the center of the heat exchange zone corresponding to chip 101. This replenishment tendency can be characterized by the capillary driving force per unit width, which is represented by the following formula:

[0088]

[0089] in, Capillary driving force per unit width, in N / m; The surface tension of the two-phase submerged coolant is expressed in N / m. Location of the water-friendly area 107 along the length of the wetting path Local static contact angle at the location; This is the cosine value corresponding to the local static contact angle; The length of the wetting path from the outer periphery of the hydrophilic zone 107 to the center of the corresponding heat exchange zone of the chip 101 is expressed in meters. The integral variable is along the wetting path length, in meters. For the hydrophilic region 107 where the static contact angle decreases in a stepped manner, the difference in the cosine value of the local static contact angle between adjacent stepped regions can be discretized and summed according to the wetting path length to obtain the equivalent value of the capillary driving force per unit width.

[0090] Static contact angle gradient distribution structures can be fabricated using a femtosecond laser dual-mirror scanning system combined with energy density modulation technology.

[0091] During fabrication, the lower surface of the copper layer 106, after pre-cleaning, is fixed on a six-axis precision machining platform. The center wavelength of the femtosecond laser output can be from 900 nm to 1100 nm, and the pulse width can be from 200 fs to 500 fs. When machining the hydrophilic region 107, the control system guides the laser beam from the outer periphery of the hydrophilic region 107 to the center of the corresponding heat exchange region of the chip 101 according to a preset Archimedean spiral trajectory. The laser single pulse energy can be linearly increased from 3 μJ to 8 μJ at the outer periphery of the hydrophilic region 107 to 12 μJ to 20 μJ at the center of the corresponding heat exchange region of the chip 101. The scanning speed can be from 300 mm / s to 800 mm / s, and the spot overlap rate can be from 75% to 90%. In a set of specific process parameters, the center wavelength of the femtosecond laser output is 1030 nm, the pulse width is 290 fs, the laser single pulse energy increases linearly from 5 μJ at the outer periphery of the hydrophilic region 107 to 15 μJ at the center of the heat exchange region corresponding to chip 101, the scanning speed is maintained at 500 mm / s, and the spot overlap rate is set to 85%.

[0092] As the laser energy density increases from the outer periphery of the hydrophilic region 107 towards the center of the corresponding heat exchange region of the chip 101, the depth of the micron-scale mesh trenches formed on the lower surface of the lower copper layer 106 gradually increases from 5 μm to 25 μm, and the packing density of the nanoscale recast particles increases simultaneously. Those skilled in the art can establish the correspondence between the laser energy parameters and the final surface contact angle through a limited number of experiments to obtain the desired gradient distribution.

[0093] After laser ablation, the lower surface of the lower copper layer 106 is immersed in a 0.5 mol / L hydrogen peroxide aqueous solution and subjected to hydrothermal oxidation at 40°C to 80°C for 60 minutes. This process allows for the in-situ growth of a copper oxide and cuprous oxide composite hydrophilic metal oxide coating with a thickness of 180 nm to 220 nm on the lower surface of the lower copper layer 106. The hydrothermal oxidation process preserves the differences in the depth of the micron-scale mesh trenches and the differences in the density of the nano-scale recast particles formed by laser processing, resulting in the composite hydrophilic metal oxide coating. The multi-level roughness of the micro- and nano-scales creates a gradient on a spatial scale, giving the composite hydrophilic metal oxide coating a high surface energy.

[0094] Based on the above structure, the static contact angle of the outer periphery of the hydrophilic region 107 can be controlled to be 40° to 50°, and the static contact angle of the center of the hydrophilic region 107 can be controlled to be 10° to 15°, thereby forming a continuous static contact angle gradient difference. The two-phase immersion coolant can be replenished along the wetting path length towards the center of the corresponding heat exchange area of ​​the chip 101, so that the high heat flux density area in the center can obtain a stronger liquid backfilling capability.

[0095] An asymmetric micro-ratchet array structure is deployed between the heat exchange zones of adjacent chips 101 and in the region corresponding to the bubble discharge path. The asymmetric micro-ratchet array structure consists of multiple micrometer-sized ratchet units arranged in the same direction along the bubble discharge path. Each micrometer-sized ratchet unit has a serrated cross-sectional profile. The serrated cross-sectional profile can be a right-angled triangle or an obtuse-angled triangle.

[0096] Each micrometer-scale ratchet unit has a steep slope facing the hydrophilic zone 107 and a gentle slope facing downstream of the bubble discharge path. The angle between the steep slope and the reference horizontal plane is greater than the angle between the gentle slope and the reference horizontal plane. Specifically, the angle between the steep slope and the reference horizontal plane can be 60° to 85°, and the angle between the gentle slope and the reference horizontal plane can be 5° to 30°. The bottom edge period length of the micrometer-scale ratchet unit can be 50 μm to 200 μm, and the vertical height can be 10 μm to 50 μm. In a specific set of structural parameters, the angle between the steep slope and the reference horizontal plane is set to 75°, the angle between the gentle slope and the reference horizontal plane is set to 15°, the bottom edge period length of the micrometer-scale ratchet unit is set to 100 μm, and the vertical height is set to 26 μm. The reference horizontal plane refers to the average plane of the lower surface of the lower copper layer 106, the heat dissipation surface of the outer casing, or the outer surface of the base plate when the micrometer-scale ratchet unit is not formed.

[0097] For copper surfaces, asymmetric micro-ratchet array structures can be fabricated using femtosecond laser processing, precision micro-milling, electrochemical micromachining, or metal microforming processes. For structures where an etchable metal microstructure layer is pre-formed on the lower surface of the copper layer 106, the heat dissipation surface of the outer shell, or the outer surface of the base plate, asymmetric micro-ratchet array structures can also be formed using three-dimensional grayscale photolithography and etching processes. After the micron-level ratchet units are formed, a fluorine-containing low surface energy coating can be formed on the surface of the micron-level ratchet units using plasma polymerization, vapor deposition, spraying, or dip coating methods.

[0098] The fluorinated low surface energy coating can be a polytetrafluoroethylene (PTFE) or PTFE-like fluorinated low surface energy coating, with a thickness of 40 nm to 60 nm, enabling the macroscopic static contact angle of the relatively hydrophobic region 108 to reach 110° to 120°. The fluorinated low surface energy coating improves the liquid repellency of the relatively hydrophobic region 108 and reduces the adhesion of boiling bubbles to the surface of the relatively hydrophobic region 108.

[0099] The asymmetric micro-ratchet array structure can alter the force state during the detachment and slippage of boiling bubbles. When boiling bubbles nucleate and enter the growth phase within the relatively hydrophobic region 108, the solid-liquid-gas three-phase contact line of the boiling bubbles spans multiple micron-scale ratchet units. When the boiling bubble boundary expands towards the steep slope side, it encounters significant geometric resistance, resulting in a change in the local advancing contact angle; when the boiling bubble boundary expands towards the gentle slope side, the geometric transition is smoother, and the local retreating contact angle changes. Due to the asymmetric structure of the steep and gentle slopes, the pinning state of the solid-liquid-gas three-phase contact line differs in the direction of bubble discharge and the reverse direction, thus generating a unidirectional net driving force along the bubble discharge path. This unidirectional net driving force is characterized by the following formula:

[0100]

[0101] in, This is the net driving force in one direction, expressed in N. The surface tension of the two-phase submerged coolant is expressed in N / m. The length of the contact line between the solid, liquid, and gas phases is expressed in meters (m). The local retraction contact angle is the micron-level ratchet unit surface, which is measured when the boiling bubble contact line retracts along the bubble discharge path direction; The local advancing contact angle is the surface of the micron-level ratchet unit, which is measured when the boiling bubble contact line advances in the opposite direction of the bubble discharge path; This is the cosine value corresponding to the local retreat contact angle; This is the cosine value corresponding to the local forward contact angle. The combined effect of the unidirectional net driving force and the natural buoyancy force of the bubbles in the two-phase submerged coolant causes the detached boiling bubbles to be transported along the bubble discharge path and reduces the probability of the boiling bubbles migrating in the opposite direction to the hydrophilic region 107.

[0102] In practical implementation, a two-phase immersion liquid cooling test platform was constructed to verify the synergistic heat transfer effect of the static contact angle gradient distribution structure and the asymmetric micro-ratchet array structure. The test platform includes a visualized sealed cooling container, a condensation assembly, a high-precision DC programmable power supply, a data acquisition module, and a high-speed camera. The two-phase immersion coolant used was the electronic fluorinated liquid HFE-7100, the test environment was one standard atmosphere, and the saturated boiling point of the two-phase immersion coolant was maintained at 61°C.

[0103] The test sample uses an IGBT power module containing four parallel-connected chips 101 to heat an equivalent copper block. Four T-type thermocouples are embedded 1 mm below the surface of the lower copper layer 106. The thermocouples have a measurement accuracy of ±0.1℃, and the data acquisition module's sampling frequency is set to 10 Hz. A high-precision DC programmable power supply provides a stepped-increase heating power to the equivalent copper block, with a single power residence time of 15 minutes to allow the system to reach thermodynamic steady state. The data acquisition module or an external computer performs image recognition processing on images captured by a high-speed camera to extract the boiling bubble detachment diameter data. The boiling bubble detachment diameter is the diameter of the equivalent circle of the projected area of ​​the boiling bubble in the image frame before it detaches from the heat exchange surface.

[0104] During the test, the system heat loss was first recorded under no-boiling load conditions, and the heat loss power was subtracted from the input power. Surface temperature Temperature measured by a thermocouple embedded 1 mm from the surface Based on Fourier's law of thermal conductivity, the following calculations were performed:

[0105] ;

[0106] in This is the distance from the thermocouple measuring point to the surface. The thermal conductivity is the equivalent of the heated copper block. The high-speed camera is set to a frame rate of 5000 fps, with a magnification that allows for a single pixel resolution better than 10 μm. It shoots from a direction perpendicular to the surface through a transparent window to capture images of the boiling bubble detachment process.

[0107] The surface heat flux density of the lower surface of the lower copper layer 106 is calculated using the following formula:

[0108]

[0109] in, The surface heat flux density of the lower copper layer 106 is expressed in W / cm². The thermal conductivity is the equivalent of the heated copper block. and These are the temperatures measured at different locations along the thickness direction; This represents the distance between the two temperature measurement locations.

[0110] The heat transfer coefficient is calculated using the following formula:

[0111]

[0112] in, The heat transfer coefficient is expressed in W / (cm²·K). The surface heat flux density of the lower surface of the lower copper layer 106; This refers to the surface temperature of the lower copper layer 106. The saturation temperature of the two-phase submerged coolant under the test pressure.

[0113] The maximum heat transfer coefficient is the highest value of the heat transfer coefficient calculated under different heat flux densities during the test. Boiling crisis refers to the transition of the heat exchange surface from nucleus boiling to a state of localized gas film coverage, characterized by a continuous increase in surface temperature during the power maintenance phase without reaching a steady state. The critical heat flux density is determined as follows: when the surface temperature increases by more than 10°C within an adjacent power step and cannot return to a steady state, the heat flux density of the previous steady state is taken as the critical heat flux density.

[0114] In one set of tests, the test samples were divided into four groups.

[0115] The first group adopts a conventional control structure. The hydrophilic region 107 on the lower surface of the lower copper layer 106 has a uniform static contact angle of 45°, while the relatively hydrophobic region 108 has a uniform static contact angle of 115° and a smooth surface without an asymmetric micro-ratchet array structure.

[0116] The second group is a single-variable test structure. The hydrophilic region 107 introduces a static contact angle gradient distribution structure of 10° to 45°, while the hydrophobic region 108 maintains a flat, non-asymmetric micro-ratchet array structure.

[0117] The third group is the single-variable test structure two. The hydrophilic zone 107 maintains a uniform 45° static contact angle, while the hydrophobic zone 108 introduces an asymmetric micro-ratchet array structure with a steep slope surface having an angle of 75° with the reference horizontal plane and a gentle slope surface having an angle of 15° with the reference horizontal plane.

[0118] The fourth group consists of composite structures that simultaneously possess a static contact angle gradient distribution structure and an asymmetric micro-ratchet array structure. All test samples were ultrasonically cleaned with anhydrous ethanol before testing and dried in a vacuum drying oven for 120 minutes. Thermodynamic testing was initiated after eliminating environmental heat leakage errors and completing adiabatic calibration.

[0119] Table 1. Comparison of the synergistic performance of static contact angle gradient distribution structure and asymmetric micro ratchet array structure;

[0120] According to the test results shown in Table 1, the first group of homogeneous hydrophilic region 107 combined with the conventional relatively hydrophobic region 108 experienced a boiling crisis when the heat flux density reached 125.4 W / cm². As the heat flux density increased, the two-phase submerged coolant underwent violent vaporization in the high-temperature region, and a large-scale gas film covered the surface of the hydrophilic region 107, obstructing the liquid return path. The second group, by increasing the static contact angle gradient distribution structure, raised the critical heat flux density to 168.7 W / cm². These results indicate that the capillary driving force per unit width generated by the static contact angle gradient distribution structure can enhance the liquid supply to the center of the heat exchange zone corresponding to chip 101; however, the relatively hydrophobic region 108 remains a flat structure, and the boiling bubble detachment ability has not been improved synchronously. The accumulation of boiling bubbles in the surrounding area still limits the further increase of the critical heat flux density. The third group reduced the boiling bubble detachment diameter from 1.85 mm to 0.95 mm by introducing an asymmetric micro ratchet array structure, indicating that the asymmetric micro ratchet array structure can promote the detachment of boiling bubbles with a smaller diameter; however, the hydrophilic region 107 is still a uniform static contact angle structure, with insufficient active liquid supply capacity and a relatively limited increase in critical heat flux density.

[0121] The fourth group, employing both a static contact angle gradient distribution structure and an asymmetric micro-ratchet array structure, increased the critical heat flux density to 224.6 W / cm², achieving a maximum heat transfer coefficient of 8.41 W / (cm²·K). At a heat flux density of 100 W / cm², the highest temperature of the equivalent chip 101 was 72.5℃, lower than the 87.3℃ of the first group, 80.1℃ of the second group, and 83.6℃ of the third group. The test results indicate that the static contact angle gradient distribution structure enhances the directional liquid replenishment capability of the hydrophilic region 107 to the center of the corresponding heat exchange region of the chip 101, while the asymmetric micro-ratchet array structure improves the directional bubble removal capability of the relatively hydrophobic region 108 along the bubble removal path. With the combination of these two structures, both liquid replenishment and bubble removal are improved, resulting in a corresponding increase in the two-phase immersion boiling heat transfer performance and a corresponding decrease in the highest temperature of the equivalent chip 101.

[0122] Alternatively, conventional metal surfaces without contact angle partitioning, overall hydrophilic surfaces, overall relatively hydrophobic surfaces, and ordinary roughened surfaces can be used as control structures. Conventional metal surfaces are used to reflect the liquid supply and bubble detachment states without wettability partitioning; overall hydrophilic surfaces are used to reflect the bubble retention state that may occur after overall enhanced liquid spreading; overall relatively hydrophobic surfaces are used to reflect the insufficient liquid supply state that may occur after overall promotion of bubble detachment; and ordinary roughened surfaces are used to reflect the heat transfer state when only the surface area or nucleation points are increased but the matching relationship between the hydrophilic region 107 and the relatively hydrophobic region 108 is not formed. The above control structures and the contact angle control region 103 can use the same chip 101 arrangement, the same DBC substrate 102 size, the same two-phase immersion coolant, the same immersion depth, and the same power loading conditions. Comparison indicators may include the highest junction temperature of the chip 101, the equivalent thermal resistance of the module, the boiling bubble detachment frequency, the location of localized dry spots, the surface temperature uniformity of the contact angle control region 103, and the contact angle retention after thermal cycling.

[0123] The contact angle control zone 103 should remain stable within the operating temperature range of the IGBT power module and in a two-phase immersion coolant environment. After undergoing at least 100 thermal cycles, the static contact angle change of the hydrophilic zone 107 and the relatively hydrophobic zone 108 should preferably not exceed 15°. Thermal cycling refers to the cyclical change between the low-load temperature and the high-load temperature of the IGBT power module. The low-load temperature can be 25°C to 40°C, and the high-load temperature can be 80°C to 120°C. The heating / cooling rate can be 1°C / min to 5°C / min, and each temperature end should be held for 10 min to 30 min. The surface treatment layer of the hydrophilic zone 107 and the relatively hydrophobic zone 108 should be stably bonded to the lower surface of the lower copper layer 106, the heat dissipation surface of the casing, or the outer surface of the base plate, reducing the possibility of peeling, flaking, or continuous detachment during the two-phase boiling bubble scouring process.

[0124] In specific implementations, the contact angle control region 103 can be located on the lower surface of the lower copper layer 106, the heat dissipation surface of the outer casing, the outer surface of the base plate, or other module heat exchange surfaces that are in direct contact with the two-phase immersed coolant. The hydrophilic region 107 can be formed by hydrophilic coatings, plasma treatment, chemical oxidation, laser microtexturing, electrochemical treatment, porous structures, static contact angle gradient distribution structures, or combinations thereof. The relatively hydrophobic region 108 can be formed by low surface energy coatings, fluorine-containing material modification, silane modification, micro-nano composite structures, asymmetric micro-ratchet array structures, or combinations thereof. The contact angle control region 103 can adopt a strip-shaped, grid-shaped, island-shaped, ring-shaped, or combination of multiple structures. The specific partitioning shape can be adjusted according to the number of chips 101, the arrangement of chips 101, the heat flux density distribution, the installation posture of the IGBT power module, and the flow state of the two-phase immersed coolant. The two-phase immersion coolant can be a fluorinated liquid, a hydrofluoroether coolant, a fluoroketone coolant, or other electrically insulating dielectric coolant. As long as the two-phase immersion coolant can undergo phase change boiling within the operating temperature range of the IGBT power module and remain compatible with the material of the contact angle control region 103, it can be used in this invention.

[0125] The two-phase immersion liquid-cooled IGBT power module of this invention can be applied to wind power converters, as well as to rail transit traction converters, new energy vehicle power converters, industrial frequency converters, flexible DC transmission converter equipment, and other high-power power electronic equipment. The contact angle adjustment area 103 is mainly formed by surface engineering treatment of the lower surface of the lower copper layer 106, the heat dissipation surface of the outer shell, or the outer surface of the base plate. It does not require changing the circuit structure of the internal chip 101 of the IGBT power module, nor does it require changing the main structure of the two-phase immersion liquid cooling system, making it easy to integrate with existing module packaging and immersion cooling systems.

[0126] This invention divides the surface wetting characteristics of the IGBT power module into two factors: liquid supply capability and bubble removal capability, and processes them separately on the same heat exchange interface through a contact angle control zone 103. The contact angle control zone 103 spatially partitions the heat exchange area corresponding to the chip 101 and the bubble discharge path, ensuring that the high heat flux density area receives two-phase immersion coolant supply, while the bubble discharge area has low bubble adhesion. The static contact angle gradient distribution structure generates a unit-width capillary driving force pointing towards the center of the heat exchange area corresponding to the chip 101 within the hydrophilic region 107, and the asymmetric micro-ratchet array structure generates a unidirectional net driving force along the bubble discharge path direction within the relatively hydrophobic region 108. The combination of these structures improves the heat exchange efficiency, heat exchange stability, and operational reliability of the two-phase immersion liquid-cooled IGBT power module.

[0127] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0128] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. It should be noted that any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A two-phase immersion liquid-cooled IGBT power module based on surface contact angle partitioning, characterized in that, This includes the chip, DBC substrate, and contact angle adjustment area; The DBC substrate includes an upper copper foil layer, a ceramic insulating layer and a lower copper layer arranged sequentially from top to bottom. The chip is disposed on the upper copper foil layer. The lower surface of the lower copper layer is a heat exchange surface that is in direct contact with the two-phase immersion coolant, used to transfer the heat generated by the chip to the two-phase immersion coolant. The contact angle adjustment region is disposed on the lower surface of the lower copper layer; The contact angle control region includes at least one hydrophilic region and at least one relatively hydrophobic region, wherein the static contact angle of the hydrophilic region is smaller than that of the relatively hydrophobic region, and the difference in static contact angle between the hydrophilic region and the relatively hydrophobic region is not less than 20°. The hydrophilic region covers at least a portion of the heat exchange area corresponding to the chip, and is used to enhance the two-phase immersion coolant supply to the heat exchange area corresponding to the chip; the relatively hydrophobic region is disposed outside the hydrophilic region, between adjacent heat exchange areas corresponding to the chip, at the edge of the contact angle control region, or on the bubble discharge path for boiling bubbles to be discharged, and is used to promote the detachment of boiling bubbles from the heat exchange surface. The heat exchange area corresponding to the chip is the orthographic projection area of ​​the chip on the lower surface of the lower copper layer, and the peripheral heat diffusion area formed around the orthographic projection area.

2. A two-phase immersion liquid-cooled IGBT power module based on surface contact angle partitioning according to claim 1, characterized in that, The surrounding heat diffusion region is an area extending outward from the projected region by 0.5 to 3 times the thickness of the ceramic insulation layer.

3. A two-phase immersion liquid-cooled IGBT power module based on surface contact angle partitioning according to claim 1, characterized in that, The static contact angle of the hydrophilic region is less than or equal to 50°, and the static contact angle of the relatively hydrophobic region is greater than or equal to 70°.

4. A two-phase immersion liquid-cooled IGBT power module based on surface contact angle partitioning according to claim 3, characterized in that, The static contact angle of the hydrophilic region is 10° to 45°, the static contact angle of the relatively hydrophobic region is 75° to 120°, and the difference in static contact angle between the hydrophilic region and the relatively hydrophobic region is not less than 30°.

5. A two-phase immersion liquid-cooled IGBT power module based on surface contact angle partitioning according to claim 1, characterized in that, The contact angle control region is composed of the hydrophilic region and the relatively hydrophobic region. The area of ​​the hydrophilic region accounts for 40% to 80% of the total area of ​​the contact angle control region, and the area of ​​the relatively hydrophobic region accounts for 20% to 60% of the total area of ​​the contact angle control region.

6. A two-phase immersion liquid-cooled IGBT power module based on surface contact angle partitioning according to claim 1, characterized in that, The contact angle control area is a strip-shaped partition structure, a grid-shaped partition structure, an island-shaped partition structure, a surrounding partition structure, or a combined partition structure formed by a combination of two or more of the above structures.

7. A two-phase immersion liquid-cooled IGBT power module based on surface contact angle partitioning according to claim 6, characterized in that, In the surrounding partition structure, the hydrophilic region is located in the heat exchange region corresponding to the chip, and the relatively hydrophobic region is located around the outer periphery of the hydrophilic region.

8. A two-phase immersion liquid-cooled IGBT power module based on surface contact angle partitioning according to claim 1, characterized in that, The hydrophilic region includes at least one of the following: a hydrophilic metal oxide coating, a plasma-treated layer, a laser microtextured layer, a chemically oxidized layer, an electrochemically roughened layer, or a hydrophilic porous layer.

9. A two-phase immersion liquid-cooled IGBT power module based on surface contact angle partitioning according to claim 8, characterized in that, The hydrophilic metal oxide coating includes at least one of aluminum oxide, titanium oxide, silicon oxide, or zinc oxide.

10. A two-phase immersion liquid-cooled IGBT power module based on surface contact angle partitioning according to claim 1, characterized in that, The relatively hydrophobic region includes at least one of the following: a fluoropolymer coating, a silane-modified layer, a low surface energy coating, a micro / nano composite structure, or a composite surface layer formed by the micro / nano composite structure and a low surface energy material.

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