Micro-reservoir pump-out resistant thermal interface structure for power module thermal interface materials

Abstract

The application discloses a micro-reservoir anti-pumping thermal interface structure of a power module thermal interface material, which comprises a substrate, a micro-reservoir array arranged on the substrate and a thermal interface material filled in the micro-reservoirs and interface gaps. The micro-reservoir array is distributed in a region outside a heat spreading angle heat transfer range of the substrate and comprises a plurality of periodically arranged micro-reservoir units, each of which is a groove structure recessed to the inside of the substrate. The application realizes the self-supply function of the thermal interface material by using the capillary action of the micro-reservoirs, and the micro-reservoir structure plays a role of elastic buffering, reduces the rigidity of the connecting interface, effectively inhibits the pumping effect and reduces the thermal fatigue damage, thereby significantly improving the long-term thermal reliability of the power module while ensuring the high thermal conductivity.

Description

Technical Field

[0001] This invention belongs to the field of power electronic device packaging and heat dissipation technology, specifically relating to a micro-reservoir anti-pumping thermal interface structure for power module thermal interface materials. Background Technology

[0002] The power module and the external heat dissipation structure are typically connected via a thermal interface material (TIM). The main function of the TIM is to fill the microscopic gaps between the power module substrate and the heatsink, reducing contact thermal resistance and improving heat transfer efficiency. Commonly used TIM materials include thermal grease, thermal gel, and phase change materials, among which thermal grease has a thermal conductivity of 5–20 W / (m·K) and is the most widely used.

[0003] However, during long-term operation, power modules repeatedly undergo heating and cooling processes due to power cycling, resulting in relative thermal deformation between the substrate and the heat sink. This thermal deformation causes the thermal interface material to be subjected to alternating compression and stretching at the contact interface, leading to the gradual extrusion of the thermal interface material from the center to the edges, producing a so-called "pump-out" effect. The pump-out effect reduces the thickness of the thermal interface material at the interface and may even cause localized drying, resulting in a significant increase in contact thermal resistance and seriously threatening the thermal reliability and lifespan of the power module.

[0004] To address the pumping problem of thermal interface materials, the industry has proposed various solutions, but all have certain limitations:

[0005] (1) Companies such as DOWSIL use gels to prepare thermal interface materials, taking advantage of the high viscosity of the gel to prevent it from being pumped out. However, the thermal conductivity of gel materials is usually less than 1.5 W / (m·K), which is much lower than the 5 to 20 W / (m·K) of thermal grease, resulting in an increase in the overall thermal resistance of the module and a decrease in heat dissipation performance.

[0006] (2) Companies such as Wolfspeed use solid-liquid two-phase / phase change thermal interface materials, with the main body being solid and the gaps filled with liquid phase. This method reduces the pumping effect by reducing the liquid content in the thermal interface material, but two-phase thermal interface materials are expensive and there is still a risk that the liquid phase will be pumped dry.

[0007] (3) Companies like Infineon use a pre-coating method, where the manufacturer pre-coates the thermal interface material before the module leaves the factory, and users can directly connect the pre-coated module to the heat sink. This method can improve the coating effect through the manufacturer's high-precision coating equipment and processes, and reduce pumping out to some extent, but the pumping out effect is still unavoidable. In addition, in order to avoid the pre-coated thermal interface material from drying out, higher requirements are placed on the storage conditions of the module.

[0008] In summary, existing technologies struggle to effectively address the pumping problem while maintaining high thermal conductivity. There is an urgent need for a novel thermal interface structure design that can maintain good thermal conductivity, fundamentally suppress the pumping effect, and reduce thermal stress. Summary of the Invention

[0009] The purpose of this invention is to provide a micro-reservoir anti-pumping thermal interface structure for power module thermal interface materials, in order to solve the technical problem that thermal interface materials in the prior art are prone to pumping out during thermal cycling, leading to increased thermal resistance.

[0010] A micro-storage anti-pumping thermal interface structure for a power module thermal interface material is characterized by comprising: a substrate, a micro-storage array disposed on the substrate, and a thermal interface material filling the gap between the micro-storages and the interface; the micro-storage array is distributed in a region outside the thermal diffusion angle heat transfer range of the substrate, and includes multiple periodically arranged micro-storage units, each micro-storage unit being a groove structure recessed into the substrate.

[0011] As a preferred embodiment of the present invention, the micro-storage unit is one or more combinations of an arc-shaped groove, a rectangular groove, or a trapezoidal groove.

[0012] As a preferred embodiment of the present invention, the groove opening width of the micro-storage unit is 0.1mm to 2.0mm, and the groove depth is 0.05mm to 1.0mm.

[0013] As a preferred embodiment of the present invention, the periodic arrangement spacing of the micro-storage units is 0.2mm to 3.0mm, and they are arranged in equal-spaced straight lines, staggered arrangements, or concentric rings.

[0014] As a preferred embodiment of the present invention, the substrate material is one of copper, aluminum, aluminum silicon carbide (AlSiC) or copper molybdenum copper (CMC) composite material, and the substrate thickness is 0.5mm to 5.0mm to adapt to the thermal expansion characteristics of SiC power modules.

[0015] As a preferred embodiment of the present invention, the micro reservoir utilizes capillary action to achieve the self-replenishment function of the thermal interface material. When the thermal interface material at the interface is pumped out, the thermal interface material in the micro reservoir automatically flows out to replenish the interface gap, maintaining the stability of the interface thermal resistance.

[0016] As a preferred embodiment of the present invention, the micro-storage structure acts as an elastic buffer, reducing the stiffness of the interface between the substrate and the heat sink, buffering the thermal stress during thermal cycling, and reducing the thermal fatigue damage of the SiC power module.

[0017] As a preferred embodiment of the present invention, the thermal interface material is one of thermally conductive silicone grease, thermally conductive gel, phase change material or metal-based composite material, and the thermal conductivity of the thermal interface material is 320 W / (m·K).

[0018] The present invention has the following beneficial effects:

[0019] (1) This invention utilizes the capillary action of the micro reservoir to achieve the self-replenishment function of the thermal interface material. After some of the thermal interface material stored in the micro reservoir is pumped out at the interface, it automatically flows out through capillary action to replenish the interface gap, maintaining the stable existence of the thermal interface material at the interface and fundamentally suppressing the impact of the pumping effect on heat dissipation performance.

[0020] (2) The micro-storage structure of the present invention acts as an elastic buffer, which is equivalent to introducing a "spring" element at the interface between the substrate and the heat sink, reducing the overall stiffness of the interface. During thermal cycling, the micro-storage structure can absorb and buffer thermal stress, reduce thermal fatigue damage to the module, and extend its service life.

[0021] (3) The present invention places the micro reservoir in a region outside the heat transfer range of the substrate thermal diffusion angle, without affecting the main heat transfer path, and achieves anti-pumping function while ensuring high thermal conductivity, thus overcoming the problem of poor thermal conductivity of gel materials.

[0022] (4) The present invention can use conventional thermal grease as the thermal interface material, with a thermal conductivity of 5 to 20 W / (m·K), which is much higher than that of gel material (1.5 W / (m·K). While ensuring anti-pumping performance, thermal conductivity is not sacrificed, and the overall thermal resistance of the module is lower.

[0023] (5) The micro reservoir structure of the present invention can be directly prepared on the substrate by means of mechanical processing, chemical etching or laser processing, which is simple and low cost. It does not require expensive two-phase thermal interface materials and has good economic efficiency and feasibility.

[0024] (6) Experimental results show that the power module with the micro-storage anti-pumping thermal interface structure of the present invention has an interface thermal resistance increase rate of less than 10% after 1000 thermal cycles, while the thermal resistance increase rate of the traditional planar structure exceeds 50%, which significantly improves the long-term thermal reliability of the power module. Attached Figure Description

[0025] Figure 1 This is a cross-sectional schematic diagram of the anti-pumping thermal interface structure of the micro-storage of the power module thermal interface material of the present invention.

[0026] Figure 2 This is a schematic diagram showing the distribution of the micro-storage array on the substrate according to the present invention;

[0027] Figure 3This is an enlarged structural schematic diagram of the micro-storage of the present invention;

[0028] In the diagram: 1. Terminal; 2. Chip; 3. DBC; 4. Solder layer; 5. Substrate; 6. Thermal grease; 7. Heat sink; 8. Thermal diffusion angle and heat transfer range; 9. Chip solder layer. Detailed Implementation

[0029] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] Please see Figures 1-3 The micro-storage anti-pumping thermal interface structure of the SiC power module thermal interface material of the present invention mainly includes a terminal 1, a chip 2, a DBC substrate 3, a solder layer 4, a substrate 5, a thermal interface material 6, a heat sink 7, a thermal diffusion angle heat transfer range 8, and a chip solder layer 9. The chip 2 is soldered to the DBC substrate 3 through the chip solder layer 9. The DBC substrate 3 is connected to the substrate 5 through the solder layer 4. The thermal interface material 6 is filled between the substrate 5 and the heat sink 7 to form a complete heat transfer path.

[0031] In a preferred embodiment, the substrate 5 is made of aluminum silicon carbide (AlSiC) composite material, with dimensions of 20mm × 20mm and a thickness of 1.5mm. The micro-reservoir array is located in the annular edge region outside the thermal diffusion angle of the substrate 5. The micro-reservoir unit is an arc-shaped groove with an opening width of 0.5mm, a depth of 0.3mm, and a semi-circular cross-section, arranged in a straight line at equal intervals of 1.0mm. The thermal interface material is high-performance thermally conductive silicone grease with a thermal conductivity of 6.0W / (m·K), completely filling the interface gap between the micro-reservoir, the substrate, and the heat sink. After 1000 thermal cycle tests at -40℃ to 125℃, the initial thermal resistance of this structure is 0.87℃ / W, and the increase rate of thermal resistance after cycling is only 12%, which is far lower than that of traditional planar structures, demonstrating excellent anti-pumping performance and long-term thermal reliability.

[0032] In a preferred embodiment, the substrate 5 is made of aluminum silicon carbide (AlSiC) composite material with a size of 20mm×20mm and a thickness of 1.5mm. This material has both high thermal conductivity and low coefficient of expansion, which can form a good thermal expansion match with the SiC chip, reduce interfacial thermal stress, and ensure that heat is transferred quickly and evenly from the chip to the heat sink.

[0033] In a preferred embodiment, the micro-reservoir array is located in the annular region at the edge of the substrate 5, outside the heat diffusion angle heat transfer range 8. For a centrally located chip heat source, the heat diffusion angle is typically 45°. The micro-reservoir array avoids the core heat transfer path and is only located in the non-main heat transfer area. This not only does not affect the outward diffusion of chip heat but also provides stable storage and replenishment space for thermal interface materials, achieving a dual balance of heat dissipation and anti-pumping.

[0034] In a preferred embodiment, the micro reservoir unit is an arc-shaped groove structure recessed into the substrate, with an opening width of 0.5 mm, a groove depth of 0.3 mm, and a semi-circular cross-section. The arc-shaped groove structure has a smooth inner wall without sharp corners, which can maximize the capillary efficiency, reduce the flow resistance of the thermal interface material, avoid stress concentration, and improve the stability of the substrate structure.

[0035] In a preferred embodiment, the micro reservoir units are arranged in a straight line with equal spacing, with a periodic spacing of 1.0 mm. The arrangement direction is parallel to the edge of the substrate, and the array is uniformly distributed and completely covered. This allows for rapid replenishment at any point on the interface when material is pumped out, ensuring that the thickness of the interface material remains stable.

[0036] In a preferred embodiment, the thermal interface material 6 is a high-performance thermally conductive silicone grease with a thermal conductivity of 6.0 W / (m²). · K) is filled inside the micro reservoir and in the interface gap between the substrate and the heat sink. This material has moderate fluidity and high thermal conductivity, enabling it to migrate rapidly under capillary action in the micro reservoir, while maintaining sufficient thickness at the interface to reduce contact thermal resistance.

[0037] In a preferred embodiment, the micro reservoir relies on capillary action to achieve self-replenishment of the thermal interface material. When thermal cycling causes material to be pumped out at the interface, creating a local void, the thermal interface material stored inside the micro reservoir automatically flows out under capillary force and replenishes the interface gap, forming a closed-loop mechanism of "pumping out-replenishing-rebalancing," thereby suppressing the increase in thermal resistance from the root cause.

[0038] In a preferred embodiment, the micro-reservoir groove structure also functions as an elastic buffer, essentially introducing a flexible buffer unit between the substrate and the heat sink to reduce the overall interface stiffness. During the thermal expansion and contraction process generated by power cycling, the micro-reservoir can absorb and release thermal stress, reducing interface fatigue damage and extending the module's service life.

[0039] Working principle:

[0040] 1. Heat-Avoiding Layout, Without Affecting Main Heat Dissipation: During chip operation, a large amount of heat is generated and rapidly conducted from the central region to the substrate via a 45° thermal diffusion angle as the primary heat transfer path. This invention precisely positions the micro-storage array in the peripheral, non-primary heat transfer area outside the thermal diffusion angle range, completely avoiding the core heat conduction channel between the chip and the heat sink. This ensures no obstruction or interference with efficient heat transfer, thereby guaranteeing that the SiC power module maintains excellent thermal conductivity and heat dissipation efficiency, achieving stable operation at high power density.

[0041] 2. Capillary Driven, Automatic Replenishment of Pumping Losses: The internal cavity of the micro-storage and the interface gap between the substrate and the heat sink form a continuous and interconnected material system. When the power module undergoes long-term power cycling and temperature fluctuations, the thermal interface material at the interface may experience pumping out due to repeated compression and stretching, resulting in material loss and thinning of the gap in localized areas. At this time, the thermal interface material stored inside the micro-storage can automatically, rapidly, and continuously flow to replenish the interface gaps under the drive of capillary forces, restoring the interface material thickness in real time and maintaining the continuity and integrity of the thermal interface. This fundamentally suppresses the sharp increase in interface thermal resistance caused by pumping out, ensuring long-term heat dissipation reliability.

[0042] 3. Elastic buffering to reduce thermal fatigue damage: The micro-storage system employs a recessed groove structure into the substrate, transforming the interface between the substrate and the heat sink from a rigid plane into a composite interface with flexible deformation and stress release capabilities. This is equivalent to introducing uniformly distributed "elastic buffer units" between the interfaces. Under repeated thermal expansion and contraction, this structure can effectively absorb and dissipate thermal stress caused by the mismatch in the thermal expansion coefficients of the materials, significantly reducing the overall stiffness of the interface, minimizing cracks, delamination, and fatigue damage caused by cyclic stress, and greatly improving the structural stability and service life of the power module.

[0043] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A micro-reservoir anti-pumping thermal interface structure for a power module thermal interface material, characterized in that, include: A substrate, a micro reservoir array disposed on the substrate, and a thermal interface material filling the gaps between the micro reservoirs and the interface; The micro reservoir array is distributed in the region outside the heat transfer range of the substrate's thermal diffusion angle and includes multiple periodically arranged micro reservoir units, each of which is a groove structure recessed into the substrate; this structure is used in conjunction with a natural convection topology-optimized heat sink.

2. The micro-storage anti-pumping heat interface structure according to claim 1, characterized in that, The micro-storage unit is one or more combinations of arc-shaped grooves, rectangular grooves, or trapezoidal grooves.

3. The micro-storage anti-pumping heat interface structure according to claim 1, characterized in that, The groove opening width of the micro-storage unit is 0.1mm to 2.0mm, and the groove depth is 0.05mm to 1.0mm.

4. The micro-storage anti-pumping heat interface structure according to claim 1, characterized in that, The periodic arrangement spacing of the micro-storage units is 0.2mm to 3.0mm, and they are arranged in equal-spaced straight lines, staggered arrangements, or concentric rings.

5. The micro-storage anti-pumping heat interface structure according to claim 1, characterized in that, The substrate material is one of copper, aluminum, aluminum silicon carbide (AlSiC) or copper molybdenum copper (CMC) composite material, and the substrate thickness is 0.5mm to 5.0mm, adapted to the thermal expansion characteristics of SiC power modules.

6. The micro-storage anti-pumping heat interface structure according to claim 1, characterized in that, The thermal interface material is one of thermally conductive silicone grease, thermally conductive gel, phase change material, or metal-based composite material, and the thermal conductivity of the thermal interface material is 3 to 20 W / (m·K).

7. The micro-storage anti-pumping heat interface structure according to claim 1, characterized in that, The micro reservoir utilizes capillary action to achieve a self-replenishing function for the thermal interface material. When the thermal interface material at the interface is pumped out, the thermal interface material in the micro reservoir automatically flows out to replenish the interface gap, maintaining the stability of the interface thermal resistance.

8. The micro-storage anti-pumping heat interface structure according to claim 1, characterized in that, The micro-storage structure acts as an elastic buffer, reducing the stiffness of the interface between the substrate and the heat sink, buffering the thermal stress during thermal cycling, and reducing thermal fatigue damage to the module.

9. A method for preparing a micro-reservoir anti-pumping thermal interface structure for a power module thermal interface material, characterized in that, The process includes the following steps: (1) determining the distribution area of ​​the micro reservoir array on the substrate based on the chip position and thermal diffusion angle of the power module; (2) processing the micro reservoirs in areas outside the heat transfer range of the substrate thermal diffusion angle using mechanical processing, chemical etching, or laser processing; (3) cleaning and surface treating the processed substrate; and (4) coating the substrate micro reservoirs and surface with thermal interface material, and assembling them with a natural convection topology optimized heat sink to form a complete heat dissipation structure.

10. The preparation method according to claim 9, characterized in that, The machining in step (2) includes milling, the chemical etching includes wet etching, and the laser processing includes laser ablation.

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