Substrate and semiconductor device

Abstract

A substrate (1) for a power module (30) comprises a lower portion (10) and an upper portion (20). The lower portion (10) comprises a cooling structure (11) configured to contact the coolant during operation of the power module (30). The upper portion (20) is coupled to the lower portion (10). The cooling structure (11) faces away from the upper portion (20) and comprises a surface (12) having a given surface structure (13, 14) comprising Regt; and at least one of a plurality of protrusions having a respective height (H) of 2 [mu] m or more with respect to a surface normal (A) perpendicular to the surface (12) of the cooling structure (11), and an average roughness.

Description

Technical Field

[0001] The present disclosure relates to a substrate for a power module and a method for manufacturing a substrate for a power module. The present disclosure further relates to a corresponding semiconductor device. Background Art

[0002] Power modules are used in the automotive field, for example, and require a reliable and efficient cooler to dissipate heat during operation. Such a cooler is fixed to the power module and guides a coolant to cool the power module.

[0003] It is desirable to provide a substrate for a power module that facilitates effective and efficient heat dissipation during operation of the power module. Utility Model Content

[0004] The embodiments of the present disclosure relate to a substrate for a power module, which can achieve reliable heat dissipation. The embodiments of the present disclosure also relate to a corresponding manufacturing method for such a substrate and a corresponding semiconductor device.

[0005] According to an embodiment, a substrate for a power module includes a lower portion having a cooling structure configured to contact a coolant during operation of the power module. The lower portion may include a cooling structure or may completely form the cooling structure itself. The substrate further includes an upper portion coupled to the lower portion. The cooling structure faces away from the upper portion and includes a surface having a given surface structure, the given surface structure including at least one of a plurality of protrusions and an average roughness of Ra>1μm, and the plurality of protrusions have a corresponding height of 2μm or greater with respect to a surface normal perpendicular to the surface of the cooling structure. The cooling structure includes a plurality of cooling pin fins and / or a plurality of cooling ribs, and the given surface structure is formed on one or more of the pin fins or ribs. In addition, the cooling structure may include other surface structures that can improve cooling efficiency. The given surface structure is also formed on the bottom surface of the upper portion of the substrate facing the lower portion. For example, the substrate is implemented as a pin-fin substrate including a plurality of cooling pin fins. The upper portion can be implemented by a plate-like substrate, and the lower portion can be implemented by a plurality of cooling pin fins. A given surface structure in the form of a minimum average roughness of Ra>1 μm and / or a plurality of protrusions with a corresponding height of 2 μm or more may be formed on the outer surface of the pin fins and / or between the pin fins on the bottom surface of the upper part of the substrate.

[0006] By using the described substrate configuration, an improved thermal behavior is possible due to specific modifications of the surface of the cooling structure. The cooling structure can be formed with a plurality of pin fins or ribs and / or other surface structures that can improve cooling efficiency, the plurality of pin fins or ribs and / or other surface structures including the above-given average roughness and / or protrusions on its surface to facilitate reliable heat dissipation during operation of the power module.

[0007] Roughness is a property of the substrate surface or of the cooling structure on the lower part of the substrate which can be quantified by the deviation of the direction of the normal vector of the actual surface from its ideal form. The average roughness value Ra is related to the average distance of the measuring points on the surface to the center line. The center line intersects the real profile in the reference section in such a way that the sum of the profile deviations in a plane parallel to the center line is distributed over the length of the measuring section. The average roughness therefore corresponds to the arithmetic mean of the absolute deviations from the mean line.

[0008] Power modules that generate strong heat due to losses during operation of power semiconductor devices require reliable and sufficient heat dissipation to avoid excessive temperatures. This can be achieved by mounting a power module including the described substrate (as the lower part of the power module) to one or more openings of a cavity of a cooler for direct liquid cooling. As a result, the back side of the substrate for the power module (corresponding to the lower part with the cooling structure) is in direct contact with the coolant, which significantly shortens the thermal path since a cooler top plate is not required. The additional thermal interface between the flat substrate and the cooler top plate may result in relatively poor thermal resistance.

[0009] Further improvements in heat dissipation can be achieved by using a substrate comprising a pin-fin or rib-type cooling structure instead of a flat substrate. On the one hand, the array of multiple cooling fins or ribs enlarges the effective area between the lower portion of the substrate and the flowing coolant. On the other hand, the multiple cooling fins or ribs disturb the flow of the coolant and help to create turbulence, so that turbulent flow is generated instead of laminar flow, resulting in even greater heat dissipation.

[0010] In conjunction with the present disclosure, it is recognized that the traditional concept of a substrate for a power module involves the speed and type of the coolant and the geometry of the cooling interface. The cooling portion of such a substrate is typically formed to be relatively flat without any significant roughness. Heat conversion (e.g., heat conversion between the back of the substrate and the coolant) is determined by the heat transfer coefficient between the two partners (i.e., between the back portion of the substrate and the coolant). This parameter is not only related to the type of material itself or the coolant flow, but also determined by different mechanical parameters. In conjunction with the present disclosure, it is recognized that the surface structure of the cooling portion can also have a significant effect on thermal performance, and the heat that can be dissipated as a result. By using a protrusion or a predetermined minimum average roughness, the heat transfer coefficient can be significantly affected, thereby providing a significant potential for further thermal improvements, and providing a further improved cooling efficiency for substrates with cooling structures such as fins or ribs. The rough surface of the cooling structure of the described substrate presents the possibility of improving heat transfer efficiency in turbulent thermal convection.

[0011] The above structure helps to enlarge the heat exchange area on one hand and supports nucleate boiling (in case of two phases) and provides wall roughness which supports turbulence near the wall and thus enhances heat exchange on the other hand. This improvement due to better heat dissipation allows higher current capabilities, size reduction through reduction of total active area of ​​the chip, higher reliability due to reduced heating of the device. When using the proposed structure with pin-fins or ribs, the thermal interface (surface) is larger on one hand and turbulent flow can be improved on the other hand. Thermal and / or flow related parameters help to improve the performance of the power module as a whole.

[0012] According to another embodiment of the substrate, a given surface structure including an average roughness of Ra>1μm is formed by at least one of etching, grinding, sandblasting, and laser irradiation. Thus, a suitably rough surface structure can be prepared to beneficially affect the heat dissipation of the power module. Other methods of preparing the roughness of the desired surface structure are also possible. A given surface structure can achieve a rough, corrugated and / or irregular surface structure, a porous structure and / or a dendritic structure. The dendritic structure may include a needle-like surface of randomly placed needles distributed on the surface of the cooling structure. For example, a dendritic, porous, or needle-like structure may be associated with a coating attached to an upper portion and / or a lower portion.

[0013] According to another embodiment of the substrate, the given surface structure comprises a coating such that the coated surface of the cooling structure comprises an average roughness of Ra>1 μm. For example, the coating may partially or completely cover a cooling structure in the form of pin fins or ribs. The coating may comprise particles and / or porous materials, dendritic structures and / or irregular needles to provide a minimum average roughness of RA>1 μm. For example, as an example, the coating may be made of nickel and / or may form a layer having a thickness in the micrometer range of up to 50 μm. Since nickel is in contact with the liquid coolant, nickel may contribute to the corrosion protection of the cooling structure. Thus, the desired roughness and / or protruding surface structure may be prepared by the coating and / or by machining the surface of the cooling structure on the lower part and optionally by a flat portion of the back side of the substrate achieved by the bottom surface of the upper part.

[0014] According to another embodiment of the substrate, a given surface structure can be modified to include a plurality of protrusions having a corresponding height of 2 μm or more, wherein the pitch or distance between the corresponding centers of two adjacent protrusions has a value of 10 μm or more with respect to a lateral direction perpendicular to the surface normal. Alternatively, the distance of the pitch can have a value of 15 μm, 20 μm, 25 μm, 30 μm, 40 μm, 50 μm to 100 μm or more. In addition, the height of the protrusion can be the same as or different from the height of the other parts. Alternatively, the height can have a value of 3 μm, 4 μm, 5 μm to 10 μm or more. Such a protrusion can be applied to a coating or a bulk material, and a method for preparing a regular structure is provided by etching or laser structuring.

[0015] The distance may represent the spacing between the outer surfaces of the protrusions facing each other. The pitch may represent the distance between the centers of adjacent protrusions. One or more protrusions may be formed into a rectangular, triangular or circular shape or other regular shape for a cross section perpendicular to the surface normal. In addition, other applicable shapes of the protrusions suitable for improving cooling efficiency are also possible. The surface normal is oriented in a direction corresponding to the height of the protrusion and is perpendicular to the lateral adjacent surface from which the protrusion extends. The protrusions may be formed to be regularly or irregularly distributed on the surface of the cooling structure depending on their purpose (e.g., different population densities). For example, the protrusions have a reproducible regular shape.

[0016] According to another embodiment of the substrate, the given surface structure comprises at least one of a plurality of protrusions having a respective height of 4 μm or more and an average roughness Ra>2 μm. Alternatively, the average roughness Ra may comprise values ​​greater than 3 μm, 4 μm, 5 μm to 10 μm or more.

[0017] The substrate material may be made of or include copper or a copper alloy, aluminum or an aluminum alloy. Alternatively, the substrate may be made of or include a composite material such as aluminum silicon carbide (AlSiC) or magnesium silicon carbide (MgSiC).

[0018] According to an embodiment, a semiconductor power module comprises an embodiment of the described substrate and an electronic device coupled to an upper portion of the substrate. The substrate may form a component of the power module, or the substrate may form an insert or additional component attached to the power module. The electronic device may include a chip, an integrated circuit and / or other discrete devices, a switching element (e.g., an IGBT or a power MOSFET and / or a diode).

[0019] According to an embodiment, a method for manufacturing an embodiment of the described substrate includes providing a lower portion having a cooling structure, the cooling structure being configured to contact a coolant during operation of the power module. The method further includes providing an upper portion coupled to the lower portion, and forming a given surface structure on a surface of the cooling structure, such that the given surface structure includes at least one of a plurality of protrusions and an average roughness of Ra>1 μm, the plurality of protrusions having a corresponding height of 2 μm or more with respect to a surface normal perpendicular to the surface of the cooling structure.

[0020] Forming a given surface structure on the cooling structure may include machining the surface by at least one of etching, grinding, sandblasting, and laser irradiation. Alternatively or additionally, forming a given surface structure on the cooling structure may include machining the surface by partially or completely coating the surface with a given coating material so that the coated surface includes an average roughness of Ra>1 μm.

[0021] Since the described semiconductor device and the described manufacturing method include or relate to embodiments of producing a substrate, the described features and characteristics of the substrate are also disclosed with respect to the semiconductor device and the manufacturing method, and vice versa.

[0022] The described rough surface including a given average roughness and / or specially designed protrusions achieves a beneficial way to enhance the heat transfer efficiency in turbulent thermal convection or at least locally provide turbulent convection in laminar flow. Therefore, implementing a rough or corrugated structure and / or a protruding structure on the surface of the cooling fins of a pin-fin substrate can improve the heat transfer coefficient and heat dissipation. The surface modification can be implemented on the cooling pin fins of the pin-fin substrate itself. In addition, the surface of the flat part of the bottom side of the upper part of the pin-fin substrate can also be modified.

[0023] The implementation or formation of a given surface structure can be done by coating the surface with any material providing a rough structure and / or by any surface machining method. On the one hand, an enlargement of the effective surface area of ​​the cooling fins or cooling structure is achieved. On the other hand, the rough surface structure supports a more efficient turbulent coolant flow due to an increase in the turbulence intensity, which improves the mixing capacity of the flow and thus improves the heat exchange.

[0024] The main benefit is directly related to the purpose of the invention, namely to improve the heat dissipation of the power module due to the rough and / or corrugated surface of the cooling structure and the resulting reduced thermal resistance. This can be used for the following different optional improvements:

[0025] Higher possible heat dissipation, thus enabling higher current capabilities of the power modules without further design changes

[0026] Lower power semiconductor device losses when operating at lower temperatures

[0027] • Longer service life with respect to power cycling (especially power cycling, especially long cycle times such as 60 seconds) due to smaller thermal swings at the same current and applied power as before.

[0028] Furthermore, the surface modification by the coating can improve the protection of the cooling structure and improve the protection of the bottom side of the back side or upper part of the base plate against corrosion and wear.The described configuration of the base plate is suitable for all power modules in direct cooling applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] An exemplary embodiment is explained below with the aid of schematic diagrams and reference numerals. The drawings show:

[0030] Figure 1 is a side view of an embodiment of a base plate for a power module;

[0031] Figure 2 is an enlarged side view of an embodiment of a surface structure of a substrate;

[0032] Figure 3 to Figure 4 is a corresponding side view of an embodiment of a surface structure of a substrate; and

[0033] Figure 5 is a flow chart of a method of an embodiment of manufacturing a substrate for a power module.

[0034] The accompanying drawings provide further understanding. It should be understood that the embodiments shown in the accompanying drawings are illustrative representations and are not necessarily drawn to scale. The same reference numerals represent elements or components having the same function. As long as the functions of elements or components correspond to each other in the accompanying drawings, their description will not be repeated for subsequent drawings. For clarity, elements may not be presented with corresponding reference numerals in all drawings. DETAILED DESCRIPTION

[0035] Figure 1 A side view of an embodiment of a substrate 1 for a power module 30 (e.g., for a semiconductor device) is illustrated. The substrate 1 includes a lower portion 10 having a cooling structure including a plurality of ribs or pin fins 11 configured to contact a coolant during operation of the power module 30. The substrate 1 further includes an upper portion 20 coupled to the lower portion 10 and configured to be coupled to the power module 30 or to form a bottom component of the power module 30. Thus, the substrate 1 may form part of the power module 30 itself, or may form an insert of a cooler on which the power module 30 (having a flat back side of a substrate, die pad, or substrate) is mounted. The substrate 1 forms a bottom component of the power module 30 (or for the power module).

[0036] The cooling structure faces away from the upper part 20 and comprises: a surface 12 having a given surface structure, the given surface structure comprising an average roughness of Ra>1 μm and / or a plurality of protrusions 14, the plurality of protrusions having a respective height H of 2 μm or more with respect to a surface normal A perpendicular to the surface 12 of the cooling structure; and pin fins 11 of the cooling structure (see Figure 2 ).therefore, Figure 1 A pin-fin base plate 1 is shown, indicating cooling pin fins 11 with modified surfaces and flat back portions between the cooling pin fins, which flat back portions may optionally also have modified surfaces (see Figure 4 ).

[0037] The given surface structure can be realized as a coating 13 which partially or completely covers the pin fins 11 (see Figure 1 ). In addition to the opportunity of roughening the coating 13 itself, the coated surface can be machined to produce the structure. Alternatively or additionally, a given surface structure may include a plurality of protrusions 14 having a plurality of protrusions extending from the surface 12 of the pin fin 11 and / or the bottom side 22 of the upper portion 20 (see Figures 2 to 4 ) has a corresponding minimum height of 2 μm extending.

[0038] Figure 2 An enlarged view of the pin fin 11 and two protrusions 14 extending outward is shown. Such a protrusion 14 may have a cylindrical, elliptical, cuboid or pyramidal shape. Therefore, for a cross section perpendicular to the drawing direction of the surface normal A, the protrusion 14 may have a circular, rectangular or triangular shape. The surface normal A may be perpendicular to the lateral or longitudinal extension direction B of the pin fin 11. The distance D may represent the closest spacing between two adjacent protrusions 14. The pitch P may represent the spacing between the centers of two adjacent protrusions 14. The distance D or the pitch P may have a value between 5 μm and 100 μm, for example 5 μm, 10 μm or 20 μm. The height H may have a value between 1 μm and 10 μm, for example 1 μm, 2 μm or 5 μm.

[0039] The surface 12 represents the outer surface of the cooling structure and the cooling pin fin 11 of the cooling structure. Thus, the surface 12 represents the bottom surface of the pin fin 11 facing away from the upper part 20 and also represents the circumferential surface of the pin fin 11 up to the bottom surface 22 of the upper part. The protrusions 14 and / or the coating 13 can be formed partially or completely on the bottom surface 12 and / or the circumferential surface 12 of the pin fin 11 and / or on the bottom surface 22 to provide the desired roughness of the cooling structure (see Figures 1 to 4 ). Figure 3 and Figure 4 Different shapes and / or possible positions of regularly and irregularly distributed protrusions 14 are illustrated.

[0040] The deliberately introduced surface structure on the surface 12 and / or 22 creates a roughness that increases the efficiency of the heat transfer in turbulent thermal convection or at least locally provides turbulent convection in laminar flow and thus contributes to reliable heat dissipation during operation of the associated power module 30. Even if the structure is formed in a microchannel with a thickness of, for example, 100 μm to have an average roughness Ra in the micrometer range> 1 μm, this significantly enhances the Nusselt number Nu, which is proportional to the convective heat transfer coefficient, and increases the pressure drop of the coolant due to the increase in the friction factor. For example, the local turbulence formed by a protruding structure with a height H of 4 μm and a pitch P of 32 μm (especially if the protrusion 14 has a triangular or rectangular shape) can effectively influence the thermal behavior. For example, compared with a height of 1 μm, the Nusselt number and the pressure drop are increased by nearly 2 times.

[0041] For example, when a coating having a dendritic, rough, needle-like and / or porous structure with a thickness of 5 μm to 30 μm is used, the rough coating 13 can also improve the heat transfer efficiency. Compared with a conventional unmodified pin-fin substrate, the heat transfer coefficient provided by the substrate 1 can be improved, thereby reducing the thermal resistance, which allows higher losses or greater current capabilities. The substrate 1 itself can be made of copper, aluminum or corresponding alloys, and can also be made of composite materials such as aluminum silicon carbide (AlSiC).

[0042] The steps of the corresponding manufacturing method for forming the substrate 1 can be as follows Figure 5 The process is carried out as shown in the flow chart. In step S1 , a lower part 10 with cooling pins 11 is provided, which form a cooling structure.

[0043] In step S2, the upper part 20 is provided, and the upper part 20 and the lower part 10 are coupled together. The upper part 20 and the lower part 10 may form separate parts, or both form adjacent parts made of one piece so that the upper part 20 and the lower part 10 are provided simultaneously in one step and the two do not need to be coupled to each other.

[0044] In step S3, a given surface structure is formed on the cooling pin fin 11 by machining, so that the surface structure includes an average roughness of Ra>1μm and / or a plurality of protrusions, which have a corresponding height H of 2μm or greater along the surface normal A. The machining and preparation of the rough surface can be completed by etching, grinding, sandblasting, laser irradiation, coating and / or any other applicable process to form the desired roughness. The machining of the cooling structure can also be completed before the cooling structure is installed on the upper part 20. For example, the roughness is prepared by forming a protrusion 14 having a minimum height of at least 2μm and a distance D or pitch P of at least 10μm. The protrusions 14 can be regularly distributed on the circumferential side surface 12 of the pin fin 11 in a triangular or rectangular shape from the corresponding cross section. These structures can be prepared by etching, shaving, laser structuring or any other applicable process. The protrusion 14 can cover a portion of the corresponding side surface 12 of the pin fin 11. The projections 14 may partially or completely surround the respective pin fin 11 so that they form a ring enclosing the respective pin fin 11. The projections 14 and / or the roughness may also be obtained on the front or bottom surface of the rib or pin fin 11 facing away from the upper portion 20.

[0045] As mentioned above, Figures 1 to 5 The embodiments shown or described in the illustrative examples of the improved substrate 1 and the method for manufacturing the improved substrate are not intended to be construed as a complete list of all embodiments. For example, the actual arrangement and method may differ from the embodiments shown in the substrate.

[0046] Reference numerals

[0047] 1 substrate

[0048] 10 Lower part of the base plate

[0049] 11 Pinfin

[0050] 12 Pin fin surface

[0051] 13 Rough coating

[0052] 14 Protrusion

[0053] 20 Upper part of the base plate

[0054] 22 Bottom surface of upper part

[0055] 30 Power Module

[0056] A Direction of the surface normal of the pin fin

[0057] B The direction of the lateral extension of the pin fin

[0058] S(i) Steps of the method for manufacturing a substrate

Claims

1. A substrate (1) for a power module (30), characterized in that: include: a lower part (10) configured to contact a coolant during operation of the power module (30), - an upper part (20) coupled to the lower part (10), and - a cooling structure (11), which is formed at the lower part (10) facing away from the upper part (20), wherein the cooling structure (11) includes a surface (12) having a given surface structure (13, 14), the given surface structure including at least one of a plurality of protrusions and an average roughness of Ra>1μm, the plurality of protrusions having a corresponding height (H) of 2μm or more with respect to a surface normal (A) perpendicular to the surface (12) of the cooling structure (11), wherein the cooling structure includes at least one of a plurality of cooling pin fins (11) and a plurality of cooling ribs, and wherein the upper part (20) includes a bottom surface (22) facing the lower part (10), and the given surface structure (13, 14) is formed on the bottom surface (22) and on at least one of the pin fins (11) and the ribs.

2. The substrate (1) according to claim 1, characterized in that The given surface structure (13, 14) includes the average roughness Ra>1 μm formed by at least one of etching, grinding, sandblasting, and laser irradiation and / or the plurality of protrusions having a corresponding height (H) of 2 μm or more.

3. The substrate (1) according to claim 1, characterized in that The given surface structure comprises a coating (13) such that the coated surface (12) of the cooling structure (11) comprises an average roughness of Ra>1 μm.

4. The substrate (1) according to claim 3, characterized in that The coating (13) comprises at least one of particles, porous materials, needle-shaped materials, dendritic materials and structuring, and partially or completely covers the cooling structure (11).

5. The substrate (1) according to any one of claims 1 to 4, characterized in that: The given surface structure comprises a plurality of protrusions (14) having respective heights (H) of 2 μm or greater, wherein a pitch (P) between respective centers of two adjacent protrusions (14) has a value of 10 μm or greater with respect to a lateral direction (B) perpendicular to the surface normal (A).

6. The substrate (1) according to claim 5, characterized in that The protrusion (14) is formed in one of a rectangular, triangular and circular shape with respect to a cross section perpendicular to the surface normal (A).

7. The substrate (1) according to claim 5, characterized in that The protrusions (14) are formed to be irregularly distributed on the surface (12) of the cooling structure (11).

8. The substrate (1) according to any one of claims 1 to 4, characterized in that: The given surface structure (13, 14) comprises at least one of a plurality of protrusions having a respective height (H) of 4 μm or more and an average roughness of Ra>2 μm.

9. The substrate (1) according to any one of claims 1 to 4, characterized in that: Included is a material made of one of copper, aluminum, copper alloy, aluminum alloy, aluminum silicon carbide, and magnesium silicon carbide.

10. A power module (30) for a semiconductor device, characterized in that: include: - A substrate (1) according to any one of claims 1 to 9, and - An electronic device coupled to the upper portion (20) of the substrate (1).

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