Semiconductor cooling device, power conversion device and method for manufacturing a semiconductor cooling device

Abstract

A semiconductor cooling device comprises a plurality of semiconductor modules, a plurality of first coolant flow paths provided according to the semiconductor modules, and a pair of flow path tubes connected to the plurality of first coolant flow paths. The plurality of semiconductor modules are arranged side by side on a substrate in a first direction such that each module faces the plurality of first coolant flow paths. Each of the pair of flow path tubes also extends along the first direction. Furthermore, in each of the plurality of semiconductor modules, a heat dissipation surface is arranged in contact with each of the plurality of first coolant flow paths in a cross-sectional direction with respect to a direction of extension of the first coolant flow paths and an arrangement direction of the plurality of semiconductor modules.Furthermore, the first coolant flow path includes a deformable section that can be deformed in the cutting direction.

Description

Technical area

[0001] The present invention relates to a semiconductor cooling device, a power conversion device and a method for manufacturing a semiconductor cooling device. State of the art

[0002] An inverter can provide high output power and low cost by using a mass-produced semiconductor module and integrating main circuit wiring using a printed circuit board. However, when cooling both surfaces of a large number of semiconductor modules to reduce thermal resistance, high dimensional accuracy is required for the semiconductor modules and the cooling water channel, resulting in increased costs. Furthermore, miniaturization and height reduction are also essential.

[0003] The following PTL 1 discloses a configuration of a cooler capable of sufficiently securing a contact area between an electronic component and a tube without increasing the number of components. Literature listPatent literature

[0004] PTL 1: JP 2005-228877 A Summary of the inventionTechnical problem

[0005] In a conventional structure, when a semiconductor module is mounted on a substrate, each module has a certain height difference, and each semiconductor module may not have a following ability with respect to a water path in contact with the semiconductor module. Therefore, even if cost reduction can be realized, there is a problem in that the reliability of the cooling device is reduced due to the variation in the heat dissipation surface caused by such a height difference. In view of this, an object of the present invention is to provide a semiconductor cooling device and a method for manufacturing the semiconductor cooling device that achieve miniaturization, cost reduction, and high heat dissipation. Solution to the problem

[0006] A semiconductor cooling device includes a plurality of semiconductor modules, each having a semiconductor element installed therein, a plurality of first coolant flow paths provided corresponding to the plurality of semiconductor modules, and a pair of flow path tubes each having inlets and outlets connected to the plurality of first coolant flow paths. The plurality of semiconductor modules are arranged side by side on a substrate in a first direction so as to face the plurality of first coolant flow paths, respectively. Each of the pair of flow path tubes further extends along the first direction.Furthermore, in each of the plurality of semiconductor modules, a heat dissipation surface is arranged in contact with each of the plurality of first coolant flow paths in a cross-sectional direction relative to an extension direction of the first coolant flow paths and an arrangement direction of the plurality of semiconductor modules. The first coolant flow path further includes a deformable portion deformable in the cross-sectional direction at a portion connected to the flow path tube.

[0007] Moreover, as a method for manufacturing a semiconductor cooling device, a method is employed which includes connecting a plurality of first refrigerant flow paths each provided corresponding to a plurality of semiconductor modules each having a semiconductor element incorporated therein and arranged side by side on a substrate, and a pair of flow path tubes connected to the plurality of first refrigerant flow paths and extending along an arrangement direction of the plurality of semiconductor modules, and mounting the plurality of connected first refrigerant flow paths and the pair of flow path tubes on the semiconductor module.

[0008] Furthermore, as another method for manufacturing a semiconductor cooling device, a method is employed which includes connecting a plurality of first coolant flow paths each provided corresponding to a plurality of semiconductor modules each having a semiconductor element incorporated therein and arranged side by side on a substrate, and connecting a pair of flow path tubes extending along an arrangement direction of the plurality of semiconductor modules to the plurality of first coolant flow paths. Advantageous effects of the invention

[0009] Accordingly, it is possible to provide a semiconductor cooling device and a method for manufacturing the semiconductor cooling device that achieve miniaturization, cost reduction, and high heat dissipation. Brief description of the drawings Fig. 1 is an overall perspective view of a semiconductor cooling device according to an embodiment of the present invention. Fig. 2 is a cross-sectional view along the line YY of Fig. 1. Fig. 3 is a cross-sectional view along the line XX of Fig. 1. Fig. 4 is a first modification of Fig. 3. Fig. 5 is a second modification of Fig. 3. Fig. 6 is a modification (third modification) of Fig. 2. Fig. 7 illustrates an example of a method for manufacturing a semiconductor cooling device.

[0010] Embodiments of the present invention will be described below with reference to the drawings. The following description and drawings are examples for describing the present invention and are omitted and simplified as appropriate for clarity of description. The present invention may also be implemented in various other forms. Furthermore, unless otherwise limited, each component may be represented as singular or plural.

[0011] The position, size, shape, range, and the like of each component illustrated in the drawings may not necessarily represent the actual position, size, shape, range, and the like, and are merely illustrated to facilitate understanding of the invention. Therefore, the present invention is not necessarily limited to the position, size, shape, range, and the like disclosed in the drawings. (Overall configuration of the embodiment and device of the present invention) (FIG. 1)

[0012] Fig. 1(a) is an overall perspective view illustrating a semiconductor cooling device mounted on a plurality of semiconductor modules included in a substrate, and Fig. 1(b) is a perspective view of the semiconductor cooling device. A semiconductor cooling device 100 (hereinafter referred to as a cooling device 100) includes a circuit board 4 (hereinafter referred to as a substrate 4) that typically mounts a plurality of semiconductor modules, each of which serves as a power converter of the power conversion device, a plurality of small-scale cooling flow paths 1 (hereinafter referred to as a first coolant flow path 1), and a pair of cooling flow path tubes 2 (hereinafter referred to as a flow path tube 2).

[0013] Each of the plurality of first coolant flow paths 1 is connected to the pair of flow path tubes 2 at both ends. A deformable portion 3 (details will be described later) is also provided at a connecting portion between the plurality of first coolant flow paths 1 and the pair of flow path tubes 2. The pair of flow path tubes 2 receives the coolant from the outside through a flow path inlet / outlet 2a and causes the coolant to flow through each of the plurality of first coolant flow paths 1. Since the first coolant flow path 1 is connected to the flow path tubes 2 in parallel, the coolant flows through the flow path at the same flow rate and the same temperature at the contact portion with each phase of the semiconductor module 10, thereby reducing the temperature difference between the phases of the semiconductor module 10. (FIG. 2)

[0014] The cooling device 100 further includes a plurality of semiconductor modules 10 each having a semiconductor element installed therein, a plurality of first coolant flow paths 1 each provided corresponding to a plurality of semiconductor modules 10, and a pair of flow path tubes 2 each having inlets and outlets connected to the plurality of first coolant flow paths 1.

[0015] In the first coolant flow path 1, in a case where the inlet side of the coolant flowing from the flow path tube 2 is defined as the front side and the outlet side of the coolant is defined as the rear side, a first coolant flow path 1b on the rear side connected to the flow path tube 2 at a position near the outlet side of the flow path tube 2 may be formed wider than a first coolant flow path 1a on the front side connected to the flow path tube 2 at a position near the inlet side of the flow path tube 2. As a result, in the first coolant flow path 1, the pressure loss in the first coolant flow path 1b on the rear side due to the coolant flowing inside does not increase, so that the pressure can be reduced as a whole.

[0016] In the cooling device 100, a plate-like insulating member 6 and a heat dissipation member 7 are bonded to a surface facing the semiconductor module 10 in the first coolant flow path 1. This eliminates the need for a fastening member for securing the insulating member 6. The insulating member 6 itself is a material with insulating properties and adhesion, such as a silicone resin plate. The heat dissipation member 7 is furthermore, for example, a thermal interface material (TIM).

[0017] In the plurality of semiconductor modules 10 contained in the substrate 4, the first coolant flow path 1 is arranged on one surface, and a second coolant flow path 13 is arranged on the other surface. By arranging the coolant flow paths on both surfaces of the semiconductor module 10 in this way, the cooling performance of the semiconductor module 10 is improved. In the second coolant flow path 13, the plate-like insulating member 6 is also bonded to a surface facing the semiconductor module 10.

[0018] The second coolant flow path 13 is further arranged to face the first coolant flow path 1 via the semiconductor module 10 and is formed to be wider than the first coolant flow path 1. Thus, the substrate 4 can be cooled. Furthermore, similar to the first coolant flow path 1, the second coolant flow path 13 is also connected to the pair of flow path tubes 2. To this end, a second heat dissipation member 12 is arranged between the second coolant flow path 13 and the substrate 4. As a result, the second coolant flow path 13 and the substrate 4 are brought into close contact with each other via the second heat dissipation member 12, so that the cooling performance is improved. The second heat dissipation member 12 is, for example, a gap filler or a heat dissipation plate.

[0019] The second coolant flow path 13 cools the plurality of semiconductor modules 10 on one surface and has higher rigidity than the first coolant flow path 1. This improves the followability of the first coolant flow path 1 to the semiconductor module 10 when the first coolant flow path 1 is screwed.

[0020] The substrate 4 is also defined as a circuit board and formed of an electrically conductive member such as a copper bus bar. That is, the substrate 4 has both a function of mounting the semiconductor module 10 and a function of electrical conduction. Furthermore, the substrate 4 has a plurality of wiring layers, each of which is connected to the plurality of semiconductor modules 10 and includes a DC wiring through which a direct current flows, and an AC wiring through which an alternating current flows. Consequently, it is possible to realize a power conversion device including the cooling device 100 capable of miniaturization, cost reduction, and high heat dissipation.

[0021] Moreover, the member mounted on each of the plurality of semiconductor modules 10 is defined as the substrate 4, and the semiconductor modules are mounted together, so that, for example, a reference surface 11 in a case where the semiconductor modules 10 are installed in the second coolant flow path 13 is easily incorporated into one process, and productivity and mountability can be improved. (FIG. 3)

[0022] Fig. 3(a) is a cross-sectional view taken along line XX of Fig. 1, and Fig. 3(b) is a view for explaining a member for fixing the configuration of Fig. 3(a). The first coolant flow path 1 includes a deformable portion 3 that is deformable in the intersection direction at a connecting portion with the pair of flow path tubes 2. The deformable portion 3 is, for example, an elastic material such as aluminum or a spring. The first coolant flow path 1 also includes a heat dissipation fin 5. Specifically, the heat dissipation fin 5 is a highly thermally conductive member such as aluminum or copper.

[0023] The pair of flow path tubes 2 connected to the first coolant flow path 1 are covered with a water path fixing member 9 such as a leaf spring. By fastening and fixing the water path fixing member 9 to a casing or the like (not shown) of the power conversion device with a screw 8, the first coolant flow path 1 is pressed against and fixed to the plurality of semiconductor modules 10 mounted on the substrate 4. This improves the adhesion between the first coolant flow path 1 and the semiconductor module 10.

[0024] The deformable portion 3 also has a shape that is easily deformed, such as a wavy shape or a thin shape. The rigidity of the deformable portion 3 is similarly lower than the rigidity of the first coolant flow path 1. Accordingly, when the first coolant flow paths 1 are pressed against the plurality of semiconductor modules 10, the deformable portion 3 is deformed by the fastening force. This particularly improves the adhesion between the first coolant flow path 1 and the semiconductor module 10.

[0025] Furthermore, the Fig. 1 to Fig. 3 that the plurality of semiconductor modules 10 are arranged facing the plurality of first coolant flow paths 1 and side by side in the first direction on the substrate 4, and the pair of flow path tubes 2 extend along the first direction. In the plurality of semiconductor modules 10, it is seen that the respective heat dissipation surfaces are in contact with the plurality of first coolant flow paths 1 in the sectional direction (the side of the vertical direction in Fig. 3) with respect to the extension direction of the first coolant flow paths 1 (the left-right direction in Fig. 3) and the arrangement direction of the plurality of semiconductor modules 10 (the direction near the depth in Fig. 3). The cutting direction refers to a wide area on the side perpendicular to the extension direction of the first coolant flow path 1 and the arrangement direction of the semiconductor modules 10, which have already been described above.

[0026] With such a configuration, the adhesion between the heat dissipation fin 5 and the semiconductor module 10 via the flow path wall of the first coolant flow path 1 is improved, while simultaneously increasing the reliability of the cooling device 100. Furthermore, since the deformable portion 3 deforms not in the arrangement direction of the semiconductor modules 10 but on one side in the cutting direction, the configuration of the first coolant flow paths 1 is arranged in parallel on the same plane along the substrate 4, while simultaneously absorbing the thickness tolerance of each of the semiconductor modules 10 with respect to the first coolant flow paths 1, so that the first coolant flow paths 1 themselves can be thinned. Therefore, the height of the entire cooling device 100 can also be reduced. (First modification)(FIG. 4)

[0027] The deformable portion 3 may, for example, be an S-shaped deformable portion 3a formed in an S shape. Consequently, since the first coolant flow path 1 is provided on the same plane as the pair of flow path tubes 2, the height of the cooling device 100 can be reduced. (Second modification)(FIG. 5)

[0028] Fig. 5(a) is a cross-sectional view of a part of the configuration of a second modification of Fig. 3, and Fig. 5(b) is a cross-sectional view of a part of the configuration of the modification shown in Fig. 5(a). The pair of flow path tubes 2 are provided in the above-described sectional direction with respect to the first coolant flow path 1, and accordingly, the deformable portion 3 is also provided in the above-described sectional direction with respect to the first coolant flow path 1. Furthermore, the deformable portion 3 is formed, for example, into a bellows. As a result, the bottom area of ​​the first coolant flow path 1 is reduced. Furthermore, since the deformable portion 3 is deformed by being compressed in the vertical direction (sectional direction), the followability of the semiconductor module 10 in the sectional direction is improved, and the reliability of the cooling device 100 is increased.Furthermore, the deformable portion 3 can be formed from an inexpensive component such as a press, thereby also reducing the cost of the entire first coolant flow path 1. Furthermore, the pair of flow path tubes 2 can also be formed from a cylindrical shape, an inexpensive press plate, or the like. (Third modification)(FIG. 6)

[0029] Each of the flow path tubes 2 has a bellows 14 between positions connected to the plurality of first coolant flow paths 1. With such a structure, the first coolant flow path 1 improves the followability for each arm of the semiconductor modules 10 and more easily absorbs the tolerance of each of the semiconductor modules 10 in the cutting direction. (Method for manufacturing a semiconductor cooling device) (FIG. 7)

[0030] A method for manufacturing the cooling device 100 is, for example, as follows. First, the plurality of first refrigerant flow paths 1, each provided corresponding to the plurality of semiconductor modules 10, each having a semiconductor element incorporated therein and arranged side by side on the substrate 4, and the pair of flow path tubes 2 connected to the plurality of first coolant flow paths 1 and extending along the arrangement direction of the plurality of semiconductor modules 10 are connected. Subsequently, the plurality of connected first coolant flow paths 1 and flow path tubes 2 are mounted on the semiconductor module 10.Since such a manufacturing method is adopted, in the step of mounting the first coolant flow path 1 on the semiconductor module 10 in a connected state, an inspection can be performed with the first coolant flow path alone, the number of steps can be reduced, and the yield can be improved.

[0031] As another method for manufacturing the cooling device 100, the following method is also disclosed in Fig. 7. First, the plurality of first refrigerant flow paths 1, each provided accordingly, are connected to the plurality of semiconductor modules 10, each having a semiconductor element incorporated therein and arranged side by side on the substrate 4. Then, as shown in Fig.As illustrated in FIG. 7, the pair of flow path tubes 2 extending along the arrangement direction of the plurality of semiconductor modules 10 are connected to the plurality of first coolant flow paths 1. By adopting such a manufacturing method, stress at a connecting portion between the first coolant flow path 1 and the flow path tube 2 can be reduced.

[0032] In addition, although the semiconductor cooling device 100 according to the present invention has been described above, for example, the first coolant flow path 1 may equally well have a three-division configuration in which the semiconductor modules 10 are pushed through two rows of the first coolant flow path 1, instead of the above-described configuration in which the first coolant flow path 1 is divided into six corresponding to each phase of the semiconductor modules 10 to absorb tolerances. In addition, although the configuration in which a second coolant flow path 13 is provided has been described above, a first coolant flow path 1 may also be provided, and the second coolant flow path 13 may be divided to correspond to each phase of the semiconductor module 10.

[0033] According to the above-described embodiment of the present invention, the following operational advantages are achieved accordingly.

[0034] (1) A plurality of semiconductor modules 10 each having a semiconductor element installed therein, a plurality of first coolant flow paths 1 each provided corresponding to a plurality of semiconductor modules 10, and a pair of flow path tubes 2 each connected to the plurality of first coolant flow paths 1 via inlets and outlets are provided. The plurality of semiconductor modules 10 are arranged side by side in the first direction on the substrate 4 so as to face the plurality of first coolant flow paths 1, respectively.The pair of flow path tubes 2 extend along the first direction, and in the plurality of semiconductor modules 10, the respective heat dissipation surfaces are arranged in contact with the plurality of first coolant flow paths 1 in the direction intersecting the extending direction of the first coolant flow paths 1 and the arrangement direction of the plurality of semiconductor modules 10. The first coolant flow path 1 also includes a deformable portion 3 deformable in the intersecting direction at a portion connected to the flow path tube 2. With this configuration, it is possible to provide a semiconductor cooling device that achieves miniaturization, cost reduction, and high heat dissipation.

[0035] (2) The deformable portion 3 is provided in a cutting direction with respect to the first coolant flow path 1. With such a configuration, since the deformable portion 3 is deformed in the vertical compression direction, the followability of the semiconductor module 10 in the cutting direction is improved, thus increasing reliability.

[0036] (3) The deformable portion 3 is formed in an S-shape. Since the first coolant flow path 1 is provided on the same plane as the flow path tube 2, such a configuration allows the height to be reduced.

[0037] (4) In the semiconductor module 10, the first coolant flow path 1 is arranged on one surface, and a second coolant flow path 2 is arranged on the other surface. Thus, both surfaces of the semiconductor module 10 can be cooled.

[0038] (5) The second coolant flow path 2 is arranged to face the first coolant flow path 1 via the semiconductor module 10 and is formed to be wider than the first coolant flow path 1. The heat dissipation member 12 is arranged between the second coolant flow path 2 and the substrate 4. Since the semiconductor module 10 and the substrate 4 are in close contact with each other, such a configuration improves the cooling performance.

[0039] (6) The second coolant flow path 2 cools the plurality of semiconductor modules 10 on one surface and has higher rigidity than the first coolant flow path 1. With such a configuration, the followability of the first coolant flow path 1 to the semiconductor module 10 at the time of screw fastening is improved.

[0040] (7) In the plurality of first coolant flow paths 1, the first coolant flow path 1b connected to the flow path tube 2 at a position near the outlet side of the flow path tube 2 is wider than the first coolant flow path 1a connected to the flow path tube 2 at a position near the inlet side of the flow path tube 2. With such a configuration, the substrate 4 can be cooled.

[0041] (8) The insulating member 6 is bonded to a surface of each of the first coolant flow path 1 and the second coolant flow path, the surface facing the semiconductor module 10. With such a configuration, it is not necessary for a fixing member to fix the insulating member 6.

[0042] (9) The power conversion device includes the semiconductor cooling device 100, and the substrate 4 includes a plurality of wiring layers, each of which is connected to the plurality of semiconductor modules 10 and includes a DC wiring through which a direct current flows and an AC wiring through which an alternating current flows. With this configuration, it is possible to provide a power conversion device that achieves miniaturization, cost reduction, and high heat dissipation.

[0043] (10) As a method for manufacturing the semiconductor cooling device 100, first, the plurality of first refrigerant flow paths 1 provided respectively corresponding to the plurality of semiconductor modules 10 each having a semiconductor element incorporated therein and arranged side by side on the substrate 4, and the pair of flow path tubes 2 connected to the plurality of first refrigerant flow paths 1 and extending along the arrangement direction of the plurality of semiconductor modules 10 are connected. Then, a method for mounting the plurality of connected first refrigerant flow paths 1 and flow path tubes 2 on the semiconductor module 10 is adopted. With such a configuration, the number of steps can be reduced and the yield can be improved.

[0044] (11) Furthermore, as another method for manufacturing the semiconductor cooling device 100, first, the plurality of first refrigerant flow paths 1 each provided correspondingly are connected to the plurality of semiconductor modules 10 each having a semiconductor element incorporated therein and arranged side by side on the substrate 4. Then, a method of connecting a pair of flow path tubes 2 extending along the arrangement direction of the plurality of semiconductor modules 10 to the plurality of first coolant flow paths 1 is adopted. With such a configuration, stress at the connecting portion between the first coolant flow path 1 and the flow path tube 2 can be reduced.

[0045] It should be noted that the present invention is not limited to the above embodiments, and various modifications and other configurations can be combined without departing from the gist of the present invention. Furthermore, the invention is not limited to those embodiments that have all the configurations described in the above-described embodiments, and also includes those in which part of the configuration is omitted. List of reference symbols 1 small cooling water passage (first coolant flow path) 1a first coolant flow path on the front 1b first coolant flow path on the back 2 coolant flow path pipe 2a Flow path inlet / outlet 3 deformable section 3a S-shaped deformable section 4 circuit board 5 Heat dissipation fin 6 Insulating element 7 Heat dissipation element 8 screw 9 Waterway fastening element 10 semiconductor modules 11 Reference surface 12 second heat dissipation element 13 second coolant flow path 14 bellows 100 semiconductor cooling device (cooling device) QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] JP 2005-228877 A

[0004]

Claims

[1] A semiconductor cooling device comprising: a plurality of semiconductor modules each having a semiconductor element incorporated therein; a plurality of first coolant flow paths each provided corresponding to the plurality of semiconductor modules; and a pair of flow path tubes each having inlets and outlets connected to the plurality of first coolant flow paths, wherein the plurality of semiconductor modules are arranged on a substrate side by side in a first direction so as to face the plurality of first coolant flow paths, each of the pair of flow path tubes extends along the first direction, in each of the plurality of semiconductor modules, a heat dissipation surface is arranged in contact with each of the plurality of first coolant flow paths in a sectional direction with respect to an extending direction of the first coolant flow paths and an arrangement direction of the plurality of semiconductor modules, and the first coolant flow path includes a deformable portion deformable in the cutting direction at a portion connected to the flow path tube. [2] The semiconductor cooling device according to claim 1, wherein the deformable portion is provided in the sectional direction with respect to the first coolant flow path. [3] The semiconductor cooling device according to claim 1, wherein the deformable portion is formed in an S-shape. [4] The semiconductor cooling device according to claim 1, wherein in the semiconductor module, the first coolant flow path is arranged on one surface and the second coolant flow path is arranged on another surface. [5] ] The semiconductor cooling device according to claim 4, wherein the second coolant flow path is arranged to face the first coolant flow path via the semiconductor module and is formed to be wider than the first coolant flow path, and a heat dissipation element is arranged between the second coolant flow path and the substrate. [6] The semiconductor cooling device according to claim 4, wherein the second coolant flow path cools the plurality of semiconductor modules on one surface and has a higher rigidity than that of the first coolant flow path. [7] The semiconductor cooling device according to claim 1, wherein in the plurality of first coolant flow paths, the first coolant flow path connected to the flow path tube at a position near an outlet side of the flow path tube is wider than the first coolant flow path connected to the flow path tube at a position near an inlet side of the flow path tube. [8] The semiconductor cooling device according to claim 4, wherein an insulating member is connected to a surface of each of the first coolant flow path and the second coolant flow path, the surface facing the semiconductor module. [9] A power conversion device comprising: the semiconductor cooling device according to one of claims 1 to 8, wherein the substrate includes a plurality of wiring layers each connected to the plurality of semiconductor modules and including a DC wiring through which a DC current flows and an AC wiring through which an AC current flows. [10] A method of manufacturing a semiconductor cooling device, the method comprising: Connecting a plurality of first refrigerant flow paths each provided corresponding to a plurality of semiconductor modules each having a semiconductor element incorporated therein and arranged side by side on a substrate, and a pair of flow path tubes connected to the plurality of first refrigerant flow paths and extending along an arrangement direction of the plurality of semiconductor modules; and Mounting the plurality of connected first coolant flow paths and the pair of flow path tubes on the semiconductor module. [11] A method of manufacturing a semiconductor cooling device, the method comprising: Connecting a plurality of first refrigerant flow paths each provided corresponding to a plurality of semiconductor modules each having a semiconductor element incorporated therein and arranged side by side on a substrate; and Connecting a pair of flow path tubes extending along an arrangement direction of the plurality of semiconductor modules to the plurality of first coolant flow paths.

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