Cooler for cooling a semiconductor device

Provided is a cooler including an upper plate configured to have a semiconductor chip to be arranged thereon, a plurality of plate-like fins arranged under the upper plate, and a coupling bar coupled to the plate-like fins. The coupling bar has a main-body portion and a plurality of comb-tooth portions protruding from the main-body portion into the flow channel, the cooler includes a plurality of openings in a plane orthogonal to an extending direction of the plate-like fins, and the openings are defined at least by the comb-tooth portions and the plate-like fins, and the openings include a first opening provided in a first flow channel that does not run below the semiconductor chip, and a second opening provided in a second flow channel that runs below the semiconductor chip, where the second opening is larger than the first opening.

The contents of the following Japanese patent application(s) are incorporated herein by reference: NO. 2017-195974 filed in JP on Oct. 6, 2017.

BACKGROUND

Technical Field

The present invention relates to a cooler.

In the conventional art, a cooler has a plurality of plate-like fins (see, for example, Patent Document 1). In addition, it is known to provide a protrusion in a coolant flow channel (see, for example, Patent Document 2) and to couple a plurality of fin plates using a coupling member (see, for example, Patent Document 3).

PRIOR ART DOCUMENTS

Patent Documents

Patent document 1: Japanese Patent Application Publication No. 2012-533868

Patent document 2: Japanese Patent Application Publication No. 2008-172014

Patent document 3: Japanese Patent Application Publication No. 2015-225953

In order to enable a cooler to more efficiently cool a semiconductor chip, it is desirable to lower the coolant flow rate in the region that makes a small contribution to the cooling and raise the coolant flow rate in the region that makes a large contribution to the cooling.

SUMMARY

A first aspect of the present invention provides a cooler configured to cool a semiconductor chip. The cooler may include an upper plate configured to have a semiconductor chip to be arranged thereon, a plurality of plate-like fins and a coupling bar. The plurality of plate-like fins may be arranged under the upper plate. The plurality of plate-like fins may form a flow channel for cooling water therebetween. The coupling bar may be coupled to the plurality of plate-like fins. The coupling bar may have a main-body portion and a plurality of comb-tooth portions, and each of the comb-tooth portions may protrude from the main-body portion into the flow channel. The cooler may include a plurality of openings in a plane orthogonal to an extending direction, and the plurality of openings may be defined at least by the plurality of comb-tooth portions and the plurality of plate-like fins . The extending direction may be a direction in which the plurality of plate-like fins extend when the cooler is seen from above. The plurality of openings may include a first opening that is provided in a first flow channel that does not run below the semiconductor chip, and a second opening that is provided in a second flow channel that runs below the semiconductor chip. The second opening may be larger than the first opening.

The coupling bar may include a front upper coupling bar and a front lower coupling bar. The front upper coupling bar and the front lower coupling bar may be differently positioned in the extending direction between an inlet of the cooling water and a region that is positioned below the semiconductor chip. The front upper coupling bar may be positioned closer to the inlet of the cooling water than to the region that is positioned below the semiconductor chip. The front upper coupling bar may be coupled with upper portions of the plurality of plate-like fins. The front lower coupling bar may be positioned closer to the region that is positioned below the semiconductor chip than to the inlet of the cooling water. The front lower coupling bar may be coupled with lower portions of the plurality of plate-like fins.

In the second flow channel that runs below the semiconductor chip, the comb-tooth portions of the front lower coupling bar may not overlap the comb-tooth portions of the front upper coupling bar in the extending direction.

In the first flow channel that does not run below the semiconductor chip, the comb-tooth portions of the front lower coupling bar may at least partly overlap the comb-tooth portions of the front upper coupling bar in the extending direction.

In the first flow channel that does not run below the semiconductor chip, upper ends of the comb-tooth portions of the front lower coupling bar may be positioned higher than a lower end of the main-body portion of the front upper coupling bar. Alternatively, in the first flow channel, lower ends of the comb-tooth portions of the front upper coupling bar may be positioned lower than an upper end of the main-body portion of the front lower coupling bar.

The cooler may include a plurality of second flow channels. The plurality of second flow channels may each include, in a plane that is positioned between the front upper coupling bar and the inlet and orthogonal to the extending direction, one of a large through hole and a small through hole. The large through hole may include an overlap in the extending direction between the second opening and a fourth opening. An upper end of the second opening may be defined by the comb-tooth portions of the front upper coupling bar. A lower end of the fourth opening may be defined by the comb-tooth portions of the front lower coupling bar. The fourth opening in the large through hole may be a fourth opening having a relatively larger opening area. The small through hole may include an overlap in the extending direction between the second opening and the fourth opening. The fourth opening in the small through hole may be a fourth opening having a relatively smaller opening area.

The inlet and an outlet of the cooling water may be differently positioned in the extending direction with the plurality of plate-like fins being sandwiched therebetween. The cooler may include a plurality of the second flow channels. The plurality of second flow channels may each include, in a plane that is positioned between the front upper coupling bar and the inlet and orthogonal to the extending direction, one of a large through hole and a small through hole. The small through hole may be positioned closer to the inlet or the outlet than the large through hole is.

The inlet and an outlet of the cooling water may be both provided on a same side with respect to the plurality of plate-like fins in the extending direction. The cooler may include a plurality of the second flow channels. The plurality of second flow channels may each include, in a plane that is positioned between the front upper coupling bar and the inlet and orthogonal to the extending direction, one of a large through hole having a relatively larger opening area and a small through hole having a relatively smaller opening area. The large through hole may be positioned closer to the inlet and the outlet than the small through hole is.

The cooler may further include at least one coupling bar that is positioned between the region that is positioned below the semiconductor chip and an outlet of the cooling water in the extending direction.

The cooler may include a back upper coupling bar and a back lower coupling bar that correspond to the at least one coupling bar and are differently positioned in the extending direction between the region that is positioned below the semiconductor chip and the outlet of the cooling water. The back upper coupling bar may be positioned closer to the outlet of the cooling water than to the region that is positioned below the semiconductor chip. The back upper coupling bar may be coupled with the upper portions of the plurality of plate-like fins. The back lower coupling bar may be positioned closer to the region that is positioned below the semiconductor chip than to the outlet of the cooling water. The back lower coupling bar may be coupled with the lower portions of the plurality of plate-like fins.

A distance between the front upper coupling bar and the front lower coupling bar may be shorter than a distance between the back upper coupling bar and the back lower coupling bar.

In the first flow channel that does not run below the semiconductor chip, a length of an overlap, in the extending direction, between the comb-tooth portions of the front upper coupling bar and the comb-tooth portions of the front lower coupling bar may be larger than a length of an overlap, in the extending direction, between the comb-tooth portions of the back upper coupling bar and the comb-tooth portions of the back lower coupling bar.

In the second flow channel that runs below the semiconductor chip, a protruding length of the comb-tooth portions of the back lower coupling bar may be larger than a protruding length of the comb-tooth portions of the front lower coupling bar.

The plurality of plate-like fins may each have a depression. In the depression, the coupling bar may be arranged. The depression may have a protrusion. The protrusion may be in contact with the coupling bar in a direction parallel to the extending direction.

The coupling bar may include at least two coupling bars. The at least two coupling bars may be spaced away from each other in the extending direction and positioned between an inlet of the cooling water and a region that is positioned below the semiconductor chip, or between the region that is positioned below the semiconductor chip and an outlet of the cooling water. A distance between two of the coupling bars in the extending direction may be equal to or larger than a thickness, in the extending direction, of a main-body portion of each of the two coupling bars.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

FIG. 1is a perspective view showing a cooler100relating to a first embodiment. For the purpose of better understanding,FIG. 1shows an upper plate10, an inlet16and an outlet18for cooling water, a plurality of plate-like fins20, and coupling bars30,40,50and60included in the cooler100. Note thatFIG. 1does not show a lower plate12and side plates14, which will be described later. InFIG. 1, the arrows W indicate the direction in which the cooling water mainly flows through the inlet16and the outlet18.

In the present example, the Z axis is orthogonal to the X axis and the Y axis. In the present example, the X, Y and Z axes define the right-handed system. The X, Y and Z axes are used to represent the relative directions in the cooler100, a semiconductor module200, which will be described later, and the like. Here, the Z-axis direction is not necessarily parallel to the gravitational direction. As used herein, the terms “above,” “upper,” “below,” “lower” and the like are associated with the direction parallel to the Z-axis direction, but these terms are also not limited to mean the relative position in the gravitational direction. Here, the position that is relatively close to the inlet16may be referred to using the terms “upstream” and “front,” and the position that is relatively close to the outlet18may be referred to using the terms “downstream” and “back.”

The cooler100may be capable of cooling a semiconductor chip to be provided on the upper plate10. The cooler100is also referred to as a heat sink. The upper plate10may constitute a part of the case through which cooling water flows from the inlet16to the outlet18. The cooler100has a plurality of plate-like fins20housed within the case. This means that the plate-like fins20are arranged below the upper plate10. The heat generated from the semiconductor chip may be transferred to the cooling water at least via the upper plate10and the plate-like fins20. The cooler100may cool the semiconductor chip based on the thermal exchange between the cooling water and the combination of the upper plate10and the plate-like fins20.

Between the respective plate-like fins20, the flow channels may be formed for the cooling water. A pump may be provided outside the cooler100. The pump may provide power to flow the cooling water through the flow channels formed between the plate-like fins20. In each flow channel, the cooling water may flow from the position corresponding to the front end (the end in the −Y direction) of the plate-like fins20to the position corresponding to the back end (the end in the +Y direction) of the plate-like fins20. Note that the cooling water may be the mixture of water and ethylene glycol or pure water. The cooling water may alternatively be the mixture of water and a different long life coolant (LLC). The cooling water may be a different type of cooling fluid.

When the cooler100is seen from above, the plate-like fins20may extend in a particular direction. In the present example, the reference numeral25represents the extending direction of the plate-like fins20, which is aligned with the Y-axis direction. In the present example, the plate-like fins20each include a zigzag portion extending in the Y-axis direction. In a different example, however, the plate-like fins20each may include a straight portion extending in the Y-axis direction in place of the zigzag portion.

The coupling bars30,40,50and60may be coupled to the plate-like fins20to provide a predetermined spacing between the adjacent ones of the plate-like fins20in the X-axis direction. For example, when the depressions of the coupling bars, which are formed by the main-body portion and two of the comb-tooth portions, mesh the depressions of the plate-like fins20, the coupling bars are coupled with the plate-like fins20. As a result of the coupling, the relative positions of the coupling bars and the plate-like fins20may be fixed. The plate-like fins20may be arranged in parallel with each other in such a manner that the individual plate-like fins20extend in a parallel direction to each other and the adjacent ones of the plate-like fins20are spaced away from each other with a predetermined distance provided therebetween.

In the present example, the coupling bar30corresponds to a front upper coupling bar, the coupling bar40corresponds to a front lower coupling bar, the coupling bar50corresponds to a back upper coupling bar, and the coupling bar60corresponds to a back lower coupling bar. In the present example, the coupling bars30and50are coupled to the upper portion of the plate-like fins20. On the other hand, the coupling bars40and60are coupled to the lower portion of the plate-like fins20in the present example. In the present example, the coupling bars30and40are positioned upstream relative to the coupling bars50and60. In addition, in the present example, the coupling bar30is positioned upstream relative to the coupling bar40, and the coupling bar50is positioned downstream relative to the coupling bar60.

FIG. 2is a top view showing the semiconductor module200having the cooler100. As shown inFIG. 2, the cooler100includes a side plate14-1that serves as the edge in the +X direction, a side plate14-2that serves as the edge in the −X direction, a side plate14-3that serves as the front edge (the edge in the −Y direction), and a side plate14-4that serves as the back edge (the edge in the +Y direction). Note that three semiconductor chips90are arranged next to each other in the X-axis direction and two in the Y-axis direction in the present example. In total, six semiconductor chips90(=3×2) are provided on the upper plate10.FIG. 2does not show the constituents above the upper plate10and thus uses the dotted lines to represent the regions that are positioned below the semiconductor chips90.

In the present example, the inlet16of the cooling water is coupled to the front side plate14-3, and the outlet18of the cooling water is coupled to the back side plate14-4. The inlet16and the outlet18may be differently positioned in the extending direction25with the plate-like fins20being sandwiched therebetween. In the present example, the inlet16and the outlet18are point-symmetrically positioned with respect to the center of the rectangle that is observed when the cooler100is seen from above. The inlet16and the outlet18may be positioned on the diagonal line of the rectangle.

In the present example, the plate-like fins20each include straight portions26that are parallel to the Y-axis direction and a wave-shaped portion28that extends in a zigzag manner in the Y-axis direction. In the present example, the straight portions26of each plate-like fin20are positioned in the vicinity of the inlet16and in the vicinity of the outlet18, and the wave-shaped portion28of each plate-like fin20extends continuously between the two straight portions26.

In the cooler100, at least two of the coupling bars may be spaced away from each other in the extending direction25. A plurality of coupling bars may be positioned on the straight portions26-1positioned in the vicinity of the inlet16. In the present example, a pair of coupling bars30and40is provided on the straight portions26-1positioned in the vicinity of the inlet16. Since the pair of coupling bars30and40is coupled with the straight portions26-1of the plate-like fins20, a simplified coupling structure can be employed between the pair of coupling bars30and40and the plate-like fins20and more rigid coupling can be achieved between the pair of coupling bars30and40and the plate-like fins20, when compared with the case where the pair of coupling bars30and40is coupled with the wave-shaped portions28of the plate-like fins20.

The coupling bars30and40may be differently positioned in the extending direction25between the inlet16of the cooling water and the regions positioned below the semiconductor chips90. In the present example, the coupling bars30and40are provided on the straight portions26-1in the vicinity of the inlet16, which are positioned upstream relative to the regions positioned below the semiconductor chips90. The coupling bar30of the present example is closer to the inlet16of the cooling water than to the regions positioned below the semiconductor chips90, and the coupling bar40of the present example is closer to the regions positioned below the semiconductor chips90than to the inlet16of the cooling water.

Since the cooling water flows in vigorously in the vicinity of the inlet16, the kinetic energy of the cooling water is higher than in the vicinity of the outlet18. Therefore, in place of a single coupling bar, the pair of upper and lower coupling bars30and40is used, to partially block the flow of the cooling water in the present example In this manner, through holes, which will be described later, can be defined by shorter comb-tooth portions when compared with the case where the through holes are defined by the comb-tooth portions of a single coupling bar. Such configurations can lower the physical load applied on the coupling bars by the cooling water. In addition, the flow velocity of the cooling water can be adjusted to an appropriate level. Furthermore, since the upper coupling bar30is positioned upstream relative to the lower coupling bar40, the flow in the Z-axis direction can be regulated. For example, in the regions positioned below the semiconductor chips90in the flow channels of the cooling water, the cooling water can achieve a higher flow velocity in the upper portion (the portion closer to the chips) than in the lower portion. Accordingly, the cooling water can more efficiently remove the heat from the upper plate10.

At least one coupling bar may be provided between the regions positioned below the semiconductor chips90and the outlet18of the cooling water in the extending direction25. In this manner, the plate-like fins20can be more stably fixed in the X-axis direction. In the present example, the cooler100has a pair of coupling bars50and60that are provided on the straight portions26-2in the vicinity of the outlet18. Note that, in a different example, only a single or no coupling bar may be provided on the straight portions26-2in the vicinity of the outlet18. According to the different example in which only a single coupling bar is provided in the vicinity of the outlet18, the number of parts constituting the cooler100can be reduced, which can reduce the cost and time of manufacturing the cooler100, for example

The coupling bars50and60may be differently positioned in the extending direction25between the regions positioned below the semiconductor chips90and the outlet18of the cooling water. In the present example, the coupling bars50and60are provided on the straight portions26-2in the vicinity of the outlet18, which are positioned downstream relative to the regions positioned below the semiconductor chips90. The coupling bar50of the present example is closer to the outlet18of the cooling water than to the regions positioned below the semiconductor chips90, and the coupling bar60of the present example is closer to the regions positioned below the semiconductor chips90than to the outlet18of the cooling water.

Since the cooler100of the present example is symmetrically structured between the upstream and the downstream, the flowing direction of the cooling water may be reversed when compared with the present example. This means that the outlet18of the present example may be alternatively configured as the inlet of the cooling water and that the inlet16of the present example may be alternatively configured as the outlet of the cooling water. The present example has advantages over the case where the cooler100is not symmetrically structured between the upstream and the downstream in terms of that the semiconductor module200can be easily assembled.

FIG. 3Ashows the coupling bar30.FIG. 3Auses the solid lines to indicate the coupling bar30. On the other hand,FIG. 3Auses the dotted lines to indicate the semiconductor chips90provided on the upper plate10, first openings71provided in first flow channels70and second openings73provided in second flow channels72. In the present example, the first flow channels70do not run below the semiconductor chips90, and the second flow channels72run below the semiconductor chips90. The differences between second flow channels72-1and second flow channels72-2will be described later.

In the present example, the coupling bar30includes a main-body portion32and a plurality of comb-tooth portions34. The comb-tooth portions34may each protrude from the main-body portion32into the flow channels through which the cooling water flows. In the present example, the comb-tooth portions34extend from the main-body portion32in the −Z direction. The main-body portion32may have the same Z-axis length across any different positions thereof in the X-axis direction. On the contrary, the comb-tooth portions34may have different Z-axis lengths between different positions thereof in the X-axis direction.

The comb-tooth portions34may have different Z-axis lengths depending on whether they are positioned in the first flow channels70or the second flow channels72. In the coupling bar30of the present example, comb-tooth portions34-1positioned in the first flow channels70have a larger Z-axis length than the comb-tooth portions34-2positioned in the second flow channels72. In the coupling bar30of the present example, the comb-tooth portions34-1positioned in the first flow channels70have a Z-axis length L1, and the comb-tooth portions34-2positioned in the second flow channels72have a Z-axis length L2(L2<L1). Note that, in the present example, the Z-axis length of the comb-tooth portions34is defined as the length from the lower end of the main-body portion32to the lower end of the comb-tooth portions34. The comb-tooth portions34may each have the same width in the X direction.

The upper end of the first openings71and the second openings73may be defined by the comb-tooth portions34. The lower end of the first openings71and the second openings73may be defined by the upper edge of a lower plate12, which will be described later. The respective ends in the X-axis direction of the first openings71and the second openings73may be defined by two of the plate-like fins20that are next to each other in the X-axis direction. Note that, however, the end surface in the +X direction of the last first opening71in the +X direction may be defined by the side plate14-1. Likewise, the end surface in the −X direction of the last first opening71in the −X direction may be defined by the side plate14-2.

In the coupling bar30, one first opening71has a smaller opening area than one second opening73. The opening area may denote the area of the opening when the opening is seen in the Y-axis direction, which is shown inFIG. 3A. In the present example, the sum of the opening areas of the first openings71positioned in the first flow channels70is also smaller than the sum of the opening areas of the second openings73positioned in the second flow channels72. In the present example, the number of the first openings71is smaller than the number of the second openings73. Since the first openings71are smaller than the second openings73, the flow rate of the cooling water can be reduced in the first flow channels70, which make small contribution to the cooling of the semiconductor chips90, and raised in the second flow channels72, which make large contribution to the cooling of the semiconductor chips90. With such configurations, the semiconductor chips90can be cooled more efficiently when compared with the case where the first openings71and the second openings73have the same area.

FIG. 3Bshows the coupling bar40. As inFIG. 3A,FIG. 3Buses the solid lines to indicate the coupling bar40. On the other hand,FIG. 3Buses the dotted lines to indicate the semiconductor chips90, third openings76and fourth openings78. In the present example, the third openings76have the same opening area as the first openings71. In the present example, the fourth openings78have a larger opening area than the third openings76.

The coupling bar40may include a main-body portion42and a plurality of comb-tooth portions44. The comb-tooth portions44may each protrude from the main-body portion42into the flow channels through which the cooling water flows. In the present example, the comb-tooth portions44extend from the main-body portion42in the +Z direction. The main-body portion42may have the same Z-axis length across any different positions thereof in the X-axis direction. On the contrary, the comb-tooth portions44may have different Z-axis lengths between different positions thereof in the X-axis direction.

Also in the coupling bar40, the comb-tooth portions44may have different Z-axis lengths depending on whether they are positioned in the first flow channels70or the second flow channels72. In the coupling bar40of the present example, comb-tooth portions44-1positioned in the first flow channels70have a larger Z-axis length than the comb-tooth portions44-2and44-3positioned in the second flow channels72. In the coupling bar40of the present example, the comb-tooth portions44-1positioned in the first flow channels70have a Z-axis length L3, and the comb-tooth portions44-2and44-3positioned in the second flow channels72respectively have a Z-axis length L4and a Z-axis length L5(L4, L5<L3). Here, the Z-axis length L3may be equal to the Z-axis length L1of the comb-tooth portions34-1positioned in the first flow channels70of the coupling bar30(L3=L1). Note that, in the present example, the Z-axis length of the comb-tooth portions44is defined as the length from the upper end of the main-body portion42to the upper end of the comb-tooth portions44. The comb-tooth portions44may each have the same width in the X direction.

In the present example, a semiconductor chip90-2is positioned between the inlet16of the cooling water and the outlet18in the X-axis direction. In addition, semiconductor chips90-1and90-3are positioned in the two regions that sandwich in the X-axis direction the region in which the semiconductor chip90-2is positioned. In the second flow channel72-2positioned below the semiconductor chip90-2, the comb-tooth portions44-3have the Z-axis length L5. On the other hand, in the second flow channels72-1positioned below the semiconductor chips90-1and90-3, which sandwich the semiconductor chip90-2in the X-axis direction, the comb-tooth portions44-2have the Z-axis length L4. In the present example, the length L4is larger than the length L5(L5<L4). The Z-axis length L5may be equal to the Z-axis length L2of the comb-tooth portions34-2of the coupling bar30that are positioned in the second flow channels72(L5=L2). The second flow channels72-1and the second flow channel72-2may be parallel to the Y-axis direction with the first flow channels70being sandwiched therebetween. In addition, the second flow channel72-2may be arranged between the two second flow channels72-1in the X-axis direction.

In the present example, the fourth openings78include fourth openings78-1that have a relatively small opening area and fourth openings78-2that have a relatively large opening area. The fourth openings78-1are openings the lower ends of which are defined by the comb-tooth portions44-2having the length L4and the fourth openings78-2are openings the lower ends of which are defined by the comb-tooth portions44-3having the length L5. Note that, in the present example, the fourth openings78-2have the same opening area as the second opening73.

The upper end of the third openings76and the fourth openings78may be defined by the lower edge of the upper plate10. The respective ends in the X-axis direction of the third openings76and the fourth openings78may be defined by two of the plate-like fins20. Note that, however, the end surface in the +X direction of the last third opening76in the +X direction may be defined by the side plate14-1. Likewise, the end surface in the −X direction of the last third opening76in the −X direction may be defined by the side plate14-2.

Also in the coupling bar40, one third opening76has a smaller opening area than one fourth opening78. In the present example, the sum of the opening areas of the third openings76positioned in the first flow channels70is also smaller than the sum of the opening areas of the fourth openings78positioned in the second flow channels72. Furthermore, in the present example, the number of the third openings76is also smaller than the number of the fourth openings78.

Since the third openings76are smaller than the fourth openings78also in the coupling bar40, the flow rate of the cooling water can be also reduced in the first flow channels70, which make small contribution to the cooling of the semiconductor chips90, and raised in the second flow channels72, which make large contribution to the cooling of the semiconductor chips90. In addition, in the coupling bar40, the fourth openings78-2in the second flow channel72-2, which is the most distant in the X-axis direction from the inlet16and the outlet18, are larger than the fourth openings78-1in the second flow channels72-1, which are the closest in the X-axis direction to the inlet16or the outlet18. With such configurations, the area of the overlap in the extending direction25between the second openings73and the fourth openings78-2in the second flow channel72-2is larger than the area of the overlap in the extending direction25between the second openings73and the fourth openings78-1in the second flow channels72-1. When the second flow channels72are seen in the Y-axis direction, the openings are defined as the gap between the end of the comb-tooth portions34and the end of the comb-tooth portions44and have a larger Z-axis length in the second flow channel72-2than in the second flow channels72-1. Accordingly, the present embodiment can reduce the imbalance in the flow rate of the cooling water among the second flow channels72.

FIG. 4is a perspective view showing how one plate-like fin20is positioned relative to the coupling bar30and the coupling bar40. In the present example, the coupling bar40is positioned downstream (in the +Y direction) relative to the coupling bar30. The coupling bar30, which is positioned closer to the upper plate10and the semiconductor chips90, is positioned upstream relative to the coupling bar40. In addition, in the present example, the comb-tooth portions34face the comb-tooth portions44in the Z-axis direction but do not overlap in the Z-axis direction. In the present example, the straight portion26of the plate-like fin20is positioned to mesh in the Z-axis direction a depression36of the coupling bar30and a depression46of the coupling bar40.

FIG. 5shows a cross-section taken along the line A-A inFIG. 4.FIG. 5shows the cross-section parallel to the Y-Z plane passing through the plate-like fin20. Here,FIG. 5shows not only the upstream straight portion26but also the downstream straight portion26. The plate-like fin20may have depressions21. The depressions21may each also have protrusions24. In the present example, the depressions21are notches indented in the +Z or −Z direction in the plate-like fin20. In the plate-like fin20, one depression21may be positioned where the plate-like fin20is coupled with a corresponding one of the coupling bars. In the present example, the plate-like fin20has depressions21-1and21-3that are both on the upper edge and respectively correspond to the upstream and downstream coupling bars30and50, and depressions21-2and21-4that are both on the lower edge and respectively correspond to the upstream and downstream coupling bars40and60.

The depression21-1on the upper edge may have a bottom portion22with which the lower portion of the main-body portion32is in contact. Likewise, the depression21-3may have a bottom portion22with which the lower portion of the main-body portion52is in contact. The bottom portions22of the depressions21may be respectively attached to the bottom portions of the main-body portions32and52using a wax material. After the coupling bars have been coupled with the depressions21, the upper portions of the main-body portions32and52and the upper portion of the plate-like fin20may form a substantially flat surface free from protrusions.

The depression21-2on the lower edge may have a top portion23with which the upper portion of the main-body portion42is in contact. Likewise, the depression21-4may have a top portion23with which the upper portion of the main-body portion62is in contact. The top portions23of the depressions21may be respectively attached to the top portions of the main-body portions42and62using a wax material. After the coupling bars have been coupled with the depressions21, the lower portions of the main-body portions42and62and the lower portion of the plate-like fin20may form a substantially flat surface free from protrusions.

The protrusions24may be provided in the upper portions of the depressions21-1and21-3on the upper edge of the plate-like fin20and in the lower portions of the depressions21-2and21-4on the lower edge of the plate-like fin20. The protrusions24may protrude in the extending direction25. The protrusions24may be in contact with the coupling bars positioned in the depressions21in the direction parallel to the extending direction25. This can rigidly fasten the plate-like fin20and the coupling bars together. In the present example, the plate-like fin20has two protrusions24in each one of the depressions21. In a different example, however, one protrusion24may be provided in each one of the depressions21.

In the depression21-1of the present example, the length of the spacing between the two protrusions24facing each other in the Y-axis direction is smaller than the Y-axis length of the main-body portion32of the coupling bar30. Likewise, in each of the depressions21-2,21-3and21-4, the length of the spacing between the two protrusions24facing each other in the Y-axis direction is smaller than the Y-axis length of the main-body portions42,52and62. When the main-body portion32of the coupling bar30meshes the pair of protrusions24, the protrusions24may be pressed by the main-body portion32and thus deformed. The restoring force of the deformed protrusions24may contribute to fasten the main-body portion32of the coupling bar30and the plate-like fin20together. Likewise, the other main-body portions42,52and62may deform the protrusions24. Here, the protrusions24may dent into the main-body portions of the coupling bars. In a different example, the protrusions24of the plate-like fin20may come into contact with the main-body portion32,42,52or62of the coupling bar30,40,50or60by pressing the protrusions24of the plate-like fin20in the +Z direction and the −Z direction.

FIG. 6includes a view (A) showing a cross-section taken along the line B-B inFIG. 2. The B-B cross-section is the cross-section of the semiconductor module200that is positioned between the coupling bar30and the inlet16and parallel to the X-Z plane orthogonal to the Y-axis direction. In the present example, the semiconductor module200includes the cooler100, a multilayered substrate80and the plurality of semiconductor chips90. As shown in the view (A) inFIG. 6, the cooler100has the lower plate12. The upper plate10, the lower plate12, and the four or front, back, left and right side plates14may constitute a case housing therein the plate-like fins20. In the view (A) inFIG. 6, the coupling bar30is positioned in front of the coupling bar40.

Although the plate-like fins20are not shown in the B-B cross-section, each of the depressions36of the coupling bar30may mesh the upper portion of a corresponding one of the plate-like fins20. In addition, each of the depressions46of the coupling bar40may mesh the lower portion of a corresponding one of the plate-like fins20. Furthermore, a portion of the plate-like fin20that mesh neither the depression36nor depression46and extends in the Y-axis direction may span in the Z-axis direction between the upper plate10and the lower plate12.

The upper plate10, the lower plate12and the side plates14, the coupling bars30,40,50and60, and the plate-like fins20may be made of copper (Cu), aluminum (Al) or magnesium (Mg), or a combination of one of copper (Cu), aluminum (Al) and magnesium (Mg) and nickel (Ni) plating thereon. Since the cooler100is made of a metal such as copper or aluminum, which exhibits relatively high thermal conductivity, the thermal exchange can be enhanced between the cooling water and the upper plate10and the plate-like fins20, when compared with the case where the cooler100is made of an insulating material or the like, which exhibits relatively low thermal conductivity. The above-mentioned copper may include an alloy that is principally made of copper, the above-mentioned aluminum may include an alloy that is principally made of aluminum or the above-mentioned nickel may include an alloy that is principally made of nickel.

The lower portion of the multilayered substrate80may be in contact with the upper plate10, and the upper portion of the multilayered substrate80may be in contact with the semiconductor chips90. The multilayered substrate80may include a first metal interconnection layer82, an insulating layer84and a second metal interconnection layer86. The insulating layer84may be sandwiched in the Z-axis direction between the first metal interconnection layer82and the second metal interconnection layer86. The first metal interconnection layer82and the second metal interconnection layer86may have a shorter length in the X- and Y-axis directions than the insulating layer84.

On the first metal interconnection layer82, the semiconductor chips90may be provided. The first metal interconnection layer82may include interconnections that electrically connect the semiconductor chips90. The first metal interconnection layer82may be an interconnection layer made of copper (Cu) or aluminum (Al).

The insulating layer84may be an insulating substrate provided between the first metal interconnection layer82and the second metal interconnection layer86. The insulating layer84may be made of a sintered ceramic material such as silicon nitride (SiNX), aluminum nitride (AlNX) or aluminum oxide (Al2O3).

The insulating layer84may be capable of reliably providing electrical insulation between the semiconductor chips90, through which large current flows, and the metal cooler100. The insulating layer84can ensure that the electrical insulation can be maintained between the semiconductor chips90and the cooler100regardless whether the cooler100is entirely made of metals. From the perspective of the cooling efficiency, it is better to use metals to make the entire of the cooler100than to use insulating materials to make a part or the entire of the cooler100. The multilayered substrate80may be divided into sections each of which include at least one of the semiconductor chips90.

FIG. 6also includes a view (B) showing the first flow channels70and the second flow channels72in the B-B cross-section. As shown in the view (B) inFIG. 6, the cooler100of the present example includes a plurality of first flow channels70and a plurality of second flow channels72. Each second flow channel72may include either large through holes77or small through holes75. In the present example, the second flow channels72-1include the small through holes75. The small through holes75may include the overlap in the Y-axis direction between the second openings73and the fourth openings78-1. On the other hand, the second flow channel72-2includes the large through holes77. The large through holes77may include the overlap in the -Y-axis direction between the second openings73and the fourth openings78-2, which have a larger opening area than the fourth openings78-1.

The large through holes77may be formed (defined) in the second flow channel72-2positioned below the semiconductor chip90-2by the gap between the pair of plate-like fins20that are next to each other in the X-axis direction and by the gap in the Z-axis direction between the comb-tooth portion34-2and the comb-tooth portion44-3. On the other hand, the small through holes75may be formed (defined) in the second flow channels72-1by the gap between the pair of plate-like fins20that are next to each other in the X-axis direction and by the gap in the Z-axis direction between the comb-tooth portion34-2and the comb-tooth portion44-2.

As has been described with reference toFIG. 3B, the protruding length of the comb-tooth portions44-2in the second flow channels72-1, in which the small through holes75are formed, is larger than the protruding length of the comb-tooth portions44-3in the second flow channel72-2, in which the large through holes77are formed. On the other hand, the protruding length of the comb-tooth portions34-2is the same in either the second flow channels72-1or second flow channel72-2. Accordingly, when seen in the extending direction25(Y-axis direction), the large through holes77have a larger opening area than the small through holes75. Furthermore, the small through holes75are provided in the second flow channels72-1, which are closer to the inlet16or outlet18than the large through holes77are. In this manner, the present embodiment can reduce the imbalance in the flow rate of the cooling water among the second flow channels72-1and72-2. The sum of the opening areas of the large through holes77in the second flow channel72-2is larger than the sum of the opening areas of the small through holes75in either one of the second flow channels72-1. The number of the pairs of the comb-tooth portion34and the comb-tooth portion44may be the same or different between the second flow channels72-1and the second flow channel72-2.

In the present example, the term “through hole” means that a continuous opening is formed in the Y-axis direction between a first coupling bar (for example, the coupling bar30) and a second coupling bar that is in the vicinity of the first coupling bar (for example, the coupling bar40). The through hole may further extend from the two coupling bars that are in the vicinity of each other. The through hole may include a continuous opening formed from the coupling bar30to the coupling bar50.

FIG. 7includes a view (A) showing a cross-section taken along the line C-C inFIG. 2. The C-C cross-section is the cross-section of the semiconductor module200that is positioned between the coupling bar30and the coupling bar40in the extending direction25and parallel to the X-Z plane orthogonal to the Y-axis direction.FIG. 7(A) only shows, in the C-C cross-section, the coupling bar40and the plate-like fins20in the internal space enclosed within the upper plate10, the lower plate12and the side plates14.

FIG. 7also includes a view (B) showing the first flow channels70and the second flow channels72in the C-C cross-section. As in the B-B cross-section, the cooler100includes in the X-Z plane the first openings76provided in the first flow channels70and the second openings78, which are larger than the first openings76, provided in the second flow channels72. The second flow channel72-2has the large through holes77, and the second flow channels72-1have the small through holes75.

FIG. 8shows how the inlet16and the outlet18are positioned relative to the through holes.FIG. 8corresponds toFIG. 2and is a top view showing the cooler100. InFIG. 8, however, for the purpose of better understanding of how the through holes are positioned in the second flow channels72, the small through holes75and the large through holes77are indicated by the solid lines and the first flow channels70, the second flow channels72and the semiconductor chips90are indicated by the dotted lines. It also should be noted thatFIG. 8does not show the plate-like fins20.

In the present example, the coupling bar50has the same structure as the coupling bar30, and the coupling bar60has the same structure as the coupling bar40. Accordingly, the second flow channels72-1have the small through holes75in the upstream and downstream portions thereof, and the second flow channel72-2has the large through holes77in the upstream and downstream portions thereof. As described above, the imbalance in the flow rate of the cooling water can be reduced by arranging one of the second flow channels72-1at the position closest to the inlet16, the other of the second flow channels72-1at the position closest to the outlet18, and the second flow channel72-2between the two second flow channels72-1in the X-axis direction. Note that the cooling water may also flow in the X-axis direction while running through the flow channel extending from the inlet16to the outlet18. For example, part of the cooling water W flows in the X-axis direction in the vicinity of the side plates14-3and14-4.

FIG. 9Ashows a cross-section taken along the line D-D inFIG. 2. The D-D cross-section is the cross-section of the semiconductor module200along the Y-Z plane that is parallel to the extending direction25. The D-D cross-section is also the cross-section of the second flow channel72-1. For better intelligibility, however, the side plates14are not shown. In the second flow channel72-1, the comb-tooth portion44-2and the comb-tooth portion34-2do not overlap in the extending direction25, and the coupling bars30and40thus form the small through hole75. Likewise, the coupling bars50and60also form the small through hole75. In this way, the flow rate can be higher in the second flow channels72than in the first flow channels70, which can contribute to more efficient cooling of the semiconductor chip90. Here, the comb-tooth portions54-1and54-2respectively correspond to the comb-tooth portions34-1and34-2. Likewise, the comb-tooth portions64-1,64-2and64-3respectively correspond to the comb-tooth portions44-1,44-2and44-3.

In the present example, the cooler100has the coupling bars30and40in the upstream portion and the coupling bars50and60in the downstream portion. The coupling bars30,40,50and60respectively have Y-axis thicknesses TFU, TFD, TBUand TBD. The coupling bar50has the main-body portion52and the comb-tooth portions54-2, and the coupling bar60has the main-body portion62and the comb-tooth portions64-2. Here, in the extending direction25of the D-D cross-section, the coupling bars have the same thickness as the comb-tooth portions of the coupling bars. Here, dFdenotes the distance between the coupling bar30and the coupling bar40in the extending direction25, and dBdenotes the distance between the coupling bar50and the coupling bar60in the extending direction25.

The distance d between the two coupling bars in the extending direction25may be equal to or larger than the thickness T of the main-body portion of the two coupling bars in the extending direction25. In the present example, TFUand TFD≤dFand TBUand TBD≤dB. The above-described configurations can prevent a case where the wax material drips off the main-body portion32and couples the comb-tooth portion34-2and the comb-tooth portion44-2together to narrow the second flow channel72-1.

FIG. 9Bshows a cross-section taken along the line E-E inFIG. 2. The E-E cross-section is the cross-section of the semiconductor module200along the Y-Z plane that is parallel to the extending direction25. The E-E cross-section is also the cross-section of the first flow channel70. For better intelligibility, however, the side plates14are not shown. In the first flow channel70, the comb-tooth portion44-1and the comb-tooth portion34-1at least partly overlap each other in the extending direction25. In this manner, the flow rate of the cooling water can be more limited in the first flow channel70, which does not run below the semiconductor chips90, than in the second flow channel72.

FIG. 9Cshows a cross-section taken along the line F-F inFIG. 2. The F-F cross-section is the cross-section of the semiconductor module200along the Y-Z plane that is parallel to the extending direction25. The F-F cross-section is also the cross-section of the second flow channel72-2. For better intelligibility, however, the side plates14are not shown. In the second flow channel72-2, the comb-tooth portion44-3and the comb-tooth portion34-2do not overlap in the extending direction25, and the coupling bars30and40thus form the large through hole77. Likewise, the coupling bars50and60also form the large through hole77. In this way, the flow rate can be higher in the second flow channels72than in the first flow channels70, and, furthermore, the imbalance in the flow rate among the second flow channels72can be reduced.

FIG. 10is a circuit diagram of the semiconductor module200. The semiconductor module200may constitute a part of an in-vehicle power module designed to drive the motor of a vehicle. In the semiconductor module200, the semiconductor chips90-1to90-6may be each an RC-IGBT semiconductor chip. In the RC-IGBT semiconductor chip, an insulated gate bipolar transistor (IGBT) and a freewheel diode (FWD) are integrally formed, and the IGBT and the FWD may be connected in inverse parallel. Note thatFIG. 10does not show the signs representative of the FWDs, but each semiconductor chip90may include a FWD.

In the semiconductor chip90-1, the emitter electrode may be electrically connected to an input terminal N1and the collector electrode may be electrically connected to an output terminal U. In the semiconductor chip90-2, the emitter electrode may be electrically connected to an input terminal N2and the collector electrode may be electrically connected to an output terminal V. In the semiconductor chip90-3, the emitter electrode may be electrically connected to an input terminal N3and the collector electrode may be electrically connected to an output terminal W. In the semiconductor chip90-4, the emitter electrode may be electrically connected to an output terminal U and the collector electrode may be electrically connected to an input terminal P1. In the semiconductor chip90-5, the emitter electrode may be electrically connected to an output terminal V and the collector electrode may be electrically connected to an input terminal P2. In the semiconductor chip90-6, the emitter electrode may be electrically connected to an output terminal W and the collector electrode may be electrically connected to an input terminal P3.

The semiconductor chips90-1to90-6may be alternately switched on and off by the signal input into the control electrode pad of the semiconductor chips90. In the present example, each semiconductor chip90is an RC-IGBT. Accordingly, when each semiconductor chip90is switched on, the IGBT region may generate heat. In addition, when each semiconductor chip90is switched off, the FWD region may generate heat. The input terminal P1may be connected to the positive side of an external power source, the input terminal N1may be connected to the negative side of the external power source, and the output terminal U may be connected to a load. The semiconductor chips90-1,90-2and90-3may constitute a lower arm of the semiconductor module200, and the semiconductor chips90-4,90-5and90-6may constitute an upper arm of the semiconductor module200.

The input terminals P1, P2and P3may be electrically connected to each other, and the other input terminals N1, N2and N3may be also electrically connected to each other. The semiconductor module200of the present example may serve as a three-phase AC inverter circuit having the output terminals U, V and W.

FIG. 11shows a cross-section of a semiconductor module400relating to a comparative example. The semiconductor module400includes a cooler310, a multilayered substrate80and a plurality of semiconductor chips90. The multilayered substrate80and the semiconductor chips90may be configured in the same manner as in the first embodiment. The cooler310of the comparative example is different from the cooler100of the first embodiment in terms of that the coupling bars30,40,50and60are not provided. The semiconductor module400is similar to a semiconductor module300, which will be described later, in that an inlet116, an outlet118, side plates114and semiconductor chips90-1ato90-6bare arranged so that the main circuit is constituted.

FIG. 12Ais a top view showing a semiconductor module300including the cooler100, for which thermal resistance simulation was conducted.FIG. 12Ashows how semiconductor chips90, an inlet116, an outlet118, small through holes75and large through hole77are positioned relative to each other. In the semiconductor module300, the inlet116is provided in the side plate114-2, and the outlet118is provided in the side plate114-1. The inlet116and the outlet118extend in parallel to the direction in which the coupling bars30,40,50and60extend (in the X-axis direction). Note that the inlet116and the outlet118may extend orthogonally to the extending direction25of the plate-like fins20(in the X-axis direction) as shown inFIG. 12A, or, in a different example, extend in parallel to the extending direction25(in the Y-axis direction), like the inlet16and the outlet18ofFIG. 8. The inlet116preferably extends in parallel to the direction orthogonal to the extending direction25of the plate-like fins20(in the X-axis direction) as shown in the example ofFIG. 12A, since this arrangement can reduce the variation in the quantity of the cooling water among the respective second flow channels72. The cooling water W fed through the inlet116may at least partly flow in the X-axis direction along the coupling bars30and50in the vicinity of the side plates114-3and114-4.

FIG. 12Bis a circuit diagram corresponding toFIG. 12A. When this thermal resistance simulation was conducted, two semiconductor chips90were provided in parallel with each other in each arm. The two chips in each arm were arranged next to each other in the extending direction25. In the present example, the semiconductor chips90-4aand90-1aconstitute the lower arm corresponding to the output terminal U, and the semiconductor chips90-4band90-1bconstitute the upper arm corresponding to the output terminal U. Likewise, in the present example, the semiconductor chips90-5aand90-2aconstitute the lower arm corresponding to the output terminal V, and the semiconductor chips90-5band90-2bconstitute the upper arm corresponding to the output terminal V. Also, in the present example, the semiconductor chips90-6aand90-3aconstitute the lower arm corresponding to the output terminal W, and the semiconductor chips90-6band90-3bconstitute the upper arm corresponding to the output terminal W.

FIG. 12Cshows the results of the thermal resistance simulations conducted for the example shown inFIGS. 12A and 12Band the comparative example in which the cooler shown inFIG. 12Ais replaced with the cooler310shown inFIG. 11. The horizontal axis represents the portion the thermal resistance of which was evaluated by the simulations. The present simulations were conducted to evaluate the thermal resistance of the central portion of the X-Y plane in the semiconductor chips90-4a,90-4b,90-5a,90-5b,90-6aand90-6bconnected to the terminals N1, P1, N2, P2, N3and P3shown inFIG. 12B. The vertical axis represents the thermal resistance Rth[° C./W]. Note that the thermal resistance Rthmay be defined based on ΔT[° C.]=Rth[° C./W]×PLOSS[W]. Here, ΔT[° C.] denotes the difference in temperature between the semiconductor chip90and the upper plate10, and PLOSS[W] denotes the energy loss in each semiconductor chip90.

As is clearly indicated by the results shown inFIG. 12C, each semiconductor chip exhibited lowered thermal resistance Rthin the first embodiment when compared with the comparative example. In addition, the variation in the thermal resistance Rthwas smaller in the first embodiment when compared with the comparative example These results prove that the first embodiment can improve the cooling efficiency of the semiconductor chips90by providing the coupling bars30,40,50and60to lower the flow rate of the cooling water in the first flow channels70and raise the flow rate of the cooling water in the second flow channels72.

FIG. 13Ashows a first modification example in the cross-section taken along the line E-E inFIG. 2. The E-E cross-section is the cross-section of the first flow channels. InFIG. 13A, the upper end of the comb-tooth portion44-1is positioned higher than the lower end of the main-body portion32of the coupling bar30. For example, the distance between the upper end of the comb-tooth portion44-1and the upper plate10is larger than 0 mm and no more than 1 mm. Here, the lower end of the comb-tooth portion34-1is aligned with the upper end of the main-body portion42of the coupling bar40. The distance between the upper end of the comb-tooth portion44-1and the upper plate10may be adjusted according to the flow rate of the cooling water in the first flow channels70. In this manner, the flow rate of the cooling water can be reduced in the first flow channels70to be lower than in the second flow channels, and the reduction can be also adjusted.

In the present example, the upper end of the comb-tooth portion64-1is also positioned higher than the lower end of the main-body portion52of the coupling bar50. For example, the distance between the upper end of the comb-tooth portion64-1and the upper plate10is also larger than 0 mm and no more than 1 mm. Here, the lower end of the comb-tooth portion54-1is also aligned with the upper end of the main-body portion62of the coupling bar60. In this manner, the flow rate of the cooling water in the first flow channels70may be adjusted in the upstream and downstream portions.

FIG. 13Bshows a second modification example in the cross-section taken along the line E-E inFIG. 2. InFIG. 13B, the lower end of the comb-tooth portion34-1is positioned lower than the upper end of the main-body portion42of the coupling bar40. For example, the distance between the lower end of the comb-tooth portion34-1and the lower plate12is larger than 0 mm and no more than 1 mm. Here, the upper end of the comb-tooth portion44-1is aligned with the lower end of the main-body portion32of the coupling bar30. The distance between the lower end of the comb-tooth portion34-1and the lower plate12may be adjusted according to the flow rate of the cooling water in the first flow channels70. In this manner, the flow rate of the cooling water can be reduced in the first flow channels70to be lower than in the second flow channels, and the reduction can be also adjusted.

In the present example, the lower end of the comb-tooth portion54-1is also positioned lower than the upper end of the main-body portion62of the coupling bar60. For example, the distance between the lower end of the comb-tooth portion54-1and the lower plate12is also larger than 0 mm and no more than 1 mm. Here, the upper end of the comb-tooth portion64-1is also aligned with the lower end of the main-body portion52of the coupling bar50. In this manner, the flow rate of the cooling water in the first flow channels70may be adjusted in the upstream and downstream portions. Alternatively, the configurations shown inFIG. 13Amay be employed in the upstream portion, and the configurations shown inFIG. 13Bmay be employed in the downstream portion. Alternatively, the configurations shown inFIG. 13Amay be employed in the downstream portion, and the configurations shown inFIG. 13Bmay be employed in the upstream portion.

FIG. 14shows a third modification example in the cross-section taken along the line E-E inFIG. 2. In the present example, the Z-axis length L1Fof the comb-tooth portion34-1is larger than the Z-axis length L3Bof the comb-tooth portion54-1. Also, the Z-axis length L3Fof the comb-tooth portion44-1is larger than the Z-axis length L1Bof the comb-tooth portion64-1. In the first flow channels70of the present example, the length LFof the overlap in the extending direction25between the comb-tooth portion34-1and the comb-tooth portion44-1is larger than the length LBof the overlap in the extending direction25between the comb-tooth portion54-1and the comb-tooth portion64-1. In this manner, the flow of the cooling water can be blocked to an appropriate degree by the coupling bars arranged in the upstream portion where the kinetic energy is higher than in the downstream portion, and the resistance provided by the coupling bars in the downstream portion against the flow of the cooling water can be made lower than in the upstream portion.

FIG. 15shows a fourth modification example in the cross-section taken along the line D-D inFIG. 2. In order to facilitate the understanding of the drawings,FIGS. 15 to 17do not show the through holes. In the present example, the spacing dFbetween the coupling bar30and the coupling bar40is smaller than the spacing dBbetween the coupling bar50and the coupling bar60. In this manner, the flow of the cooling water can be blocked to an appropriate degree by the coupling bars arranged in the upstream portion where the kinetic energy is higher than in the downstream portion, and the resistance provided by the coupling bars in the downstream portion against the flow of the cooling water can be made lower than in the upstream portion. Furthermore, the downstream coupling bars50and60can be assembled more easily since the spacing dBbetween the downstream coupling bars is larger than the spacing dFbetween the upstream coupling bars. This is also advantageous.

FIG. 16shows a fifth modification example in the cross-section taken along the line D-D inFIG. 2. In the second flow channels72of the present example, the protruding length L4Bof the comb-tooth portion64-2is larger than the protruding length L4Fof the comb-tooth portion44-2. For example, the protruding length L4Bof the comb-tooth portion64may be no less than 1.5 times and no more than 5 times, no less than twice and no more than 4 times, or no less than 2.5 times and no more than 3 times as large as the protruding length L4Fof the comb-tooth portion44-2. In this way, in the downstream portion, the flow of the cooling water can be directed toward the upper plate10. In the present example, the protruding length L2Fof the comb-tooth portion34-2is the same as the protruding length L2Bof the comb-tooth portion54-2. When compared with the case where the protruding lengths L4Band L4Fare the same, the pressure loss can be reduced in the present example while the improved cooling efficiency can be achieved in the downstream portion, where the cooling is more difficult than in the upstream portion.

FIG. 17shows a sixth modification example in the cross-section taken along the line D-D inFIG. 2. In the present example, the cooler100has a single downstream coupling bar. In this manner, the pressure loss can be reduced when compared with the exemplary case where the pair of the upper and lower coupling bars is provided in the downstream portion. Note that the cooler100of the present example does not have the coupling bar50and only has the coupling bar60. In this manner, the flow of the cooling water can be directed toward the upper plate10directly below the semiconductor chips90-4,90-5and90-6. Accordingly, the improved cooling efficiency can be achieved in the downstream portion, where the cooling is more difficult than in the upstream portion.

FIG. 18shows how the inlet16and the outlet18are positioned relative to the through holes in a semiconductor module210relating to a second embodiment. In the present example, the inlet16and the outlet18of the cooling water are positioned to overlap each other in the extending direction25. In this case, the cooling water more easily flows in the flow channels that are close to the inlet16or outlet18and less easily flows in the flow channels that are distant from the inlet16or outlet18.

Considering this, in the present example, the flow channel that is the closest to the inlet16or outlet18in the X-axis direction and that runs below the semiconductor chips90is configured as the second flow channel72-1, which has the small through holes75. On the other hand, the flow channels that are the most distant from the inlet16or outlet18in the X-axis direction and run below the semiconductor chips90are configured as the second flow channels72-2, which have the large through holes77. In this manner, the imbalance in the flow rate among the second flow channels72can be reduced. In addition, the present example has some configurations in common with the first embodiment, which can produce the same advantageous effects. Note that the cooling water may also flow in the X-axis direction while running through the flow channel extending from the inlet16to the outlet18. For example, in the vicinity of the side plate14-3, the flow of the cooling water W can branch in the +−X directions after the inlet16. In addition, for example, in the vicinity of the side plate14-4, the flow of the cooling water W in the +−X directions proceeds toward the outlet18.

FIG. 19shows how the inlet16and the outlet18are positioned relative to the through holes in a semiconductor module220relating to a third embodiment. In the present example, the plurality of semiconductor chips90are arranged differently than in the above-described example To be specific, two semiconductor chips90are arranged next to each other in the X-axis direction and three semiconductor chips90are arranged next to each other in the Y-axis direction. In total, six semiconductor chips90(=2×3) are arranged on the upper plate10. Note that the arrows W indicate the direction in which the cooling water W mainly flows.

The inlet16and the outlet18of the cooling water are both provided on the same side with respect to the plate-like fins20in the extending direction25. In the present example, the inlet16and the outlet18are both coupled to the side plate14-3while being spaced away from each other in the X-axis direction. In addition, the semiconductor module220of the present example includes a partitioning plate-like fin29between the inlet16and the outlet18. The partitioning plate-like fin29extends in the extending direction25from the side plate14-3but does not reach the side plate14-4. The partitioning plate-like fin29may be capable of blocking the path that may extend along the side plate14-3from the inlet16to the outlet18. In the present example, the cooling water can flow in a substantially U-shaped manner. To be more specific, the cooling water of the present example can enter through the inlet16formed in the side plate14-3, flow toward the side plate14-4, which faces the side plate14-3in the extending direction25, subsequently flow in the X-axis direction in the vicinity of the side plate14-4, and finally leave the side plate14-4and flow toward the outlet18formed in the side plate14-3.

The large through holes77may be positioned closer to the inlet16and the outlet18than the small through holes75are. In the present example, the large through holes77and the small through holes75are respectively arranged in the upstream and downstream portions in the second flow channel72that is the closest to the inlet16. On the other hand, the small through holes75and the large through holes77are respectively arranged in the upstream and downstream portions in the second flow channel72that is the closest to the outlet18. Since the cooling water vigorously flows in through the inlet16, the cooling water can still vigorously flow in the vicinity of the side plate14-4. Therefore, in the present example, the small through holes75are positioned in the vicinity of the side plate14-4, instead of the large through holes77. The present example has some configurations in common with the first embodiment, which can produce the same advantageous effects.