Power Conversion Device

Abstract

To provide a power converter that can be reduced in size and in price.SOLUTION: A power converter 1 comprises a circuit board 2, a bus bar 3, and a heat sink 4. On the heat sink 4 is provided a through hole 4a for fixing both of the circuit board 2 and the bus bar 3. The power converter 1 comprises: a heat radiation material 5 disposed between the circuit board 2 and the heat sink 3; and a conductive terminal block 6 fixed by soldering to the circuit board 2. A bolt 8 is fixed in the through hole 4a by a nut 9 in a state of the terminal block 6 being in contact with the bus bar 3, which forms a conduction path between the circuit board 2 and the bus bar 3 via the terminal block 6.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a power converter, and more particularly to an assembly structure for a power converter in which a bus bar is fastened to a circuit board that requires heat dissipation by a heat sink. [Background technology]

[0002] For example, in vehicles equipped with high-voltage batteries, a power conversion device is used to convert power to match the rated voltage of each electrical component, using the high-voltage power supplied from the high-voltage battery to drive electrical components that operate at a lower voltage.

[0003] A power conversion device uses various electronic components such as capacitors in addition to various circuit boards, such as a power conversion circuit and a control circuit that controls the power conversion circuit. The circuit boards, capacitors, and other electronic components are each connected to a bus bar, which is a metal plate for transmitting power. A power source such as a battery is also connected to the bus bar. When the power conversion circuit is operating, each component transmits power to another component via the bus bar.

[0004] Circuit boards and electronic components must be controlled so that their operating temperatures do not exceed their respective operating temperatures, and are mounted on heat sinks to improve heat dissipation. Meanwhile, power conversion devices are being required to be more compact, and it is becoming necessary to achieve both compensation for operating temperatures and miniaturization.

[0005] Patent Document 1 discloses a power conversion device with improved cooling efficiency. In the power conversion device of Patent Document 1, bus bars are soldered onto a circuit board assembly, and the circuit board assembly is fixed to a DC-DC converter case. The bus bars and circuit board are cooled by a coolant that flows through a coolant channel formed between the DC-DC converter device and the inverter device. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-099044 Summary of the Invention [Problem to be solved by the invention]

[0007] In conventional power conversion devices, the bus bars and circuit board are connected by soldering, and cooling is performed using a refrigerant. When a heat sink is used for heat dissipation, the heat sink and circuit board are screwed together, and then the circuit board and bus bars are screwed together. However, there is a demand for technology that can provide even smaller power conversion devices at a lower price. [Means for solving the problem]

[0008] The invention of claim 1 relates to a power converter. The power converter includes a circuit board, a bus bar, and a heat sink having through holes for fixing both the circuit board and the bus bar. The power converter further includes a heat dissipation material disposed between the board and the heat sink, a conductive terminal block soldered to the circuit board, and screw fastening means inserted into the terminal block to fix the circuit board and the bus bar to the through holes in the heat sink. The power converter of the present invention is characterized in that the terminal block and the bus bar are fixed to the through holes in a contacting state by the screw fastening means, thereby forming a conductive path between the circuit board and the bus bar via the terminal block.

[0009] In the power conversion device of the present invention, it is preferable that the screw fastening means is composed of a bolt and a nut, and the circuit board and bus bar are fixed to the heat sink by fastening the bolt that has passed through the bus bar and the terminal block with the nut inserted into the through hole of the heat sink.

[0010] In the power converter of the present invention, the through-hole of the heat sink is preferably covered with an insulating coating, and the heat sink and the terminal block, and the heat sink and the nut are preferably insulated from each other.

[0011] In the power conversion device of the present invention, the screw fastening means may be a screw and a second terminal block having a thread formed by tapping. In this case, with the second terminal block inserted into the through-hole of the heat sink, the circuit board and the bus bar are fixed to the heat sink by fastening the screw that has passed through the bus bar and the terminal block.

[0012] When the screw fastening means is a second terminal block that is tapped with a screw, it is preferable to provide a second heat dissipation material between the bus bar and the heat sink. [Effects of the Invention]

[0013] In the power conversion device according to the present invention, the heat sink has through holes for fastening both the circuit board and the bus bars, and the circuit board and the bus bars can be connected to the same through holes in the heat sink with a single screw fastening means. This configuration reduces the number of screw fastening means and the size of the circuit board. As a result, a more compact power conversion device can be provided at lower cost.

[0014] The manufacturing process for the power converter according to the present invention can eliminate the steps of forming the through holes in the heat sink and the screw fastening step compared to the conventional method, thereby further reducing the manufacturing cost. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a partial cross-sectional view of a power converter according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a partial cross-sectional view of a power converter according to a second embodiment of the present invention. [Figure 3] FIG. 3 is a partial cross-sectional view of a power converter according to a third embodiment of the present invention. [Figure 4] FIG. 4 is a partial cross-sectional view of a power converter according to a fourth embodiment of the present invention. [Figure 5]FIG. 5 is a partial cross-sectional view of a power converter according to a fifth embodiment of the present invention. [Figure 6] FIG. 6 is a partial cross-sectional view of a power converter according to a sixth embodiment of the present invention. [Figure 7] FIG. 7 is a partial cross-sectional view of a conventional power converter. [Figure 8] FIG. 8 is a partial cross-sectional view of a conventional power converter. [Figure 9] FIG. 9 is a partial cross-sectional view of a conventional power converter. DETAILED DESCRIPTION OF THE INVENTION

[0016] The most preferred embodiments of the power conversion device of the present invention will be listed below.

[0017] The screw fastening means for fastening both the circuit board and the bus bar to the through-hole at the same location on the heat sink is a bolt and nut, or a screw and a tapped terminal block.

[0018] A conductive terminal block (collar) forms a conductive path between the circuit board and the bus bar. Meanwhile, the heat sink is preferably insulated from both the terminal block and the screw fastening means by covering the through-hole with an insulating coating. Furthermore, it is more preferable to cover the lower end of the terminal block with an insulating coating. The most preferred material for the insulating coating is a fluororesin.

[0019] The most suitable heat dissipating material is a fluororesin. [Example]

[0020] Hereinafter, with reference to the drawings, a power conversion device embodying the present invention will be described with reference to Examples 1 to 6. Components having common configurations among the examples will be assigned the same reference numerals and redundant explanations will be omitted.

[0021] [Example 1] 1 shows a power converter 1 according to a first embodiment. The power converter 1 includes a circuit board 2, a bus bar 3, and a heat sink 4. The power converter 1 further includes a heat dissipation material 5 disposed between the circuit board 2 and the heat sink 4, and a conductive terminal block 6 fixed to the circuit board 2 by soldering.

[0022] The heat sink 4 is provided with a through hole 4a for fixing both the circuit board 2 and the bus bar 3. The inside of the through hole 4a is covered with an insulating coating 7a made of fluororesin.

[0023] The terminal block 6 in this embodiment has a cylindrical opening in the center and a "flange" formed at one end, and is a conductive member also known as a "flanged collar." The terminal block 6 is soldered to the circuit board 2 with the underside of the flange in contact with the upper surface of the circuit board 2 and the cylindrical portion connected to the flange penetrating the circuit board 2. The length of the cylindrical portion of the terminal block 6 is longer than the combined thickness of the circuit board 2 and the heat dissipation material 5, and when the power conversion device 1 is assembled, the lower end of the terminal block 6 reaches the through-hole 4a of the heat sink 4.

[0024] Bolts 8 and nuts 9 are used as fixing means for screwing and fixing both the circuit board 2 and the bus bar 3 to the heat sink 4. The bolts 8 have a length required to pass through the washers 10, the bus bar 3, and the terminal block 6. The nuts 9 have a diameter that allows them to be inserted into the through holes 4a from the underside of the heat sink 4.

[0025] The through hole 4a of the heat sink 4 of this embodiment has an upper portion formed with a diameter that allows insertion of the terminal block 6. The lower portion of the through hole 4a has a larger diameter than the upper portion, and a step is formed at the boundary between the upper and lower portions.

[0026] In the power conversion device 1 of this embodiment, a heat dissipation material 5 is placed on the upper surface of a heat sink 4, and a circuit board 2 is placed on the upper surface of that. The circuit board 2 is placed in a position where the opening of a soldered terminal block 6 is inserted into the through-hole 4a of the heat sink 4, and the cylindrical portion of the terminal block 6 passes through the heat dissipation material 5. Furthermore, a bus bar 3 is placed on the flange of the terminal block 6. The bus bar 3 has fixing holes formed therein, and the fixing holes are aligned with the opening of the terminal block 6.

[0027] In the process of assembling the power converter 1 of this embodiment, the bolt 8 is inserted into the through-hole 4a of the heat sink 4 after passing through the washer 10, the fixing hole of the bus bar 3, and the opening of the terminal block 6. To secure the bolt, a nut 9 with a diameter larger than that of the upper part of the through-hole 4a is inserted from the lower part of the through-hole 4a. The nut 9 comes into contact with the lower end of the heat sink 4 and the terminal block 6 at the step between the upper and lower parts of the through-hole 4a and stops, thereby fixing the bolt 8 protruding from the terminal block 6. At this time, the heat sink 4 and the nut 9 are insulated from each other by the insulating coating 7a on the through-hole 4a and the insulating coating 7b on the lower end of the terminal block 6. The heat sink 4 and the terminal block 6 are also insulated from each other.

[0028] By fastening the terminal block 6 and the bus bar 3 with bolts 8 and nuts 9, the terminal block 6 and the bus bar 3 are pressed together, and the bus bar 3 and the circuit board 2 soldered to the terminal block 6 are fixed to the heat sink 4. Because the terminal block 6 is conductive, a conductive path is formed between the circuit board 2 and the bus bar 3. At this time, the heat dissipation material 5 is deformed by being pressed by the bolts 8 and nuts 9, as if it is being crushed between the circuit board 2 and the heat sink 4, and heat is efficiently conducted from the circuit board 2 to the heat sink 4.

[0029] In the power conversion device 1 of this embodiment, by fixing both the circuit board 2 and the bus bar 3 to the same through hole 4a in the heat sink 4, it is possible to reduce the number of bolts 8 and nuts 9 required to fix the circuit board 2 and the bus bar 3, and to reduce the number of through holes in the heat sink 4. Furthermore, the power conversion device 1 as a whole can be made smaller, and at the same time, the number of manufacturing steps can be reduced, enabling manufacturing at lower cost.

[0030] [Example 2] 2 shows a power converter 11 according to a second embodiment. The differences from the first embodiment are the length of the cylindrical portion of the terminal block 16 and the shape of the through-hole 14a of the heat sink 4.

[0031] The terminal block 16 of this embodiment is formed so that the length of the cylindrical portion is equal to the combined dimension of the thickness of the circuit board 2 and the thickness of the heat dissipation material 5 after pressure deformation during assembly. When assembling the power conversion device 11, the lower end of the terminal block 16 is abutted against the upper surface of the heat sink 4 and fixed thereto.

[0032] In this embodiment, the through hole 14a in the heat sink 4 has a diameter large enough to insert the bolt 8 into the upper portion. The lower portion of the through hole 4a has a larger diameter than the upper portion, forming a step at the boundary between the upper and lower portions. The diameter of the nut 9 used to screw the bolt 8 is larger than the diameter of the upper portion of the through hole 14a and smaller than the diameter of the lower portion of the through hole 14a. The nut 9 inserted into the through hole 14a comes into contact with the heat sink 4 at the step at the boundary between the upper and lower portions of the through hole 14a, thereby fixing the bolt 8 protruding from the terminal block 16. By screwing the bolt 8 and the nut 9 together, the terminal block 16 and the bus bar 3 are pressed into contact with each other. The bus bar 3 and the circuit board 2 soldered to the terminal block 16 are fixed to the heat sink 4, forming a conductive path between the circuit board 2 and the bus bar 3.

[0033] [Example 3] FIG. 3 shows a power converter 21 according to a third embodiment. In the power converter 21 of the present embodiment, a circuit board 22a is disposed below a heat sink 4, and a circuit board 22b is disposed above the heat sink 4. Heat dissipation materials 5 are disposed between the heat sink 4 and each of the circuit boards 22a and 22b. A conductive terminal block 26 is soldered to the circuit board 22a. A conductive terminal block 27 is soldered to the circuit board 22b.

[0034] The through-hole of the heat sink 4 of this embodiment is a cylindrical opening having a uniform diameter. The inside of the through-hole is covered with an insulating coating 7a.

[0035] In this embodiment, the terminal block 27 has a blind hole with a thread formed by tapping. The terminal blocks 26 and 27 are soldered to the circuit boards 22a and 22b so as to penetrate the circuit boards 22a and 22b, respectively. When the power converter 21 is assembled, the cylindrical portions of the terminal blocks 26 and 27 are inserted into the through-hole 4a of the heat sink 4, and the ends of the terminal blocks 26 and 27 come into contact with each other, forming a conductive path.

[0036] In this embodiment, bolts 28 and terminal blocks 26 and 27 are used as fixing means for screwing and fixing all of circuit boards 22a, 22b and bus bar 3 to heat sink 4. Bolt 28 has a length necessary to pass through washer 10, bus bar 3, and terminal block 26 and reach the blind hole of terminal block 27.

[0037] In the power converter 21 of this embodiment, the bus bar 3 is disposed below the flange of the terminal block 26. The bus bar 3 has a fixing hole formed therein, and the fixing hole is aligned with the opening of the terminal block 26.

[0038] In the process of assembling the power converter 21 of this embodiment, the bolt 28 passes through the washer 10, the fixing hole of the bus bar 3, and the through-hole of the terminal block 26, and is screwed into the blind hole of the terminal block 27. When the bolt 28 and the terminal blocks 26, 27 are screwed together, the bus bar 3 and the terminal block 26 are pressed into contact, and the bus bar and the circuit board are electrically connected. In addition, the heat dissipation material 5 is deformed as if it is crushed between the circuit board 2 and the heat sink 4, thereby efficiently conducting heat from the circuit board 2 to the heat sink 4.

[0039] In the power converter 21 of this embodiment, the two circuit boards 22a, 22b arranged on both sides of the heat sink 4 are fixed to the bus bar 3 at the same location, thereby reducing the number of bolts required for fixing. As a result, the power converter 21 as a whole can be made smaller, and at the same time, the number of manufacturing steps can be reduced, enabling manufacturing at lower cost.

[0040] [Example 4] 4 shows a power converter 31 according to a fourth embodiment. In the power converter 31 of this embodiment, a circuit board 2 is disposed above a heat sink 4, and a bus bar 3 is disposed below the heat sink 4. A heat dissipation material 5 is disposed between the circuit board 2 and the heat sink 4, and a heat dissipation material 5 is also disposed between the circuit board 2 and the bus bar 3. A conductive terminal block 36 is soldered to the circuit board 2.

[0041] The through-hole of the heat sink 4 of this embodiment is a cylindrical opening having a uniform diameter. The inside of the through-hole is covered with an insulating coating 7a.

[0042] The terminal block 36 in this embodiment has a blind hole with a thread formed by tapping. The cylindrical portion of the terminal block 36 has two diameter stages, a large diameter section and a small diameter section, forming a step on the outer surface. The large diameter section has a diameter larger than the through-hole of the heat sink 4, and the small diameter section has a diameter that allows it to be inserted into the through-hole of the heat sink. The step between the large diameter section and the small diameter section is covered with an insulating coating 7b.

[0043] The length of the large diameter portion of the terminal block 36 is set to be equal to the combined dimension of the thickness of the circuit board 2 and the thickness of the heat dissipation material 5 after it has been pressed and deformed by assembly. The length of the small diameter portion is set to be equal to the combined dimension of the thickness of the heat sink 4 and the thickness of the heat dissipation material 5 after it has been pressed and deformed by assembly. When assembling the power conversion device 31, the step at the boundary between the large diameter portion and the small diameter portion of the terminal block 16 is positioned by abutting against the upper surface of the heat sink 4.

[0044] In this embodiment, bolts 8 and terminal blocks 36 are used as fixing means for screwing and fixing the circuit board 2 and bus bar 3 to the heat sink 4. The bolts 8 have a length required to pass through washers 10 and fixing holes in the bus bar 3 and reach blind holes in the terminal blocks 36.

[0045] In the process of assembling the power converter 31 of this embodiment, the bolt 8 passes through the washer 10 and the fixing hole of the bus bar 3, and is screwed into the blind hole of the terminal block 36. Upon completion of assembly, the distance between the circuit board 2 and the heat sink 4 is accurately determined by the length of the large diameter portion of the terminal block 36. In addition, the step between the large diameter portion and the small diameter portion of the terminal block 36 is covered with the insulating coating 7b, thereby ensuring insulation between the heat sink and the collar.

[0046] [Example 5] FIG. 5 shows a power converter 51 according to a fifth embodiment. In the power converter 51 of this embodiment, a circuit board 2 is disposed above a heat sink 4, and a bus bar 3 is disposed below the heat sink 4. A heat dissipation material 5 is disposed between the circuit board 2 and the heat sink 4, and a separate heat dissipation material 5 is also disposed between the circuit board 2 and the bus bar 3. A conductive terminal block 56 is soldered to the circuit board 2. The through hole of the heat sink 4 of this embodiment is a cylindrical opening with a uniform diameter. The inside of the through hole is covered with an insulating coating 7a.

[0047] The terminal block 56 in this embodiment has a blind hole with a thread formed by tapping. The length of the terminal block 56 is set to be equal to the combined dimension of the thickness of the circuit board 2, the bus bar 3, and the heat sink 4, and the thickness of the two sheets of heat dissipation material 5 after pressure deformation during assembly. When the power conversion device 51 is assembled, the end of the terminal block 56 reaches the boundary surface between the heat dissipation material 5 and the bus bar 3.

[0048] In this embodiment, bolts 8 and terminal blocks 56 are used as fixing means for screwing and fixing the circuit board 2 and bus bars 3 to the heat sink 4. The bolts 8 have a length required to pass through washers 10 and fixing holes in the bus bars 3 and to be screwed into blind holes in the terminal blocks 56.

[0049] In the process of assembling the power converter 51 of this embodiment, the bolts 8 pass through the washers 10 and the fixing holes of the bus bars 3 and are screwed into the blind holes of the terminal blocks 56. When the assembly is complete, the bus bars 3 and the terminal blocks 56 are pressed together to form a conductive path. The bus bars 3 and the circuit board 2 are electrically connected via the terminal blocks 56.

[0050] [Example 6] FIG. 6 shows a power converter 61 according to a sixth embodiment. In the power converter 61 of this embodiment, a circuit board 22a is disposed below the heat sink 4, and a circuit board 22b is disposed above the heat sink 4. Heat dissipation materials 5 are disposed between the heat sink 4 and each of the circuit boards 22a and 22b. A conductive terminal block 66 is soldered to the circuit board 22a. A conductive terminal block 67 is soldered to the circuit board 22b. The terminal block 66 has a through hole with a thread formed by tapping. The terminal block 67 has a blind hole with a thread formed by tapping.

[0051] The cylindrical portion of the terminal block 67 in this embodiment is formed with two diameter stages, a large diameter section and a small diameter section, and a step is formed on the outer surface. The large diameter section has a diameter larger than the through-hole of the heat sink 4, and the small diameter section has a diameter that allows it to be inserted into the through-hole of the heat sink. The step between the large diameter section and the small diameter section is covered with an insulating coating 7b.

[0052] The length of the cylindrical portion of the terminal block 66 is longer than the combined dimension of the thickness of the circuit board 22a and the thickness of the heat dissipation material 5 after press-deformation due to assembly, and is set so that it protrudes a predetermined length into the through-hole 4a of the heat sink 4 during assembly. The length of the large-diameter portion of the terminal block 67 is formed to be equal to the combined dimension of the thickness of the circuit board 22b and the thickness of the heat dissipation material 5 after press-deformation due to assembly. The length of the small-diameter portion of the terminal block 67 is shorter than the thickness of the heat sink 4, and the combined length of the terminal block 66 protruding into the through-hole 4a and the length of the small-diameter portion of the terminal block 67 matches the thickness of the heat sink 4. With this configuration, when the power converter 61 is assembled, the terminal block 66 and the terminal block 67 come into contact within the through-hole 4a of the heat sink 4, forming a conductive path.

[0053] In this embodiment, bolts 28 and terminal blocks 66, 67 are used as fixing means for screwing and fixing all of circuit boards 22a, 22b and bus bar 3 to heat sink 4. Bolt 28 has a length necessary to pass through washer 10, bus bar 3, and terminal block 66 and reach the blind hole of terminal block 67. In the process of assembling power converter 61 of this embodiment, bolt 28 passes through washer 10, the fixing hole of bus bar 3, and the through hole of terminal block 66, and is screwed into the blind hole of terminal block 67. By screwing bolt 28 and terminal blocks 66, 67, bus bar 3 and terminal blocks 66, 67 are pressed into contact, and bus bar 3 and circuit boards 22a, 22b are electrically connected.

[0054] [Conventional example 1] FIG. 7 shows a power converter 101 according to a first conventional example. In power converter 101, circuit board 2 and bus bar 3 are fixed to heat sink 104 in separate fixing holes, and therefore dedicated fixing screws 108 for fixing circuit board 2 to heat sink 104 and dedicated fixing screws 109 for fixing bus bar 3 to heat sink 104 are used. A dedicated terminal block 106 is disposed between bus bar 3 and heat sink 104. In conventional power converter 101, dedicated screws are used to fix circuit board 2 and bus bar 3, and because circuit board 2 and bus bar 3 are fixed in separate locations, heat sink 104 requires multiple blind holes for fixation, and each blind hole requires threading or the embedding of dedicated pedestals 107.

[0055] [Conventional example 2] FIG. 8 shows a power converter 111 of Conventional Example 2. In the power converter 111, a circuit board 2 is fixed to each side of a heat sink 114. Bus bars 113a and 113b are arranged to provide conductive paths on both sides of the heat sink 114. The circuit board 2 and the bus bars 113a and 113b are fixed to separate fixing holes in the heat sink 114. The heat sink 114 requires a large number of blind holes for fixing, and each blind hole requires threading or embedding a dedicated base 107.

[0056] [Conventional example 3] 9 shows a power converter 121 of Conventional Example 3. In power converter 121, some circuit boards 2 and bus bars 123a are fixed with screws to the same fixing holes in heat sink 124. However, in other parts, circuit boards 2 and bus bars 3 are fixed to different fixing holes. In addition, a conductive path is required to connect the top and bottom of heat sink 124, and a complex arrangement of bus bars 123a and 123b is required.

[0057] As described above with reference to the embodiments, the power converter of the present invention has a configuration in which the circuit board and the bus bars are fixed to the heat sink by screws in the same through-holes. This configuration reduces the number of screw fastening means used compared to conventional power converters, thereby enabling the power converter to be made smaller and more affordable. [Industrial Applicability]

[0058] The power conversion device according to the present invention is suitably mounted on various vehicles as well as any industrial equipment. [Explanation of symbols]

[0059] 1,11,21,31,51,61,101,111,121 Power conversion device 2,22a,22b circuit board 3,123a,123b busbar 4,104,114,124 Heatsink 4a through hole 5 Heat dissipation material 6,16,26,27,36,56,66,67,106 Terminal block 7a, 7b Insulation coating 8 volts 9 Nuts 10 Washers

Claims

1. A power conversion device including a circuit board, a bus bar, and a heat sink having a through hole for fixing both the circuit board and the bus bar, The power conversion device further comprises: a heat dissipation material disposed between the circuit board and the heat sink; a conductive terminal block soldered to the circuit board; a screw fastening means inserted into the terminal block to fasten the circuit board and the bus bar to the through-hole of the heat sink; It is equipped with the screw fastening means is fixed to the through hole in a state in which the terminal block and the bus bar are in contact with each other, thereby forming a conductive path between the circuit board and the bus bar via the terminal block; A power conversion device characterized in that the through hole of the heat sink is covered with an insulating coating, and the heat sink and the terminal block, and the heat sink and the screw fastening means are insulated from each other.

2. The screw fastening means is composed of a bolt and a nut, 2. The power conversion device according to claim 1, wherein the circuit board and the bus bar are fixed to the heat sink by fastening the bolt that has passed through the bus bar and the terminal block with the nut inserted into the through hole of the heat sink.

3. the screw fastening means is a screw and a second terminal block having a thread formed by tapping, 2. The power conversion device according to claim 1, wherein the circuit board and the bus bar are fixed to the heat sink by fastening screws that pass through the bus bar and the terminal block with the second terminal block inserted into a through hole of the heat sink.

4. 4. The power conversion device according to claim 3, further comprising a second heat dissipation material between the bus bar and the heat sink.

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