Printed circuit board assembly

Abstract

The invention relates to a printed circuit board assembly, comprising: a first printed circuit board (1) having an upper side (11) and a lower side (12), at least one electrical component (3) to be cooled arranged on the lower side (12) of the first printed circuit board (1), and a heat sink (4), arranged underneath the first printed circuit board (1), which is designed to cool the at least one component (3) to be cooled. A hold-down device (5), connected to the first printed circuit board (1), is provided, which is designed to exert pressure on the upper side (11) of the first printed circuit board (1). The hold-down device (5) has fastening means (53) for fastening a second printed circuit board (2) that extends parallel to the first printed circuit board (1), wherein the hold-down device (5) is arranged between the first printed circuit board (1) and the second printed circuit board (2).

Description

[0001] PCB layout

[0002] Description

[0003] The invention relates to a printed circuit board arrangement according to the preamble of patent claim 1.

[0004] It is known to press printed circuit board-based power electronics assemblies onto a heat sink for cooling by means of screw connections, whereby the components to be cooled are typically designed as surface-mounted (SMD) components (SMD = "surface-mounted device") or through-hole (THT = "through-hole technology") and are located on the underside of the printed circuit board.

[0005] The goal is to minimize any gap between the component to be cooled and the heat sink, which would otherwise impair the thermal connection between the electrical component and the heat sink. If multiple components need to be cooled, gaps with different dimensions to the heat sink may exist, which must be compensated for.

[0006] A good thermal connection is required to press the components to be cooled against the heat sink. A certain amount of contact pressure is required to ensure full-surface contact between the component to be cooled and the heat sink, particularly to compensate for unevenness and tilting. Accordingly, it is advisable to implement numerous screw connections that press the components to be cooled against the heat sink. On the other hand, a large number of screw connections results in numerous holes in the circuit boards, which is complex to manufacture and limits the options for routing the conductor tracks and arranging the components.

[0007] The present invention is based on the object of providing a printed circuit board arrangement which enables a thermal connection of a component to be cooled to a heat sink in an effective manner and at the same time enables an effective construction of the printed circuit board arrangement.

[0008] This object is achieved by a printed circuit board assembly having the features of claim 1. Embodiments of the invention are specified in the dependent claims.

[0009] The invention then considers a printed circuit board arrangement comprising a first printed circuit board with a top side and a bottom side, at least one electrical component to be cooled arranged on the bottom side of the first printed circuit board, and a heat sink arranged below the first printed circuit board, wherein the heat sink is designed to cool the at least one component to be cooled.

[0010] In this case, a hold-down device connected to the first circuit board is provided, which is designed to exert a pressure on the upper side of the first circuit board, wherein the hold-down device has fastening means for fastening a second circuit board which extends parallel to the first circuit board, and wherein the hold-down device is arranged between the first circuit board and the second circuit board.

[0011] The inventive solution is based on the idea of ​​using a hold-down device which, by exerting pressure on the top side of the first circuit board, presses the first circuit board or the electrical components arranged on the underside of the first circuit board against the heat sink. The use of a hold-down device, in particular, provides additional rigidity, since the hold-down device prevents or reduces upward warping of the circuit board when the electrical components arranged on the underside of the circuit board are pressed against the heat sink. In this way, uniform pressure is provided on the circuit board, at least in the area in which the components to be cooled are arranged, so that the components to be cooled also exert uniform contact pressure on the heat sink.This ensures a good thermal connection between the components to be cooled and the heat sink, thus ensuring effective cooling. The additional rigidity also makes it possible to reduce the number of screw connections required and / or to provide them only in peripheral areas, thus reducing manufacturing effort. At the same time, the reduced number of holes in the circuit board increases design freedom in the arrangement of the conductor tracks and components.

[0012] A further advantage associated with the invention is that the integration of fastening means for attaching a second circuit board into the hold-down device provides fastening structures that allow the second circuit board to be installed at the desired distance within the circuit board assembly. This eliminates the need for additional measures, such as the attachment of fastening points and / or spacer sleeves to the first circuit board to define the desired distance between the two circuit boards.

[0013] Finally, the present invention also allows electrical components arranged on the underside of the second circuit board to be cooled. Such electrical components cannot be cooled by the heat sink. If the hold-down device is made of metal, the hold-down device can take on the function of absorbing heat from electrical components of the second circuit board and thermally spreading it across the surface within the plane of the hold-down device. The hold-down device therefore serves as a heat sink for components of the second circuit board that are to be cooled. The second circuit board typically contains components that have lower power dissipation than the components of the first circuit board cooled by the heat sink, so that cooling by the hold-down device is sufficient.

[0014] It should be noted that, for the purposes of the present invention, the side of the circuit board on which an electrical component to be cooled is arranged and which borders a heat sink is always referred to as the underside of the circuit board. Typically, this is the side of the circuit board closer to the ground in terms of the vertical plumb line. Of course, the circuit board and heat sink can also be arranged upside down or vertically, and accordingly point upwards or to the side, in which case, for the purposes of the present invention, the underside of the circuit board also borders the heat sink.

[0015] One embodiment of the invention provides that the hold-down device is arranged at a distance from the first circuit board and is connected to the first circuit board only at specific points (i.e., in a local area). The hold-down device has projections on its underside that extend toward the top side of the first circuit board, bear against it, and exert pressure on it. The projections extending toward the top side of the first circuit board ensure that uniform pressure is exerted on the top side of the first circuit board, preventing it from locally deforming or bulging.

[0016] In particular, it is provided that the projections are formed in those areas of the hold-down device that are adjacent to areas of the circuit board in which the first circuit board has electrical components to be cooled, which are pressed against the heat sink. This is because the risk of the circuit board bulging is particularly high in such areas.

[0017] A further embodiment provides for a thermally conductive material to be arranged between the retainer and the first circuit board. This allows the retainer to also be used to cool electrical components located on the top side of the first circuit board.

[0018] A thermally conductive material within the meaning of the present invention is, for example, a thermally conductive paste or a thermally conductive mat. Such a thermally conductive material is also referred to as a thermal interface material (TIM). Thermally conductive materials are used to thermally bridge a gap between various components, for example, an electrical component to be cooled and the surface of a heat sink.

[0019] In a further embodiment, the hold-down device can be arranged at a distance from the second circuit board and connected to the second circuit board only at specific points. The hold-down device forms projections on its upper side that extend toward the underside of the second circuit board and rest against it. This prevents warping of the second circuit board and ensures that the second circuit board rests evenly against the hold-down device.

[0020] Furthermore, it can be provided that a thermally conductive material is arranged between the hold-down device and the second circuit board. This further improves or effectively provides the described effect of the hold-down device acting as a heat sink for electrical components connected to the second circuit board. The thermally conductive material is, for example, a thermally conductive paste or a thermally conductive mat. In a further embodiment, it is provided that the fastening means of the hold-down device, which serve to fasten the second circuit board, comprise bores in the form of threaded bores or simple bores. Threaded bores serve to accommodate fastening screws via which the second circuit board is connected to the hold-down device.Simple holes (without thread) are used to pass fastening screws through the hold-down device, whereby such screws are then screwed to a housing structure, for example.

[0021] In this case, it can be provided that the threaded holes are formed at least partially in the projections formed on the upper side of the hold-down device. Furthermore, it can be provided that the holes are formed in spacer sleeves of the hold-down device, which extend both in the direction of the first circuit board and in the direction of the second circuit board and define a distance between the hold-down device and the two circuit boards. In this embodiment, the spacer sleeves and the holes formed therein serve to accommodate threaded screws that extend into a housing structure.

[0022] A further embodiment of the invention provides that the circuit board is attached to a housing structure that forms the heat sink or accommodates the heat sink. In the second case, for example, the housing structure forms a cavity, and the heat sink is arranged in the cavity of the housing structure.

[0023] A further embodiment provides first fastening screws that extend from the top of the second circuit board through the retainer and through the first circuit board into the housing structure, connecting the second circuit board, the retainer, and the first circuit board to the housing structure. The first fastening screws are thus screwed into the housing structure, connecting the second circuit board, the retainer, and the first circuit board.

[0024] In this case, it can be provided that the first fastening screws are arranged only in the edge region of the first circuit board. Furthermore, it can be provided that the first fastening screws extend through the fastening means of the hold-down device, which are designed as holes.

[0025] Alternatively or in addition to the first fastening screws, a further embodiment provides second fastening screws that extend from the top of the retainer through the first circuit board into the heat sink. The second fastening screws are thus screwed into the heat sink and connect the retainer and the first circuit board.

[0026] Alternatively or in addition to the first and / or second fastening screws, a further embodiment provides third fastening screws that extend from the top side of the second circuit board into the hold-down device and are screwed to the hold-down device via threaded holes. The threaded holes form the fastening means for securing the second circuit board. The third fastening screws are thus screwed to the hold-down device and connect the second circuit board to the hold-down device.

[0027] The hold-down device is designed, for example, as a rigid plate or rigid frame of a defined height and has greater rigidity than the first and second circuit boards. The aforementioned projections protrude upwards and downwards from the hold-down device and define its distance from the two circuit boards.

[0028] In some embodiments, the retainer is made of a metal or a metal alloy, for example, aluminum or an aluminum alloy. This is particularly the case when the retainer serves as a heat sink for electrical components connected to the second circuit board. Another embodiment provides for the retainer to be designed as a plastic-metal hybrid. For example, a metal core is provided that is overmolded with a plastic. This hybrid design can avoid insulation problems.

[0029] In further embodiments, a ceramic material is provided as the material for the retainer. A ceramic material has the advantage of high electrical insulation properties. Another advantage is greater rigidity compared to polymers and metals. However, thermal properties may be inferior to metals.

[0030] A further embodiment provides that the at least one electrical component to be cooled is thermally coupled to the heat sink via a thermally conductive material. The thermally conductive material thermally bridges a gap between the underside of the electrical component to be cooled and the surface of the heat sink. Such gaps arise, for example, from tilting during assembly. In principle, however, it is also possible to press the electrical component to be cooled directly onto the heat sink. The present invention is fundamentally suitable for cooling any electrical components that are connected to a printed circuit board. The electrical components can be assemblies such as so-called prepackage modules with integrated electrical components and SMD contacts or THT contacts, as well as individual electrical components.

[0031] Embodiments provide that the electrical components to be cooled are power electronics components or assemblies, in particular electrical components that interact to control and operate an electric motor. For example, the at least one electrical component to be cooled is an element of an inverter for an electric motor.

[0032] The heat sink used can, in principle, be designed in any way. Typically, the heat sink includes cooling fins. The heat sink can be either actively cooled or passively cooled.

[0033] The invention is explained in more detail below with reference to the figures of the drawing using several exemplary embodiments. They show:

[0034] Figure 1 shows an embodiment of a printed circuit board arrangement comprising two printed circuit boards and a hold-down device, wherein the hold-down device presses down one printed circuit board and has fastening means for fastening the other printed circuit board;

[0035] Figure 2 shows a circuit board arrangement according to Figure 1, wherein additional heat-conducting materials are arranged between the hold-down device and the two circuit boards.

[0036] Figure 1 shows an embodiment of a printed circuit board assembly according to the present invention. The printed circuit board assembly comprises a first printed circuit board 1 and a second printed circuit board 2, which are arranged spaced apart from one another and run parallel. Both printed circuit boards 1, 2 have a top side 11, 21 and a bottom side 12, 22.

[0037] The first circuit board 1 has one or more electrical components 3 on its underside 12 that are to be cooled. Two such components 3 are shown in Figure 2, although this is to be understood merely as an example. For example, it can be provided that a plurality of electrical components 3 are arranged in two or more rows on the underside 12 of the first circuit board 1. The electrical components 3 are, for example, power electronics components, for example, elements of an inverter. The electronic components 3 can be designed as prepackage modules.

[0038] In one embodiment, the electrical components 3 are power semiconductors of an inverter formed by the electronic components 3 and other components arranged on the circuit board 1. Such additional components are only partially shown in Figure 1. The additional components include, for example, capacitors 9, which are arranged on the top side 11 of the circuit board 1. The inverter implemented on the circuit board 1 receives a direct voltage on the input side (schematically represented by arrow A) and outputs an alternating voltage on the output side (schematically represented by case B).

[0039] The electrical components 3 are connected to the circuit board 1, for example, via surface mounting, with the components 3 being SMD components. However, this is merely an example.

[0040] The electrical components 3 to be cooled are cooled by a heat sink 4. For this purpose, they are pressed against the heat sink 4 on their underside with pressure, which establishes full-surface contact with the heat sink 4. The heat sink 4 can have numerous designs. For example, it consists of a metal such as aluminum or an aluminum alloy and has cooling surfaces 45. The heat sink 3 is, for example, an active heat sink that is actively cooled by a fan (not shown) or by means of a liquid cooling system (not shown). Alternatively, the heat sink 4 is designed as a passive heat sink.

[0041] The heat sink 4 is arranged in a cavity 71 of a housing structure 7, which is, for example, a motor housing of an electric motor. In alternative embodiments, the housing structure 7 may form the heat sink, with no separate heat sink 4 being provided. In this case, the electrical components 3 to be cooled are pressed against a surface of the housing structure 7.

[0042] The respective electrical component 3 is connected to the heat sink 4 via a thermally conductive material 61. The thermally conductive material 61 is formed, for example, by a thermally conductive paste or a thermally conductive mat and thermally couples the electrical component 3 to the heat sink 4. In doing so, it bridges a gap that, without such a thermally conductive material 61, can extend between the underside of the electrical component 3 and the surface of the heat sink 4.

[0043] Extending between the first circuit board 1 and the second circuit board 2 is a hold-down device 5, which has a top side 51 and a bottom side 52 and is formed by a flat structure. The hold-down device 5 is made of a metal or a metal alloy, such as aluminum or an aluminum alloy, and is more rigid than the circuit boards 1, 2. It is designed as a plate with a defined height or thickness. The hold-down device 5 fulfills two functions. Firstly, it exerts pressure on the top side 11 of the first circuit board 1. Secondly, it serves to secure the second circuit board 2.

[0044] To exert pressure on the top side 11 of the printed circuit board 1, the hold-down device 5 comprises projections 54 on its underside 52, which protrude toward the first printed circuit board 1 and bear against it. Due to the increased rigidity of the hold-down device 5, it prevents warping of the printed circuit board 11, which can occur when the printed circuit board 1 with the components 3 to be cooled is pressed against the heat sink 4. A homogeneous pressure is provided, with which the electrical components 3 are pressed against the heat sink 4.

[0045] It is provided that the projections 54 are formed in the hold-down device 5 in such a way that their position corresponds to the position of an electrical component 3 to be cooled, so that a uniform pressure of an electrical component 3 against the heat sink 4 is ensured via the projections 54.

[0046] To provide for fastening the second circuit board 2 to the hold-down device 5, the hold-down device 5 comprises fastening means. These are at least partially formed by threaded holes. Thus, the hold-down device 5 comprises threaded holes 53, which serve to receive fastening screws 83 extending from the top side 21 of the second circuit board 2 into the hold-down device 5. The threaded holes 53 are formed, for example, in projections 55, which extend from the top side 51 of the hold-down device 5 toward the second circuit board 2 and bear against its underside 22. Furthermore, the projections 55 precisely position and define the distance between the second circuit board 2 and the hold-down device 5.

[0047] The hold-down device 5 further forms spacer sleeves 56, in which an upwardly projecting projection and a downwardly projecting projection merge directly into one another and have a common bore 53. These bores 53, which can be designed as simple bores or as threaded bores, serve to accommodate further fastening screws 81, which extend from the top side 21 of the second circuit board 2 through the hold-down device 5 (namely the spacer sleeve 56) and the first circuit board 1 into the housing structure 7 and are screwed therein. The two circuit boards 1, 2 and the hold-down device 5 are fastened to the housing structure 7 via the fastening screws 81. The fastening screws 81 are arranged only in the edge region of the circuit boards 1, 2 and the hold-down device 5.

[0048] As shown in Figure 1, the circuit board assembly further comprises fastening screws 82, which extend from the top side 51 of the hold-down device 5 through the first circuit board 1 into the heat sink 4 and are screwed therein. The fastening screws 82 provide the compressive force with which the electrical components 3 to be cooled are pressed against the heat sink 4. Since this function is also provided by the hold-down device 5 and its projections 54, it is possible to reduce the number of fastening screws 82 or even to dispense with them entirely. This has the advantage, among other things, that fewer drill holes need to be formed in the first circuit board 1, so that there are fewer restrictions on the placement of components on the circuit board 1 and the routing of the conductor tracks.

[0049] Furthermore, fastening screws 84 are provided which screw the heat sink 4 to the housing structure 7.

[0050] The respective fastening screws 81-84, for example, are designed as metal screws.

[0051] Figure 2 shows an embodiment of a printed circuit board assembly whose structure corresponds to the printed circuit board assembly in Figure 1, so that reference is made to the relevant explanations. In Figure 2, two additional thermally conductive materials 62, 63 are provided, which extend between the hold-down device 5 and the first printed circuit board 1 and between the hold-down device 5 and the second printed circuit board 2, respectively. The use of such thermally conductive materials 62, 63 means that the metallic hold-down device 5 can act as an additional heat sink. This applies in particular to electrical components arranged on the second printed circuit board 2 (not separately shown) and which require less cooling than the electrical components 3, which are cooled by the heat sink 4. This also applies to electrical components arranged on the top side of the first printed circuit board 1 (not separately shown).

[0052] It should be noted that the projections 54 shown in Figure 1, which extend toward the first circuit board 1, are not visible in Figure 2 due to the depiction of the heat-conducting material 62, but are also present. The same applies to the upwardly projecting projections 55, which are only partially shown in Figure 2.

[0053] It should also be noted that the circuit boards 1, 2 and their components are shown only schematically in Figure 1 and only insofar as they are relevant to the present invention. In particular, the circuit boards 1, 2 may have additional components not shown (on the top and / or bottom). The structure and contacting of the circuit boards are also not shown separately. The circuit boards 1, 2 may generally consist of a plurality of circuit board layers.

[0054] It is understood that the invention is not limited to the embodiments described above, and various modifications and improvements may be made without departing from the concepts described herein. For example, the circuit board assembly may include additional circuit boards and components mounted thereon.

[0055] It is further noted that any of the described features may be used separately or in combination with any other features, provided they are not mutually exclusive. The disclosure extends to and encompasses all combinations and subcombinations of one or more features described herein. Where ranges are defined, these include all values ​​within these ranges, as well as all subranges that fall within a range.

Claims

Patent claims 1. Printed circuit board arrangement comprising: a first printed circuit board (1) with a top (11) and a bottom (12), at least one electrical component (3) to be cooled arranged on the bottom (12) of the first printed circuit board (1), a heat sink (4) arranged below the first printed circuit board (1) and configured to cool the at least one electrical component (3), characterized by a retainer (5) connected to the first printed circuit board (1) and configured to exert pressure on the top (11) of the first printed circuit board (1), wherein the retainer (5) has fastening means (53) for fastening a second printed circuit board (2) extending parallel to the first printed circuit board (1), and wherein the retainer (5) is arranged between the first printed circuit board (1) and the second printed circuit board (2).

2. Printed circuit board arrangement according to claim 1, characterized in that the retainer (5) is arranged at a distance from the first printed circuit board (1) and is only connected to the first printed circuit board (1) at points, wherein the retainer (5) forms projections (54) on its underside (52) which project towards the top (11) of the first printed circuit board (1) and bear against it.

3. Printed circuit board arrangement according to claim 2, characterized in that the projections (54) are formed in such areas of the retainer (5) which are adjacent to areas of the first printed circuit board (1) in which the first printed circuit board (1) has electrical components (3) to be cooled which are pressed against the heat sink (4).

4. Printed circuit board arrangement according to one of the preceding claims, characterized in that a thermal conductivity material (62) is arranged between the retainer (5) and the first printed circuit board (1).

5. Printed circuit board arrangement according to one of the preceding claims, characterized in that the hold-down device (5) is spaced apart from the second printed circuit board (2) arranged and connected only at points to the second circuit board (2), wherein the retainer (5) forms projections (55) on its upper side (51) which extend towards the underside (22) of the second circuit board (2) and lie against it.

6. Printed circuit board arrangement according to one of the preceding claims, characterized in that a thermal conducting material (63) is arranged between the retainer (5) and the second printed circuit board (2).

7. Printed circuit board arrangement according to one of the preceding claims, characterized in that the fastening means of the retainer (5), which serve to fasten the second printed circuit board (2), comprise bores (53) in the form of threaded bores or simple bores.

8. Printed circuit board arrangement according to claim 7, insofar as it relates back to claim 5, characterized in that the threaded bores (53) are formed at least partially in the projections (55) formed on the top side (51) of the retainer (5).

9. Printed circuit board arrangement according to claim 7, characterized in that the bores (53) are formed in spacer sleeves (56) of the retainer (5) which extend both in the direction of the first printed circuit board (1) and in the direction of the second printed circuit board (2) and define a distance of the retainer (5) to the two printed circuit boards (1 , 2).

10. Printed circuit board arrangement according to one of the preceding claims, characterized in that the first printed circuit board (1) is attached to a housing structure (7) which forms the heat sink or accommodates the heat sink (5).

11. Printed circuit board arrangement according to claim 10, characterized in that the heat sink (4) is arranged in a cavity (71) of the housing structure (7).

12. Printed circuit board arrangement according to claim 10 or 11, characterized by first fastening screws (81) extending from the top (21) of the second printed circuit board (2) through the retainer (5) and through the first printed circuit board (1) into the housing structure (7) and connecting the second printed circuit board (2), the retainer (5) and the first printed circuit board (1) to the housing structure (7).

13. Printed circuit board arrangement according to claim 12, characterized in that the first fastening screws (81) are arranged in the edge region of the first printed circuit board (1).

14. Printed circuit board arrangement according to claim 12 or 13, insofar as it relates back to claim 7, characterized in that the first fastening screws (81) extend through the bores (53) of the retainer (5).

15. Printed circuit board arrangement according to one of the preceding claims, characterized by second fastening screws (82) extending from the top (51) of the retainer (5) through the first printed circuit board (1) into the heat sink (4).

16. Printed circuit board arrangement according to one of the preceding claims, insofar as it relates back to claim 7, characterized by third fastening screws (83) which extend from the top (21) of the second printed circuit board (2) into the retainer (5) and are screwed to the retainer (5) through the threaded holes (53).

17. Printed circuit board arrangement according to one of the preceding claims, characterized in that the retainer (5) is designed as a rigid plate or as a rigid frame and has a higher stiffness than the first printed circuit board (1) and the second printed circuit board (2).

18. Printed circuit board arrangement according to one of the preceding claims, characterized in that the retainer (5) is made of metal or of a metal alloy or of a plastic-metal hybrid.

19. Printed circuit board arrangement according to one of the preceding claims, characterized in that the at least one electrical component (3) to be cooled is thermally coupled to the heat sink (4) via a thermal conducting material (61).

20. Printed circuit board arrangement according to one of the preceding claims, characterized in that the at least one electrical component (3) to be cooled is an element of an inverter for an electric motor.

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