Printed circuit board arrangement and method for its manufacture

Abstract

The invention relates to a printed circuit board arrangement comprising: a printed circuit board (1) having a top (11) and a bottom (12), at least one electrical module (2) having a top (21) and a bottom (22) and arranged with its top (21) on the bottom (12) of the printed circuit board (1), and a heat sink (3) against which the electrical module (2) rests with its bottom (22) via a thermally conductive material (4). The bottom (22) of the electrical module (2) has a height profile (25), and a gap (5) is formed between the top (31) of the heat sink (3) and the bottom (22) of the electrical module (2), in which the thermally conductive material (4) is arranged.It is provided that the heat sink (3) is structured in the area of ​​its surface (31) where the electrical module (2) rests against the thermally conductive material (4) with its underside (22) such that the structuring (35) compensates for the height profile (25) of the underside (22) of the electrical module (2), so that the gap (5) has a constant height. The invention further relates to a method for manufacturing such a printed circuit board arrangement.

Description

[0001] The invention relates to a printed circuit board arrangement according to the preamble of patent claim 1 and a method for producing such a printed circuit board arrangement.

[0002] It is common practice to press printed circuit board-based power electronics assemblies onto a heat sink for cooling using screw connections and / or a retaining clamp. The electrical modules to be cooled—also known as prepackage modules—are located on the underside of a printed circuit board. The thermal connection of the modules to be cooled to the heat sink can be achieved using a thermal interface material (TIM), which compensates for height tolerances between adjacent modules. Depending on the thermal interface material used and the cooling method employed (water cooling or air cooling), such height tolerances can result in a deterioration in thermal resistance of 50–100%.

[0003] So-called gap fillers are used as thermal interface materials. These are thermal pads or thermal gels with good thermal properties that compensate for the height differences between the prepackage modules and a heat sink, thus minimizing thermal resistance. For effective use of the gap fillers, a minimum gap height recommended by the manufacturer should be observed. For example, gap fillers are known whose thermal conductivity is limited to a maximum of 7.5 W / m·K and which require a minimum gap height of 0.2 mm to avoid lifetime problems. However, ensuring a minimum gap height recommended by the manufacturer complicates the design of the PCB stack.

[0004] The invention is based on the object of providing a printed circuit board assembly in which a required minimum gap height is maintained between the electrical modules to be cooled and a heat sink. Furthermore, a method for producing such a printed circuit board assembly is to be specified.

[0005] This object is achieved by a printed circuit board assembly having the features of claim 1 and a method having the features of claim 15. Embodiments of the invention are specified in the dependent claims.

[0006] Accordingly, in a first aspect, the invention considers a printed circuit board assembly comprising a printed circuit board with a top side and a bottom side, and at least one electrical module with a top side and a bottom side, wherein the at least one electrical module is arranged with its top side on the bottom side of the printed circuit board. The printed circuit board assembly further comprises a heat sink, against which the electrical module rests with its bottom side via a thermally conductive material. The bottom side of the electrical module has a height profile, and a gap is formed between the top side of the heat sink and the bottom side of the electrical module, in which gap the thermally conductive material is arranged.

[0007] It is further provided that the heat sink is structured in the area of ​​its surface in which the electrical module rests with its underside via the thermally conductive material in such a way that the structuring compensates for the height profile of the underside of the electrical module, so that the gap between the top side of the heat sink and the underside of the electrical module has a constant height.

[0008] The inventive solution is based on the idea of ​​creating a gap of constant height between the top of the heat sink and the bottom of the electrical module by adapting the surface of the heat sink to the existing height profile of the electrical module. The existing height profile of the electrical module is based on a tolerance chain that includes the attachment of the electrical module to the bottom of the circuit board via a solder layer, possible bending of the circuit board, tilting of the electrical module on the bottom of the circuit board, and a tolerance in the thickness of the electrical module. The inventive solution does not aim to reduce the existing tolerance chain (although suitable measures can be implemented additionally for this purpose).Rather, the existing tolerance chain is accepted, but its effects are compensated by a corresponding structuring of the heat sink, so that the result is an optimized gap of constant height between the heat sink and the respective electronic module.

[0009] By geometrically adapting the heat sink surface, each thermal interface between an electrical module and the heat sink surface has the same gap. This has the advantage that the electrical modules can be cooled more evenly and the thermal optimum of the thermal interface material used can be achieved. The improved cooling also provides increased power density.

[0010] A further advantage associated with the solution according to the invention is that the gap dimensions between the electrical module and the heat sink can be reduced overall, since a tolerance value no longer needs to be maintained to ensure the required minimum gap height. This makes it possible to use other types of thermally conductive materials in the gap between the electrical module and the heat sink that have higher thermal conductivity. Examples of these include metal-based thermally conductive materials with a thermal conductivity of, for example, up to 80 W / m K.

[0011] It should be noted that, for the purposes of the present invention, the side of the circuit board facing the electrical module is always referred to as the underside of the circuit board. Accordingly, the side of the electrical module facing the circuit board is always referred to as the top side of the electrical module, regardless of its actual spatial positioning.

[0012] One embodiment of the invention provides that the gap height is equal to a minimum gap height, which corresponds to a preferred thickness of the thermally conductive material. Such a minimum, preferred gap height is typically specified by the manufacturer of the thermally conductive material. This makes it possible to use the thermally conductive material at its thermal optimum. One example of this is that the gap height is at least 0.2 mm.

[0013] One embodiment of the invention provides that the height profile of the underside of the electrical module is a three-dimensional height profile and indicates a tilt of the electrical module. A three-dimensional height profile means that the underside of the electrical module is measured three-dimensionally, so that each point on the underside is assigned an x-value, a y-value, and a z-value. Any type of tilt and even stepped sections can be detected in this way, whereby a tilt can occur, for example, around one or two axes. A corresponding, inverse three-dimensional height profile is also formed in the corresponding section on the top side of the heat sink.

[0014] One embodiment provides for the circuit board assembly to comprise multiple electrical modules, with the respective height profile being a three-dimensional height profile and including any absolute height differences between different electrical modules. Absolute height differences are differences in the distance between the underside of the electrical module and the underside of the circuit board. Such possible height differences result from the respective z-values ​​of the respective profile.

[0015] Furthermore, the structuring of the heat sink can be provided such that the surface of the heat sink forms structured contact surfaces corresponding to the number of electrical modules, which are inclined and / or offset in height from one another. In this case, the underside of the electrical module and the associated structured contact surface of the heat sink can each be rectangular, so that the structuring in the surface of the heat sink occurs in rectangular areas.

[0016] A further embodiment of the invention provides that the printed circuit board assembly comprises a plurality of electrical modules, each with its own height profile, and that the heat sink is structured such that the respective height profile is balanced for all electrical modules and a gap of constant height is provided. The present invention makes it possible to detect and balance the respective height profile for each individual electrical module.

[0017] It can be provided that the electrical modules and the structured contact surfaces arranged on the underside of the circuit board are arranged in several rows. Such several rows of electrical modules and structured contact surfaces can be arranged in parallel, forming a grid.

[0018] The introduction of structured contact surfaces into the top of the heat sink can be achieved in a variety of ways. One embodiment involves structuring the surface of the heat sink using machining processes such as milling. Abrasive processes such as thermal or chemical ablation can also be used.

[0019] Another embodiment provides that the heat sink and the structuring of its surface have been provided by 3D printing.

[0020] In one embodiment, the thermally conductive material is a gap filler made of elastomers, including elastomers made of thermally conductive silicone materials. In another embodiment, the thermally conductive material is a metal-based thermally conductive material with a thermal conductivity of up to 80 W / m K. This enables particularly high thermal conductivity.

[0021] According to one embodiment of the invention, the printed circuit board assembly further comprises a hold-down device that exerts a force on the top side of the printed circuit board and presses the electrical module against the heat sink. A hold-down device can prevent any warping of the printed circuit board.

[0022] A further embodiment provides for the electrical module to be arranged in a cavity of the heat sink and pressed against the heat sink within the cavity. The circuit board rests on the side of the heat sink cavity, either directly or via an additional thermally conductive material.

[0023] In a further aspect of the invention, the present invention relates to a method for producing a printed circuit board assembly, comprising the following steps: - Arranging at least one electrical module on the underside of a printed circuit board; - three-dimensional measurement of the underside of at least one electrical module; - Determining a height profile of the underside of the at least one electrical module from the data obtained during the measurement; - Structuring the surface of a heat sink in such a way that for each electrical module a height profile inverse to the height profile of the electrical module is introduced into the surface of the heat sink, - Arranging a thermally conductive material between the surface of the heat sink and the underside of the at least one electrical module, - thermally coupling the at least one electrical module to the heat sink, wherein due to the inverse height profile in the heat sink, the underside of the electrical module forms a gap of constant height to the surface of the heat sink and the thermally conductive material is arranged in this gap of constant height.

[0024] This aspect of the invention is based on the idea of ​​measuring the underside of the respective electrical module three-dimensionally, determining a height profile from this and, on the basis of the data obtained, incorporating an inverse height profile into the surface of the heat sink.

[0025] In this case, it can be provided that a hold-down device is additionally provided, which exerts a force on the top side of the circuit board and presses the electrical module against the heat sink. This can, in particular, prevent warping of the circuit board.

[0026] A further embodiment of the method provides that the heat sink is kept as a semi-finished product, and during the step of structuring the surface of the heat sink, only the surface of the semi-finished product is machined. The semi-finished products already include other relevant structures such as holes and other geometric dimensions. This limits the effort required to keep heat sinks adaptable according to the invention in stock. The structuring of the surface of the heat sink to create an inverse height profile can be carried out in a comparatively short time, for example, using a CNC machine tool. The input data for the surface processing of the heat sink can be generated automatically, for example, using a white light interferometer, in just a few minutes.

[0027] A further embodiment provides that the structuring of the surface of the heat sink comprises that the heat sink and the structuring of its surface are provided by 3D printing.

[0028] An embodiment of the method according to the invention provides that the structuring of the surface of the heat sink comprises forming structured contact surfaces in the surface of the heat sink corresponding to the number of electrical modules, which contact surfaces extend obliquely and / or are offset from one another in terms of their height.

[0029] Furthermore, it can be provided that several rows of electrical modules are arranged on the underside of the circuit board and corresponding rows with structured contact surfaces are formed in the surface of the heat sink.

[0030] The invention is explained in more detail below with reference to the figures of the drawing using several exemplary embodiments. They show: Fig. 1 shows an embodiment of a printed circuit board assembly comprising a printed circuit board, electrical modules and a heat sink, wherein the surface of the heat sink is structured such that a height profile of the underside of the electrical modules is balanced; Fig. 2 shows, by way of example, a view from below of a plurality of electrical modules which are attached to the underside of a printed circuit board, showing the respective height profile which the electrical modules form on their underside; Fig. 3 shows, by way of example, a view from above of the surface of a heat sink in which a plurality of structured contact surfaces are formed which run obliquely and / or are offset in height from one another, wherein the structured contact surfaces compensate for height profiles of the respectively associated electrical module; Fig. 4 shows a further embodiment of a printed circuit board assembly comprising a printed circuit board, electrical modules, and a heat sink, wherein the surface of the heat sink is structured such that a height profile of the underside of the electrical module is balanced, wherein the printed circuit board assembly further comprises a hold-down device; and Fig. 5 a flow diagram of a method for producing a printed circuit board assembly according to the Fig. 1 and Fig. 4.

[0031] The Fig. 1 shows a printed circuit board assembly comprising a printed circuit board 1 with a top side 11 and a bottom side 12, electrical modules 2 with a top side 21 and a bottom side 22 and a heat sink 3 with a top side 31 and a bottom side 32.

[0032] The printed circuit board 1 consists of a plurality of printed circuit board layers (not shown separately) which are arranged one above the other, with the uppermost printed circuit board layer forming the top side 11 and the lowermost printed circuit board layer forming the bottom side 12.

[0033] The electrical modules 2 are arranged on the underside 12 of the circuit board 1 with their upper side 21. The Fig. 1 shows two electrical modules 2. However, this is only an example. On the one hand, several such electrical modules 2 can be arranged one behind the other, forming rows (where the other electrical modules of a row are in the Fig. 1 are not recognizable), on the other hand, a different number of electrical modules 2 or rows of electrical modules 2 can be arranged next to one another.

[0034] The connection of an electrical module 2 to the circuit board 1 is achieved, for example, via surface mounting. Electrical contacts on the top side 21 of the electrical module 2 (not shown separately) are electrically connected via solder connections 81, 22 to corresponding electrical contacts on the bottom side 12 of the circuit board 11 (not shown separately). For example, each electrical module 2 has electrical contacts for a source terminal, a gate terminal, and a drain terminal of the electrical module 2.

[0035] Between the top side 22 of the electrical module 2 and the bottom side 12 of the printed circuit board 1 is a gap caused by the solder connections 81, 82, which is filled with an underfill material 7. The underfill material 7 is applied after the electrical module 2 has been attached to the bottom side 12 of the printed circuit board 1 using an underfill process, whereby the underfill material spreads into the gap by capillary action. Alternatively, an injection molding process can be used instead of an underfill process.

[0036] The electrical module 2 can be designed in a variety of ways. In some embodiments, it contains a semiconductor component, in particular a power semiconductor such as a power MOSFET or an IGBT component. The semiconductor component is arranged, for example, on a ceramic circuit carrier (not shown separately), which serves to electrically insulate the semiconductor component from the heat sink 3 and simultaneously thermally connect it to the heat sink 3.

[0037] As in the Fig. 1 is exaggerated for clarity, the electrical module 2 is not aligned completely horizontally, but tilted. This applies to both of the electrical modules 2 shown (as well as possibly further electrical modules 2 arranged on the underside 12 of the printed circuit board 1), whereby the tilt can be different and the distance of the underside 22 of the respective electrical module 2 from the underside 12 of the printed circuit board 1 can vary. This is due to the fact that each electrical module 2 is attached to the underside 12 of the printed circuit board with a tolerance chain, whereby the tolerance chain includes the attachment of the electrical module 2 to the underside 12 of the printed circuit board 1 via the solder connections 81, 82. This can lead to a tilt of the respective electrical module 2 on the underside of the printed circuit board 12.Furthermore, any deflection of the circuit board 2 as well as any tolerances in the thickness of the respective electrical module contribute to the tolerance chain.

[0038] Tilting of the electrical module 2 and any existing height differences relative to the underside 12 of the printed circuit board 1 are associated with a height profile 25 of the underside 22 of the electrical module 2. The height profile 25 can be defined such that the position in three-dimensional space is determined for each point on the underside 22 of the electrical module 2, which position is specified, for example, via an x-coordinate, a y-coordinate, and a z-coordinate. The height profile 25 indicates tilting and, via the z-coordinate, also height differences between the individual electrical modules 2.

[0039] The Fig. Figure 2 shows, by way of example, several electrical modules 2 which are arranged on the underside 12 of a printed circuit board 1, wherein the view of the Fig. 2 from below, so that the respective underside 22 of the electrical modules 2 is shown. It can be seen that the respective underside 22 forms a height profile 25. The height profile 25 of the electrical modules 2 includes partial tilts of the underside 22, but also absolute height differences. The z-coordinate varies overall between the value 1.539 mm and 1.872 mm, which indicates the distance to a (assumed to be flat) underside 12 of the circuit board 1.

[0040] In the Fig. 2, the electrical modules 2 are arranged in six rows. The electrical modules 2 are interconnected and form, for example, the logical switches of a three-phase inverter with three phases U, V, and W. However, this is only an example.

[0041] The electrical modules 2 require cooling by the heat sink 3. For this purpose, the heat sink 3 has a cavity or recess 33 into which the modules 2 to be cooled protrude, wherein the modules 2 to be cooled come into thermal contact with the heat sink 3 on their underside.

[0042] Due to the tilting of the electrical modules 2 and the height profile 25, a gap 5 is necessarily present between the underside 22 of the electrical module 2 and the top side 31 of the heat sink 3. However, such a gap 5 impairs the thermal connection to the heat sink 3. To improve the thermal connection, a thermally conductive material or gap filler 4 is arranged between the modules 2 to be cooled and the heat sink 3.

[0043] Due to the height profile 25 of the underside, the height of the gap 5 and thus also the thickness of the thermally conductive material 4 arranged in the gap would vary if the surface 31 of the heat sink 3 were exactly flat and horizontal. This is considered disadvantageous, since gap filler manufacturers recommend a minimum gap height for gap fillers to avoid lifetime problems.

[0044] To provide a gap 5 of constant height, the surface 31 of the heat sink 3, in the area where the electrical module 2 rests with its underside 22 via the thermally conductive material 4, has a structuring 35 that is inverse to the height profile 25 of the underside 22 of the electrical module 2 and thus compensates for the height profile 25 of the underside 22 of the electrical module 2. For this purpose, the surface 31 of the heat sink 3 forms structured contact surfaces that run obliquely or are inclined and / or are offset in height from one another.

[0045] A corresponding structuring of the surface 31 of the heat sink 3 shows, for example, the Fig. 3. The Fig. Figure 3 shows the upper side 31 of a heat sink 3, which comprises a cavity 33 for accommodating the electrical modules 2. A plurality of structured contact surfaces 36 are formed in the cavity 33 as a structure 35, each of which individually forms a height profile. The structured contact surfaces 36 correspond in arrangement and orientation to the undersides 22 of the electrical modules 2 of the Fig. 2. They are each square in shape. Each height profile 25 of one of the electrical modules 2 is thus individually assigned a structured contact surface 36, which compensates for the individual height profile 25 of the respective electrical module 2, so that a gap of constant height is formed between each of the electrical modules 2 and the associated structured contact surface 36. The height of the gap 5 is dimensioned, for example, such that it corresponds to the thickness of the thermally conductive material preferred by the manufacturer. In some embodiments, the height of the gap 5 is 0.2 mm.

[0046] According to the Fig. 1, it is further provided that the printed circuit board 1 is screwed to the heat sink 3 via metal screws 6. The metal screws 6 are screwed into through-holes 15 that extend from the printed circuit board 1 into the heat sink 3. The metal screws 3 rest on the top side 11 of the printed circuit board 1 via washers and / or metallizations 60. They provide a compressive force with which the printed circuit board 1 is pressed against the heat sink 3. In particular, they provide the compressive force with which the electrical modules 2 to be cooled, arranged on the underside 12 of the printed circuit board 1, are pressed against the surface 31 of the heat sink 3 via the thermally conductive material 4 to provide a good thermal transition.

[0047] The heat sink 3 can have numerous configurations. It is made, for example, of a metal such as aluminum or an aluminum alloy and has cooling surfaces (not shown separately). 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 3 is designed as a passive heat sink.

[0048] To improve the thermal contact between the electrical module 2 to be cooled and the heat sink 3, it is known to use hold-down devices that press the circuit board 1 against the heat sink 3. Such a hold-down device is shown in the Fig. 4. The basic structure is the same as in the Fig. 1. A hold-down device 4 is additionally located above the circuit board 1. This hold-down device may be a plate, for example, with projections 91 on its underside that press against the top side 11 of the circuit board 1 and counteract warping of the circuit board 1. The projections 91 may be ribs and / or point-shaped projections. In other embodiments, the hold-down device 9 rests against the top side 11 of the circuit board 1 over its entire surface. The hold-down device 9 allows the contact pressure to be uniformed across the surface of the circuit board 1.

[0049] The hold-down device 9 is made of a mechanically stiffer material than the circuit board, for example stainless steel.

[0050] The Fig.Figure 5 shows process steps of a method for manufacturing a printed circuit board assembly. In a first step 51, at least one electrical module is arranged on the underside of a printed circuit board. Subsequently, the underside of the electrical module is measured three-dimensionally in step 52. This can be done using known methods and devices for 3D profile measurement of structures, for example, using a white light interferometer.

[0051] From the data obtained during the measurement, a height profile of the underside of the electrical module is determined in step 53. Each point on the underside of the electrical module is assigned a three-dimensional spatial point.

[0052] Subsequently, according to step 54, the surface of a heat sink is structured such that, for each electrical module, a height profile inverse to the height profile of the electrical module is introduced into the surface of the heat sink. This creates structured contact surfaces in the top side of the heat sink that are inclined and / or offset in height from one another. The specific processing of the surface can be carried out, for example, using machining processes, for example, relatively quickly using CNC machining. In an alternative embodiment, the heat sink 3 and the structuring of its surface 31 are produced by 3D printing.

[0053] It can be provided that the heat sink is kept as a semi-finished heat sink, which, for example, already has all holes and other geometric adjustments Only the specific processing required to produce the structured contact surfaces is then required.

[0054] Furthermore, according to step 55, a thermally conductive material is arranged between the surface of the heat sink and the underside of the at least one electrical module. This can be a thermally conductive material made of an elastomer (plastic or silicone) with a thermal conductivity of up to 7.5 W / m·K. It can also be provided that a thermally conductive material with high thermal conductivities is used, for example, metal-based thermally conductive materials with a thermal conductivity of up to 80 W / m·K.

[0055] Subsequently, in step 56, the at least one electrical module is thermally coupled to the heat sink. Due to the inverse height profile, the underside of the electrical module forms a gap of constant height with the surface of the heat sink. The thermally conductive material is arranged in the constant-height gap.

[0056] It may be provided that the circuit board is additionally protected against warping by a hold-down device.

[0057] 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. It is further understood 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

[1] Printed circuit board assembly comprising: - a printed circuit board (1) having a top side (11) and a bottom side (12), - at least one electrical module (2) having a top side (21) and a bottom side (22) and arranged with its top side (21) on the bottom side (12) of the printed circuit board (1), - a heat sink (3) against which the electrical module (2) rests with its underside (22) via a heat-conducting material (4), wherein - the underside (22) of the electrical module (2) has a height profile (25) and a gap (5) is formed between the upper side (31) of the heat sink (3) and the underside (22) of the electrical module (2), in which gap the heat-conducting material (4) is arranged, characterized by , that the heat sink (3) is structured in the area of ​​its surface (31) in which the electrical module (2) rests with its underside (22) via the heat-conducting material (4) in such a way that the structuring (35) compensates for the height profile (25) of the underside (22) of the electrical module (2), so that the gap (5) has a constant height. [2] Printed circuit board arrangement according to claim 1, characterized by that the height of the gap (5) is equal to a minimum gap height which corresponds to a preferred thickness of the thermally conductive material (4). [3] Printed circuit board arrangement according to claim 1 or 2, characterized by that the height of the gap (5) is at least 0.2 mm. [4] Printed circuit board arrangement according to one of the preceding claims, characterized by that the height profile (25) of the underside (22) of the electrical module (2) is a three-dimensional height profile and indicates a tilt of the electrical module (2). [5] Printed circuit board arrangement according to one of the preceding claims, characterized by that the printed circuit board arrangement comprises a plurality of electrical modules (2), wherein the respective height profile is a three-dimensional height profile and also includes possible height differences between different electrical modules (2). [6] Printed circuit board arrangement according to one of the preceding claims, characterized by that the structuring (35) of the heat sink (3) comprises that the surface (31) of the heat sink (3) forms structured contact surfaces (36) corresponding to the number of electrical modules (2), which run obliquely and / or are offset in height from one another. [7] Printed circuit board arrangement according to claim 6, characterized by that the underside (22) of the electrical module (2) and the associated structured contact surface (36) of the heat sink (3) are each rectangular. [8] Printed circuit board arrangement according to one of the preceding claims, characterized by in that the printed circuit board arrangement has a plurality of electrical modules (2), each having its own height profile (25), and the heat sink (3) is structured in such a way that the respective height profile (25) is balanced for all electrical modules (29) and a gap (5) of constant height is provided. [9] Printed circuit board arrangement according to claim 8, as far as dependent on claim 6, characterized by that the electrical modules (2) arranged on the underside (12) of the printed circuit board (1) and the structured contact surfaces (36) are arranged in several rows. [10] Printed circuit board arrangement according to one of the preceding claims, characterized by that the structuring of the surface (31) of the heat sink (3) has been provided by a machining or abrasive process. [11] Printed circuit board arrangement according to one of claims 1 to 9, characterized bythat the heat sink (3) and the structuring of its surface (31) have been provided by 3D printing. [12] Printed circuit board arrangement according to one of the preceding claims, characterized by that the thermal conductivity material (5) is a metal-based thermal conductivity material with a thermal conductivity of up to 80 W / m·K. [13] Printed circuit board arrangement according to one of the preceding claims, characterized by that the printed circuit board arrangement further comprises a hold-down device (9) which exerts a force on the upper side (11) of the printed circuit board (1). [14] Printed circuit board arrangement according to one of the preceding claims, characterized by that the electrical module (2) is arranged in a cavity (33) of the heat sink (3). [15] A method of manufacturing a printed circuit board assembly comprising the steps of: - arranging (51) at least one electrical module (2) on the underside (12) of a printed circuit board (1); - three-dimensional measurement (52) of the underside (12) of the at least one electrical module (2); - determining (53) a height profile (25) of the underside (22) of the at least one electrical module (2) from the data obtained during the measurement; - Structuring (54) the surface (31) of a heat sink (3) in such a way that for each electrical module (2) a height profile inverse to the height profile (25) of the electrical module (2) is introduced into the surface (31) of the heat sink (3), - arranging (55) a thermally conductive material (4) between the surface (31) of the heat sink (3) and the underside (22) of the at least one electrical module (2), - thermal coupling (56) of the at least one electrical module (2) to the heat sink (3), wherein due to the inverse height profile (35) in the heat sink (3), the underside (22) of the electrical module (2) forms a gap (5) of constant height to the surface (31) of the heat sink (3) and the heat-conducting material (4) is arranged in this gap (5) of constant height. [16] Method according to claim 15, characterized by that a hold-down device (9) is further provided which exerts a force on the upper side (11) of the printed circuit board (1) and presses the electrical module (2) against the heat sink (3). [17] Method according to claim 15 or 16, characterized by that the heat sink (3) is kept as a semi-finished product and in the step of structuring (54) the surface (31) of the heat sink (3) only the surface of the semi-finished product is machined. [18] Method according to one of claims 15 to 17, characterized bythat the structuring (54) of the surface (31) of the heat sink (3) is carried out by a CNC machine tool on the basis of the data of the height profile (25). [19] Method according to one of claims 15 to 17, characterized by that the structuring (54) of the surface (31) of the heat sink (3) comprises that the heat sink (3) and the structuring of its surface (31) are provided by 3D printing. [20] Method according to one of claims 15 to 19, characterized by that the structuring (54) of the surface (31) of the heat sink (3) comprises that structured contact surfaces (36) are formed in the surface (31) of the heat sink (3) according to the number of electrical modules (2), which contact surfaces run obliquely and / or are offset from one another in terms of their height.

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