WO2018202245A1

WO2018202245A1 - Heat sink

Info

Publication number: WO2018202245A1
Application number: PCT/DE2018/100400
Authority: WO
Inventors: Jörg KEGELER
Original assignee: Schaeffler Technologies AG & Co. KG
Priority date: 2017-05-05
Filing date: 2018-04-25
Publication date: 2018-11-08
Also published as: DE102017109682A1

Abstract

The invention relates to a heat sink for absorbing heat from a heat-producing component. The aim of the invention is to provide a cost-effective, lightweight heat sink which has good thermal conductivity together with good electrical insulation properties. To achieve this, the heat sink comprises a multi-layer plate having a plurality of layers, on which a plurality of conductor tracks (1-6) which are insulated from one another are arranged, • all conductor tracks (1-6) being designed as open conductor tracks, thus not allowing the formation of a closed circuit, • the conductor tracks (1-6) of each layer having at least one conductor track section that vertically partially overlaps at least one conductor track section of a conductor track (1-6) of a neighbouring layer, and • the partially overlapping conductor tracks (1-6) running either in different directions, or in the same direction with a lateral offset to one another.

Description

heatsink

The invention relates to a heat sink for cooling a heat-producing component. A heat-producing component in this context may be, for example, a power electronic system, a transformer or a dynamoelectric machine.

Heat sinks for such applications usually consist of a good heat-conductive metal such as aluminum or copper. The good thermal conductivity of these metals is accompanied by good electrical conductivity. This can be particularly problematic in high power AC powered applications. In these applications, there is a risk that eddy currents are induced in the heat sink, which lead to power loss. In order to avoid these eddy current losses, heat sinks made of ceramic materials such as aluminum oxide and aluminum nitrite are used in particular in power electronics for cooling components. Despite their good thermal conductivity, these materials have a high electrical resistivity. A disadvantage of these materials is their comparatively high price.

For example, from DE 10 2013 201758 A1 it is known to use plastics with thermally conductive fillers in order to ensure a good thermal conductivity with electrically insulating material. In the document cited here, this material is arranged for improved heat dissipation around a stator body of an electrical machine.

The invention has for its object to provide a low-cost and heat sink with low mass and good thermal conductivity with good electrical insulation properties available. This object is achieved by a heat sink with the features according to claim 1. Such a heat sink comprises a multilayer board with a plurality of layers, on which a plurality of mutually electrically insulated tracks are arranged, wherein all tracks are formed as an open circuit, which does not allow a closed circuit, wherein the tracks of each layer each at least one Have conductor track portion, which is arranged vertically in partial overlap with at least one conductor track portion of a conductor of an adjacent layer, wherein the conductor tracks arranged in partial overlap either have a different direction course or extend in the same direction and have a lateral offset from one another.

Advantageous embodiments of the invention can be found in the dependent claims. Due to the inventive partial overlap of the tracks of two adjacent layers of the heat transfer is promoted by the multilayer board in the vertical direction. Lateral, a minimum isolation distance between the conductors arranged on a layer must be maintained in order to ensure the desired electrical insulation strength. Nevertheless, a good heat conduction in the lateral direction can be achieved by first transporting the heat in the vertical direction. This is made possible by the partial coverage of the tracks of adjacent layers.

According to a first alternative of the invention, the conductors of the adjacent layers, which are arranged in mutually partial vertical overlap, run in different directions. This enables a lateral propagation of the heat quantity initially exchanged vertically between the conductors.

According to a second alternative of the invention, this is also possible with directionally parallel conductors, in which the conductors, arranged in partial overlap, of two different adjacent layers have a lateral offset from one another.

Because the conductor tracks are designed as open conductor tracks which do not allow a closed circuit, eddy current losses within the heat sink can be avoided.

Preferably, the multilayer board is constructed on the basis of an electrically non-conductive substrate made of glass fiber reinforced epoxy resin. Such a material represents, for example, FR-4, which is frequently used in the manufacture of printed circuit boards. Compared with a conventional aluminum or copper heat sink, the use of such a multilayer printed circuit board as a heat sink significantly saves weight. Preferably, the interconnects of the various layers are arranged so that a good overlap arises between them. This can be realized in an advantageous embodiment of the invention in that the conductor tracks are formed on each layer as a parallel duri fenden strip, the course of two adjacent layers are arranged offset by 90 ° to each other. The overlap area of two vertically adjacent conductor tracks represents in this embodiment a crossing point of the conductor tracks.

Alternatively, a good overlap between the interconnects of the different layers can be realized in that all interconnects are strip-shaped and of the same direction and the mutually parallel interconnects of each layer have a lateral offset to the mutually parallel interconnects of an adjacent layer. The resulting schindeiförmige coverage of the tracks allows over the entire extent of each strip a heat transfer to the or the vertically adjacent tracks.

Of course, other non-strip-shaped conductor tracks within the scope of the invention are also conceivable, which enable lateral heat transfer within the multilayer board via two adjacent layers each by suitable arrangement of the conductor strips involved. For example, the desired effect could also be achieved by means of a meandered conductor track guidance, as long as it is ensured that the conductor tracks are either arranged in different directions in the different layers or have a lateral offset from one another. Furthermore, it is always important to ensure that no closed conductor loops are formed even with such an embodiment of the strip conductors.

The heat transfer between the interconnects of the different layers can be improved in a further advantageous embodiment of the invention by thermally conductive VIAs that connect interconnects of different layers together. These thermally conductive VIAs are preferably thermally and electrically conductive connections between the interconnects of adjacent layers. In order to avoid eddy current losses, it is advantageous in this embodiment to arrange the thermally conductive VIAs in such a way that no closed conductor loops result from the connection of the conductor tracks. The thermal conductivity of the heat sink depends crucially on how high the conductor track portion is within the multilayer board. On the other hand, it is essential for the efficiency of the system to be cooled to avoid eddy current losses within the heat sink. A high copper content with simultaneous suppression of eddy current losses can be achieved while maintaining the necessary isolation distance, that in an advantageous embodiment of the invention, the conductor tracks in the vertical direction less than 3 mm, preferably less than 1 mm wide.

In order to enable the heat transfer between the interconnects, an embodiment of the invention has proven to be advantageous in which the insulation distance between the interconnects is less than 150 μηι.

A heat sink according to an embodiment of the present invention features similarly good heat conduction properties as conventional heat sinks made of materials such as copper, aluminum, magnesium or steel. In comparison to such heat sinks, which are often used in the field of power electronics or for cooling electrical machines, the invention enables a significant weight reduction. In addition, it can be avoided that forms eddy currents within the heat sink, which reduce the efficiency of the system to be cooled. Thus, the invention can be advantageously used as a heat sink for a dynamoelectric machine for heat dissipation of a stator winding of the dynamoelectric machine.

In the following, the invention will be explained in more detail with reference to the embodiments illustrated in the figures.

Show it:

Figure 1: A first embodiment of a designed as a multilayer board heat sink and

Figure 2: A second embodiment of a designed as a multilayer board heat sink. FIG. 1 shows a first embodiment of a heat sink designed as a multilayer board. Shown is a cross section of the multilayer board. The multilayer board comprises three stacked individual boards, each carrying on its top and on its underside interconnects 1-6. The uppermost arranged single board carries on its upper side conductor tracks 1, which are aligned in the form of a strip in the direction of the plane of the drawing. At the bottom of this top board there are further tracks 2, which also strip-shaped. These further printed conductors 2 are arranged offset by 90 ° to the printed conductors 1 at the top of the board. As a result, each of the conductor tracks 1 on the upper side comprises a section which is arranged vertically in register with a conductor track section of the conductor tracks 2 on the underside of this individual board. Due to the very small isolation distance between the superposed conductor track sections, a heat transfer between the conductor track sections in the overlap area is very possible. Below the uppermost arranged individual boards are two other boards, which are equipped in the same way as the top board with strip-shaped in tracks 3, 4, 5, 6 at their respective top and bottom.

All traces 1-6 begin and end in the insulating substrate. That is, they do not form closed tracks that allow current to flow. In this way, no eddy currents can form within the multilayer board.

To prevent eddy current losses from forming within a single printed circuit trace 1 -6, the printed conductors have only a very narrow width of not more than 3 mm, preferably even less than 1 mm.

During the manufacturing process, the single boards described above are first manufactured, wherein the respective tracks 1-6 are coated on a substrate 8 made of glass fiber reinforced epoxy resin. Subsequently, insulating prepreg layers not shown here are arranged between the various individual boards, by means of which the adjacent printed conductors of the individual printed circuit boards lying one above the other are electrically isolated from one another.

The tracks 1-6 are made of copper and are located on a substrate of FR-4. The substrates coated with the tracks are each separated by one or two blades Prepreg material stacked on top of each other. Subsequently, the resulting total stack is laminated to produce a mechanical bond between the substrates.

The cross-section of the resulting multilayer board shows that the interconnects 3 at the top of the middle single board have a coverage area with the tracks 2, which are located on the underside of the top single board. For the conductor tracks 3 at the top of the middle board also run in a strip shape and parallel in the direction of the drawing plane - as well as the conductor tracks 1 at the top of the top individual boards. The illustrated arrows indicate how the heat in the covering region between the printed conductors 2, 3 can be transported here, for example, from right to left in a lateral direction over the thin prepreg layer between the uppermost and lowermost individual printed circuit boards. In this way, a heat transfer at the top of the middle single board is made possible from right to left, although the tracks 3 are only extended in the direction of the plane of the drawing. It is a heat transfer within the multilayer board allows, as it is known in the prior art only of massive metal heat sinks, which have a much higher mass compared to the solution proposed here and are also subject to the mentioned eddy current problem. FIG. 2 shows a second embodiment of a heat sink designed as a multilayer board. Again, the multilayer board comprises three individual boards, which are each equipped on their top and bottom with strip-shaped in tracks 1-6. Again, the tracks 1-6 do not form closed loops, so that no possibility for a closed circuit and the associated formation of eddy currents is created.

In contrast to the embodiment according to FIG. 1, however, here all conductor tracks 1-6 extend in the direction of the plane of the drawing. Nevertheless, there is always an overlap area between the respectively vertically adjacent conductor tracks 1-6. This is due to the fact that the vertically adjacent conductor tracks 1-6 each have a lateral offset from one another. As a result of this lateral offset, the heat within the multilayer board can also propagate from left to right in the represented cross section, as indicated by the arrows, although the strip-shaped conductor tracks 1-6 are all oriented in the direction of the plane of the drawing. To improve the vertical heat transfer between the different layers of the multilayer board thermal VIASs 7 are provided in the embodiment shown here. These are holes that are filled with a thermally good conductive material and penetrate the multilayer board vertically at different points. The thermal VIAs 7 are distributed at regular intervals within the multilayer board and connect the conductor track sections of several layers. Since their thermal conductivity is significantly higher than that of the insulation material, the thermal VIAs 7 allow a further improved heat transfer in the vertical direction. If a metallic material is used as a filler within the holes, the thermal VIAs 7 must be arranged so that closed conductor loops are prevented.

List of reference conductors

thermal VIAs

substratum

Claims

claims

Heatsink comprising a multi-layer board having a plurality of layers on which a plurality of mutually electrically insulated conductor tracks (1-6) are arranged, wherein

All tracks (1-6) are formed as an open track, which does not allow a closed circuit,

Wherein the conductor tracks (1-6) of each layer each have at least one conductor track section which is arranged vertically in partial overlap with at least one track section of a conductor track (1-6) of an adjacent layer,

Wherein the conductor tracks (1 -6) arranged in partial overlapping either have a different directional course or run in the same direction and have a lateral offset from one another.

Heatsink according to claim 1, wherein the conductor tracks (1-6) are formed on each layer as parallel strips, the course of two adjacent layers are arranged offset by 90 ° to each other.

Heatsink according to claim 1, wherein all the conductor tracks (1-6) are strip-shaped and directionally identical and the mutually parallel conductor tracks (1-6) of each layer a lateral offset to the mutually parallel conductor tracks (1-6) of an adjacent layer exhibit.

Heat sink according to one of the preceding claims, wherein the multilayer board thermally conductive VIAs (7), the interconnects (1-6) of different layers connect together.

Heatsink according to claim 4, wherein the thermally conductive VIAs (7) are arranged such that by the connection of the conductor tracks (1-6) no closed conductor loops are formed.

6. Heatsink according to one of the preceding claims, wherein the conductor tracks (1-6) in the vertical direction less than 3 mm, preferably less than 1 mm wide.

7. Heatsink according to one of the preceding claims, wherein the isolation distance between the tracks 1 -6 is less than 150 pm.

8. Heatsink according to one of the preceding claims, wherein the multilayer board comprises an electrically non-conductive substrate (8) made of glass fiber reinforced epoxy resin.

9. A dynamoelectric machine with a heat sink according to one of the preceding claims for cooling a stator winding of the dynamoelectric machine.