EP3375261A1

EP3375261A1 - Multi-layer printed circuit board having a printed coil and method for the production thereof

Info

Publication number: EP3375261A1
Application number: EP16810237.4A
Authority: EP
Inventors: Jörg KEGELER
Original assignee: Schaeffler Technologies AG and Co KG
Current assignee: Schaeffler Technologies AG and Co KG
Priority date: 2015-11-13
Filing date: 2016-11-09
Publication date: 2018-09-19
Also published as: CN113490325A; CN108353494A; US10638596B2; WO2017080554A1; DE102015222400A1; US20180317313A1; CN108353494B

Abstract

The invention relates to a multi-layer printed circuit board, comprising vertically superimposed flat coils (1-6) which are electrically connected in series or in parallel to form a first solenoid coil (20). In order to improve the heat dissipation of the multi-layer printed circuit board, it is proposed that in each case two vertically adjacent flat coils (1,2) are arranged laterally offset relative to each other in such a manner that conductor track sections (26) of one flat coil (2) are arranged vertically in a partial overlap with two conductor track sections (7) of the other flat coil (1) in a cross section (8) perpendicular to the surface of the multi-layer printed circuit board.

Description

MULTI LAYER PLATINUM WITH PRINTED COIL AND METHOD FOR THE PRODUCTION THEREOF

The invention relates to a multilayer board with a solenoid coil formed from superimposed flat coils and a method for their preparation.

Under a multilayer board or multilayer board is to be understood a circuit board having a plurality of vertically superimposed planes, which are each equipped with tracks. The arranged on the different levels interconnects can be electrically connected to each other via so-called VIAs. These VIAs, also called electrical feedthroughs, are usually realized by a vertical bore, which is metallized at its inner diameter.

For example, from DE 10 2008 062 575 A1 discloses a multilayer board according to the preamble of claim 1 is known. Here, a linear motor is disclosed, the primary part is designed as a multilayer board. The various layers of this multilayer board are mostly filled with currentable windings. Opposite turns each form a coil of a phase of the linear motor. In this way, a particularly lightweight and compact primary part for a linear motor can be realized, which is particularly suitable as a rotor for highly dynamic applications. FIG. 1 shows, in a cross section 8, perpendicular to the surface of a multilayer board, an arrangement of flat coils 1-6 known from the prior art for forming a solenoid coil. In each level of the multilayer board is here, for example, a flat coil 1 - 6, each with three turns, which extend spirally either from the inside out or from outside to inside. For example, a first flat coil 1 is wound from outside to inside and electrically connected to an underlying second flat coil 2 via an electrical VIA. The second flat coil 2 in turn is spirally wound from the inside to the outside and in turn via a further not shown here further electrical VIA with a third flat coil 3 connected in the third level of the multilayer board. In this way, a solenoid is created, which extends over six levels of

Multilayer board extends. The multilayer board technology is also particularly suitable for realizing applications with high electrical power in a compact and lightweight design. An example of this is already mentioned primary part of the linear motor from DE 10 2008 062 575 A1, which is realized as a multilayer printed circuit board. Due to the high currents in such applications, cooling is a particular challenge. For example, as shown in FIG. 1, the heat generated in internal conductor tracks must be conducted laterally to the outer edge of the board, where it can then be dissipated to the surface of the board. Between the individual tracks of one turn of each flat coil, an isolation distance must be provided which may be of the order of a few hundred micrometers. The electrical insulation is ensured for example by prepreg layers whose thermal conductivity is low. Accordingly, it is a particular challenge to dissipate the heat from the central region of such a multilayer board. The invention has for its object to improve the cooling of coils that are realized in the form of a multilayer board.

This object is achieved by a multilayer board with the features according to claim 1. Furthermore, the object is achieved by a method for producing a solenoid coil on a multilayer board according to claim 10.

Advantageous embodiments of the invention can be found in the dependent claims.

The multilayer board according to the invention comprises a plurality of vertically stacked flat coils. The flat coils are first applied, for example, on a plurality of individual boards, wherein the individual boards are preferably stacked to form the multilayer board. Preferably, each individual board arranged both on the top and on the underside of each a flat coil. In this way, two stacked individual boards form a stack of four flat coils, wherein the stacked individual boards are preferably separated from each other by an insulating layer, for example a prepreg layer.

The vertically superimposed flat coils according to the invention are electrically connected in series. This can preferably be implemented with electrical vias, also called VIAs. The electrically connected in series flat coils form the first solenoid coil according to the invention. Each individual pancake coil is preferably spirally wound in its respective plane. For example, runs a first flat coil, for example, in the top layer of

Multilayer board is located in the plane of the multilayer board spiraling from the inside out. On the other hand, when viewed in the vertical direction of the board, the second flat coil arranged below the first flat coil runs spirally from outside to inside.

In this context, a spiral course of the winding is to be understood as meaning any type of winding in which the individual windings of the flat coil are formed by a single planar conductor track and enclose in one plane. The conductor track can be characterized by rounding, but also square.

The invention is now based on the knowledge that the thermal conductivity of the multilayer board - especially in the lateral direction - can be significantly improved if two vertically adjacent flat coils are laterally offset from each other so that in a cross section perpendicular to the surface of the multilayer board Track sections of a flat coil are arranged vertically in partial overlap with two conductor track sections of the other flat coil. In this way, the heat generated in an inner turn of a flat coil can be transferred very easily to a turn of a vertically and laterally adjacent flat coil which, viewed in the lateral direction, is closer to the edge of the circuit board. Because the isolation distance between the conductor track sections, the are located vertically in partial coverage, can be realized much lower process reasons, as the isolation distance between two windings, which are arranged in the same plane of the printed circuit board. The distance between two turns in a plane between the involved track sections can not be chosen arbitrarily small for technical process reasons. By contrast, the individual boards of the multilayer board can be electrically insulated from one another by a comparatively thin prepreg layer. This prepreg layer can be reduced, for example, to the range of only 40 μm in order to ensure sufficient electrical insulation, while the interconnect distance between the individual windings can not be selected to be less than 200 μm for reasons of process engineering.

Accordingly, the heat transfer between conductor sections of vertically adjacent flat coils, which are located in partial vertical coverage, much better than between two arranged in the same plane trace sections of different turns of the flat coil succeeds.

The lateral offset of the stacked flat coils according to the invention has the consequence that the cross section is interspersed over its entire lateral extent with conductor track sections. The heat transfer between two conductor track sections takes place mainly in the vertical direction, where due to the small isolation distance, a relatively small thermal resistance prevails. This has the consequence that the lateral heat conduction within the multilayer board is ensured almost like a continuous metal layer through the entire circuit board.

A particularly low thermal resistance can be realized between two vertically adjacent flat coils whose windings are electrically connected in parallel. In this case, the said turns of the two vertically adjacent flat coils must be separated only by a very thin prepreg layer, for example with a thickness between 20 and 40 μιτι. Due to the inventive lateral offset of these adjacent flat coils can be in the small thickness the insulating layer used between the adjacent flat coils an excellent heat transfer between the interconnected conductor sections, which are arranged in partial overlap to each other realize. Particularly advantageous is an embodiment of the invention, in which the individual coils arranged on flat coils, one of which is located at the top and one on the underside of the Einzellayers are electrically connected in series, while two vertically adjacent flat coils, the two different conductor carriers are assigned to be electrically connected in parallel. In this way it is very easy to realize a small insulation distance by selecting a correspondingly thin prepreg layer between the two vertically adjacent flat coils, which are assigned to separate individual conductor plates.

The multilayer board according to the invention already significantly improves the heat dissipation of only a single solenoid coil, which is arranged on the board. However, in many applications it is convenient to arrange multiple solenoid coils on the multilayer board. This is the case, for example, in the case of a linear motor which has a primary part which is designed as a multilayer printed circuit board according to one of the embodiments described here, and a secondary part which has permanent magnets and is spaced from the primary part via an air gap.

Thus, an advantageous embodiment of the invention is characterized in that the multilayer board has at least one second solenoid coil arranged laterally offset from the first solenoid coil, wherein outer conductor sections of flat coils of the second solenoid coil in a comb-like manner into outer conductor sections of the flat coils of the first solenoid coil engage, so that in the said cross section in each case an outer conductor section of the second solenoid coil is arranged with at least one outer conductor section of the first solenoid coil vertically in partial overlap. Thus, a shingled arrangement of the conductor track sections in the said cross-section is continued beyond the coil boundaries. An outer trace portion of the first solenoid coil is in partial overlap with an outer trace portion of the second solenoid coil, possibly with two such outer trace portions of the second solenoid coil. The heat that enters the outer trace section of the first

Solenoid coil is introduced, can thus be transmitted in the vertical direction over a relatively small insulation distance to the outer trace portion and the outer trace portions of the second solenoid coil. In this way, the heat transfer in the lateral direction from the central inner region of the multilayer board can be excellently transmitted even beyond coil boundaries into the outer edge region of the multilayer board, as would be the case with a solid metal plate.

The heat generated in the solenoid coil (s) of the multilayer board can advantageously be routed to one or both surfaces of the multilayer board if the multilayer board has a passive printed conductor structure which is galvanically isolated from all current-carrying tracks of the multilayer board is arranged laterally offset from the first solenoid coil and comb-like engages in the outer conductor tracks of the pancake of the first solenoid coil. Thus, in this embodiment as well, a kind of shingle-like covering of conductor track sections is provided in order to facilitate the lateral heat transport. In this case, it is provided to transfer the heat from the first solenoid coil to the passive, non-current-conducting strip conductor structure. This passive track structure now makes it possible to dissipate the heat to the surface or surfaces of the multilayer board. This heat transfer to the one or more surfaces of the multilayer board is facilitated by the fact that the passive circuit pattern does not have to be isolated to the extent that the conductor tracks of the solenoid coil or the

Solenoid coils would require.

In a particularly advantageous embodiment of the invention, the heat transport from the passive printed conductor structure to one or both surfaces can be facilitated by virtue of the multilayer printed circuit board having thermally conductive VIAs which penetrate the passive printed conductor structure vertically. These thermally conductive VIAs have the task of transposing previously essentially laterally through the multilayer board. ported heat in the vertical direction, for example, to transport to a arranged on the surface of the multilayer board heat sink.

In this case, it is possible for a cooling body to be arranged on only one surface of the multilayer board. Alternatively, however, both surfaces of the

Multilayer board for cooling to be provided with a heat sink.

A particularly good heat transfer from the thermally conductive VIAs to the one or more heat sinks can be achieved in a particularly advantageous embodiment of the invention in that the thermally conductive VIAs are in contact with a heat sink disposed on a surface of the multilayer board. This is especially the case when arranged on the multilayer board

Solenoid coils can only be operated with moderate voltages. A moderate voltage in this sense is given, for example, if the potential differences within the board are not more than 150 V. In this case, it is not necessary to further isolate the thermally conductive VIAs in front of the heat sink. Here, both surfaces of the multilayer board for

Heat dissipation should be provided with a heat sink. In this case it is expedient that the thermally conductive VIAs be in contact with both heat sinks.

However, when working with very high voltages within the multilayer board, an embodiment of the invention is advantageous in which the multilayer board has an insulating cover layer which covers at least one near-surface flat coil and the thermal VIAs. If necessary, such an insulating cover layer must be provided on both surfaces of the multilayer board in order to ensure protection against inadmissibly high contact voltages. A high voltage in this sense is given, for example, when potential differences within the multilayer board can be more than 500 V. In particular, between two adjacent flat coils, which are electrically connected in parallel, it is desirable to keep the isolation distance as low as possible. This results, on the one hand, in optimum heat transport when implementing the teaching according to the invention. On the other hand, the height of the Multilayer board designed no larger than necessary. A particularly thin insulating layer between two vertically adjacent flat coils can be ensured in an advantageous embodiment of the invention in that layers of the multilayer board are mechanically connected to one another by a backcoat layer lying between said adjacent flat coils. This is advantageously on a prepreg layer for separating the vertically stacked individual boards, at the top and bottom of each at least one flat coil is applied dispensed. In particular, when the multilayer board according to the invention is to be used as a primary part of a linear motor, an embodiment of the invention is advantageous in which the first solenoid coil is penetrated perpendicular to the surface of the multilayer board by an iron core. If further solenoid coils are provided next to the first solenoid coil, it is advantageous to also pass through the other solenoid coils with iron cores.

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

1 shows a cross section through a multilayer board with a solenoid coil according to the prior art,

Figure 2 is a cross-section through an embodiment of the invention

Multi-layer board, in which a first solenoid coil can be seen,

3 shows a cross section through a further embodiment of the multilayer board according to the invention with two solenoid coils,

FIG. 4 shows a cross section through a further embodiment of the multilayer board according to the invention with a first solenoid coil and a passive printed conductor structure,

5 shows a cross section through a further embodiment of the multilayer board with the first solenoid coil according to FIG. 4 and the passive printed conductor structure, FIG. Figure 6 is a plan view of an embodiment of the invention

Multilayer board with six laterally adjacent solenoid coils and

Figure 7 is a schematic representation of a linear motor whose primary part in

Form of an embodiment of the multilayer board according to the invention is realized.

FIG. 1 shows a solenoid coil known from the prior art, referred to as

Multilayer board is formed. The multilayer board is made up of three stacked individual boards. Each of these three boards has both on the top of the board and on the underside of the single board a spiral flat coil 1 - 6. Thus, the top single board of the stack carries on its top a first flat coil 1, of which in the cross section 8 three turns can be seen , which are arranged laterally side by side. On the underside of this single board, which forms the uppermost level of the stack, there is a second flat coil 2 whose winding sense corresponds to that of the first flat coil 1.

Below this first plane, which is formed by the first individual board with the first flat coil 1 and the second flat coil 2, there is a second single board, on the upper side of a third flat coil 3 is applied and on the underside a fourth flat coil 4 is arranged , These flat coils 3, 4 correspond in their winding form the flat coils 1, 2 of the first level. Finally, located on the lowest level of the multilayer board another single board, on top of which a fifth flat coil 5 is arranged and on the underside of a sixth flat coil 6 is arranged. In the form of the winding, the fifth and sixth flat coils 5, 6 correspond to the flat coils 1, 2, 3, 4 arranged above them.

During the manufacturing process, the individual boards are first manufactured with their associated flat coils 1-6. Subsequently, insulating, not shown here prepreg layers are arranged between the various individual boards, are electrically isolated by the respective lower flat coils of a single board 2, 4 of the underlying upper flat coils 3, 5 of each arranged below individual board. The traces of the various pancake coils are typically copper and are located on a PCB substrate, such as FR4, which forms the respective single layer or single board. After the various substrates have been stacked separately by one or two sheets of prepreg material, the resulting stack is laminated to provide a mechanical bond between the substrates.

In order to form a solenoid coil from the different flat coils 1 - 6, the flat coils 1 - 6 still have to be electrically contacted with each other. This is usually done by electrical via, so-called VIAs, which are not shown in Figure 1.

The conductor track sections of the various turns of each flat coil 1 - 6 must be sufficiently far apart in the lateral direction to ensure electrical insulation between the individual turns. However, this electrical insulation gap must be overcome even in the removal of heat that arises in the inner turns of each flat coil 1 - 6 and can be dissipated at the edge of the multilayer board toward the surface. FIG. 1 shows, by way of example, the heat flow of the innermost turn of the third flat coil 3. In particular, if the cross section of each conductor track is to be chosen large in order to be able to conduct as high a current as possible, this results in a spacing of the conductor tracks in the lateral direction alone of the order of a few hundred microns. Thus, it can be seen that this electrical isolation distance represents an obstacle to the cooling of the multilayer board.

Figure 2 shows a cross section 8 through an embodiment of the multilayer board according to the invention. Again, the multilayer board forms a solenoid coil, which is formed by electrical interconnection of a total of six flat coils 1 - 6, which are arranged in vertically superimposed planes. Again, a first single layer carries on its upper side the first flat coil 1 and on the underside of the second flat coil 2. Both flat coils 1, 2 were applied to a PCB substrate before the formation of the multilayer stack. The same applies to the third flat coil 3 and the fourth flat coil 4, which were also applied to a PCB substrate prior to the fabrication of the overall stack. Likewise, the fifth flat coil 5 was applied to the top of a third single-layer board and the sixth flat coil 6 on the underside of this single board.

In contrast to the prior art illustrated in FIG. 1, however, in each case two flat coils 1 - 6 immediately adjacent in the vertical direction are arranged offset from each other in the lateral direction. In this way it is ensured that, for example, each conductor track section 26 of the second flat coil 2 is arranged vertically in partial overlap with two conductor track sections 7 of the first flat coil. Likewise, for example, the conductor track portion of the third flat coil 3, which represents the mean turn, arranged by two vertically above-lying conductor track portions of the second flat coil 2 in partial coverage. The drawn arrows visualize how the heat transfer from the inner turns of each flat coil 1 to 6 to the outer edge region of each flat coil 1 to 6 is improved by the lateral offset of the flat coils immediately adjacent in the vertical direction. By way of example, this is shown in FIG. 2 for the heat transport of the second and third flat coils 2, 3. Due to the sectional coverage area between two conductor track sections, which are adjacent in the vertical direction, only a significantly smaller distance has to be bridged by electrically and thus also heat-insulating material.

It can also be seen in FIG. 2 that the distance between the second flat coil 2 and the third flat coil 3 in the vertical direction is smaller than the distance between the first flat coil 1 and the second flat coil 2. Likewise, the distance between the fourth flat coil 4 and the fifth flat coil 5 is significantly smaller than the distance between the fifth flat coil 5 and the sixth flat coil 6. This is due to the underlying connection technology between the above-mentioned single layers. If only a very thin prepreg material or alternatively a pure baked enamel layer is used to connect the individual boards, the insulating connecting layer between the stacked individual boards can be selected to be smaller than the thickness of the substrate on which the Flat coils of each individual board are arranged. In this way, as far as the required electrical isolation distance permits, the heat conduction from the central inner portion of the solenoid coil to the outer portion of the solenoid coil can be further enhanced.

Figure 3 shows a cross section 8 of an embodiment of a multilayer board according to the present invention, in which on the multilayer board two

Solenoid coils are arranged laterally adjacent to each other. The first

Solenoid coil, which is arranged on the left in the cross section 8, comprises three vertically superimposed flat coils 1-6, which are each arranged laterally offset from one another in the manner already described in connection with FIG. Viewed laterally, the pancakes 1-6 of the first solenoid coil engage in a comb-like manner in a directly laterally adjacent second solenoid coil with pancakes 9-14. The engagement occurs in the area of the respective outer conductor sections 27, 15. As can be seen, the comb-like engagement ensures that in each case an outer conductor section 15 of the second solenoid coil with at least one outer conductor section 27 of the first solenoid coil is arranged vertically in partial overlap. This overlap enables heat transfer between the two solenoid coils involved in a particularly effective manner. As can be seen, only the relatively small vertical distance between two vertically adjacent outer conductor track sections of the two solenoid coils must be overcome in order to allow the lateral heat transfer. In this way, a multiplicity of solenoid coils can be arranged laterally side by side on a multilayer board and, in this case, an excellent heat transport in the lateral direction in the multilayer board can be ensured, which approaches the thermal behavior of a solid metal layer. FIG. 4 shows a further embodiment of a multilayer board according to the present invention in a cross section 8. In turn, six vertically stacked flat coils 1-6 of a first solenoid coil can be seen. The arrangement of the flat coils 1 - 6 essentially corresponds to the arrangement already in use. Samnnenhang was explained with Figure 2. In the left-hand area of the cross-section 8, a passive printed conductor structure 16 can be seen, which comb-like engages in the outer conductor track sections 27 of the first solenoid coil. This passive conductor track structure 16 excludes current flow, that is, it is galvanically isolated from all current-carrying elements of the multilayer board. The passive interconnect structure 16 has the task of transporting in the manner already described in the lateral direction through the multilayer board heat in a very effective manner vertically to one or both surfaces of the multilayer board. On one of these surfaces, a heat sink 18 is arranged by way of example, via which the heat is finally released to the environment. Of course, such a heat sink 18 may additionally be on the bottom of the illustrated multilayer board. In order to transport the heat in an optimal manner from the passive printed conductor structure 16 in the vertical direction in the direction of the heat sink 18, the passive printed conductor sections 16 are penetrated by thermally conductive VIAs 17. These may be, for example, bores which are subsequently filled with a thermally highly conductive metal. Since the interconnect structure 16 is not electrically effective, the short circuit caused by the thermally conductive VIAs of the individual interconnects of the passive interconnect structure 16 is harmless.

As can be seen in FIG. 4, the illustrated thermally conductive VIA 17 is in direct contact with the heat sink 18. This results in a nearly ideal heat conduction behavior between the passive printed conductor structure 16 and the heat sink 18. However, should the solenoid coil be at a higher voltage can be acted upon, it may be that the insulation distance between the outer conductor portions 27 of the solenoid coil and the passive interconnect structure 16 is not sufficient to ensure sufficient contact protection. For high voltage applications, therefore, a further advantageous embodiment of the invention, which is shown in Figure 5 is recommended. As an example, it is called an application in a converter with direct voltage intermediate circuit and an intermediate circuit voltage of 750 V. The structure corresponds essentially to the cross-section 8 already shown in Figure 4, but now an insulating prepreg layer 19 has been applied between the heat sink 18, the conductor tracks of the uppermost first flat coil 1 and the thermal VIA 17. Likewise, such an insulating layer 19 is located on the underside of the board, to which optionally also another, not shown here, heat sink can be located. The prepreg layer is selected to be thin enough so as not to obstruct the heat transfer from the thermally conductive VIA 17 to the heat sink 18. At the same time, however, it is so thick that sufficient contact protection for the multilayer board is ensured. By the prepreg 19 on both surfaces of

Multilayer board results in a perfectly smooth surface of the board.

Figure 6 shows an embodiment of the multilayer board according to the invention in a plan view. The multilayer board serves as the primary part 22 of a linear motor. In addition to a first solenoid coil 20 and a second solenoid coil 21, four further identical solenoid coils are located laterally next to the already mentioned coils. Each individual solenoid coil is constructed such that it has the lateral offset of the adjacent flat coils according to the invention viewed in the vertical direction. Furthermore, the outermost trace portions of each grip

Solenoid coil comb-like in the outermost trace portions of the immediately laterally adjacent solenoid coil, wherein this engagement is realized in the manner shown in Figure 3. As a result, a thermal conductivity within the multilayer board between the individual solenoid coils is ensured in the lateral direction, which comes close to that of a solid metal plate. Figure 7 shows schematically a linear motor with a primary part 22, which may be constructed as shown in Figure 6 as a multilayer board. Such a primary part 22 is very compact and lightweight, so that it is particularly well suited for highly dynamic applications. This primary part 22 is in an electromagnetic interaction with a secondary part 23. The secondary part comprises permanent magnets 24 which are embedded in a soft iron bed. Primary part 22 and secondary part 23 are spaced apart by an air gap 25. By means of suitable energization of the solenoid coils present in the primary part 27, a translationally highly dynamic movement of the primary part 22 can be realized. LIST OF REFERENCES

1 first flat coil

2 second flat coil

3 third flat coil

4 fourth flat coil

5 fifth flat coil

6 sixth flat coil

7, 26 trace sections

8 cross section

9 - 14 flat coils of the second solenoid coil

15 outer trace portions of the second solenoid coil

16 passive conductor track structure

17 thermally conductive VIAs

18 heat sinks

19 insulating cover layer

20 first solenoid coil

21 second solenoid coil

22 primary part

23 secondary part

24 permanent magnets

25 air gap

Claims

claims

1 . Mulilayer board with vertically superimposed flat coils (1 -6), which are connected to form a first solenoid coil (20) electrically in series or in parallel, characterized in that each two vertically adjacent flat coils (1, 2) are arranged laterally offset from one another in that, in a cross-section (8) perpendicular to the surface of the multilayer board, conductor track sections (26) of one flat coil (2) are arranged vertically in partial overlap with two conductor track sections (7) of the other flat coil (1).

2. Mulilayer board according to claim 1, wherein the multilayer board has at least one second solenoid coil (21) which is arranged laterally offset from the first solenoid coil (20), said outer conductor sections (15) of flat coils (9-14) of second solenoid coil (21) comb-like in outer trace portions (27) of the flat coils (1-6) of the first solenoid coil (20) engage, so that in said cross-section (7) in each case an outer conductor track portion (15) of the second

Solenoid coil (21) with at least one outer conductor portion (14) of the first solenoid coil (20) is arranged vertically in partial overlap.

3. Mulilayer board according to one of the preceding claims, wherein the multilayer board has a passive printed conductor structure (16), which is galvanically isolated from all current-carrying conductor tracks of the multilayer board, laterally offset from the first solenoid coil (20) and comb-like in the outer conductor portions (27) of the flat coils (1-6) of the first solenoid coil (20) engages.

4. Mulilayer board according to claim 3 with thermal conductive VIAs (17), which penetrate the passive interconnect structure (16) vertically.

5. Mulilayer board according to claim 4, wherein the thermally conductive VIAs (17) with a arranged on a surface of the multilayer board heat sink (18) are in contact.

6. Mulilayer board according to claim 4, wherein the multilayer board has an insulating cover layer (19), which covers at least one near-surface flat coil (1, 9) and the thermal VIAs (17).

7. Mulilayer board according to one of the preceding claims, wherein planes of the multilayer board are mechanically connected to each other by a lying between adjacent flat coils baking enamel layer.

8. Mulilayer board according to one of the preceding claims, wherein the first

Solenoid coil (20) perpendicular to the surface of the Mulilayer board is interspersed by an iron core.

9. linear motor having a primary part (22) which is formed as a multilayer board according to one of the preceding claims, and a secondary part (23) with permanent magnets (24) which is spaced via an air gap (25) from the primary part (22).

10. A method for producing a solenoid coil on a multilayer board, in which flat coils (1 -5) are arranged vertically one above the other in different planes of the multilayer board and connected in series or in parallel via electrical feedthroughs,

characterized in that each two vertically adjacent flat coils (1, 2) are arranged laterally offset from each other so that in a cross section (8) perpendicular to the surface of the multilayer board conductor track sections (26) of a flat coil (2) vertically in partial coverage with two conductor track sections (7) of the other flat coil (1) are arranged.