WO2005069318A1

WO2005069318A1 - Magnetic element

Info

Publication number: WO2005069318A1
Application number: PCT/CH2004/000011
Authority: WO
Inventors: Jürgen MATERNE
Original assignee: Delta Energy Systems (Switzerland) Ag
Priority date: 2004-01-13
Filing date: 2004-01-13
Publication date: 2005-07-28

Abstract

A coil of a high current magnetic element (1) with a magnetic core (5) that is mounted on a substrate (2) is formed by pieces of thick U-shaped wires (7.1 - 7.8) that are fitted over the magnetic core (5) and into corresponding holes (6) in the substrate (2) and interconnected in the required manner by grooves (9.1 - 9.10) on the lower surface of the substrate that are plated with copper and filled with solder. In this manner, the manufacturing of high current magnetic elements where thick wires have to be wound around the core can be realised with a high degree of automation that is without the need to manually wind a thick wire around the magnetic core.

Description

Magnetic element

Technical Field

The invention relates to a magnetic element with a magnetic core and a coil wound around said magnetic core, where said coil includes a first section formed by a wire. The invention further relates to a method for forming such a magnetic element and an electric and/or electronic circuit, particularly a filter circuit, with such a magnetic element. Background Art

In many electric and/or electronic devices magnetic elements such as for example inductors, transformers or chokes are used. Thousands of different applications exist. Some of them, for example current or voltage converters for high power applications or specific filter devices require magnetic elements that are able to conduct high currents. In such applications not only the electric and/or electronic components are designed for high currents but also the electric conductors have to have a large cross sectional area in order to conduct these high currents without suffering any damages.

This is particularly true for high current devices that comprise a magnetic element with a magnetic core where a wire coil is wound around the core. Since it is difficult or even impossible to automate the process of winding a thick wire around a core, such magnetic elements have to be hand-crafted. Hence, the manufacturing of these devices is rather laborious, that is painstaking, time-consuming and expensive.

Summary of the invention

It is an object of the invention to create a magnetic element pertaining to the technical field initially mentioned, that enables a manufacturing with a higher degree of automation that is with reduced manufacturing costs.

The solution of the invention is specified by the features of claim 1. According to the invention, in a magnetic element that includes a magnetic core and a coil that is wound around said magnetic core, the coil includes a first and a second section. The first section of the coil is formed by a wire. The second section of the coil is formed by a groove on a substrate that is filled with solder.

It is understood that the coil may include any reasonable number of turns wound around the core. It may for example include exactly one turn or a fraction of a turn. It may also include a multiple of a turn or a multiple of a fraction of a turn. It is further understood that the coil may include more than one first and/or more than one second section. Typically, the coil includes first and second sections alternately. It is also understood that the magnetic element may include further coils that may or may not be designed according to the invention.

It does not matter on which surface of the substrate the groove is provided. That is whether it is on the same or the opposite side of the substrate as the wire. A magnetic element with a coil according to the invention can be manufactured without the need to wind a wire manually around the core. That is because each single turn of the coil can be composed of one or more wire sections and one or more groove sections on the substrate where the groove sections on the substrate can be manufactured automatically during the manufacturing of the substrate and the wire section can be realised automatically during the assembling process of the magnetic element. During this assembling process the wire sections, which for example are U-shaped pieces of wire, are fitted over the magnetic core and electrically conductively connected to the solder in the grooves so as to form the coil.

Another advantage of the invention is the fact that the mechanical stability of the substrate and hence also of the circuit implemented on the substrate is increased by the hardened solder provided in the groove.

It is in each case difficult to wind a thick wire around a magnetic core, independent of the specific shape of the magnetic core. However, if the core has a ring like shape, that is a shape with a hole, it is particularly difficult to produce thick wire coils around the core, because for each turn of the coil the wire has to be fed through the hole with its entire length. In these cases, the potential to simplify the manufacturing process and to reduce the manufacturing costs is rather great. So the core of the magnetic element preferably has a ring like shape.

As already lined out, different magnetic elements such as inductors, transformers, filters or other magnetic elements can be implemented. In a preferred embodiment of the invention, the magnetic element is a choke, for example a filter choke. The term high current as used throughout the description, means, unlike otherwise mentioned, a current in the range of a couple of amperes to some dozens or even some hundreds of amperes.

It is clear that magnetic elements according to the invention can also be manufactured with thin wires. However, since it is harder to wind thick wires around a coil than thin wires, it is preferred to manufacture magnetic elements where thick wires have to be used to fulfil the given requirements. These requirements, for example the required cross sectional area of the wire that forms the first section or sections of the coil, depends on the particular application. Generally, it can be said that the higher the current to conduct, the larger the cross sectional area of the wire has to be. Therefore, in an advantageous embodiment of the invention wires with a cross sectional area larger than 1.5 mm² (square millimetres) are used to realise the coil of the magnetic element. It is even more preferred that the cross sectional area of the wire is between 3 mm² and 9 mm².

In this connection it is to mention that, although in most cases wires with a round cross section are used, the shape of the wire's cross section does not matter in principle.

It is further to mention that the electrical requirements also depend on the material of the magnetic core and/or other properties of the electric and/or electronic circuit to implement.

The cross sectional area of the groove that is filled with solder also depends on the particular application and should approximately match the cross sectional area of the wire.

Hence, the width of the grooves is preferably between 0.5 mm and 3 mm and more particularly between 1 mm and 1.5 mm. The depth of the grooves and with it the cross sectional area of the solder that finally fills the groove is chosen to meet the requirements of the specific application. Here it is to mention that the maximum depth of the groove is limited by the thickness of the substrate.

Because it is simple to produce, a groove with a rectangular cross section is preferred. However, other shapes such as for example V-shapes, circular, semicircular or other shapes of the groove are possible as well. As mentioned above, the depth of the grooves can be freely chosen between very small and the thickness of the substrate. That is a groove may either reach from the upper surface of the substrate to the lower surface of the substrate or it may - following the definition of a blind hole - be a blind groove, which means that its depth is smaller than the thickness of the substrate. Because a blind groove less affects the mechanical stability of the substrate, such grooves are preferred.

Another object of the invention is to create a method for forming a magnetic element pertaining to the technical field initially mentioned, that is possible to carry out with a higher degree of automation.

This object is achieved by a method as specified by the features of claim 7. According to the invention, the method for forming a magnetic element with a magnetic core and a coil wound around said magnetic core includes the steps of providing a groove on a substrate, filling this groove with solder, connecting said solder electrically conductively to a wire and winding said wire at least partially around the magnetic core such that the wire forms a first section of the coil and the solder filled groove forms a second section of the coil.

All of these steps can be automated to a high degree which lowers the costs for the manufacturing of such magnetic elements significantly.

The electric and/or electronic circuit that includes the magnetic element may also include further mechanical, electric, electronic or other components which may or may not have any electrical connections to other components. During the soldering process, not only the groove is filled with solder, but also other components that are possibly present may be soldered to the substrate or otherwise interconnected. For example the wire pieces that form the first sections of the coil may be soldered to the substrate during the soldering process.

In a preferred embodiment, the groove is plated, particularly with copper, before it is filled with solder during the soldering process. This plating process can also be automated. Typically, such a plating process is also a part of existing manufacturing processes of printed circuit boards. During the plating process, all areas of a printed circuit board (or a substrate) that have to be covered with solder, are plated.

During the plating process, not only the grooves are plated, but also other parts of the substrate that need to have a layer of conductive material on the surface. For example the inner walls of a hole, a small area around each hole on the surface of the substrate or other areas that serve to establish electrical contacts to other circuits.

In order to form the coil, the solder in the groove and the wire have to be electrically conductively connected. This is preferably done by providing a hole in the substrate at an end region of the groove and fitting said wire into said hole. During the soldering process the groove and the hole is filled with solder such that the solder in the groove is electrically conductively connected to the solder in the hole and such that the wire is soldered into the hole.

It would also be possible to connect the wire to the solder in the groove in any other suitable way such as for example to directly solder the wire into the groove or to provide an extra wire that interconnects the groove and the wire. However, in the first case it is more difficult to fix the wire on the substrate previous to the soldering process and in the second case an increased effort is required to produce the magnetic element.

During the manufacturing process of the magnetic element, the magnetic core has to be positioned on the substrate. This is typically done after the grooves are provided on the substrate and the plating of the substrate but before the wire pieces are fitted into the holes on the substrate and the soldering process. It is preferably done such that the wire and the solder in the groove that are electrically conductively connected during the following soldering process, form the coil that is wound around the magnetic core.

The manufacturing of a magnetic element according to the invention and/or an electric and/or electronic circuit with such a magnetic element may also include additional steps like for example the producing of the substrate, testing and cleaning.

It is a further object of the invention to create an electric and/or electronic circuit, particularly a filter circuit, with a magnetic element as described above. This object is achieved by the electric and/or electronic circuit as specified by the features of claim 1 1. According to the invention, such an electric and/or electronic circuit can be implemented by electrically conductively connecting a magnetic element as described above to any number of other electric and/or electronic components in any suitable way so as to form the desired circuit. For example, the invention is particularly suited for forming a filter circuit for high current applications.

Other advantageous embodiments and combinations of features come out from the detailed description below and the totality of the claims.

Brief description of the drawings

The drawings used to explain the embodiments show:

Fig. 1 A perspective view of a magnetic element according to the invention;

Fig. 2a a top view of the magnetic element shown in fig. 1 ;

Fig. 2b a bottom view of the magnetic element shown in fig. 1 ;

Fig. 3 a series of different types of grooves;

Fig. 4 a detailed view of grooves filled with solder;

Fig. 5 a magnetic core for a magnetic element according to the invention;

Fig. 6 another magnetic core for a magnetic element according to the invention;

Fig. 7 a further magnetic core for a magnetic element according to the invention;

Fig. 8 a cross section of a magnetic core for a magnetic element according to the invention;

Fig. 9 a cross section of another magnetic core for a magnetic element according to the invention; Fig. 10 a cross section of a further magnetic core for a magnetic element according to the invention;

Fig. 1 1 a cross section of a further magnetic core for a magnetic element according to the invention;

Fig. 12 an electric and/or electronic circuit with a magnetic element according to the invention;

Fig. 13 a perspective view of a further embodiment of a magnetic element according to the invention and

Fig. 14 a bottom view of the magnetic element of fig. 13.

In the figures, the same components are given the same reference symbols.

Preferred embodiments

Figures 1 and 2 show a magnetic element 1 according to the invention. The magnetic element 1 includes a magnetic core 5 with a wheel like shape. The magnetic core 5 is arranged substantially parallel on the upper surface 3 of a substrate 2. On one edge of the substrate 2, four contact links 8 are provided in order to electrically connect the magnetic element to an external electrical circuit.

The substrate 2 has a plurality of through holes 6 from its upper surface 3 to its lower surface 4. The magnetic element further includes a plurality of pieces of wire 7.1, 7.2, 7.3, 7.4, 7.5, 7.6, 7.7, 7.8 that are formed such that each piece has a U-like shape. Each piece of wire 7.1 , ..., 7.8 is fitted over the magnetic core 5 and each end of a wire is fitted into a hole 6 and soldered into that hole 6 so as to electrically connect two holes 6.

On its lower surface 4, the substrate 2 has a plurality of grooves 9.1 , 9.2, 9.3, 9.4, 9.5, 9.6, 9.7, 9.8, 9.9, 9.10 that are filled with solder. Each groove leads from a hole 6 to another hole 6 or from a hole 6 to a contact link 8 to produce an electrical connection between them. The wires 7.1, ..., 7.8 and the grooves 9.1, ..., 9.10 are arranged on the substrate 2 in order to produce an electrical connection between two contact links 8. In the example shown, the grooves and wires are arranged such that two coils are formed that are wound around the magnetic core 5. The first coil is produced by groove 9.1, wire 7.1, groove 9.2, wire 7.2, groove 9.3, wire 7.3, groove 9.4, wire 7.4 and groove 9.10. The second coil is produced by groove 9.5, wire 7.5, groove 9.6, wire 7.6, groove 9.7, wire 7.7, groove 9.8, wire 7.8 and groove 9.9.

In this manner, only one coil or any number of coils each with any required number of turns can be realised. In the case where two or more coils are realised, the grooves and wires can be chosen such that all coils have the same direction of rotation or such that some coils have the same and the other coil or the other coils have the opposite direction of rotation.

The substrate 2 itself is a substrate as known in the art. It is made by any suitable base material such as for example Polyimide or FR4 with a thickness in the range of some tenth of a millimetre to some millimetres or even centimetres. Single or double side substrates can be used as well as multilayer substrates. The necessary grooves can either be realised all on the same side of the substrate or the grooves can be provided on both sides of the substrate. In order to increase the current carrying capacity it is also possible to realise an electrical connection between two holes 6 or a hole 6 and a contact link 8 by more than one groove 9.

In other embodiments of the invention blind holes could be used instead of through holes. In this case, the ends of the wires 7 would be fitted into the blind holes and soldered therein.

Figure 3 shows different examples of groove shapes that can be used for implementation of a magnetic element according to the invention. Particularly, fig. 3 shows a straight groove 10.1 that is deep and narrow, a straight groove 10.2 that is fine and broad, a V- groove 10.3, a round-nose groove 10.4, a groove 10.5 with a substantially circular cross section, a groove 10.6 with a ridged face, a dovetail groove 10.8 and a groove 10.7 that totally cuts through the substrate 2. The shape of the grooves cross section can be chosen in any suitable way. There are several criteria that depend on the shape of the groove. For example the mechanical stability or the surface area of the hardened solder in the groove.

In figure 4, three straight grooves 10.1 1, 10.12, 10.13 are shown, each being plated, that is each having a thin copper layer 1 1 on the surfaces of the grooves 10.1 1 , 10.12, 10.13. The plating is done with any suitable process as known in the art. The layer thickness of the copper layer 1 1 is in the range from some micrometres to some dozens or even some hundreds of micrometres.

The cross sectional area of the solder within the grooves 10.1 1 , 10.12, 10.13 and with it the current carrying capacity of the magnetic element can be controlled by the amount of solder 12 that is inserted. Only a small amount of solder 12 is inserted into the groove 10.1 1. An increased amount of solder 12 is inserted into the groove 10.12. And an even further increased amount of solder 12 is inserted into the groove 10.13 where the copper layer 1 1 also covers a part of the upper surface of the substrate 2 in the vicinity of the groove 10.13.

However, the amount of solder 12 in a groove also depends on the particular soldering process used in the manufacturing process of the magnetic element. Any known soldering process such as for example reflow-soldering or wave-soldering can be applied and any known type of solder such as for example different alloys of tin, lead, silver, antimony or other materials can be used in combination with any suitable type of flux.

It is understood that the spaces between the substrate 2 and the copper layer 1 1 and between the copper layer 1 1 and the solder 12 is only shown for reasons of simplicity. In fact there exists a tight connection between the substrate 2 and the copper layer 1 1 and between the copper layer 1 1 and the solder 12.

Figures 5, 6 and 7 show different types of magnetic cores 5.1, 5.2, 5.3 that may be used to manufacture a magnetic element according to the invention. Figures 5 and 6 show for example ring-shaped magnetic cores 5.1 , 5.2 that include an opening around which the magnetic flux may circulate. The magnetic core 5.1 has a circular shape with a circular opening and the magnetic core 5.2 has a rectangular shape with a rectangular opening. Fig. 7 shows a rod-like magnetic core 5.3 without an opening. However, as previously outlined, the invention is advantageously applied in the manufacturing of magnetic elements where a coil has to be wound around a ring-shaped magnetic core.

The magnetic cores may also have different cross sections such as shown in figures 8 to 1 1 together with a corresponding shape of a wire that may be used to realise a coil. Figure 8 shows a magnetic core 5.1 1 having a square cross section. The corresponding wire 7.1 1 also has a substantially square shape. Figure 9 shows a magnetic core 5.12 having a rectangular cross section and a corresponding wire 7.12. Figure 10 shows a magnetic core 5.13 having a circular cross section and a corresponding wire 7.13. And finally, Figure 1 1 shows a magnetic core 5.14 having an elliptical cross section and a corresponding wire 7.14.

In figure 12, an application of the invention, a high current filter circuit 20 is shown. The filter circuit 20 includes a printed circuit board 23 that is fitted with a plurality of components 21 such as for example mechanical, electric and/or electronic components. The components 21 are mounted on the substrate 2 by means of legs 22 soldered into corresponding holes. The components could as well be mounted on the substrate 2 by other mounting techniques such as surface mounting or other known mounting methods. The filter circuit 20 further includes two magnetic elements 1 according to the invention as shown in figure 1. The magnetic elements are mechanically fixed to the printed circuit board 23 by means of the contact links 8 that are fitted into corresponding recesses within the printed circuit board 23. The necessary electrical connections between the magnetic elements 1 and the printed circuit board 23 are also established via the contact links 8.

A further embodiment of a magnetic element 1.1 according to the invention is shown in figures 13 and 14 which show a perspective view and a bottom view respectively. In this embodiment the magnetic core 5 does not lie on the substrate 2 but it stands on it and only a single coil is realised with the wires 7 and the solder filled grooves 9.

In summary, it is to be noted that each single step of the manufacturing process of a magnetic element according to the invention, that is the producing of the grooves, the plating of the grooves, the equipping of the substrate with the magnetic core, the wires and possibly other components as well as the soldering can be automated. Except for the producing of the grooves and the filling of the grooves with solder, all other steps listed are known in the art of manufacturing a printed circuit board. In this manner, a high degree of automation is achievable wherefore the costs for producing such circuit can be kept low.

It is further to note that in comparison with a conventional trace on the surface of a substrate, the invention allows for a higher current carrying capacity. First this capacity is increased because the cross sectional area of the copper plating is increased. This is because the surface area of a groove of a certain width is substantially higher than the surface area of a flat trace of the same width. Second, the current carrying capacity is further increased because of the solder that fills the groove. Furthermore, the solder, when it is hardened, has the effect that the mechanical stability of the substrate can be improved.

Claims

1. Magnetic element (1) with a magnetic core (5) and a coil wound around said magnetic core, where said coil includes a first section formed by a wire (7.1-7.8), characterised in that said coil includes a second section formed by a groove (9.1 -9.10) on a substrate (2) filled with solder.

2. Magnetic element according to claim 1 , characterised in that said magnetic core has a ring like shape.

3. Magnetic element according to claim 1 or 2, characterised in that said magnetic element is a choke.

4. Magnetic element according to any of claims 1 to 3, characterised in that said wire has a cross sectional area larger than 1.5 mm², particularly between 3 mm² and 9 mm².

5. Magnetic element according to any of claims 1 to 4, characterised in that said groove has a width in a range of 0.5 mm to 3 mm, particularly in a range of 1 mm to 1.5 mm.

6. Magnetic element according to any of claims 1 to 5, characterised in that said groove is a blind groove.

7. Method for forming a magnetic element (1) with a magnetic core (5) and a coil wound around said magnetic core, characterised in that a groove (9.1 -9.10) is provided on a substrate (2), said groove is filled with solder, said solder is electrically conductively connected to a wire (7.1-7.8) and said wire is at least partially wound around said magnetic core such that said wire forms a first section of said coil and said groove filled with solder forms a second section of said coil.

8. Method according to claim 7, characterised in that said groove is plated before it is filled with solder, where the groove is particularly plated with copper.

9. Method according to claim 7 or 8, characterised in that said solder is connected to said wire by providing a hole in the substrate at an end region of the groove and soldering said wire into said hole.

10. Method according to any of claims 7 to 9, characterised in that said core is positioned on said substrate such that said wire and said solder in said groove form said coil.

1 1. Electric and/or electronic circuit (20), particularly a filter circuit, with a magnetic element (1) that includes a magnetic core (5) and a coil wound around said magnetic core, where said coil includes a first section formed by a wire (7.1-7.8), characterised in that said coil includes a second section formed by a groove (9.1-9.10) on a substrate (2) filled with solder.