Improved manufacturing method for a ferrite circulator integrated into a multilayer board and associated multilayer board

Abstract

Improved manufacturing process for a ferrite circulator integrated into a multilayer board and associated multilayer board. This process comprises the steps of: preparing (210) magnets (12) and ferrites (10); gluing (220) the ferrites onto a first conductive layer (22); preparing (230) a first laminate (30) having, on one face, blind holes (38) and, on an opposite face, a second conductive layer (34); encapsulating (240) the ferrites in the first laminate, each ferrite being received in a blind hole; etching (250) the first conductive layer to form gyromagnetic cells (52), each cell being aligned with a ferrite; gluing the magnets, each magnet being aligned with a ferrite; preparing a second laminate having, on one face, blind holes and, on an opposite face, a third conductive layer; encapsulating the magnets in the second laminate; and finalize the component. Figure for the abbreviation: Figure 1

Description

Title of the invention: Improved manufacturing method of a ferrite circulator integrated in a multilayer board and associated multilayer board

[0001] The general field of the present invention is that of network antennas, which are antennas consisting of the assembly of a plurality of elementary antennas.

[0002] More specifically, the present invention relates to a method of integrating a ferrite circulator into a laminated component comprising a stack of conductive and insulating layers, said component being able to advantageously offer other functionalities, in particular that of a radiating element of an elementary antenna.

[0003] Document US 6611 180 B1 discloses a method for manufacturing a laminated component incorporating a ferrite circulator. This method involves preparing a circulator board, a conductive layer of which has been etched to create a plurality of patterns called gyromagnetic cells (also called "Y" tracks in this document, since their geometry is reminiscent of that of a "Y"). This method also involves preparing a plurality of elements, each element resulting from the bonding of a magnet to a ferrite disc, preparing a support board, one face of which has a plurality of recesses, and force-fitting each magnet / ferrite disc element into a corresponding recess to obtain an assembly. Finally, this method involves stacking this assembly on the circulator board, so that each magnet / disc element is arranged opposite a "Y" track to form a ferrite circulator.Finally, a hot pressing and gluing step makes it possible to obtain a multilayer circuit integrating a ferrite circulator.

[0004] This method of the state of the art has various drawbacks. The first drawback lies in the fact that it does not guarantee good electrical continuity between a gyromagnetic cell and the ferrite disc of the associated magnet / disc element. Indeed, there is a high risk that a residual gap will remain around the gyromagnetic cell, in particular between the gyromagnetic cell and the ferrite disc, leading to a reduction in performance, or even a significant disturbance of the gyromagnetic effect (effect on which the operation of a ferrite circulator is based).

[0005] Indeed, the manufacturing uncertainty regarding the thickness of a ferrite disc, as well as the manufacturing uncertainty regarding the depth of the recess receiving this ferrite disc in the support card, mean that the transverse face of the ferrite disc opposite the gyromagnetic cell can be located away from the latter and not in direct contact with the latter.

[0006] The second drawback associated with the manufacturing method of the prior art is linked to the mechanical tolerances in the XY plane, of the different proposed production stages.

[0007] The positioning of the ferrites by inserting them by force into recesses made by machining in an organic layer of the support card induces a first risk of decentering with the rest of the circulator (i.e. with the gyromagnetic cell) linked to the XY tolerance of these recesses.

[0008] Stacking the assembly on the circulator board induces a second risk of decentering in the XY plane, because it is necessary to align the assembly carrying the magnet / ferrite disc elements with the circulator board carrying the gyromagnetic cells:

[0009] this operation is generally carried out by the use of matching pins, the positioning of which is carried out by drilling holes which also have positioning inaccuracies in the XY plane.

[0010] Finally, pressing and gluing the assembly onto the circulator board introduces a third risk of misalignment in the XY plane. Despite the presence of the matching pins, the materials expand differently from each other, which degrades the quality of the stack.

[0011] However, it is necessary to have very good alignment of the components for optimal operation of the circulator thus manufactured.

[0012] Consequently, the manufacturing method of the prior art does not guarantee obtaining high-performance circulators, i.e. exhibiting the gyromagnetic effect in a given frequency band, low losses and maximum isolation between channels.

[0013] The aim of the present invention is to solve these problems.

[0014] For this purpose, the invention relates to a method for manufacturing a component consisting of a multilayer printed circuit board integrating a ferrite circulator, the method comprising the steps of: preparing a plurality of magnets and a plurality of ferrite discs; bonding the plurality of ferrite discs on the surface of a first conductive layer; preparing a first laminate having, on one face, blind holes and, on an opposite face, a second conductive layer; encapsulating the ferrite discs in the first laminate, each ferrite disc being received in a corresponding blind hole; etching the first conductive layer to form therein a plurality of gyromagnetic cells, each gyromagnetic cell being located in line with a corresponding ferrite disc; bonding the plurality of magnets, each magnet being placed in line with a corresponding ferrite disc;preparing a second laminate, the second laminate having, on one side, blind holes and, on an opposite side, a third conductive layer; encapsulating the plurality of magnets in the second laminate; and finalizing the component.;

[0015] According to particular embodiments, the manufacturing method comprises a or more of the following characteristics, taken individually or in all technically possible combinations:

[0016] - encapsulating consists of pressing and polymerizing the prepared laminate;

[0017] - a laminate comprises a second continuous prepreg layer interposed between each ferrite disc and the second conductive layer and between each magnet and the third conductive layer;

[0018] - a laminate comprises a plastic layer having a permittivity di electrical greater than 6;

[0019] - the first conductive layer is thinned before etching a plurality of gyromagnetic cells;

[0020] - metallized vias are made to establish electrical continuity between the second conductive layer and each ferrite disc, the plurality of magnets being bonded to the second conductive layer;

[0021] - the magnets being first magnets, the method further comprises the steps comprising: preparing a plurality of second magnetic elements; bonding the plurality of second magnetic elements, each magnetic element being placed in line with a corresponding ferrite disc, such that the corresponding ferrite disc is between a first magnet and a second magnetic element; preparing a third laminate, the third laminate having, on one face, blind holes and, on an opposite face, a fourth conductive layer; and encapsulating the second magnetic elements in the third laminate; steps for integrating into the multilayer printed circuit board a radiating element functionality, the radiating element being connected by a metallized via to one end of a corresponding gyromagnetic cell; each ferrite disc is made of a ferrite ceramic whose transverse faces are covered with a conductive film;the bonding of the plurality of ferrite discs, the plurality of first magnets and / or second magnetic elements uses a robotic arm in order to obtain precise positioning relative to a reference mark; a final step of cutting the multilayer printed circuit board to obtain a plurality of elementary components; and a multilayer printed circuit board resulting from the implementation of a manufacturing method.;

[0022] The invention also relates to an integrated ferrite circulator resulting from the implementation of the preceding manufacturing method.

[0023] The invention and its advantages will be better understood on reading the detailed description which follows of a particular embodiment, given solely by way of non-limiting example, this description being made with reference to the appended drawings in which:

[0024] [Fig.l][Fig.2][Fig.3] The drawings schematically represent the three parts of a figure illustrating a preferred embodiment of the manufacturing method according to the invention, each step of the method, shown on the left of the figure, leading to a component, shown in section on the right of the figure. General information

[0025] According to the invention, each ferrite disc is first fixed precisely (in position and in electrical continuity) on the conductive layer carrying the gyromagnetic patterns or “Y” tracks, before being encapsulated in a multilayer laminate adapted so as to guarantee perfect dimensional control of the manufactured magnetic structure, in particular of the continuity between the ferrite and the conductive track and the ferrite / gyromagnetic cell / magnet alignment, and, consequently, the characteristics of the manufactured circulator.

[0026] Preferred embodiment of the manufacturing method

[0027] A particular embodiment of the manufacturing method 200 will be presented with reference to the first, second and third parts of the attached figure.

[0028] Step 210

[0029] Step 210 consists of preparing a plurality of N ferrite discs 10 as well as a plurality of N first magnets 12 and N second magnets 14.

[0030] Each ferrite disc 10 is made up of a cylindrical ferrite ceramic 15, the transverse faces of which are respectively covered with conductive films, for example gold, referenced 16 and 17 in the figure.

[0031] Ferrite ceramics are produced by ceramic sintering processes and sorted after manufacture, to guarantee controlled dimensional tolerances.

[0032] Similarly, the magnets are sorted after manufacture, to guarantee the required dimensional tolerances.

[0033] Step 220

[0034] Step 220 consists of gluing the plurality of ferrite discs 10 on the surface of a first conductive layer 22 in order to obtain a component 20.

[0035] The first layer 22 is preferably made of copper.

[0036] The first layer 22 is rigid. More precisely, it has a sufficient thickness to give it rigidity preventing any deformation during the implementation of the bonding step 220.

[0037] If it is made of copper, the first conductive layer 22 typically has a thickness between 35 and 75 μm.

[0038] The face of the first conductive layer 22 to receive the ferrite discs 10 is covered with a suitable conductive glue.

[0039] For the implantation of the ferrite discs 10, a pick and place machine is used. Such a machine has a robotic arm that can be programmed to transfer a ferrite disc from a storage area to a predefined location on the first conductive layer 22, with very high precision and repeatability.

[0040] Each ferrite disc 10 is thus placed in a precise position relative to a reference mark linked to the component.

[0041] Furthermore, electrical continuity is established with certainty between the first conductive layer 22 and the ferrite ceramic 15. There is no residual gap between the facing surfaces that could degrade the gyromagnetic effect on which the operation of a ferrite circulator is based.

[0042] Step 230

[0043] Step 230 consists of preparing the constituents of a first laminate 30 intended to encapsulate the ferrite discs 10 of the component 20.

[0044] The first laminate 30 is for example a single-sided laminate consisting of a stack of layers successively comprising: a first layer of prepreg 31, a layer of plastic 32, a second layer of prepreg 33 and an external layer of copper (advantageously supported by a layer of plastic), called the second conductive layer 34.

[0045] Prepregs comprise a fibrous reinforcement (glass fiber) mixed with a thermosetting polymer in a metastable (pre-crosslinked) state.

[0046] The plastic from which the first plastic layer 32 is made is selected to have a maximum dielectric permittivity (typically greater than 6), so as to be able to produce the most compact controlled impedance interconnections possible.

[0047] The face of the first laminate 30 opposite the second conductive layer 34 has a plurality of blind holes 38. Each blind hole is intended to receive a ferrite disc 10. A blind hole 38 passes through the first pre-preg layer 31 and the first plastic layer 32, but not the second pre-preg layer 33, nor the second conductive layer 34.

[0048] The diameter of each blind hole 38 is larger than the nominal diameter of a ferrite disc 10 so as to contain the ferrite discs without being in contact with them, with minimum intervals, to compensate for any dispersion on this dimension during the manufacture of the ferrite discs 10, as well as on the positioning of each ferrite relative to each blind hole 38.

[0049] Step 240

[0050] Step 240 is the actual encapsulation step leading to component 40. The first laminate 30 is approached from above the first conductive layer 22 carrying the ferrite discs 10 so as to house each of them in a corresponding blind hole.

[0051] Then, a pressing operation under vacuum and at high temperature (typically at around 200°C) causing the polymerization of the layers 31 and 33 is carried out to ensure the setting of the first laminate 30, its bonding to the first conductive layer 22 and to the upper face of each ferrite disc 10.

[0052] A homogeneous insulating layer 42 is thus produced.

[0053] It should be noted that the pressing makes it possible to force the polymer of the first and second pre-impregnated layers, 31 and 33, into the lateral gaps existing between a ferrite disc 10 and the blind hole 38 receiving it. Thus, the ferrite ceramic 15 is in contact over its entire lateral face with the material of the insulating layer 42.

[0054] The presence of the second pre-impregnated layer 33, which is a continuous layer, makes it possible to compensate for any manufacturing dispersion over the thickness of the ferrite discs 10. Thus, the distance between the first and second conductive layers, 22 and 34, is controlled.

[0055] Step 250

[0056] After turning the component over so that the first layer 22 is accessible from above, step 250 consists of working the first conductive layer 22 so as to obtain an intermediate component 50.

[0057] The first conductive layer 22 is optionally thinned to reduce its thickness to less than 40 μm, i.e. to a thickness similar to that of the second conductive layer 34.

[0058] The first conductive layer 22 is etched to form a plurality of gyromagnetic cells or “Y” shaped tracks, each “Y” shaped track 52 being in line with an associated ferrite disk 10. The ends of a “Y” shaped track are intended to be connected respectively to the transmission path, to the reception path, and to the radiating element of an elementary antenna.

[0059] Known chemical etching techniques with masks of suitable shape are implemented here.

[0060] Step 260

[0061] After turning the component over so that the second conductive layer 34 is accessible from above, step 260 consists of piercing the second conductive layer 34 with a plurality of holes going up to the conductive film on the surface of each ferrite disc 10. Each hole is then electrochemically metallized to produce a via 66 electrically connecting the second conductive layer 34 and each ferrite disc 10.

[0062] Here, for example, a focused laser is used to make the holes.

[0063] A component 60 is thus obtained for which electrical continuity is achieved between the second conductive layer 34 and each ferrite disc 10.

[0064] Step 270

[0065] Step 270 consists of gluing the plurality of first magnets 12 onto the surface exposed from the second conductive layer 34 in order to obtain an intermediate component 70.

[0066] The surface to receive the first magnets 12 is covered with a suitable glue.

[0067] For the implantation of the first magnets 12, a pick and place machine is used. Each first magnet 12 is thus placed in a precise position relative to a reference mark linked to the component.

[0068] A first magnet 12 is arranged so as to be in line with a corresponding ferrite disc 10.

[0069] Step 280

[0070] Step 280 consists of preparing the constituents of a second laminate 80 intended to encapsulate the first magnets of the component 70.

[0071] The second laminate 80 is for example a single-sided laminate consisting of a stack of layers successively comprising: a first layer of prepreg 81, a layer of plastic 82, a second layer of prepreg 83 and an external layer of copper (advantageously supported by a layer of plastic), called third conductive layer 84.

[0072] Prepregs comprise a fibrous reinforcement (glass fiber) mixed with a thermosetting polymer in a metastable (pre-crosslinked) state.

[0073] The plastic from which the plastic layer 82 is made is selected to have a maximum dielectric permittivity (typically greater than 6), for the same reasons as those indicated previously.

[0074] The face of the second laminate 80 opposite the third conductive layer 84 has a plurality of blind holes 88. Each blind hole 88 is intended to receive a first magnet 12. A blind hole 88 passes through the first pre-preg layer 81 and the plastic layer 82, but not the second pre-preg layer 83, nor the third conductive layer 84.

[0075] The diameter of each blind hole 88 is larger than the nominal diameter of a first magnet 12, so that the latter is contained in the corresponding blind hole without being in contact with it. A minimum lateral gap is therefore provided to take into account manufacturing dispersions on the diameter of the first magnets, as well as on the position of each magnet relative to each blind hole 88.

[0076] Step 290

[0077] Step 290 is an encapsulation step making it possible to obtain an intermediate component 90 during which the second laminate 80 is approached from above the second conductive layer 34 carrying the first magnets 12 so as to house each of them in a corresponding blind hole 88.

[0078] To cause the polymerization of the layers 81 and 83, a pressing operation under vacuum and at high temperature (typically around 200°C) is carried out leading to the setting of the second laminate 80, its bonding to the second conductive layer 34 and to the upper face of each first magnet 12. A homogeneous insulating layer 92 is thus produced.

[0079] The pressing makes it possible to force the polymer of the first and second prepreg layers, 81 and 83, into the lateral gaps existing between a first magnet 12 and the blind hole 88 receiving it. Thus, the magnet is in contact over its entire lateral face with the material of the insulating layer 92.

[0080] The presence of the second pre-impregnated layer 83, which is a continuous layer, makes it possible to compensate for any manufacturing dispersion over the height of the first magnets 12. Thus, the distance between the second and third conductive layers, 34 and 84, is controlled.

[0081] Step 300

[0082] Step 300 consists of working the third conductive layer 84 to delimit copper tracks or areas 102 at the right of each ferrite disc 12, which will allow the creation of electrical connections between the elementary component obtained and the equipment in which it will be integrated.

[0083] Known chemical etching techniques with masks of suitable shape are implemented here.

[0084] Metallized vias 104 are then made between each track 102 and the corresponding “Y” track 52.

[0085] The drilling of the vias is carried out by laser.

[0086] Component 100 is obtained at the end of this step.

[0087] Step 310

[0088] After turning the intermediate component 100 so that the “Y” tracks 52 are accessible from above, step 310 consists of depositing a spacer layer 112 on the exposed surface of the “Y” tracks 52 to produce an intermediate component 110.

[0089] Step 320

[0090] Step 320 consists of adhering the plurality of second magnets 14 to the exposed surface of the spacer layer 112 to obtain the component 120.

[0091] The surface of the spacing layer 112 to receive the second magnets 14 is covered with a suitable glue.

[0092] For the implantation of the second magnets 14, a pick and place machine is used. Each second magnet 14 is thus placed in a precise position relative to a reference mark linked to the component. A second magnet 14 is arranged so as to be in line with a ferrite disc 10 cor- respondent.

[0093] Step 330

[0094] Step 330 consists of preparing the constituents of a third laminate 130 intended to encapsulate the second magnets 14 of the component 120.

[0095] The third laminate is for example a single-sided laminate consisting of a stack of layers successively comprising: a first layer of prepreg 131, a layer of plastic 132, a second layer of prepreg 133 and an external layer of copper (advantageously supported by a layer of plastic), called the fourth conductive layer 134.

[0096] Prepregs comprise a fibrous reinforcement (glass fiber) mixed with a thermosetting polymer in a metastable (pre-crosslinked) state.

[0097] The plastic from which the first plastic layer is made is selected to have a maximum dielectric permittivity (typically greater than 6), as previously explained.

[0098] The face of the third laminate 130 opposite the fourth conductive layer 134 has a plurality of blind holes 138. Each blind hole 138 is intended to receive a second magnet 14. A blind hole 138 passes through the first prepreg layer 131 and the plastic layer 132, but not the second prepreg layer 133, nor the fourth conductive layer 134.

[0099] The diameter of each blind hole 138 is larger than the theoretical diameter of a second magnet 14 so as to provide a lateral gap making it possible to absorb the dispersions of manufacturing of the second magnets and positioning of each blind hole 138.

[0100] Step 340

[0101] Step 340 is the actual encapsulation step for obtaining a component 140. The third laminate 130 is approached from above the spacer layer 112 carrying the second magnets 14 so as to house each of them in a corresponding blind hole 138.

[0102] Then, a pressing operation is carried out under vacuum and at high temperature (typically around 200°C) to cause polymerization and ensure the setting of the third laminate 130, its bonding to the layer 112 and to the upper face of each second magnet 14. An insulating layer 142 is thus produced.

[0103] The pressing makes it possible to force the polymer of the first and second prepreg layers, 131 and 133, into the lateral gaps existing between a second magnet 14 and the blind hole 138 receiving it. Thus, the magnet 14 is in contact over its entire lateral face with the material of the insulating layer 142.

[0104] The presence of the second layer of pre-impregnated 133, which is a continuous layer, makes it possible to compensate for any manufacturing dispersion over the height of the second magnets 14. Thus, the distance between the first and fourth conductive layers, 34 and 134, is controlled.

[0105] Step 350

[0106] At this stage of the method 200, the production of the ferrite circulators 160 in the thickness of the multilayer card is complete. The method can continue (step 350) by stacking various layers of single-layer laminate to give the manufactured multilayer printed circuit board (or PCB) other functions, in particular the function of radiating element of the elementary antenna.

[0107] For example, in the card 150, obtained at the end of step 350, three conductive layers have been added to produce a radiating element 180: the circuit 154, obtained by etching the fourth conductive layer 134 to constitute an excitation plane connected to the end of a “Y” track 52 by a via 153; the layer 156 forms a ground plane provided with slots; and the layer 158 is a radiating plane.

[0108] The conductive layers 154 and 156 on the one hand and the conductive layers 156 and 158 on the other hand are separated by insulating layers 155 and 157.

[0109] Connection pads 152 are produced on the tracks 102 for connection (by means of solder alloy balls, for example) to the equipment in which the elementary component will be integrated.

[0110] Step 350 preferably ends with a cutting of the card 150 carried out so as to isolate each elementary component. For example, the card 150 is cut to obtain three identical elementary components, referenced 2, 4 and 6 in the figure. Alternative embodiments and Advantages

[0111] In the embodiment presented in detail above, the ferrite circulator is composed of a gyromagnetic cell, a ferrite disk in contact with the gyromagnetic cell, and first and second magnets arranged on either side of the ferrite disk.

[0112] Having two magnets makes it possible to guide the magnetic field lines so that the latter is as homogeneous as possible when passing through the ferrite disc and the gyromagnetic cell.

[0113] Alternatively, the circulator comprises a different number of ferrite discs (for example two ferrite discs arranged on either side of the gyromagnetic cell) and / or a different number of magnets.

[0114] In yet another variant, one of the two magnets is replaced by a magnetic element, which is made of a material making it possible to force the orientation of the lines of the magnetic field generated by the other magnet to create a homogeneous field. For example, this magnetic element is made of steel.

[0115] In the embodiment presented in detail above, the first magnet (or the magnetic element implemented in place of this first magnet) is arranged away from the ferrite. The presence of metallized vias between the ferrite and this first magnet (or this magnetic element) makes it possible to adjust the coupling between these elements. Alternatively, the first magnet (or the magnetic element implemented in its place) is placed in direct contact with the ferrite.

[0116] Those skilled in the art will understand how the manufacturing method presented above can be adapted depending on the structure of the ferrite circulator that one wishes to integrate into the multilayer card.

[0117] Advantageously, to avoid demagnetization of the magnet(s) during an encapsulation step (the temperature to which the component is brought then risks significantly reducing, or even eliminating, the magnetization of the magnet, if this temperature is too close to, or even higher than, the Curie temperature of the material constituting the magnet), the material constituting the magnet and the materials constituting the laminate are selected so that the temperature to be reached for the polymerization of the composite is far from the Curie temperature of the magnet. For example, for a polymerization temperature of 200°C, the magnets used are advantageously made of Samarium-Cobalt (SmCo), having a Curie temperature of 450°C.

Claims

Claims

1. A method of manufacturing (200) a component (150) consisting of a multilayer printed circuit board incorporating a plurality of ferrite circulators (160), the method comprising the steps of: - preparing (210) a plurality of magnets (12) and a plurality of ferrite discs (10); - bonding (220) the plurality of ferrite discs (10) on the surface of a first conductive layer (22); - preparing (230) a first laminate (30) having, on one face, blind holes (38) and, on an opposite face, a second conductive layer (34); - encapsulating (240) the ferrite discs (10) in the first laminate, each ferrite disc being received in a corresponding blind hole (38); - etching (250) the first conductive layer (22) to form a plurality of gyromagnetic cells (52) therein, each gyromagnetic cell being located in line with a corresponding ferrite disc (10);- bonding (270) the plurality of magnets (12), each magnet being placed in line with a corresponding ferrite disc (10); - preparing (280) a second laminate (80), the second laminate having, on one face, blind holes (88) and, on an opposite face, a third conductive layer (84); - encapsulating (290) the plurality of magnets (12) in the second laminate (80); and, - finalizing the component (150). the first conductive layer (22) being thinned before etching a plurality of gyromagnetic cells (52) therein.;

2. The method of claim 1, wherein encapsulating (240, 290) comprises pressing and curing the prepared laminate (30, 80).

3. A method according to claim 1 or claim 2, wherein a laminate (30, 80) comprises a second continuous prepreg layer (33, 83) interposed between each ferrite disc (10) and the second conductive layer (34) and between each magnet (12) and the third conductive layer (84).

4. A method according to any one of claims 1 to 3, wherein a laminate (30, 80) comprises a plastic layer (32, 82) having a dielectric permittivity greater than 6.

5. A method according to any preceding claim, wherein metallized vias (66) are provided (260) to establish electrical continuity between the second conductive layer (34) and each ferrite disc (10), the plurality of magnets being bonded to the second conductive layer.

6. Method according to any one of the preceding claims, characterized in that, the magnets being first magnets, the method further comprises the steps of: - preparing (210) a plurality of second magnetic elements (14); - bonding (320) the plurality of second magnetic elements (14), each magnetic element being placed in line with a corresponding ferrite disc (10), so that the corresponding ferrite disc is between a first magnet and a second magnetic element; - preparing a third laminate (130), the third laminate having, on one face, blind holes (138) and, on an opposite face, a fourth conductive layer (134); and, - encapsulating (330) the second magnetic elements (14) in the third laminate (130).

7. A method according to any preceding claim, comprising steps for integrating into the multilayer printed circuit board a radiating element functionality, the radiating element being connected by a metallized via to one end of a corresponding gyromagnetic cell.

8. A method according to any preceding claim, wherein each ferrite disc is made of a ferrite ceramic (15) whose transverse faces are covered with a conductive film (16, 17).

9. A method according to any preceding claim, wherein the bonding of the plurality of ferrite discs (10), the plurality of first magnets and / or second magnetic elements uses a robotic arm to achieve precise positioning relative to a reference frame.

10. Method according to any one of the preceding claims, comprising a final step of cutting the multilayer printed circuit board to obtain a plurality of elementary components.

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