EP1157395B1 - Discrete inductive-type electronic component, method for the production thereof - Google Patents

Abstract

The device uses micro-machining of layers to form the magnetic elements. The procedure for fabrication of inductive type components includes simultaneous micro-machining of a number of parts on a first substrate of magnetic material. Conductive tracks are formed on a multi-layer substrate and arms (8a,b,c) are placed over this, providing the support for a magnetic circuit. The conductive tracks end on contact pads (7a, 7b) which are part of the multi-layer substrate, but which are folded around on to the top of the magnetic circuit and glued in place. The resulting component is suitable for surface mounting.

Description

The invention relates to a discrete electronic component of the inductive type. and a method of making such components. In particular, these components are used in surface mounting techniques (SMD), in particular inductors or transformers.

The production of electronic components for surface mounting is well known, especially for the realization of resistances or capacities, but this poses problems for the serial production of coils inductance or transformers with millimeter dimensions, due that they are currently made separately from each other.

In many electronic applications, we need inductive type electronic components as an interface, for example, between voltage levels provided by a power source and integrated circuit input voltages. These inductive elements serve including flattening ripples on signals. Often the values of inductance need to be high, of the order of mH. Usually the realization of such inductive elements poses no problem if one uses ferrite cores with electrical windings to order dimensions of the centimeter. However, when the size of the components needs to be reduced, it there are serious constraints on the technology to use to realize them at high inductance values.

Likewise, for the realization of antenna of small dimensions formed of a winding and a magnetic core, the market needs a technology allowing inexpensive and large-scale manufacturing.

We know coils of the SMD type proposed by Coilcraft in Cary, Illinois, USA, i.e. coils that can be mounted on metal areas produced on hybrid structures, in particular in ceramic. These coils are composed of a magnetic core on which a metal wire is wrapped around the central part and whose ends are each connected on a metal range of end portions of on either side of the central part. The metal pads can serve as contact with corresponding metal areas made on a hybrid structure including connection tracks to different electronic components. The value of these coils is a maximum of 10 µH for dimensions of 3 mm x 3 mm x 2.5 mm. We understand that they are carried out one after the other because it is necessary to wrap a wire around each magnetic circuit so independent, which requires time in manufacturing and a high cost.

US patent US 5,463,365 describes a coil which includes a magnetic core and a winding part formed of a plurality of laminated sheets comprising windings arranged in a spiral around the nucleus so as to be coaxial. The connection between the windings is finding on superimposed sheets is done through holes metallized well known to those skilled in the art. This way of doing things stack a number of sheets or layers, including sheets made of polyimide resin, depending on the number of turns of metal wires desired for the coil design.

The manufacture of these coils recommended in this American patent is complicated because, to obtain a component of the SMD type which can be mounted on a hybrid structure, the given embodiments present, in addition the arrangement of a magnetic core with its winding stack, a whole infrastructure with a cover on both sides of the circuit magnetic and several output terminals, all of which are not used if the component only includes one winding. The shape of said component can be compared to that of a component with a plastic case encapsulation, which is not suitable for very small dimensions. Of more, the assembly of this component is performed piece by piece.

In the US patent US 5,760,671, a transformer is described. having two magnetic flux paths defined by a magnetic circuit in ferrite having the shape of an eight, this transformer comprising a wafer formed of stacked layers with printed circuits defining the primary and secondary windings of this transformer. The plate has an opening for the central arm of the magnetic circuit which is surrounded by the windings. These windings are raised from the base of the magnetic circuit by steps arranged in corners of two openings defined by the magnetic circuit.

This transformer is used for voltages up to 400 V for dimensions exceeding one centimeter. At these dimensions, the manufacturing such components pose no particular problem, but cannot be used as a SMD type component. The assembly of the wafer with the two-part magnetic circuit is done piece by piece, as well as the bonding of the two parts of the magnetic circuit.

Patent application GB 2 317 751 describes an inductor or a transformer arranged to be mounted on a printed circuit. The structure magnetic also has the shape of an eight surrounding a coil printed on a brochure. The inductive element is then placed on the printed circuit board to which it is electrically connected by a conventional wire technique conductive or metal tabs, or by conductive pins.

Patent application WO 98/57338 describes an inductor or a transformer with a magnetic structure also having the shape of an eight and formed by a multilayer coil. The coil is formed by a stack of flat coils printed on a flexible sheet. In addition, the patent application describes a electronic components manufacturing process discrete inductive type, in particular inductor coils, transformers or antennas.

The invention proposes to overcome the drawbacks of the prior art with regard to concerns the manufacture of inductive components, in particular dimensions millimeter.

The invention proposes in particular to provide a method for carrying out a plurality of inductors or transformers in batch so as to avoid difficult part-by-part mounting of the different parts making up each coil or each transformer has millimeter dimensions.

For this purpose, each identical or equivalent part of a batch of components inductive is manufactured in or on the same substrate so as to have a plurality of identical or equivalent parts connected to each other by elements of bond machined in the substrate or by a support integral with this substrate, before being separated once the assembly of the different parts is completed. By this process, we saves manufacturing time and greatly facilitates the handling of different parts, which reduces the cost price.

In the context of carrying out the present invention, it has been found that it is possible to obtain high inductance values, of the order of mH, at millimeter dimensions while reducing the current flowing through the winding.

The manufacturing process of inductive type electronic components, object of the invention, and of the components obtained by this process of manufacturing, also objects of the invention, are defined precisely in the attached claims.

• la figure 1 représente un des substrats ayant subi un micro-usinage selon le procédé de l'invention avec des parties de circuit magnétique identiques et reliées les unes aux autres,
• la figure 2 représente un usinage par électro-érosion d'un substrat selon un mode de mise en oeuvre du procédé objet de l'invention,
• la figure 3 représente une plaquette multicouche de circuits imprimés avec plusieurs enroulements métalliques,
• la figure 4 représente une première partie de circuit magnétique avec un enroulement métallique sur une plaquette de circuits imprimés insérée entre les bras du circuit magnétique,
• la figure 5 représente une bobine d'inductance obtenue selon le procédé objet de l'invention,
• la figure 6 est une vue éclatée et la figure 7 est une vue de dessus d'une antenne selon l'invention, et
• la figure 8 est une vue de dessus d'un ensemble d'antennes après assemblage en lot et avant séparation en composants distincts.

Other advantages and particular characteristics of the present invention will be described with the aid of the following description made with reference to the appended drawings, given by way of nonlimiting examples, in which:

• FIG. 1 represents one of the substrates having undergone a micro-machining according to the method of the invention with parts of identical magnetic circuit and connected to each other,
• FIG. 2 represents machining by electro-erosion of a substrate according to an embodiment of the method which is the subject of the invention,
• FIG. 3 represents a multilayer plate of printed circuits with several metal windings,
• FIG. 4 represents a first part of the magnetic circuit with a metal winding on a printed circuit board inserted between the arms of the magnetic circuit,
• FIG. 5 represents an inductance coil obtained according to the process which is the subject of the invention,
• FIG. 6 is an exploded view and FIG. 7 is a top view of an antenna according to the invention, and
• Figure 8 is a top view of a set of antennas after assembly in a batch and before separation into separate components.

The production of inductors, transformers or antennas with millimeter dimensions pose certain problems when handling of the elements to be assembled, in particular cores or magnetic ferrite circuits. In order to overcome these difficulties, the process according to the invention proposes to produce these inductive components in a batch (called “batch-processing” in English), providing for three stages main mounting of parts of magnetic circuits with their metal windings. One mode of implementation of this process will be described below using Figures 1 to 3.

First of all, a first step consists in practicing micro-machining on a flat substrate, 1 mm thick and 10 x 10 cm ² in area for example, made of magnetic material such as ferrite, to obtain a plurality first parts of magnetic circuit 1 which are identical and connected to each other by connecting elements 2 (see FIG. 1). Each first part of the magnetic circuit consists of a base 9 and three arms 8a, 8b and 8c projecting from this base. The central arm 8b has a width twice that of each of the arms 8a and 8c located at the ends of the base 9. This first substrate has been placed and maintained on a working support, in particular of the type of those used during sawing of integrated circuit boards. All the first parts are therefore maintained with constant spacing because they are connected by the connecting elements 2 which are of the same material as the first parts of the magnetic circuit in the variant of FIG. 1. In another variant, the first parts are secured to a working support which has the function of materially connecting these first parts during the batch manufacturing process of the inductive components so as to maintain them in respective predetermined positions.

We can plan to build a thousand magnetic circuits simultaneously according to the process which is the subject of the invention for the same substrate initial magnetic.

Once the first step is completed, we bring a printed plate 5, visible in Figure 3, arranged so that the arms 8a, 8b and 8c are inserted into openings 6a, 6b and 6c made in this plate in number corresponding to the number of arms in the first substrate machined with identical spacings. The plate 5 includes a plurality of windings 12 each consisting of at least one wound metal track in the form of a spiral on a layer or sheet that this plate has. A winding 12 can include a set of deposited metal tracks on a set of layers forming a multilayer plate, these tracks being connected from one layer to another by the technique of conductive holes 11 (by example with copper) well known to those skilled in the art. Each winding 12 ends with two electrical contact pads 7a and 7b, outside the projection of the magnetic circuit in the general plane of the plate, intended to be used once the component produced at the connection of this one with corresponding ranges of a hybrid structure, according to the mounting technique for SMD type components. We preferably plan that all of the electrical contact pads are located on the same layer of the plate using, where appropriate, said hole technique conductors.

The printed plate 5 consists of layers or sheets of resin polyimide. Openwork parts can be provided around the windings to facilitate separation of completed components, such as shown in Figure 3. Note that two windings can be provided coaxial on the same layer. In addition, it is possible to provide metal tracks on both sides of the same layer. In this last case, care must be taken to ensure the necessary electrical insulation if there are several layers printed.

In the case of an inductor as shown in the figure 5, the first part 1 is associated with a single winding with two tracks metal arranged respectively on both sides of the plate 4, this winding ending with two contact pads 7a and 7b.

In the case of a transformer, the magnetic circuit includes two windings each with at least two contact pads. It is planned to preferably that the contact pads of these two windings are located on the same outer layer of the plate 5. If the secondary winding of the transformer has more than two contact pads, you can have a variable voltage ratio between primary and secondary.

The third step of the process consists in coming to fix, in particular by bonding, a second substrate of a magnetic material, such as ferrite, on the first substrate. The second substrate is micro-machined so as to making a plurality of second parts 13 of magnetic circuit connected to them to each other by connecting elements of the same material, so similar to what is shown in Figure 1. Each second part 13 comes close each first part 1 of the magnetic circuit with the plate printed 5 inserted between the base 9 of the first part 1 and the second corresponding part 13 which also defines at least one base.

The shape of the second parts of the magnetic circuit can be similar to the shape of the first parts of the magnetic circuit, the free ends of the arms of the first and second parts then being located opposite each other.

In another variant, the second parts are integral with a working support, in particular an adhesive sheet, which has the function of binding materially the second parts during the batch assembly.

The second parts 13 of magnetic circuit may not consist that in a crossbeam forming a base simply landing on the arms of the first part and covering them entirely so that once both connected parts, the resulting magnetic circuit has the general shape of a eight. This configuration is used in the case where the plate 5 comprises by example two layers for a single winding 12 defining a coil inductance as shown in Figure 5. If, on the other hand, the thickness of the multilayer plate had to be larger than the height of the arms of the first part of the magnetic circuit, especially if it includes four or more layers for a transformer, preferably provided to use second parts equivalent to the first parts to ability to close magnetic circuit.

Once these three important steps are completed, it is possible to separate components by machining or cutting appropriate. Note that the first and second magnetic parts can form a coil core, including an antenna, not closed on itself, as in the embodiment of Figures 6 and 7 described by the after.

According to a preferred embodiment of the method of the invention, it provision is made to arrange the electrical contact pads of a component on at minus a tongue formed in the plate 5 during this machining or cutting if this has not already been done in a preliminary stage or during the formation of the multilayer plate 5. Thus, a tab can have one or more contact areas. Thereafter, with reference to FIG. 4, we folds the tabs 16 and 18 having the electrical contact pads 7a and 7b on an external surface of the magnetic circuit, in particular on the back of the base 9 of its first part 1, and we glue them on this base. Figure 4 shows by arrows the direction of folding of the tabs 16 and 18 with, at their ends, said areas 7a and 7b. These ranges are intended to be welded in particular on electrical contact pads provided on a hybrid structure for the connection of the inductor or the transformer with other components of the hybrid structure.

Note that it is possible, in an advantageous variant, to fold the tabs 16 and 18 with their respective ranges before the separation of the components, provided that the plate 5 is perforated or cut around tabs 16 and 18.

As can be seen in Figures 4 and 5, the plate 4 cut from plate 5 has portions extending beyond the width of the circuit magnetic. These portions can also be folded in the direction of the base of the magnetic circuit and glued with insulation against the arms and the base of the circuit. This saves space.

When gluing the second part with the first part of the circuit magnetic, it is possible that the glue at least partially covers the plate multilayer 4 so as to fix it securely to the magnetic circuit.

Micro-machining for the production of the first and second parts of magnetic circuit can preferably consist of machining by electro-erosion as shown schematically in Figure 2. We use a electrode 3 with raised patterns for producing a plurality of circuit parts magnetic fields defined by the electrode. The electrode could in some cases include areas with different patterns to achieve different magnetic circuit parts from one zone to another on the same substrate.

Micro-machining for the production of the first and second parts circuit can also use a sandblasting technique.

Micro-machining for the production of the first and second parts of magnetic circuit and for the separation of components can use a laser, in particular for the cutting steps.

The dimensions of the inductive type component can have in particular a width I between 0.5 mm and 1 mm and a length L between 1.4 mm and 2.8 mm for a height h from 1 mm to 1.5 mm. Each arm rises for example about 0.2 mm above the base 9. The arm central has a width double the width of the two arms located at ends of the base and its value is for example around 0.4 mm. In these dimensions, we can place a multilayer printed circuit board comprising one or two windings, for example a winding with a number N of turns equal to 56 or 18. In the case where N = 56, the value of the inductance is about 1 mH, while for N = 18, the value of the inductance is approximately 0.1 mH.

The metal tracks of the plate 4 are obtained in particular at using a plasma etching process 10 to 15 µm deep. They are for example 50 µm wide. The gap between two tracks (called "Pitch" in English) of the same winding is 14 µm for a inductance with a value of 1 mH and 44 µm for an inductance of 0.1 mH. The metallized holes are approximately 100 µm wide.

The manufacture of all these windings on the multilayer plate 5 is known to those skilled in the art.

Other forms of the closed magnetic circuit can be envisaged. Instead of three arms, the magnetic circuit can have only two. Under these conditions, it is necessary that the two bases are each of a double the thickness of the figure eight shape; which generates components of greater height. The process according to the invention can also be used for make coils with a core. In the latter case, there is only one only one arm per component.

With the aid of FIGS. 6 to 8, an antenna formed according to will be described below the method of the invention. This antenna 22 is essentially formed of three parts. It comprises a first base 24 made of magnetic material and a arm 26 projecting from this base, a plate 28 on which is provided an electrical winding 12 of the type described above, and a second base 30 made of magnetic material. By magnetic material, we understand a ferromagnetic material having relatively magnetic permeability high.

Each of the two bases 24 and 30 has the general shape of a V extending in two planes parallel to each other and substantially perpendicular to the direction of the arm 26. Preferably, the plate 28 is fixed to the core so that its general plan is also appreciably perpendicular to the direction of said arm. The plate 28 has a opening 6 into which the arm 26 of the base 24 is introduced. In the variant shown, the free ends of the two branches defining the V shape of each of the bases have projecting parts 34 and 36 towards the general plane of the plate 28. Bases 24 and 30 and the arm 26 which connects them materially and magnetically together form a core antenna. Each of the bases has its two branches connected by a part of link at which arm 26 is located. Projecting in the plane general antenna, the antenna core has the general shape of an X ensuring sensitivity of the antenna as a function of the direction in said plane general. Note that the base 30 may also have a similar arm on the arm 26. However, only one arm made of one material with one or the other of the two bases is sufficient as long as its height is equal or greater than the thickness of the plate 28.

The arrangement of the antenna 22 is particularly interesting for the the two bases forming the antenna core and the plate serving as support for a flat winding extend in parallel planes allowing an easy assembly of the three intervening parts. So the direction or the maximum sensitivity plane of the antenna is parallel to the plane general defined by the flat winding 12, unlike a wound antenna on a bar-shaped core whose direction of maximum sensitivity is perpendicular to the plane defined by the turns of the coil. In others terms, the direction of maximum sensitivity or the plane of maximum sensitivity of an antenna formed by a coil and a magnetic core is generally parallel to the magnetic axis of the coil. On the other hand, the antenna 22 has maximum sensitivity in one or more directions substantially perpendicular (s) to the magnetic axis of the winding 12 forming a coil antenna.

Note that the bases forming the antenna core can present, in the general plan of this antenna defined by the plate 28, diverse and different contours. In particular, the basics can be formed of a simple bar, at least one of which comprises an arm 26 making protruding in a substantially perpendicular direction. Preferably, the arm is located at two respective ends of the bases, which extend from these two ends in opposite general directions.

The arrangement of the various parts forming the antenna 22 allows a inexpensive batch manufacturing according to the process of the present invention. Sure Figure 8 has been shown a lot of antennas after assembly and before separation of antennas. The bases 24 are arranged on an adhesive support 40. This support 40 can be assembled to the material substrate ferromagnetic in which the bases 24 are micro-machined. So the basics 24 are regularly and precisely arranged on the substrate 40. Then, a plate formed by the assembly of plates 28 and connection arms 42 is brought. As previously described, openings 6 in the middle plates 28 are provided so that they can be inserted in the set of arms 26 of the antenna cores. Finally, a plurality second bases 30 is provided to form the batch of antennas. These bases 30 are also arranged on an adhesive support not shown and similar to support 40. Once bases 24 and 30 are assembled, for example by gluing, at least one of the adhesive supports is removed and a step of cutting arms 42 is provided to form separate antennas each other. Finally, when an adhesive support is kept for said cutting step, the antenna lot can remain assembled at adhesive substrate remaining until mounting in respective devices in which it is planned to integrate them.

Finally, note that the electrical contact areas of the windings can advantageously be arranged, as in the mode described above, on tabs connected to the plate 28 to facilitate connection of the winding 12 to the electronic device in which the antenna 22 is integrated. In an advantageous variant, it is provided that these tabs are folded and attached to the back of the first or second base 24 or 30 so that the electrical contact area (s) located on each tab facing outward. This allows easy mounting of the antennas 22 according to a mounting technique in surface (SMD).

Inductive components arranged for surface mounting find applications especially in the field of telecommunications, help for the hearing impaired, and others portable devices.

Claims (15)

1. Method for manufacturing discrete electronic components of the inductive type, in particular inductance coils, transformers or antennae, including the following steps :

   micro-machining a first substrate of magnetic material so as to batch process a plurality of first parts (1) connected to each other by first connecting elements (2) or a first connecting support (40) and each forming a first base (24; 9) and at least an arm (26; 8b) projecting from said first base;

   forming a plate (5) with openings (6; 6a, 6b, 6c) passing right through it and disposed in a corresponding way to the arms (26; 8a, 8b, 8c) of said first parts of said first substrate, at least an electrically conductive winding (12) per first part being carried by said plate around one (6; 6b) of said openings;

   placing said plate on the first substrate so that it is inserted via its openings between said arms;

   micro-machining a second substrate of magnetic material so as to batch process a plurality of second parts (30; 13) connected to each other by second connecting elements or a second connecting support and each forming at least a second base;

   placing the second micro-machined substrate on said first substrate and said plate, and connecting the second parts of the second substrate to the respective first parts of the first substrate so as to batch process a plurality of cores or magnetic circuits each associated with at least one winding (12); and

   separating the plurality of components obtained by machining or cutting said plate (5) so as to form a plurality of distinct plates (4; 28) respectively associated with said plurality of cores or magnetic circuits.
2. Method according to claim 1, characterised in that each winding (12) ends in two electric contact pads (7a, 7b) located outside the projection of said first and second bases on said plate, said plate being either formed directly with tongues (16, 18) at the ends of which said contact pads are located, or cut so as to form such tongues, this method including a step of folding said tongues so as to bring their ends against the back of said first or second base where they are secured so as to provide components able to be used in surface mounting techniques.
3. Method according to claim 2, characterised in that at least a part of said tongues each have at their respective ends several contact pads.
4. Method according to claim 1 or 2, characterised in that said second parts are substantially identical to said first parts.
5. Method according to any of claims 1 to 4, characterised in that said magnetic material is ferrite.
6. Method according to any of claims 1 to 5, characterised in that said micro-machining performed on the first and second substrates is electro-erosion machining using an electrode (3) with patterns in relief.
7. Method according to any of claims 1 to 5, characterised in that the micro-machining performed on the first and second substrates uses a sand blasting technique.
8. Electronic component of the inductive type, in particular an inductance coil, transformer or antenna, obtained by the method according to claim 1 and including:

   a first part (1) made of magnetic material forming a first base (9) and at least an arm (8b) projecting above said first base;

   a second part (13) made of magnetic material forming at least a second base and being secured to the free end of said arm of said first part so as to define therewith a core or a magnetic circuit,

   a plate (4) inserted between said first and second bases and having an opening for the passage of said arm, this plate (4) carrying at least one electrically conductive winding (12) which surrounds said arm (8b), this winding ending by at least two electric contact plates (7a, 7b) located outside the projection of said first and second bases in the general plane of said plate, characterised in that said at least two electric contact pads are located on at least one tongue (16, 18) formed of at least one layer or sheet of said plate, the end of said at least one tongue being folded and secured onto an external surface of said first or second base such that said electric contact pads are turned outwards.
9. Component according to claim 8, characterised in that said first and second parts (1, 13) made of magnetic material together form a closed magnetic circuit with three arms (8a, 8b, 8c) connecting said first and second bases, said winding surrounding the central arm (8b).
10. Component according to claim 9, characterised in that the plate (4) includes two tongues (16, 18) each having at least one electric contact pad, these tongues being folded and secured onto the same external surface of said magnetic circuit.
11. Antenna (22) obtained by the method according to claim 1 and formed of a core of magnetic material and a winding (12) of conductive material, characterised in that said core is formed of a first part, defining a first base (24) and an arm (26) projecting from this first base, and a second part defining a second base (30) and assembled to said first part at the free end of said arm, said winding being supported by a plate (28) having in the central region of the winding an opening (6) in which said arm is inserted, said first and second bases extending into first and second substantially parallel planes which are substantially perpendicular to the direction of said arm.
12. Antenna according to claim 11, characterised in that said plate has a general plane which is substantially parallel to said first and second planes.
13. Antenna according to claim 11 or 12, characterised in that said arm (26) is located substantially at a first end of said first base and at a second end of said second base, these first and second bases extending respectively from these first and second ends along opposite general directions.
14. Antenna according to claim 13, characterised in that said first and second bases each have the general shape of a V with two branches connected by a connecting part, said arm connecting the two bases at respective connecting parts so that these two bases have, in projection onto said first or second plane, the general shape of an X.
15. Antenna according to claim 14, characterised in that projecting parts (34, 35) in the direction respectively of said second plane and said first plane are provided at the free ends of said branches of the first base and of the second base.

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