EP1022750A1 - Discrete electronic inductive component, and method of manufacture of such components - 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 used in techniques surface mounting (SMD), including inductors or transformers.

The production of electronic components for surface mounting is well known, in particular 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 magnetic ferrite cores with electric windings dimensions of the order of a centimeter. However, when the size of components must be reduced, there are serious constraints on the technology to be used to achieve them at high inductance values.

We know coils of the SMD type proposed by Coilcraft in Cary, Illinois, USA, i.e. coils that can be mounted on metallic 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.

American 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 magnetic circuit in two parts is done piece by piece, as well as the bonding of the two parts of the magnetic circuit.

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

The invention proposes in particular to provide a method for producing a plurality of inductors or transformers in batch so as to avoid difficult part-by-part mounting of the various constituent parts each coil or each transformer to these millimeter dimensions. AT this effect, 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 connecting elements machined in the substrate or by a support integral with this substrate, before being separated once the assembly of the different games ended. By this process, we save manufacturing time and we greatly facilitates the handling of the 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, the order of mH, to millimeter dimensions while decreasing the current crossing the winding.

The method of manufacturing electronic components of the type inductive, object of the invention, and such a component capable of being obtained by this manufacturing process, also subject of the invention, are defined specifically in the appended 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.

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 identical magnetic circuit parts 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 inductor obtained according to the method which is the subject of the invention.

The production of inductors or transformers at millimeter dimensions pose certain problems when handling elements to be assembled, in particular magnetic ferrite circuits. In order to overcome these difficulties, the method according to the invention proposes to carry out these inductive components in batch (called “batch-processing” in English), by providing three main stages for mounting the circuit parts magnetic with their metallic windings.

First, a first step is to practice micro-machining on a flat substrate, 1 mm thick and 10 x 10 cm2 surface for example, of magnetic material such as ferrite, for obtaining a plurality of first parts of magnetic circuit 1 which are identical and connected to each other by connecting elements 2 (see the figure 1). Each first part of the magnetic circuit consists of a base 9 and three arms 8a, 8b and 8c rising from this base. The central arm 8b has a width twice that of each of the arms 8a and 8c located at ends of the base 9. This first substrate was laid and maintained on a work support, in particular of the type of those used when sawing 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 magnetic circuit in the variant of FIG. 1. In another variant, the first parts are integral with the work support which then has the function of materially connecting the first parts.

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 just insert a plate printed multilayer 5, visible in FIG. 3, so that the arms 8a, 8b and 8c are inserted into openings 6a, 6b and 6c made in this number plate corresponding to the number of arms of the first machined substrate. The plate 5 comprises a plurality of windings 12 each consisting of at least one metal track wound in the form of spiral on a layer or sheet that this plate has. A winding 12 may include a set of metal tracks connected from layer to layer the other by the technique of conductive holes 11 (for example with copper) well known to those skilled in the art. Each winding 12 ends by two electrical contact pads 7a and 7b, outside the projection of the magnetic circuit in the general plane of the plate, intended to serve a times the component made at the connection of it with pads corresponding to a hybrid structure, according to the mounting technique of SMD type components. It is preferably provided that all of the electrical contact pads are located on the same layer of the plate using, where appropriate, said technique of conductive holes.

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 should 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 with each 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 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 that realize a plurality of second parts 13 of magnetic circuit corresponding to the first parts 1 of the magnetic circuit and connected 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 equivalent to the shape of the first parts of the magnetic circuit, the free ends of the arms of the first and second parts being located the one in front of the other.

The second parts 13 of magnetic circuit may not consist that in a cross member forming a base simply landing on the arms of the first part and covering them entirely without overshoot so that once the two parts are connected, the resulting magnetic circuit presents the general shape of an eight. This configuration is used in case the plate 5 comprises for example two layers for a single winding 12 defining an inductor as shown in Figure 5. If, by against, the thickness of the multilayer plate had to be greater than the height of the arms of the first part of the magnetic circuit, in particular at case it includes four or more layers for a transformer it is preferably planned to use second parts equivalent to first parts to be able to close the magnetic circuit.

Once these three important steps are completed, it is possible to separate components by machining or cutting appropriate. According to a preferred embodiment of the process of the invention, it is planned to have the electrical contact pads of a component on at least one tab 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 the back of the magnetic circuit, in particular on the base 9 of its first part 1, and we stick 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 areas are intended to be welded in particular on electrical contact pads provided on a structure hybrid for connection of inductor or 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.

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 in relief 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 about 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.

Inductive components for surface mounting find applications especially in the field of telecommunications, aid for the hearing impaired, as well as for other portable devices.

Claims (10)

Inductive type electronic component, in particular coil inductance or transformer, comprising a first part (1) in magnetic material forming a first base (9) with at least one arm (8b) rising above this first base, a second part (13) in magnetic material forming at least a second base and being attached to the free end of said arm of said first part so as to define with the latter 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 winding (12) electrically conductive which surrounds said arm (8b), this winding ending with at least two electrical contact pads (7a, 7b) located outside the projection of said first and second bases in the plane general of said wafer, characterized in that said at least two electrical contact pads are located on at least one tab (16, 18) formed of at least one layer or sheet of said wafer, the end of said at least one tab being folded and fixed to the back of said first or second base so that said electrical contact pads are facing outwards. Component according to claim 1, characterized in that said first and second parts (1, 13) of magnetic material form together a closed magnetic circuit with three arms (8a, 8b, 8c) connecting said first and second bases, said winding surrounding the arm central (8b). Component according to claim 2, characterized in that the plate (4) comprises two tongues (16, 18) each having at least an electrical contact pad, these tabs being bent respectively on one side and on the other of said magnetic circuit. Method for manufacturing discrete electronic components of the inductive type, comprising the following steps: micro-machining a first substrate of magnetic material so as to produce in batch a plurality of first parts (1) connected to each other by first connecting elements (2) or a first connecting support and each forming a first base ( 9) with at least one arm (8b) rising from this first base; producing a plate (5) with openings (6a, 6b, 6c) passing through it right through and arranged correspondingly to the arms (8a, 8b, 8c) of said first parts of said first substrate, at least one winding (12) electrically conductive by the first part being carried by said plate around one (6b) of said openings; placing said plate on the first substrate so that it is inserted through its openings between said arms; micro-machining a second substrate made of magnetic material so as to produce in batch a plurality of second parts (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 micromachined 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 produce a plurality of cores or magnetic circuits each associated with at least one winding (12) surrounding said arm (8b) rising from this first base; and separating the plurality of components obtained by machining or cutting said plate (5) so as to form a plurality of distinct plates (4) associated respectively with said plurality of cores or magnetic circuits. Method according to claim 4, characterized in that each winding (12) ends with two electrical 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 are located said contact pads, is cut so as to form such tabs, this process comprising a step of folding said tabs so as to bring their ends against the back of said first or second base where they are attached to provide components that can be used in surface mounting techniques. Method according to claim 5, characterized in that at least part of said tabs have at their respective ends each several contact areas. Method according to claim 4 or 5, characterized in that said second parts are substantially identical to said first parts. Method according to one of claims 4 to 7, characterized in that that said magnetic material is ferrite. Method according to one of Claims 4 to 8, characterized in that that said micro-machining performed on the first and second substrates is a machining by EDM using an electrode (3) with raised patterns. Method according to one of Claims 4 to 8, characterized in that that micromachining performed on the first and second substrates uses a technique with a sandblast.

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