EP0789423A1 - Method of making an electrical connection by adhesion of a rigid terminal to a conductive track, a rigid terminal for carrying out this method and its application to a heating plate for a heating vessel - Google Patents

Abstract

A procedure consists of attaching a circular or rectangular plate with a space terminal (21) to the surface of an electrical component (10) such as a heating resistance, using an electrically conducting adhesive (4). The joint can incorporate copper strands (3) from an electrical cable, the strands having a diameter of 0.5-0.8 mm. The adhesive is in the form of a thermostable conducting resin, such as a silver-charged polyimide, which is dried and reticulated after the joint has been made.

Description

The invention relates to a method of producing an electrical connection by bonding a rigid terminal on a conductive track.

It also relates to a rigid terminal for implementing the method.

It applies more particularly, although not exclusively, to the production of an electrical connection for a heating plate or for a heating container, in particular for a kettle.

An example of a heating plate has been described in French patent application FR-A-2 692 426, in the name of the Applicant. Such a heating plate comprises in particular a metal support surmounted by a layer of vitreous composition, itself supporting a resistive track. The latter is advantageously deposited by screen printing and heating resistance form.

A heating plate thus designed has many advantages. First of all, it is particularly suitable for heating a kettle. It is easily cleaned, which is also advantageous from a hygienic point of view, and allows a high thermal efficiency. Finally, because of its small thickness, it is easily placed inside a kettle.

According to this patent application, the electrical connections at the ends of the resistive track are carried out by bonding, using a conductive material, as shown more particularly in Figure 3 of this patent application. To do this, a wire or a metal strip is drowned in a drop conductive resin deposited on the conductive track. One then proceeds to a phase of drying and crosslinking of the resin.

For certain specific applications, it appears desirable to use rigid metal lugs or similar members, instead of directly bonding the electric wire to the resistive track. This method makes it possible, in particular, to easily dismantle the plate, by disconnecting the electric wires for supplying the current, these wires being provided with a terminal lug complementary to the lug glued to the resistive track.

However, during the drying and crosslinking phase of the resin, gases are formed. For bonding the terminal on the above-mentioned resistive track, it is necessary to promote the flow of gases. Indeed, if this is not the case, gas bubbles are formed under the solid surfaces of the terminals. These gas bubbles remain trapped and weaken the contacts, both from a mechanical and electrical point of view.

On the other hand, the Applicant has found that the flow of gases resulting from the drying and crosslinking phase of the resin was satisfactory when it was a question of bonding multi-strand electrical wires, directly on the resistive tracks. This flow takes place under particularly good conditions when the diameter of the strands is in the range of 0.2 to 0.8 mm.

It is however difficult to connect a connection to a flexible electric wire.

• a) réalisation à l'extrémité d'une cosse en matériau conducteur de l'électricité d'une zone formée de brins ou de lamelles;
• b) enrobage de cette zone formée de brins ou de lamelles par ladite substance de collage conductrice de l'électricité;
• c) et application de ladite zone sur ladite couche de matériau conducteur pour réaliser ledit collage.

According to the invention, the method of producing an electrical connection by bonding using an electrically conductive substance is characterized in that it comprises at least the following steps:

• a) production at the end of a terminal made of electrically conductive material of an area formed of strands or strips;
• b) coating of this zone formed of strands or lamellae by said electrically conductive bonding substance;
• c) and application of said zone on said layer of conductive material to effect said bonding.

• a) insertion, dans une cosse en matériau conducteur de l'électricité et comportant un orifice, d'un segment de fil électrique multibrins dans ledit orifice;
• b) enrobage de ce segment de fil électrique multibrins par ladite substance de collage conductrice de l'électricité;
• c) et application de l'ensemble "segment de fil électrique-cosse sur ladite couche de matériau conducteur, pour réaliser ledit collage.

According to a first version of the invention, the method comprises at least the following steps:

• a) insertion, in a terminal made of electrically conductive material and comprising an orifice, of a segment of multi-strand electric wire in said orifice;
• b) coating of this segment of multi-strand electric wire with said electrically conductive bonding substance;
• c) and application of the assembly “segment of electric wire-terminal on said layer of conductive material, to effect said bonding.

• a) réalisation d'une série de lamelles dans au moins une zone sensiblement plane d'une cosse rigide, réalisée en matériau conducteur de l'électricité:
• b) enrobage de cette zone munie desdites lamelles par ladite substance de collage conductrice de l'électricité;
• c) et pose de la zone munie des lamelles sur ladite couche de matériau conducteur, pour réaliser ledit collage.

According to a second version of the invention, the method comprises at least the following steps:

• a) production of a series of strips in at least one substantially flat area of a rigid terminal, made of electrically conductive material:
• b) coating this zone provided with said strips with said electrically conductive bonding substance;
• c) and placing the zone provided with strips on said layer of conductive material, in order to carry out said bonding.

The invention also relates to an electrical connection thus produced.

The invention also relates to its application to a heating plate for a heating container, in particular for a kettle.

• la figure 1 illustre un exemple de plaque chauffante comportant une piste résistive;
• la figure 2 illustre un exemple de connexion selon l'invention, mettant en oeuvre une cosse en forme de rivet;
• la figure 3 illustre un exemple de connexion selon l'invention, mettant en oeuvre une cosse en forme de rondelle;
• la figure 4 illustre un exemple de réalisation d'une cosse rigide à coller sur une piste selon un mode de réalisation préféré de l'invention;
• les figures 5 à 7 illustrent des variantes supplémentaires de cosses rigides à coller sur une piste selon l'invention.

The invention will be better understood and other characteristics and advantages will appear on reading the description which follows with reference to the appended figures, and among which:

• FIG. 1 illustrates an example of a heating plate comprising a resistive track;
• FIG. 2 illustrates an example of connection according to the invention, using a lug in the form of a rivet;
• FIG. 3 illustrates an example of connection according to the invention, using a terminal in the shape of a washer;
• FIG. 4 illustrates an exemplary embodiment of a rigid terminal to be bonded to a track according to a preferred embodiment of the invention;
• Figures 5 to 7 illustrate additional variants of rigid lugs to be bonded to a track according to the invention.

We will place ourselves below in the context of the preferred application, that is to say making connections for a heating plate intended for a heating container, of the kettle type or the like.

Figure 1 schematically illustrates an example of a heating plate 1, seen from below. This comprises a thick metallic support 12, generally circular, coated with a layer 11 of electrically insulating glassy composition. A resistive track 10 composed of a vitreous base charged with metallic particles is applied to the latter, advantageously by screen printing. The track 10 has the shape of a spiral, the ends 10a and 10b of which are intended to be connected to a source of electric current.

To fix the ideas, the thickness of the layer 11 of vitreous composition is at least equal to 300 μm and preferably equal to approximately 400 μm. The thickness of the resistive track is typically between 8 and 30 μm. For a more detailed description of this exemplary embodiment of a heating plate 1, reference will be made with advantage to the aforementioned French patent application FR-A-2,692,426.

According to the arrangements described in this patent application, the electrical connections with current supply wires were made directly by bonding them, using a conductive resin on the ends of the resistive track, 10a and 10b respectively.

If one wishes, no longer to directly glue the electrical wires or metal tabs, but rigid lugs, one is confronted with the problems which have been recalled, namely the formation of gas bubbles trapped under the solid surfaces thereof . These gas bubbles have the harmful effect of weakening the contacts, both from a mechanical and electrical point of view.

We will now describe the method of producing an electrical connection by bonding a terminal on a conductive track according to the invention, with reference to FIGS. 2 and 3.

FIG. 2 illustrates a first example of embodiment of a connection using a terminal in the form of a rivet 2.

FIG. 3 illustrates a second exemplary embodiment of a connection using a terminal in the shape of a washer 2.

In both cases, and according to an important characteristic, the production method according to the invention comprises a first step during which a first end 30 of a segment of electric wire multi-strand 3 is threaded, either in the neck 20 of a rivet 2, or in the central orifice 20 'of a washer 2. The other end, 31, is disposed below the rivet 2 or of the washer 2' , and the strands of this end come out in a divergent peripheral bundle.

Advantageously, the electric wire 3 is composed of copper strands, the diameters of which preferably lie in a range 0.2 to 0.8 mm.

During a second step, the multi-strand wire 3 is coated with a thermostable conductive resin 4.

• "CEMOTA HT 100" de la marque "CEMOCLA".

By way of nonlimiting example, a polyimide resin loaded with silver, in particular the resins available commercially, under the following references and brands can be used:

• "CEMOTA HT 100" from the brand "CEMOCLA".

In a subsequent step, the assembly is applied to the resistive track 10, more precisely one or the other of the ends of the conductive track, for example the end 10a, as illustrated in FIGS. 2 and 3. We do then undergo, in a conventional manner per se , a drying and crosslinking cycle, the precise characteristics of which (time, temperature, etc.) depend on the type of adhesive used and are indicated by the supplier.

The strands, in particular those, 31, located between the solid surfaces of the terminal and the resistive track 10 play the role of "drains", evacuating the gas bubbles which form during this step.

After the crosslinking step, the connector thus produced is ready to receive any suitable connection system, such as a plug-in terminal 5 (for example on a tab 21 of the terminal 2 '), crimping, etc.

On reading the above, it is easy to see that the invention achieves the goals it has set for itself.

While retaining the advantages of a connection using a multi-strand electrical wire bonded to the resistive track (in particular with good mechanical strength and good electrical quality of the contacts), it also makes it possible to obtain the advantages linked to the use of lugs. rigid.

It should be clear, however, that the invention is not limited to only the examples of embodiments precisely described, in particular in relation to FIGS. 2 and 3.

First of all other terminal structures can be used, the structures in the form of a rivet 2 or in the form of a flat washer 2 ′, having only been described to better set the ideas. One can use, in particular, eyelet-shaped lugs.

Other types of conductive adhesives can also be used. The materials that can be used are essentially linked to the specific application envisaged and are part of a simple technological choice within the reach of those skilled in the art.

We will now describe the method of producing an electrical connection by bonding a terminal on a conductive track according to the invention, with reference to FIGS. 4 to 7.

More particularly, FIG. 4 illustrates an exemplary embodiment of a rigid terminal to be bonded to a track, according to a preferred embodiment of the invention.

In what follows, the elements common with FIG. 2 bear the same references and will only be described again as necessary.

In this embodiment, the terminal, referenced 6, is entirely symmetrical with respect to an axis Δ passing through a central zone thereof. We have assumed (in the example described) that this axis is substantially perpendicular to the track 10, in its end zone 10a.

It consists of a central zone, 61, raised relative to the surface, 10a, of the runway, 10, of two lateral wings, 63 and 64, and of a substantially vertical central blade, 60. This latter form, the terminal itself, allowing connections. You can put on it, for example, a female terminal 5.

According to one of the main characteristics of the invention, the lateral wings, 62 and 63, are provided with cutouts, for example at their ends, which leave only a series of thin strips 64 and 65, respectively. In the example of Figure 3, each wing, 63 and 64, has three strips of this type.

It is these strips, 64 and 65, which play the role of the copper strands 3 of FIG. 2, that is to say the role of "drains".

Indeed, the bonding on the surface 10a of the track 10 is carried out in a manner quite similar to what has been previously recalled, using a thermostable conductive resin 4, which coats the strips, 64 and 65 It is therefore unnecessary to recall this step of the process. A drying and crosslinking cycle is also carried out in a conventional manner per se , the precise characteristics of which (time, temperature, etc.) depend on the type of adhesive used and are indicated by the supplier.

The thin strips, 64 and 65, evacuate the gas bubbles which form during this stage. The surface defined by these strips, 64 and 65, must be sufficient to obtain good adhesion of the terminal on the surface 10a of the track 10.

To obtain this advantageous effect, as indicated, it is necessary that the strips are sufficiently fine. Typically, the width of the strips, 64 and 65, will be chosen less than or at most equal to 1 mm. The sheet used does not differ in any way from that of the lugs of the known art: one can choose, for example, nickel-plated steel, brass or copper.

The terminal 6, according to the invention, also has other advantageous characteristics. The vertical blade 60, used for the connectors, is preferably folded around an axis Δ _p , such that it coincides with the pivot axis of the blade 60 relative to the base of the terminal 6. It s 'ensue that the terminal can be placed, stably, on the surface 10a of the track 10, especially during the passage to the oven to obtain the crosslinking of the resin. This feature facilitates the automation of the process steps.

In addition, the central zone, as indicated, is raised relative to the surface 10a of the runway 10. It forms a trigger guard with sides, 67 and 68 inclined. This geometric characteristic plays the role of a stiffener at the base of the terminal 6.

Finally, if the terminal 6 is provided with a cutout 66 adjacent to the blade 60, this arrangement makes it possible to limit the effects of any expansions. Indeed, these expansions are to be feared in the case of the preferred application of the invention, since the track 10 is a heating resistive track. This cutting is usually carried out automatically since the blade 60 is generally obtained by cutting a strip, followed by folding.

Although the rigid terminal structure 6 which has just been described is particularly advantageous, in particular because of its symmetry, it is possible to design a large number of configurations.

Three examples of additional constructions of rigid lugs to be glued on a track in accordance with the invention will now be described with reference to FIGS. 5 to 7.

These three structures have in common the fact of appearing in the general form of an "L".

The terminal 6a shown in FIG. 5 has a vertical blade 60 for the connections and a single wing 64a, obtained by folding, for example at 60 ° in order to obtain good stabilization of the tongue of glue. The latter, according to the main characteristic of the invention comprises thin strips 640a obtained by cutting. These strips 640a are parallel to the surface of the blade 60.

The terminal 6a shown in FIG. 6 also includes a blade 60 for the connectors and a single wing 64b, obtained by folding. The latter, according to the main characteristic of the invention, comprises fine strips 640b obtained by cutting. The only notable difference is that these strips 640b are orthogonal to the surface of the blade 60.

Finally, the terminal 6c, illustrated by FIG. 7, has a structure similar to that of FIG. 4, in that the strips are oriented to be parallel to the surface of the blade 60. However, the wing 64c, forming the base of the terminal 6c, is divided in two and has two series of strips, 640c and 641c, respectively.

This arrangement offers the advantage of a larger bonding surface, better stability, and, because of the multiplication of the lamellae, allows better evacuation of gas bubbles. It therefore lends itself more easily to the production of a terminal for which the blade 60 is inclined and no longer vertical.

On reading the above, it is easy to see that the invention achieves the goals it has set for itself.

The above version of the invention simplifies the bonding process and makes it more "industrial". In particular, it is no longer necessary to have recourse to a foreign element (the segment of multi-strand electric wire). In addition, the manufacture of lugs is neither more complex nor more expensive than the production of a terminal according to the known art. The production of the strips can be carried out by cutting, at the same time as the conventional parts of a terminal. The materials that can be used do not differ from those of the known art.

Of course, the invention is not limited to the only examples of embodiments precisely described, in particular in relation to FIGS. 4 to 7.

First, other pod structures can be used, for example rivet-shaped structures (of the type shown in FIG. 2), in the form of a flat washer or in the form of an eyelet. It suffices that the base of these terminals has at least one zone provided with fine strips.

Other types of conductive adhesives can also be used. The materials that can be used are essentially linked to the specific application envisaged and are part of a simple technological choice within the reach of those skilled in the art.

Although particularly suitable for making connections for hot plates, in particular for kettles, the invention cannot be confined by only one type of application. It applies equally well to the realization of connection by bonding of all terminals on a track made of resistive material using a conductive resin, or more generally a conductive adhesive.

Claims (18)

Method for making an electrical connection by bonding using an electrically conductive substance (4), characterized in that it comprises at least the following steps: a) production at the end of a terminal (2,2 ′, 6) of electrically conductive material of an area formed by strands (3) or strips (64, 65); b) coating of this zone formed of strands or strips by said electrically conductive bonding substance (4); c) and applying said zone to said layer of conductive material (10a) to effect said bonding. Method according to claim 1, characterized in that it comprises at least the following steps: a) insertion, in a terminal (2.2 ') of electrically conductive material and comprising an orifice (20,20'), of a segment of multi-strand electric wire (3) in said orifice (20,20 '); b) coating of this segment of multi-strand electric wire (3) with said substance (4) of conductive bonding of electricity; c) and application of the assembly "segment of electric wire (3) - terminal (2.2 ′)" to said layer of conductive material (10a), in order to produce said bonding. Method according to claim 2, characterized in that said segment of electric wire (3) is made of copper and in that the strands (30, 31) composing this segment of multi-strand electric wire (3) have a diameter included in the range 0 , 5 to 0.8 mm. Method according to claim 2, characterized in that said bonding substance being a resin thermostable (4) conductive of electricity, an additional step of drying and crosslinking of this resin (4) is carried out. Method according to Claim 4, characterized in that the said resin (4) is a silver-loaded polyimide. Electrical connection made according to any one of Claims 1 to 5, characterized in that the said terminal is a rivet (2) comprising a neck (20). Electrical connection made according to any one of Claims 1 to 5, characterized in that the said terminal is a flat washer (2 ') comprising a central orifice (20'). Connection according to either of Claims 6 and 7, characterized in that the said layer of electrically conductive material on which the said terminal (2,2 ') is bonded is a resistive track (10) forming a heating resistor. Application of a connection according to any one of Claims 6 to 8 to a heating plate (1) for a heating container, in particular for a kettle. Method according to claim 1, characterized in that it comprises at least the following steps: a) production of a series of lamellae (64,65) in at least one substantially flat zone (62,63) of a rigid terminal (6), made of electrically conductive material; b) coating of this zone (64,65) provided with said lamellae (64,65) with said substance (4) of conductive bonding of electricity; c) and placing the zone (64,65) provided with the lamellae (64,65) on said layer of conductive material (10a), to effect said bonding. A method according to claim 10, characterized in that each of said strips (62,63) has a width at most equal to 1 mm. Method according to Claim 10, characterized in that the said bonding substance being a thermostable resin (4) which conducts electricity, an additional step of drying and crosslinking of this resin (4) is carried out. Method according to claim 12, characterized in that said resin (4) is a silver-loaded polyimide. Rigid thimble (6) for implementing the method according to any one of claims 10 to 13, characterized in that it comprises at least one flat wing (62, 63) forming a support intended to be placed on said layer of conductive material (10a) and a blade (60) intended to make an electrical connection with external connector elements (5) and in that each flat wing (62, 63) has a cut-out zone, so as to obtain, between these cuts, said lamellae (62,63). Lug according to claim 14, characterized in that said support comprises a central body (61,66,67) raised relative to said layer of conductive material (10a) and forming a bridge, so as to obtain a stiffening of the support of the terminal (6), and two flat side wings (62, 63) each provided with a series of strips (64, 65), and in that said blade (60) intended to make an electrical connection with connection elements outside (5) is folded at 60 ° relative to the support (62,61,63). Lug according to claim 15, characterized in that said blade (60) intended to make at least one electrical connection with external connector elements (5) is folded along an axis (Δ _p ) coincident with its pivot axis relative to said support (62,61,63). Lug according to claim 15, characterized in that said central body (61) comprises a cutout (66) adjacent to said blade (60) intended to make an electrical connection with external connector elements (5), so as to limit expansion effects when the terminal (6) is subjected to a rise in temperature. Application of a terminal according to any one of Claims 14 to 17, to a heating plate (1) for a heating container, in particular for a kettle, said layer of electrically conductive material on which said terminal (6) is bonded is a resistive track (10) forming a heating resistance.

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