FR2629300A1 - Assembly including two insulating substrates carrying conducting tracks, and method of joining these substrates - Google Patents

Abstract

The assembly 1 includes two insulating substrates 2, 3 each carrying conducting tracks 4, 5. The mechanical connection of the substrates 2, 3 is provided by a mass 9 of insulating adhesive material. The electrical connection of each track 4 to the corresponding track 5 is provided by one or more wires 7 made of conducting material, these wires being insulated from each other and forming part of a fabric segment 6 arranged between the substrates 2, 3. The method of manufacturing the assembly 1 is also described.

Description

ASSEMBLY COMPRISING TWO INSULATING SUBSTRATES CARRYING TRACKS
CONDUCTORS AND METHOD FOR ASSEMBLING SUCH SUBSTRATES
The present invention relates to an assembly comprising two insulating substrates each carrying conductive tracks, electrical connection means comprising connecting elements made of an electrically conductive material arranged between the substrates so that each track of one of the substrates is electrically connected to the corresponding track of the other substrate by at least one connection element, and mechanical connection means comprising a mass of insulating adhesive material disposed between substrates and adhering to these substrates.

 The present invention also relates to a method of assembling two insulating substrates carrying conductive tracks, comprising the introduction between the substrates of connection elements made of an electrically conductive material and of a mass of insulating adhesive material, the mechanical connection of the substrates using the mass of adhesive material and the electrical connection of each conductive track of one of the substrates with the corresponding conductive track of the other substrate using at least one of the connecting elements.

 In the known assemblies and methods which meet the above definitions and which are described, for example, in patent CH-A-607,666 or in patent application EP-AO 068,793, the elements of electrical connection between each track of a substrate and the corresponding track of the other substrate consist of particles of small dimensions dispersed in the mass of adhesive material, These particles can be grains of a metallic powder, such as a copper powder, d gold or silver, or carbon fiber.

 In order for the electrical connection between each track of a substrate and the corresponding track of the other substrate to be properly established, the dimensions of all the particles in the direction perpendicular to the substrates must be practically constant. Otherwise, the distance between the substrates would be determined by the size of the larger particles, and some tracks between which there are smaller particles may not be connected.

 Before being incorporated into the adhesive material, these particles must therefore be sorted, which is not very simple to carry out and which significantly increases the cost price of the process and of the device obtained by this process.

In addition, the number of particles per unit volume of adhesive material must also be between two fairly close limits at any point of the mass of the mixture;
If this condition is not fulfilled, the tracks of one of the substrates located in areas where the concentration of particles is insufficient may not be connected to the corresponding tracks of the other substrate or, on the contrary, short circuits may produce between adjacent tracks in areas where the concentration of particles is too high.

 However, at the time of the introduction of the particles into the adhesive material, as well as at the moment when the mixture of particles and of adhesive material must be put in place, it is of course necessary that this adhesive material is in a liquid state or all at least pasty.

 As long as this material is in this liquid or pasty state, the conductive particles tend to agglomerate together and / or to accumulate at the bottom of the container containing the mixture. It is therefore quite difficult to obtain the homogeneous distribution of the particles in the adhesive material which is necessary for obtaining correct electrical connections.

 Likewise, the quantity of mixture deposited on one or other of the substrates during the assembly operation must be very precisely dosed to avoid burrs -produced by an excess of mixture or an insufficient mechanical bond of the substrates due to too little of this mixture. In the latter case, the electrical connection between certain tracks may also not be made.

 It can be seen that, despite their apparent simplicity, the known assembly methods are not very easy to implement, nor very inexpensive, and that they do not always guarantee a correct electrical connection between each conductive track of one of the substrates and the corresponding track of the other substrate.

 An object of the present invention is to provide an assembly of the same kind as that which has been defined above but which does not have the defects of known assemblies, that is to say in which each track of one of the substrates and the corresponding track of the other substrate are certainly electrically connected and in which there can be no short circuit between two adjacent tracks of the same substrate.

 For this purpose, the assembly according to the invention is characterized in that the electrical connection means comprise a segment of fabric comprising wires made of said conductive material isolated from each other and constituting the connection elements, and by the fact that the tissue segment is attached to the substrates by the insulating adhesive material.

 Another object of the present invention is to provide an assembly method which does not have the drawbacks of known methods, that is to say a method which is simple to implement and by which the electrical connection between each track of one of the substrates and the corresponding track of the other substrate is certainly established, without there being any risk of short-circuiting between two adjacent tracks.

 For this purpose, the method according to the invention is characterized in that the introduction of the connecting elements is carried out by interposing between the substrates a segment of fabric comprising threads of said conductive material isolated from each other and by arranging the segment of fabric so that at least one of the son of conductive material extends between each track of one of the substrates and the corresponding track of the other substrate and constitutes one of the connecting elements, and thereby that it involves fixing the segment of fabric to the substrates using the mass of adhesive material.

The invention will now be described in detail using the drawing in which:
- Figure 1 is a partial sectional view of an embodiment of an assembly according to the invention, this section being taken along line II of Figure 2;
- Figure 2 is another partial sectional view of the assembly of Figure 1, this section being made along line II-II of this Figure 1;
- Figure 3 is a perspective view, greatly enlarged, of part of a segment of tissue used in all of Figures 1 and 2; and
- Figure 4 is a partial sectional view, similar to that of Figure 1, of another embodiment of an assembly according to the invention.

 The assembly 1 shown in Figures 1 and 2 comprises two insulating substrates 2 and 3 which are partially arranged opposite one another.

 The faces of the substrates 2 and 3 which are turned towards each other each carry a plurality of conductive tracks designated by 4 and 5 respectively.

 In the area where the substrates 2 and 3 are opposite one another all these conductive tracks 4 and 5 are parallel to each other.

 By way of nonlimiting example, the assembly 1 can be a device for developing and displaying any information.

 In such a case, the substrate 2, for example, can be constituted by one of the plates of a liquid crystal display cell, and the tracks 4 can be connected to the control electrodes of the cell.

 Still in this case, the substrate 3 can then be constituted by a flexible or rigid film carrying the integrated circuit for controlling the cell, and the tracks 5 can be connected to the terminals of this integrated circuit.

 The two substrates 2 and 3 are arranged so that each track 4 is located opposite the corresponding track 5.

 The assembly 1 also comprises a segment of fabric 6 disposed between the substrates 2 and 3 and in contact with the tracks 4 and 5.

 This segment of fabric 6, part of which is shown, very enlarged, in FIG. 3, comprises a plurality of first threads 7 which all extend in a direction substantially parallel to the direction of tracks 4 and 5.

 In the embodiment shown in Figures 1 and 2, all these wires 7 are made of an electrically conductive material. These wires 7 can be, for example, copper, silver, gold or carbon.

 The fabric segment 6 also comprises a plurality of second threads 8 which all extend in a transverse direction relative to the direction of the threads 7. All these threads 8 are made of an insulating material, which can be a plastic material such as, for example, a polyester or a polyamide, an organic material such as silk or cotton, or glass.

 Fabrics that can be used to make segment 6 are commercially available.

For example, the Swiss Silk Society in Bluter, in
Zürich (Switzerland) sells, under the trade name of Carbotex, such fabrics in which the conductive wires such as the wires 7 are made of carbon and the insulating wires such as the wires 8 are made of a polyamide.

 Similarly, the Hexel-Genin Company, in Villeurbane (France) sells, under the trade name of Textoglass, such fabrics in which the conducting wires such as the wires 7 are also made of carbon and the insulating wires such as the wires 8 are in glass or aramid (trade name of a polyamide from the Dupont de Nemours house).

 The fabric in which the segment 6 is cut must of course be chosen so that each track 4 is electrically connected to the corresponding track 5 in the finished assembly 1.

 One way of fulfilling this condition consists in choosing a fabric in which the pitch of the conducting wires 7, that is to say the distance separating their axes, is equal to the pitch of the conducting tracks 4 and 5 or is a sub-multiple of this last step.

 It is also possible to choose a fabric in which the pitch of the conducting wires-7 is less than the width of the conducting tracks 4 and 5.

 It should be noted in this connection that it is advantageous to choose a fabric in which the pitch of the wires 7 is as small as possible, because the lower the ratio between this pitch and that of the conductive tracks 4 and 5, the lower the error which can be admitted in the position of the tissue segment 6 relative to the substrates 2 and 3 is large.

 It can be seen that, by the very fact that the segment 6 is a segment of fabric, the conducting wires 7 and the insulating wires 8 pass alternately from one face to the other of this segment 6.

 As the wires 7 extend parallel to the direction of the tracks 4 and 5, each wire 7 which is in contact with a track 4 is therefore also in contact with the corresponding track 5. These wires 7 therefore constitute the electrical connection elements between these tracks.

 In addition, it can be seen that each thread 7 is maintained, over its entire length, at a certain distance from the two other threads 7 which are adjacent to it by the threads 8 which pass between them from one face to the other of the segment of fabric. 6.

 The wires 7 are therefore isolated from each other, and no short-circuit can occur between two tracks 4 or two adjacent tracks 5.

 In the embodiment shown in Figures 1 and 2, the assembly 1 also includes a mass 9 of insulating adhesive material disposed between the substrates 2 and 3 in the area where these face each other. This mass 9 of adhesive material is solid, and it adheres to the two substrates 2 and 3, thus ensuring the mechanical connection of these and, consequently, the maintenance of the segment of tissue 6 between these substrates 2 and 3 and wires 7 in electrical contact with tracks 4 and 5.

 The material of the mass 9 can be chosen fairly freely from the numerous adhesive materials well known to specialists. This choice will not be described in detail here, because it depends on many factors such as the nature of the substrates 2 and 3, the conductive tracks 4 and 5 and the wires 7 and 8 of the tissue segment 6.

 It can simply be recalled here that, whatever the material chosen, it must obviously be able to be brought into a first state where it is fluid, that is to say liquid or pasty, and where it adheres to the substrates 2 and 3 as well as, preferably, tracks 4 and 5. In addition, this material must be able to be brought into a second state where it is solid and continues to adhere to substrates 2 and 3 and, if necessary, tracks 4 and 5 when she was contacted with them while she was in her first state.

 By way of nonlimiting example, the material of the mass 9 can be an adhesive plastic material called two-component material such as an epoxy resin. Such a material is supplied by its manufacturer in the form of an unpolymerized resin and a hardener, both in liquid or pasty form. Its first state is that in which it is found after these two components have been mixed.

Its second state is that in which it is found when the resin is polymerized.

 Still by way of example, the mass material 9 can be a thermoplastic material such as a polyamide, which is in its second state, solid, at room temperature, which passes into its first state, fluid, when it is heated to a temperature above its melting temperature and which returns to its second state when cooled to this melting temperature.

 The assembly 1 represented in FIGS. 1 and 2 # can be produced by implementing various methods, some of which will now be described by way of nonlimiting examples.

 In a first method, a determined quantity of adhesive material in its fluid state is deposited on one of the substrates, for example the substrate 2, at the location where the mass of material 9 in the finished assembly 1 will be located.

 The tissue segment 6, previously cut to the desired dimensions, is then deposited on the adhesive material, while the latter is still in its fluid state, so that the conductive wires 7 extend parallel to the tracks 4.

 Still while the adhesive material is in its fluid state, the second substrate, that is to say the substrate 3 in this example, is then applied against the tissue segment 6, in a position and an orientation such as the tracks 4 and 5 are parallel to each other and that the corresponding tracks are opposite one another.

 This application of the substrate 3 against the substrate 2 is carried out with sufficient force for the tissue segment 6 to come into contact at least with the tracks 4 carried by the substrate 2.

 The adhesive material is then put into its second state, the force mentioned above preferably remaining applied to the substrates 2 and 3 until the adhesive material is sufficiently hard so that these substrates no longer risk moving one compared to each other.

 In another method of producing the assembly 1, the tissue segment 6, previously cut to the desired dimensions is firstly impregnated with the adhesive material while the latter is in its fluid state.

 This segment of fabric 6 thus impregnated is then placed at the desired location on one of the substrates, the substrate 2 for example, while the adhesive material is still in its fluid state and always taking care that the conductive wires 7 be parallel to tracks 4.

 As in the first method described above, the second substrate, that is to say the substrate 3 in this example, is then applied against the tissue segment 6, and the adhesive material is brought into its solid state. Also in this case, a force is preferably applied to the substrates 2 and 3 while the adhesive material is still in its fluid state, and this force is maintained until this adhesive material is in its solid state, to ensure that the conducting wires 7 come into good contact with the conducting tracks 4 and 5.

 In the case where the adhesive material is a thermoplastic material, it is obviously possible to allow this material to cool, and therefore to resume its solid state, between the stages of the processes described above where it is fluid.

 It is thus possible to impregnate a relatively large piece of fabric in advance with such a thermoplastic adhesive material brought into its liquid state by heating to an adequate temperature, and to cut the segment of fabric 6 only after this material has resumed its state. solid by cooling.

 In such a case, the adhesive material can also be deposited on one of the substrates in the form of a solid film, of adequate dimensions, then place the segment of fabric 6 on this film, then, on this segment 6 the second substrate.

 The two substrates are then subjected to a force tending to apply them against each other using a tool of suitable shape heated to a temperature such that the adhesive material takes its fluid state. The tool is then cooled, so that this adhesive material returns to its solid state.

 It should be noted that, in the embodiment shown in FIGS. 1 and 2, the diameter of the wires 7 is substantially equal to that of the wires 8. However, in other embodiments which have not been shown, the conducting wires 7 can have a diameter greater than that of the wires 8. This arrangement can be advantageous, because it makes it easier to obtain good contact between the conducting wires 7 and the tracks 4 and 5 and therefore to reduce the force which '' apply to substrates 2 and 3 to obtain this contact.

 In the embodiment shown in FIGS. 1 and 2, the mechanical holding function of the substrates 2 and 3 is provided by the mass of adhesive material 9.

FIG. 4 represents another embodiment of an assembly according to the invention, designated by the reference 1 ′, which does not include the mass of adhesive material 9 of the assembly 1 of FIGS. 1 and 2
All the other elements of the assembly 1 'are similar to the corresponding elements of the assembly 1 and are designated by the same references.

 In assembly 1 ′, the mechanical bonding function of the substrates 2 and 3 is also ensured by a mass of adhesive material, but this consists of the insulating threads 8 of the tissue segment 6 themselves, which are in a thermoplastic material and which adhere to these substrates 2 and 3 as well as to the conductive tracks 4 and 5.

 The fabrication of the assembly 1 is very similar to that of the assembly 1 and will not be described in detail here.

 It should simply be noted that in this case, the adhesive material which provides the mechanical connection of the substrates is introduced between them by the introduction of the tissue segment 6 # itself.

 In addition, if the wires 7 and 8 have the same diameter, the force which is applied to the substrates 2 and 3 in the manner described above must be sufficient so that the wires 7 situated between the tracks 4 and 5 are slightly crushed, so that the wires 8 surely come into contact with the substrates 2 and 3 and are themselves slightly crushed. It is thus guaranteed that, in the finished assembly 1 ′, the contact surface between the wires 8 and the substrates 2 and 3 or the tracks 4 and 5 is sufficient for the mechanical connection of these substrates to be properly ensured. It may be noted in this connection that the thickness of the tracks 4 and 5 has been exaggerated in FIGS. 1, 2 and 4, and that the wires 7 must not be deformed much so that the wires 8 come into contact with the substrates 2 and 3.

 While the force mentioned above is applied to the substrates 2 and 3, it is obviously necessary to heat the wires 8 to a temperature at least equal to the melting point of the thermoplastic material from which they are made, then to cool them. so that they resume their solid state. This heating and cooling can obviously be carried out using the tool used to apply this force to these substrates.

 It can be seen that, in the case of the assembly 1 ′, it is not necessary for the wires 7 and the wires 8 to have the same diameter. It is easy to see that it is even advantageous to use a segment of fabric 6 whose insulating wires 8 have a diameter greater than that of the conducting wires 7, because the force which must be exerted on the substrates 2 and 3 during manufacture of the assembly 1 ′ can then be limited to that which must be exerted so that the wires 8 deform when they are heated and that the wires 7 come into contact with the tracks 4 and 5. This force is obviously less than that which must be exerted when the wires 8 have the same diameter as the wires 7. Furthermore, in this case, the contact surface of the wires 8 with the substrates 2 and 3 or with the tracks 4 and 5 is higher, which improves the mechanical bonding of the substrates.

  In the embodiments which have been described above, all the threads of the fabric segment 6 which are parallel to the tracks 4 and 5 and which are designated by the reference 7, are made of a conductive material.

 In other embodiments of the present invention, which have not been shown, only part of these wires parallel to the tracks 4 and 5 is made of a conductive material, one or more wires of insulating material, also parallel to these tracks 4 and 5, being interposed between two wires of conductive material and woven, like the latter, with the insulating wires such as the wires 8.

 In such a case, it is obviously necessary to ensure that the distance separating the axes of two adjacent conductive wires fulfills the conditions which have been stated above in the case where all the wires parallel to the tracks 4 and 5 are made of a conductive material .

Claims (16)

 1. Assembly comprising two insulating substrates (2, 3) each carrying conductive tracks (4, 5), electrical connection means comprising connecting elements made of an electrically conductive material arranged between the substrates (2, 3) so that each track (4, 5) of one of the substrates (2, 3) is electrically connected to the corresponding track (4, 5) of the other substrate (2, 3) by at least one connecting element, and mechanical connection means comprising a mass of insulating adhesive material (9) disposed between the substrates (2, 3) and adhering to these substrates (2, 3), characterized in that the electrical connection means comprise a segment of fabric ( 6) comprising wires of said conductive material (7) insulated from each other and constituting the connecting elements, and by the fact that the segment of fabric (6) is fixed to the substrates (2, 3) by the insulating adhesive material (9).  2. Assembly according to claim 1, characterized in that the fabric segment (6) comprises wires made of an insulating material (8) woven with the wires made of conductive material (7) and arranged transversely relative to the latter, and by the fact that the son of conductive material (7) are insulated from each other at least by the son of insulating material (8) passing between them from one face to the other of the segment of fabric (6).  3. An assembly according to claim 1, characterized in that the son of conductive material (7) are isolated from each other at least by son of an insulating material arranged on either side of each wire of conductive material ( 7).  4. Assembly according to one of claims 1 to 3, characterized in that the insulating adhesive material (9) is a thermoplastic material.  5. An assembly according to claim 4, characterized in that at least part of the son of insulating material (8) is made of said thermoplastic material.  6. An assembly according to claim 5, characterized in that the mass of insulating adhesive material (9) consists of said son of thermoplastic material.  7. The assembly of claim 1, characterized in that the fabric segment (6) is impregnated with the insulating adhesive material.  8. A method of assembling two insulating substrates (2, 3) carrying conductive tracks (4, 5), comprising the introduction between the substrates (2, 3) of connecting elements made of an electrically conductive material and of a mass of insulating adhesive material, the mechanical connection of the substrates using the mass of adhesive material and the electrical connection of each conductive track (4, 5) of one of the substrates (2, 3) with the conductive track (4, 5) corresponding to the other substrate (2, 3) using at least one of the connecting elements, characterized in that the introduction of the connecting elements is carried out by interposing between the substrates ( 2, 3) a segment of fabric (6) comprising threads of said conductive material (7) isolated from each other and arranging the segment of fabric (6) so that at least one of the threads of conductive material (7 ) extends between each track (4, 5) of one of the substrates (2, 3) and the corresponding track (4, 5) of the other substrate (2, 3 ) and constitutes one of the connecting elements, and by the fact that it comprises the attachment of the tissue segment (6) to the substrates (2, 3) using the mass of adhesive material (9).  9. Method according to claim 8, characterized in that the segment of fabric (6) comprises wires made of an insulating material (8) woven with the wires made of conductive material (7) and arranged transversely with respect to the latter, and by the fact that the son of conductive material (7) are isolated from each other at least by the son of insulating material (8) passing between them from one face to the other of the fabric segment (6).  10. Method according to claim 8, characterized in that the son of conductive material (7) are isolated from each other at least by son of an insulating material arranged on either side of each wire of conductive material ( 7).  11. Method according to one of claims 8 to 10, characterized in that the insulating adhesive material is capable of being put in a first state where it can adhere to the substrates (2, 3) and in a second state where it is; solid, and by the fact that the mechanical connection of the substrates (2, 3) involves putting the adhesive material successively in its first and in its second state and bringing the substrates (2, 3) into contact with the mass adhesive material (9) while the adhesive material is in its first state and while it is being put into its second state.  12. Method according to claim 11, characterized in that the adhesive material is a thermoplastic material capable of being brought into its first state by heating to a temperature equal to or greater than a determined temperature.  13. The method of claim 12 characterized in that at least part of the son of insulating material (8) is of said thermoplastic material, and that the introduction of the mass of insulating adhesive material (9) is also carried out interposing the tissue segment (6) between the substrates (2, 3).  14. Method according to claim 8, characterized in that the introduction of the mass of adhesive material (9) is carried out independently of the introduction of the tissue segment (6).  15. Method according to claim 8, characterized in that it comprises an impregnation of the tissue segment (6) with the adhesive material, and in that the tissue segment (6) is interposed between the substrates (2, 3) after this impregnation.  16. The method of claim 8, characterized in that the tissue segment (6) is first fixed to one of the substrates (2, 3) and that the other substrate (2, 3) is then attached to the fabric segment (6).