Abstract:
The invention relates to an electronic textile comprising a textile substrate having a substrate electrode, and an electronic component having a component electrode. The component electrode is in electrically conductive contact with the substrate electrode via a coupling layer having a directionally dependent conductance so as to preferentially allow an electrical current to flow between the substrate electrode and the component electrode. As the coupling layer does not have to be patterned to prevent the occurrence of parasitic electrical currents, the electrically conductive contact between the substrate electrode and the component electrode has an improved reliability.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to an electronic textile comprising a textile substrate having a substrate electrode, and an electronic component having a component electrode, the component electrode being in electrically conductive contact with the substrate electrode via a coupling layer. 
         [0002]    The invention also relates to a method of manufacturing the electronic textile according to previous paragraph. 
       BACKGROUND OF THE INVENTION 
       [0003]    A textile is a material comprised of interlacing fibers, that can for instance be manufactured by weaving, knitting, crocheting, knotting, or pressing fibers together. Many types of textiles are used in our every day life. When electronic components (i.e. devices that work by controlling the flow of electrons) are integrated into a textile new application fields emerge. When the textile is an integral part of the electrical circuit comprising the electronic components, an electronic textile is obtained. 
         [0004]    An example of an electronic component is a LED package in the form of a surface mounted device (SMD-LED), which can be attached to a textile substrate by gluing, soldering, snap button connection or stitching. The resulting light-emitting textile that could open up a wide range of new interior and apparel applications, ranging from illumination to atmosphere creation to messaging. 
         [0005]    An electronic textile is known from UK patent application GB2396252A. The known light-emitting textile comprises SMD-LED&#39;s that are fixed by an electrically conductive epoxy to a fabric member having electrically conductive textile tracks. 
         [0006]    A drawback of the known electronic textile is a poor reliability of the electrically conductive contact between the SMD-LED&#39;s and the electrically conductive textile tracks comprised in the fabric member. 
       SUMMARY OF THE INVENTION 
       [0007]    It is an object of the invention to provide an electronic textile comprising a textile substrate having a substrate electrode, and an electronic component having a component electrode, the component electrode being in electrically conductive contact with the substrate electrode via a coupling layer, wherein the coupling layer comprises a material that enables an improved reliability of the electrically conductive contact. 
         [0008]    It is a further object of the invention to provide a method for manufacturing the electronic textile according to the previous paragraph. 
         [0009]    According to a first aspect of the invention the object is realized by an electronic textile comprising a textile substrate having a substrate electrode, and an electronic component having a component electrode, the component electrode being in electrically conductive contact with the substrate electrode via a coupling layer, characterized in that the coupling layer comprises an anisotropically conductive material. 
         [0010]    An anisotropically conductive material is a material that has a directionally dependent electrical conductance. In other words, the electrical conductance of the material is different when measured along different axes. In the context of this invention, the anisotropically conductive material is provided such that the direction of highest electrical conductance is between the substrate electrode and the component electrode. 
         [0011]    The electrically conductive epoxy used in the known electronic textile serves to improve the electrical contact between the component electrode and the substrate electrode. However, as the electrically conductive epoxy is an isotropically conductive material (i.e. the electrical conductance of the material is similar when measured along different axes), it has to be applied in a patternwise manner in order to prevent the occurrence of a parasitical electrical current (i.e. an undesired electrical current that is due to an unintentional cause). 
         [0012]    The inventors have realized that a proper patternwise application of an coupling layer on a textile substrate is seriously hampered by dimensional instabilities of the textile substrate, meaning that dimensions of the textile substrate may, for instance, change as a result of stretching or heating the textile substrate. As a result, the reliability of the electrically conductive contact between the substrate electrode and the component electrode cannot be optimally improved by using a coupling layer comprising an isotropically conductive material. 
         [0013]    In contrast to a coupling layer comprising an isotropically conductive material, the tolerance of applying a coupling layer comprising an anisotropically conductive material is much larger as it can be applied to cover an area that extends beyond the area wherein the electronic component has to be in electrically conductive contact with the textile substrate. Consequently, the use of a coupling layer comprising an anisotropically conductive material is much less sensitive to dimensional instabilities of the textile substrate, and it may act as an under fill layer to improve the mechanical reliability of the connection between the textile substrate and the electronic component. 
         [0014]    An additional advantage is that the coupling layer, when present at locations on the textile substrate where no electronic component is connected, can be used as an adhesive for attaching a second layer to the textile substrate, such as a covering textile layer to improve the appearance and/or the robustness of the electronic textile. 
         [0015]    In a first embodiment of the electronic textile according to the invention, the anisotropically conductive material comprises an electrically insulative binder and electrically conductive particles. When in such a coupling layer the electrically conductive particles are dispersed in the electrically insulative binder at a concentration that is too low to allow the pre-existence of an electrically conductive path, only at the location where the electronic component has been provided on the textile substrate will an electrically conductive path be created as a result of compressing the anisotropically conductive material. Electrically conductive contact between the component electrode and the substrate electrode can either be made by direct physical contact between the substrate electrode and the component electrode, or by indirect contact via electrically conductive particles that have been trapped between the component electrode and the substrate electrode. 
         [0016]    In a second embodiment of the electronic textile according to the invention, the anisotropically conductive material comprises an electrically insulative binder and electrically conductive particles, wherein the electrically conductive particles are elastic. The elasticity of the electrically conductive particles results in them being reversibly deformable under stress, such as when they get trapped between the component electrode and the substrate electrode. In this way, the electrically conductive contact between the component electrode and the substrate electrode is further improved as the reversibly deformed electrically conductive particles exert a pressure on both electrodes. 
         [0017]    In a third embodiment of the electronic textile according to the invention, the anisotropically conductive material comprises an electrically insulative binder and electrically conductive particles, wherein the electrically insulative binder is a compound chosen from the group consisting of thermosetting and thermoplastic synthetic resins. This embodiment further improves the reliability of the electrically conductive contact between the substrate electrode and the component electrode as compressive strain in the thermosetting or thermoplastic synthetic resins causes the electronic component to be pulled towards the textile substrate. 
         [0018]    In a fourth embodiment of the electronic textile according to the invention, the substrate electrode comprises an electrically conductive yarn, and the anisotropically conductive material is an outer layer of the electrically conductive yarn. This embodiment allows the use of an electrically conductive yarn as substrate electrode that can be insulated while at the same time allowing for an improved mechanical and electrically conductive contact to be made to the component electrode. 
         [0019]    In a fifth embodiment of the electronic textile according to the invention, the electronic component comprises a clamping member. This embodiment further improves the reliability of the electrically conductive contact between the substrate electrode and the component electrode by the clamping member pulling the electronic component towards the textile substrate. 
         [0020]    According to a second aspect of the invention the object is realized by a method of manufacturing an electronic textile comprising a textile substrate having a substrate electrode, and an electronic component having a component electrode, the method comprising the steps of providing one of the substrate electrode and the component electrode with a coupling layer that is electrically insulative in a direction along the layer and that is arranged to permit electrical conductivity in a direction normal to the coupling layer, and establishing an electrically conductive contact between the substrate electrode and the component electrode via the coupling layer. 
         [0021]    In a first embodiment of the method according to the invention, the coupling layer comprises an electrically insulative binder and electrically conductive particles, and wherein the step of establishing an electrically conductive contact between the substrate electrode and the component electrode via the coupling layer comprises an application of pressure in a direction normal to the coupling layer. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]    Examples of the invention will now be described in detail with reference to the accompanying drawings, in which: 
           [0023]      FIG. 1  shows a schematic cross-section of a first embodiment of an electronic textile according to the invention; 
           [0024]      FIG. 2  shows a schematic cross-section of a second embodiment of an electronic textile according to the invention; 
           [0025]      FIG. 3  shows a schematic cross-section of an electrically conductive particle that may be used in an electronic textile according to the invention; 
           [0026]      FIG. 4  shows a schematic cross-section of a third embodiment of an electronic textile according to the invention; 
           [0027]      FIG. 5  shows a textile substrate for use in an embodiment of an electronic textile according to the invention; 
           [0028]      FIG. 6  shows a perspective view and a cross-section of a first yarn that can be used in the textile substrate of  FIG. 5 ; 
           [0029]      FIG. 7  shows a perspective view and a cross-section of a second yarn that can be used in the textile substrate of  FIG. 5 ; 
           [0030]      FIG. 8  shows a method of manufacturing an electronic textile according to the invention. 
       
    
    
       [0031]    It should be noted that these figures are diagrammatic and not drawn to scale. For the sake of clarity and convenience, relative dimensions and proportions of parts of these figures have been shown exaggerated or reduced in size. 
       DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0032]    In the following description, the present invention is described with reference to exemplary electronic textiles according to the invention. 
         [0033]      FIG. 1  shows a schematic cross-section of the electronic textile  1  according to the invention. The electronic textile  1  comprises the textile substrate  11  having the substrate electrode  111 , and the electronic component  12  having the component electrode  121 . The substrate electrode  111  is connected to the component electrode  121  via the anisotropically conductive material  13 . 
         [0034]    Preferably the anisotropically conductive material  13  is applied as a tape, but it can also be applied as a foil, a paste, a grid, or in the form of areas such as strips. 
         [0035]    In  FIG. 1 , the anisotropically conductive material  13  comprises the electrically insulative binder  131  and electrically conductive particles  132 . The electrically insulative binder  131  comprises a thermosetting synthetic resin, and the electrically conductive particles  132  are spherical particles with a diameter of about 3 to 5 micrometer. Alternatively, a thermoplastic synthetic resin may also be used as electrically insulative binder. 
         [0036]    In the state wherein the anisotropically conductive material  13  is applied (i.e. before the electronic component  12  has been connected to the textile substrate  11 ), it is electrically insulative as the electrically conductive particles  132  are spaced too far apart to form an electrically conductive path. For this purpose, the concentration of the electrically conductive particles  132  in the anisotropically conductive material  13  is preferably in a range of about 5 to 10 volume percent. 
         [0037]    During connection of the electronic component  12 , pressure is exerted on the anisotropically conductive material  13 , and the material is locally compressed so that the electrically conductive particles  132  move closer together. As the electrically insulative binder  131  comprises a thermosetting synthetic resin, a force is exerted at locations where the anisotropically conductive material  13  is compressed, the force being such that the electronic component  12  is being pulled towards the textile substrate  11 . 
         [0038]    At the location  14 , the component electrode  121  is connected to the substrate electrode  111 , and the anisotropically conductive material  13  has been compressed to such an extent that several electrically conductive particles  132  have been trapped between the component electrode  121  and the substrate electrode  111 , thereby creating an electrically conductive path between the two electrodes. In  FIG. 1 , the component electrode  121  and the substrate electrode  111  are connected via a monolayer of electrically conductive particles  132 . Of course, the connection may, at least partly, also be formed by a multilayer of electrically conductive particles  132 , or by direct physical contact between the component electrode  121  and the substrate electrode  111 . 
         [0039]    At the location  15 , where the component electrode  121  is not connected to the substrate electrode  111 , the anisotropically conductive material  13  acts as a non-conductive under fill layer, and improves the adhesive strength between the electronic component  12  and the textile substrate  11 . 
         [0040]    At the location  16 , the anisotropically conductive material  13  is not compressed. Here it is exposed and available for attachment of an auxiliary layer, such as a protective and/or decorative layer. 
         [0041]      FIG. 2  shows a schematic cross-section of the electronic textile  2  according to the invention. The electronic textile  2  comprises the textile substrate  21  having the substrate electrode  211 , and the electronic component  22  having the component electrode  221 . The substrate electrode  211  is connected to the component electrode  221  via the anisotropically conductive material  23 . The anisotropically conductive material  23  comprises the electrically insulative binder  231  and electrically conductive particles  232 . 
         [0042]    The electrically conductive particles  232  are elastic, which means that they are capable of reversibly deforming under stress. For this purpose, the electrically conductive particles  232  comprise a synthetic resin core  233  that is coated with an electrically conductive material  234 , such as a metal. Preferably, the synthetic resin core  233  is coated with a Ni—Au layer, as Ni provides the electrically conductive particles  232  with a high hardness, and Au with a high corrosion resistance and a high conductance. At the location  24 , the component electrode  221  is connected to the substrate electrode  211 , and the anisotropically conductive material  23  has been compressed to such an extent that several electrically conductive particles  232  have been trapped between the component electrode  221  and the substrate electrode  211 , thereby creating an electrically conductive path between the two electrodes. Furthermore, when the trapped electrically conductive particles  232  are deformed, their elasticity causes them to constantly press outward on both the substrate electrode  211  and the component electrode  221 , thereby improving the reliability of the electrically conductive contact between the two electrodes. 
         [0043]      FIG. 3  shows a schematic cross-section of the electrically conductive particle  332 , that may also be used as electrically conductive particle in an anisotropically conductive material. The electrically conductive particle  332  comprises a synthetic resin core  333  that is coated with an electrically conductive material  334 , such as a Ni—Au layer. The electrically conductive particle  332  further comprises an electrically insulative outer layer  335 , that can be pushed away when the electrically conductive particle  332  is trapped and deformed between the substrate electrode  311  and the component electrode  321 , allowing the electrically conductive layer  234  to establish an electrically conductive connection between the substrate electrode  311  and the component electrode  321 . The electrically insulative outer layer  335  prevents the electrically conductive particle  332  from forming an electrically conductive contact in a direction perpendicular to the direction wherein it is deformed, such as the direction parallel to the plane of the textile substrate. 
         [0044]      FIG. 4  shows a schematic cross-section of the electronic textile  4  according to the invention. The electronic textile  4  comprises the textile substrate  41  having the substrate electrode  411 , and the electronic component  42  having the component electrode  421 . The substrate electrode  411  is connected to the component electrode  421  via the anisotropically conductive material  43 . The anisotropically conductive material  43  comprises the electrically insulative binder  431  and electrically conductive particles  432 . 
         [0045]    In order to increase the pressure that is used to compress the anisotropically conductive material  43  at the locations  44  and  45 , so as to obtain an improved mechanical and electrically conductive connection between the electronic component  42  and the textile substrate  41 , the electronic component  42  comprises clamping members  422 . In  FIG. 4 , the clamping members  422  have penetrated through the textile substrate  41 . Alternatively, a clamping member may also be used that wraps around an edge of a textile substrate. A clamping member and a component electrode may be integrated into a single element. 
         [0046]    Next to the anisotropically conductive materials  13 ,  23 , and  43  as shown in  FIGS. 1 ,  2 , and  4 , respectively, other types of anisotropically conductive materials may be used in an electronic textile according to the invention. 
         [0047]    A first example of an alternative anisotropically conductive material comprises a quantum tunneling composite. A quantum tunneling composite comprises electrically conductive particles dispersed in an electrically insulative binder. Similarly as for the anisotropically conductive material  13  of  FIG. 1 , without pressure, the electrically conductive particles are too far apart to conduct an electrical current, but when pressure is applied they move closer to the extent that electrons can tunnel through the electrically insulative binder. 
         [0048]    A second example of an alternative anisotropically conductive material comprises an electrically insulative binder and electrically conductive particles that are aligned such that electrically conductive paths exist in a direction normal to the surface of the anisotropically conductive material. In contrast to the examples presented above, here the anisotropically conductive material is already anisotropically conductive prior to connection of an electronic component to a textile substrate. The electrically conductive particles may have been aligned by applying an external stimulus, such as a magnetic field, or via a self-alignment process. 
         [0049]      FIG. 5  shows the textile substrate  51  for use in a further embodiment of an electronic textile according to the invention. The textile substrate  51  comprises electrically conductive warp and weft yarns  511  and  512 , respectively, and electrically insulative yarns  513 . The electrically conductive warp and weft yarns  511  and  512  are partly exposed at the surface  514  of the textile substrate  51 , making them available for connecting to electronic components, for instance via the connector areas  515  and  516 . 
         [0050]      FIG. 6  shows a perspective view and a cross-section of the yarn  611 . The yarn  611  can be used as electrically conductive warp or weft yarn in the textile substrate  51  of  FIG. 5 . The electrically conductive yarn  611  comprises a bundle of electrically conductive fibers  612 , the bundle being coated with an outer layer  613 . The outer layer  613  is an anisotropically conductive material according to any of the anisotropically conductive materials described hereinbefore. Accordingly, the outer layer  613  is electrically insulative in the direction  614  along the yarn  611 , and it is arranged to permit electrical conductivity in the directions  615  normal to the yarn  611 . 
         [0051]      FIG. 7  shows a cross-section of the yarn  711 . The yarn  711  can be used as electrically conductive warp or weft yarn in the textile substrate  51  of  FIG. 5 . The electrically conductive yarn  711  comprises electrically conductive fibers  712 , each of which is separately coated with an outer layer  713 . The outer layer  713  is an anisotropically conductive material according to any of the anisotropically conductive materials described hereinbefore. Accordingly, the outer layer  713  is electrically insulative in the direction  714  along the yarn  711 , and it is arranged to permit electrical conductivity in the directions  715  normal to the yarn  711 . 
         [0052]    An additional advantage of the yarns  611  and  711  is that the properties of the outer layers  613  and  713 , respectively, may be chosen such as to improve the weavability of the yarns. 
         [0053]      FIG. 8  schematically shows a method of manufacturing the electronic textile  8  comprising the textile substrate  81  having the substrate electrode  811 , and the electronic component  82  having the component electrode  821 . 
         [0054]    In the first phase (a), the coupling layer  83 , comprising the thermosetting electrically insulative binder  831  and the electrically conductive particles  832 , is applied to the substrate electrode  811 . During step (a), the coupling layer  83  is softened by increasing its temperature (dependent on the composition of the coupling layer  83 , but typically up to a temperature of about 100 degrees Celsius), and pressure (typically about 1 MPa) is applied to laminate the coupling layer  83  onto the textile substrate  81 . 
         [0055]    In the second phase (b), the electronic component  82  is positioned relative to the textile substrate  81  such that the projection of the component electrode  821  on the textile substrate  81  overlaps with the substrate electrode  811 . The electronic component  82  is then moved towards the textile substrate  81  by applying a pressure (typically about 4 to 5 MPa) in the direction  84  normal to the textile substrate  81 . Similarly as during step (a), also during step (b) the coupling layer  83  is softened by increasing its temperature. Again, the conditions for softening the coupling layer  83  are dependent on the composition of the coupling layer  83 . Preferably, during step (b) the coupling layer  83  is softened to a higher extent than during step (a), typically by increasing the temperature of the coupling layer  83  up to about 200 degrees Celsius. The component electrode  821  is pressed into the softened coupling layer  83  towards the substrate electrode  811  to an extent that an electrically conductive connection is obtained between the component electrode  821  and the substrate electrode  811 . Typically, the electronic component  82  is held down for approximately 10 seconds. 
         [0056]    In the third phase (c), the pressure on the electronic component  82  is released, and the temperature of the coupling layer  83  is reduced to room temperature, in order to obtain the electronic textile  8 . 
         [0057]    While in  FIG. 8  the coupling layer  83  is applied in the form of a layer that is laminated onto a substrate, a coupling layer can also be applied from a liquid phase, by a coating technique comprising for instance jetting, printing, spraying, or dispensing from a syringe. Furthermore, while in  FIG. 8 , prior to establishing an electrically conductive contact between the substrate electrode  811  and the component electrode  821 , the substrate electrode  811  is provided with the coupling layer  83 , it is also possible to first provide a component electrode with a coupling layer. 
         [0058]    While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments. 
         [0059]    Variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word “comprising” does not exclude other elements, and the indefinite article “a” or “an” does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.