Abstract:
Flexible LED assemblies ( 300 ) are described. More particularly, flexible LED ( 320 ) assemblies having flexible substrates ( 302 ) with conductive features ( 304, 306 ) positioned on or in the substrate, and layers of ceramic ( 310 ) positioned over exposed portions of the substrate to protect against UV degradation, as well as methods of making such assembles, are described.

Description:
FIELD 
       [0001]    The present description relates to flexible LED assemblies. 
       BACKGROUND 
       [0002]    Flexible circuits and assemblies are often used as connectors in various applications of electronics equipment, such as printers, computers, monitors and the like. Such circuits offer a benefit over previously used rigid circuit boards in both flexibility and space savings. 
         [0003]    The move to more highly flexible materials for circuits has created challenges, such as the greater degradation of, e.g., a flexible polyimide substrate versus a conventional ceramic substrate when exposed to UV light from LEDs mounted to such circuits. The present description aims to provide a solution that maintains the flexibility of the LED while preventing degradation of the circuitry substrate. 
       SUMMARY 
       [0004]    In one aspect, the present description relates to a flexible LED assembly. The flexible LED assembly includes a flexible polymer substrate, a first and second conductive feature and a layer of ceramic. First conductive feature is positioned within and on a surface of the flexible substrate. Second conductive feature is positioned within and on the surface of the flexible substrate at a distance from the first conductive feature, such that a portion of the flexible polymer substrate between the first and second conductive features is exposed. A layer of ceramic is positioned on the exposed flexible polymer surface between the first and second conductive features. 
         [0005]    In another aspect, the present description relates to a flexible LED assembly. The flexible LED assembly includes a flexible polymer substrate, a first conductive feature and a layer of ceramic. The flexible polymer substrate has a via that extends through it. First conductive feature is positioned on a bottom surface of the flexible substrate and a portion of the first conductive feature is positioned beneath the via. The layer of ceramic is positioned on the top surface of the flexible polymer substrate. Optionally, the assembly may include a second via in the flexible polymer substrate and a second conductive feature positioned on a bottom surface of the flexible substrate, where a portion of the second conductive feature is positioned beneath the second via. 
         [0006]    In yet another aspect, the present description relates to a method of making an LED assembly. The method includes the steps of applying a layer of ceramic to the surface of a substrate, the substrate comprising, prior to application of the ceramic, first portions on which the exposed top surface is polymer and second portions on which the exposed top surface is a conductive metal, removing the ceramic from the second portions of the surface of the substrate, and surface finishing the conductive metal in the second portions of the surface of the substrate. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is a cross-sectional view of a flexible LED assembly according to the present description. 
           [0008]      FIG. 2  is a cross-sectional view of a flexible LED assembly according to the present description. 
           [0009]      FIG. 3  is a cross-sectional view of a flexible LED assembly according to the present description. 
           [0010]      FIG. 4  is a cross-sectional view of a flexible LED assembly according to the present description.  FIGS. 5 a -5 c    provide a flow chart illustrating a method of making a flexible LED assembly according to the present description. 
           [0011]      FIGS. 6 a -6 c    provide a flow chart illustrating a method of making a flexible LED assembly according to the present description. 
       
    
    
       [0012]    The figures are not necessarily to scale. Like numbers used in the figures refer to like components. However, it will be understood that the use of a number to refer to a component in a given figure is not intended to limit the component in another figure labeled with the same number. 
       DETAILED DESCRIPTION 
       [0013]    Various exemplary embodiments of the disclosure will now be described with particular reference to the Drawings. Exemplary embodiments of the present disclosure may take on various modifications and alterations without departing from the spirit and scope of the disclosure. Accordingly, it is to be understood that the embodiments of the present disclosure are not to be limited to the following described exemplary embodiments, but are to be controlled by the limitations set forth in the claims and any equivalents thereof. 
         [0014]    In the following description, reference is made to the accompanying drawings that forms a part hereof and in which are shown by way of illustration. It is to be understood that other embodiments are contemplated and may be made without departing from the scope or spirit of the present disclosure. The following detailed description, therefore, is not to be taken in a limiting sense. 
         [0015]    Unless otherwise indicated, all numbers expressing feature sizes, amounts, and physical properties used in the specification and claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the foregoing specification and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by those skilled in the art utilizing the teachings disclosed herein. 
         [0016]    As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” encompass embodiments having plural referents, unless the content clearly dictates otherwise. As used in this specification and the appended claims, the term “or” is generally employed in its sense including “and/or” unless the content clearly dictates otherwise. 
         [0017]    Spatially related terms, including but not limited to, “lower,” “upper,” “beneath,” “below,” “above,” and “on top,” if used herein, are utilized for ease of description to describe spatial relationships of an element(s) to another. Such spatially related terms encompass different orientations of the device in use or operation in addition to the particular orientations depicted in the figures and described herein. For example, if an object depicted in the figures is turned over or flipped over, portions previously described as below or beneath other elements would then be above those other elements. 
         [0018]    As used herein, when an element, component or layer for example is described as forming a “coincident interface” with, or being “on” “connected to,” “coupled with” or “in contact with” another element, component or layer, it can be directly on, directly connected to, directly coupled with, in direct contact with, or intervening elements, components or layers may be on, connected, coupled or in contact with the particular element, component or layer, for example. When an element, component or layer for example is referred to as being “directly on,” “directly connected to,” “directly coupled with,” or “directly in contact with” another element, there are no intervening elements, components or layers for example. 
         [0019]      FIG. 1  provides a cross-sectional view of a flexible LED assembly  100  according to the present description. Flexible LED assembly  100  includes a flexible polymer substrate  102 . Flexible polymer substrate  102  may, in a preferred embodiment, be made of polyimide. Alternatively, substrate  102  may be PET, liquid crystalline polymer, polycarbonate, polyether ether ketone, thermoplastic polymer, or another appropriate flexible material. Flexible polymer substrate  102  will generally be a dielectric material. Assembly  100  includes a first conductive feature  104  that is positioned within and on a surface of the flexible substrate  102 . For example, first conductive feature is clearly positioned within the plane of the substrate but also is positioned on surface portions  105   a ,  105   b  of substrate  102 . Assembly  100  further includes a second conductive feature  106  that is also positioned within and on the surface (see, e.g., surface portions  107   a ,  107   b ) of the flexible substrate. 
         [0020]    Second conductive feature is positioned at a distance from the first conductive feature  104 , such that a portion of the flexible polymer substrate between the first and second conductive feature  108  is exposed. In at least one embodiment, the first and second conductive features may be made up of copper, although other conductive materials may be used. Finally, a layer of ceramic  110  is positioned on the exposed flexible polymer surface  108  between the first and second conductive features. Ceramic  110  may also be positioned on the surface of the substrate the opposite sides of first and second conductive features, such that any exposed portion of the flexible substrate  102  is covered with ceramic. In certain embodiments, ceramic  110  may be Al 2 O 3 , AIN, or BN, each of which provides appropriate UV shielding capabilities, though other ceramics with UV-shielding properties may be utilized. 
         [0021]      FIG. 2  illustrates another embodiment of a flexible LED assembly  200  according to the present description. In this embodiment, the flexible LED assembly includes a flexible polymer substrate  202  with a via  212  extending therethrough. A first conductive feature  204  is positioned on a bottom surface  205  of the flexible substrate, and a portion of the conductive feature  204  is positioned beneath the via  212 . A layer of ceramic  210  is positioned on the top surface  207  of the flexible polymer substrate. Additionally, flexible LED assembly  200  may include a second via  214  in the flexible polymer substrate, and a second conductive feature  206  positioned on a bottom surface  205  of the flexible substrate. At least a portion of second conductive feature  206  is positioned beneath the second via  214 . First and second conductive features may have the properties described with respect to the conductive features in assembly  100 , as may ceramic layer, and flexible polymer substrate (to the corresponding features with the same name). 
         [0022]    Of course, as the construction in  FIGS. 1 and 2  illustrate flexible LED assemblies, ultimately an LED will be mounted to the constructions. A number of appropriate LED constructions may be used.  FIG. 3  illustrates one such construction. Flexible LED assembly  300  includes an LED  320  that is mounted on both first conductive feature  304  and second conductive feature  306 . Flexible polymer substrate  302  is shielded from UV light emitted from LED  320  by layer of ceramic  310 . This particular construction may be one in which the LED  320  is a flip chip or a lateral die. Where the LED  320  is a flip chip, it may be bonded to first conductive feature  304  and second conductive feature  306  using a soldering technique. Alternatively, the LED may be eutectic bonded to the first and second conductive features. 
         [0023]    In a different embodiment, the LED may be wire bonded to one or both of the first and second conductive features.  FIG. 4  illustrates one exemplary construction. In this case, Flexible LED assembly  400  includes an LED  420  that is mounted on the first conductive feature  404 , but not on the second conductive feature  406 . As in the other constructions, the flexible polymer substrate  402  is shielded from UV light emitted from the LED by the layer of ceramic. However, here the LED is wire bonded to second conductive feature  406 . It may also be wire bonded to first conductive feature  404 , or may be attached to the first conductive feature using epoxy binding adhesive, conductive paste, anisotropic conductive paste (ACP), anisotropic conductive film (ACF) or eutectic bonding. 
         [0024]    In another aspect, the present description relates to a method of making an LED assembly. Such a method is illustrated in  FIGS. 5 a -5 c   . The first step in the method, as illustrated in  FIG. 5 a   , is applying a layer of ceramic  510  to the surface  532  of the substrate  530 , where the substrate includes, prior to application of ceramic  510 , first portions on which the exposed top surface is polymer (i.e. first portions  522 ), and second portions on which the exposed top surface is a conductive metal  526  (i.e. second portions  524 ). In one embodiment, ceramic layer  510  may be applied using a sputtering process. The ceramic layer  510  applied may be any appropriate material described with respect to ceramic layer  110 , for example, aluminum nitride. In one exemplary embodiment, conductive metal  526  may be copper. 
         [0025]    The next step, shown in  FIG. 5 b   , is to remove the ceramic  510  from the second portions  524  of the surface of the substrate. The removal step may be accomplished through a number of appropriate means. For example, in one case, a tacky liner may be laminated onto the regions of the ceramic  510  that correspond to the second portions. When the tacky liner is removed, it peels away the ceramic covering second portions  524 . Alternatively, the ceramic  510  may be removed from over second portions using a bristle brush technique, i.e., mechanically brushing off the ceramic using an abrasive substrate. In yet another case, the ceramic layer may be removed from over the second portion  524  using a micro-etching process. 
         [0026]    Next, the method includes surface finishing the conductive metal  526  in the second portions  524  of the surface of the substrate. As illustrated, surface finishing may involve doing some sort of plating on second portion  524  of the surface. For example, surface finishing may include plating by means of electroless plating, electroplating or immersion plating. In one embodiment (shown by way of example in  FIG. 5 c   ), surface finishing may include first plating a layer of nickel  536 , and then plating a layer of gold or silver  538 . 
         [0027]    The same sort of process may also be used to a flexible LED assembly similar to that illustrated in  FIG. 2 . Such a process is illustrated in  FIGS. 6 a -6 c   . Here, again the first step (illustrated in  FIG. 6 a   ) is applying a layer of ceramic  610  to the surface  632  of the substrate  630 , where the substrate includes, prior to application of ceramic  610 , first portions on which the exposed top surface is polymer (i.e. first portions  622 ), and second portions on which the exposed top surface is a conductive metal  626  (i.e. second portions  624 ). 
         [0028]    The next step, shown in  FIG. 6 b   , is to remove the ceramic  610  from the second portions  624  of the surface of the substrate. The removal step may be accomplished through a number of appropriate means, such as those described above with respect to  FIG. 5   b.    
         [0029]    Finally, the method includes surface finishing the conductive metal  626  in the second portions  624  of the surface of the substrate. As illustrated, surface finishing may involve doing some sort of plating on second portion  624  of the surface. For example, surface finishing may include plating by means of electroless plating, electroplating or immersion plating. In one embodiment (shown by way of example in  FIG. 6 c   ), surface finishing may include first plating a layer of nickel  636 , and then plating a layer of gold or silver  638 . 
         [0030]    The following is a list of exemplary embodiments. 
         [0000]    Embodiment  1  is a flexible LED assembly comprising: 
         [0031]    a flexible polymer substrate; 
         [0032]    a first conductive feature positioned within and on a surface of the flexible substrate; 
         [0033]    a second conductive feature positioned within and on the surface of the flexible substrate at a distance from the first conductive feature, such that a portion of the flexible polymer substrate between the first and second conductive features is exposed; and 
         [0034]    a layer of ceramic positioned on the exposed flexible polymer surface between the first and second conductive features. 
         [0000]    Embodiment  2  is the flexible LED assembly of embodiment  1 , further comprising an LED mounted on both the first and second conductive features, wherein the flexible polymer substrate is shielded from UV light emitted from the LED by the layer of ceramic.
 
Embodiment  3  is the flexible LED assembly of embodiment  1 , wherein the flexible polymer substrate comprises polyimide.
 
Embodiment  4  is the flexible LED assembly of embodiment  1 , wherein the flexible polymer substrate comprises PET, liquid crystalline polymer, polycarbonate, polyether ether ketone, or thermoplastic polymer.
 
Embodiment  5  is the flexible LED assembly of embodiment  1 , wherein the first and second conductive features comprise copper.
 
Embodiment  6  is the flexible LED assembly of embodiment  1 , wherein the ceramic comprises Al 2 O 3 , AIN, or BN.
 
Embodiment  7  is the flexible LED assembly of embodiment  2 , wherein the LED comprises a flip chip.
 
Embodiment  8  is the flexible LED assembly of embodiment  7 , wherein the flip chip is bonded using a soldering technique.
 
Embodiment  9  is the flexible LED assembly of embodiment  2 , wherein the LED comprises a wire bonded
 
         [0035]    LED. 
         [0000]    Embodiment  10  is the flexible LED assembly of embodiment  2 , wherein the LED comprises a lateral die.
 
Embodiment  11  is the flexible LED assembly of embodiment  2 , wherein the LED is eutectic bonded to the first and second conductive features.
 
Embodiment  12  is the flexible LED assembly of embodiment  1 , further comprising an LED that is mounted on first conductive feature but not the second conductive feature, wherein the flexible polymer substrate is shielded from UV light emitted from the LED by the layer of ceramic.
 
Embodiment  13  is the flexible LED assembly of embodiment  12 , wherein the LED is attached to the first conductive feature using epoxy binding adhesive, conductive paste, anisotropic conductive paste (ACP), anisotropic conductive film (ACF) or eutectic bonding.
 
Embodiment  14  is the flexible LED assembly of embodiment  1 , wherein the flexible polymer substrate comprises a dielectric.
 
Embodiment  15  is a flexible LED assembly comprising:
 
         [0036]    a flexible polymer substrate comprising a via extending therethrough; 
         [0037]    a first conductive feature positioned on a bottom surface of the flexible substrate, a portion of the first conductive feature being positioned beneath the via; 
         [0038]    and 
         [0039]    a layer of ceramic positioned on the top surface of the flexible polymer substrate. 
         [0000]    Embodiment  16  is the flexible LED assembly of embodiment  15 , further comprising a second via in the flexible polymer substrate, and a second conductive feature positioned on a bottom surface of the flexible substrate, a portion of the second conductive feature being positioned beneath the second via.
 
Embodiment  17  is a method of making an LED assembly, comprising:
 
         [0040]    applying a layer of ceramic to the surface of a substrate, the substrate comprising, prior to application of the ceramic, first portions on which the exposed top surface is polymer and second portions on which the exposed top surface is a conductive metal, 
         [0041]    removing the ceramic from the second portions of the surface of the substrate, and 
         [0042]    surface finishing the conductive metal in the second portions of the surface of the substrate. 
         [0000]    Embodiment  18  is the method of embodiment  17 , wherein removing the ceramic from the second portions of the surface of the substrate comprises laminating a tacky liner onto the regions of ceramic corresponding to the second portions, and peeling the ceramic from the second portions by removing the tacky liner.
 
Embodiment  19  is the method of embodiment  17 , wherein removing the ceramic from the second portions of the surface of the substrate comprises utilizing a bristle brush technique.
 
Embodiment  20  is the method of embodiment  17 , wherein removing the ceramic from the second portions of the surface of the substrate comprises micro-etching the ceramic.
 
Embodiment  21  is the method of embodiment  17 , wherein the conductive metal comprises copper.
 
Embodiment  22  is the method of embodiment  17 , wherein surface finishing the conductive metal comprises electroless plating, electroplating, or immersion plating.
 
Embodiment  23  is the method of embodiment  17 , wherein surface finishing the conductive metal comprises first plating a layer of nickel and then plating a layer of gold or silver.
 
Embodiment  24  is the method of embodiment  17 , wherein the layer of ceramic is applied using a sputtering process.
 
Embodiment  25  is the method of embodiment  17 , wherein the ceramic comprises aluminum nitride.