Abstract:
A patterned conductive layer on a flexible substrate includes pads for mounting an array of LEDs, conductive strips, and conductive tabs that couple the conductive strips to the pads. The desired circuit configuration is created by removing select tabs by punching holes or otherwise piercing the flexible substrate at the location of the tabs. In some embodiments, the patterned conductive layer is arranged to permit each LED to be mounted in either of two mirrored orientations, and in some embodiments, the patterned conductive layer is arranged to permit a separation between LEDs that is not predefined by the pattern. In some embodiments, the unmodified patterned conductive layer is arranged to provide a parallel circuit configuration, and the modified patterned conductive layer is arranged to provide a series or series-parallel configuration.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to the field of light emitting devices, and in particular to a flexible substrate with a patterned conductive layer for mounting an array of light emitting devices. 
       BACKGROUND OF THE INVENTION 
       [0002]    The ever expanding use of semiconductor light emitting devices has produced a highly competitive market for these devices in a variety of configurations. In this market, performance and price are often significant for providing product distinction among vendors. 
         [0003]    To achieve high light output intensity, an array of light emitting devices is typically used. Such arrays may be configured in a variety of circuit configurations. Series configurations may be used to provide a uniform current to each device, whereas parallel configurations may be used to allow the use of a low voltage supply. Series-parallel configurations may be used to achieve a particular combination of performance features. 
         [0004]    Conventionally, a patterned conductive layer is formed on a substrate, such as a printed circuit board with a conductive layer that is etched to create the desired interconnections between the devices that will be mounted on the board. Flexible substrates may also be used, with the desired interconnections formed by etching or by printing conductive ink on the substrate. Other forms of substrates and patterned conductive interconnections may also be used. 
         [0005]    Each different circuit configuration requires a different pattern of conductive traces (different ‘layouts’). This requires the creation of different layout masks for etching, or different print patterns for printing each different pattern. In addition to the added design costs for developing each different pattern, the variety of patterns often precludes the economies of scale available for large production quantities. 
       SUMMARY OF THE INVENTION 
       [0006]    It would be advantageous to provide a substrate with a patterned conductive layer that can be modified to provide a variety of circuit configurations. It would further be advantageous to provide the modifications using a simple process that can be applied independent of the production of the substrate. 
         [0007]    To better address one or more of these concerns, in an embodiment of this invention, the patterned conductive layer includes pads for mounting an array of LEDs, conductive strips, and conductive tabs that couple the conductive strips to the pads. The desired circuit configuration is created by removing select tabs by punching holes in a flexible substrate. In some embodiments, the patterned conductive layer is arranged to permit each LED to be mounted in either of two mirrored orientations, and in some embodiments, the patterned conductive layer is arranged to permit a separation between LEDs that is not predefined by the pattern. In some embodiments, the unmodified patterned conductive layer is arranged to provide a parallel circuit configuration, and the modified patterned conductive layer is arranged to provide a series or series-parallel configuration. 
         [0008]    By providing a configurable substrate, economies of scale can be obtained without regard to the eventual configuration. By providing a simple technique for removing portions of the patterned conductive layer, such as punching or otherwise severing the flexible circuit, the modifications may be performed by each purchaser of the configurable substrate, independent of the provider of the configurable substrate. In like manner, the configurable substrate enables rapid prototyping of potential circuit designs, to evaluate the performance of an array of LEDs that are interconnected using such circuit designs. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The invention is explained in further detail, and by way of example, with reference to the accompanying drawings wherein: 
           [0010]      FIGS. 1A-1E  illustrate an example substrate with a patterned conductive layer that may be configured to provide a parallel arrangement of an array of light emitting devices, and a serial arrangement. 
           [0011]      FIGS. 2A-2C  illustrate an example substrate with a patterned conductive layer that may be configured to facilitate series-parallel arrangements of an array of light emitting devices. 
           [0012]      FIGS. 3A-3C  illustrate an example substrate with a patterned conductive layer that facilitates a two dimensional arrangement of an array of light emitting devices that may be configured in a variety of different circuit arrangements. 
       
    
    
       [0013]    Throughout the drawings, the same reference numerals indicate similar or corresponding features or functions. The drawings are included for illustrative purposes and are not intended to limit the scope of the invention. 
       DETAILED DESCRIPTION 
       [0014]    In the following description, for purposes of explanation rather than limitation, specific details are set forth such as the particular architecture, interfaces, techniques, etc., in order to provide a thorough understanding of the concepts of the invention. However, it will be apparent to those skilled in the art that the present invention may be practiced in other embodiments, which depart from these specific details. In like manner, the text of this description is directed to the example embodiments as illustrated in the Figures, and is not intended to limit the claimed invention beyond the limits expressly included in the claims. For purposes of simplicity and clarity, detailed descriptions of well-known devices, circuits, and methods are omitted so as not to obscure the description of the present invention with unnecessary detail. 
         [0015]      FIGS. 1A-1E  illustrate a substrate  100  with a patterned conductive layer that may be configured to provide a parallel arrangement of an array of light emitting devices ( FIGS. 1B-1C ), and a serial arrangement ( FIGS. 1D-1E ). 
         [0016]    As illustrated in  FIG. 1A , the patterned conductive layer includes conductive strips  120 ,  130  upon a substrate material  110 . The lateral extent of the substrate  100 , and thereby substrate material  110  and strips  120 ,  130 , is not fixed, and may be sized to accommodate the number of light emitting devices that are to be mounted on the substrate  100  for any particular purpose. 
         [0017]    The substrate material  110  may be rigid or flexible, although the principles of this invention are particularly well suited for a flexible substrate material  110 . On a flexible substrate material  110 , such as a thin insulating polymer film, the conductive strips may be formed by etching metal foil cladding (normally of copper) from polymer bases, plating metal or printing of conductive inks upon polymer bases, and other conventional processes. 
         [0018]    In an example embodiment using a flexible substrate material  110 , the substrate  100  may be provided on a continuous roll, and cut to size for each different application. Of particular note, such a roll may be provided by the producer of the substrate  100 , and cut to size at the purchaser&#39;s locale, using common tools such as a knife or scissor. 
         [0019]    In a typical application, the substrate  100  is designed to accommodate a particular family of light emitting devices with a well-defined pair of conductive pads for providing external power to each device. The width  122 ,  132  of each of the conductive strips  120 ,  130  and the space  125  between the conductive strips  120 ,  130  are sized to accommodate the mounting of the light emitting devices via these conductive pads. In a preferred embodiment, the strips  120 ,  130  accommodate the mounting of the light emitting devices in either of two mirrored orientations, as detailed below; accordingly, the widths  122 ,  130  of the strips  120 ,  130  may be equal for some embodiments. 
         [0020]      FIG. 1B  illustrates the mounting of an array of four light emitting devices  150 A- 150 D (collectively, devices  150 ) upon the substrate  100 . In this example configuration, the P-conductive pad  151  of each device  150  is mounted upon the conductive strip  120 , and the N-conductive pad  152  of each device  150  is mounted upon the conductive strip  130 , thereby forming a parallel circuit arrangement, as illustrated in  FIG. 1C . In operation, an external power source is coupled to the circuit via connections  140 +,  140 − to the strips  120 ,  130 , respectively. 
         [0021]    The light emitting devices  150  may be mounted on the strips  120 ,  130  using any of a variety of conventional techniques, including soldering or using a conductive adhesive to couple the pads  151 ,  152  to the strips  120 ,  130 , respectively. In like manner, the external connection  140 +,  140 − to the strips  120 ,  130  may be via a wire-attach process, via the use of connectors that clamp onto the substrate  100 , via the attachment of rigid pins to the strips  120 ,  130 , that are plugged into a power source, and so on. 
         [0022]    Of particular note, in the arrangement of  FIG. 1B , each of the light emitting devices  150  may be any light emitting device with pads that are accommodated by the size and spacing of the strips  120 ,  130 . In some embodiments, they may all be of the same type or color emission; in other embodiments, they may be a mix of types or color emissions. Although the strips  120 ,  130  are illustrated as having a width  122 ,  132  that corresponds to the width of the pads  151 ,  152  of the light emitting devices  150 , one of skill in the art will recognize that substantially wider widths  122 ,  132  may accommodate a larger variety of light emitting device sizes. 
         [0023]    In the alternative strips  120 ,  130  may include several parallel strips that can be used collectively as one large strip or to accommodate a variety light emitting device sizes or a variety of pad arrangements. In these embodiments, connections may be made or broken to configure the parallel strips. 
         [0024]    Also of note, the spacing  155  between light emitting devices  150  is not constrained by the pattern of conductors  120 ,  130  of the substrate  100 , and may be selected based on each particular application. For example, in an arrangement for providing a ring of light sources around the perimeter of an object, the number of, and the spacing between the light emitting devices  150  may be based on the angular width of the light emission pattern (field of view) of each device, so that no ‘dark spots’ are produced. 
         [0025]      FIG. 1D  illustrates the use of the same substrate  100  to provide a different circuit configuration of the array of light emitting devices  150 . 
         [0026]    In the example of  FIG. 1D , a combination of select ‘breaks’  170 A- 170 C (collectively, breaks  170 ) in the conductive strips  120 ,  130  and select orientations of the light emitting devices  150  provides a series circuit configuration of the light emitting devices  150 . 
         [0027]    Light emitting device  150 A is mounted in a first orientation, with its P-pad coupled to the conductive strip  120 , and its N-pad coupled to the conductive strip  130 . The light emitting device  150 B is mounted in a second, mirrored, orientation, with its P-pad coupled to the conductive strip  130 , and its N-pad coupled to the conductive strip  120 . 
         [0028]    A break  170 A is introduced in the conductive strip  120 , between devices  150 A and  150 B, for example, by punching a hole through the strip and underlying flexible substrate. This break decouples the P-pad of device  150 A and the N-pad of device  150 B, resulting in a series connection of the devices  150 A- 150 B. Current will flow from  150 A P-pad, through  150 A, to  150 A N-pad, to  150 B P-pad, through  150 B, to  150 B N-pad. 
         [0029]    In like manner, device  150 C is oriented in the first orientation (P-Pad to strip  120 ), and device  150 D is oriented in the second, mirrored orientation (P-Pad to strip  130 ), and breaks  170 B,  170 C decouple the P-pad of device  150 B from the N-pad of device  150 C, and the P-pad of device  150 C from the N-pad of device  150 D, placing devices  150 C and  150 D in series with the aforementioned series connection of devices  150 A and  150 D, as illustrated in  FIG. 1E . External power is coupled to this series arrangement via connections  140 + and  140 −. 
         [0030]    One of skill in the art will recognize that alternative circuit configurations may be provided via different breaks in the conductive strips  120 ,  130  and different orientation of the light emitting devices  150 . For example, breaks  170 A and  170 C may be omitted, devices  150 A and  150 B may both be placed in the first orientation (P-pads to strip  120 ), and devices  150 C and  150 D may both be placed in the second orientation (P-pads to strip  130 ), which will provide a parallel arrangement of devices  150 A- 150 B in series with a parallel combination of devices  150 C- 150 D. Other configurations are also feasible. 
         [0031]    The breaks  170  may be introduced using any number of a variety of techniques, depending upon the materials used for forming the substrate  100 , the tools available for introducing the breaks, and so on. In a simple scenario of a flexible substrate material  110 , a simple manual or automated punch-tool may be used to introduce each break in the conductive strips  120 ,  130 . Alternatively, manual razor-cuts may be used to remove select sections of the strips  120 ,  130  in the substrate. For larger volume applications, a numerical-control (NC) machine may be also programmed to create the selected breaks via drilling or other actions. The breaks  170  may extend through the substrate material  110 , but need only be formed such that current does not flow from one side of the break  170  to the other. Although each break  170  is illustrated as being between the light emitting devices, one of skill in the art will recognize that the break  170  may be introduced before the light emitting devices  150  are mounted, and may be situated beneath the mounted light emitting devices  150 , allowing a reduced spacing between the devices  150 . 
         [0032]    Of particular note, as with the example of  FIG. 1B , the creation of the selected breaks, the mounting of the light emitting devices, the cutting of the substrate to size, and providing connections for an external source, may be performed by the purchaser of ‘bulk’ substrate  100 , independent of the production of the substrate  100 . This allows the producer of the substrate  100  to produce the substrate  100  in large quantities, while allowing the user of the substrate  100  to purchase and configure the substrate  100  based on the requirements for each different application. 
         [0033]      FIG. 2A-2C  illustrate another substrate  200  with patterned conductive layer that facilitates series-parallel arrangements of an array of light emitting devices. 
         [0034]    The patterned conductive layer on the substrate material  110  includes a plurality of horizontal strips  220 A- 220 D (collectively, strips  220 ), with vertical tabs  230  interconnecting these strips at regular intervals. For ease of reference, the term “tab” is used herein to indicate a conductive element between two conductors that may be severed so as to isolate the conductors on either side of the tab. As in the previous figures, the substrate material  110  may be a flexible polymer substrate, and the conductive layer may be etched metal, conductive ink, and so on. 
         [0035]    Like the conductive strips  120 ,  130  in  FIGS. 1A-1E , two of the conductive strips  220 B,  220 C are situated to allow for the mounting of light emitting devices via their conductive tabs in either of two mirrored orientations. As contrast to the conductive strips  120 ,  130  in  FIG. 1B , which may be used without the introduction of breaks, the conductive strips  220 A- 220 D are in contact with each other, via the tabs  230 , and therefore breaks must be created in order for the conductor pattern to form a circuit for operating the light emitting devices. 
         [0036]      FIG. 2B  illustrates the mounting of four light emitting devices  150 A- 150 D on the center pair of conductor strips  220 B,  220 C, and select breaks  170  (labeled  170 A- 170 K). Breaks  170 A- 170 E create a series connection between the light emitting devices  150 A and  150 B. Breaks  170 E- 170 K create a series connection between light emitting devices  150 D and  150 C. The conductive strip  220 A couples the P-pads of devices  150 A and  150 D to the connector  140 +, and the conductive strip  220 D couples the N-pads of devices  150 B and  150 C to the connector  140 −, for coupling to an external power source. 
         [0037]    This combination of select breaks  170 A- 170 K and select orientations of the devices  150  provides the illustrated series-parallel circuit illustrated in  FIG. 2C . One of skill in the art will recognize that a variety of different circuits may be formed using the substrate  200 . As in the example of  FIG. 1A , the lateral extent of the substrate  200  is not pre-defined, and may be sized to accommodate as many light emitting devices as the application requires. 
         [0038]      FIGS. 3A-3C  illustrate a substrate  300  with a patterned conductive layer that facilitates a two dimensional arrangement of an array of light emitting devices. 
         [0039]    The patterned conductive layer includes pads  310  for mounting the light emitting devices, conductive strips  320 , and conductive tabs  330  that couple the pads  310  to the strips  320 . As in the example of  FIG. 2A , all of the conductive elements on the substrate  110  are coupled together, and breaks must be introduced to form an operational circuit configuration for the light emitting devices. 
         [0040]      FIG. 3B  illustrates an example mounting of light emitting devices  150 A- 150 H and select breaks  170  (labeled  170 A- 170 M) that provides the illustrated circuit arrangement illustrated in  FIG. 3C . 
         [0041]    The breaks  170 B,  170 E,  170 H, and  170 M isolate the positive external connection  140 + from the negative external connection  140 −, and couple the P-pads of devices  150 C and  150 H to the connection  140 +. The breaks  170 I- 170 L place the devices  150 F,  150 G, and  150 H in series between the connections  140 + and  140 −. 
         [0042]    The breaks  170 A and  170 C- 170 G result in a parallel connection of devices  150 A,  150 B,  150 D, and  150 E. The P-pads of this parallel combination are coupled to the N-pad of device  150 C, placing this parallel connection in series with device  150 C, from connection  140 + to  140 −. 
         [0043]    Although the example substrate  300  illustrates an arrangement for mounting a 3×3 array of light emitting devices, one of skill in the art will recognize that both the horizontal and vertical extent of the substrate  300  may be larger or smaller than illustrated. In an example embodiment, the substrate  300  may be provided on a roll or a sheet containing hundreds or thousands of mounting locales, and the purchaser may slice the roll or sheet in either or both directions to form the desired two-dimensional substrate for the particular application. 
         [0044]    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. 
         [0045]    For example, it is possible to operate the invention in an embodiment wherein other elements are also mounted on the patterned conductive layer, such as ESD (ElectroStatic Discharge) protection devices, and others. 
         [0046]    Other 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 or steps, 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.