Abstract:
The present invention relates to a substrate ( 1 ) comprising: a first segment ( 5   a ) provided with a first contact pad ( 22   a ) for connection of a first light emitting element ( 2   a ); and a second segment ( 5   b ) provided with a second contact pad ( 22   b ) for connection of a second light emitting element ( 2   b ), wherein the substrate is provided with at least one through-hole ( 6   a - c ) that extends from an edge ( 8,9 ) of the substrate to a point within the substrate, such that a relative movement, in a plane of the substrate, can be achieved between the first segment ( 5   a ) of the substrate and the second segment ( 5   b ) of the substrate by applying a mechanical force to the substrate. This makes very accurate alignment to a multiple cavity optical system possible without adjusting the optics, thereby enabling a more convenient and time efficient process in production.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a substrate for mounting a plurality of light emitting elements, and to a method of manufacturing such a substrate. The present invention also relates to a light output device comprising such a substrate, and to a method of assembling such a light output device. 
       BACKGROUND OF THE INVENTION 
       [0002]    Today light emitting elements that are mounted on a substrate, such as light emitting diodes (LEDs) mounted on a printed circuit board (PCB), are increasingly used in illumination devices. To generate a desired beam shape, such an LED-based illumination device may often comprise an optical system with an optical element, such as a collimator, arranged for each of the LEDs. As an example thereof, a known illumination device  100 , where an optical system  101  with multiple collimators  102  is arranged over a plurality of LEDs  103  mounted on a PCB  104 , is schematically illustrated in  FIG. 1 . 
         [0003]    To optimize the performance of the optical system in  FIG. 1 , each of the LEDs must be aligned to its respective collimator. This can be done by adjusting the collimator, or, if each LED is mounted on a separate printed circuit board (PCB), by adjusting the position of the printed circuit board on which the LED is arranged. However, to facilitate assembly and/or exchangeability of the LEDs, it is often preferred to use one printed circuit board with multiple LEDs arranged thereon. Therefore, after the LEDs have been mounted on the printed circuit board, the LEDs have fixed position relative to each other. This means the only alignment that is left in the optical system is the adjustment of the collimators, which can be a very inconvenient and time spending process in production. 
         [0004]    Thus, there is a need to facilitate the alignment of light emitting elements to their respective optical elements, even though the light emitting elements are mounted on the same substrate. 
       SUMMARY OF THE INVENTION 
       [0005]    It is an object of the present invention to overcome this problem, and to facilitate alignment of light emitting elements to their respective optical elements, even though the light emitting elements are mounted on the same substrate. 
         [0006]    According to an aspect of the invention, this and other objects are achieved by a substrate comprising: a first segment provided with a first contact pad for connection of a first light emitting element; and a second segment provided with a second contact pad for connection of a second light emitting element, wherein the substrate is provided with at least one through-hole that extends from an edge of the substrate to a point within the substrate, such that a relative movement, in a plane of the substrate, can be achieved between the first segment of the substrate and the second segment of the substrate by applying a mechanical force to the substrate. 
         [0007]    The present invention is based on the realization that by providing at least one through-hole that extends from an edge of the substrate to a point within the substrate, it is possible to enhance the flexibility of a rigid substrate, such that different segments of the substrate can be moved relative each other in the plane of the substrate. The inventor has further realized that appropriate arrangement of such through-holes allows a relative movement, in the plane of the substrate, between a first contact pad for connection of a first light emitting element and a second contact pad for connection of a second light emitting element, in response to a mechanical force applied to the substrate. Thereby, it is possible to change a relative position between first and second light emitting elements (which are fixedly mounted to the first and second contact pads), allowing each of the first and second light emitting elements to be aligned to a respective optical element. This makes very accurate alignment to a multiple cavity optical system possible without adjusting the optics, thereby enabling a more convenient and time efficient process in production. Further, as the light emitting elements are arranged on a single substrate it still allows easy assembly and/or exchangeability compared to a design where the light emitting elements are arranged on separate substrates. 
         [0008]    As is recognized by a person skilled in the art, the shape and size of the through-hole may vary. However, the through-hole may preferably have an elongated shape, such as a substantially straight elongate groove, channel, or slit that penetrates through the plane of the substrate. 
         [0009]    The substrate may be provided with a plurality of through-holes, each of the through-holes extending from an edge of the substrate to a point within the substrate. By increasing the number of through-holes enhanced flexibility can be achieved. The flexibility is also enhanced by increased length of the through-hole. 
         [0010]    According to an embodiment, the through-hole(s) may be L-shaped. An L-shaped through-hole allows segments on opposite sides thereof to be moved in both dimensions of the plane of the substrate. This makes it easier to adjust the position of the light emitting element along any desired direction in the plane of the substrate, and thereby facilitates alignment. 
         [0011]    A subset of the plurality of through-holes may extend from a first edge of the substrate, whereas the rest of the through-holes may extend from a second edge of the substrate opposite the first edge. 
         [0012]    An end of the through-hole located within the substrate may preferably have a rounded shape. An advantage with a rounded shape is that the stress is distributed over a larger area of the substrate during flexure, thereby reducing the risk that the substrate breaks. 
         [0013]    The substrate may be a (rigid) electrically non-conducting substrate provided with electrical track(s) that provides electrical connection to the contact pads, such as a printed circuit board (PCB). The electrical track and the contact pads may e.g. be etched on a printed circuit board, or discrete elements that may be attached by e.g. an adhesive. An advantage is that conversion of a conventional substrate, such as a printed circuit board, into a flexible substrate enables a cost-efficient solution. 
         [0014]    Furthermore, the substrate according to the present invention may advantageously be included in a light output device, further comprising a first light emitting element connected to the first contact pad; and a second light emitting element connected to the second contact pad. 
         [0015]    The light output device may further comprise an optical system provided with a first optical element intended to receive light from the first light emitting element, and a second optical element intended to receive light from the second light emitting element, wherein each of the first and second light emitting elements can be aligned with its respective optical element by applying a mechanical force to the substrate. 
         [0016]    The substrate and the optical system may include corresponding sets of reference elements adapted to mate during alignment, so that a more accurate alignment can be achieved. 
         [0017]    The set of reference elements on the substrate may be a set of reference holes, and the set of reference elements on the optical system may be a corresponding set of protrusions adapted to mate with the reference hole(s). This solution is typically easier in production, compared to a solution where the substrate has the protrusions and the optical element has the reference holes. The protrusion(s) may be tapered, or have a chamfered edge, such that the protrusion pushes the different segments of the substrate into the right positions, when the protrusion(s) of the optical system are introduced into the reference hole(s). 
         [0018]    According to another aspect of the invention, there is provided a method of manufacturing a flexible substrate, comprising the steps of: providing a substrate comprising a first segment provided with a first contact pad for connection of a first light emitting element; and a second segment provided with a second contact pad for connection of a second light emitting element; 
         [0019]    forming at least one through-hole that extends from an edge of said substrate to a point within said substrate, such that a relative movement, in a plane of the substrate, can be achieved between the first segment of the substrate and the second segment of the substrate by applying a mechanical force to said substrate. 
         [0020]    This aspect provides similar advantages as discussed in relation to the previous aspect. 
         [0021]    The formation of the through-hole(s) in the substrate may include making a (circular) through-hole in the substrate and making a cut from the through-hole to the edge of the substrate. In this way it is possible to form a through-hole that is wider at the inner end of the through-hole, such that the stress is distributed over a larger area of the substrate during flexure, thereby reducing the risk that the substrate breaks. However, the through-hole may also be produced in other ways, e.g. the through-hole(s) can be punched or milled to achieve a desired shape. 
         [0022]    The method may include the step of providing a set of reference elements in the substrate. The reference element(s) facilitates alignment of the light emitting elements to their respective optical elements. 
         [0023]    Furthermore, the method of manufacturing a substrate according to the present invention may advantageously be included in a method of assembling a light output device, further comprising the steps of: mounting a first light emitting element to the first contact pad on the substrate and a second light emitting element to the second contact pad on the substrate. 
         [0024]    The method may further comprise the steps of: providing an optical system provided with a first optical element intended to receive light from the first light emitting element, and a second optical element intended to receive light from the second light emitting element; arranging the optical system over the light emitting elements; and aligning each of the first and second light emitting elements with its respective optical element by applying a mechanical force to the substrate. During alignment a set of reference elements on the optical system may be mated with a corresponding set of reference elements on the substrate. 
         [0025]    It is noted that the invention relates to all possible combinations of features recited in the claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0026]    This and other aspects of the present invention will now be described in more detail, with reference to the appended drawings showing embodiment(s) of the invention. 
           [0027]      FIG. 1  schematically illustrates an LED-based illumination device with a optical system with multiple collimators according to prior art; 
           [0028]      FIG. 2  schematically illustrates a substrate according to an embodiment of the 
           [0029]    invention; 
           [0030]      FIG. 3   a - c  schematically illustrates various configurations of through-holes that achieve a one-dimensional flexibility; 
           [0031]      FIG. 4  schematically illustrates a configuration of through-holes that achieves a two-dimensional flexibility; 
           [0032]      FIG. 5  schematically illustrates a light output device according to an embodiment of the invention; 
           [0033]      FIG. 6  is a flow chart showing the steps of producing a light output device according to an embodiment of the invention; and 
           [0034]      FIG. 7   a - b  schematically illustrates alignment between the light emitting elements and their respective optical elements. 
       
    
    
     DETAILED DESCRIPTION  
       [0035]      FIG. 2  schematically illustrates a substrate  1  according to an embodiment of the invention. The substrate  1  can be a (rigid) electrically non-conducting substrate comprising a first segment  5   a  provided with a first contact pad  22   a  for connection of a first light emitting element, and a second segment  5   b  provided with a second contact pad  22   b  for connection of a second light emitting element. Optionally, the substrate may include additional contact pads such that more light emitting elements can be connected to the substrate. For instance, in the illustrated example in  FIG. 2 , there is a third contact pad  22   c  for connection of a third light emitting element to a third segment  5   c  of the substrate. The substrate can also include electrically conductive path(s)  3  within and/or fabricated on the substrate to connect the contact pads in any desired configuration. This can be achieved, e.g. by using a conventional printed circuit board (PCB), such as e.g. an IMS-board (MCPCB), or a FR4-board. 
         [0036]    The substrate  1  is provided with a first set of through-holes  6   a - c  that extends from an edge  8 , 9  of the substrate to a point  20  within the substrate, in such a way that a relative movement, in the plane of the substrate, can be achieved between the first segment  5   a  of the substrate and the second segment  5   b  of the substrate. Thus, the arrangement is such that a portion of the substrate located at the inner end  20  of each through-hole will act as a flexible hinge that allows relative movement, in the plane of the substrate, between adjacent segments  5   a - b  in response to a mechanical force applied to the segments  5   a - b.    
         [0037]    Although it may suffice with a single through-hole  6   a - c,  it is often preferred to provide additional through-holes for increased flexibility. For instance, in the example illustrated in  FIG. 2 , there are three through-holes  6   a - c  arranged in-between the first contact pad  22   a  and the second contact pad  22   b.  Each through-hole, here has a straight elongate shape, such as a groove, channel, or slit that penetrates through the substrate. To reduce the risk that the substrate breaks when flexed the through-hole may preferably have a rounded shape at the inner end  20  of the through-hole. 
         [0038]    Moreover, adjacent through-holes preferably extend from opposite edges of the substrate. For instance, in the example illustrated in  FIG. 2 , the first set of through-holes  6   a - c  has two of the through-holes  6   a , 6   c  extending from a first edge  8 , and the third through-hole  6   b,  located in-between the two other through-holes, extending from a second edge  9  of the substrate, opposite the first edge. 
         [0039]    As is recognized by a person skilled in the art, additional set(s) of through-holes may be formed in the substrate if there are additional contact pads that should be movable in relation to the other contacts pads. For instance, in the illustrated example in  FIG. 2 , there is a second set of through-holes  7   a - c  that extends from an edge  8 , 9  of the substrate to a point within the substrate, such that the third contact pad  22   c  is moveable in relation to the second contact pad  22   b.  This allows relative movement, in the plane of the substrate, between all of the contact pads  22   a - c  on the substrate. 
         [0040]    The through-holes illustrated in  FIG. 2  and  FIG. 3   a,  primarily enable (one-dimensional) relative movement between the segments along a first direction (illustrated as x-direction in  FIG. 3   a ) substantially perpendicular to the extension of the through-holes. As is recognized by a person skilled in the art, the desired effect can be achieved also for other shapes of the through-hole. Two examples of alternatively shaped through-holes that achieve one-dimensional relative movement between the segments are illustrated in  FIG. 3   b - c.    
         [0041]    It is also possible to design the through-hole(s) such that segments of the substrate on opposite sides of the through-hole(s), can be moved relative each other, in both dimensions of the plane of the substrate (illustrated as x- and y-directions in  FIG. 4 ). This can be achieved by using one or more L-shaped ( 6   a - b ) through-holes as illustrated in  FIG. 4 . 
         [0042]      FIG. 5  schematically illustrates a light output device according to an embodiment of the invention. 
         [0043]    Here, the light output device comprises the substrate  1  described above in relation to  FIG. 2 . A first light emitting element  2   a  is electrically and thermally connected to the first contact pad  22   a  on the substrate  1 , and a second light emitting element  2   b  is electrically and thermally connected to the second contact pad  22   b  on the substrate. In the illustrated example in  FIG. 5 , there is also a third light emitting element  2   c  connected to the third contact pad  22   c  on the substrate. Each light emitting element can be a light emitting diode (LED), such as a chip or die mounted directly on the contact pad. The light output device may also comprise components required for driving and controlling the light emitting elements. 
         [0044]    The light output device can further comprise an optical system  10  arranged over the light emitting elements. The optical system comprises a first optical element  11   a  intended to receive light from the first light emitting element  2   a,  and a second optical element  11   b  intended to receive light from the second light emitting element  2   b.  Optionally, the optical system may include additional optical elements intended to receive light from additional light emitting elements. For instance, in the illustrated example in  FIG. 3 , there is a third optical element  11   c  intended to receive light from the third light emitting element  2 c. 
         [0045]    The optical elements are here collimating reflectors. Each collimating reflector can use a reflective surface (e.g. as a cavity provided with a reflective surface) or be based on total internal reflection (TIR) (e.g. by using a body portion made of polycarbonate or PMMA) as is well-known in the art. 
         [0046]    Preferably, the substrate  1  and the optical system  10  are provided with corresponding sets of reference elements  12 ,  13  to ensure proper alignment of the optical elements  11   a - c  to the light emitting elements  2   a - c  on the substrate. For instance, the optical system can include one or more protrusions  13  (e.g. pins) mating with one or more corresponding reference holes  12  in the substrate, or vice versa. The reference elements are preferably arranged near the light emitting elements to ensure sufficient accuracy. 
         [0047]    Optionally, the substrate can be thermally connected to a heat dissipation element  18 , such as a heat sink. 
         [0048]    Upon operation of the light output device, current is supplied to the light emitting elements via the electrically conductive traces of the substrate, whereby the light emitting elements emit light. The radiation pattern of the emitted light may be shaped by the optical components of the optical system. Here, the emitted light is collimated. Further, heat generated by the light emitting elements can be transferred by direct thermal contact from the substrate to the heat sink, for cooling of the light emitting elements. 
         [0049]    A method of manufacturing a flexible substrate according to an embodiment of the present invention will now be described with further reference to the flow chart in  FIG. 6 . 
         [0050]    In step S 1 , a (rigid) electrically non-conducting substrate  1  is provided. The substrate comprises a first segment  5   a  provide with a first contact pad  22   a  for connection of a first light emitting element  2   a,  and a second segment  5   b  provided with a second contact pad  22   b  for connection of a second light emitting element  2   b.  The substrate may include electrically conductive path(s) within and/or fabricated on the substrate to connect various components on the board in desired configurations. The substrate may typically be a conventional printed circuit board (PCB), such as e.g. an IMS-board (MCPCB), or a FR4-board. 
         [0051]    In step S 2 , a set of through-holes  6   a - c  is formed in the substrate. The through-holes  6   a - c  extends from an edge of the substrate to a point within the substrate, and are arranged in such a way that relative movement, in the plane of the substrate, between the first segment  5   a  of the substrate and the second segment  5   b  of the substrate can be achieved in response to a mechanical force applied to the substrate. For instance, each through-hole can be formed by making an initial (circular) through-hole  20 , in the substrate and then make a cut (that penetrates the plane of the substrate) from the initial through-hole  20  to the edge of the substrate. However, the through-holes can also be formed in other ways, such as by punching out or milling, and may take other shapes. Further, it is noted that the electrical layout has been designed so that the electrical tracks  3  runs along the small bridges of the substrate that are formed between the edges  8 , 9  of the substrate and the inner end  20  of the through-holes. 
         [0052]    Preferably, in step S 3 , a set of reference elements  12  are formed in the substrate. Each reference elements may e.g. be a reference hole  12 , in the substrate adapted to receive a corresponding protrusion  13  in the optical system. The reference elements are preferably arranged near the light emitting elements. 
         [0053]    A method of assembling a light output device according to an embodiment of the present invention will now be described with reference to  FIG. 6 . 
         [0054]    In step S 4 , light emitting elements, such as light emitting diodes (LEDs), are mounted to the contact pads of the substrate manufactured according to step S 1 -S 3 . Thus, the first light emitting element  2   a  is connected to the first contact pad on the substrate, and the second light emitting element  2   b  is connected to the second contact pad. This can be achieved by arranging the substrate in a soldering jig (not shown) and connecting the light emitting elements to the contact pads by means of soldering. It is noted that the light emitting elements are mounted at a predetermined position relative the reference elements. Thus, to enhance the accuracy, and ensure that each light emitting elements is mounted at its intended position on the substrate (relative to the reference elements  12  in the substrate), the soldering jig is preferably provided with a set of reference elements (e.g. protrusions, or pins) that corresponds to the reference elements  12  on the substrate, and to the reference elements used by the optical system. 
         [0055]    In step S 5 , an optical system  10  with a plurality optical elements  11   a - b  is provided. The optical system here comprises a first optical element  11   a  intended to receive light from the first light emitting element  2   a,  and a second optical element  11   b  intended to receive light from the second light emitting element  2   b.    
         [0056]    In step S 6 , the optical system  10  is arranged over the light emitting elements  2   a - b.    
         [0057]    In step S 7 , each light emitting element is aligned to its corresponding optical element by individually adjusting the position of each light emitting element in the plane of the substrate, by applying a force to the segments  5   a - b  of the substrate. As illustrated in  FIG. 7   a - b,  this can be achieved by using tapered protrusions  13  on the optical system that cause the different segments of the substrate to move into their proper positions (i.e. the position where the light emitting element is aligned with its corresponding optical element), when the protrusions  13  of the optical system is introduces into the reference holes  12  in the substrate. As illustrated in  FIG. 7   c,  the optical system may also have a protrusion with a chamfered edge that presses on the edge of the substrate when the optical system is arranged over the light emitting elements. 
         [0058]    The displacement of the light emitting elements that are possible during alignment may vary, and depends on the length and the number of through-holes. Typically, it may be possible to change the distance between two adjacent light emitting elements by about ±0.5 mm, or more. 
         [0059]    The person skilled in the art realizes that the present invention by no means is limited to the preferred embodiments described above. On the contrary, many modifications and variations are possible within the scope of the appended claims. For example, it is not limited to an optical system with collimating reflectors, but the above described invention may beneficially be used in all applications that use light emitting elements on a substrate, where individual alignment of the light emitting elements with optical component(s), such as lenses, TIR optics or light guides, is desired. The light output device may be used in a variety of applications such as e.g. automotive head/tail light and spot lights.