Patent Publication Number: US-8974083-B2

Title: Low-cost multi functional heatsink for LED arrays

Description:
FIELD OF THE INVENTION 
     The present invention relates to a lighting device and a method of manufacturing the same, wherein the lighting device comprises a cell structure of polygonal cells, which is a heat sink, and light sources arranged to be cooled by the cell structure. 
     BACKGROUND OF THE INVENTION 
     Lighting devices using arrays of light sources are of great interest for applications such as backlight for displays and illumination panels. Such arrays are typically made by arranging the light sources, such as for example LEDs (Light Emitting Diodes) on a large area PCB (Printed Circuit Board). Further, since illumination applications are desirable, often high power light sources are requested, causing a need for a heat sink on which the PCB is mounted. However, the large area PCB is relatively expensive. A lighting device of basically the presented kind is shown in WO 2007/124277, where the lighting device includes columns of LED light sources mounted on printed circuit boards. The boards are arranged on a heat sink. This prior art solution uses several smaller PCBs, which may reduce the cost to a certain extent. On the other hand, the wiring is increased, which is negative. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide a lighting device providing a less expensive solution. 
     The object is achieved with a lighting device and a method of manufacturing a lighting device according to the present invention as defined in the appended claims. 
     Thus, according to one aspect of the invention, there is provided a lighting device comprising a cell structure of polygonal cells, which is a heat sink, and light sources arranged to be cooled by the cell structure. The light sources are arranged in at least some of the cells, one light source in each cell, and are attached to and electrically connected with the cell structure. The cell structure is arranged to provide the light sources with power. 
     According to another aspect of the invention, there is provided a method of manufacturing a lighting device, comprising: 
     providing a heat sink as a cell structure of polygonal cells; 
     arranging the light sources in at least some of the cells, one light source in each cell;
         thermally connecting the light sources with the cell structure by attaching the light sources to the cell structure;   electrically connecting the light sources with the cell structure; and   providing the cell structure with power supply terminals.       

     A heat sink cell structure of polygonal cells is known per se from WO 2007/124277, but merely as a heat sink supporting the PCBs. However, according to the present invention the PCBs have been omitted and the light sources are individually mounted in the cells of the cell structure. Thus, no additional common support structure is needed for supporting the light sources. Furthermore, the cell structure is employed as both heat sink and electric connector for the light sources. 
     According to an embodiment of the lighting device, the cell structure comprises several wall elements, wherein each cell that contains a light source is formed by at least two wall elements, which are electrically insulated from each other. Thereby a simple power supply structure is obtained where the wall elements are used as conductors. 
     According to an embodiment of the lighting device, the wall elements are strips, which have been bent to form the polygonal cells. This structure provides for a simple manufacture. 
     According to an embodiment of the lighting device, the wall elements are electrically interconnected in groups, each group having a common power supply terminal. Thereby a simple power supply connection is obtained. 
     According to an embodiment of the lighting device, each light source is attached to the cell structure by means of combined thermally and electrically conducting connections. Thereby a simple interface between the light source and the cell structure is achieved. 
     Corresponding embodiments of the manufacturing method provide corresponding advantages, and will not be further explained. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be described in more detail and with reference to the appended drawings in which: 
         FIG. 1  is a schematic front perspective view of an embodiment of the lighting device according to the present invention; 
         FIGS. 2 and 3  are respectively schematic front perspective and rear perspective views of a portion of the lighting device shown in  FIG. 1 ; 
         FIG. 4  is a schematic rear perspective view of the lighting device shown in  FIG. 1 ; 
         FIG. 5  is a schematic front plan view of a portion of the lighting device shown in  FIG. 1 ; and 
         FIG. 6  is a schematic side view of a stack of adhered sheets from which heat sinks are to be cut out and formed. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     According to an embodiment the lighting device of the present invention, as shown in the figures, it comprises a cell structure of polygonal cells  101 , and light sources  103  arranged in cells  105  of the cell structure  101 . More particularly, the cells  105  are hexagonal and are arranged adjacent to each other. Thus, the cell structure  101  constitutes a honeycomb structure. However, alternative cell shapes are possible, such as squares, rectangular or trapezium shapes, all depending on bond line width and rate of extension. The cell structure  101  is made from a material which is a good thermal and electric conductor, such as aluminium, copper, steel, alloys and metal plated materials. This is since the cell structure  103  is employed as an electric conductor for supplying power to the light sources  103 , and as a heat sink for the light sources  103 . Consequently, the light sources  103  are attached to the cell structure  101  by means of electrically and thermally conducting connections as will be further described and exemplified below. 
     The light sources  103  are arranged in at least some of the cells  105 . As best seen in  FIGS. 2 and 3 , each light source  103  is physically attached to the cell  105 . The light source  103  comprises a light emitter, here LED,  107 , and a light emitter support  109 , which has an attachment portion  111  at each respective end thereof. In this embodiment the emitter support  109  is constituted by two connection pieces  109   a ,  109   b  of copper strip, or some other appropriate material as exemplified above, protruding in opposite directions from the light emitter  107 . Each connection piece  109   a ,  109   b  is attached, at one end thereof, to the light emitter  107 , and attached, at the other end thereof, to a wall portion  113  of the cell  105  at the attachment portion  111 . Thus, the connection pieces  109   a ,  109   b  constitute the above-defined thermally and electrically conducting connections. Since the cells are hexagonal there are six such wall portions  113  embodying the cell  105 . Each attachment portion  111  is formed as a 90 degree bend followed by a 180 degree bend in the opposite direction, of an end portion of the piece  109   a, b , forming a hook shaped portion with a narrow slot. The attachment portion  111  consequently extends perpendicular to a main plane of the light emitter  107 , and rearwards thereof. Thereby it is possible to mount the light source  103  in the cell  105  by moving the light source  103  into the cell  105  from a rear side of the cell structure  101 , while aligning the attachment portions  111  with the wall portions  113  of the cell  105  such that the wall portions  113  are received in the slots. Then, if necessary, the attachment portions  111  are secured to the wall portions  113 , such as by ultrasonic welding or some other method which forms a thermally and electrically conductive bond. Instead of copper other materials are applicable as understood by the person skilled in the art. 
     The cell structure  101  comprises a plurality of wall elements  117 , which are strip shaped and which are connected with each other by means of an adhesive at equidistant interconnection portions  119 . The polygonal cells  105  have been formed by bending the strip shaped wall elements  117  after adhering them. The adhesive is electrically non-conductive, i.e. insulating, such that two adhesively interconnected adjacent wall elements  117  are electrically insulated from each other. The wall elements  117  are electrically interconnected in groups, by means of interconnection members  121 , see  FIG. 4 . Each group consists of at least two wall elements  117 . Each interconnection member  121  is an electrically conductive U shaped clamp that has been clamped over two adjacent wall elements  117  at an interconnection portion  119 . Preferably the interconnection clamps  121  are made from the same material as the wall elements  117 . Each group of interconnected wall elements  117  has a common power supply terminal  123 ,  125 , which is attached to one of the wall elements of the group. By means of a combination of how the interconnection members  121  and the light sources  103  are arranged in the cell structure  101 , the light sources  103  are connected in series and/or in parallel, as illustrated in  FIG. 5 . 
     Referring to  FIG. 6 , an embodiment of a method of manufacturing the lighting device is performed as follows. A first sheet  601  of an electrically conductive material is placed on a support surface. For example, the sheet is an aluminum foil. The top surface of the sheet  601  is provided with a number of adhesive stripes  603  extending across the width of the sheet  601 . The adhesive stripes  603  consist of, for instance, glue or double side adhesive tape. The width of the stripes and the distance between the adhesive stripes  603  determine the size of the cell to be formed at a later stage. Then a second sheet  605  is placed on top of the first sheet  601 . Adhesive stripes  607  are provided on the top surface of the second sheet  605 . The adhesive stripes  607  on the second sheet  605  are displaced longitudinally of the sheet relative to the adhesive stripes  603  on the first sheet  601 . A third sheet  609  having adhesive stripes  611  aligned with those of the first sheet  601 , a fourth sheet  613  having the adhesive stripes  615  aligned with those on the second sheet  605 , etc. are arranged. Thus, the plurality of sheets are stacked on top of each other, while providing the top surface of all but the top most sheet with a number of adhesive stripes. Then the adhesive is cured, and the stack of sheets  617  is longitudinally cut into several sub-stacks. Finally, each sub-stack is opened to a honeycomb cell structure. More particularly, the sheets of the sub-stack are distanced from each other at the non-adhered portions while forming the cells  105  described above. Where the adhesive stripes have been applied, the final result is the above-mentioned interconnection portions  119 . 
     According to an alternative method of manufacture, a single long foil is rewound several turns on a large diameter drum, while parallel adhesive stripes are applied on the foil surface. The adhesive is cured and then the stacked ring of foil is removed from the drum. Sub-stacks are cut off and opened into a cell structure. 
     Above, embodiments of the lighting device and method of manufacturing the lighting device according to the present invention as defined in the appended claims have been described. These should be seen as merely non-limiting examples. As understood by a skilled person, many modifications and alternative embodiments are possible within the scope of the invention. 
     For instance, light sources of different types are applicable, such as LED&#39;s incandescent lamps, Compact Fluorescent, OLED, etc. 
     It is to be noted, that for the purposes of this application, and in particular with regard to the appended claims, the word “comprising” does not exclude other elements or steps, that the word “a” or “an”, does not exclude a plurality, which per se will be apparent to a person skilled in the art.