Abstract:
Disclosed herein is a method for producing an LED array grid including the steps of (i) arranging N electrically conducting parallel wires, where N is an integer &gt;1, thus creating an array of wires having a width D perpendicular to a direction of the wires, (ii) arranging LED components to the array of wires such that each LED component is electrically coupled to at least two adjacent wires, (iii) stretching the array of wires such that the width D increases, and arranging the stretched LED array grid onto a plate or between two plates

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a method for production of an illumination system, an illumination system produced with said method, and a winding device. 
       TECHNICAL BACKGROUND 
       [0002]    Light emitting diodes (LEDs) have been used as backlight for displays and illumination panels for some time, where a large number of low power LEDs are arranged in an array. LEDs are well suited for this purpose for several reasons. They are, for instance, durable structures with a long lifetime, which reduces the maintenance needed. Also, they have a low power consumption and are operated at lower voltages, which reduces costs of operation and risks related to high voltage applications. In relation to this they have an high light output. Prior art techniques include the arrangement of LEDs on printed circuit boards (PCBs). This is, however a costly solution, especially when the LEDs are on a large pitch an larger areas are to be illuminated. 
       SUMMARY OF THE INVENTION 
       [0003]    In order to provide a LED array that is suitable for the above and other purposes where a large area illumination is needed and at the same time solving the drawbacks in prior art solutions the present invention provides a method for production of a LED array grid, comprising the steps of:
       arranging N electrically conducting wires (W 1 -W N ) in parallel, where N is an integer &gt;1, thus creating an array of wires, said array having a width D perpendicular to a length direction of the wires,   arranging LED components to the array of wires such that each LED component is electrically coupled to at least two adjacent wires,   stretching the array of wires such that the width D increases.       
 
         [0007]    By using low cost assembly processes on very small printed circuit boards and a novel design of these boards it is possible to make the interconnects for large area arrays with wires by a simple winding/soldering process. The novel design of the PCBs refers to that the resulting LED components preferably are adapted for use in the inventive method by the provision of dedicated locations on the LED components adapted for contact with the wire, e.g. locations in which the electrical contact is facilitated and/or the wire is kept in position. Further, the use of a wire instead of a large area printed circuit board further decreases the cost for the LED array grid. By using the inventive method it is possible to achieve several advantages in comparison to known techniques. According to the method the production steps can be performed in a limited space, which facilitates operation reduces construction costs, while the end result can be a large LED array grid with any desired pitch. 
         [0008]    According to one or more embodiments the LED components are arranged such that the LED components are regularly distributed after stretching of the grid and in one or more embodiments the LED components are arranged such that, in a direction perpendicular to the length direction of the wires, there is a row of LED component bridging every other gap between adjacent wires. 
         [0009]    In one or more embodiments adjacent rows of LED components are shifted such that if a first row bridges every other gap between adjacent wires starting at a first gap, the adjacent row bridges every other gap between adjacent wires starting at an adjacent gap. When stretched this can result in a LED array grid where the wires forms diamond-shaped openings. 
         [0010]    In one or more embodiments the rows are arranged in row pairs and wherein adjacent row pairs of LED components are shifted in such a way that if a first row pair bridges every other gap between adjacent wires starting at a first gap, the adjacent row pair bridges every other gap between adjacent wires starting at an adjacent gap. After stretching this arrangement can result in a LED array grid with equidistant rows and columns. 
         [0011]    In one or more embodiments the array of wires are formed by winding a wire in a helical fashion around an assembly drum and wherein a winding of the array of wires can leave the assembly drum after the step of securely fixing each LED component to said two adjacent wires included in the winding is finalized, thus creating a cylinder shaped grid of wires and LED components. The use of an assembly drum makes it possible to generate a continuous assemble process where components are fed in one end and a refined product is achieved in the other. 
         [0012]    In one or more embodiments the method further comprises the step of cutting the wire at least once along each winding of the cylinder shaped grid. This step is beneficial in the cases where a planar LED array grid is desired. 
         [0013]    The LED components are preferably soldered, glued or similar to the wires or comprise IDC type fasteners (IDC—insulation displacement connector) in order to provide a durable LED array grid and ensure a reliable electrical contact. 
         [0014]    According to one or more embodiments the method further comprises the steps of:
       preparing a leadframe material for a substrate,   folding the substrate in order to obtain “snap-lock” positions for a wire,   placing/interconnecting LEDs by means of wire bonding or flip-chip,   over moulding the LEDs with a clear compound   back etch carrier substrate,   dice into components.       
 
         [0021]    The resulting LED components are suitable for use in the inventive LED array grid, as well as for other applications. 
         [0022]    The invention also relates to a winder device for production of a LED array grid, which winder device according to one embodiment comprises rotatable pins extending essentially in the same direction and being arranged along a circumference, thus forming a winding drum, wherein said rotatable pins are provided with threads adapted to effectively locate an electrically conducting wire being wound around the drum, thus creating a parallel array of wires, 
         [0023]    wherein rotation of said pins transports the array of wires along the length of the pins, 
         [0024]    said device further comprising means for arranging LED components to the array of wires, and 
         [0025]    means for securely fixing each LED component to said two adjacent wires. 
         [0026]    The winder device is well suited for production of the inventive LED array grid. 
         [0027]    In one or more embodiments the winder device further comprises a gear coupling the rotation of the drum to the rotation of each of the pins such that one revolution of the drum results in one revolution of each pin. This feature results in that one “turn” of the resulting cylindrical LED array grid will be wound of the drum during each revolution of the drum. This means that the rate at which the grid is fed off the device equals the rate at which the wire is fed onto the device, which is beneficial. 
     
    
     
       DESCRIPTION OF DRAWINGS 
         [0028]      FIG. 1  is a graphical flowchart showing an outline of one embodiment of the inventive method. 
           [0029]      FIG. 2  is a perspective view illustrating LED components arranged on a PCB used for a soldered version. 
           [0030]      FIG. 3   a - c  are perspective views illustrating the production steps for LED components that are of IDC (insulation displacement connector) type. 
           [0031]      FIG. 4  is a perspective partial view showing details of a device performing the inventive method. 
           [0032]      FIG. 5  is a perspective view from behind of the device of  FIG. 4 . 
           [0033]      FIG. 6  is a schematic view of an alternative embodiment of the inventive method. 
           [0034]      FIG. 7  is a perspective view of a LED array grid according to one embodiment of the invention arranged between two glass plates. 
           [0035]      FIGS. 8   a  and  8   b  are schematic views illustrating the structure of LED components which are adapted for soldered or glued wires as interconnect. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0036]      FIG. 1  shows the main steps of the inventive method. It illustrates an example of how LEDs  102  for use in the present invention can be arranged on a PCB  104 , see also  FIG. 2 . The LEDs  102  can be prepackaged LEDs or naked dyes. In this example the PCB  104  is provided with a specific hole pattern and when the PCB  104  is diced into separate LED components  106  the holes  108  can be defined such as to provide attachment points used in a soldering process later on in the inventive method. It is cost efficient to arrange the LEDs  102  with a low pitch on a PCB  104  and to make as much use of the PCB material as possible. 
         [0037]    After this preparing step the actual assembly takes place. A wire  110  is wound around an assembly drum  112 , to be described in more detail later, and the separate LED components  106  are arranged in specific slots  114  that locates them before the wire  110  is wound into the holes  108  forming the attachment points. The wire is generally indicated with  110 , while each individual “turn” of the wire is designated W n , n=1, 2 etc, W 1  being the first turn of the wire  110 , W 2  the second, and so forth. The assembly drum  112  rotates so that a feed device, schematically shown at  116  in  FIG. 4 , which feed device  116  contains a set of LED components  106 , can be a fixed device in the sense that it does not need to move in order to position the LED components  106  correctly in the slots  114 . This also means that equipment, such as soldering devices (not shown), can have a fixed location. 
         [0038]    While the assembly drum  112  rotates, the wire  110  being wound on the drum  112  will gradually be fed off the drum, which also will be described later on in relation to  FIGS. 4 and 5 . 
         [0039]    The assembly process can continue indefinitely or, in practice, as long as needed. The thus created, cylindrical, LED array grid is generally cut and unfolded, which is shown as the next illustrative step in the flow chart of  FIG. 1 . Finally the LED array grid is stretched to create a large area LED array grid  100 , the size of which is adapted to its intended use. From  FIG. 1  and the above description it should be clear that a width of the grid, being a function of the diameter (or the circumference) of the assembly drum  112 , is limited, while the length if the LED array grid  100  is infinite, at least theoretically. Some processing steps in order to obtain the final lighting product remains. It should be mentioned that soldering is only one example of a fastening technique that could be used. There are alternatives such as laser welding, ultrasonic techniques, etc. 
         [0040]    Obviously, the arrangement can be the opposite, i.e. the drum  112  is static while other equipment revolves around it. Combinations of these two extremes are also anticipated. 
         [0041]      FIG. 2  illustrates a small pitch assembly of LEDs  102  on a PCB material. The assembly is shown after being diced into individual LED components  106 . It can be noticed how the dicing is offset so as to transform the holes  108  into suitable soldering points. 
         [0042]      FIG. 3   a - c  illustrates a few steps in the construction of IDC-type LED components  206 . It is shown how LEDs  102  are arranged on a metal substrate  204  or lead frame, after which the substrate  204  is cut or punched into separate LED components  206  (see  FIG. 3   c ). An advantage with the IDC-type LED components  206  is that they do not have to be soldered onto the wire  100 . Also, the wire  100  could be insulated while still permitting the IDC-type LED components  206  to be fastened and electrically connected to the wire  100 . The use of IDC-type LED components  206  makes the step of attaching the LED components  206  to the wire  100  a bit more flexible. The LED components can be arranged in a slot, corresponding to slot  114  prior to the wire  110  being wound around the assembly drum  112 , but they could equally well be arranged on the wire  110  after said wire have been wound onto the assembly drum  112 . 
         [0043]      FIG. 4  illustrates a detail of the assembly drum  112  during an assembly process. The drum  112  has a main body  118  which rotates around an axis A with a predetermined speed. The drum  112  also comprise rotating pins  120 . These pins  120  are driven to rotate, e.g., by a belt or gears (not shown) as the drum  112  rotates. The pins  120  are on one end provided with coarse threads  122 , as shown in  FIGS. 4 and 5 . As the drum  112  rotates a wire  100  is wound onto the drum  112  and positioned by the threads  122 . The rotation of the pins  120  will, by means of the threads  122 , gradually feed the wire  100  off the assembly drum  112 . At the same time the rotating pins  120  are the operative part onto which the wire  100  is wound. Between adjacent pins, on their threaded end, the LED locating slots  114  are arranged. These serves to, together with the wire  110 , locate the LED components  106  until they are fastened to the wire  110 . A component feed device  116  is arranged to position LED components  106 ,  206  in the locating slots, after which the components can be fastened to the wire  110 . The rotation of the drum body  118 , the rotation of the rotating pins  120 , and the pin threads  122  are so arranged that the component feed device  116 , as well as the fastening of LED components  106 ,  206 , can take place in a fixed position, which makes it possible to simplify the equipment needed for these operations. 
         [0044]      FIG. 5  shows the assembly drum  112  from behind, and also shows how the LED array grid  100  starts to be fed off the drum. 
         [0045]    The assembly process as described has some advantages regarding the simplicity of surrounding equipment such as the component feed and the soldering device. However, the inventive idea could also be realised in a planar approach, as schematically shown in  FIG. 6 , in which the single wound wire  110  and the assembly drum  112  is replaced by several individual, parallel wires  210  being fed in a plane to a mounting area  212  where LED components  106 ,  206  are attached along the length of the wires  210 . The arrow in  FIG. 6  indicates the feeding direction. Just like in the previously mentioned embodiment, the resulting LED array grid  100  can be stretched to a desired length, which obviously is dependent the distribution of LED components  106 ,  206  on the LED array grid. This planar approach has an advantage in that the width of the final LED array grid potentially is more easy to vary, in terms of production equipment. From the above description of the assembly using an assembly drum features not specifically related to the use of a drum, also can be applied to the planar approach 
         [0046]    Note that the described and showed distribution of LED components on the wire grid is given as an example only. The LED components  106 ,  206  could equally well be given an alternative distribution, as long as it would enable suitable stretching opportunities. An example of an alternative distribution is that the LED components are placed in alternately in groups of one, which should be read in the context that the LED components  106 ,  206  in the drawings are arranged alternately in groups of two. 
         [0047]    The LED array grid that is created with the inventive method is extremely cost efficient in comparison to a known PCB solution, i.e. a solution in which a PCB forms the entire area of the array grid. The cost for one square meter LED array if a PCB is used will exceed 50 Euro, while the cost for the wire mesh solution is less than 1 Euro. 
         [0048]    Suitable, but not exclusive applications for the inventive LED array grid  100  are backlighting for LCD displays, an alternative to compact fluorescent lamps and sphere lighting like light emitting walls or windows. 
         [0049]    A novel usage includes the arrangement of the LED array grid  100  on a glass plate, or sandwiched between two glass plates  302 ,  304  as exemplified in  FIG. 7 . The space between the glass plates can be filled with polyvinyl butyral (PVB). The PVB provides for a strong sandwich structure bonding the glass plates and also reduces reflections thanks to its optical properties. As conductor for the electrical current, a transparent layer on one of the glass plates can be used, such as indium tin oxide (generally called ITO) or fluor doped tin oxide (generally called FTO). The LEDs are bonded to this coated glass, e.g. with conductive adhesive or solder. However, both ITO and FTO possess a high sheet resistance which limits the power of the LEDs, furthermore it is not easy to make a reliable interconnect between LEDs and layers of ITO or FTO, which is why the use of an LED array grid  100  is advantageous from this perspective. 
         [0050]    The LED array grids can also be bonded to the glass plate by means of self-bonding wires. Such wires are coated with a first strong isolating layer—this layer has a high melting point (&gt;300° C.)—and a second isolation layer with a lower melting point (&lt;200° C.). This second layer is in case of making coils used for bonding the wires within a coil to make it rigid. The heat can be applied by a current through the wires or by placing the coil in an oven, it is also possible to use a solvent to obtain adhesion. In cases where the LEDs are thinner than the wires the same bonding principle can be used by applying temperature and pressure on the glass-LED sandwich structure. 
         [0051]    The use of wires, e.g. a 0.3 mm diameter copper wire as compared to a transparent layer of ITO or FTO gives huge advantages in terms of efficiency, mainly coupled to the much higher resistance per length unit for said transparent layers. 
         [0052]      FIGS. 8   a  and  8   b  are schematic views exemplifying a LED component construction, or LED package, which is particularly suitable for the purposes of the inventive LED array grid  100 , and also the sandwich construction described above. The method for producing the LED package involves the steps of:
       preparing a leadframe material  204  for a substrate,   folding the substrate in order to obtain various “snap-lock” positions  208  for a wire  210  which will be attached in use,   placing/interconnecting LEDs  202  by means of wire bonding or flip-chip,   over moulding with a clear compound  224     back etch carrier substrate,   dice into components  306 .         
         [0059]    The above construction can also comprise a heatsink arranged in thermal contact with the LEDs. 
         [0060]    It should be noted that each wire could if needed consist of two, or more, conductors, as illustrated in  FIGS. 8   a - b.