Abstract:
A display made from a display panel and a circuit board that are surface mounted to one another. The surface mount interconnections may be distributed across the display avoiding the need to situate the contacts around the periphery. Particularly, in large area displays made up of a plurality of abutting displays, making interconnections in the peripheral areas may be disadvantageous. The row and column contacts may be redundant to improve the yield and life time of the display. Contacts adjacent edges may be displaced into available space, spaced away from the edges.

Description:
BACKGROUND  
         [0001]    This invention relates generally to modular large area displays.  
           [0002]    Large area displays use a number of modules which are connected together. Each of the modules produces a portion of an overall image which is discernible from the composite of modules. Large area displays made in a modular format have advantages since the probability of forming defects is a function of how large is the device being made. Thus, the yield may be higher with devices made in smaller sizes and then assembled into a larger structure.  
           [0003]    Each pixel includes a light altering member which produces light of a particular color. Commonly, a single pixel will include light altering elements for each color in a tri-color color space such as red, green and blue.  
           [0004]    In emissive displays, such as organic light emitting device (OLED) displays, each subpixel associated with a particular color is sandwiched between row and column electrodes. In one example, the row, column and OLED material may be deposited on a transparent panel such as a glass panel. The OLED material may produce light when an appropriate potential is applied across it by way of the row and column electrodes. Conventionally, the column electrodes are made light transmissive using indium tin oxide, for example. Thus, light output from the emitting material passes through the column electrodes and out through the glass panel.  
           [0005]    The glass panel and its associated electrodes and OLED material may be referred to as a display panel. The display panel may be attached to a circuit board which conditions signals for the display panel. Thus, an electrical connection is needed between the display panel and the circuit board. This connection may be made using solder balls and surface mount connections between the display panel and the circuit board.  
           [0006]    Traditionally, such connections are made around the periphery of the overall display. However, this has many disadvantages including the fact that the available edge space may be limited in some cases. In addition, the edge regions may be subject to disruption from impact or the use of sealing materials to interface one module with adjacent modules.  
           [0007]    Thus, there is a need for better ways to interconnect the display panel with the circuit board in a course of making large area displays. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    [0008]FIG. 1 is a greatly enlarged cross-sectional view of one embodiment of a large area display in accordance with the present invention;  
         [0009]    [0009]FIG. 2 is a greatly enlarged, partial cross-sectional view taken generally along the lines  2 - 2  in FIG. 1;  
         [0010]    [0010]FIG. 3 is a less enlarged cross-sectional view corresponding to FIG. 2 but showing a larger area in accordance with one embodiment of the present invention; and  
         [0011]    [0011]FIG. 4 is a schematic depiction of contact layout in accordance with one embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0012]    Referring to FIG. 1, a display  10 , in one embodiment, may be an organic light emitting device (OLED) display, however, the present invention is not limited to a particular display technology. The display  10  includes a display panel  12 . In one embodiment, the display panel  12  includes a transparent glass sheet  13  having attached thereto a tri-pixel  15 . The tri-pixel  15 , in an OLED embodiment, may include a sandwich of a column electrode followed by an OLED material followed by row electrode. The row electrode may be formed of a metal or other conductive material. The column electrode is conventionally formed of a transparent conductive material, such as indium tin oxide (ITO).  
         [0013]    Light is generated by the OLED material in response to the development of a potential across the material by the row and column electrodes. As a result, the OLED material emits light which passes through the column electrode of the tri-pixel  15  and the glass sheet  13  to be emitted by the display  10 .  
         [0014]    Control over the tri-pixels  15  may be provided through a circuit board  18  which receives signals from driver circuits  20 . For example, the driver circuits  20  may indicate the color and intensity to drive the various tri-pixels  15 . This information may be distributed by the circuit board  18  to the appropriate tri-pixels  15 . Thus, the circuit board  18  may provide a signal distribution function to distribute signals processed by the driver circuits  20  to the individual tri-pixels  15 . In one embodiment, the circuit board  18  may be a ceramic circuit board such as an alumina circuit board including appropriate vias and interconnections.  
         [0015]    The connections between the display panel  12  and the circuit board  18  may be implemented using interconnects  14  in the form of solder balls or other surface mount interconnection technologies. The interconnects  14  may be affixed to the circuit board  18  and/or display panel  12  using heat. Then the display panel  12  and circuit board  18  are brought together to physically and electrically interconnect the circuit board  18  to the display panel  12  by reflowing the solder to form the interconnects  14 . At the same time, solder balls between the driver circuits  20  and the circuit board  18  may be reflowed, in one embodiment.  
         [0016]    Referring to FIG. 2, the display panel  12  may include a matrix of row electrodes  22   a,    22   b  and  22   c.  As described previously, the row electrodes  22  may be made of a metal. The row electrodes  22  are deposited on top of the light emitting material, which is not shown in FIG. 2. Beneath the light emitting material is an array of column electrodes  24   a  and  24   b.  Each column electrode  24  actually includes three separate lines, one line for each color of the tri-pixel indicated as P. Thus a line  25  is provided for each of the three colors of the pixel P. Thus the pixel P is defined by the region where row electrodes  22  and triset of column electrodes  24  overlap.  
         [0017]    In one embodiment, an entire row of pixels is addressed or activated at one time. Thus, potential is applied to a given row electrode  22 . Every pixel along the row then has its row activated. Each column electrode  24  is then selectively activated to activate a particular pixel at a particular intensity, if desired. Thus, in one pixel, the red subpixel may be activated whereas in the next pixel, the green subpixel may not be illuminated. The intensity of illumination of each pixel may be adjusted through appropriate column signals.  
         [0018]    The column signals originating, for example, in the driver circuits  20  may pass through the circuit board  18 . From the circuit board  18 , those signals may pass through interconnects  14  to interconnect contact pads  28  on the display panel  12 . From the contact pads  28 , signals may pass, for example, through metallizations  34  to column line contacts  32 . The column line contact  32  contacts a particular line  25  of a set of three column lines  24 . Generally, as shown in FIG. 2, the column connections are made by metallizations  34  which extend between adjacent rows  22  and run generally parallel thereto. Thus, the metallizations  34  run transversely to the direction of the column electrodes  24  in the space provided between adjacent rows  22 .  
         [0019]    The same space may be utilized to provide the pads  28  from the interconnects  14  for the row electrodes  22 . The metallizations  30  for the row electrodes  22  run generally transversely to the row electrodes  22  and parallel to the length of the column electrodes  24 . Each row interconnect system includes a pad  28  which makes contact to a solder ball or other interconnect  14  and a metallization  30  which runs from the pad  28  to a row contact  26 . The row contact  26  contacts a particular row electrode  24  and provides an electrical connection thereto.  
         [0020]    Thus, a system of pads  28 , metallizations  30  and  34 , and contacts  26  and  32  may all be deposited directly on to the display panel  12  in accordance with one example of a fabrication process. This may facilitate the fabrication of the display panel  12 . Further, spaces are provided between basic column electrodes  24  that may be utilized for making connections to row electrodes  22  and likewise spaces may be provided between adjacent row electrodes  22  that may be utilized for making column electrode  24  connections.  
         [0021]    Turning next to FIG. 3, a portion of the display panel  12  is illustrated. The display panel  12  includes a horizontal edge  100  and a vertical edge  102 . Ideally, connections are spaced well away from the edges  100  and  102  because of the possibility of disruption. In particular, when one display  10  is abutted to an adjacent display  10 , sealing material may be utilized along that interface. This may interfere with the contacting process. Thus, it may be desirable to keep a field along the edges  100 ,  102  as free as possible from interconnections.  
         [0022]    In this regard, the edge proximate column metallizations  34  extend away from the edge  102 . Similarly, the edge proximate row metallization  30  extend away from the edge  100 . In the display portion shown in FIG. 3, one row contact  26  is provided to each row electrode  22 .  
         [0023]    However, redundancy may be desirable and additional row connections may be provided to the same row electrode in a portion of the display  10  that repeats the pattern shown in FIG. 3. Similarly, redundant column connections are provided along the length of the column electrodes  24 . Thus, when any row electrode  22  is activated, the potential applied to a column electrode  24  may be repeated a large number of times along the exact same column electrode  24  to provide redundancy and fail safe operation as well as to distribute the potential equally along the lines  25 .  
         [0024]    Because ITO, which may be utilized for the column electrodes  24 , is not as good a conductor as aluminum or silver, there may be resistive voltage drops along the column electrodes  24 . To reduce the magnitude of these resistive voltage drops, it is desirable to provide multiple connections along the length of the column electrodes  24  at spaced locations along the column electrodes.  
         [0025]    Referring to FIG. 4, the layout of the row and column interconnections in the display portion of FIG. 3 may be better understood. A series of column connections  40   a  and  40   c  are provided from the vertically oriented space E between adjacent column electrodes  24  to three column lines  25 . Each column connection  40  includes three sets of pads  18 , metallizations  34  and contacts  32 .  
         [0026]    In one embodiment, the column connections  40  are provided to every other set of vertically displaced pixels such as the pixels indicated at A and C. In addition, the column connection  40   b  is interposed in the otherwise vacant pixel space B. In one embodiment, a series of horizontal spaces A, B, C, and D may be provided in a repeated fashion along the display panel  12 . Every other space, such as the space B and D, may be left vacant.  
         [0027]    The region F between adjacent sets of column electrodes  24 , may be devoted to a vertical strip of row connects  50 .  
         [0028]    A field for the column connection  40   g  may be provided along the pixel region C. The column connections  40  may skip the field B, and may be repeated again as indicated at  40   h  in the field A.  
         [0029]    Thus, redundant contacts may be provided while at the same time avoiding, to the greatest possible extent, placing contacts in the areas along peripheral edges. In some cases, available space between adjacent banks of contacts may be utilized near the edges to contain contacts that would otherwise be provided along the edge fields. Redundant column and row contacts are desirable. In many cases, multiple redundant contacts across the surface of the display panel  12  may be advantageous.  
         [0030]    In addition, it may be desirable to maximize the area of the contacts to the greatest possible extent to minimize the total contact resistance.  
         [0031]    Thus, with embodiments of the present invention, interconnections may be made within the pixel areas between the active areas and driver circuits across the face of the display panel  12 . Thus, it is not necessary to undertake the relatively hazardous design of positioning the contacts around the periphery of the actual display producing elements.  
         [0032]    While the present invention has been described with respect to a limited number of embodiments, those skilled in the art will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover all such modifications and variations as fall within the true spirit and scope of this present invention.