Electronic Device Display with a Backlight

Abstract

An electronic device may include display layers such as liquid crystal display layers and a backlight unit that provides illumination for the display layers. The backlight unit may include light-emitting diodes that emit light into the edge of a light guide film. To minimize the inactive area of the display, the light-emitting diodes may be tightly spaced to approximate a line light source instead of point light sources. Color and/or luminance compensation layers may be incorporated at various locations within the backlight structures to ensure that the backlight provided to the display layers is homogenous. A thin-film transistor layer of the display may be coupled to a printed circuit board by a flexible printed circuit. The flexible printed circuit may have additional solder mask layers to improve robustness, may include encapsulation, and may have traces with a varying pitch.

What is claimed is: 
     
         1 . An electronic device comprising:
 display layers; and   a backlight unit that provides backlight for the display layers, the backlight unit comprising:
 a light guide film having a plurality of light-scattering structures; 
 a plurality of light-emitting diodes that emit light into an edge of the light guide film, wherein each of the plurality of light-scattering structures extends perpendicular to the edge of the light guide film along an upper surface of the light guide film; and 
 a turning film formed over the light guide film, wherein the turning film includes a plurality of prisms that extend parallel to the edge of the light guide film along a lower surface of the turning film. 
   
     
     
         2 . The electronic device defined in  claim 1 , wherein the turning film further comprises a base film portion and wherein each of the plurality of prisms extends from a lower surface of the base film portion. 
     
     
         3 . The electronic device defined in  claim 2 , wherein each of the plurality of prisms has a planar surface that meets a curved surface at a vertex. 
     
     
         4 . The electronic device defined in  claim 2 , wherein each of the plurality of prisms has a first curved surface that meets a second curved surface at a vertex. 
     
     
         5 . The electronic device defined in  claim 4 , wherein the first curved surface has a first curvature and the second curved surface has a second curvature that is the same as the first curvature. 
     
     
         6 . The electronic device defined in  claim 4 , wherein the first curved surface has a first curvature and the second curved surface has a second curvature that is different than the first curvature. 
     
     
         7 . The electronic device defined in  claim 2 , wherein each of the plurality of prisms has a curved surface with a rounded tip. 
     
     
         8 . The electronic device defined in  claim 1 , wherein each light-scattering structure has a triangular cross-section with first and second planar surfaces that meet at an angle that is larger than ninety degrees. 
     
     
         9 . The electronic device defined in  claim 1 , wherein each light-scattering structure has a semi-circular cross-section. 
     
     
         10 . The electronic device defined in  claim 1 , wherein each light-scattering structure has a triangular cross-section with a rounded tip. 
     
     
         11 . The electronic device defined in  claim 1 , wherein the plurality of light-scattering structures includes a first subset of light-scattering structures that have a first shape and a second subset of light-scattering structures that have a second shape and wherein the light-scattering structures that have the first shape alternate with the light-scattering structures that have the second shape. 
     
     
         12 . The electronic device defined in  claim 11 , wherein each of the first subset of light-scattering structures has a first height and each of the second subset of light-scattering structures has a second height that is different than the first height. 
     
     
         13 . The electronic device defined in  claim 1 , wherein the turning film controls a first viewing angle in a first dimension and the light guide film controls a second viewing angle in a second dimension that is orthogonal to the first dimension. 
     
     
         14 . The electronic device defined in  claim 1 , further comprising laser dots on a lower surface of the turning film. 
     
     
         15 . An electronic device comprising:
 display layers; and   a backlight unit that provides backlight for the display layers, the backlight unit comprising:
 a light guide film; 
 a plurality of light-emitting diodes that emit light into an edge of the light guide film; and 
 a turning film formed over the light guide film; and 
 a brightness enhancement film that is interposed between the turning film and the display layers, wherein the brightness enhancement film includes a diffusive pressure sensitive adhesive layer. 
   
     
     
         16 . The electronic device defined in  claim 15 , wherein the light guide film has a plurality of light-scattering structures that extend perpendicular to the edge of the light guide film. 
     
     
         17 . The electronic device defined in  claim 16 , wherein the turning film includes a plurality of prisms that extend parallel to the edge of the light guide film. 
     
     
         18 . The electronic device defined in  claim 17 , wherein the turning film controls a first viewing angle in a first dimension and the light guide film controls a second viewing angle in a second dimension that is orthogonal to the first dimension. 
     
     
         19 . The electronic device defined in  claim 15 , wherein the brightness enhancement film includes an additional pressure sensitive adhesive layer and wherein the diffusive pressure sensitive adhesive layer is attached to and in direct contact with the additional pressure sensitive adhesive layer. 
     
     
         20 . An electronic device comprising:
 display layers; and   a backlight unit that provides backlight for the display layers, the backlight unit comprising:
 a flexible printed circuit; 
 a light guide film having a plurality of light-scattering structures; and 
 a plurality of light-emitting diodes mounted on the flexible printed circuit that emit light into an edge of the light guide film, wherein each of the plurality of light-scattering structures extends perpendicular to the edge of the light guide film along an upper surface of the light guide film, wherein the plurality of light-scattering structures includes a first subset of light-scattering structures that have a first height and a second subset of light-scattering structures that have a second height that is different than the first height, and wherein the light-scattering structures that have the first height alternate with the light-scattering structures that have the second height.