Abstract:
A method for manufacturing a diffuser for a backlight module is disclosed. The method includes providing a transparent substrate; forming a first transparent photoresist layer on the transparent substrate; spreading a plurality of masking particles on the first transparent photoresist layer; exposing and developing the first transparent photoresist layer; removing the masking particles; etching the exposed region of the first transparent photoresist layer to form a first scattering array; and optionally forming a passivation layer on the first transparent photoresist layer.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method for manufacturing a diffuser for a backlight module and, more particularly, to a method for manufacturing a diffuser using particles as a mask. 
     2. Description of Related Art 
     Currently, flat panel displays, such as LCDs and PDPs are gradually replacing the traditional CRT displays and becoming the main stream of displays due to their light weight and thin size. 
     Contemporary flat panel displays use backlight modules as their sources of light. Generally, a backlight module includes a light source, a light guide, and two diffusers. The diffusers are used to make a uniform dispersion of light and prevent the displaying zone of a display from suffering non-uniform illumination. 
     The common methods for manufacturing a diffuser include the particle adhesion method and the sandblast method. In the particle adhesion method, the scattering particles are adhered on the surface of a transparent substrate by using an adhesive, as shown in  FIG. 1 , so that the light is scattered by the particles and becomes uniform. The sandblast method firstly forms a non-uniform surface on the transparent substrate by sand grinding. The light from the light source is scattered by the non-uniform surface to harmonize the light. The disadvantages of the particle adhesion method lie in that the scattering particles cannot be dispersed uniformly in the adhesive due to the gravity or static electricity factors, and the sieving of particle size of the scattering particles is complex and needs to be done carefully because it will affect the performance of light diffusion. Besides, those scattering particles are mostly made of hard inorganic materials, such as silica or calcium carbonate, which will damage the surface of a liquid crystal (LC) cell through direct contact and therefore a passivation layer is further needed. 
     The Japanese patent JP5173130 disclosed a light guide having functions of diffusion, reflection, and total reflection, wherein the function of diffusion is achieved through roughening the surface of the light guide by using the sandblast method. However, the sandblast method cannot precisely control the roughness of the surface and the uniformity thereof so that the quality of light guide is not easily controlled in mass production. 
     Therefore, it is desirable to provide a method for manufacturing a diffuser for a backlight module to mitigate and/or obviate the aforementioned problems. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to provide a method for manufacturing a diffuser for a backlight module, wherein the masking particles are utilized for carrying out the photolithography processes, which simplifies the manufacturing of a diffuser, avoids the complex step of dispersing particles, and provides a diffuser having an excellent diffusing efficiency. 
     To achieve the object, the method for manufacturing a diffuser for a backlight module of the present invention includes providing a transparent substrate; forming a first transparent photoresist layer on said transparent substrate; spreading a plurality of masking particles on said first transparent photoresist layer; exposing and developing said first transparent photoresist layer; removing said masking particles; etching the exposed region of said first transparent photoresist layer to form a first scattering array; and optionally forming a passivation layer on said first transparent photoresist layer. 
     In brief, the present invention uses particles as a mask to form a suitably patterned and sized photoresist, which aids the following etching step to form a desired diffuser. According to the experiment results, the diffuser having preferred diffusing efficiency is obtained as the particle size of the masking particles is close to the wavelength of the light source. The method disclosed herein not only controls the precision of the diffusing efficiency well, but also can flexibly choose the particle size of the masking particles according to the wavelength of the light source, and therefore achieves a high yield of diffusers, which achieves the best performance of light diffusion. 
     Other objects, advantages, and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a diffuser in the prior art; and 
         FIGS. 2   a  to  2   g  are perspective views of each step of a preferred embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The material of the transparent substrate is not restricted in the method for manufacturing a diffuser for a backlight module of the present invention. Preferably, the transparent substrate is made of acrylates, polyethylene terephthalate (PET), or polycarbonate (PC). The kind of the photoresist is not restricted. Preferably, the photoresist has at least one photo-sensitive polymer and one photo initiator. More preferably, the photoresist is a polyacrylate-based photoresist. The material of the masking particles in the present invention is not restricted, and preferably is selected from the group consisting of glass, TiO 2 , silica, and polystyrene. The particle sizes of the masking particles are not restricted, and may be adjusted according to the light source. Preferably, the particle sizes range from 100 nm to 50 μm. The material of the passivation layer in the method of the present invention is not restricted. Preferably, the passivation layer is made of polyacrylates, polycarbonate, polyethylene terephthalate (PET), or polyethylene (PE). The quantity of layers of the scattering array in the method for manufacturing a diffuser for a backlight module of the present invention is not restricted and may optionally be two layers, three layers, etc. by repeating the manufacturing steps of the scattering array. Preferably, there are three layers of scattering array. With reference to  FIGS. 2   a  to  2   g , there are shown perspective views of each step of a preferred embodiment of the present invention. As shown in  FIG. 2   a , a transparent substrate  1  is provided firstly, and then a first photoresist layer  2  is formed thereon. The photoresist layer can be made of any well-known photoresist, such as polyacrylates, polystyrene, or polyethylene. In the present embodiment, the first photoresist layer is made of polymethylmethacrylate (PMMA). The application manner of the photoresist is not restricted. 
     After the formation of the photoresist, a plurality of masking particles  3  is spread on the photoresist layer  2  for functioning as a mask in a subsequent photolithography process. The material of the masking particles is not restricted and can be any kind of opaque materials, such as glass, TiO 2 , silica, or polystyrene. In the present embodiment, the masking particles are made of polystyrene. The particle size can be chosen flexibly according to the wavelength of the light source of the backlight module in order to obtain the best diffusion efficiency. The particle size of the masking particles used in the present invention ranges from 2 to 100 μm. The spreading method of the masking particles  3  is not restricted and may be a random or uniform spreading. Furthermore, the density of the masking particles on the first photoresist layer  2  may be adjusted according to the requirement of process. 
     After the lithography process has been carried out, the region  21  covered by the masking particles  3  is not photo-polymerized, and the region  22  which was not covered by the masking particles  3  is photo-polymerized, as shown in  FIG. 2   c . The aforementioned difference facilitates the following etching process. 
     As shown in  FIG. 2   d , the masking particles are removed by washing with pure water and ultra-sonic vibration, and then the region  22  of the photoresist layer is etched by using 2.38% TMAH aq. or 0.67% KOH aq. for 60 secs. As a result, the region  21  of the photoresist layer is left and forms the first scattering array. 
     Afterwards, a second photoresist layer  4  is formed on the first scattering array and then a plurality of masking particles  31  is spread on the second photoresist layer  4 , as shown in  FIG. 2   e . The material of the second photoresist layer is not restricted and can be any commonly used photoresist that has a refractive index equaling or differing from that of the first photoresist layer. In the present embodiment, the second photoresist layer is made of polymethylmethacrylate (PMMA). Both the material and particle size of the masking particles  31  are the same as the masking particles  3  spread on the first photoresist layer  2 . However, the material and particle size of the masking particles  31  mainly depend on the requirements of the process and masking particles  31  having different material and particle size from masking particles  3  are also practical. Similarly, the spreading method of the masking particles  31  is not restricted, and may be adjusted according to the requirements of the process. The spreading method in the preferred embodiment is uniform density spreading. 
     As shown in  FIG. 2   f , after the lithography process has been carried out, the masking particles  31  have been removed, and the developed region of the second photoresist layer has been etched, the undeveloped region  41  of the second photoresist layer is left and forms a second scattering array. 
     Finally, a passivation layer  5  is formed on the second scattering array, as shown in  FIG. 2   g . On the one hand the passivation layer  5  shields the scattering arrays, and on the other it guards the displaying panel of a display. The material of the passivation layer  5  is not restricted and may be PET or PE of the prior arts. In the present embodiment the passivation layer  5  is made of PE. 
     The embodiment aforesaid forms a first scattering array firstly, and then forms a second scattering array. Actually, it is optional to form the second scattering array or not, or even a third scattering array, a fourth scattering array, . . . etc. may be further added if needed. All of the scattering arrays can be formed by any one processe illustrated above. 
     Concluding from the aforementioned, the method for manufacturing a diffuser for a backlight module of the present invention applies the photolithography process using particles as a mask. The particle sizes of the masking particles are chosen to form a scattering array that fits the various wavelengths of light sources, which consequently achieves the best performance of light diffusion. Moreover, the spreading method of the masking particles is flexible. With careful selection of the spreading method, the diffusers manufactured by the present invention have a high diffusion performance and are suitable for various displays. 
     Although the present invention has been explained in relation to its preferred embodiment, it is to be understood that many other possible modifications and variations can be made without departing from the spirit and scope of the invention as hereinafter claimed.