Patent Publication Number: US-2013248503-A1

Title: Method for forming metal mask and laser drilling apparatus for forming the same

Description:
BACKGROUND OF THE DISCLOSURE 
     1. Field of the Disclosure 
     The invention relates to a method for forming a metal mask and a laser drilling apparatus for forming the same, and more particularly, to a yield-enhanced method for forming a metal mask and a laser drilling apparatus. 
     2. Brief Description of the Related Art 
     A traditional evaporation mask for an active-matrix organic light-emitting diode (AMOLED) is fabricated by first forming multiple micro mesh holes in a thin metal plate having a thickness of about 40 μm using a pattern etching process so as to form an evaporation mesh. Each of the mesh holes in the evaporating mesh has a size of just about 50 μm, and a pitch between neighboring ones of the mesh holes is just about 70 μm. 
     U.S. Pat. Pub. No. 2011/0183271 discloses another method for forming the evaporation mesh. The method is performed by first forming multiple slot holes in a thin metal plate and then trimming sidewalls of the slot holes with inclined surfaces using laser beams so as to form mesh holes in the evaporation mesh. 
     Referring to  FIG. 10 , an evaporation mesh  80 , after completed, is placed on a metal frame  82 . The evaporation mesh  80  has each side clipped by clips (not shown) and is stretched outwards to be flat. However, the evaporation mesh  80  and the mesh holes  801  therein have sizes of micrometer level, and thus it is difficult to stretch the evaporation mesh  80  to be flat without any deformation of the mesh holes  801  in the evaporation mesh  80 . 
     In general, during stretching an evaporation mesh to be flat, the evaporation mesh requires being compared with a mother glass. If mesh holes in the evaporation mesh align with standard mesh holes in the mother glass, there is no deformation of the mesh holes in the evaporation mesh after stretched by the clips. Next, the evaporation mesh is welded with the metal frame and a total pitch is checked by a total-pitch measuring device so as to determine if the mesh holes in the evaporation mesh are positioned within allowable tolerances. The mesh holes in the evaporation mesh are required to pass double standard tests to see if a total pitch error is within ±5 μm and if a precision error compared with the standard mesh holes in the mother glass is within ±3 μm. If the comparison result does not pass the standard tests, there is deformation or shift of the mesh holes in the evaporation mesh when the evaporation mesh is stretched by the clips. At this time, stretching forces exerted by the clips requires being adjusted until the comparison result passes the standard test. 
     The above method for forming the evaporation mask has complicated steps and the mesh holes in the evaporation mesh are subject to deformation when the evaporation mesh is stretched by the clips. Thus, it is time consuming to adjust the stretching forces exerted by the clips. Besides, in the process of welding the evaporation mesh with the metal frame, it is possible that the mesh holes in the evaporation mesh deform or shift. Thus, checking the total pitch error should be performed after the welding process. Accordingly, the traditional method for forming the evaporation mask for an active-matrix organic light-emitting diode (AMOLED) is time inefficient and low yielding. 
       FIG. 11  is a schematic view illustrating a method for forming another evaporation mask for an active-matrix organic light-emitting diode (AMOLED) disclosed in Taiwan Pat. Pub. No. 200526794. A thin metal plate  91  is first placed on a mesh  920  at a center of a mesh frame  92 , and the mesh  920  has the thin metal plate  91  kept with a flat surface. Next, multiple mesh holes  910  are formed in the thin metal plate  91  by laser cutting. Next, a fixing frame  93  is placed at a bottom of the thin metal plate  91  and the fixing frame  93  and the thin metal plate  91  are pressed together by a fixture set  94  and  95 . Next, the fixing frame  93  and the thin metal plate  91  are welded together. Next, the fixing frame  93  and the thin metal plate  91  are cut from the mesh frame  92  such that the evaporation mask can be obtained. 
     SUMMARY OF THE DISCLOSURE 
     The present invention is directed to a yield-enhanced method for forming a metal mask and a laser drilling apparatus. 
     The method includes performing a metal-frame feeding process to place a metal frame on a worktable having a supporting structure and to mount the metal frame to a periphery of the supporting structure, next performing a thin-metal-plate feeding process to place a thin metal plate in a flat manner on a top surface constructed by the metal frame and the supporting structure, next performing a welding process to weld the thin metal plate with the metal frame so as to form a prototype mask, and next performing a laser drilling process to form multiple mesh holes in the thin metal plate of the prototype mask using a laser drilling apparatus. 
     In one embodiment, the laser drilling apparatus includes a platform, a carrying mechanism movably mounted on the platform, a laser head mounted on the carrying mechanism, and a computer controlling movement of the carrying mechanism and the laser head and controlling the laser head to perform the laser drilling process. 
     In one embodiment, the laser drilling apparatus includes an inspection device mounted on the carrying mechanism. 
     In one embodiment, the method includes performing an inspection process and an adjustment process. During the laser drilling process performed by the laser head, the computer controls the inspection device to perform the inspection process and performs the adjustment process to the laser head such that the mesh holes in the thin metal plate, made by the laser drilling process, can meet standard. 
     In one embodiment, the method includes performing another inspection process by the inspection device. After the laser drilling process performed by the laser head, the computer controls the inspection device to perform the inspection process for inspecting if the mesh holes in the thin metal plate, made by the laser drilling process, meet standard. 
     Compared with prior art, in accordance with the present invention, the laser drilling process is performed after the thin metal plate is placed on the metal frame in a flat manner and welded with the metal frame. Accordingly, the deformation or shift of the mesh holes in the metal mask can be avoided and the metal mask has an improved yield. 
     The accompanying drawings are included to provide a further understanding of the invention, and are incorporated as a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a flow chart of a method for forming a metal mask in accordance with the present invention. 
         FIG. 2  is a schematic view of a metal frame placed on a worktable in accordance with the present invention. 
         FIG. 3  is a schematic view of a thin metal plate placed on a metal frame and a supporting structure in a flat manner in accordance with the present invention. 
         FIG. 4  is a schematically front view of a laser drilling apparatus. 
         FIG. 5  is a schematically top view of a laser drilling apparatus. 
         FIG. 6  is a schematic view of a laser drilling process in accordance with the present invention. 
         FIG. 7  is a three dimensional view of a mesh hole in accordance with the present invention. 
         FIG. 8  is a cross sectional view along the line A-A in  FIG. 7 . 
         FIG. 9  is a cross sectional view along the line B-B in  FIG. 7 . 
         FIG. 10  is a schematic view of a traditional method for forming an evaporation mask for an active-matrix organic light-emitting diode (AMOLED). 
         FIG. 11  is another schematic view of another traditional method for forming an evaporation mask for an active-matrix organic light-emitting diode (AMOLED). 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Illustrative embodiments accompanying with figures are now described below to lead the characteristics, contents, advantages and effects of the invention to be understood by the Examiner. Figures are illustrated only for explanation, but are not drawn to scale and precise arrangement, and thus the scope of the invention should not be limited by the scale and arrangement illustrated in the figures. 
       FIG. 1  is a flow chart of a method for forming a metal mask in accordance with the present invention. The method can be used to form, but not limited to, an evaporation mask, fine pitch metal mask (FMM), for an organic light-emitting diode. Alternatively, the method can be used to form a general metal mask, such as print mask used for a touch panel or in an IC packaging process. The method includes a metal-frame feeding process S 1 , a thin-metal-plate feeding process S 2 , a welding process S 3  and a laser drilling process S 4 , wherein the metal-frame feeding process S 1 , thin-metal-plate feeding process S 2  and welding process S 3  are performed on a stretching machine. 
     Referring to  FIG. 2 , the stretching machine includes a worktable  7 , a supporting structure  71  on a top surface of the worktable  7  and a welding apparatus (not shown). The metal-frame feeding process S 1  is performed to place a metal frame  1  on the worktable  7  and to mount the metal frame  1  to a periphery of the supporting structure  71 . The supporting structure  71  includes, but not limited to, multiple supporting sticks  710 . Referring to  FIG. 3 , the thin-metal-plate feeding process S 2  is performed to place a thin metal plate  2  having a thickness of just about 40 μm on a top surface constructed by the metal frame  1  and the supporting structure  71 . Alternatively, the thin-metal-plate feeding process S 2  can be performed by stretching so as to make a top surface of the thin metal plate  2  become a plane. The welding process S 3  is performed to weld the thin metal plate  2  with the metal frame  1  so as to form a prototype evaporation mask. 
     The laser drilling process S 4  is performed to form multiple mesh holes in the thin metal plate  2  using a laser drilling apparatus  3  as shown in  FIGS. 4 and 5 . The laser drilling apparatus  3  includes a platform  35 , a carrying mechanism  37 , at least one laser head  39  and a computer (not shown). 
     The platform  35  is used to carry the thin metal plate  2  and the metal frame  1  which are welded together. The platform  35  includes a supporting structure having multiple supporting sticks  355  supporting the thin metal plate  2  such that the thin metal plate  2  has a top surface kept in a flat manner. 
     The carrying mechanism  37  includes a first moving part  371  and a second moving part  372 . The first moving part  371  is mounted to a set of tracks  350  on the platform  35  and movable along the tracks  350 . The second moving part  372  is mounted to the first moving part  371  and movable relatively to the first moving part  371 . 
     The laser head  39  is mounted on the second moving part  372  of the carrying mechanism  37  and used to drill holes in the thin metal plate  2  by laser. In one embodiment, the laser drilling apparatus  3  includes multiple laser heads  39  simultaneously controlled to drill holes in the thin metal plate  2  by laser during the laser drilling process S 4 , and thereby the speed of drilling holes can be enhanced. Alternatively, holes can be drilled in a vertical or inclined angle by the laser heads  39 , as shown in  FIG. 6  showing an example of drilling holes in an inclined angle by laser, such that each of the mesh holes  20  in the evaporation mask is tapered from bottom to top, as shown in  FIGS. 7-9 . 
     Referring to  FIGS. 4 and 5 , the computer is used to control movement of the carrying mechanism  37  and to control the laser head  39  to perform the laser drilling process S 4  to the thin metal plate  2 . The computer controls operation of the carrying mechanism  37  using an instrument (now shown) capable of precisely measuring a length such that the laser head  39  on the carrying mechanism  37  can precisely move to targeted positions for drilling holes. 
     In one embodiment, referring to  FIGS. 4 and 5 , the laser drilling apparatus  3  contains an inspection device  6  mounted on the second moving part  372  of the carrying mechanism  37 , wherein the inspection device  6  is equipped with a CCD. In accordance with the present invention, the method includes performing an inspection process using the inspection device  6 , wherein the inspection process may include the following two types: 
     In one type, when the laser drilling process S 4  performed using the laser head  39 , the computer of the laser drilling apparatus  3  controls the inspection device to perform the inspection process in real time and then based on the result from the inspection process, determines if an adjustment process to the laser head  39  is performed such that the mesh holes in the thin metal plate  2 , made by the laser drilling process S 4 , can meet standard. For example, the mesh holes meet, but not limited to, a standard of a precision error within ±3 μm and a total pitch error within ±5 μm. Accordingly, the mesh holes formed in the evaporation mask can be ensured to meet standard using this way of inspecting the mesh holes in real time during the mesh holes are being formed. 
     In the other type, after the laser drilling process S 4  performed by the laser head  39 , the computer controls the inspection device  6  to perform another inspection process for inspecting if the mesh holes in the thin metal plate, made by the laser drilling process, meet standard. For example, the mesh holes  20  meet, but not limited to, a standard of a precision error within ±3 μm and a total pitch error within ±5 μm. 
     Compared with prior art, in accordance with the present invention, the laser drilling process is performed after the thin metal plate is placed on the metal frame in a flat manner and welded with the metal frame. Accordingly, the deformation or shift of the mesh holes in the metal mask can be avoided and it does not take too much time to adjust the stretching forces exerted by the clips. Thus, the metal mask has an improved yield. 
     Unless otherwise stated, all measurements, values, ratings, positions, magnitudes, sizes, and other specifications that are set forth in this specification, including in the claims that follow, are approximate, not exact. They are intended to have a reasonable range that is consistent with the functions to which they relate and with what is customary in the art to which they pertain. Furthermore, unless stated otherwise, the numerical ranges provided are intended to be inclusive of the stated lower and upper values. Moreover, unless stated otherwise, all material selections and numerical values are representative of preferred embodiments and other ranges and/or materials may be used. 
     The scope of protection is limited solely by the claims, and such scope is intended and should be interpreted to be as broad as is consistent with the ordinary meaning of the language that is used in the claims when interpreted in light of this specification and the prosecution history that follows, and to encompass all structural and functional equivalents thereof.