Patent Publication Number: US-2018034009-A1

Title: Mask and method for making same

Description:
FIELD 
     The subject matter herein generally relates to a mask and a method for making the mask, and particularly relates to a mask for depositing an organic light emitting material layer on a substrate. 
     BACKGROUND 
     The method for making an organic light emitting diode (OLED) display panel generally includes a step of forming an organic light-emitting material layer on a substrate (e.g., a thin film transistor substrate) by vapor deposition. A mask is used in the step of forming the organic light-emitting material layer on the substrate and the mask is positioned on the substrate. The mask defines a plurality of through holes, thus evaporated material from an evaporation source can pass through the through holes and be deposited on the substrate. The organic light-emitting material deposited on the substrate by each through hole corresponds to a sub-pixel of the OLED display panel. Typically, the size of each through-hole is designed to be equal to the size of a sub-pixel. However, a size of the sub-pixel formed by using the mask is often greater than a size of the desired sub-pixels because of gaps between the mask and the substrate during the deposition process. This phenomenon is called shadow effect. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Implementations of the present technology will now be described, by way of example only, with reference to the attached figures. 
         FIG. 1  is a planar view of an exemplary embodiment of a mask for depositing an organic light-emitting layer. 
         FIG. 2  is a cross-sectional view of the mask along line II-II of  FIG. 1 . 
         FIG. 3  is an isometric view showing two modified examples of the magnetic elements of the mask of  FIG. 1 . 
         FIG. 4 a    through  FIG. 4 g    are cross-sectional views showing manufacturing processes of a first exemplary embodiment of a method for making the mask of  FIG. 1 . 
         FIG. 5 a    through  FIG. 5 f    are cross-sectional views showing manufacturing processes of a second exemplary embodiment of a method for making a mask. 
         FIG. 6  is a cross-sectional view showing the mask of  FIG. 1  in use. 
     
    
    
     DETAILED DESCRIPTION 
     It will be appreciated that for simplicity and clarity of illustration, where appropriate, reference numerals have been repeated among the different figures to indicate corresponding or analogous elements. In addition, numerous specific details are set forth in order to provide a thorough understanding of the exemplary embodiments described herein. However, it will be understood by those of ordinary skill in the art that the exemplary embodiments described herein may be practiced without these specific details. In other instances, methods, procedures, and components have not been described in detail so as not to obscure the related relevant feature being described. Also, the description is not to be considered as limiting the scope of the exemplary embodiments described herein. The drawings are not necessarily to scale and the proportions of certain parts may be exaggerated to better illustrate details and features of the present disclosure. 
     The term “coupled” is defined as connected, whether directly or indirectly through intervening components, and is not necessarily limited to physical connections. The connection can be such that the objects are permanently connected or releasably connected. The term “comprising” when utilized, means “including, but not necessarily limited to”; it specifically indicates open-ended inclusion or membership in the so-described combination, group, series, and the like. 
       FIG. 1  and  FIG. 2  illustrate a mask  100  according to an exemplary embodiment. The mask  100  includes a plastic layer  10  and a frame  20  coupled to the plastic layer  10 . As shown in  FIG. 2 , the plastic layer  10  includes a first surface  101  and a second surface  103 . The first surface  101  and the second surface  103  are on opposite sides of the plastic layer  10  facing away from each other. The frame  20  is on the first surface  101  and covers a periphery of the plastic layer  10 . The frame  20  extends along the periphery of the first surface  101  and forms a closed rectangular. The plastic layer  10  defines a plurality of openings  11  spaced apart from each other. Each opening  11  extends through the plastic layer  10  from the first surface  101  to the second surface  103 . In the present exemplary embodiment, the plurality of openings  11  are arranged in an array. 
     The plastic layer  10  is made of a common plastic material, such as, but not limited to, polyimide. The frame  20  is configured to support the plastic layer  10  and improve a strength of the mask  100 . The frame  20  may be made of a metal or an alloy. In some exemplary embodiments, the frame  20  can be made of a magnetic metal or an magnetic alloy. 
     When depositing an organic light-emitting material layer of the OLED display panel on a substrate, a mask and the substrate (e.g., a thin film transistor substrate) are placed in a deposition apparatus (e.g., a vapor deposition machine, not shown) having a magnetic plate (not shown); and the magnetic plate, the substrate, and the mask are stacked in that order. The mask is required to be magnetized. Without magnetization, a gap would form between the mask and the substrate. The mask being magnetized causes attraction between the mask and the magnetic plate to bring and keep the mask and the substrate close together, which reduces or avoids shadow effect. 
     When the frame  20  is made of a magnetic metal or alloy, the mask  100  is magnetic. However, the frame  20  only covers a periphery of the plastic layer  10 , thus other portions of the plastic layer  10  may not be closely attached to the substrate. To solve this problem, the frame  20  further includes a plurality of magnetic elements  30  protruding from the first surface  101  of the plastic layer  10 . The magnetic elements  30  are spaced apart from each other. The frame  20  surrounds the plurality of magnetic elements  30 . The magnetic elements  30  do not cover any opening  11 . In the present exemplary embodiment, each magnetic element  30  is located between four adjacent openings  11 . 
     Each magnetic element  30  may be made of ink containing magnetic particles. The magnetic particles may be iron particles, nickel particles, or cobalt particles as conventionally used in the art. Alternatively, each magnetic element  30  may be made of a magnetic metal or an magnetic alloy, such as iron, cobalt, nickel, or invar alloy. When the magnetic element  30  is made of a magnetic metal or an magnetic alloy, it is preferable that the frame  20  and the magnetic elements  30  are made of a same material. 
     As shown in  FIG. 1  and  FIG. 2 , each magnetic element  30  includes a bottom surface  31  opposite to the first surface  101  and at least one side surface  33  connected between the bottom surface  31  and the first surface  101 . Each magnetic element  30  has a substantially frustum-like shape, and each magnetic element  30  tapers from the first surface  101  towards the bottom surface  31 . A size of a cross section of each magnetic element  30  parallel to the first surface  101  gradually becomes smaller along a direction from the first surface  101  towards the bottom surface  31 . Thus, the at least one side surface  33  of each magnetic element  30  is inclined with respect to the first surface  101  of the plastic layer  10  (e.g., the internal angle between the side surface  33  and the first surface  101  is 25-70 degrees). 
     As shown in  FIG. 6 , when a substrate  80  is deposited to form an organic light-emitting layer, the mask  100  is stacked on the substrate  80 , and the substrate  80  is located at a side of the mask  100  having the second surface  103 . Evaporated material from a side of the mask  100  having the first surface  101  passes through the openings  11  and is deposited on the substrate  80 . The side surface  33  of each magnetic element  30  is inclined to the first surface  101  of the plastic layer  10 , which facilitates the introduction of the evaporated material into the openings  11  along the side surface  33 . Thus, the evaporated material can be deposited on a predetermined position of the substrate  80  with a precise demarcation, which further reduces or avoids shadow effect. It is to be understood that the inclination angle of the side surface  33  to the first surface  101 , and the height and shape of the magnetic element  30 , can be adjusted so that the evaporated material can be deposited to a predetermined position of the substrate  80 . 
     In the present exemplary embodiment, as shown in  FIG. 1  and  FIG. 2 , each magnetic element  30  includes the bottom surface  31  having a regular octagon shape and eight side surfaces  33  connected between the bottom surface  31  and the first surface  101 . Each side face  33  is inclined to the first surface  101  of the plastic layer  10 . 
     The shape of the magnetic element  30  may be adjusted as desired. As shown in  FIG. 3 , one magnetic element  30  includes a bottom surface  31  having a rectangle shape and four side surfaces  33  connected between the bottom surface  31  and the first surface  101 . Another magnetic element  30  can include a bottom surface  31  having a circular shape and a curved side surface  33  connected between the bottom surface  31  and the first surface  101 . For simplicity,  FIG. 3  only shows magnetic elements  30  which have different shapes on the plastic layer  10 ; and  FIG. 3  simply shows the plastic layer  10  and the magnetic elements  30 , other elements and features are not shown. 
     It is to be understood that the shapes of the magnetic element  30  are not limited to those shown in the figures, but may be various other regular or irregular shapes. 
     As in  FIG. 1 , the magnetic elements  30  are arranged uniformly. It is to be understood that an arrangement of the magnetic elements  30  may be adjusted as appropriate, and is not limited to the uniform arrangement shown in  FIG. 1 . For example, the magnetic elements  30  may be arranged densely in a region of the plastic layer  10  attracting the magnetic plate (not shown), for reinforcement. The magnetic elements  30  may be arranged sparsely in other regions of the plastic layer  10 . 
     A method for making the mask  100  according to a first exemplary embodiment includes the following steps. The magnetic element  30  of the mask  100  is made of an ink containing magnetic particles. 
     Step S 1 : As shown in  FIG. 4 a   , a metal plate  40  is provided and a plastic layer  10  is formed on a surface of the metal plate  40 . 
     The plastic layer  10  may be formed on the metal plate  40  by injection molding. The metal plate  40  may be made of a metal or an alloy. The plastic layer  10  may be made of polyimide. 
     Step S 2 : as shown in  FIG. 4 b    through  FIG. 4 d   , the metal plate  40  is partially etched to remove a central portion of the metal plate  40 , and remaining portion of the metal plate  40  is formed as a frame  20  that covers only a periphery of the plastic layer  10 . 
     The step S 2  may include the following steps: forming a photoresist layer  50  on a surface of the metal plate  40  away from the plastic layer  10  as shown in  FIG. 4 b   ; exposing and developing the photoresist layer  50  to make the photoresist layer  50  partially cover the metal plate  40  as shown in  FIG. 4 c   ; etching and removing the portion of the metal plate  40  that is not covered by the photoresist layer  50 , and the remaining metal plate  40  forms a frame  20  that covers a periphery of the plastic layer  10  as shown in  FIG. 4 d   . The remaining photoresist layer  50  is finally removed. 
     Step S 3 : as shown in  FIG. 4 e   , a plurality of magnetic elements  30  spaced apart from each other are formed on the surface of the plastic layer  10  having the frame  20 . 
     The plurality of magnetic elements  30  are surrounded by the frame  20 . Each magnetic element  30  is made of ink containing magnetic particles. The plurality of magnetic elements  30  are formed on the plastic layer  10  by an ink-jet printing process. The shape and the size of the magnetic element  30  can be controlled by adjusting parameters of the ink-jet printing process (e.g., ink ejection amount, ink ejection speed, viscosity of the ink, etc.), thus the magnetic element  30  tapers along a direction away from the plastic layer  10 . For example, the height and area of the magnetic element  30  can be controlled by controlling ink ejection amount when forming a magnetic element  30 . 
     Step S 4 : as shown in  FIG. 4 f    through  FIG. 4 g   , a plurality of openings  11  are formed in the plastic layer  10 . 
     Each opening  11  extends through the plastic layer  10 . The step S 4  may include the following: providing a shielding film  300  defining a plurality of through holes  310 ; positioning the shielding film  300  at a side of the plastic layer  10  having the frame  20  as shown in  FIG. 4 f   ; laser-etching a portion of the plastic layer  10  not covered by the frame  20  and the magnetic elements  30  to form a plurality of openings  11  as shown in  FIG. 4 g   , each through hole  310  corresponding to one opening  11 . 
     A method for making the mask  200  according to a second exemplary embodiment includes the following steps. The magnetic elements  30  and the frame  20  of the mask  100  are made of a same material. 
     Step S 1 : as shown in  FIG. 5 a   , a metal plate  40  is provided and a plastic layer  10  is formed on a surface of the metal plate  40 . 
     The plastic layer  10  may be formed on the metal plate  40  by injection molding. The metal plate  40  may be made of a magnetic metal or an magnetic alloy, such as invar alloy. The plastic layer  10  may be made of polyimide. 
     Step S 2 : as shown in  FIG. 5 b    through  FIG. 5 d   , the metal plate  40  is etched to remove a portion of the metal plate  40 , and remaining portion of the metal plate  40  forms a frame  20  and a plurality of magnetic elements  30  spaced apart from each other. The frame  20  covers only a periphery of the plastic layer  10 . The plurality of magnetic elements  30  is surrounded by the frame  20 . 
     The step S 2  may include the following: forming a photoresist layer  60  on the surface of the metal plate  40  away from the plastic layer  10  as shown in  FIG. 5 b   ; exposing and developing the photoresist layer  60  to make the photoresist layer  60  partially cover the metal plate  40 , as shown in  FIG. 5 c   ; wet-etching the portion of the metal plate  40  not covered by the photoresist layer  60 . The remaining metal plate  40  forms a frame  20  and a plurality of magnetic elements  30  spaced apart from each other, as shown in  FIG. 5 d   , and the remaining photoresist layer  60  is finally removed. The shape of the magnetic element  30  can be adjusted by controlling parameters of the wet etching process so that the magnetic element  30  tapers along a direction away from the plastic layer  10 . 
     Step S 3 : as shown in  FIG. 5 e    through  FIG. 5 f   , a plurality of openings  11  is defined in the plastic layer  10 . 
     Each opening  11  extends through the plastic layer  10 . The step S 3  may include the following: providing a shielding film  300  defining a plurality of through holes  310 ; positioning the shielding film  300  at a side of the plastic layer  10  having the frame  20  as shown in  FIG. 5 e   ; laser-etching the plastic layer  10  not covered by the frame  20  and the magnetic elements  30  to form a plurality of openings  11  as shown in  FIG. 5 f   , each through hole  310  corresponding to one opening  11 . 
     It is to be understood, even though information and advantages of the present exemplary embodiments have been set forth in the foregoing description, together with details of the structures and functions of the present exemplary embodiments, the disclosure is illustrative only. Changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the present exemplary embodiments to the full extent indicated by the plain meaning of the terms in which the appended claims are expressed.