Patent Publication Number: US-2018040855-A1

Title: Deposition mask for making oled display panel

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority from U.S. provisional application Ser. No. 62/370,729 filed on Aug. 4, 2016 which is incorporated herein by reference. 
    
    
     FIELD 
     The subject matter herein generally relates to a deposition mask for depositing an organic light emitting layer. 
     BACKGROUND 
     Display devices, particularly organic light-emitting diode (OLED) display devices, are manufactured by forming an organic light emitting layer on a substrate (such as thin film transistor substrate) through vapor deposition. Generally, a deposition mask is required during deposition of the organic light emitting layer. A plurality of openings is defined in the deposition mask. Then the evaporated material from an evaporation source passes through the openings to be deposited on the substrate. Each opening corresponds to one subpixel of the OLED display panel. Generally, a dimension of each of the openings is designed to be equal to a dimension of the sub-pixel. However, some sub-pixels formed by using the deposition mask have dimensions that are greater than the designed dimensions. For example, when a desired pixel pattern is designed to have a width of x μm and a length of y μm. Using the deposition mask and evaporation process above creates a shadow effect in sub-pixel patterns where a sub-pixel pattern has a width larger than the defined x μm and a length larger than the defined y μm. Therefore, there is need to improve the process of creating sub-pixel patterns to improve the properties and performance of a display device. 
    
    
     
       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 plan view of a first exemplary embodiment of a deposition mask. 
         FIG. 2  is a cross-sectional view of the deposition mask of  FIG. 1  along line II-II. 
         FIG. 3  is a plan view of a mask unit of the deposition mask of  FIG. 1 . 
         FIG. 4  is a plan view of a second exemplary embodiment of a deposition mask. 
         FIG. 5  is a cross-sectional view of the deposition mask of  FIG. 4  along line V-V. 
     
    
    
     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 embodiments described herein. However, it will be understood by those of ordinary skill in the art that the embodiments described herein can 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 embodiments described herein. The drawings are not necessarily to scale and the proportions of certain parts have been exaggerated to better illustrate details and features of the present disclosure. 
     Several definitions that apply throughout this disclosure will now be presented. 
     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 first exemplary embodiment of a deposition mask  10 . The deposition mask  10  includes a supporting plate  11  and a plurality of mask units  13  coupled to a surface of the supporting plate  11 . The supporting plate  11  is configured to support the plurality of mask units  13 . Each of the plurality of mask units  13  is spaced apart from one another. The supporting plate  11  defines a plurality of through holes  111 . Each through hole  111  corresponds to one of the mask units  13 . A dimension of each through hole  111  is smaller than a dimension of each mask unit  13 . Thus, each mask unit  13  can completely cover over one of the through holes  111 . Moreover, the through holes  111  are arranged in an array, and thus the mask units  13  covering the through holes  111  of the supporting plate  11  are also arranged in an array on the supporting plate  11 . 
     The supporting plate  11  is made of a metal or an alloy. In an exemplary embodiment, the supporting plate  11  may be made of a metal or alloy having magnetic properties. For example, the supporting plate  11  is made of an invar alloy. Each mask unit  13  can be made of a plastic, and the plastic can be one selected from a group consisting of: polyimide (PI), polyethylene terephthalate (PET), polycarbonate (PC), ethylene (PE), poly ether ether ketone (PEEK), polyetherimide (PEI), polyamide (PA), poly tetra fluoro ethylene (PTFE), poly propylene (PP), poly phenilen sulfide (PPS), poly ethylene naphthalate (PEN), and poly propylene (PP). 
     In an exemplary embodiment, each mask unit  13  is substantially rectangular. Each mask unit  13  defines a plurality of openings  131 , each opening  131  being spaced apart from one another.  FIGS. 1-3  show a number of the plurality of openings  131 . The plurality of openings  131  extend through the mask unit  13 . As shown in  FIG. 2 , each opening  131  of the mask unit  13  is adjacent to and air communicatively with each corresponding through hole  111 . In this exemplary embodiment, each opening  131  is substantially rectangular. 
     As shown in  FIG. 3 , each mask unit  13  includes a center portion  133  and an edge portion  135  located at a periphery of the center portion  133  and surrounding the center portion  133 . In each mask unit  13 , the dimensions of the openings  131  gradually decrease along a direction from the edge portion  135  towards the center portion  133 . 
     As shown in  FIG. 3 , in this exemplary embodiment, the openings  131  in one single mask unit  13  comprise three types of openings  131  along a direction from the edge portion  135  towards the center portion  133 . The openings  131  includes a plurality of first openings  1311  located in the center portion  133 , a plurality of third openings  1313  located in the edge portion  135 , and a plurality of second openings  1312  located between the center portion  133  and the edge portion  135 . Each first opening  1311  has a dimension that is smaller than a dimension of each second opening  1312 , and each second opening  1312  has a dimension that is smaller than a dimension of each third opening  1313 . The dimension of each third opening  1313  is substantially equal to a required dimension of one sub-pixel of the OLED display panel to be formed. That is, a dimension of the openings  131  having the largest dimension in a single mask unit  13  is substantially equal to a required dimension of one sub-pixel of the OLED display panel to be formed. 
     When depositing an organic light emitting layer on a substrate (not shown), such as thin film transistor substrate, the substrate is located at a side of the deposition mask  10  having the mask units  13 . Evaporated material from an evaporation source passes through the through hole  111  and the openings  131  to be deposited on the substrate. Each opening  131  corresponds to the form of one sub-pixel of the OLED display panel. By using the deposition mask  10  herein disclosed, the shadow effect can be effectively reduced or eliminated. 
       FIG. 4  and  FIG. 5  illustrates a second exemplary embodiment of a deposition mask  20 . The deposition mask  20  includes a supporting plate  21  and a plurality of mask units  23  coupled to a surface of the supporting plate  21 . Each of the plurality of mask units  23  is spaced apart from one another. The supporting plate  21  is configured to support the mask units  23 . The supporting plate  21  defines a plurality of through holes  211 . Each through hole  211  corresponds to one of the mask units  23 . The dimension of each through hole  211  is smaller than a dimension of each mask unit  23 . Thus, each mask unit  23  can completely cover one of the through holes  211 . Moreover, the through holes  211  are arranged in an array, and thus the mask units  23  covering the through holes  211  of the supporting plate  21  are also arranged in an array on the supporting plate  21 . 
     The supporting plate  21  is made of a metal or an alloy. In an exemplary embodiment, the supporting plate  21  may be made of a metal or alloy having magnetic properties. For example, the supporting plate  21  is made of an invar alloy. Each mask unit  23  can be made of one selected from a group consisting of PI, PET, PC, PE, PEEK, PEI, PA, PTFE, PP, PPS, PEN, and PP. 
     In an exemplary embodiment, each mask unit  23  is substantially rectangular. Each mask unit  23  defines a plurality of openings  231 . Each opening  231  is spaced apart from one another. The plurality of openings  231  extends through the mask unit  23 . As shown in  FIG. 5 , each opening  231  of the mask unit  23  is adjacent to and air communicatively with each corresponding through holes  211 . In this exemplary embodiment, each opening  231  is rectangular. 
     The supporting plate  21  includes a center portion  213  and an edge portion  215  located at a periphery of the center portion  213  and surrounding the center portion  213 . In the deposition mask  20 , the dimensions of the openings  131  gradually decrease along a direction from the edge portion  215  towards the center portion  213 . 
     As shown in  FIG. 4 , in this exemplary embodiment, the openings  231  in the entire deposition mask  20  comprise five types of openings  231  along a direction from the edge portion  215  towards the center portion  213 . The openings  231  includes a plurality of first openings  2311  located in the center portion  213 , a plurality of fifth openings  2315  located in the edge portion  215 , and a plurality of second openings  2312 , a plurality of third openings  2313 , and a plurality of fourth openings  2314  located between the center portion  213  and the edge portion  215 . The plurality of second openings  2312  is located at a periphery of the first openings  2311  and surrounds the first openings  2311 . The plurality of third openings  2313  is located at a periphery of the second openings  2312  and surrounds the second openings  2312 . The plurality of fourth openings  2314  is located at a periphery of the third openings  2313  and surrounds the third openings  2313 . The plurality of fifth openings  2315  is located at a periphery of the fourth openings  2314  and surrounds the fourth openings  2314 . Each first opening  2311  has a dimension that is smaller than a dimension of each second opening  2312 , and each second opening  2312  has a dimension that is smaller than a dimension of each third opening  2313 . Each third opening  2313  has a dimension that is smaller than a dimension of each fourth opening  2314  and each fourth opening  2314  has a dimension that is smaller than a dimension of each fifth opening  2315 . The dimension of each fifth opening  2315  is substantially equal to the dimension of one sub-pixel of the OLED display panel. In a single mask unit  23 , the dimensions of the openings  231  gradually decrease along a direction from edge portion  215  of the deposition mask  20  towards the center portion  213  of the deposition mask  20 . 
     When an organic light emitting layer is deposited on a substrate (not shown), such as thin film transistor substrate, the substrate is located at a side of the deposition mask  20  having the mask units  23 . Evaporated material from an evaporation source passes through the through hole  211  and the openings  231 , and reaches the substrate. Each opening corresponds to the form of one sub-pixel of the OLED display panel. By using this deposition mask  20 , the shadow effect can be effectively reduced. 
     The embodiments shown and described above are only examples. Many details are often found in the art such as other features of a display device. Therefore, many such details are neither shown nor described. Even though numerous characteristics and advantages of the present technology have been set forth in the foregoing description, together with details of the structure and function of the present disclosure, the disclosure is illustrative only, and changes may be made in the detail, especially in matters of shape, size, and arrangement of the parts within the principles of the present disclosure, up to and including the full extent established by the broad general meaning of the terms used in the claims. It will therefore be appreciated that the embodiments described above may be modified within the scope of the claims.