Patent Publication Number: US-2017369982-A1

Title: Screen tensioning device used during fabricating mask plate and screen tensioning method

Description:
TECHNICAL FIELD 
     Embodiments of the present disclosure relate to a screen tensioning device used during fabricating a mask plate and a screen tensioning method. 
     BACKGROUND 
     At present, during the process of fabricating a color filter layer of an OLED (Organic Light-Emitting Diode) display screen, a mask plate having a pattern is used for masking process and a pattern as required is formed on a substrate to be evaporated by vacuum evaporation. A conventional mask plate comprises a screen and a screen frame. When the screen and the screen frame are combined, it is necessary to use a screen tensioning device to tension the screen on the screen frame. And then the screen is fastened to the screen frame, thereby forming a mask plate as required. 
     As shown in  FIG. 1 , the screen tensioning device  00  of the conventional arts mainly comprises a screen tensioning machine  21  and a jig  25  disposed on the screen tensioning machine  21 . During use, a screen frame  22  and an aligned substrate  23  are placed on the screen tensioning machine  21 , a screen  24  is disposed on the screen frame  22 , and the aligned substrate  23  is positioned directly under the screen  24 . The main steps of fabricating a mask plate by use of the screen tensioning device are as follows: placing and fixing the screen frame  22  and the aligned substrate  23  on the screen tensioning machine  21 , disposing the screen  24  on the screen frame  22  and clamping edges of the screen  24  by the jig  25 ; tensioning the screen  24  by use of the jig  25  so that the pattern on the screen  24  is aligned with the pattern on the aligned substrate  23 ; and then fastening the screen  24  onto the screen frame  22 , thereby forming a required mask plate. 
     However, when the mask plate is used for masking process, the screen  24  of the fabricated mask plate is sagged by the gravity of the screen  24  itself, which results in that it is difficult to align the pattern on the screen  24  with the region to be deposited with pattern on the substrate to be evaporated. Thus, the position accuracy of the pattern formed by evaporating the organic materials on the substrate to be evaporated would be affected. 
     SUMMARY 
     Embodiments of the present disclosure provides a screen tensioning device used during fabrication of mask plate and a screen tensioning method used during fabrication of mask plate. When using the mask plate fabricated by the screen tensioning device, the position accuracy of the pattern formed by evaporating the organic materials onto the substrate to be evaporated is be improved. 
     At least one embodiment of the present disclosure provides a screen tensioning device used during fabrication of mask plate, comprising a screen tensioning machine base and a jig provided on the screen tensioning machine base, the screen tensioning device further comprising a magnetic plate positioned above the screen tensioning machine base, and an upwardly-directed vertical suction force acting on the screen of the mask plate to be fabricated by the magnetic plate is equal to an upwardly-directed vertical suction force acting on the screen of the mask plate by a magnetic field system in a vacuum evaporation chamber during masking process. 
     At least one embodiment of the present disclosure provides a screen tensioning method used during fabrication of mask plate, which is applicable to the screen tensioning device according to any one of claims  1  to  5 , the screen tensioning method comprising: 
     placing and fixing the screen frame and an aligned substrate onto the screen tensioning machine base; 
     disposing the screen on the screen frame and positioning the screen under the magnetic plate, wherein the magnetic plate generates an upwardly-directed vertical suction force on the screen, and the upwardly-directed vertical suction force acting on the screen by the magnetic plate is equal to the upwardly-directed vertical suction force acting on the screen by a magnetic field system in a vacuum evaporation chamber during evaporation; 
     clamping an edge of the screen by the jig in the screen tensioning device and tensioning the screen by use of the jig so that the pattern on the screen is aligned with the pattern on the aligned substrate; and 
     combining the aligned screen and the screen frame so as to form a mask plate as required. 
     Compared with the screen tensioning device of the conventional arts, the screen tensioning device used during fabrication of mask plate and the screen tensioning method used during fabrication of mask plate according to an embodiment of the present disclosure is additionally provided with a magnetic plate, so that a magnetic field environment in the vacuum evaporation chamber can be simulated when the mask plate is fabricated. That is to say, in the present disclosure, the mask plate is fabricated in a magnetic field environment which is similar to the magnetic field environment in the vacuum evaporation chamber. In this case, the mask plate are applied with identical forces in the vertical direction in fabrication and in use, i.e., the mask plate is subjected to its own gravity which is in vertically downward direction and a suction force by the magnetic field which is in vertically upward direction, which makes the position of the pattern (referred to the pattern on the screen of the mask plate) of the mask plate in fabrication is the same position as the pattern of the mask plate in use, thereby facilitating the alignment of the pattern on the screen of the mask plate with a region of the substrate to be evaporated where a pattern needs to be deposited. Therefore, compared with the conventional arts, when using the mask plate fabricated by the screen tensioning device according to the embodiment of the present disclosure, the position accuracy of the pattern formed by evaporating the organic materials onto the substrate to be evaporated can be improved. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order to clearly illustrate the technical solutions of the embodiments of the disclosure, the drawings of the embodiments will be briefly described in the following; it is obvious that the drawings described below are only related to some embodiments of the disclosure and thus are not limitative of the disclosure. 
         FIG. 1  is a side view of a screen tensioning device used during fabrication of mask plate in the conventional arts; 
         FIG. 2  is a side view of a screen tensioning device used during fabrication of mask plate according to an embodiment of the present disclosure; 
         FIG. 3  is an illustrative view of a screen tensioning device used during fabrication of mask plate according to an embodiment of the present disclosure; and 
         FIG. 4  is a flow chart of a screen tensioning method used during fabrication of mask plate according to an embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     In order to make objects, technical details and advantages of the embodiments of the disclosure apparent, the technical solutions of the embodiment will be described in a clearly and fully understandable way in connection with the drawings related to the embodiments of the disclosure. It is obvious that the described embodiments are just a part but not all of the embodiments of the disclosure. Based on the described embodiments herein, those skilled in the art can obtain other embodiment(s), without any inventive work, which should be within the scope of the disclosure. 
     As illustrated in  FIG. 2 , the screen tensioning device  20  used during fabrication of mask plate according to an embodiment of the present disclosure comprises a screen tensioning machine  21 , a jig  25  disposed on the screen tensioning machine  21  and a magnetic plate  26  positioned above the screen tensioning machine  21  and matching a screen  24 . The screen tensioning machine  21  is configured to carry a screen frame  22  and an aligned substrate  23  (which can be an aligned glass substrate) as well as the screen  24  disposed on the screen frame  22 , in addition to installing the jig  25 . The jig  25  is configured to clamp the screen  24  and can tension the screen  24 . For the sake of cost-saving, the screen tensioning machine  21  and the jig  25  as illustrated in  FIG. 1  can be used as the screen tensioning machine base  21  and the jig  25  respectively. The magnetic plate  26  is provided to apply a vertically upward suction force on the screen plate  24 . For example, the magnetic plate  26  can be a magnetic plate made of a permanent magnet material or a plate-like electromagnet. 
     When the mask plate is fabricated, firstly, the screen frame  22  and the aligned substrate  23  are placed and fixed onto the screen tensioning machine  21 , the screen  24  is disposed on the screen frame  22  and is positioned under the magnetic plate  26  which apply a vertically upward suction force on the screen  24 , wherein the vertically upward suction force acting on the screen  24  of the mask plate to be fabricated by the magnetic plate  26  is equal to a vertically upward suction force applied on the screen  24  of the mask plate by the magnetic field system in the vacuum evaporation chamber. And then, edges of the screen  24  are clamped by the jig  25  and the screen  24  is tensioned by use of the jig  25 , so that the pattern on the screen  24  is aligned with the pattern on the aligned substrate  23 . In practical, a CCD (Charge-coupled Device) camera can be used to determine whether the pattern of the screen  24  is aligned with the pattern of the aligned substrate  23 . And then, after determining that the pattern of the screen  24  is aligned with the pattern of the aligned substrate  23 , the screen  24  is combined with the screen frame  22 . For example, the screen frame  22  and the screen  24  can be welded together by a laser welding apparatus so as to form a mask plate. 
     In can be seen from the above that compared with the screen tensioning device of the conventional arts, the screen tensioning device used during fabrication of mask plate according to an embodiment of the present disclosure is additionally provided with a magnetic plate, so that a magnetic field environment in the vacuum evaporation chamber can be simulated when the mask plate is fabricated. That is to say, in the present disclosure, the mask plate is fabricated in a magnetic field environment which is similar to the magnetic field environment in the vacuum evaporation chamber. In this case, the mask plate are applied with identical forces in the vertical direction in fabrication and in use, i.e., the mask plate is subjected to its own gravity which is in vertically downward direction and a suction force by the magnetic field which is in vertically upward direction, which makes the position of the pattern (referred to the pattern on the screen of the mask plate) of the mask plate in fabrication is the same position as the pattern of the mask plate in use, thereby facilitating the alignment of the pattern on the screen of the mask plate with a region of the substrate to be evaporated where a pattern needs to be deposited. Therefore, compared with the conventional arts, when using the mask plate fabricated by the screen tensioning device according to the embodiment of the present disclosure, the position accuracy of the pattern formed by evaporating the organic materials onto the substrate to be evaporated can be improved. 
     Hereinafter, the screen tensioning device used in fabrication of mask plate according to an embodiment of the present disclosure will be described in detail. Regarding components and position or connection relationships of the components of the screen tensioning device used in fabrication of mask plate according to the present embodiment, the description in the above-described embodiment can be referred to, and a description thereof is omitted here. 
     In  FIG. 2 , the aligned substrate  23  and the magnetic plate  26  can be supported by different supporting structures (not illustrated in  FIG. 2 ) on the screen tensioning machine  21  and a supporting structure configured to support the aligned substrate  23  has a height different from that of a supporting structure configured to support the magnetic plate  26 . For example, the height of the supporting structure configured to support the magnetic plate  26  is greater than that of the supporting structure configured to support the aligned substrate  23 . The supporting structures can be supporting pins for example. 
     In the present embodiment, to make the conditions of the magnetic field environment in fabrication of the mask plate consistent with the conditions of the magnetic field environment in use of the mask plate, the vertically upward suction force applied on the screen  24  by the magnetic plate  26  is required to be equal to the vertically upward suction force applied on the screen  24  by the magnetic field system in the vacuum evaporation chamber. When the vertically upward suction force applied on the screen  24  by the magnetic plate  26  and the vertically upward suction force applied on the screen  24  by the magnetic field system in the vacuum evaporation chamber are not equal, it is necessary to adjust the suction force applied on the screen  24  by the magnetic plate  26  to achieve a required suction force. For example, the adjustment of the suction force can be achieved by moving the magnetic plate  26  in the vertical direction relative to the screen tensioning machine  21 . That is to say, the suction force applied on the screen  24  by the magnetic plate  26  can be adjusted by adjusting the distance between the magnetic plate  26  and the screen  24 . The suction force applied on the screen  24  by the magnetic plate  26  can be gauged on basis of sagging degree of the screen  26 . 
     When the sagging degree of the screen  24  is relatively great, the suction force applied on the screen  24  by the magnetic plate  26  can be considered as relatively low. In this case, to reduce the sagging degree of the screen  26 , it is necessary to increase the suction force applied on the screen  24  by the magnetic plate  26 , i.e., it is necessary to move the magnetic plate  26  towards the screen  24 . When the sagging degree of the screen  24  is relatively low, the suction force applied on the screen  24  by the magnetic plate  26  can be considered as relatively great. In this case, to increase the sagging degree of the screen  24 , it is necessary to decrease the suction force applied on the screen  24  by the magnetic plate  26 , i.e., it is necessary to move the magnetic plate  26  away from the screen  24 . 
     Therefore, in one embodiment of the present disclosure, as illustrated in  FIG. 3 , the screen tensioning device  20  used in fabrication of mask plate can further comprise a sagging degree detection module  27  configured to detect the sagging degree of the screen  24 ; a magnetic plate position adjustment module  28  connected with the sagging degree detection module  27  and the screen  24 , which adjusts the distance between the magnetic plate  26  and the screen tensioning machine  21  in the vertical direction according to the sagging degree of the screen  24  detected by the sagging degree detection module  27 . The sagging degree detection module  27  can be a laser flatness detecting device, which judges the sagging degree of the screen  24  by emission and reflection optical paths of laser. The magnetic plate position adjustment module  28  can be a manipulator and the like. 
     The magnetic plate position adjustment module  28  can comprise a comparison unit  281  connected with the sagging degree detection module  27  and configured to compare the sagging degree of the screen  24  detected by the sagging degree detection module with a preset sagging degree and generate a comparison result. 
     The screen tensioning device  20  can further comprise an executing unit  282  connected with the comparing unit  281  and the magnetic plate  26  and configured to acquire the comparison result from the comparing unit  281  and adjust the distance between the magnetic plate  26  and the screen tensioning machine  21  in the vertical direction according to the comparison result. 
     The executing unit  282  can be configured to move the magnetic plate  26  towards the screen  24  when the sagging degree detected by the magnetic plate position adjustment module  28  is greater than the preset sagging degree, to move the magnetic plate  26  away from the screen  24  when the detected sagging degree is less than the preset sagging degree, and to fix the position of the magnetic plate  26  when the detected sagging degree is equal to the preset sagging degree. In the context of the present disclosure, the preset sagging degree refers to a sagging degree generated by the suction force applied on the screen  24  by the magnetic field system for absorbing the mask plate and the gravity of the screen  24  itself when the mask plate is used for performing masking in the vacuum evaporation chamber. 
     In can be seen from the above that when the mask plate is fabricated by the screen tensioning device used in fabrication of mask plate according to the embodiment of the present disclosure, a magnetic field environment in the vacuum evaporation chamber is simulated, so that the mask plate is applied with identical forces in the vertical direction in fabrication and in use, i.e., the mask plate is subjected to its own gravity which is in vertically downward and a magnetic field suction force which is in vertically upward, which makes the pattern (referred to the pattern on the screen of the mask plate) of the mask plate in fabrication is in the same position as the pattern of the mask plate in use. The position accuracy of the pattern formed by evaporating the organic materials onto the substrate to be evaporated can be improved. 
     In addition, in order that the magnetic plate  26  generates a uniform magnetic field to the screen  24 , for example, the magnetic plate  26  generates a magnetic field covering the entire screen  24 , in one embodiment of the present disclosure, the magnetic plate  26  is configured to have the same size as the screen  24  (it is to be noted that the “same size” here means the magnetic plate  26  and the screen  24  have the same plane area on their respective planes when the magnetic plate  26  and the screen  24  are arranged in parallel). The magnetic plate  26  can be a large magnet or can be comprised of a plurality of small magnets. When the magnetic plate  26  is comprised of a plurality of small magnets, the suction force acting on the screen  24  by the magnetic plate  26  can be also adjusted by increasing or decreasing the number of magnets, so that the sagging degree of the screen  24  can be adjusted. 
     As illustrated in  FIG. 4 , at least one embodiment of the present disclosure provides a screen tensioning method used during fabrication of mask plate, which is applicable to the above-described screen tensioning device. The screen tensioning method comprises the following steps. 
     A step  31  of placing and fixing the screen frame  22  and the aligned substrate  23  onto the screen tensioning machine base. 
     A step  32  of disposing the screen  24  on the screen frame  22  and positioning the screen  24  under the magnetic plate  26 , the magnetic plate  26  generating an upwardly-directed vertical suction force on the screen  24 . To make the environmental conditions during fabrication of the mask plate and the environmental conditions during use of the mask plate as consistent as possible, the upwardly-directed vertical suction force acting on the screen  24  by the magnetic plate  26  is equal to the upwardly-directed vertical suction force acting on the screen  24  by the magnetic field system in the vacuum evaporation chamber during masking process. In one embodiment of the present disclosure, the magnetic plate  26  and the screen  24  are of the same size, so that it is easier that the upwardly-directed vertical suction force acting on the screen  24  by the magnetic plate  26  is made equal to the upwardly-directed vertical suction force acting on the screen  24  by the magnetic field system in the vacuum evaporation chamber during masking process. 
     To adjusting the suction force acting on the screen  24  by the magnetic plate  26 , it is required that the magnetic plate  26  is movable in the vertical direction relative to screen tensioning machine base  21 . The suction force acting on the screen  24  by the magnetic plate  26  can be gauged by sagging degree of the screen  26 . Therefore, the screen tensioning method further comprises the following steps. 
     A step  33  of detecting the sagging degree of the screen  24  by use of the sagging degree detection module. 
     A step  34  of adjusting the distance between the magnetic plate  26  and the screen tensioning machine base  21  in the vertical direction according to the sagging degree of the screen  24  detected by the sagging degree detection module. In practical, the step comprises that the comparing unit  281  in the magnetic plate position adjustment module  28  compares the sagging degree of the screen  24  detected by the sagging degree detection module with the preset sagging degree and generates a comparison result; that the executing unit  282  in the magnetic plate position adjustment module  28  acquires the comparison result and adjusts the distance between the magnetic plate  26  and the screen tensioning machine base  21  in the vertical direction according to the comparison result. For example, the executing unit  282  moves the magnetic plate  26  towards the screen  24  when the sagging degree detected by the sagging degree detection module  27  is greater than the preset sagging degree, moves the magnetic plate  26  away from the screen  24  when the sagging degree detected by the sagging degree detection module  27  is less than the preset sagging degree, and fixes the position of the magnetic plate  26  when the sagging degree detected by the sagging degree detection module  27  is equal to the preset sagging degree. In fact, adjusting the distance between the magnetic plate  26  and the screen tensioning machine base  21  in the vertical direction aims to adjust the distance between the magnetic plate  26  and screen  24  in the vertical direction so as to adjust the suction force applied on the screen  24  in the vertical direction by the magnetic field generated by the magnetic plate  26 . 
     A step  35  of clamping the edge of the screen  24  by the jig  25  in the screen tensioning device  20  and tensioning the screen  24  by use of the jig  25  so that the pattern on the screen  24  is aligned with the pattern on the aligned substrate  23 . 
     A step  36  of combining the aligned screen  24  and the screen frame  22  so as to form a mask plate as required. 
     In can be seen from the above that compared with the screen tensioning method of the conventional art, the screen tensioning method used during fabrication of mask plate according to the embodiment of the present disclosure is additionally provided with a step of providing a magnetic plate so as to provide an upwardly-directed vertical force to the screen and simulate a magnetic field environment in the vacuum evaporation chamber. That is to say, in the present disclosure, the mask plate is fabricated in a magnetic field environment which is similar to the magnetic field environment in the vacuum evaporation chamber. In this case, the mask plate is applied with consistent forces in the vertical direction during fabrication and during use, i.e., the mask plate is subjected to its own gravity which is downwardly directed and a suction force by the magnetic field which is upwardly directed, which makes the position of the pattern (referred to the pattern on the screen of the mask plate) during fabrication of the mask plate is the same as the position of the pattern during use of the mask plate, thereby facilitating the alignment of the pattern on the screen of the mask plate with a region of the substrate to be evaporated where a pattern needs to be deposited. Therefore, compared with the conventional art, when using mask plate fabricated by the screen tensioning device according to the embodiment of the present disclosure, the positional accuracy of the pattern formed by evaporating the organic materials onto the substrate to be evaporated can be improved. 
     Each of the embodiments in the present disclosure is described in a progressive manner. The same and similar portions of the various embodiments can be cross-referenced. Each embodiment is illustrated with a focus on the differences from other embodiments. In particular, for the embodiment of the screen tensioning method, since it is substantially similar to the embodiment of the screen tensioning device, the description thereof is relatively simple and the relevant portions described in the embodiment of the screen tensioning device can be referred to. 
     The foregoing are merely exemplary embodiments of the disclosure, but are not used to limit the protection scope of the disclosure. The protection scope of the disclosure shall be defined by the attached claims. 
     The present disclosure claims priority of Chinese Patent Application No. 201510250442.6 filed on May 15, 2015, the disclosure of which is hereby entirely incorporated by reference as a part of the present disclosure.