Manufacturing method of flexible display device

Abstract

The invention relates to a manufacturing method of a flexible display device, and the method comprises the steps: S1, arranging a shielding layer with a vacant or hollow structure on a transparent mother board, so as to form a laser shielding region and a vacant region on the transparent mother board; s2, the transparent mother board is coated with colorless polyimide precursor liquid and cured into a CPI film, and the CPI film covers the laser shielding area and the blank area; s3, a thin film circuit is arranged on the CPI film; s4, laser is used for irradiating the transparent mother board, the part, corresponding to the blank area, of the bottom of the CPI film is ablated by the laser and is separated from the transparent mother board, the part, corresponding to the laser shielding area, of the bottom of the CPI film is not ablated by the laser and is kept to be bonded with the transparent mother board, and the CPI film is in a temporary fixing state; and S5, performing mechanical stripping on the CPI film to obtain the flexible display device. According to the CPI film stripping device, mechanical damage to a CPI film can be reduced in the CPI film stripping process, smoothness damage caused by laser ablation can be avoided, and the surface smoothness of the CPI film is guaranteed.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of display devices, in particular to a manufacturing method of a flexible display device. BACKGROUND

[0002] With the rapid development of flexible electronic technology, colorless polyimide (CPI) has become the core substrate material of flexible display devices such as flexible touch screens and foldable display screens due to its excellent optical transparency, high thermal stability and good mechanical flexibility. Compared with traditional polyimide, CPI has significantly higher light transmittance in the visible light range, which can meet the application requirements of high transparency display interface.

[0003] Typical flexible display devices are usually composed of CPI substrates integrated with thin film circuits (such as touch control circuits, display driver circuits). They generally include non-transparent film areas and transparent areas: the non-transparent areas contain non-transparent film layers such as metal films, metal lines and light shielding layers (such as BM) that constitute thin film circuits, while the transparent areas can be blank areas or transparent electrode (such as ITO electrode) areas. In the transparent area, the CPI substrate needs to maintain a very high smoothness to avoid light scattering effects.

[0004] Currently, the preparation process of flexible display devices usually adopts the following process: first, CPI precursors (such as polyamic acid) are coated on a transparent mother board (such as a glass or quartz substrate) to form a CPI film (i.e. colorless polyimide film) through solidification; then, thin film circuits are prepared on the surface of the CPI film; finally, the CPI film and the thin film circuit composite structure are separated from the transparent mother board through a stripping process. The stripping process is a key step in realizing the formation of flexible devices, which can be mainly divided into two categories: (1) direct mechanical stripping: achieved by physical tearing, but local stress deformation can easily cause damage to the thin film circuit; (2) laser stripping: the CPI film bottom is ablated from the back of the transparent mother board using laser to achieve separation. Although this method reduces the risk of mechanical damage, the control of laser energy is difficult, and the ablation process may cause the inner surface of the CPI film to be roughened, causing light scattering problems in the transparent area, which significantly reduces the optical transparency of the flexible display device. SUMMARY

[0005] The technical problem to be solved by the present application is to provide a manufacturing method of a flexible display device, which can not only reduce mechanical damage to the CPI film during the CPI film stripping process, but also avoid the smoothness damage caused by laser ablation, which is beneficial to ensure the surface smoothness of the CPI film. The technical solution adopted is as follows: A manufacturing method of a flexible display device, characterized in that it comprises the following steps: S1, setting a shielding layer with a reserved or hollow structure on the front surface of the transparent mother plate to form a laser shielding area and a reserved area on the front surface of the transparent mother plate; S2, coating a colorless polyimide precursor solution on the front surface of the transparent mother plate and curing to form a CPI film, the CPI film covering the laser shielding area and the reserved area; S3, setting a thin film circuit on the surface of the CPI film; S4, irradiating the back surface of the transparent mother plate with a laser, the laser passing through the transparent mother plate and the reserved area of the shielding layer to act on the bottom of the CPI film, the part of the bottom of the CPI film corresponding to the reserved area being ablated by the laser to separate from the transparent mother plate, and the part of the bottom of the CPI film corresponding to the laser shielding area not being ablated by the laser to remain bonded to the transparent mother plate, so that the CPI film is in a temporary fixed state; S5, mechanically peeling the CPI film in the temporary fixed state to separate it from the transparent mother plate and the shielding layer, to obtain the flexible display device.

[0006] In the manufacturing method of the flexible display device, in step S1, the transparent mother plate can be a transparent glass substrate or a transparent quartz substrate; in step S2, the thickness of the CPI film is in a standard range of 10-100 μm; in step S3, the thin film circuit generally includes two types of core components, metal lines and transparent electrodes: the metal lines are formed by patterning copper, molybdenum-aluminum-molybdenum, silver or other metal or alloy thin films, and the transparent electrodes are made of ITO, AZO or other transparent conductive thin films through a patterning process, and the patterning process is generally realized by using photolithography technology; in steps S4-S5, the back surface of the transparent mother plate is irradiated with a laser to separate part of the CPI film from the transparent mother plate, so that the CPI film is in a temporary fixed state, the mechanical peeling force on the CPI film can be reduced as a whole, the damage to the thin film circuit is reduced, and the design of the shielding layer can effectively protect the bottom of the CPI film in the laser shielding area from being ablated by the laser, so as to maintain the smoothness of the surface; in step S5, the CPI film in the temporary fixed state is mechanically peeled to separate it from the transparent mother plate and the shielding layer, and finally the flexible display device composed of the CPI film and the thin film circuit can be obtained.

[0007] Generally, the thin film circuit can also integrate a transparent photosensitive resin coating (as an insulating layer) or an ink coating (as a light shielding layer) to expand the functional characteristics. Thus, based on the light transmittance of the above-mentioned film layer structure and after the superposition thereof, as a preferred scheme of the present application, the flexible display device has a light transmittance region and a non-light transmittance region; the shielding layer in the step S1 only shields the light transmittance region and avoids the non-light transmittance region; in the step S4, the laser is applied to the non-light transmittance region, so that the CPI film bottom corresponding to the non-light transmittance region is pre-peeled from the transparent mother board. Specifically, the non-light transmittance region is the region where the high-sensitivity fine metal lines are located, and the light transmittance region is the region where the non-fine metal lines are located. By shielding the light transmittance region with the shielding layer, the laser ablation to the CPI film bottom of the light transmittance region in the step S4 can be avoided to affect the smoothness and transparency thereof, and even if a micro-damage is caused to the non-fine metal lines (such as the electrodes at the tail end of the lines) in the step S5, the function of the flexible display device will not be affected.

[0008] As a further preferred scheme of the present application, the shielding layer is arranged at the bottom of the light transmittance region, and the shielding layer is left empty or hollowed out at the positions corresponding to the non-light transmittance region.

[0009] As a still further preferred scheme of the present application, the shielding layer has a grid-shaped hollow structure at the positions corresponding to the light transmittance region. Thus, for the flexible display device with a larger light transmittance region, the temporary adhesion of the CPI film to the transparent mother board in the region can also be maintained to maintain the flatness thereof.

[0010] As a preferred scheme of the present application, in the step S1, alignment marks are pre-prepared on the shielding layer; in the step S3, the alignment of the film layers of the thin film circuit is performed according to the alignment marks, so that the pattern of the thin film circuit is fitted into the pattern of the shielding layer. The fitting here has the same meaning as that in the printing industry, so that the cooperation of the shielding layer and the thin film circuit in the light transmittance region and the non-light transmittance region can be achieved in the step S4.

[0011] As a preferred scheme of the present application, the laser is an ultraviolet laser. Specifically, the laser adopts an ultraviolet laser with a wavelength of 100-280 nm, which can directly penetrate the transparent mother board to act on the CPI film bottom, and the peeling is mainly achieved by chemical action and less by thermal action, so that the damage of the laser thermal action to the flexible display device can be avoided or reduced.

[0012] As a further preferred scheme of the present application, the main body of the shielding layer adopts a zinc oxide film. The shielding layer adopts a zinc oxide film as the main body, which can effectively shield and absorb the ultraviolet laser.

[0013] As another further preferred scheme of the present application, the main body of the shielding layer adopts a dielectric reflective film. The shielding layer adopts a dielectric reflective film as the main body, which can effectively reflect the ultraviolet laser, avoiding the heat effect caused by the absorption of the ultraviolet laser by the shielding layer, thereby avoiding the influence on the CPI film and its thin film circuit.

[0014] As a further preferred scheme of the present application, the dielectric reflective film comprises a plurality of first dielectric layers and a plurality of second dielectric layers which are alternately stacked, the material of the first dielectric layer is Al2O3 or LaF3, and the material of the second dielectric layer is AlF3. In this way, the shielding layer has good stability and high reflectivity to the ultraviolet laser, which can effectively avoid the laser ablation of the CPI film at the bottom of the shielding area; since the second dielectric layer in the shielding layer adopts AlF3 material, it is difficult to be etched, so it is generally necessary to form a shielding layer pattern on the shielding layer by using a mask deposition method. In order to facilitate the mask, the shielding area is generally designed in a dot-like distribution.

[0015] In addition, the dielectric reflective film can also be a multilayer film formed by alternately stacking Al2O3 / HfO2, MgF2 / LaF3, and SiO2 / Ta2O5. Although the ultraviolet reflectivity of these dielectric reflective films is relatively low, they can effectively protect the CPI film at the bottom from being ablated by the laser, and these dielectric reflective films can be etched by dry etching or wet etching to form the required shielding layer pattern. The shielding layer pattern can be dot-like distribution, grid-like distribution, or a more flexible shielding area for a particular area.

[0016] As a preferred scheme of the present application, the surface of the shielding layer is further covered with a silicon nitride film. The silicon nitride film is used to further reduce the adhesion between the CPI film and the shielding layer, thereby avoiding damage to the shielding layer during the tearing process of the CPI film in step S5.

[0017] As a preferred scheme of the present application, in the step S5, when the CPI film is mechanically peeled, the edge area of the CPI film ablated by the laser and separated from the transparent mother board is used as the starting position of the peeling. In this way, the CPI film and the transparent mother board can be separated, and the mechanical force during peeling is further reduced.

[0018] Compared with the prior art, the present application has the following advantages: The manufacturing method of the present application can precisely control the laser action range in step S4 by setting the shielding layer with the reserved or hollow structure on the front surface of the transparent mother plate in step S1 to form the laser shielding area and the reserved area, so that the CPI film part is separated from the transparent mother plate, and the double damage problem in the CPI film peeling process is solved. On the one hand, the mechanical peeling force on the CPI film in step S5 can be reduced as a whole, the damage of the mechanical peeling to the key parts of the thin film circuit is reduced through differential mechanical design, and the design of the shielding layer can effectively protect the bottom of the CPI film in the laser shielding area from the smoothness damage caused by laser ablation, so as to maintain the surface smoothness, thereby realizing the double optimization of process reliability and functional integrity. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 is a schematic diagram of step S1 in the manufacturing method provided by the preferred embodiment of the present application.

[0020] Figure 2 is a schematic diagram of step S2 in the manufacturing method provided by the preferred embodiment of the present application.

[0021] Figure 3 is a schematic diagram of step S3 in the manufacturing method provided by the preferred embodiment of the present application.

[0022] Figure 4 is a schematic diagram of step S4 in the manufacturing method provided by the preferred embodiment of the present application.

[0023] Figure 5 is a cross-sectional schematic diagram of Figure 4 .

[0024] Figure 6 is a schematic diagram of step S5 in the manufacturing method provided by the preferred embodiment of the present application. DETAILED DESCRIPTION

[0025] As shown in Figures 1-6 , the manufacturing method of the flexible display device comprises the following steps: S1, a shielding layer 2 with a reserved or hollow structure is arranged on the front surface of a transparent mother plate 1 to form a laser shielding area 21 and a reserved area 22 on the front surface of the transparent mother plate 1; S2, a colorless polyimide precursor solution is coated on the front surface of the transparent mother plate 1 and is cured to form a CPI film 3, and the CPI film 3 covers the laser shielding area 21 and the reserved area 22; S3, a thin film circuit 4 is arranged on the surface of the CPI film 3; S4, the back of the transparent mother plate 1 is irradiated by the laser 5, the part of the bottom of the CPI film 3 corresponding to the reserved area 22 is ablated by the laser 5 to form an ablation part 31 and is separated from the transparent mother plate 1, the part of the bottom of the CPI film 3 corresponding to the laser shielding area 21 is not ablated by the laser 5 and remains to be bonded to the transparent mother plate 1 through the bonding part 32, so that the CPI film 3 is in a temporary fixed state; S5, the CPI film 3 in the temporary fixed state is mechanically peeled to obtain the flexible display device 10.

[0026] In the embodiment, the transparent mother plate 1 is a transparent glass substrate or a transparent quartz substrate.

[0027] In the embodiment, the thickness of the CPI film 3 is in a standard range of 10-100 μm.

[0028] In the embodiment, the thin film circuit 4 includes a metal circuit 41 and a transparent electrode 42, the metal circuit 41 is formed by patterning a copper, molybdenum-aluminum-molybdenum, silver or other metal or alloy thin film, and the transparent electrode 42 is made of an ITO, AZO or other transparent conductive thin film through a patterning process, and the patterning process is generally realized by using a photolithography technology.

[0029] The thin film circuit 4 can also integrate a transparent photosensitive resin coating (as an insulating layer) or an ink coating (as a light shielding layer) to expand the functional characteristics. Based on the light transmission of the above-mentioned film layer structure and the superposition thereof, in the embodiment, the flexible display device 10 has a light transmission area 101 and a non-light transmission area 102; in step S1, the shielding layer 2 is arranged at the bottom of the light transmission area 101, and the shielding layer 2 is reserved or hollowed at the part corresponding to the non-light transmission area 102; in step S4, the laser 5 acts on the non-light transmission area 102, so that the part of the bottom of the CPI film 3 corresponding to the non-light transmission area 102 is pre-peeled from the transparent mother plate 1. Specifically, the non-light transmission area 102 is the area where the high-sensitivity fine metal circuit 41 is located, and the light transmission area 101 is the area where the non-fine metal circuit 41 is located. The shielding layer 2 only shields the light transmission area 101 and avoids the non-light transmission area 102, so as to avoid that the part of the bottom of the CPI film 3 in the light transmission area 101 is ablated by the laser 5 in step S4 and affects the smoothness and transparency thereof, and even if the non-fine metal circuit 41 (such as the electrode at the tail end of the circuit) is micro-damaged in step S5, the function of the flexible display device 10 will not be affected.

[0030] In the embodiment, in step S1, the alignment mark 23 is pre-made on the shielding layer 2; in step S3, the alignment of each film layer of the thin film circuit 4 is implemented according to the alignment mark 23, so as to realize the fitting between the pattern of the thin film circuit 4 and the pattern of the shielding layer 2. Thus, the cooperation of the shielding layer 2 and the thin film circuit 4 in the light transmission area 101 and the non-light transmission area 102 can be realized in step S4.

[0031] In the embodiment, the laser 5 is an ultraviolet laser, and the main body of the shielding layer 2 is a zinc oxide film. Specifically, the laser 5 is an ultraviolet laser with a wavelength of 100-280 nm, which can directly penetrate the transparent base plate 1 to act on the bottom of the CPI film 3, and the peeling is mainly realized by chemical action and less by thermal action, so that the damage of the flexible display device 10 caused by the thermal action of the laser 5 can be avoided or reduced; the shielding layer 2 uses a zinc oxide film as the main body, which can effectively shield and absorb ultraviolet laser.

[0032] In the embodiment, in the step S5, when the CPI film 3 is mechanically peeled, the edge region of the CPI film 3 ablated by the laser 5 and separated from the transparent base plate 1 is used as the starting position of the peeling, so that the CPI film 3 can be guided to separate from the transparent base plate 1, and the mechanical force generated during the peeling is further reduced.

[0033] In addition, it should be noted that the specific embodiments described in the specification can have different part names, and any equivalent or simple changes made according to the structure, features and principles of the patent concept of the present application shall be included in the protection scope of the present application. Those skilled in the art can make various modifications or supplements to the described specific embodiments or use similar ways to replace them, as long as they do not deviate from the structure of the present application or exceed the scope defined by the present claims, which shall belong to the protection scope of the present application.

Claims

1. A method of manufacturing a flexible display device, characterized by The method comprises the following steps: S1, providing a shielding layer with a reserved or hollow structure on the front surface of a transparent mother board to form a laser shielding area and a reserved area on the front surface of the transparent mother board; S2, applying a colorless polyimide precursor solution on the front surface of the transparent mother board and curing to form a CPI film, the CPI film covering the laser shielding area and the reserved area; S3, providing a thin film circuit on the surface of the CPI film; S4, irradiating the back surface of the transparent mother board with a laser, the laser passing through the transparent mother board and the reserved area of the shielding layer to act on the bottom of the CPI film, the part of the bottom of the CPI film corresponding to the reserved area being ablated by the laser to separate from the transparent mother board, the part of the bottom of the CPI film corresponding to the laser shielding area not being ablated by the laser to remain bonded to the transparent mother board, so that the CPI film is in a temporary fixed state; S5, mechanically peeling the CPI film in the temporary fixed state to separate it from the transparent mother board and the shielding layer, and obtaining the flexible display device.

2. The method of claim 1, wherein: The flexible display device has a light-transmitting area and a non-light-transmitting area; the shielding layer in step S1 only shields the light-transmitting area and avoids the non-light-transmitting area; in step S4, the laser acts on the non-light-transmitting area, so that the part of the bottom of the CPI film corresponding to the non-light-transmitting area is pre-peeled from the transparent mother board.

3. The method of claim 2, wherein: The shielding layer is provided at the bottom of the light-transmitting area and is reserved or hollow at the part of the shielding layer corresponding to the non-light-transmitting area.

4. The method of claim 3, wherein: The part of the shielding layer corresponding to the light-transmitting area has a grid-shaped hollow structure.

5. The method of claim 1, wherein: In step S1, alignment marks are pre-made on the shielding layer; in step S3, each film layer of the thin film circuit is aligned according to the alignment marks, so that the pattern of the thin film circuit is fitted with the pattern of the shielding layer.

6. The method of claim 1, wherein: The laser is an ultraviolet laser.

7. The method of claim 6, wherein: The main body of the shielding layer is a zinc oxide film.

8. The method of claim 6, wherein: The main body of the shielding layer is a dielectric reflective film.

9. The method of claim 8, wherein: The dielectric reflective film comprises a plurality of first dielectric layers and a plurality of second dielectric layers alternately stacked, the material of the first dielectric layer being Al2O3 or LaF3, and the material of the second dielectric layer being AlF3.

10. The method of claim 1, wherein: The surface of the shielding layer is further covered with a silicon nitride film.

11. The method of claim 1, wherein: In step S5, when the CPI film is mechanically peeled, the edge area of the CPI film ablated by the laser to separate from the transparent mother board is taken as the starting position of peeling.

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