Method for high-efficiency laser lift-off of polyimide thin film

Abstract

The present invention relates to a method for high-efficiency laser lift-off of a polyimide thin film. The method comprises: adding a layer of a porous polyamide acid thin film as a sacrificial layer between a substrate and a polyimide thin film, and then performing laser cutting and lift-off, wherein the sacrificial layer is prepared by dissolving a fluorine-containing diamine monomer, a fluorine-free diamine monomer and a fluorine-containing dianhydride monomer in an aprotic solvent to prepare a polyamide acid solution, coating the surface of a glass substrate with the polyamide acid solution, placing the glass substrate in a coagulating bath to obtain a porous polyamide acid thin film, forming a substrate / porous polyamide acid thin film structure, and then preparing a polyimide thin film. By means of the method of the present invention, the lift-off time is shortened, the polyimide thin film is effectively removed, and the integrity of the polyimide thin film is ensured.

Description

A method for efficient laser exfoliation of polyimide films Technical Field

[0001] This invention relates to the field of laser cutting, peeling, and heat treatment production technology, and specifically to a method for efficient laser peeling of polyimide films. Background Technology

[0002] Laser lift-off (LLO) is a key process in flexible display manufacturing. Its core function is to precisely separate the flexible display panel from the rigid mother glass substrate while protecting the fragile circuitry and light-emitting layer, thus transferring the flexible display device onto the target flexible substrate to manufacture products such as flexible displays. However, this technology also faces challenges in application: on the one hand, due to its inherent performance limitations (such as light absorption characteristics and thermal conductivity), polyimide materials may experience incomplete lift-off, interface residues, and damage to the functional layers during laser lift-off, affecting the performance and yield of flexible display devices; on the other hand, laser lift-off process parameters (such as laser wavelength, energy density, pulse width, and scanning speed) need to be precisely controlled. Otherwise, excessive energy may lead to damage to the functional layers of the display device, material ablation, and thermal deformation, while insufficient energy may result in poor lift-off effect and low efficiency. Summary of the Invention

[0003] The purpose of this invention is to provide a laser peeling method for polyimide films, which solves the technical problems of existing polyimide film peeling methods being complex, having low peeling efficiency, or damaging the polyimide film.

[0004] The objective of this invention is achieved through the following technical solution:

[0005] A method for efficient laser peeling of polyimide films is characterized by: adding a porous polyamic acid film as a sacrificial layer between the substrate and the polyimide film before laser cutting and peeling; the specific steps are as follows:

[0006] (1) Fluorinated diamine monomer, non-fluorinated diamine monomer and fluorinated dianhydride monomer are dissolved in an aprotic solvent to form a precursor solution, and polyamic acid solution is obtained by stirring in a water bath under an inert atmosphere.

[0007] (2) Coating the surface of a glass substrate with a polyamic acid solution and placing it in a coagulation bath for 2-3 hours results in a porous polyamic acid film, forming a substrate / porous polyamic acid film structure.

[0008] (3) The precursor liquid used to prepare the polyimide film is coated on the surface of the porous polyamic acid film, annealed, and thermally imidized to obtain the polyimide film, forming a substrate / porous polyamic acid film / polyimide film structure.

[0009] (4) Place the substrate / porous polyamic acid film / polyimide film structure under a laser and cut and peel the polyimide film off the substrate using laser ablation technology.

[0010] Furthermore, in step (1), the molar ratio of fluorinated diamine monomer, non-fluorinated diamine monomer and fluorinated dianhydride monomer is 0.5-0.8 mol: 0.5-0.2 mol: 1 mol, and the solid content of the precursor solution is 12-18 wt%.

[0011] Furthermore, the fluorinated diamine monomer is 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (TFMB); the non-fluorinated aromatic diamine monomer is 4,4'-diaminodiphenyl ether (oda); the fluorinated diamine monomer is 4,4′-(hexafluoroisopropylidene) bisphthalic anhydride (6FDA); and the aprotic solvent is NMP (N-methylpyrrolidone).

[0012] The present invention has the following technical effects:

[0013] Using a porous polyamic acid film as a sacrificial layer, a high-energy-density laser beam interacts with the material to form a stable and intelligent heat treatment production line for laser ablation. This improves the ablation speed of the polyimide film, shortens the glass removal time, and achieves a stable ablation effect with high ablation efficiency. It effectively removes the polyimide film from the substrate surface and ensures the integrity and property stability of the removed polyimide film. Attached Figure Description

[0014] Figure 1: Schematic cross-sectional view of the substrate / porous polyamic acid film / polyimide film stack in this invention, where 1 is the substrate, 2 is the sacrificial layer, and 3 is the polyimide film.

[0015] Figure 2: A physical image of the porous polyamic acid film prepared by coagulation bath in Example 1.

[0016] Figure 3: Porous polyamic acid film / polyimide film stacked structures prepared by pure polyimide film, Example 1, Comparative Example 1 and Comparative Example 2, (a) pure polyimide film; (b) Example 1; (c) Comparative Example 1; (d) Comparative Example 2.

[0017] Figure 4: (a) Scanning electron microscope (SEM) cross-sectional image of the unannealed sacrificial layer film prepared in Example 1; (b) Scanning electron microscope (SEM) cross-sectional image of the sacrificial layer film after annealing; (c) Scanning electron microscope (SEM) cross-sectional image of the porous polyamic acid film after laser exfoliation; (d) Scanning electron microscope (SEM) cross-sectional image of the polyimide film after annealing and laser exfoliation.

[0018] Figure 5: Time comparison chart of complete peeling from glass substrate by laser in Example 1, Comparative Example 1, and Comparative Example 2 under different laser densities. Embodiments of the present invention

[0019] The following examples are only used to further illustrate the present invention.

[0020] Example 1

[0021] A method for efficient laser exfoliation of polyimide films includes the following steps:

[0022] (1) A precursor solution with a solid content of 12% was prepared by dissolving TFMB (fluorinated diamine monomer), ODA (non-fluorinated aromatic diamine monomer), and 6FDA (fluorinated dianhydride monomer) in NMP solvent. The solution was heated to 30°C in a water bath under an inert atmosphere and stirred at 200 rpm for 1.5 h. Then it was cooled to room temperature and stirred for another 12 h to obtain a pale yellow polyamic acid solution. The molar ratio of fluorinated diamine monomer, non-fluorinated diamine monomer, and fluorinated dianhydride monomer was 0.7 mol: 0.3 mol: 1 mol.

[0023] (2) A polyamic acid solution is spin-coated onto the surface of a glass substrate at a temperature of 40°C and placed in a coagulation bath for 2.5 h to form a porous polyamic acid film, thereby forming a substrate / porous polyamic acid film structure. The spin-coating speed is 1500 rpm and the spin-coating time is 60 s. The coagulation bath is formed by mixing NMP, sodium dodecyl sulfate and water in a mass ratio of 40 g: 5 g: 60 g.

[0024] (3) A colorless precursor solution (6FDA 1.4332g, ODA 0.969g, TFMB 1.5497g, NMP 50g, stirred vigorously in an ice-water bath for 18h under a nitrogen atmosphere) was coated on the surface of a porous polyamic acid film and subjected to annealing treatment. The polyimide film was obtained by thermal imidization, forming a substrate / porous polyamic acid film / polyimide film structure. The annealing treatment was performed by curing at 55°C for 50min, then heating at 115°C for 40min, heating at 155°C for 40min, heating at 205°C for 40min, heating at 265°C for 40min, and then cooling to room temperature to complete the thermal imidization process and obtain the substrate / porous polyamic acid film / polyimide film structure.

[0025] (4) The substrate / porous polyamic acid film / polyimide film structure is placed under a laser with a wavelength of 450 nm and a laser energy density of 90 mJ / cm². 2 The laser beam is used for laser cutting and peeling, and the laser moving speed is 0.5 mm / s.

[0026] In Example 1, the sacrificial layer thickness of the porous polyamic acid film was 160 μm, and the total peeling time was 71 min. No polyimide film residue remained on the substrate surface after peeling, indicating excellent polyimide film integrity. Figure 2 shows: (a) a scanning electron microscope (SEM) image of the unannealed porous polyamic acid film prepared on the substrate in Example 1, revealing distinct pore structures of different sizes; (b) a cross-sectional SEM image after annealing, showing a significant change in pore size structure after annealing; (c) an SEM image of the porous polyamic acid film after laser peeling, showing that laser treatment caused the sacrificial layer to absorb laser energy, leading to increased porosity and subsequent pore rupture and peeling; and (d) a thin polyimide film after laser peeling, exhibiting excellent film integrity with no obvious damage.

[0027] Experiment (1)

[0028] By adjusting the spin-coating time of the sacrificial layer, sacrificial layers of equal area but different thicknesses were obtained. Then, polyimide films of equal area and thickness were prepared. The effect of the sacrificial layer thickness on the laser ablation of the polyimide films was investigated. The ablation efficiency refers to the percentage of intact films obtained from each group of 100 laser-ablated polyimide films. Here, "intact and undamaged" means that the residual polyimide film on the substrate after ablation has a thickness of less than 10 nm and thermal damage (edge ​​heat-affected zone) of less than 100 nm. The results are shown in Table 1.

[0029] Table 1:

[0030] Spin coating speed (rpm) Sacrificial layer thickness (μm) Average peel time (min) Polyimide film peel efficiency -0 126 74% 1000 202 134 89% 1100 195 93 94% 1300 177 86 95% 1500 160 71 96% 1700 149 52 96% 1900 135 44 95% 2000 130 40 71%

[0031] Under the same laser treatment, the peel time of the polyimide film showed significant differences with varying sacrificial layer thickness. When the spin coating rate was 1100–1900 rpm and the obtained sacrificial layer thickness was 135–195 μm, the peel time decreased significantly with increasing sacrificial layer thickness while maintaining high peel efficiency. However, when the spin coating thickness was thicker, the annealing process had an ineffective effect on the porosity and component distribution of the sacrificial layer, leading to a decrease in the utilization rate of laser energy during laser treatment, resulting in a significant increase in peel time and a decrease in peel efficiency. Conversely, when the sacrificial layer thickness was smaller, although the peel time decreased, the thinner sacrificial layer was completely imidized under annealing, significantly increasing its adhesion to the polyimide film. This failed to reduce peel damage and instead had a counterproductive effect, leading to a decrease in peel efficiency.

[0032] Experiment (II)

[0033] By adjusting the composition of the polyamic acid solution used to prepare the sacrificial layer (TFMB, a fluorinated diamine monomer, is designated as "T" in the table; ODA, an unfluorinated aromatic diamine monomer, is designated as "O" in the table; and 6FDA, a fluorinated dianhydride monomer, is designated as "F" in the table; and the solid content of the solution is kept at 12 wt%), a sacrificial layer of the same thickness as in Example 1 was obtained. The effect of the sacrificial layer composition on the laser exfoliation of the same polyimide film was then investigated, and the results are shown in Table 2.

[0034] Table 2:

[0035] Average peel time (min) of polyamic acid solution components; peel efficiency of polyimide film; -12674% T:O:F=0.8:0.2:18493% T:O:F=0.6:0.4:17095% T:O:F=0.5:0.5:16794% T:O:F=0.4:0.6:18881% T:O:F=0.3:0.7:18279% T:O:F=0.2:0.8:17977% T:O:F=1:0:16680% T:O:F=0:1:19482%

[0036] It can be seen that as the proportion of TFMB in the polyamic acid solution used to prepare the sacrificial layer gradually decreases, the laser exfoliation time of the polyimide film first shortens and then lengthens. The exfoliation efficiency of the same polyimide film generally shows a gradually decreasing trend. Furthermore, when the ratio of TFMB to ODA is less than 1:1, the exfoliation efficiency of the polyimide film decreases significantly, resulting in more severe damage. When there is no ODA in the polyamic acid solution, although the exfoliation time is the shortest, the exfoliation efficiency is not ideal. When there is no TFMB in the polyamic acid solution, the exfoliation time is longer, and the damage to the polyimide film is also more pronounced.

[0037] Comparative Example 1

[0038] Compared with Example 1, the annealing process is as follows:

[0039] The substrate was cured at 55°C for 50 min, then heated to 115°C for 30 min, then to 145°C for 30 min, then to 175°C for 30 min, then to 205°C for 30 min, then to 235°C for 30 min, then to 265°C for 30 min, and finally cooled to room temperature to complete the thermal imidization process, thus obtaining the substrate / porous polyamic acid film / polyimide film structure.

[0040] Compared with Example 1, Comparative Example 1 increased the number of temperature stages for heating, changing from 4 stages to 6 stages, with each stage having a 30°C interval and a shorter heating time for each stage.

[0041] Comparative Example 2

[0042] Compared with Example 1, the annealing process is as follows:

[0043] Each film was cured at 55°C for 50 min, then heated to 115°C for 40 min, then to 165°C for 40 min, then to 215°C for 40 min, then to 265°C for 40 min, and finally cooled to room temperature to complete the thermal imidization process and obtain the substrate / porous polyamic acid film / polyimide film structure.

[0044] Compared with Example 1, Comparative Example 1 increased the temperature range of the heating, while maintaining the original 4 heating ranges, but the temperature interval between each heating range was 50°C.

[0045] Figure 3 shows the porous polyamic acid film prepared on the substrate surface in this invention, and Figure 4 shows the polyimide film prepared on the pure substrate surface, as well as the substrate / porous polyamic acid film / polyimide film structure prepared in Example 1, Comparative Example 1 and Comparative Example 2.

[0046] Experiment (III)

[0047] Using different annealing procedures in Example 1 and Comparative Example 1, substrate / porous polyamic acid film / polyimide film structures were prepared. The effect of annealing on the sacrificial layer and its final influence on the laser lift-off of the polyimide film were investigated. The results are shown in Table 3.

[0048] Table 3:

[0049] Average peel time (min) for the test groups; peel efficiency of polyimide film; Example 17: 197%; Comparative Example 1: 193.86%; Comparative Example 2: 111.283%.

[0050] It can be seen that in Comparative Example 1, the more segmented heating and annealing treatments significantly affected the sacrificial layer structure, resulting in longer peeling times during laser exfoliation and a marked decrease in the peeling efficiency of the polyimide film. In Comparative Example 2, the heating interval was kept constant at 50°C, leading to even longer peeling times during laser exfoliation and a further decrease in the peeling efficiency of the polyimide film. In contrast, this invention employs four segmented heating stages, with the temperature interval between each stage increasing progressively.

[0051] The substrate / porous polyamic acid film / polyimide film structures prepared in Example 1, Comparative Example 1, and Comparative Example 2 were subjected to laser peeling at different laser densities. The peeling time comparison is shown in Figure 5. As the laser density increases, the peeling time of the polyimide film is shorter. However, compared with Comparative Example 1 and Comparative Example 2, the peeling time of Example 1 decreases more with the increase of laser density. This is because different annealing processes have different effects on the sacrificial layer structure, resulting in differences in the final utilization rate of laser energy.

[0052] The above embodiments are in the pilot stage, so the laser used is a picosecond laser with a laser movement rate of 0.5 mm / s. In order to study whether the sacrificial layer in this invention can also play a corresponding role in actual industrial production when faced with a faster laser movement rate, we tried to use an industrial excimer laser for laser ablation (laser movement rate of 200 mm / s).

[0053] Example 2

[0054] A method for efficient laser exfoliation of polyimide films includes the following steps:

[0055] (1) A precursor solution with a solid content of 12% was prepared by dissolving TFMB (fluorinated diamine monomer), ODA (non-fluorinated aromatic diamine monomer), and 6FDA (fluorinated dianhydride monomer) in NMP solvent. The solution was heated to 30°C in a water bath under an inert atmosphere and stirred at 200 rpm for 1.5 h. Then it was cooled to room temperature and stirred for another 12 h to obtain a pale yellow polyamic acid solution. The molar ratio of fluorinated diamine monomer, non-fluorinated diamine monomer, and fluorinated dianhydride monomer was 0.7 mol: 0.3 mol: 1 mol.

[0056] (2) A polyamic acid solution is spin-coated onto the surface of a glass substrate at a temperature of 40°C and placed in a coagulation bath for 2.5 h to form a porous polyamic acid film, thereby forming a substrate / porous polyamic acid film structure. The spin-coating speed is 1500 rpm and the spin-coating time is 60 s. The coagulation bath is formed by mixing NMP, sodium dodecyl sulfate and water in a mass ratio of 40 g: 5 g: 60 g.

[0057] (3) The colorless precursor solution used to prepare the polyimide film (6FDA 1.4332g, ODA 0.969g, TFMB 1.5497g, NMP 50g, stirred vigorously in an ice-water bath for 18h under nitrogen atmosphere) was coated on the surface of the porous polyamic acid film and annealed. The polyimide film was obtained by thermal imidization, forming a substrate / porous polyamic acid film / polyimide film structure. The annealing process was to cure at 55°C for 50min, then heat to 115°C for 40min, heat to 155°C for 40min, heat to 205°C for 40min, heat to 265°C for 40min, and then cool to room temperature to complete the thermal imidization process and obtain the substrate / porous polyamic acid film / polyimide film structure.

[0058] (4) The substrate / porous polyamic acid film / polyimide film structure is placed under a laser with a wavelength of 450 nm and a laser energy density of 90 mJ / cm². 2 The laser beam is used for laser cutting and peeling, and the laser moving speed is 200 mm / s.

[0059] By adjusting the composition of the polyamic acid solution used to prepare the sacrificial layer to be without TFMB and without ODA (the solid content of the solution was kept at 12wt%), a sacrificial layer with the same thickness as in Example 2 was obtained. The effect of the sacrificial layer composition on the laser ablation of polyimide films with the same thickness and area on the surface of the sacrificial layer was detected, and the results are shown in Table 4.

[0060] Table 4:

[0061] Average peel time (s) of polyamic acid solution components; peel efficiency of polyimide film; pure PI film; 2380%; Example 2997%; T:O:F=1:0:1882%; T:O:F=0:1:11785%

[0062] It can be seen that when the polyamic acid solution used to prepare the sacrificial layer is free of TFMB and ODA, its influence on peeling time and peeling efficiency of polyimide film is consistent with that in the small-scale test, compared with Example 2. This indicates that the sacrificial layer prepared by the present invention with specific components effectively reduces peeling time and improves peeling efficiency of polyimide film by laser peeling, while reducing damage to the film during peeling.

[0063] Comparative Example 3

[0064] Compared with Example 2, the annealing process is as follows:

[0065] Each film was cured at 55°C for 50 min, then heated to 115°C for 30 min, then to 145°C for 30 min, then to 175°C for 30 min, then to 205°C for 30 min, then to 235°C for 30 min, then to 265°C for 30 min, and finally cooled to room temperature to complete the thermal imidization process, thus obtaining the substrate / porous polyamic acid film / polyimide film structure.

[0066] Compared with Example 2, Comparative Example 3 increased the number of temperature stages for heating, changing from 4 stages to 6 stages, with each stage heating at 30°C, and shortened the heating time for each stage.

[0067] Comparative Example 4

[0068] Compared with Example 2, the annealing process is as follows:

[0069] Each film was cured at 55°C for 50 min, then heated to 115°C for 40 min, then to 165°C for 40 min, then to 215°C for 40 min, then to 265°C for 40 min, and finally cooled to room temperature to complete the thermal imidization process and obtain the substrate / porous polyamic acid film / polyimide film structure.

[0070] Compared with Example 2, Comparative Example 4 increased the temperature range of the heating, while maintaining the original 4 heating ranges, but the interval between each heating range was 50°C.

[0071] Using different annealing procedures in Examples 2 and 3 and 4, substrate / porous polyamic acid film / polyimide film structures were prepared. The effect of annealing on the sacrificial layer and its final influence on the laser lift-off of the polyimide film were investigated. The results are shown in Table 5.

[0072] Table 5:

[0073] Average peel time (s) of the test groups; peel efficiency of polyimide film; Example 2: 99.7%; Comparative Example 3: 16.88%; Comparative Example 4: 24.84%.

[0074] It can be seen that at higher laser moving speeds, the peeling time and peeling efficiency of the polyimide film in Examples 2, 3, and 4 are consistent with the trends observed in Examples 1, 1, and 2 in the small-scale test. This indicates that at industrial-scale high laser moving speeds, the specific sacrificial layer prepared in this invention can effectively reduce the peeling time during laser peeling, while simultaneously improving peeling efficiency and reducing damage to the polyimide film during peeling.

[0075] This invention utilizes a specifically formulated polyamic acid solution for spin coating, combined with a step-by-step annealing process with progressively increasing temperatures. This effectively regulates the porous distribution and component structure of the polyamic acid film while maintaining a functional pre-film on its surface. The porous structure of the sacrificial layer in the porous polyamic acid film provides a large specific surface area, optimizing its absorption and scattering characteristics for a specific green wavelength laser during irradiation. This better matches the laser source wavelength used in practical applications, enabling more efficient absorption of laser energy. The relatively low energy density laser energy is absorbed by the pore walls and the material within the pores, undergoing multiple reflections and scatterings between the pore walls. This increases the energy residence time and range of action within the sacrificial layer, promoting energy transfer to the surrounding area and improving energy utilization efficiency. This allows the sacrificial layer to reach the required energy threshold for peeling more quickly under laser irradiation, achieving efficient peeling while simultaneously reducing laser damage to the polyimide film.

[0076] Furthermore, due to the differences in physicochemical properties between the prepared porous polyamic acid film and the polyimide film, the physical changes of the sacrificial layer during laser irradiation, such as thermal expansion and phase transition due to energy absorption, are asynchronous with those of the adjacent polyimide film layer. This difference leads to stress concentration at the interface. When the stress exceeds the interfacial bonding force, the sacrificial layer separates from the polyimide film, achieving selective peeling and avoiding unnecessary damage to other functional layers, thus ensuring the integrity of the flexible display device's performance. Moreover, under the action of laser energy, the polyamic acid film can undergo a thermal decomposition reaction. During the decomposition process, the chemical structure changes, the intermolecular forces weaken, and the material strength decreases, making it easier to peel off from the multilayer structure. The thermal decomposition products may have low adhesion or volatility, which helps the sacrificial layer detach from the substrate or other layers, further promoting the peeling process and improving the peeling effect and efficiency.

Claims

1. A method for efficient laser exfoliation of polyimide films, characterized in that: A porous polyamic acid film is added between the substrate and the polyimide film as a sacrificial layer before laser cutting and peeling. The specific steps are as follows: (1) Fluorinated diamine monomer, non-fluorinated diamine monomer and fluorinated dianhydride monomer are dissolved in an aprotic solvent to form a precursor solution, and polyamic acid solution is obtained by stirring in a water bath under an inert atmosphere. (2) Coating the surface of a glass substrate with a polyamic acid solution and placing it in a coagulation bath for 2-3 hours results in a porous polyamic acid film, forming a substrate / porous polyamic acid film structure. (3) The precursor liquid used to prepare the polyimide film is coated on the surface of the porous polyamic acid film, annealed, and thermally imidized to obtain the polyimide film, forming a substrate / porous polyamic acid film / polyimide film structure. (4) Place the substrate / porous polyamic acid film / polyimide film structure under a laser and cut and peel the polyimide film off the substrate using laser ablation technology.

2. The method as described in claim 1, characterized in that: In step (1), the molar ratio of fluorinated diamine monomer, non-fluorinated diamine monomer and fluorinated dianhydride monomer is 0.5-0.8 mol: 0.5-0.2 mol: 1 mol, and the solid content of the precursor solution is 12-18 wt%.

3. The method as described in claim 2, characterized in that: In step (1), the fluorinated diamine monomer is 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (TFMB); the non-fluorinated aromatic diamine monomer is 4,4'-diaminodiphenyl ether (oda); the fluorinated diamine monomer is 4,4′-(hexafluoroisopropylidene) bisphthalic anhydride (6FDA); and the aprotic solvent is NMP (N-methylpyrrolidone).

4. A method for efficient laser peeling of polyimide films, characterized in that, Includes the following steps: (1) A precursor solution with a solid content of 12wt% was prepared by dissolving TFMB (fluorinated diamine monomer), ODA (non-fluorinated aromatic diamine monomer), and 6FDA (fluorinated dianhydride monomer) in NMP solvent. The solution was heated to 30°C in a water bath under an inert atmosphere and stirred at 200-250 rpm for 1.5 h. Then it was cooled to room temperature and stirred for another 12 h to obtain a polyamic acid solution. The molar ratio of fluorinated diamine monomer, non-fluorinated diamine monomer, and fluorinated dianhydride monomer was 0.7 mol: 0.3 mol: 1 mol. (2) A polyamic acid solution is spin-coated onto the surface of a glass substrate at a temperature of 40°C and placed in a coagulation bath for 2.5 hours to form a porous polyamic acid film, thereby forming a substrate / porous polyamic acid film structure. The spin-coating speed is 1500 rpm and the spin-coating time is 60 s. The coagulation bath is formed by mixing NMP, sodium dodecyl sulfate and water in a mass ratio of 40 g: 5 g: 60 g. (3) The precursor liquid for preparing the polyimide film is coated on the surface of the porous polyamic acid film and annealed. The polyimide film is obtained by thermal imidization to form a substrate / porous polyamic acid film / polyimide film structure. The annealing process is to cure at 55°C for 50 min, then heat to 115°C for 40 min, heat to 155°C for 40 min, heat to 205°C for 40 min, heat to 265°C for 40 min, and then cool to room temperature to complete the thermal imidization process. (4) The substrate / porous polyamic acid film / polyimide film structure is placed under a laser with a wavelength of 450 nm and a laser energy density of 90 mJ / cm². 2 The laser beam is used for laser cutting and peeling.

Images