Preparation method of tempered infrared cut-off filter for module

Abstract

The invention relates to the technical field of optical filters, and particularly discloses a preparation method of a tempered infrared cut-off optical filter for a module, comprising the following steps: S1, pretreatment of a glass substrate: cutting, cleaning and drying the glass substrate to obtain an optical filter primary product; s2, chemical toughening treatment: carrying out chemical toughening treatment in an annealing furnace; s3, post-cleaning and inspection: cleaning and drying the optical filter, and detecting the performance of the optical filter; s4, optical coating: coating an infrared cut-off interference film system on the surface of the optical filter; and S5, assembling a finished product. According to the invention, a compact pressure stress layer is formed on the surface of the optical filter through a chemical tempering process; when the optical filter is subjected to an external force, the compressive stress layer can effectively counteract a part of tensile stress, so that the bending strength, the impact strength and the surface microhardness of the optical filter are greatly improved; the chemical tempering process does not change the optical intrinsic characteristics of the base material; and the influence on the original key optical properties such as transmittance, steepness of cut-off and the like is extremely small.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of optical filters, and in particular to a preparation method of a tempered infrared cut-off filter for a module. BACKGROUND

[0002] The infrared cut-off filter is a key optical element in a camera module, which filters out infrared light to make the color restoration of the imaging sensor more realistic. With the increasing demand for imaging quality in the fields of smart phones, autonomous driving, security monitoring, etc., the size of the main sensor of the camera module is increasing. Correspondingly, the size of the infrared cut-off filter used must also increase.

[0003] However, while the size is increasing, in order to meet the demand for thinness of the module, the thickness of the infrared cut-off filter does not increase, but instead develops from the traditional standard thickness of 0.21mm to 0.11mm or even thinner specifications. This trend of being large and thin significantly reduces the mechanical strength of the filter, making it prone to breakage or micro-cracks due to stress or slight impact during subsequent module assembly, transportation and use. The breakage of the filter will directly cause the failure of the entire camera module, seriously affecting the production yield, reliability and service life of the module.

[0004] Currently, the industry generally adopts passive protection measures such as optimizing jig design and improving dispensing process to address this problem, but these methods do not fundamentally improve the strength of the material itself.

[0005] For example, Chinese Patent CN104977638B discloses a preparation method of an infrared cut-off filter, which includes the steps of cutting, shaping, slicing, chamfering, grinding, double-sided chemical polishing and coating. The infrared cut-off filter produced by this patent has high quality, low scrap rate and high production efficiency.

[0006] However, this patent cannot solve the problem of breakage or micro-cracks due to stress or slight impact, and the production yield, reliability and service life are not good. SUMMARY

[0007] The present application aims to provide a preparation method of a tempered infrared cut-off filter for a module to solve the problems raised in the background art.

[0008] To achieve the above-mentioned purpose, the present application provides the following technical solution: A preparation method of a tempered infrared cut-off filter for a module, comprising the following steps: S1, glass substrate pretreatment: clean and dry the infrared cut-off filter glass substrate cut to the target size to obtain a preliminary product of the filter with a predetermined size; S2, chemical toughening treatment: the filter initial product is placed in a bearing fixture to ensure it is in a flat, stress-free state, and then sent to an annealing furnace for chemical toughening treatment; S3, post-cleaning and inspection: the filter after chemical toughening treatment is taken out, ultrasonic cleaning and drying are performed, and then the stress distribution uniformity is detected by a polarized stress instrument, and the breaking strength is sampled and tested by a strength tester; S4, optical coating: on the surface of the filter after toughening and inspection, an infrared cutoff interference film system is coated by vacuum sputtering or electron beam evaporation; S5, finished product assembly: the coated and toughened infrared cutoff filter is assembled into a module support according to its optical direction for subsequent module packaging.

[0009] As a further scheme of the application: in the S2 step, the chemical toughening treatment method is one of high-temperature crystallization toughening method or low-temperature high-pressure toughening method.

[0010] As a further scheme of the application: the specific steps of the high-temperature crystallization toughening method are as follows: The filter initial product is immersed in a mixed salt molten liquid containing , and treated at a temperature region between the softening point (such as 500-700℃) and the transition point (1000-1200℃) of the filter initial product; the or in the filter initial product exchanges ions with the in the mixed salt molten liquid for 2-6h, forming an ion exchange layer rich in on the surface of the filter initial product; then cooled to room temperature at a rate not greater than 5℃ / min, forming a double-layer exchange layer with lithium petalite (such as ) on the outside of the surface layer and lithium metasilicate microcrystallization (such as ) on the inside of the surface layer; For example, the composition of the filter initial product is selected as follows: .

[0011] As a further scheme of the application: the specific steps of the low-temperature high-pressure toughening method are as follows: The filter initial product is immersed in an alkali ion salt molten liquid (such as ) containing alkali ions with a larger radius than the original alkali ions in the glass (such as ) at a temperature not higher than the softening point of the glass (such as 500-700℃) and not lower than 500℃; at the same time, an inert gas is applied to exert a static pressure of 1.0-5.0MPa, and treated for 4-10h, so that the alkali ions on the surface of the filter initial product exchange with the alkali ions in the molten salt, and after cooling, a compressive stress layer is formed due to the volume difference of the ions.

[0012] As a further scheme of the present application: in the high-temperature crystallization tempering method, the mixed salt molten liquid is composed of a molten liquid, a molten liquid and a molten liquid.

[0013] As a further scheme of the present application: in the low-temperature high-pressure tempering method, the alkali ion salt molten liquid is one of a molten liquid or a molten liquid.

[0014] As a further scheme of the present application: in the low-temperature high-pressure tempering method, the applied external pressure is negatively correlated with the thickness of the filter raw product, and the relationship formula is as follows: wherein, P is the pressure, H is the thickness of the filter raw product, K is the pressure coefficient, and the value range is 0.05-0.2 MPa·mm; For example, for a white filter raw product that has been precisely cut into 12 mm x 10 mm, with a thickness of 0.11 mm; 0.15 MPa·mm is taken; then the minimum pressure to be applied is 0.15 MPa.

[0015] As a further scheme of the present application: in the S4 step, the infrared cutoff interference film system is plated by vacuum sputtering or electron beam evaporation, and the infrared cutoff interference film system is formed by alternately stacking a high-refractive-index material layer and a low-refractive-index material layer; wherein the high-refractive-index material is or , and the low-refractive-index material is .

[0016] Compared with the prior art, the present application has the following beneficial effects: The present application forms a dense compressive stress layer on the surface of the filter through the chemical tempering process; when the filter is subjected to external force, the compressive stress layer can effectively offset part of the tensile stress, thereby greatly improving the bending strength, impact strength and surface microhardness of the filter; and the chemical tempering process does not change the optical intrinsic properties of the base material; it has little effect on the key optical performance such as the original transmittance and cutoff steepness of the infrared cutoff filter, and can meet the imaging requirements of the module; at the same time, the strengthened filter significantly improves the reliability of the camera module under harsh conditions such as falling and vibration, and greatly improves the product yield and service life. DETAILED DESCRIPTION

[0017] The application will be further described in connection with specific examples. The scope of the application is not limited to the examples. Example 1

[0018] In the embodiment of the application, an aluminosilicate glass substrate (composition: ) with a thickness of 0.11 mm is selected and cut into a desired size; The initial filter product is placed in a quartz fixture and immersed in a mixed molten solution of , and at 800°C for 4 h.

[0019] After being taken out, it is slowly cooled to room temperature at a rate of 4°C / min; after being washed and inspected, an infrared cutoff film composed of and is alternately plated on the surface thereof by vacuum sputtering. Example 2

[0020] In the embodiment of the application, an aluminosilicate glass substrate (composition: ) with a thickness of 0.21 mm is selected; The initial filter product is placed in a quartz fixture and immersed in a mixed molten solution of , and at 900°C for 3 h.

[0021] After being taken out, it is slowly cooled to room temperature at a rate of 4°C / min; after being washed and inspected, an infrared cutoff film composed of and is alternately plated on the surface thereof by vacuum sputtering. Example 3

[0022] In the embodiment of the application, an aluminosilicate glass substrate (composition: ) with a thickness of 0.11 mm is selected and cut into a desired size; The initial filter product is placed in a fixture in an autoclave and immersed in a molten solution of at 550°C, a nitrogen pressure of 1.5 MPa is applied, and the product is kept for 8 h; After being taken out, it is washed and inspected, and an infrared cutoff film composed of and is alternately plated on the surface thereof by vacuum sputtering. Example 4

[0023] In the embodiment of the application, an aluminosilicate glass substrate (composition: ) with a thickness of 0.21 mm is selected and cut into a desired size; The initial filter product is placed in a fixture in an autoclave and immersed in a molten solution of In the molten liquid, nitrogen pressure of 1.5 MPa is applied for 6 h; After the treatment, the glass substrate is taken out, washed and inspected, and then a layer of metal film is deposited on the surface of the glass substrate by vacuum sputtering and to form an infrared cut-off film.

[0024] In order to better illustrate the technical effects of the present application, the following examples are provided for illustration: I. Select the same batch of blue glass substrates of two specifications (8 mm x 8 mm x 0.21 mm and 8 mm x 8 mm x 0.11 mm), and divide them into six groups after cutting for treatment; II. Control group 1 and control group 2: prepared by the method disclosed in Comparative Document 1 (Preparation method of infrared cut-off filter, CN104977638B); without any toughening treatment, representing the most common production process at present; wherein the glass substrate in control group 1 has a thickness of 0.11 mm, and the glass substrate in control group 2 has a thickness of 0.21 mm, Experimental groups 1-4 are prepared by the methods of Examples 1-4 of the present application, respectively.

[0025] III. The surface compressive stress (test method / standard: surface stress meter), compressive stress depth (test method / standard: surface stress meter), Vickers hardness (test method / standard: micro Vickers hardness tester), fracture load (test method / standard: four-point bending test), module drop test yield (test method / standard: 1.5 m height, cement floor), and key topographic features (test method / standard: white light interferometer) of each group of samples are tested, respectively; and the results of control group 1, experimental group 1 and experimental group 3 are recorded in Table 1 below; the results of control group 2, experimental group 2 and experimental group 4 are recorded in Table 2 below.

[0026] Table 1 No. Performance Index Control Group 1 Experimental Group 1 Experimental Group 2 1 Surface Compressive Stress < 50 MPa > 700 MPa 450 ~ 500 MPa 2 Compressive Stress Layer Depth Not Applicable 20 ~ 30 μm 40 ~ 50 μm 3 Vickers Hardness 550 HV 690 HV 630 HV 4 Breaking Load Reference Value (100%) 310% 280% 5 Module Drop Test Yield 85.0% 99.5% 98.0% 6 Key Morphological Features No Change Slight Warping (< 8 μm) Minimal Deformation (< 3 μm) Table 2 No. Performance Index Control Group 2 Experimental Group 2 Experimental Group 4 1 Surface Compressive Stress < 50 MPa > 750 MPa 480 ~ 520 MPa 2 Compressive Stress Layer Depth Not Applicable 15 ~ 20 μm 35 ~ 45 μm 3 Vickers Hardness 540 HV 675 HV 620 HV 4 Breaking Load Reference Value (100%) 280% 320% 5 Module Drop Test Yield 60.0% 97.5% 99.00% 6 Key Morphological Features No Change Slight Warping (< 10 μm) Minimal Deformation (< 5 μm) From Table 1 and Table 2 above, it can be concluded that: 1) In terms of fundamental strengthening indicators (surface compressive stress and depth): Comparative Document 1 preparation method (control groups 1-2): the infrared cut-off filter prepared almost has no surface compressive stress, and the glass substrate is in a fragile original state.

[0027] The preparation method (experimental groups 1-4) of the present application: two schemes (high-temperature crystallization tempering method and low-temperature high-pressure tempering method) are used to prepare infrared cut-off filters; both of them successfully introduce huge surface compressive stress; among them, the high-temperature crystallization tempering method obtains an extremely high surface stress of more than 700 MPa through crystallization, which is difficult to achieve by traditional physical or ordinary chemical tempering; although the surface stress of the low-temperature high-pressure tempering method is moderate, the depth of the compressive stress layer is greater; the deeper compressive stress layer can more effectively prevent the surface micro-cracks from expanding to the inside, and the impact resistance is particularly outstanding.

[0028] 2) On the mechanical properties of the material (hardness and breaking load): Vickers hardness: the hardness of experimental groups 1-4 is greatly improved compared with control groups 1-2; this indicates that the tempered filter surface is more resistant to scratching and is not easy to be scratched during assembly and cleaning, thereby improving the yield and service life.

[0029] Breaking load: the breaking load of experimental groups 1-4 is significantly improved compared with control groups 1-2; this means that the filter can withstand several times the previous bending stress without breaking. This directly solves the problem of breaking of large-size thin glass during dispensing and assembly due to stress.

[0030] 3) On the terminal reliability (module drop test yield): The module drop yield of control groups 1-2 is low, which means that a part of the products will fail in the test due to the breakage of the filter; after using the scheme of the present application, the yield is greatly improved; this directly proves that the present application can greatly improve the overall reliability and durability of the camera module, thereby bringing great value to the customers.

[0031] 4) On the process applicability (key topographic features): the high-temperature crystallization tempering method has slight warping due to high-temperature treatment, which may need to be corrected later in some applications with extremely high requirements for flatness; the low-temperature high-pressure tempering method perfectly maintains the geometric shape of the glass through the low-temperature high-pressure process, and the deformation control is small, and it is particularly suitable for ultra-thin filters with extremely high requirements for dimensional stability.

[0032] In summary, the two chemical tempering schemes provided by the present application, from micro (surface stress, hardness) to macro (breaking load), from laboratory tests (four-point bending) to practical applications (module drop), all show significant and quantitative advantages over traditional methods. For applications that pursue extreme strength, the high-temperature crystallization tempering method is the first choice, and its strength indicators are the most outstanding. For applications that pursue extremely high reliability, zero deformation and are suitable for ultra-thin specifications, the low-temperature high-pressure tempering method has irreplaceable advantages.

[0033] The above merely describes preferred specific embodiments of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art, according to the technical solution and inventive concept of the present application, makes equivalent replacement or change within the technical range disclosed by the present application, which should be covered within the protection scope of the present application.

Claims

1. A method for preparing a tempered infrared cut-off filter for a module, characterized in that, Includes the following steps: S1. Pretreatment of glass substrate: The infrared cut-off filter glass substrate cut to the target size is cleaned and dried to obtain the initial filter product of the predetermined size. S2. Chemical tempering treatment: Place the initial filter product into the support fixture to ensure that it is flat and stress-free, and then send it into the annealing furnace for chemical tempering treatment. S3. Post-cleaning and inspection: The chemically tempered filter is taken out, ultrasonically cleaned and dried, and then its stress distribution uniformity is detected by a polarizing stress meter, and its breaking strength is sampled and inspected by a strength tester. S4. Optical Coating: An infrared cutoff interference film is deposited on the surface of a tempered and inspected filter by vacuum sputtering or electron beam evaporation. S5. Finished Product Assembly: The coated tempered infrared cut-off filter is assembled into the module bracket according to its optical direction for subsequent module packaging.

2. The method for preparing a tempered infrared cut-off filter for a module according to claim 1, characterized in that, In step S2, the chemical tempering treatment method is either high-temperature crystallization tempering or low-temperature high-pressure tempering.

3. The method for preparing a tempered infrared cut-off filter for a module according to claim 2, characterized in that, The specific steps of the high-temperature crystallization tempering method are as follows: Immerse the initial filter sample in a solution containing... In a molten mixture of mixed salts, the primary filter sample is treated within a temperature range between its softening and transition points; this process causes the primary filter sample to... or With mixed salt melt Ion exchange is performed for 2–6 hours, forming a rich ion exchange layer on the surface of the initial filter. An ion exchange layer; then cooled to room temperature at a rate not exceeding 5℃ / min, forming an outer surface layer. Lithium nepheline has a double-layer exchange layer of microcrystalline lithium metasilicate on the inner side of its surface.

4. The method for preparing a tempered infrared cut-off filter for a module according to claim 2, characterized in that, The specific steps of the low-temperature high-pressure tempering method are as follows: At a temperature not higher than the glass softening point and not lower than 500°C, the initial filter sample is immersed in a molten alkali salt containing alkali ions with radii larger than the original alkali ions in the glass; simultaneously, an inert gas is passed through to apply a static pressure of 1.0–5.0 MPa, and the sample is treated for 4–10 hours, so that the alkali ions on the surface of the initial filter sample exchange with the alkali ions in the molten salt, and after cooling, a compressive stress layer is formed due to the volume difference of the ions.

5. The method for preparing a tempered infrared cut-off filter for a module according to claim 2, characterized in that, In the high-temperature crystallization tempering method, the mixed salt molten liquid is Molten liquid, Molten liquid and Composition of molten liquid mixture.

6. The method for preparing a tempered infrared cut-off filter for a module according to claim 2, characterized in that, In the aforementioned low-temperature, high-pressure tempering method, the alkali ion salt molten liquid is... Molten liquid or One of the components of a molten liquid.

7. The method for preparing a tempered infrared cut-off filter for a module according to claim 3, characterized in that, In the aforementioned low-temperature high-pressure tempering method, the applied external pressure is negatively correlated with the thickness of the initial filter product, and the relationship formula is as follows: ,in, For pressure, The initial thickness of the filter. This is the pressure coefficient.

8. The method for preparing a tempered infrared cut-off filter for a module according to claim 1, characterized in that, In step S4, the infrared cutoff interference film is deposited by vacuum sputtering or electron beam evaporation, and the infrared cutoff interference film is composed of alternating layers of high-refractive-index material and low-refractive-index material; wherein, the high-refractive-index material is... or Low refractive index materials are .