A laser processing technique for polyimide film ultra-large taper micropore array

Abstract

The application discloses a kind of polyimide film super large taper micro-hole array laser processing processes, by the sequential coupling of three spiral scanning processing and fixed point pulse processing, process super large taper micro-hole array on polyimide film;Processing steps include: using hexagonal honeycomb distribution to determine hole spacing;According to the requirement of inlet diameter, set three spiral scanning parameters, wherein the outer diameter of the first circle and the second circle is the same and mutually presents 120º rotation offset, the outer diameter of the third circle is less than the former two circles and presents 120º rotation offset with the second circle;According to the thickness of film, determine scanning laser power;According to the requirement of outlet diameter, determine fixed point processing energy and pulse number;Processing once forming;The present application can realize the taper hole processing of 25 μm and 50 μm thickness polyimide film inlet diameter greater than 40 μm, outlet diameter 2 μm~4 μm, outlet aperture error less than 0.5 μm, hole making rate greater than 150 holes / s, hole wall smooth without residue, suitable for batch production of high-end medical mesh type atomizer sheet.

Description

Technical Field

[0001] This invention relates to the field of ultrafast laser polymer material processing technology, specifically to a laser processing technology for an ultra-large taper micropore array of polyimide thin film. Background Technology

[0002] Polyimide (PI) is a heterocyclic polymer containing imide groups (-R-CO-NH-CO-R'-) in its molecule. It possesses excellent high-temperature and low-temperature resistance and an extremely low coefficient of thermal expansion. Simultaneously, PI is chemically stable, almost insoluble in all organic solvents, making it suitable for solvent filtration in the chemical and pharmaceutical industries, and showing broad application prospects in biological and medical fields. For example, high-end mesh-type nebulizers often use PI membranes as the core nebulizer plate substrate material, requiring the fabrication of a high-density, ultra-large tapered micropore array on its surface to achieve the function of atomizing liquid medication. To meet the atomization requirements, it is often necessary to process through-holes with a near-standard tapered shape on the membrane surface. Due to its application in the medical field, smooth pore walls without residue are required. Furthermore, the processed material is relatively thin, typically less than 50 μm. To reduce the size of the atomized droplets, the outlet diameter of the nebulizer plate's tapered orifice often needs to be controlled to below 3 micrometers, resulting in extremely high taper of the processed holes. This places extremely high demands on processing precision, making the fabrication process extremely difficult and challenging to achieve using traditional processing methods. Ultrafast laser processing technology has attracted attention due to its non-contact nature, small heat-affected zone, and high processing precision, making it highly suitable for such processing needs. The original PI laser exhibits two main absorption peaks at 258 nm and 405 nm, with the absorption edge extending to approximately 534 nm. 355 nm, as a common wavelength for ultraviolet lasers, has relatively high photon energy (approximately ~3.5 eV), which can directly excite electrons, breaking chemical bonds in molecules (such as CC, CN, C=O, etc.) to ablate them, leading to photochemical decomposition and minimal heat-affected zone.

[0003] The patent application entitled "A Laser Processing Method and System for Micro-holes in Ultrathin Materials" (Publication No. CN119820150A) pre-groups the array of holes to be processed, considers the heat-affected zone of the laser, and ensures that only one hole appears in the heat-affected zone within one processing cycle, thus obtaining the hole spacing number. Based on the hole spacing number, the holes to be processed are divided into N layers, and the N layers are processed in multiple rounds using a fixed-point impact processing method to reduce the heat effect. Finally, the processing method is used to process a micro-hole array with a diameter of 7 μm ± 1 μm. This patent is suitable for processing straight holes or micro-tapered holes, but the hole shape is uncontrollable and it is difficult to achieve the requirement of smaller hole diameters. A patent application titled "A High-Efficiency Manufacturing Method for Femtosecond Laser Thin Film Micro-holes" (Publication No. CN108326451A) provides three switchable punching modes: motion rotary cutting, galvanometer-based micro-hole punching, and fixed array rotary cutting. The fixed array rotary cutting mode reduces the hole position switching time from 50 ms to below 10 ms by using four sets of galvanometers to cover the width and time-division control of the motorized mirror switching. It also uses a 355 nm ultraviolet laser to break CC and CN bonds through photochemical action for cold processing. This patent has significant advantages in micro-hole processing efficiency, but the equipment structure is complex and costly, and the fixed array method lacks flexibility. A patent application titled "A Femtosecond Laser Conical Hole Processing System" (Publication No. CN213998253U) uses the deflection of a parallel glass plate to control the lateral shift of the laser beam, making the beam direction a controllable cone to achieve conical hole processing. However, this system can only control the deflection direction of the focused beam and is difficult to achieve micro-hole array processing with controllable aperture. Summary of the Invention

[0004] To overcome the shortcomings of the prior art, the present invention aims to propose a laser processing technology for ultra-large tapered micropore arrays of polyimide films. This technology utilizes scanning processing to reduce heat accumulation on the material surface and uses ultraviolet ultrafast laser single-photon energy to directly decompose the chemical bonds of the material for photochemical ablation. This process enables the processing of tapered holes with an inlet diameter greater than 40 μm, an outlet diameter of 2 μm to 4 μm, and an outlet aperture error of less than 0.5 μm on the polyimide film, achieving a hole formation rate of greater than 150 holes / s.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A laser processing technique for an ultra-large tapered micropore array of polyimide thin film includes the following steps: Step 1: Determine the spacing between each hole based on the area and number of holes required for the machining area; the holes are distributed in a hexagonal honeycomb pattern. Step 2: Determine the parameters for galvanometer scanning based on the required diameter of the conical hole inlet. Use a three-turn spiral scanning process to remove the substrate material and form the conical hole. The three-turn spiral consists of multiple semi-circular arcs with offset centers. The outer diameters of the first and second spirals are the same. The second spiral is 120° off-center from the first spiral. The outer diameter of the third spiral is smaller than the first two spirals and is 120° off-center from the second spiral. Step 3: Determine the laser energy for scanning based on the thickness of the polyimide film; Step 4: Determine the fixed-point machining energy and laser pulse number based on the required diameter of the tapered hole exit. After the spiral scanning machining is completed, perform fixed-point pulse machining in situ. Step 5: Processing in one step. Based on the pre-set process parameters, complete the drawing of the scanning path and the setting of processing parameters. At the same time, the coaxial air blowing system introduces high-speed air to remove the smoke and dust generated during processing. The laser power in the processing technology is 0.05 W ~ 0.2 W, the laser repetition frequency is 300 kHz ~ 800 kHz, the laser output wavelength is 355 nm, and the galvanometer scanning speed is 200 mm / s ~ 500 mm / s.

[0006] The hole spacing mentioned in step one is determined according to the following formula: , where [x] is the floor function, r is the radius of the processed circular area, N is the number of holes, and the hole spacing is determined according to the processing requirements.

[0007] In step two, the multiple circular arcs with offset centers in the three-turn spiral have a fixed starting diameter and a fixed pitch. The outer diameter of the spiral is determined by the number of turns, which in turn determines the size of the inlet diameter of the machined tapered hole.

[0008] In step three, when the thickness of the polyimide film to be processed is 25 μm, the scanning laser power is 0.05 W ~ 0.1 W; when the thickness of the polyimide film to be processed is 50 μm, the scanning laser power is 0.1 W ~ 0.2 W.

[0009] In step four, for a 25 μm thick polyimide film, the laser power for point processing is 0.05 W ~ 0.07 W, and the number of pulses is greater than 130; for a 50 μm thick polyimide film, the laser power for point processing is 0.05 W ~ 0.07 W, and the number of pulses is greater than 160.

[0010] The laser processing technology achieves a conical hole inlet diameter greater than 40 μm, an outlet diameter of 2 μm to 4 μm, an outlet hole diameter error of less than 0.5 μm, and a hole formation rate greater than 150 holes / s on the polyimide film.

[0011] The processing system for implementing the laser processing technology includes an ultraviolet picosecond laser, a collimating beam expander, a two-dimensional scanning galvanometer, an F / θ field mirror, and a high-precision, high-flatness nano-ceramic adsorption platform. The laser emitted by the ultraviolet picosecond laser passes sequentially through the collimating beam expander, the two-dimensional scanning galvanometer, and the F / θ field mirror to irradiate the polyimide film adsorbed on the high-precision, high-flatness nano-ceramic adsorption platform.

[0012] The two-dimensional scanning galvanometer works in conjunction with the F / θ field mirror.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention achieves independent and precise control of the inlet and outlet diameters of a conical hole by sequentially coupling three-turn spiral scanning machining with fixed-point pulse machining; the number of spiral turns and the outer diameter determine the inlet diameter, while the fixed-point pulse machining energy determines the outlet diameter; the hole shape and diameter are controllable and can achieve smaller hole diameters.

[0014] 2. This invention employs a hexagonal honeycomb hole distribution design, maximizing the average distance between holes at the same hole density, effectively reducing the heat accumulation effect of laser processing; combined with the high-speed scanning of the two-dimensional galvanometer system, the hole-making rate can reach over 150 holes / s. The processing system of this invention has a simple structure, balancing processing efficiency and system flexibility, making it suitable for industrial mass production.

[0015] 3. This invention only requires parameter setting to complete the scanning path drawing and processing parameter configuration, achieving one-time processing without the need for layering or multiple processing rounds. Compared to the cumbersome process of pre-grouping and multi-layer processing of hole rows in CN119820150A, and the complex system of multiple sets of galvanometers covering the width and time-division control of electric reflector switching in CN108326451A, this invention significantly simplifies the process flow, significantly reduces equipment costs, and significantly improves operational convenience. After processing, the hole walls directly meet the usage requirements, eliminating the need for subsequent cleaning or chemical etching steps. Attached Figure Description

[0016] Figure 1 This is a flowchart of the processing technology of the present invention.

[0017] Figure 2 This is a schematic diagram of the processing system and process principle required for the processing technology of this invention.

[0018] Figure 3 This is a schematic diagram showing the specific structural parameters of the three-turn spiral process of the present invention. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0020] Reference Figure 1 A laser processing technology for an ultra-large tapered micropore array of polyimide thin film includes the following steps: S1. Determine the spacing between each hole based on the required area and number of holes to be processed. When a laser acts on the surface of a thin film material, it causes the temperature of the affected area to rise; ultrafast laser processing is characterized by cold processing. To avoid heat accumulation due to laser effects, given the required processing area and number of holes, the distance between holes must be maximized. For the same hole density, a hexagonal honeycomb distribution results in the largest average hole spacing. Therefore, the hole spacing is set as follows: [x] is the floor function, r is the radius of the processed circular area, and N is the number of holes. The hole spacing is determined according to the processing requirements. S2, determine the scanning path parameters based on the required diameter of the conical aperture inlet; the main purpose is to determine the number of spiral turns. (Using...) Figure 2 The three-spiral scanning machining method shown is used to remove the base material and form the conical hole. The spiral is composed of multiple semi-circular arcs with offset centers. The specific parameters of the spiral are as follows: Figure 3 As shown, the spiral's initial diameter *di*, pitch *p*, and outer diameter *de* are all considered. The outer diameter can also be determined by the number of spiral coils *n*. The process involves sequentially scanning with spirals that are 120° apart. The first spiral 10 and the second spiral 11 have the same outer diameter *de*, resulting in an asymmetrical hole shape after the first spiral. The second spiral 11 rotates 120° relative to the first spiral 10, removing some of the remaining material from the asymmetrical portion after the first spiral. The first two spirals remove most of the material from the hole, initially forming the hole shape. The third spiral 12 has a smaller outer diameter *de* than the first two spirals, primarily removing material from the center of the hole. It rotates 120° relative to the second spiral, forming a more standard conical hole. When the spiral's pitch and initial diameter are fixed, the outer diameter of the spiral scan, i.e., the number of spiral coils, determines the inlet diameter of the processed conical hole. The actual inlet diameter, considering the spot size and heat accumulation, will be larger than the spiral's outer diameter. Further verification is needed based on specific requirements.

[0021] S3. The laser energy required for scanning processing is determined based on the PI film thickness. Different film thicknesses require different laser energies to remove as much material as possible during the scanning phase without penetrating the material. 25 μm and 50 μm thicknesses are the most common. Due to the high UV absorption rate of polyimide, even slight changes in laser energy result in significant differences in ablation intensity. When processing a 25 μm thick PI film, the laser power is 0.05 W ~ 0.1 W. When processing a 50 μm thick PI film, the laser power is 0.1 W ~ 0.2 W.

[0022] S4. Determine the spot processing energy and laser pulse number based on the required taper hole exit diameter. The method for machining the hole is a spiral scanning sequence coupled with 13 spot pulses. After the triple spiral scanning is completed, set the in-situ spot impact processing laser energy according to the specific taper hole exit diameter requirement. For a 25 μm thick PI film, the spot processing laser power is 0.05 W, 0.06 W, or 0.07 W, with a pulse number greater than 130. For a 50 μm thick PI film, the spot processing laser power is 0.05 W, 0.06 W, or 0.07 W, with a pulse number greater than 160. S5, one-time forming. Based on the pre-set process parameters, the scanning path is drawn, and the entire process is performed. At the same time, the coaxial air blowing system introduces high-speed air at 0.8 MPa to remove the dust generated during processing.

[0023] In step five, the laser power is 0.05 W to 0.2 W; the laser pulse repetition frequency is 300 kHz to 800 kHz; the laser output wavelength is 355 nm; and the galvanometer scanning speed is 200 mm / s to 500 mm / s.

[0024] The machining system that implements this machining process is as follows: Figure 2 As shown, it includes an ultraviolet picosecond ultrafast laser 1. The laser beam generated by the ultraviolet picosecond ultrafast laser 1 is collimated by a collimating and expanding lens 2, and then enters a two-dimensional scanning galvanometer 5 through a first reflecting mirror 3 and a second reflecting mirror 4. The two-dimensional scanning galvanometer 5 works in conjunction with an F / θ field mirror 6. A coaxial air blowing system 7 outputs high-speed compressed air, and a polyimide film 8 is adsorbed onto a high-precision, high-flatness nano-ceramic adsorption platform 9.

[0025] Example 1 uses a 25 μm thick polyimide film to process an ultra-large tapered micropore array with an inlet diameter of 50 μm and an outlet diameter of 2.5 μm. The pore array is distributed in a hexagonal honeycomb pattern, and the pore spacing is set to 70 μm according to the formula. The processing area is a circular area with a diameter of 3 mm, and the total number of pores is about 1700. The specific process parameters are as follows: The ultraviolet picosecond laser has an output wavelength of 355 nm and a repetition rate of 400 kHz. Helical scanning stage: laser power 0.05 W, galvanometer scanning speed 250 mm / s; parameters of the three-turn helix: first turn starting diameter 12 μm, number of turns 3; second turn starting diameter 12 μm (rotated 120º relative to the first turn), number of turns 3; third turn starting diameter 12 μm (rotated 120º relative to the second turn), number of turns 1; pitch is 2 μm for all turns. Point-to-point impact stage: laser power 0.05W, pulse number 220, in-situ point-to-point processing; The coaxial air blowing system is supplied with 0.8 MPa compressed air.

[0026] After processing, the pore morphology was measured using a scanning electron microscope (SEM). The results showed that the average inlet diameter was 49.4 μm, the average outlet diameter was 2.4 μm, the outlet pore diameter error was ≤ ±0.3 μm, and the pore walls were smooth with no melt or residue, which fully met the requirements for use of high-end medical mesh nebulizer plates.

[0027] Example 2 modifies the parameters of Example 1 as follows: ultraviolet picosecond laser repetition frequency 300 kHz; helical scanning stage: laser power 0.1 W, galvanometer scanning speed 200 mm / s; fixed-point impact stage: laser power 0.06 W, pulse number 180; the effect of this example is similar to that of Example 1, but the inlet aperture is larger, at 54 μm.

[0028] Example 3: The parameters of Example 1 are changed as follows: ultraviolet picosecond laser repetition frequency 800 kHz; helical scanning stage: laser power 0.07W, galvanometer scanning speed 500 mm / s; fixed-point impact stage: laser power 0.07W; the effect of this example is similar to that of Example 2.

[0029] Example 4 uses a 50 μm thick polyimide film. The target processing aperture is an ultra-large tapered micropore array with an inlet diameter of 50 μm and an outlet diameter of 3 μm. The pore array is also hexagonal honeycomb distributed, the pore spacing is set to 70 μm, the processing area is a circular area with a diameter of 3 mm, and the total number of pores is about 1700. The specific process parameters are as follows: The ultraviolet picosecond laser has an output wavelength of 355 nm and a repetition rate of 400 kHz. Helical scanning stage: laser power 0.1 W, galvanometer scanning speed 200 mm / s, spot diameter 4.5 μm. Three-turn helix parameters: first turn starting diameter 10 μm, number of turns 3; second turn starting diameter 10 μm (rotated 120º relative to the first turn), number of turns 3; third turn starting diameter 10 μm (rotated 120º relative to the second turn), number of turns 1; pitch 2 μm for all turns. Point-to-point impact stage: laser power 0.07W, pulse count 300, in-situ point-to-point processing; The coaxial air blowing system is supplied with 0.8 MPa compressed air; After processing, the pore morphology was measured using a scanning electron microscope (SEM). The results showed that the average inlet diameter was 50.2 μm, the average outlet diameter was 3 μm, the outlet pore diameter error was ≤ ± 0.4 μm, and the pore walls were smooth with no melt or residue, which fully met the requirements for use of high-end medical mesh nebulizer plates.

[0030] Example 5: The parameters of Example 4 were changed as follows: ultraviolet picosecond laser repetition frequency 300 kHz; helical scanning stage: laser power 0.2 W, galvanometer scanning speed 400 mm / s; fixed-point impact stage: laser power 0.07 W; the effect of this example is similar to that of Example 4, with an average inlet diameter of 53.2 μm.

[0031] Example 6: The parameters of Example 4 are changed as follows: ultraviolet picosecond laser repetition frequency 800 kHz; helical scanning stage: laser power 0.15 W, galvanometer scanning speed 500 mm / s; fixed-point impact stage: laser power 0.05 W; the effect of this example is similar to that of Example 4.

[0032] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A laser processing technology for an ultra-large taper micropore array of polyimide thin film, comprising the following steps: Step 1: Determine the spacing between each hole based on the area and number of holes required for the area to be machined; The holes are distributed in a hexagonal honeycomb pattern. Step 2: Determine the parameters for galvanometer scanning based on the required diameter of the conical hole inlet. Use a three-turn spiral scanning process to remove the substrate material and form the conical hole. The three-turn spiral consists of multiple semi-circular arcs with offset centers. The outer diameters of the first and second spirals are the same. The second spiral is 120° off-center from the first spiral. The outer diameter of the third spiral is smaller than the first two spirals and is 120° off-center from the second spiral. Step 3: Determine the laser energy for scanning based on the thickness of the polyimide film; Step 4: Determine the fixed-point machining energy and laser pulse number based on the required diameter of the tapered hole exit. After the spiral scanning machining is completed, perform fixed-point pulse machining in situ. Step 5: Processing in one step. Based on the pre-set process parameters, complete the drawing of the scanning path and the setting of processing parameters. At the same time, the coaxial air blowing system introduces high-speed air to remove the smoke and dust generated during processing. The laser power in the aforementioned processing technology is 0.05 W ~ 0.2 W, the laser repetition frequency is 300 kHz ~ 800 kHz, the laser output wavelength is 355 nm, and the galvanometer scanning speed is 200 mm / s ~ 500 mm / s.

2. The laser processing technology according to claim 1, characterized in that, The hole spacing mentioned in step one is determined according to the following formula: , where [x] is the floor function, r is the radius of the processed circular area, N is the number of holes, and the hole spacing is determined according to the processing requirements.

3. The laser processing technology according to claim 1, characterized in that, In step two, the multiple circular arcs with offset centers in the three-turn spiral have a fixed starting diameter and a fixed pitch. The outer diameter of the spiral is determined by the number of turns, which in turn determines the size of the inlet diameter of the machined tapered hole.

4. The laser processing technology according to claim 1, characterized in that, In step three, when the thickness of the polyimide film to be processed is 25 μm, the scanning laser power is 0.05 W ~ 0.1 W; when the thickness of the polyimide film to be processed is 50 μm, the scanning laser power is 0.1 W ~ 0.2 W.

5. The laser processing technology according to claim 1, characterized in that, In step four, for a 25 μm thick polyimide film, the laser power for point processing is 0.05 W ~ 0.07 W, and the number of pulses is greater than 130; for a 50 μm thick polyimide film, the laser power for point processing is 0.05 W ~ 0.07 W, and the number of pulses is greater than 160.

6. The laser processing technology according to claim 1, characterized in that, The processing technology achieves a conical hole inlet diameter greater than 40 μm, an outlet diameter of 2 μm to 4 μm, an outlet hole diameter error of less than 0.5 μm, and a hole formation rate greater than 150 holes / s on the polyimide film.

7. A processing system implementing the laser processing technology of claim 1, characterized in that: It includes an ultraviolet picosecond laser, a collimating beam expander, a two-dimensional scanning galvanometer, an F / θ field mirror, and a high-precision, high-flatness nano-ceramic adsorption platform. The laser emitted by the ultraviolet picosecond laser passes sequentially through the collimating beam expander, the two-dimensional scanning galvanometer, and the F / θ field mirror to irradiate the polyimide film adsorbed on the high-precision, high-flatness nano-ceramic adsorption platform.

8. The processing system according to claim 7, characterized in that: The two-dimensional scanning galvanometer works in conjunction with the F / θ field mirror.

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