Method for preparing high-voltage leak holes by drilling holes in tungsten foil using femtosecond laser and combining it with PDMS

Abstract

This invention discloses a method for producing a high-voltage leak hole by drilling holes in tungsten foil using a femtosecond laser and combining it with PDMS. This method, which falls within the field of standard leak holes, involves first drilling holes in the tungsten foil using a femtosecond laser. Acetone, acetic acid, and isopropyl alcohol are then used to remove oxides and other contaminants from the surface of the foil, resulting in a clean tungsten foil. A PDMS polymer layer is then applied to the tungsten foil to produce a high-voltage leak hole made by combining PDMS and tungsten foil. The resulting leak hole offers precise and controllable conductance, a low background leak rate, and easy replacement of the PDMS. It also possesses a certain pressure-bearing capacity, enabling a more precisely controlled leak rate over a wider pressure range.

Description

Technical Field

[0001] The invention relates to a standard leak hole and a manufacturing method thereof, in particular to a method for preparing a high-voltage leak hole by drilling a hole on a tungsten foil with a femtosecond laser and combining the hole with PDMS. Background Art

[0002] A standard leak is a device that can generate a known gas flow rate or gas molecule flux. It is widely used in vacuum technology, vacuum measurement, vacuum leak detection and other fields. Currently, the commonly used standard leaks are mainly capillary, microtube, thin film and micro-electromechanical system (MEMS) types. According to the gas passage mechanism, it can be divided into permeability standard leaks and channel-type standard leaks. A permeability standard leak refers to a leak component that uses the permeation phenomenon of gas in solid materials to generate a constant gas flow rate. It is usually made of materials such as quartz and Teflon. It has the advantages of high manufacturing precision, controllable size, and not easy to clog. A channel-type standard leak refers to a leak component that uses the flow of gas in a tiny channel to generate a constant gas flow rate. It is usually made of materials such as glass and metal. It has the advantages of simple structure, clear flow state, and stable leakage rate.

[0003] However, these standard leaks all have drawbacks. Capillary and microtube standard leaks are prone to clogging and rupture, membrane standard leaks have high background leak rates and are difficult to precisely control conductance, and MEMS standard leaks are complex and expensive to manufacture. Current channel-type standard leaks suffer from low manufacturing precision, uncontrollable dimensions, and susceptibility to clogging. Permeation-type standard leaks also suffer from complex structures, unclear flow patterns, and unstable leak rates. Summary of the Invention

[0004] The present invention aims to overcome the shortcomings of the above-mentioned prior art and provide a method for preparing a high-voltage leak hole by using a femtosecond laser to punch a hole in a tungsten foil and combining it with PDMS, so as to obtain a more accurate and controllable leak rate and improve the pressure bearing capacity of the leak hole.

[0005] The present invention adopts the following technical solutions to achieve the purpose of the invention:

[0006] The method of the present invention for preparing a high-voltage leak hole by drilling a hole in a tungsten foil using a femtosecond laser and combining the hole with PDMS comprises the following process steps:

[0007] Step 1: Clean the surface of the tungsten foil by first wiping it with acetone and then blowing it with dry nitrogen to obtain a clean tungsten foil; then use a femtosecond laser to punch holes in the tungsten foil to form a circular hole array structure on the surface of the tungsten foil;

[0008] Step 2: using acetone, acetic acid, and isopropyl alcohol (IPA) to remove oxides and other contaminants on the surface of the tungsten foil to obtain a perforated tungsten foil with a clean surface;

[0009] Step 3: Lay the PDMS polymer layer onto the tungsten foil with the array of circular holes, heat it on a hot plate at 100°C, and finally purge it with a clean dry nitrogen flow to obtain a new high-pressure resistant leak hole made of PDMS and tungsten foil.

[0010] The method of the present invention for preparing a high-voltage leak hole by drilling a hole in tungsten foil using a femtosecond laser and combining it with PDMS is also characterized in that: in the step 1, the tungsten foil used is a circular metal foil with a thickness of 1 mm and a diameter of 13 mm.

[0011] The method of the present invention for preparing a high-voltage leak hole by drilling holes in tungsten foil using a femtosecond laser and combining it with PDMS is also characterized in that: in step 1, the circular hole array is composed of 25 circular holes with a diameter of 10 μm.

[0012] The method of the present invention for preparing a high-voltage leak hole by drilling holes in tungsten foil using a femtosecond laser and combining it with PDMS is also characterized in that: in the step 2, the diameter of the 25 circular holes in the surface-cleaned punched tungsten foil is 10 μm, distributed in a 5×5 array, and each circular hole is spaced 250 μm apart.

[0013] The method of the present invention for preparing a high-voltage leak hole by drilling a hole in a tungsten foil using a femtosecond laser and combining it with PDMS is also characterized in that: in the step 3, the thickness of the PDMS polymer layer is 20 μm.

[0014] PDMS (polydimethylsiloxane) is a commonly used polymer material with excellent comprehensive properties, such as high permeability, low wettability, good thermal stability and mechanical strength. It has great application value in the vacuum field. Its good mechanical strength enables it to withstand large pressure differences, making it an ideal material for making high-pressure standard leaks. Compared with existing technologies, the present invention has the following beneficial effects:

[0015] 1. By adjusting the parameters of femtosecond laser drilling, the present invention can obtain perforated tungsten foils with different pore diameters and different numbers of circular holes, thereby changing the conductance value and obtaining high-voltage standard leaks with different conductance values;

[0016] 2. The present invention can obtain high-pressure standard leaks with different conductance values by adjusting the thickness of the PDMS layer used;

[0017] 3. The present invention uses PDMS as the standard leak material, which has good mechanical strength and flexibility and can withstand large pressure differences without easily breaking or deforming. The combination of perforated tungsten foil can obtain a larger pressure range. The permeability of PDMS changes little with pressure, which can ensure that the conductance of the standard leak is relatively constant.

[0018] 4. The present invention uses a femtosecond laser to punch holes in tungsten foil. The femtosecond laser pulse time is extremely short, which can reduce the oxidation, melting, cracking and other phenomena of the material, and obtain a high-precision small hole array to meet the processing requirements of micro-nano scale;

[0019] 5. The PDMS polymer layer of the present invention is easy to manufacture and obtain, and its thickness is easy to control. When the thickness of the PDMS polymer layer, the number of holes punched in the tungsten foil, and the hole diameter are known, the leak rate value can be directly calculated using the classical theory of vacuum science and independently calibrated, thereby solving the problem in the prior art that the leak rate of the standard leak hole must be calibrated with the help of other equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a schematic diagram of the process flow for obtaining a perforated tungsten foil covered with PDMS;

[0021] Figure 2a and Figure 2b The front and side views of the perforated tungsten foil covered with PDMS are shown, respectively;

[0022] Figure 3 This is a schematic diagram of a system for measuring leak rate based on a helium mass spectrometer leak detector;

[0023] Numbers in the figure: 1-tungsten foil, 2-PDMS polymer layer, 3-exhaust system, 4-exhaust system inlet valve, 5-outlet valve, 6-leak outlet valve, 7-leak, 8-leak inlet valve, 9-vacuum pressure gauge, 10-pressure stabilizing chamber, 11-gas inlet valve, 12-helium mass spectrometer leak detector, 13-helium mass spectrometer leak detector inlet valve, 14-front and rear stage isolation valves, 15-gas supply system. DETAILED DESCRIPTION

[0024] The present invention will be described in detail below with reference to the accompanying drawings.

[0025] See also Figure 1 and Figure 2a and Figure 2b The present invention provides a method for preparing a high-voltage leak hole by drilling a hole in a tungsten foil using a femtosecond laser and combining it with PDMS, comprising: a tungsten foil 1 and a PDMS polymer layer 2;

[0026] See also Figure 1 and Figure 2a and Figure 2b The following describes a method for preparing a high-voltage leak hole by drilling a hole in a tungsten foil using a femtosecond laser and combining it with PDMS, including the following steps:

[0027] (1) Since the cleanliness of the surface of the tungsten foil 1 will affect the drilling effect of the femtosecond laser, the tungsten foil 1 needs to be pretreated before using femtosecond laser to drill holes. Acetone, isopropyl alcohol (IPA) and acetic acid are used to remove oxides, surface dust and other pollutants on the surface of the tungsten foil 1. After each step of treatment, the tungsten foil 1 is cleaned with deionized water and finally purged with nitrogen gas to dry the tungsten foil 1 to obtain a tungsten foil 1 with a clean surface. Figure 1 As shown in Figure (a).

[0028] (2) A femtosecond laser with a central wavelength of 800 nm and a pulse width of 60 fs is used to punch holes in the tungsten foil 1, so that a 5×5 array of through holes with a diameter of 10 μm and a hole spacing of 250 μm is formed on the tungsten foil 1. Compared with the traditional processing form, the femtosecond laser hardly produces a thermal effect. The punched tungsten foil 1 is obtained by femtosecond laser punching. The appearance and size of the microhole array are observed and measured with a microscope to ensure that the size, number and spacing of the holes meet the preset requirements, such as Figure 1 As shown in Figure (b).

[0029] (3) Mix the PDMS prepolymer and curing agent in proportion, then put them into a vacuum box to remove bubbles, spin-coat the mixed PDMS onto a glass substrate, put it into an oven for curing, peel off the cured PDMS from the glass substrate, and cut it into the required size to obtain PDMS2 with a thickness of 20 μm. Fit PDMS2 tightly to the punched tungsten foil 1, place it on a hot plate and heat it at 100 ° C for 3 minutes, turn off the heating plate, and naturally cool it to room temperature to make the two firmly bonded. Then you can get a high-voltage leak consisting of PDMS2 and punched tungsten foil 1, as shown in the figure. Figure 1 Figure (c), Figure 2a and Figure 2b shown.

[0030] (4) The pressure bearing capacity of the fabricated high-pressure PDMS leak can be derived from the following process:

[0031] Calculation and derivation of the pressure bearing capacity of high-pressure leaks:

[0032]

[0033] Formula (1) is the stress on the PDMS film, where Δp is the pressure difference on both sides of the PDMS leak hole; t is the thickness of the PDMS permeable membrane 2 in the high-pressure leak hole; and R is the radius of the sphere formed by the pressure difference on a single small hole in the leak hole.

[0034]

[0035] Formula (2) is the radius of the sphere formed by the pressure difference of a single small hole in the PDMS leak. In formula (2), a is the radius of the single small hole in the PDMS leak, that is, the radius of the small hole punched in tungsten foil 1; Δp is the pressure difference on both sides of the PDMS leak; t is the thickness of the PDMS permeable membrane in the high-pressure leak; E is the elastic modulus of PDMS2; and γ is the Poisson number of PDMS2. R can be related to the offset δ along the small hole axis in a second-order Taylor expansion, that is:

[0036]

[0037] The relationship between the pressure difference Δp on both sides of the leak hole and the deformation δ of PDMS2 along the hole axis is obtained by combining equations (1), (2) and (3), as shown in equation (4):

[0038]

[0039] Equation (4) expresses the pressure difference Δp across the PDMS2, its thickness t, Young's modulus E, Poisson's ratio γ, the radius a of the pore in the tungsten foil 1, and the deformation δ of the PDMS2 along the pore axis. Equation (4) can be used to calculate the theoretical pressure-bearing capacity of a high-pressure leak.

[0040] (5) The passage of gas through PDMS2 involves three steps: gas molecules adsorb on one side of PDMS2; gas molecules diffuse to the other side of PDMS2; and gas molecules desorb from the other side of PDMS2. This permeation process can be described by Fick's law. Fick's first law states that the diffusion flux per unit time through a cross-sectional area perpendicular to the diffusion direction is proportional to the concentration gradient at that cross-sectional area.

[0041]

[0042] In formula (5), J is the diffusion flux, C is the concentration, and D is the diffusion coefficient. When the permeation process stabilizes, the diffusion flux J is expressed by (6):

[0043]

[0044] In formula (6), t is the thickness of PDMS, and ΔC is the gas concentration difference on both sides of the leak hole. The concentration can be replaced by gas partial pressure:

[0045]

[0046] In formula (7), k is the gas permeability of PDMS2, and Δp is the pressure difference on both sides of the leak hole. The leakage rate of the leak hole is given by the following formula:

[0047]

[0048] In formula (8), Q is the leak rate of the leak hole; A is the effective penetration area, that is, the sum of the through-hole areas of the tungsten foil 1; R is the gas constant, and T is the ambient temperature of the leak hole. Combining formulas (7) and (8), the expression for the leak rate can be derived:

[0049]

[0050] According to the above formula, the leakage rate of PDMS can be calculated.

[0051] (6) See Figure 3 , build a leak conductance measurement system based on a helium mass spectrometer leak detector to measure the PDMS leak. First, the inlet valve 4, outlet valve 5, leak outlet valve 6, leak inlet valve 8, gas inlet valve 11, helium mass spectrometer leak detector inlet valve 13 and front and rear stage isolation valves 14 of the exhaust system are all in the closed state. Open the inlet valve 4, outlet valve 5, leak outlet valve 6, leak inlet valve 8 and front and rear stage isolation valves 14 of the exhaust system, use the exhaust system 3 to evacuate the entire system, and after the value of the vacuum pressure gauge 9 stabilizes, it means that the exhaust is completed, and the conductance measurement of the PDMS leak can be carried out. Close the inlet valve 4, leak inlet valve 8 and front and rear stage isolation valves 14 of the exhaust system. Open the gas inlet valve 11, and the gas supply system 15 inflates the pressure stabilizing chamber 10. The pressure of the front stage can be known through the vacuum pressure gauge 9. The value of the vacuum pressure gauge before and after is the pressure difference where the leak 7 is located. Close gas inlet valve 11, open outlet valve 5, leak outlet valve 6, leak inlet valve 8, and helium mass spectrometer leak detector inlet valve 13, and helium mass spectrometer leak detector 12 can now measure the conductance of leak 7. The gas extraction system 3 consistently achieves the same vacuum level. By varying the amount of gas supplied to the plenum chamber 10 by the gas supply system 15, different pressure differentials can be achieved, thereby determining the conductance of the leak under different pressure differentials.

[0052] (7) After obtaining the conductance of the leak hole through step (6), it is compared with the theoretical calculated values obtained in steps (4) and (5), and it can be verified that the high-pressure PDMS leak hole produced by femtosecond laser drilling has sufficient strength to withstand high pressure difference and has a stable leak rate under different pressures. The high-pressure leak hole prepared by the present invention by drilling holes in tungsten foil with a femtosecond laser and combining it with PDMS has a more accurate and controllable leak rate, strong pressure resistance, and is not easy to be damaged. It makes up for the shortcomings of traditional leak holes such as low manufacturing precision, uncontrollable size, easy clogging, complex structure, unclear flow state, and unstable leak rate.

Claims

1. A method for preparing a high-voltage leak hole by drilling a hole in tungsten foil using a femtosecond laser and combining it with PDMS, characterized in that The process steps include: Step 1: Clean the surface of the tungsten foil by first wiping it with acetone and then blowing it with dry nitrogen to obtain a clean tungsten foil; then use a femtosecond laser to punch holes in the tungsten foil to form a circular hole array structure on the surface of the tungsten foil; Step 2: Using acetone, acetic acid and isopropyl alcohol to remove oxides and other contaminants on the surface of the tungsten foil to obtain a perforated tungsten foil with a clean surface; Step 3: Lay the PDMS polymer layer onto the tungsten foil with the array of circular holes, heat it on a hot plate at 100°C, and finally purge it with a clean dry nitrogen flow to obtain a new high-pressure resistant leak hole made of PDMS and tungsten foil.

2. The method for preparing a high-voltage leak by drilling a hole in tungsten foil using a femtosecond laser and combining it with PDMS according to claim 1, characterized in that: The tungsten foil used is a circular metal foil with a thickness of 1 mm and a diameter of 13 mm.

3. The method for preparing a high-voltage leak by drilling a hole in tungsten foil using a femtosecond laser and combining it with PDMS according to claim 1, characterized in that: In step 1, the circular hole array is composed of 25 circular holes with a diameter of 10 μm.

4. The method for preparing a high-voltage leak hole by drilling a hole in tungsten foil using a femtosecond laser and combining it with PDMS according to claim 1, characterized in that: In step 2, the diameter of the 25 circular holes in the surface-cleaned perforated tungsten foil is 10 μm, and they are distributed in a 5×5 array, with an interval of 250 μm between each circular hole.

5. The method for preparing a high-voltage leak by drilling a hole in tungsten foil using a femtosecond laser and combining it with PDMS according to claim 1, characterized in that: In step 3, the thickness of the PDMS polymer layer is 20 μm.

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