Leak inspection device and leak inspection method

Abstract

To significantly shorten the leak response time of the leak flow rate of a probe gas leaking from a device under test in a leak inspection by a vacuum container method using a large-capacity vacuum container.SOLUTION: A second vacuum pump 4 of exhaust speed S and compression ratio m is provided, separately from a first vacuum pump 3, between a vacuum container 1 and a helium gas detector 5. The conductance of the vacuum container 1 and the second vacuum pump 4 are connected by an inlet piping 4a of C1. The conductance of the second vacuum pump 4 and the helium gas detector 5 is connected by an outlet piping 4b of C2. The vacuum container 1 is evacuated by the first vacuum pump 3, and a first vacuum valve 14 is closed and a second vacuum valve 15 is opened when the inner pressure P1 of the vacuum container 1 reaches ultimate pressure P* [Pa] for causing the inlet pressure 5 of the helium gas detector 5 to drop to permissible upper-limit pressure or below, with the vacuum container 1 evacuated by the second vacuum pump 4 and pumping of the helium gas detector 5 actuated at the same time.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a leak testing device and a leak testing method, and more particularly to a leak testing device and a leak testing method that can significantly shorten the leak response time for the leak flow rate of a detection gas leaking from a test object in a leak testing by a vacuum container method using a large-volume vacuum container, thereby significantly shortening the leak testing time for the test object. [Background technology]

[0002] Some parts and containers in various industries, such as the mechanical and electrical industries, require leak testing. The vacuum chamber method is used to test these parts and containers for leaks. The vacuum chamber method introduces a probe gas into the test object placed inside a vacuum chamber with a specified degree of vacuum, and detects the probe gas leaking from the test object into the vacuum chamber with a probe gas detector. However, if the test object, such as a part or container, is large, a large-volume vacuum chamber is required for leak testing using the vacuum chamber method, which creates the problem of long time required for leak testing.

[0003] The reasons why leak testing using the vacuum vessel method using a large-volume vacuum vessel takes a long time are: (1) it takes time to evacuate a large-volume vacuum vessel, and (2) when the probe gas that has leaked into the large-volume vacuum vessel is detected using a probe gas detector, the leak response time for the leak flow rate of the probe gas is long.

[0004] Patent Document 1 discloses that by placing a bag-shaped body containing a porous member inside a vacuum vessel, the spatial volume of the vacuum vessel can be reduced, thereby shortening the evacuation time.

[0005] Non-Patent Document 1 is an explanatory paper about leak inspection of a vacuum vessel that contains a test object, and discloses a leak inspection when the vacuum pump of the device and the helium leak detector, which is a detection gas detector, are performed in parallel for the vacuum vessel. Non-Patent Document 1 discloses that when performing a leak inspection with parallel evacuation, attention must be paid to the split flow ratio, which is the ratio of the flow rate of gas flowing to the vacuum pump and the flow rate of gas flowing to the helium leak detector.

[0006] Non-Patent Document 1 also discloses that when performing a leak test using a helium leak detector, which is a detection gas detector, the leak response time (τ) for the leak flow rate of helium gas is expressed as τ = V / Se, where V is the volume of the vacuum vessel and Se is the effective pumping speed at the connection between the vacuum vessel and the vacuum pump (the exhaust port of the vacuum vessel), and that the leak response time becomes longer when the volume V of the vacuum vessel is large. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 3570333 [Non-patent literature]

[0008] [Non-Patent Document 1] https: / / doi.org / 10.1380 / vss.61.505, Surface and Vacuum Vol.61, No.8, pp.505-509, 2018, Special feature "Vacuum equipment maintenance course" Summary of the Invention [Problem to be solved by the invention]

[0009] The evacuation time, which is one of the reasons why leak testing takes so long, can be solved by reducing the internal volume of the vacuum vessel as described in Reference 1. It is also obvious that evacuating the vacuum vessel using a vacuum pump with a high evacuation speed is also effective.

[0010] On the other hand, it is disclosed that the leakage response time of the detection gas detector becomes long when the volume of the vacuum vessel is large, but no measures for increasing this leakage response time are disclosed.

[0011] 7 is an explanatory diagram showing the main components of a conventional leak test device 500. That is, first, the inside of the vacuum container 1 is evacuated to a predetermined pressure by the first vacuum pump 3, and then the first vacuum valve 14 is closed and the first vacuum pump 3 is stopped. Next, the second vacuum valve 15 is opened and the leakage flow rate of helium gas leaking from the test object 11 is measured by the helium gas detector 5.

[0012] Details will be given later, but the reason why the leak response time is long is because the pumping speed and pressure (upper limit pressure) at the inlet 5a of the detection gas detector (helium gas detector 5) are set small compared to the pumping speed of the vacuum pump (first vacuum pump 3) of a normal vacuum device. The reason why the pumping speed and upper limit pressure at the inlet 5a of the detection gas detector are set small is to make the detection sensitivity of the detection gas detector very high. For example, the helium leak detector, which is the detection gas detector, has an inlet pumping speed of 5×10 -3 m 3 / s, the allowable upper limit pressure is set to a small 2 Pa, and the lower limit of the detection undetectable flow rate is 10 -12 Pa·m 3 It is possible to detect extremely small leak flow rates of up to 1 / s.

[0013] In general, the leakage flow rate Q of helium gas detected by the helium gas detector 5 is expressed as follows: P1 is the internal pressure of the vacuum vessel 1, V is the internal volume of the vacuum vessel 1, Se is the effective pumping speed at the connection between the vacuum vessel 1 and the inlet pipe 4a, and Q is a constant leakage flow rate (hereinafter referred to as the "saturated leakage flow rate") leaking from the test object 11 into the inside of the vacuum vessel 1. ∞ When this is done, the time change in the leakage flow rate Q is the saturated leakage flow rate (Q ∞ ) minus the exhaust flow rate (Se×P1), so the following equation 100 holds. (Formula 100): V×(ΔP1 / Δt)=-Se×P1+Q ∞

[0014] Equation 100 is a first-order linear differential equation for the internal pressure P1 of the vacuum vessel 1. If P1=P0 at t=0, the internal pressure P1 is described by the following equation 101. (Formula 101):P1=(P0-Q ∞ / Se)exp(-t / V / Se)+Q ∞ / Se

[0015] By multiplying both sides of equation 101 by the effective pumping speed Se, the leakage flow rate Q is expressed by the following equation 102. (Equation 102): Q = Se × P1 = (P0 × Se-Q ∞ )exp(-t / V / Se)+Q ∞

[0016] For convenience of explanation, in Equation 102, P0 × Se ≪ Q ∞ Assuming this, the above equation 102 can be written as the following equation 103. (Equation 103): Q = Q ∞ (1-exp(-t / V / Se))

[0017] FIG. 8 is a graph showing the time transition of the leakage flow rate Q expressed by the above formula 103. The leakage response time τ is defined as V / Se (=τ), and this leakage response time τ is the time when the leakage flow rate Q becomes the saturated leakage flow rate Q ∞ The time from any time t1 to any time t1 when the tangent L1 of the leakage flow rate Q at the saturation leakage flow rate Q ∞ For example, if the internal volume V of the vacuum vessel 1 is 0.5 m 3 , the effective pumping speed at the inlet of the helium gas detector 5 is 0.25 m 3 / s, the leak response time τ is 200s (=0.5m 3 / 0.25m 3 / s).

[0018] In leak inspection of various parts, the leakage flow rate threshold Qt [Pa m 3 / s] is set, helium gas is introduced into the part, and the leak flow rate is measured until time t2, which is equal to or longer than the leak response time τ, but generally, the test repetition time is required to be within 60 seconds. Therefore, the above-mentioned leak response time of 200 seconds is very long.

[0019] Therefore, the present invention has been made in consideration of the problems of the prior art described above, and its object is to provide a leak inspection device and a leak inspection method which can significantly shorten the leak response time for the leak flow rate of the detection gas leaking from the test object in leak inspection by the vacuum container method using a large-volume vacuum container, thereby significantly shortening the leak inspection time of the test object. [Means for solving the problem]

[0020] In order to achieve the above object, the leak test device according to the present invention includes a vacuum vessel (1) for accommodating a test object (11) under a predetermined vacuum environment, a first vacuum pump (3) for evacuating the inside of the vacuum vessel (1) to a predetermined vacuum pressure (P1), a third vacuum pump (12) for evacuating the inside of the test object (11), a search gas source (13) for supplying a search gas into the test object (11), and a search gas detector (5) for detecting the leakage flow rate of the search gas leaking from the test object (11). The leak testing device (100, 200) is characterized in that a second vacuum pump (4) having an exhaust speed (S) greater than the exhaust speed of the detection gas detector (5) is provided between the vacuum container (1) and the detection gas detector (5), and the second vacuum pump (4) is connected to the detection gas detector (5) via an outlet pipe (4b) whose conductance (C2) is preset so that the pressure (P5) at the inlet portion (5a) of the detection gas detector (5) is equal to or lower than the allowable upper limit pressure.

[0021] In the above configuration, the search gas molecules diffused inside the vacuum vessel (1) are sucked in by the second vacuum pump (4) having a high pumping speed (S), thereby increasing the effective pumping speed (Se) at the outlet of the vacuum vessel (1), thereby shortening the leak response time (V / Se).

[0022] On the other hand, by providing the second vacuum pump (4) upstream of the detection gas detector (5), if the exhaust pressure (P3) of the second vacuum pump (4) is applied directly to the inlet portion (5a) of the detection gas detector (5), there is a risk that the inlet pressure (P5) of the detection gas detector (5) will exceed the allowable upper limit pressure.

[0023] However, in the above configuration, the exhaust port of the second vacuum pump (4) and the inlet (5a) of the detection gas detector (5) are connected by the outlet pipe (4b) with a preset conductance (C), which causes a pressure drop in the outlet pipe (4b) so that the inlet pressure (P5) of the detection gas detector (5) is kept below the allowable upper limit pressure. As a result, it is possible to significantly shorten the leak response time while maintaining the detection sensitivity of the detection gas detector (5).

[0024] A second feature of the leak testing device according to the present invention is that a fourth vacuum pump (6) for assisting the evacuation of the second vacuum pump (4) is provided in parallel with the detection gas detector (5) downstream of the second vacuum pump (4).

[0025] In the above configuration, the second vacuum pump (4) and the fourth vacuum pump (6) are used to evacuate the vacuum vessel (1), thereby significantly shortening not only the leak response time but also the evacuation time. Also, if it is difficult to set the inlet pressure (P5) of the detection gas detector (5) below the allowable upper limit pressure using only the evacuation speed (S) of the second vacuum pump (4), it is possible to set the inlet pressure (P5) of the detection gas detector (5) below the allowable upper limit pressure by evacuating the exhaust port of the second vacuum pump (4) using the fourth vacuum pump (6).

[0026] The third feature of the leak test device according to the present invention is that the second vacuum pump (4) has an exhaust speed of 0.05 m 3 / s or more and a compression ratio of 10 or more.

[0027] In the above configuration, it is possible to increase the effective pumping speed (Se) at the outlet of the vacuum chamber (1).

[0028] In order to achieve the above-mentioned object, the leak testing method of the present invention is a leak testing method in which a detection gas is supplied into a test object (11) placed inside a vacuum vessel (1) maintained at a predetermined vacuum pressure, and the leakage flow rate of the detection gas leaking from the test object (11) is measured by a detection gas detector (5). The leak testing method is characterized in that a second vacuum pump (4) having an exhaust speed (S) greater than that of the detection gas detector (5) is connected to the vacuum vessel (1), and the exhaust port of the second vacuum pump (4) is connected to an outlet pipe (4b) whose conductance (C2) is preset so that the pressure (P5) at the inlet portion (5a) of the detection gas detector (5) is equal to or lower than the allowable upper limit pressure, and the exhaust flow from the second vacuum pump (4) is transferred to the inlet portion (5a) of the detection gas detector (5) while being reduced in pressure by the outlet pipe (4b).

[0029] With the above-mentioned configuration, the leak response time can be significantly shortened, and the leak flow rate can be measured with the detection sensitivity of the detection gas detector (5) being excellent.

[0030] A second feature of the leak inspection method according to the present invention is that the inside of the vacuum vessel (1) is evacuated to a vacuum by using both the first vacuum pump (3) and the second vacuum pump (4).

[0031] In the above configuration, the ultimate pressure (P * ) the time required to evacuate the inside of the vacuum vessel (1) to a vacuum level of 1000 MPa (1200 MPa).

[0032] A third feature of the leak testing method according to the present invention is that a fourth vacuum pump (6) is provided in parallel with the detection gas detector (5) downstream of the second vacuum pump (4), and the inside of the vacuum vessel (1) is evacuated to a vacuum while the exhaust gas from the second vacuum pump (4) is exhausted by the fourth vacuum pump (6).

[0033] In the above configuration, even if the exhaust pressure (P5) of the second vacuum pump (4) rises and the pressure (P5) at the inlet (5a) of the detection gas detector (5) exceeds the allowable upper limit pressure, the fourth vacuum pump (6) lowers the exhaust pressure (P5) of the second vacuum pump (4) so ​​that the pressure (P5) at the inlet (5a) of the detection gas detector (5) is equal to or lower than the allowable upper limit pressure. In this way, by measuring the leakage flow rate while exhausting the exhaust gas of the second vacuum pump (4) with the fourth vacuum pump (6), it is possible to measure the leakage flow rate of the detection gas while maintaining the high detection sensitivity of the detection gas detector (5).

[0034] A fourth feature of the leak inspection method according to the present invention is that the time for introducing the probe gas into the test body (11) and measuring the leakage flow rate of the probe gas is set to be at least the time at which the leakage flow rate over time is measured in advance and the measured leakage flow rate becomes 63% or more of the saturated leakage flow rate.

[0035] In the above configuration, the leak response time is significantly reduced, so the saturated leak flow rate (Q ∞ ) is also shortened. Therefore, even if the pass / fail of the leak flow rate is judged based on the time required for the leak flow rate to reach 63% or more of the saturated leak flow rate, it is possible to keep the time required for one leak test within the required cycle time. Effect of the Invention

[0036] According to the leak testing method of the present invention and the leak testing device which implements the same, the leak response time for the leak flow rate of the detection gas leaking from the test object in leak testing by the vacuum container method using a large-volume vacuum container can be significantly shortened, thereby making it possible to significantly shorten the leak testing time for the test object. [Brief description of the drawings]

[0037] [Figure 1] 1 is an explanatory diagram showing a configuration of a main part of a leak test device according to a first embodiment of the present invention; [Diagram 2] FIG. 2 is a process diagram showing a leak inspection process using the leak inspection device according to the first embodiment of the present invention. [Diagram 3] 4 is a graph showing the measurement results of the helium leakage flow rate over time measured by the leak check device according to the first embodiment of the present invention. [Figure 4] FIG. 5 is an explanatory diagram showing the configuration of a main part of a leak test device according to a second embodiment of the present invention. [Diagram 5] FIG. 6 is a process diagram showing a leak inspection process using a leak inspection device according to a second embodiment of the present invention. [Figure 6] 10 is a graph showing the results of measurement of the helium leakage flow rate over time measured by the leak check device according to the second embodiment of the present invention. [Figure 7] FIG. 1 is an explanatory diagram showing a configuration of a main part of a conventional leak test device. [Figure 8] 13 is a graph showing the time progression of the leakage flow rate Q expressed by the above formula 103. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0038] The present invention will now be described with reference to the accompanying drawings.

[0039] (First embodiment) FIG. 1 is an explanatory diagram showing the configuration of the main parts of a leak test device 100 according to a first embodiment of the present invention. This leak test device 100 includes a vacuum vessel 1 capable of accommodating a test object 11 and capable of maintaining a vacuum inside, a vacuum gauge 2 for measuring the degree of vacuum inside the vacuum vessel 1, and a pressure gauge for measuring the pressure inside the vacuum vessel 1 at a predetermined ultimate pressure P *the second vacuum pump 4 sucks in and compresses helium molecules that have leaked into the vacuum vessel 1 and transfers them to a helium gas detector 5; a third vacuum pump 12 evacuates the inside of the test object 11; a helium gas detector 5 measures the leakage flow rate of helium molecules leaking from the test object 11; a helium gas cylinder 13 supplies helium molecules to the evacuated inside of the test object 11; a first vacuum valve 14 cuts off communication between the vacuum vessel 1 and the first vacuum pump 3; a second vacuum valve 15 cuts off communication between the vacuum vessel 1 and the second vacuum pump 4; a first shutoff valve 16 cuts off communication between the test object 11 and the third vacuum pump 12 or the helium gas cylinder 13; a second shutoff valve 17 turns on / off the evacuation of the test object 11 by the third vacuum pump 12; and a third shutoff valve 18 turns on / off the supply of helium molecules to the test object 11.

[0040] This leak testing device 100 is a leak testing device for introducing helium gas into a test object 11 placed in a vacuum vessel 1 maintained at a prescribed vacuum level, and measuring the leakage flow rate of helium gas leaking from the test object 11 into the vacuum vessel 1. In particular, when the internal volume of the vacuum vessel 1 is large, it is configured to be able to significantly shorten the detection time (leak response time) from the start of measurement until the leak flow rate reaches 63% of the saturated value, compared to conventional leak testing devices.

[0041] Here, the various units used in this specification are SI units, and the various units under vacuum conform to JIS Z 8126-1:2021 Vacuum Technology - Terminology - Part 1: General Terminology of the Japanese Industrial Standards. In other words, high-pressure gas pressure and pressure under vacuum are expressed as absolute pressure (= gauge pressure + atmospheric pressure), and the unit is Pa (Pascal). The exhaust speed of the vacuum pump and the conductance of the piping are expressed as volumetric flow rate, and the unit is m 3 / s (cubic meters per second). Gas flow rates such as leak flow rates are expressed as PV value flow rates, and the unit is Pa m 3 / s (Pascal cubic metres per second) will be used.

[0042] The leak test device 100 according to the first embodiment has a capacity of, for example, 1×10 -6 This configuration allows for detection of a helium gas leak flow rate (hereinafter referred to as "gross leak flow") of more than Pa·m3 / s in a short time. In this way, when the leakage flow rate of helium gas is relatively high, the inlet pressure P5 of the inlet portion 5a of the helium gas detector 5 can be set to a high pressure, for example, 1500 Pa or less. In this case, helium molecules introduced from the inlet portion 5a are supposed to be exhausted through the auxiliary vacuum pump 5d of the helium gas detector 5, but helium molecules with a small mass number diffuse back in the opposite direction to the exhaust direction and are forced to a high vacuum (10 -3 The pressure in the analytical tube 5b is maintained at a constant pressure (order of Pa). The configuration of the leak test device 100 will be described below.

[0043] The vacuum vessel 1 has an internal volume of, for example, 0.5 m 3 (=500 L). Vacuum gauge 2 can use a Pirani vacuum gauge.

[0044] The first vacuum pump 3 has a nominal pumping speed of, for example, 1.05 m 3 / s, and a compound pump consisting of a Roots type vacuum pump (not shown) and an oil rotary vacuum pump (not shown) connected in the rear stage of the Roots type vacuum pump can be used.

[0045] The inlet pipe 3a connecting the vacuum vessel 1 and the first vacuum pump 3 is, for example, a cylindrical pipe having an inner diameter of 80 mm and a length of 1 m. The inner diameter of the first vacuum valve 14 is, for example, 80 mm, which is a large diameter.

[0046] The second vacuum pump 4 is a gas transport type vacuum pump that compresses and exhausts the sucked gas molecules (air and helium), and may be, for example, a turbo molecular pump. The nominal pumping speed S of the second vacuum pump 4 is, for example, 1.0 m 3 / s, and the maximum compression ratio is, for example, 10 8 Here, the pressure in the vacuum vessel 1 during the leak test is 10 0 Pa to 101 Since the pressure is on the order of Pa, the pumping speed of the turbo molecular pump, which is the second vacuum pump 4, is reduced by about 3 / 4 to 1 / 20. For example, at 5 Pa, the pumping speed is 0.35 m 3 / s, 0.1 m at 20 Pa 3 / s. The compression ratio of this pump when performing the leak test is 10 2 From 10 1 For example, it becomes 80 at 5 Pa and 25 at 20 Pa.

[0047] The second vacuum valve 15 and piping (hereinafter collectively referred to as inlet piping 4a) connecting the vacuum vessel 1 and the second vacuum pump 4 are, for example, L-shaped valves with an inner diameter of 155 mm and a length of 400 mm, since it is necessary to set the effective pumping speed Se of the intake port of the inlet piping 4a (exhaust port of the vacuum vessel 1) high at the pressure of the vacuum vessel 1 when the leak test is performed. Moreover, the two upstream and downstream pipes connecting the vacuum vessel 1 or the second vacuum pump 4 to the second vacuum valve 15 are, for example, pipes with an inner diameter of 155 mm and a length of 200 mm.

[0048] The molecular flow conductance of this inlet pipe 4a is 0.43 m 3 / s. Here, the pressure in the vacuum vessel 1 during the leak test is 10 0 Pa to 10 1 Since the gas (air and helium) flows as a viscous flow from the intermediate flow, the conductance C1 [m3 / s] of the inlet pipe 4a becomes about 10 times larger. For example, at 5 Pa, it becomes 5.4 m 3 / s, 20m at 20Pa 3 / s.

[0049] The outlet pipe 4b connecting the second vacuum pump 4 and the helium gas detector 5 is a cylindrical pipe having an inner diameter of 23 mm and a length of 1.5 m, for example, because it is necessary to set the effective pumping speed Se of the intake port (exhaust port of the second vacuum pump) of the outlet pipe 4b high at the pressure of the exhaust port of the second vacuum pump 4 when the leak test is performed. The molecular flow conductance value of this outlet pipe 4b is 1×10 -3 m 3Here, the pressure at the exhaust port of the second vacuum pump 4 during the leak test is several hundreds of Pa, and since the gas (air and helium) flows as a viscous flow, the conductance C2 [m3 / s] of the outlet pipe 4b becomes about 100 times larger. For example, when the pressure at the exhaust port of the second vacuum pump 4 is 500 Pa, the conductance C2 is 1.25×10 -1 m 3 / s.

[0050] The third vacuum pump 12 may be, for example, a positive displacement vacuum pump that operates at a low vacuum, such as an oil rotary pump.

[0051] The helium gas detector 5 is composed of an analytical tube 5b for measuring the helium partial pressure in a vacuum, a high vacuum pump 5c for maintaining the intake port of the analytical tube 5b at a predetermined vacuum level, an auxiliary pump 5d for reducing the back pressure (pressure on the exhaust port side) of the high vacuum pump 5c, and a vacuum exhaust pipe 5e for connecting the inlet 5a to each of the pumps 5c and 5d. Generally, the intake port of the analytical tube 5b is maintained at a vacuum level of 10 -3 The high vacuum pump 5c is set to a high vacuum of less than 1 Pa. A turbo molecular pump is used as the high vacuum pump 5c, and an oil rotary type pump or a scroll type vacuum pump is used as the backing pump 5d.

[0052] Helium molecules that enter analytical tube 5b are ionized by a filament (not shown), accelerated by an electric field, and then their course is bent by a magnetic field (Lorentz force). The magnitudes of the electric field and magnetic field are set so that only helium ions of mass 4 reach an ion collector (not shown). Helium gas detector 5 introduces helium molecules into analytical tube 5b by the reverse diffusion phenomenon, in which helium molecules in a vacuum diffuse in the opposite direction to the pump exhaust direction.

[0053] Moreover, inside the helium gas detector 5, the pressure at the outlet of the vacuum exhaust pipe 5e corresponds to the intake pressure (suction pressure) of the high vacuum pump 5c or the backing pump 5d. Therefore, the inlet pressure P5 [Pa] at the inlet 5a of the helium gas detector 5 varies depending on the detection range of the leak flow rate. For example, for gross leak flow, the inlet pressure P5 [Pa] at the inlet 5a is set to 1500 Pa or less. When the leak flow rate is 1×10 -6 Pa·m 3 / s (hereinafter referred to as "fine leak flow"), the inlet pressure P5 [Pa] at the inlet portion 5a is set to 100 Pa or less, for example.

[0054] In addition, the helium gas detector 5 has a different helium suction port in the pump depending on the detection range of the leak flow rate. When the leak flow rate is a fine leak flow, the helium suction port is provided, for example, at a midpoint between the intake port and exhaust port of the high vacuum pump 5c. On the other hand, when the leak flow rate is a gross leak flow, the helium suction port is provided, for example, at a midpoint between the intake port and exhaust port of the auxiliary pump 5d.

[0055] The first shutoff valve 16, the second shutoff valve 17, and the third shutoff valve 18 are each constituted by a solenoid valve.

[0056] FIG. 2 is a process diagram showing a leak inspection process performed by the leak inspection device 100 according to the first embodiment of the present invention. In process P1, the test object 11 is set in the vacuum container 1. Then, a test pipe 1a communicating with a third vacuum pump 12 and a helium gas cylinder 13 is connected to the test object 11.

[0057] In process P2, the first vacuum valve 14 is opened and the inside of the vacuum vessel 1 is evacuated by the first vacuum pump 3. The ultimate pressure P * was set to 20 Pa.

[0058] In process P3, the second shutoff valve 17 is opened, and the inside of the test object 11 is evacuated by the third vacuum pump 12. Note that process P3 may be performed simultaneously with the above process P2.

[0059] In process P4, the first vacuum valve 14 is closed and the evacuation by the first vacuum pump 3 is stopped.

[0060] In process P5, the second shutoff valve 17 is closed to stop the evacuation by the third vacuum pump 12. Note that process P5 may be performed simultaneously with the above process P4.

[0061] In process P6, the second vacuum valve 15 is opened and the vacuum vessel 1 is evacuated by the second vacuum pump 4.

[0062] In process P7, the helium gas detector 5 determines whether there is any helium leakage inside the vacuum vessel 1.

[0063] In process P8, the third shutoff valve 18 is opened to supply helium gas from the helium gas cylinder 13 to the test object 11, and the leakage flow rate is measured.

[0064] The leak test performance of the leak test device 100 according to the first embodiment of the present invention was examined as follows.

[0065] Test piece 11 is 1×10 -6 Pa·m 3 A standard helium leak that realizes a helium gas leak rate of 1000 s was used and installed in the vacuum vessel 1.

[0066] As the leak inspection performance of the leak inspection device 100, the exhaust time of the vacuum vessel 1 from atmospheric pressure to 20 Pa and the time transition of the leak signal of the standard helium leak in the helium gas detector 5 with and without the second vacuum pump 4 were measured. Here, the ultimate pressure P * The reason for setting the pressure at 20 Pa is that in the above process P6, the gas in the vacuum vessel 1 is compressed using the second vacuum pump 4 and transferred to the helium gas detector 5, so that the inlet pressure P5 at the inlet 5a of the helium gas detector 5 rises, but the inlet pressure P5 must be kept below the allowable upper limit pressure of 1500 Pa during gross leak flow.

[0067] The ultimate pressure P of the vacuum vessel 1 by the first vacuum pump 3 * can be determined based on the allowable upper limit pressure of the inlet pressure P5 of the helium gas detector 5 as follows:

[0068] First, the following formula 1 is established for the inlet pipe 4a (piping to the second vacuum valve 15). (Formula 1): Q1=C1×(P1-P2) Here, Q1 is the volumetric flow rate of air and helium gas at the inlet pipe 4a [Pa m 3 / s]. P1 is the internal pressure [Pa] of the vacuum vessel 1 after the start of evacuation by the second vacuum pump 4, and the pressure is P1 <P * Furthermore, P2 is the intake pressure of the second vacuum pump 4 [Pa].

[0069] Moreover, at the suction port of the second vacuum pump 4, the following formula 2 holds. (Formula 2):Q1=S×P2 S is the pumping speed of the second vacuum pump 4 [m 3 / s].

[0070] Therefore, by substituting Equation 2 into Equation 1 and solving for P2, the following Equation 3 is obtained. (Formula 3): P2=C1 / (C1+S)×P1

[0071] On the other hand, the exhaust pressure of the second vacuum pump 4 is P3 [Pa] and the conductance of the outlet pipe 4b is C2 [m 3 / s], and the inlet pressure of the helium gas detector 5, the pumping speed at the inlet 5a, and the volumetric flow rate of helium gas are P5 [Pa], S5 [m 3 / s], Q2 [Pa m 3 / s], The following formula 4 holds for the outlet pipe 4b. (Formula 4): Q2=C2×(P3-P5)=C2×(mP2-P5)(∵P3 / P2=m)

[0072] Moreover, at the inlet portion 5a of the helium gas detector 5, the following formula 5 holds. (Formula 5): Q2=S5×P5

[0073] Here, by substituting Equation 4 into Equation 5 and solving for P5, the following Equation 6 is obtained. (Formula 6): P5=m×C2 / (C2+S5)×P2

[0074] Here, by substituting Equation 3 into Equation 6 and rearranging, the following Equation 7 is established. (Formula 7):P5=[mC1C2 / {(C1+S)(C2+S5)}]P1

[0075] Since the inlet pressure P5 of the helium gas detector 5 is 1500 Pa or less, [mC1C2 / {(C1+S)(C2+S5)}]P1≦1500, that is, the following formula 8 is established. (Formula 8): P1≦1500×[{(C1+S)(C2+S5)} / mC1C2]

[0076] Therefore, the right side of Equation 8 is expressed as the ultimate pressure P of the vacuum vessel 1 by the first vacuum pump 3. * If we define this as the ultimate pressure P * corresponds to the internal pressure of the vacuum vessel 1 at which the vacuum evacuation of the vacuum vessel 1 is switched from the first vacuum pump 3 to the second vacuum pump 4, and is determined by the allowable upper limit pressure (≦1500 Pa) of the inlet pressure P5 of the helium gas detector 5, the conductance C1 of the inlet piping 4a, the conductance C2 of the outlet piping 4b, the pumping speed S and compression ratio m of the second vacuum pump 2, and the pumping speed S5 at the inlet 5a of the helium gas detector 5.

[0077] In formula 8, the inlet pressure P5 of the helium gas detector 5 is set to the allowable upper limit pressure of 1500 Pa, and the ultimate pressure P of the vacuum vessel 1 by the first vacuum pump 3 is * was calculated as follows. The compression ratio of the second vacuum pump 4 was set to m = 10. Then, the pressure of the inlet pipe 4a was about 150 Pa, so C1 = 1.5 × 10 2 m 3 / s. The pumping speed S of the second vacuum pump 4 is 3×10 -2 m 3On the other hand, the conductance C2 of the outlet pipe 4b is 3.9×10 -1 m 3 The pumping speed S5 at the inlet 5a of the helium gas detector 5 was estimated to be 5×10 -3 m 3 / s. Substituting these values ​​into Equation 8, the ultimate pressure of the vacuum vessel 1, P * was calculated to be 152 Pa. In other words, the internal pressure P1 of the vacuum vessel 1 is 152 Pa (=P * ) or less. If it is operated at a high pressure, a load is placed on the second vacuum pump 4 and the helium gas detector 5. Therefore, in the actual leak inspection of the first embodiment, the internal pressure P1 of the vacuum vessel 1 is allowed to reach 20 Pa, and then the first vacuum pump 3 is switched to the second vacuum pump 4.

[0078] When the vacuum vessel 1 was evacuated from atmospheric pressure by the first vacuum pump 3, the reached pressure P * The pumping speed of the first vacuum pump 3 reached 20 Pa. This was because the pumping speed of the first vacuum pump 3 was 1.05 m 3 / s, and the evacuation time of the vacuum vessel 1 can be shortened by the evacuation at such a high evacuation speed.

[0079] Next, the first vacuum valve 14 was closed to terminate the evacuation by the first vacuum pump 3 (process P4), the second vacuum valve 15 was opened to switch the flow path to the helium gas detector 5, and a leak-free measurement was carried out for 5 seconds (process P7). Then, the helium standard leak was opened to introduce helium gas and start the leak measurement (process P8).

[0080] 3 is a graph showing the measurement results of the helium leak flow rate over time measured by the leak test apparatus 100 according to the first embodiment of the present invention. -6 Pa·m 3 Helium gas at a flow rate of 1×10 / s was leaked into the vacuum vessel 1. The solid line indicates the leak signal of the leak test device 100 with the second vacuum pump 4, the dashed line indicates the leak signal of the conventional leak test device 500 without the second vacuum pump 4, and the dashed and dotted line indicates the saturated leak flow rate of 1×10-6 Pa·m 3 / s is 63%.

[0081] The leak signal began to be measured 2 to 3 seconds after the start of leakage in both leak testing apparatus 100 and conventional leak testing apparatus 500. This time delay typically appears when a small amount of helium gas leaks into large vacuum vessel 1, and is considered to be the time required for the helium gas that has leaked into vacuum vessel 1 to diffuse through the large volume of vacuum vessel 1 and reach helium gas detector 5.

[0082] The leak signal (dashed line) of the conventional leak inspection device 500 without the second vacuum pump 4 was 10 -8 Pa 3 / s. However, it then increases slowly and drops to 10 / s after 20 seconds. -7 Pa·m 3 / s, but then increases more slowly to 2×10 after 40 s -7 Pa·m 3 / s. This leak signal was 6.3 × 10 -7 Pa·m 3 The leak response time to reach 1 / s was a long 152 seconds. The vacuum exhaust process, which is a process prior to leak signal measurement, takes 14 seconds, the no-leak measurement process takes 5 seconds, and there is an atmospheric exposure process of about 5 seconds after that, so the process with this conventional leak inspection device requires about 180 seconds (= 14 seconds + 5 seconds + 152 seconds + 5 seconds ≒ 3 minutes). This long process time makes it difficult to apply to mass production sites.

[0083] On the other hand, the leak signal (solid line) of the leak inspection device 100 equipped with the second vacuum pump 4 was 6.3 × 10 -7 Pa·m 3 / s, and after 10 s it reaches 1×10 -6 Pa·m 3 / s. This is due to the gas compression effect of the second vacuum pump 4. The process time of this leak inspection device 100 was a very short time of 34 s (= 14 s + 5 s + 10 s + 5 s). This short process time can be adapted to mass production sites.

[0084] Second embodiment FIG. 4 is an explanatory diagram showing the configuration of the main parts of a leak test device 200 according to a second embodiment of the present invention. This leak test device 200 is a 1×10 -6 Pa·m 3 This is used to detect a minute amount of helium gas leak flow (fine leak flow) of less than 1 / s. Therefore, the inlet pressure P5 of the helium gas detector 5 needs to be set low, at 100 Pa (the allowable upper limit pressure) or less.

[0085] In this leak test device 200, a fourth vacuum pump 6 is provided in parallel with the helium gas detector 5 via a branch pipe 6a at the rear of the second vacuum pump 4. This is because the flow rate of a minute leak of helium is measured, so the allowable upper limit pressure of the inlet pressure P5 of the helium gas detector 5 is low at 100 Pa, and the ultimate pressure P of the vacuum vessel 1 is low at 100 Pa. * This is because it is necessary to evacuate the gas to 5 Pa. Furthermore, a third vacuum valve 19 and a fourth vacuum valve 20 are provided in front of the helium gas detector 5 and the fourth vacuum pump 6, respectively. The rest of the configuration is the same as that of the leak test device 100 described above.

[0086] The fourth vacuum pump 6 may be, for example, an oil rotary vacuum pump or a positive displacement vacuum pump that operates at a low vacuum, such as a scroll pump. The intake pressure is P4 [Pa], and the exhaust pressure is equal to atmospheric pressure. The exhaust speed S4 of the fourth vacuum pump 6 is, for example, 8.3×10 -2 [m 3 / s].

[0087] The branch pipe 6a has an inner diameter of 23 mm, a length of 1.5 m, and a conductance of C3 [m 3 / s] cylindrical piping.

[0088] Now, let us calculate the volumetric flow rate Q3 [Pa·m3 / s] of the helium gas flowing through the branch pipe 6a.

[0089] First, the following formula 9 is established for the branch pipe 6a. (Equation 9): Q3 = C3 × (P3 - P4)

[0090] Moreover, at the suction port of the third vacuum pump 6, the following formula 10 holds. (Formula 10): Q3 = S4 × P4

[0091] Therefore, by substituting Equation 9 into Equation 10 and solving for P4, the following Equation 11 is obtained. (Formula 11): P4=C3 / (C3+S4)×P3=mC3 / (C3+S4)×P2(∵P3 / P2=m)

[0092] By substituting Equation 3 into Equation 11, the following Equation 12 is obtained. (Formula 12):P4=[mC1C3 / {(C1+S)(C3+S4)}]P1

[0093] Therefore, by substituting Equation 12 into Equation 10, the volumetric flow rate Q3 of the helium gas flowing through the branch pipe 6a is expressed by the following Equation 13. (Formula 13):Q3=[mC1C3 / {(C1+S)(C3+S4)}]P1×S4

[0094] On the other hand, the volumetric flow rate Q2 of the helium gas flowing through the outlet pipe 4b is expressed by the following equation 14 from equation 7. (Formula 14):Q2=[mC1C2 / {(C1+S)(C2+S5)}]P1×S5

[0095] Therefore, the volumetric flow rate of the helium gas exhausted from the second vacuum pump 4 is equal to the sum of "Q2 in Equation 14" and "Q3 in Equation 13." In addition, the branch ratio Q2 / Q3 is expressed by the following Equation 15. (Formula 15): Q2 / Q3={(C2×S5) / (C2+S5)}×{(C3+S4) / (C3×S4)}=(1 / C3+1 / S4) / (1 / C2+1 / S5) Equation 15 indicates that when the flow division ratio Q2 / Q3 is, for example, 3:5, the leakage flow rate of helium gas detected by the helium gas detector 5 corresponds to 3 / 8 times the leakage flow rate leaking from the test object 11, and the leakage flow rate leaking from the test object 11 is 8 / 3 times the leakage flow rate of helium gas detected by the helium gas detector 5.

[0096] FIG. 5 is a process diagram showing a leak inspection process performed by the leak inspection device 200 according to the second embodiment. In process P1, the test object 11 is set in the vacuum container 1. Then, a test pipe 1a communicating with a third vacuum pump 12 and a helium gas cylinder 13 is connected to the test object 11.

[0097] In process P2, the first vacuum valve 14 is opened and the inside of the vacuum vessel 1 is evacuated by the first vacuum pump 3. The ultimate pressure P * was set to 5 Pa.

[0098] In process P2-1, when the vacuum vessel 1 is evacuated by the first vacuum pump 3, when the pressure in the vacuum vessel 1 reaches 1000 Pa, the second vacuum valve 15 and the fourth vacuum valve 20 are opened, and the inside of the vacuum vessel 1 is also evacuated by the second vacuum pump 4 and the fourth vacuum pump 6.

[0099] In process P3, the second shutoff valve 17 is opened, and the inside of the test object 11 is evacuated by the third vacuum pump 12. Note that process P3 may be performed simultaneously with the above process P2.

[0100] In process P4, the first vacuum valve 14 is closed and the evacuation by the first vacuum pump 3 is stopped.

[0101] In process P4-1, when the evacuation of the vacuum vessel 1 by the first vacuum pump 3 is stopped, the fourth vacuum valve 20 is closed to also stop the evacuation of the vacuum vessel 1 by the fourth vacuum pump 6. Note that this process P4-1 can be omitted.

[0102] In process P5, the second shutoff valve 17 is closed to stop the evacuation by the third vacuum pump 12. Note that process P5 may be performed simultaneously with the above process P4.

[0103] In process P6′, the third vacuum valve 19 is opened to transfer the exhaust from the second vacuum pump 4 to the helium gas detector 5.

[0104] In process P7, the helium gas detector 5 determines whether there is any helium leakage inside the vacuum vessel 1.

[0105] In process P8, the third shutoff valve 18 is opened to supply helium gas from the helium gas cylinder 13 to the test object 11, and the leakage flow rate is measured.

[0106] The leak test performance of the leak test device 200 according to the second embodiment of the present invention was examined as follows.

[0107] Test piece 11 has a flow rate of 1×10 -8 Pa·m 3 A standard helium leak of 0.5 m / s was installed in the vacuum vessel 1. The internal volume of the vacuum vessel 1 was 0.5 m 3 A Pirani vacuum gauge was used as the vacuum gauge 2 to measure the pressure in the vacuum vessel 1. The first vacuum pump 3, which serves as a vacuum exhaust system for evacuating the vacuum vessel 1, is composed of a Roots type vacuum pump and an oil rotary vacuum pump connected in the rear stage, and has an exhaust speed of, for example, 1.05 m 3 Here, the inlet pipe 3a from the vacuum vessel 1 to the first vacuum pump 3 has an inner diameter of 80 mm and a length of 1 m, for example.

[0108] A third vacuum valve 19 with a large diameter of 212 mm inside diameter was attached to the vacuum vessel 1 as a vacuum exhaust system for detecting helium gas, and a second vacuum pump 4 with an exhaust speed S of 1.0 m 3 / s, helium compressibility 10 3A turbo molecular pump of 1000 mm diameter was used. A helium leak detector was installed as a helium gas detector 5 via a third vacuum valve 19 and an outlet pipe 4b of 23 mm inner diameter x 1.5 m length in the rear stage of the second vacuum pump 4 to detect helium gas, and a pumping speed of 8.3 x 10 was also installed via a fourth vacuum valve 20 and a branch pipe 6a of 23 mm inner diameter x 1.5 m length in order to maintain the inlet pressure P5 of the helium gas detector 5 at 100 Pa or less during evacuation to 1000 Pa or less and helium detection. -2 m 3 A fourth vacuum pump 6 of / s was installed.

[0109] As the leak test performance of the leak test apparatus 200 according to the second embodiment, the evacuation time from atmospheric pressure of the vacuum vessel 1 to 5 Pa and the time transition of the leak signal of the standard helium leak in the helium gas detector 5 of a conventional leak test apparatus without a vacuum pump 4 were measured. * The reason for setting the pressure at 5 Pa is that in a later process, the gas in the vacuum vessel 1 is compressed using the second vacuum pump 4 and transferred to the helium gas detector 5, so that the inlet pressure P5 of the helium gas detector 5 rises, but the inlet pressure P5 must be kept below the allowable upper limit pressure of 100 Pa at the inlet 5a of the helium gas detector 5.

[0110] In the second embodiment, since the pressure at the inlet 5a of the helium gas detector 5 reached 150 Pa, which was greater than the allowable upper limit pressure of 100 Pa, by only performing evacuation using the high vacuum pump 5c of the helium gas detector 5, evacuation using the fourth vacuum pump 6 was also performed at the same time, and leakage flow rate measurement was performed using the helium gas detector 5.

[0111] The vacuum vessel 1 was evacuated from atmospheric pressure by the first vacuum pump 3, and when the pressure in the vacuum vessel 1 was below 1000 Pa, the second vacuum pump 4 was also evacuated. The internal pressure of the vacuum vessel 1 reached 5 Pa in 21 seconds. 5 Even when evacuating to 5 Pa, which is five orders of magnitude lower than the atmospheric pressure, the use of the first vacuum pump 3 and the second vacuum pump 4 allows the evacuation time to be shortened.

[0112] Next, the first vacuum valve 14 was closed to terminate the evacuation by the first vacuum pump 3, and while simultaneously performing evacuation by the fourth vacuum pump 6, a leak-free measurement was carried out for 5 seconds using the helium gas detector 5. Then, -8 Pa·m 3 A standard helium leak with a flow rate of 10000 / s was opened to introduce helium gas and start leak measurement. Here, the flow ratio of the helium gas detector 5 and the fourth vacuum pump 6 is 3:5, so the saturated leak flow rate Q ∞ is 3.8 x 10 -9 Pa·m 3 / s(=1×10 -8 Pa·m 3 / s×3 / 8).

[0113] 6 is a graph showing the measurement results of the helium leak flow rate over time using the leak test device 200. Here, helium gas was leaked from a standard helium leak into the vacuum vessel 1 at time 0 s. The solid line indicates the leak signal of the leak test device 200 with the second vacuum pump 4, the dashed line indicates the leak signal of a conventional leak test device 500 without the second vacuum pump 4, and the dashed and dotted line indicates the saturated leak flow rate of 3.8 × 10 -9 Pa·m 3 / s = 63% (= 2.4 × 10 -9 Pa·m 3 / s).

[0114] The leak signal begins to be measured 7 to 10 seconds after the start of leakage in both leak test apparatus 200 and conventional leak test apparatus 500. This time delay is considered to be the time required for the helium gas leaked into vacuum vessel 1 to diffuse through the large-volume vacuum vessel 1 and reach the helium gas detector 5, as in the first embodiment. The delay time is longer compared to the first embodiment because the helium concentration is lower.

[0115] The leak signal (dashed line) of the conventional leak inspection device 500 not equipped with the second vacuum pump 4 in FIG. 6 shows a gradual rise and reaches 1×10 -10 Pa·m 3 / s, but then the increase becomes more gradual and remains at 6×10-10 Pa·m 3 / s. This leak signal was 2.4 × 10 -9 Pa·m 3 The leak response time to reach 1 / s was as long as 175 seconds. Therefore, the process of this conventional leak inspection device 500 requires about 200 seconds, making it difficult to apply to mass production sites.

[0116] On the other hand, the leak signal (solid line) from the leak inspection device 200 equipped with the vacuum pump 4 in FIG. 6 is 1×10 -9 Pa·m 3 / s, and after 10 s it drops to 2.4 × 10 -9 Pa·m 3 / s. This is due to the gas compression effect by the second vacuum pump 4. The process time of the leak test apparatus 200 according to the second embodiment was a very short time of 41 seconds. This short process time is adaptable to mass production sites.

[0117] The above describes the embodiments of the present invention with reference to the drawings. The embodiments of the present invention are not limited to those described above, and various modifications and changes can be made within the scope of the technical features of the present invention. For example, instead of helium, it is also possible to use other gases (e.g., hydrogen, argon, air) as the detection gas. Also, instead of a helium leak detector which is a helium gas detector, it is also possible to use a quadrupole mass spectrometer or a discharge emission gas analyzer as the detection gas detector. Explanation of symbols

[0118] 1 Vacuum container 2 Vacuum gauge 3. First vacuum pump 3a Inlet piping 4. Second Vacuum Pump 4a Inlet pipe 4b Outlet piping 5. Helium gas detector 5a Entrance 5b Analysis tube 5c High Vacuum Pump 5d Auxiliary pump 6. No. 4 Vacuum Pump 11 Test subject 12. Third Vacuum Pump 13 Helium gas cylinder 14 First vacuum valve 15 Second vacuum valve 16 First shutoff valve 17 Second shutoff valve 18 Third shutoff valve 19 Third vacuum valve 20 Fourth Vacuum Valve 100 Leak inspection device 200 Leak inspection device P1 Internal pressure of the vacuum vessel P2 Intake pressure of second vacuum pump P3 Exhaust pressure of second vacuum pump P4 Intake pressure of the fourth vacuum pump P5 Helium gas detector inlet pressure C1 Inlet pipe conductance C2 Outlet piping conductance C3 Branch pipe conductance Q1 Volumetric flow rate of helium gas flowing through the inlet pipe Q2 Volumetric flow rate of helium gas flowing through the outlet pipe Q3 Volumetric flow rate of helium gas flowing through the branch pipe

Claims

1. a vacuum vessel (1) for accommodating a test object (11) under a predetermined vacuum environment; a first vacuum pump (3) for evacuating the inside of the vacuum vessel (1) to a predetermined vacuum pressure (P1); a third vacuum pump (12) for evacuating the inside of the test object (11); A probe gas source (13) for supplying a probe gas into the inside of the test object (11); A leak test device (100, 200) comprising a detection gas detector (5) for detecting a leakage flow rate of the detection gas leaking from the test object (11), A second vacuum pump (4) having an exhaust speed (S) greater than the exhaust speed of the detection gas detector (5) is provided between the vacuum vessel (1) and the detection gas detector (5); The second vacuum pump (4) is connected to the detection gas detector (5) via an outlet pipe (4b) having a conductance (C2) preset so that the pressure (P5) at the inlet (5a) of the detection gas detector (5) is equal to or lower than the allowable upper limit pressure. A leak inspection device characterized by:

2. 2. The leak test device according to claim 1, A fourth vacuum pump (6) for assisting the second vacuum pump (4) in evacuation is provided in the rear stage of the second vacuum pump (4) in parallel with the detection gas detector (5). A leak inspection device characterized by:

3. 2. The leak inspection method according to claim 1, The second vacuum pump (4) has an exhaust speed of 0.05 m ３ / s or more and the compression ratio is 10 or more A leak inspection device characterized by:

4. A leak inspection method for supplying a detection gas into a test object (11) placed inside a vacuum vessel (1) maintained at a predetermined vacuum pressure, and measuring a leakage flow rate of the detection gas leaking from the test object (11) by a detection gas detector (5), The leak inspection method is characterized in that a second vacuum pump (4) having an exhaust speed (S) greater than that of the detection gas detector (5) is connected to the vacuum vessel (1), and an exhaust port of the second vacuum pump (4) is connected to an outlet pipe (4b) having a conductance (C2) preset so that the pressure (P5) at the inlet part (5a) of the detection gas detector (5) is equal to or lower than an allowable upper limit pressure, and the exhaust flow from the second vacuum pump (4) is transferred to the inlet part (5a) of the detection gas detector (5) while reducing the pressure through the outlet pipe (4b). A leak inspection method comprising:

5. 5. The leak inspection method according to claim 4, The inside of the vacuum vessel (1) is evacuated to a vacuum by using the first vacuum pump (3) and the second vacuum pump (4) in combination. A leak inspection method comprising:

6. 5. The leak inspection method according to claim 4, A fourth vacuum pump (6) is provided in parallel with the detection gas detector (5) at the rear stage of the second vacuum pump (4), and the inside of the vacuum vessel (1) is evacuated to a vacuum while the exhaust gas of the second vacuum pump (4) is exhausted by the fourth vacuum pump (6). A leak inspection method comprising:

7. 5. The leak inspection method according to claim 4, The time for which the detection gas is introduced into the test object (11) and the leakage flow rate of the detection gas is measured is set to be equal to or longer than the time when the measured leakage flow rate becomes 63% or more of the saturated leakage flow rate by measuring the time transition of the leakage flow rate in advance. A leak inspection method comprising:

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