JP2008275355A - Leakage inspection method and leakage inspection device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve inspection sensitivity for leakage detection while keeping simplicity without regarding the relation of the trade off between the sensitivity and simplicity. <P>SOLUTION: The leakage inspection method of this invention is provided with a step for immersing inspecting parts 4 into a heated liquid 2 for inspection, and a step for changing pressure applied on the liquid 2 for inspection. The pressure is repeated between a reference pressure state P1 which is under a prescribed reference pressure and a reduced pressure state P2 which is under the pressure reduced from the prescribed reference pressure, and the period of reduced pressure state P2 is shorter than the period of the reference pressure state P1. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an inspection method and an inspection apparatus for evaluating leakage of a component to be inspected in an optical device, a high-frequency device, a capacitor, or the like.

  The inspection of comparatively large leaks in hermetic sealing parts such as electronic devices is described in, for example, JIS standard JIS-C60068-2-17 “Environmental test method-Electrical / electronic-Sealing (hermeticity) test method”. There is a Qc test. In this test method, a part to be inspected such as a hermetic sealing part is immersed in a test liquid, and the presence or absence of a leak is inspected based on bubbles released from the part to be inspected. In order to release the bubbles, the gas pressure inside the part to be inspected needs to be higher than the outside. As the method, the following three methods are known.

  The first method (hereinafter referred to as “Method 1”) is described in the above-mentioned Qc test method or Patent Document 1, and the part to be inspected is immersed in a test liquid so that the pressure outside the part to be inspected is substantially reduced. This is a test method in a container whose pressure is reduced to 0 atm. The second method (hereinafter, “method 2”) is a method of immersing in a high-temperature liquid. The third method (hereinafter referred to as “method 3”) is a method in which an inspected part is impregnated with an impregnating liquid having a boiling point lower than that of the test liquid, and then the inspected part is immersed in a high temperature test liquid. . “Method 1” is also described in the MIL standard.

JP-A-10-281916

  Each of these methods has advantages and disadvantages. In “Method 1”, the pressure outside the part to be inspected is reduced to almost 0 atm. Therefore, if there is a leak, the pressure difference between the inside and outside of the part to be inspected is almost 1 atm regardless of the initial pressure. Can do. Therefore, there is an advantage that the sensitivity of leak detection may be compared with “Method 2”. However, when the pressure is reduced, the air dissolved in the liquid grows as bubbles. This makes it impossible to distinguish between the bubbles dissolved in the test liquid (hereinafter referred to as dissolved bubbles) and the above-described bubbles (hereinafter referred to as leaked bubbles) that are discharged from the component to be inspected and inspect for leaks. . For this reason, it is necessary to prepare a degassed liquid as a test liquid in advance, and this degassing takes time.

  “Method 2” has the advantage that it can be easily evaluated in a short time compared to the other two methods, by simply immersing in a liquid whose temperature has been raised. However, there is a disadvantage that the sensitivity of leak detection is low compared to the other two methods.

  “Method 3” has the advantage of being most sensitive as compared to the other two methods because the pressure inside the component to be inspected can be increased to the vapor pressure at the temperature of the impregnating liquid of the test liquid. However, since the impregnation liquid is impregnated, there is a problem that it takes time and labor compared to the other two methods.

  That is, the sensitivity of leak detection may be in the order of “Method 3”, “Method 1”, and “Method 2”, and the convenience may be in the order of “Method 2”, “Method 1”, and “Method 3”. As described above, the conventional leak inspection has a problem in that sensitivity and simplicity have a trade-off relationship.

  The present invention has been made to solve the above-described problems, and an object thereof is to increase the sensitivity of leak detection while appropriately maintaining simplicity.

  The leak inspection method according to claim 1 includes (a) a step of immersing the part to be inspected in a heated test liquid, and (b) a step of changing a pressure applied to the test liquid. In the step (b), the pressure is a reference pressure state in which a predetermined reference pressure is applied and a reduced pressure state in which a pressure reduced from the predetermined reference pressure is applied. It is shorter than the time of the pressure state.

  According to the leak inspection method of the present invention, it is possible to increase the sensitivity of leak detection while maintaining simplicity.

<Embodiment 1>
There are three known leak inspection methods. The first method (hereinafter referred to as “method 1”) is a method in which a part to be inspected is immersed in a test liquid and tested in a container whose pressure outside the part to be inspected is reduced to almost 0 atm. The second method (hereinafter, “method 2”) is a method of immersing in a high-temperature liquid. The third method (hereinafter referred to as “method 3”) is a method in which an inspected part is impregnated with an impregnating liquid having a boiling point lower than that of the test liquid, and then the inspected part is immersed in a high temperature test liquid. . Before describing the leak inspection method and the leak inspection apparatus according to the present embodiment, factors that reduce the sensitivity of leak detection in “Method 1” to “Method 3” will be considered.

  FIGS. 2A to 2C show that when the component to be inspected 4 is immersed in the test liquid 2, the gas inside the component to be inspected 4 is formed as a bubble (hereinafter referred to as a leak bubble 12) through the leak path 11. FIG. 4 shows the state of the discharge to the outside of the part to be inspected 4 in time series.

  Assuming that the shape of the opening of the leak path 11 is circular, the shape of the leak bubble 12 is partially spherical due to surface tension until it is released from the leak path 11 as shown in FIG. . At this time, the surface tension tends to reduce the size of the leak bubble 12. The pressure due to the surface tension is 2σ / r where r is the bubble radius and σ is the surface tension.

  When the stage of FIG. 2 (c) in which the leak bubble 12 starts to expand beyond the stage of FIG. 2 (b), the pressure rise is rapidly reduced. Therefore, the surface tension pressure becomes maximum when the leak bubble 12 becomes hemispherical as shown in FIG. That is, the state of FIG. 2B becomes a bottleneck in the discharge of the leak bubbles 12.

  In the stage of FIG. 2B, twice the bubble radius r coincides with the opening diameter D of the leak path 11, and the pressure due to the surface tension is 4σ / D. If this pressure is greater than or equal to the pressure difference between the inside and the outside of the component 4 to be inspected, the leak bubble 12 does not grow and is not released, so that the leak cannot be detected.

  For example, in the case of “Method 2” immersed in a fluorocarbon heated to 125 ° C. as a test liquid 2 from a room temperature of 25 ° C., the pressure increase due to the temperature rise is 35000 Pa (≈101300 × ((125 + 273) / ( 25 + 273) -1)). On the other hand, when the surface tension of the fluorocarbon is 10 mN / m, the opening diameter of the leak path 11 where the pressure of bubble contraction due to the surface tension is the same as the pressure generated by the temperature rise is 1.1 μm. That is, in this example, when the opening diameter of the leak path 11 is 1.1 μm or less, the leak bubble 12 does not grow and the leak cannot be detected.

  In addition, once the leak bubbles 12 are released from the component 4 to be inspected, the internal pressure of the component 4 to be inspected decreases, so that the leak bubbles 12 are less likely to be released thereafter. On the other hand, immediately after the part 4 to be inspected is immersed in the test liquid 2, bubbles other than the leak bubbles 12 are involved. Therefore, even when the opening diameter of the leak path 11 is larger than 1.1 μm, if the leak bubble 12 is generated immediately after the part to be inspected 4 is immersed in the test liquid 2, it becomes difficult to detect the leak.

  Based on the above considerations, in order to increase the sensitivity of leak detection, it is conceivable to use a liquid having a small surface tension, or to give a pressure difference between the inside and the outside of the component 4 to be inspected that can overcome the surface tension.

  However, since the surface tension of the fluorocarbon is already small, it is difficult to greatly improve the detection sensitivity by changing the material of the test liquid 2. Further, in order to obtain a pressure difference between the inside and the outside of the component to be inspected 4 that only overcomes the surface tension, if the outside is kept under vacuum, the test liquid 2 is degassed as in “Method 1”. There is a problem that a process is required and takes time.

  Therefore, a leak inspection method according to the present embodiment that solves this problem will be described. FIG. 1 is a diagram showing a leak inspection apparatus for realizing the leak inspection method according to the present embodiment. The leak inspection apparatus according to the present embodiment includes a container composed of a transparent container 1 and a lid 5, a test liquid 2, a support 3, a component 4 to be inspected, a piston 6, a motor 8, and a belt 9. A pressurizing mechanism including a roller 10 and a controller 7 are provided.

  The container composed of the transparent container 1 and the lid 5 has a space inside, and the heated test liquid 2 and the component 4 to be inspected immersed in the test liquid 2 can be sealed in the space. is there. Hereinafter, this space is referred to as a sealed space.

  For the test liquid 2, for example, fluorocarbon is used. The test liquid 2 is heated to 125 ° C., for example. The transparent container 1 desirably has a temperature adjustment function in order to keep the temperature of the test liquid 2 constant.

  The component to be inspected 4 is, for example, a hermetic sealing component, and the number thereof may be singular or plural. The lid 5 is provided with a cylinder and a piston 6 that can be displaced in the vertical direction in FIG. 1 inside the cylinder.

  The pressurizing mechanism including the piston 6, the motor 8, the belt 9, and the roller 10 applies pressure to the air in the upper empty space in the container and applies pressure to the test liquid 2. When the piston 6 is displaced in the direction of increasing the volume of the sealed space, that is, upward in FIG. 1, the pressure applied to the air in the container decreases and the pressure applied to the test liquid 2 also decreases. .

  In the present embodiment, the controller 7 controls the motor 8 to rotate based on a sequence designated in advance. The power for rotating the motor 8 is transmitted to the piston 6 via the belt 9 and the roller 10. The displacement of the piston 6 in the vertical direction in FIG. 1 is controlled according to the rotation of the motor 8. Thus, the controller 7 performs control to change the pressure applied by the pressurizing mechanism.

  In the sequence, the rotation angle, timing, and cycle for rotating the motor 8 are designated in advance. Based on this sequence, the controller 7 repeats the pressure applied by the pressurizing mechanism between a reference pressure state where a predetermined reference pressure is applied and a reduced pressure state where a pressure reduced from the predetermined reference pressure is applied. Is controlled to be shorter than the time of the reference pressure state.

  By such control of the controller 7, the pressure of the air in the container changes as shown in FIG. The pressure in the reference pressure state P1 is equal to or higher than the atmospheric pressure, and the pressure in the reduced pressure state P2 is smaller than the atmospheric pressure. In the present embodiment, the pressure in the reference pressure state P1 is 1 atm, the time in the reference pressure state P1 is 100 msec, the pressure in the depressurized state P2 is 0.7 atm, and the time in the depressurized state P2 is 1 sec.

  A leak inspection method of the leak inspection apparatus configured as described above will be described. As shown in FIG. 1, the leak inspection apparatus places a component to be inspected 4 on a support 3 and immerses the component under inspection 4 in a heated test liquid 2.

  The leak inspection apparatus accommodates the test liquid 2 and the component to be inspected 4 immersed in the test liquid 2 in a container composed of the transparent container 1 and the lid 5. Then, pressure is applied to the test liquid 2 by applying pressure to the air in the upper empty space in the container by a pressurizing mechanism including the piston 6, the motor 8, the belt 9, and the roller 10.

  The controller 7 performs control to change the pressure applied to the air in the upper empty space in the container by the pressurizing mechanism as shown in FIG. The pressurizing mechanism applies pressure to the air in the upper empty space in the container and applies pressure to the test liquid 2. Therefore, the leak inspection apparatus changes the pressure applied to the test liquid 2 by the pressurizing mechanism and the controller 7 as shown in FIG.

  When attention is again paid to the process of releasing the leak bubbles 12, as described above, the surface tension pressure is maximized because the diameter of the leak bubbles 12 is the same as the opening of the leak path 11 (FIG. 2). b).

  At this stage, when the pressure applied to the test liquid 2 is reduced from the reference pressure state P1 to the reduced pressure state P2, the pressure difference between the inside and outside of the component 4 to be inspected is a leak in the stage before and after FIG. The pressure of the surface tension of the bubble 12 is exceeded. Therefore, even if the opening diameter of the leak path 11 is small, the leak bubbles 12 are emitted.

  The time required for the leak bubbles 12 to be released is the time required to exceed the states before and after FIG. 2B, and may be instantaneous. For example, when the pressure applied to the test liquid 2 is reduced from 1 atm to 0.7 atm, the leak bubble 12 is released if the time for applying 0.7 atm is at least about 100 msec.

  On the other hand, when the test liquid 2 is depressurized, the air dissolved in the test liquid 2 is a bubble (hereinafter referred to as dissolved bubble) whose core is dust, dust or the like adhering to the surface of the component 4 to be inspected or the inner surface of the transparent container 1. Grow as. The speed at which the dissolved bubbles grow depends on the degree of pressure reduction applied to the test liquid 2, the solubility coefficient of air in the test liquid 2, the diffusion coefficient of air in the test liquid 2, and the like. Specifically, the growth of dissolved bubbles becomes faster as the degree of decompression is larger, the solubility coefficient of air is larger, and the diffusion coefficient of air is larger.

  As in the above example, dissolved bubbles are also generated when the pressure applied to the test liquid 2 is reduced from 1 atm to 0.7 atm. However, when the time for applying a pressure of 0.7 atm to the test liquid 2 is shorter than 1 sec, the size is too small to be visually confirmed.

  In other words, when the pressure applied to the test liquid 2 is 0.7 atm, in order to make the bubble that can be visually confirmed only the leak bubble 12, the time applied at 0.7 atm is set as the leak bubble. What is necessary is just to set it as the range shorter than the time (1 sec) when the time which 12 is discharge | released (100 msec) or more, and a dissolved bubble grows into the bubble of the size which can be confirmed visually. Therefore, in the present embodiment, the pressure in the reduced pressure state P2 is 0.7 atm, and the time in the reduced pressure state P2 is 100 msec.

  Next, the leak inspection apparatus returns the pressure applied to the test liquid 2 to the reference pressure state P1 again. Then, dissolved bubbles having a size that cannot be visually confirmed dissolve in the test liquid 2 again. The time required for the dissolved bubbles to dissolve again in the test liquid 2 increases as the size of the grown dissolved bubbles increases.

  Here, if the time of the reference pressure state P1 is short, the dissolved bubbles will grow to a visible size when the decompression state P2 is set next. Therefore, the time of the reference pressure state P1 needs to be sufficiently longer than the time required for the dissolved bubbles to dissolve again in the test liquid 2. Therefore, the leak inspection apparatus makes the time in the reference pressure state P1 longer than the time in the reduced pressure state P2. In the present embodiment, the pressure in the reference pressure state P1 is 1 atm, the time in the reference pressure state P1 is 1 sec, and the time is longer than 100 msec in the reduced pressure state P2. Therefore, no dissolved bubbles are generated even when the pressure is reduced to the reduced pressure state P2.

  According to the leak inspection apparatus and the leak inspection method according to the present embodiment as described above, no dissolved bubbles are generated from the test liquid 2, and only the leak bubbles 12 are generated. Therefore, the leak bubble 12 can be reliably confirmed without misidentifying the dissolved bubble as the leak bubble 12. In this way, the sensitivity of leak detection can be increased while maintaining the same degree of convenience as “Method 2” without degassing the test liquid 2 in advance.

  Moreover, the pressure applied to the test liquid 2 can be easily changed by changing the pressure applied to the air in the upper empty space in the container.

  In the present embodiment, the pressure in the reference pressure state P1 is 1 atmosphere. However, the pressure is not limited to this, and the pressure in the reference pressure state P1 may be further increased as long as the pressure is lower than the pressure in the component 4 to be inspected. In this case, the time for the reference pressure state P1 can be further shortened.

  Further, the pressurizing mechanism for applying pressure to the air in the container is not limited to the mechanism shown in the present embodiment, but is a diaphragm pump (membrane pump) having a membrane that can be deformed in the vertical direction, or a gear. A mechanism including a pump such as a pump or a turbo pump may be used. Even in those cases, the same effect as the present embodiment can be obtained.

<Embodiment 2>
In the leak inspection method of the first embodiment, the presence / absence of a leak is determined based on the presence / absence of a leak bubble 12 as in the prior art. That is, the airtightness of the component 4 to be inspected was evaluated by the zero-zero determination. In the present embodiment, the airtightness of the component 4 to be inspected is evaluated by a method different from that of the first embodiment. Hereinafter, the configuration and processes to be newly described are the same as those in the first embodiment.

  FIG. 4 shows the pressure of air in the container constituted by the transparent container 1 and the lid 5. In the present embodiment, as shown in FIG. 4, after the reference pressure state P1, the controller 7 sets the degree of decompression in each of the repeated decompression states P2 to P4 in the order of the decompression state P2, the decompression state P3, and the decompression state P4. Increase with time. Here, the pressure in the reference pressure state P1 is, for example, 1 atm.

  In order to generate the leak bubbles 12 when the opening diameter of the leak path 11 is small, it is necessary to increase the degree of decompression in the decompressed states P2 to P4. Therefore, in the leak inspection apparatus and leak inspection method according to the present embodiment as described above, the degree of decompression is increased with time. Therefore, by recording the pressure indicators P1 to P4 of the pressure at which the leak bubbles 12 are generated, for example, the opening diameter of the leak path 11 of the component 4 to be inspected can be quantified and evaluated with the indicators P1 to P4. That is, by classifying the airtightness of the component 4 to be inspected into the indicators P1 to P4, the product management of the component 4 to be inspected can be made precise. In this embodiment, the indicators P1 to P4 are classified, but the number may be small or large.

  In the above-described leak inspection apparatus and leak inspection method, as shown in FIG. 4, each time the pressure takes each of the reduced pressure states P2 to P4, the degree of pressure reduction in the reduced pressure states P2 to P4 is increased. However, the present invention is not limited to this, and as shown in FIG. 5, the controller 7 may repeat the depressurized states P2 to P4 a plurality of times at the same depressurization degree.

  As described above, by repeating the reduced pressure states P2 to P4 a plurality of times at the same reduced pressure level, the leak bubbles 12 can be easily confirmed, and oversight can be reduced.

  In the first embodiment as well, by repeatedly performing the depressurized state P2 a plurality of times at the same depressurization degree, the leak bubbles 12 can be easily confirmed, and oversight can be reduced.

<Embodiment 3>
In the above embodiment, the controller 7 performs control to change the pressure applied by the pressurizing mechanism based on a sequence designated in advance. In the present embodiment, unlike the above-described embodiments, the sensitivity of leak detection is increased while maintaining the same level of convenience as “Method 2” without using a sequence. Hereinafter, the configuration and process to be newly described are the same as those in the first embodiment.

  In the present embodiment, the pressure applied by the pressurizing mechanism changes sinusoidally or cosinely with respect to time, as shown in FIG. Specifically, in FIG. 1, the roller 10 continues to rotate in one direction of the arrow via the belt 9 by the power that the motor 8 rotates. And it carries out by the roller 10 displacing piston 6 to the up-down direction of FIG. Here, the minimum value of the pressure is smaller than atmospheric pressure, and the time average of the pressure is equal to or higher than atmospheric pressure.

  According to the leak inspection method and the leak inspection apparatus according to the present embodiment as described above, no dissolved bubbles are generated from the test liquid 2, and only the leak bubbles 12 are generated. Therefore, the leak bubble 12 can be reliably confirmed without misidentifying the dissolved bubble as the leak bubble 12. Thus, the sensitivity of leak detection can be increased while maintaining simplicity. Further, in the present embodiment, the motor 8 need only be turned on at the start of the inspection and turned off after the end of the inspection without performing complicated sequence control by the controller 7. In this way, since only the rotational speed needs to be controlled, the leak inspection apparatus can be realized with a simpler mechanism than in the first embodiment.

1 is a schematic diagram showing a leak inspection apparatus according to Embodiment 1. FIG. 6 is a diagram showing a leak inspection method according to Embodiment 1. FIG. 6 is a diagram showing a leak inspection method according to Embodiment 1. FIG. 6 is a diagram showing a leak inspection method according to Embodiment 2. FIG. 6 is a diagram showing a leak inspection method according to Embodiment 2. FIG. 6 is a diagram showing a leak inspection method according to Embodiment 3. FIG.

Explanation of symbols

  1 transparent container, 2 test liquid, 3 support, 4 parts to be inspected, 5 lid, 6 piston, 7 controller, 8 motor, 9 belt, 10 roller, 11 leak path, 12 leak bubble.

Claims (9)

(A) immersing the part to be inspected in a heated test liquid;
(B) changing the pressure applied to the test liquid,
In the step (b),
The pressure repeats a reference pressure state applied with a predetermined reference pressure and a reduced pressure state applied with a pressure reduced from the predetermined reference pressure,
The time in the reduced pressure state is shorter than the time in the reference pressure state,
Leak inspection method. In the step (b),
Increasing the degree of decompression in each of the repeated decompression states with time,
The leak inspection method according to claim 1. In the step (b),
Repeating the reduced pressure state multiple times at the same degree of vacuum,
The leak inspection method according to claim 1 or 2. (A) immersing the part to be inspected in a heated test liquid;
(B) changing the pressure applied to the test liquid,
In the step (b),
The pressure changes in a sinusoidal or cosine waveform with respect to time, the minimum value of the pressure is smaller than atmospheric pressure, and the time average of the pressure is equal to or higher than atmospheric pressure.
Leak inspection method. In the step (b), the pressure is applied to the air in the upper empty space in the container in which the test liquid is stored, and the pressure is applied to the test liquid.
The leak inspection method according to claim 1. A container having a space inside and capable of sealing a heated test liquid and a component to be inspected immersed in the test liquid in the space;
A pressure mechanism for applying pressure to the air in the upper empty space in the container and applying the pressure to the test liquid;
A controller that performs control to change the pressure applied by the pressurizing mechanism,
The controller is
The pressure applied by the pressurizing mechanism repeats a reference pressure state in which a predetermined reference pressure is applied and a reduced pressure state in which a pressure reduced from the predetermined reference pressure is applied. Control to be shorter than the pressure state time,
Leak inspection device. The controller is
Increasing the degree of decompression in each of the repeated decompression states with time,
The leak inspection apparatus according to claim 6. The controller is
Repeating the reduced pressure state multiple times at the same degree of vacuum,
The leak inspection apparatus according to claim 6 or 7. A container having a space inside and capable of sealing a heated test liquid and a component to be inspected immersed in the test liquid in the space;
A pressure mechanism that applies pressure to the air in the upper empty space in the container and applies the pressure to the test liquid;
The pressure applied by the pressurizing mechanism changes in a sine waveform or a cosine waveform with respect to time, the minimum value of the pressure is smaller than atmospheric pressure, and the time average of the pressure is equal to or higher than atmospheric pressure. is there,
Leak inspection device.

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