JP2695754B2 - Air filter leak inspection method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air filter leak inspection method using silica particles as aerosol particles for leak inspection, and more particularly to a HEPA filter,
The present invention relates to a method for inspecting an ultra-high performance air filter such as an ULPA filter for a leak.

[0002]

2. Description of the Related Art 99.97 fine particles having a particle diameter of 0.3 μm are used.
For ultra-high performance air filters such as HEPA filters and ULPA filters that collect at an efficiency of more than 10%, a leak test is performed on each filter in order to confirm that there is no leakage from the pinholes of the filter media or the bonding portion with the frame. Will be Leak inspection is performed by introducing aerosol particles into the airflow on the upstream side of the filter while sending air to the air filter, and scanning the suction probe of a particle detector such as a particle counter or a photometer on the downstream surface of the filter. It detects leaked particles.

[0003] As aerosol particles for leak inspection, J
Dioctyl phthalate (DOP) particles, defined as 13 or 14 dusts in IS Z 8912,
Commonly used. A method of generating DOP particles is to immerse a nozzle called a Ruskin nozzle in a DOP liquid, and generate DOP particles having a particle diameter of 1 micron or less by a compressed air flow ejected from a nozzle hole. Its structure is JIS B
9927.

[0004] DO inspection is also required for leak inspection of ultra-high performance air filters used in clean rooms for manufacturing electronic devices.
P particles are used. DOP attached to the filter medium during the leak test gradually evaporates in the air passing through the filter and scatters in the clean room. When the DOP adheres to the surface of the silicon wafer, there arises a problem of deteriorating the characteristics of electronic devices manufactured from the silicon wafer, such as a decrease in withstand voltage of the insulating film.

[0005] In order to avoid contamination of a clean room due to volatilization of liquid mist adhering to a filter such as a DOP, several methods using solid particles have been proposed.

One is a European standard (EUROVE).
NT 4/4, "Sodium chloride a
erosol test for filters u
sing frame photometric te
In this method, particles of sodium chloride or the like are generated by spraying an aqueous solution of sodium chloride or the like and drying the produced droplets as described in “Chnique”). Therefore, there is a danger that the filter media will be contaminated and scattered in the clean room.

There is also a method of generating fine particles of polystyrene latex by spraying a suspension of polystyrene latex particles for a filter assay and drying the produced droplets. Polystyrene latex particles are unlikely to be a source of contamination in the electronic device manufacturing process, but they are likely to aggregate in the dispersion medium and make it difficult to increase the solids concentration in the suspension. In order to generate particles, see JP-A-5-31.
A complicated and special device as disclosed in Japanese Patent No. 7671 is required.

[0008] In addition, airborne dust in the air may be used as particles for filter inspection. However, since the concentration fluctuates due to weather conditions and the like, the reliability of leak inspection is low. For example,
If the dust concentration is too low, the number of particles leaking to the downstream side with the leak is reduced, so that the leak may be overlooked. In addition, there is a risk that the filter media will be contaminated by heavy metals and the like contained in the atmospheric dust and scattered in the clean room.

[0009]

Therefore, the above method has the following problems.

(1) When a leak test is performed on DOP particles, DOP attached to the air filter re-scatters from the air filter, causing secondary contamination in a clean area.

(2) When a leak test is performed with an aqueous solution of sodium chloride or the like, the filter medium is contaminated with sodium chloride, which causes secondary contamination of a clean area.

(3) When a leak test is performed using polystyrene latex particles, a complicated and special device is required to generate high-concentration particles required for the test.

(4) When a leak test is performed with air dust, the air filter is contaminated by the air dust, which causes secondary contamination in a clean area. In addition, since the concentration of atmospheric dust varies depending on weather conditions and the like, the reliability of the leak test decreases.

The present invention has been made in order to solve the above-mentioned problems, and an object of the present invention is to use silica particles so that secondary contamination does not occur and silica particles are downstream of the filter. It is an object of the present invention to provide a method for inspecting a leak of an ultra-high performance air filter which does not contaminate a clean area even if it scatters.

Another object of the present invention is to provide a method for inspecting a leak of a high-performance air filter which can be performed by using a relatively inexpensive device conventionally used.

It is still another object of the present invention to provide a leak inspection method for a high performance air filter which can increase the reliability of the leak inspection.

Still another object of the present invention is to provide a method capable of efficiently and inexpensively manufacturing a high-performance air filter with improved reliability by using the above-described leak inspection method.

[0018]

According to the method for inspecting a leak of an air filter of the present invention, a suspension of colloidal silica is sprayed and then dried, and the produced silica particles are introduced into an air stream on the upstream side of the air filter. And detecting the silica particles leaking downstream of the air filter using a particle detector, thereby achieving the above object.

The air filter is generally made of HE
It is a high-performance filter such as a PA filter or an ULPA filter.

The suspension of the particulate silica particles is colloid
It is preferably a suspension of silica particles .

[0021]

[0022]

The present invention will be described in more detail as follows.

In order to avoid secondary contamination due to scattering of aerosol particles adhering to the filter during the leak inspection of the filter, the aerosol particles for the leak inspection are in a solid form having no volatility. Silica containing no metal or organic components (S
i0 ₂₎ to use the particle.

The suspension of colloidal silica used in the present invention is a colloidal solution of high molecular weight silicic anhydride, and the particle size of the colloidal particles is usually 0.1 μm or less. The colloid particles have a very fine spherical shape and are monodispersed and stably present in the liquid phase due to the potential of the particle surface. When the solid content concentration of the silica particles in the suspension exceeds 15% by weight, the silica concentration is too high and the nozzle of the Collison atomizer is easily clogged, resulting in poor workability.
As shown in (1), the amount is less than 10 ¹⁰ per minute, so that the content is preferably 0.4 to 15% by weight, more preferably 0.5 to 12% by weight. To spray this suspension, a conventionally known device is used.
It can be used litho N'atomaiza.

Since the sprayed silica particles are in the form of droplets, the water in the droplets is dried before being injected into the airflow upstream of the ultra-high performance filter to be inspected. A conventionally known dryer is used to dry the droplets.

The silica particles leaking to the downstream side of the filter are detected by using a particle detector such as a particle counter according to the procedure specified in JIS B9927, and the presence or absence of the leak is determined. In order to increase the leak detection sensitivity and increase the reliability, the higher the particle concentration on the upstream side of the filter, the better. In the case of leak inspection of an ultra-high performance air filter for electronic device manufacturing clean room, the particle size is 0.1μm
Preferably, more than 10 ¹⁰ larger aerosol particles can be generated per minute. For this purpose, as shown in FIG. 1, when the particle size of the silica in the suspension to be sprayed is 0.055 μm, the concentration of the solid content of the silica in the liquid is 0.4% by weight or more. In the case of 18 μm, the content is preferably 1% by weight or more.

The present invention can be used for leak inspection of various filters. For example, an air filter for a biological clean room, a filter for a mask, a filter for a gas line, and a filter for a disk device may be mentioned. In particular, it is suitably used for a clean room in an electronic device manufacturing process.

[0029]

By spraying a suspension of colloidal silica and then drying it, more than 10 ¹⁰ aerosol particles having a particle diameter of more than 0.1 μm can be generated per minute.

Injecting the generated silica particles into the air stream on the upstream side of the ultra-high performance air filter, and detecting the silica particles leaking to the downstream side of the air filter using a particle detector. Thus, the presence or absence of a leak in the filter can be determined.

As described above, by using silica particles as the aerosol particles, it is possible to avoid secondary contamination of a clean area due to organic substances, metals, and the like generated from the aerosol particles attached to the filter during the leak test. Also,
As described above, particles required for a leak test can be easily generated at a high concentration, so that the reliability of the leak test can be improved.

[0032]

Embodiments Hereinafter, specific embodiments will be described.

First, the outline of a silica particle generator used in this embodiment and a leak inspection device for an ultra-high performance air filter using silica particles will be described.

As shown in FIG. 2, a silica particle generator A is charged with a colloidal silica suspension and contains a Collison type atomizer 16 in a particle generator 10.
And an air supply pipe 11 through which compressed air is sent to the generator 10.
And a filter 12, a regulator 13, a flow meter 14, and a pressure gauge 15 connected to the air supply pipe 11, and a drying cylinder for feeding fine droplets containing colloidal silica particles generated by the generator 10 due to the inflow of the air. And 17.
In the drawing, reference numeral 18 denotes an air supply pipe for sending air to the drying cylinder 17, and a valve 19 and a flow meter 20 are connected to the air supply pipe 18, respectively.

As shown in FIG. 3, a leak inspection apparatus B for an ultra-high performance air filter includes a test chamber 21 in which a test filter 20 is disposed, an air supply pipe 22 for sending clean air to the test chamber 21, Chamber 21
A path 23 for sampling air upstream of the filter 20, a path 24 for sampling air downstream of the filter 20, and a particle counter 2.
5 and a silica aerosol particle generator A shown in FIG. 2 for introducing the silica aerosol into the air supply pipe 22. 26 is a filter in the figure, 27
Is a blower, 28 is an orifice flow meter, 29 is a manometer, and 30 is a sampling probe.

A colloidal silica solution having an average particle size of 0.055 μm and a solid content of 50% was prepared, and this was diluted 6.25 times with pure water having a specific resistance of 10 ¹⁸ MΩm to obtain a solid solution having a solid content of 8%. A suspension of colloidal silica was made. This suspension is charged into a particle generator 10 equipped with a Corison type atomizer 16 as shown in FIG.
The liquid was applied to the generator 10 at a flow rate of min to generate fine droplets containing colloidal silica particles.

The droplets are mixed with air at room temperature and normal pressure at a flow rate of 70 l / min, which is filtered through a filter 12 and dried over silica gel, and dried to form colloidal particles of silica (hereinafter also referred to as silica particles). ). The generated silica particles are collected by a Nuclepore filter,
The particle size of the silica particles was measured with a scanning electron microscope, and it was confirmed that silica particles having a particle size of 0.1 μm or more were generated (FIG. 4). FIG. 4 is a copy of a scanning electron micrograph at a magnification of 5.000 times, and the white portion in the figure indicates silica particles.

Using the silica particles, a leak test of an air filter for a clean room was performed using the apparatus shown in FIG. The concentration of silica particles on the upstream side of the filter was 3.5 × 10 ⁹ particles / m ³ for particles having a particle diameter of 0.1 μm or more. Air filter for clean room has vertical 61c
m, the width is 122 cm, and the allowable leak rate is 0.001% or less at an air volume of 20 m ³ / min.

Six filters were prepared and the outer diameter was 0.1
Drill a hole in the filter medium with a needle of
Particles leaking to the downstream of the filter from each leak location are detected by a particle counter (μLPC110 Turbo, manufactured by PMS) with two artificial leaks, and the leak rate of each leak (particles downstream of the filter) Concentration / particle concentration on the upstream side of the filter).

Next, the leak rate was determined with the same filter by a conventional method. The measuring device having the structure shown in FIG. 3 was used in the same manner as above. DOP particles were generated from a raskin nozzle type generator in JIS B9927 and injected into the airflow upstream of the filter. Particles leaking to the downstream of the filter from each leak point are measured with a photometer (JIS
Z4812 light scattering relative densitometer, manufactured by ATI,
TDA-2E), and the leak rate of each leak was determined.

FIG. 5 shows a plot of the leak rate determined using the silica particles on the ordinate and the leak rate determined using the DOP particles on the abscissa. From this, it was confirmed that the leak measurement result by the method of the present invention was in good agreement with that by the conventional DOP.

[0042]

As described above, according to the present invention, the following effects can be obtained.

[0043] (1) as tracer particles to be introduced in order filter upstream to detect leaks, silica particles (Si
Since O ₂ ) is used, particles adhering to the filter do not volatilize as in the case of using current DOP particles, and therefore, no secondary contamination occurs on the downstream side of the filter. Further, even if the silica particles are scattered downstream of the filter, they do not contain metals or organic substances harmful to the electronic device manufacturing process such as sodium, and thus do not pollute the clean area.

(2) The colloidal silica has a particle size of 0.1 μm.
The particles having a particle size of m or less are stably dispersed without being aggregated in the liquid phase at a high concentration. Therefore, by spraying a solution in a known manner (Koriso N'a Tomah <br/> Isa), silica aerosol particles (particle size 0.1μm or more) is relatively easily generated in the high concentration (10 ¹⁰ / min or more), and the reliability of the leak test can be improved.

(3) The leak rate obtained by detecting the silica particles leaking from the leak location with a particle counter is in good agreement with the value obtained by the conventional measuring method using DOP. Applicable as a law.

(4) A high-performance air filter with improved reliability can be manufactured efficiently and inexpensively by using the above-described leak inspection method.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the solid content concentration in a silica suspension and the amount of silica aerosol generated.

FIG. 2 is a schematic view showing a method for generating silica particles.

FIG. 3 is a schematic view showing a method for inspecting a leak of an ultra-high performance air filter using silica particles.

FIG. 4 is a copy of a photograph showing the structure of silica particles taken by a scanning electron microscope.

FIG. 5 is a diagram showing the correlation between the leak rate measurement results of the ultra-high performance air filter by the conventional method and the method of the present invention.

[Explanation of symbols]

 Reference Signs List A A silica particle generator 16 Collison atomizer 10 Particle generator 17 Drying cylinder B Ultra-high performance air filter leak inspection device 20 Test filter 21 Test chamber

Claims (3)

(57) [Claims] 1. A particle having a particle size of 0.055 to 0.18 μm.
Using the particulate silica, the solid content concentration of the particulate silica is
0.4 to 15 to prepare the weight percent of the suspension, dried after spraying a suspension of the particulate silica, the silica particles having a particle diameter of more than 0.1 [mu] m, 10 ¹⁰ per 1 minute Generated above, throwing the generated silica particles into the airflow on the upstream side of the air filter, and detecting the silica particles leaking to the downstream side of the air filter using a particle detector, Inspection method for air filter including: 2. The method according to claim 1, wherein the air filter is a HEPA filter or a ULPA filter. Wherein a suspension of the particulate silica particles, the suspension is a claim 1 or 2 leak inspection method of the air filter according colloidal silica particles.