JPS6332488B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a metal filter for screening ultrafine particles having uniform pore size, high mechanical strength, and high pore size.

Conventionally, filters for screening dust, nonmetallic inclusions in steel, pigments, abrasives, etc., and measuring particle size distribution are made by electroplating metals such as nickel or copper onto a conductive substrate having a photolithographic resist pattern. It is manufactured by
This filter has pores of ~25μ, but filters with pores of 5μ or less are also manufactured as required.

FIGS. 1 and 2 are schematic cross-sectional views of metal filter manufacturing by a conventional method. In order to obtain a metal filter with a finer pore diameter than conventional ones, for example, a pore diameter of 5 μm or less, a conductive film on which a photoresist layer has been previously provided is used as shown in FIG. A resist pattern 2 is formed on a substrate 1, for example, a metal plate made of copper, nickel, chrome, stainless steel, etc., by photolithography (Fig. 1a), and a metal 3 such as nickel or copper is electroplated on the exposed part of the substrate. After manufacturing a filter with a pore diameter of 5μ or more (Fig. 1b), the filter 3 is peeled off from the substrate 1 (Fig. 1c), and after the resist is removed, it is further plated to reduce the pore diameter (Fig. 1c). 1d) method, or as shown in FIG. 2, gold, silver,
A mesh-like pattern is formed by a photoetching method through a photoresist layer (not shown) on which a conductive film 5 of platinum, palladium, chromium, tin oxide, indium oxide, etc. is provided.
Figure b), then electroplating metal such as nickel or copper on this conductive substrate (Figure 2 c) to produce a filter with an pore diameter of 5μ or more. Peel it off (second
d), and further plating to reduce the pore diameter (Fig. 2 e method is used to manufacture a filter with a desired pore diameter. The resist pattern on the film has a large pitch, and as the pore diameter is reduced, the pore area ratio is further reduced.

The photosensitive material used in this case can be used to
Since the pore diameter of the initial resist pattern is 5μ or more, it is not necessary to use photoresists used for microfabrication, such as solvent-based resists such as AZ resist (Shippray), waycoat (Hunt), and KMR (Kodatsu). Water-soluble resists whose main ingredients are polyvinyl alcohol, casein, brew, gelatin, egg white, and ciara, etc., whose resolution is inferior to those of solvent-based resists, are also used.
However, the metal filters obtained by these methods have the disadvantage that the shape of the openings is poor and the aperture ratio is extremely low.Also, with these methods, if you want to increase the aperture ratio, you cannot increase the metal thickness. Ta. Furthermore, when the metal is thin, the weight of the metal itself causes wrinkles and sagging in the metal filter, which changes the dimensions and positional accuracy of the opening, and the mechanical strength is low, making it easy to break. The drawback was that it lacked practicality. Normally, when used as a metal filter for sieving, the metal thickness must be 5μ to maintain mechanical strength.
The above is necessary.

In order to improve the above-mentioned drawbacks of conventional metal filters, the present invention, as a result of various researches, uses a smooth conductive substrate, thickens the photoresist film,
And by precipitating metal with fine crystal grains,
Without reducing the pore diameter by plating,
The present invention provides a method for manufacturing a metal filter for sieving fine particles, which has a uniform fine pore size of 25 μm or less, has a high aperture ratio, and has mechanical strength by electroforming on a conductive substrate.

Hereinafter, the above-described present invention will be explained in detail with reference to the drawings. FIG. 3 is a cross-sectional view schematically showing each step of an example of a method for manufacturing a metal filter using a photomask P. First, Figure 3a
As shown in FIG. 2, an original plate having a fine pattern is brought into close contact with a photoresist layer 22 provided on a conductive substrate 21 using a photomask P, and then burned with ultraviolet light or deep ultraviolet light 20. Thereafter, a resist pattern 22A is obtained by developing as shown in FIG. 3b. Next, a metal filter can be manufactured by electroplating the metal 23 as shown in FIG. 3c using a conventional electroforming method, and then peeling off the metal 23 as shown in FIG. 3d.

The conductive substrate used above must have a smooth surface in order to make the pore diameter uniform (within a tolerance of 10%), and the surface roughness must be 0.5 μ or less. For example, when manufacturing a metal filter with a pore diameter of 25μ or less using a metal plate made of copper, nickel, stainless steel, etc., the surface roughness can be improved by chemical methods such as electrolytic polishing or chemical polishing, or mechanical methods such as buffing. Should be 0.5μ or less.
Also, there should be no undulations, dents, scratches, etc. On the other hand, even when a conductive substrate having a conductive film formed on an insulating material such as glass is used, the smoothness and defects such as scratches are the same. The roughness of the substrate surface affects the uniformity of the coating thickness of the photosensitive material and the adhesion between the mask original and the conductive substrate during exposure, and the higher the surface roughness, the worse the resolution of the photosensitive material. Therefore, if the surface roughness is rougher than 0.5μ, the uniformity of the pore diameter will be significantly lacking and it cannot be applied to the present invention.

In the present invention, since the thickness of the metal layer is 5 μm or less than the thickness of the photoresist layer, a metal filter having a uniform pore diameter almost equivalent to that of the mask pattern can be obtained. The thickness of the photoresist used is 5μ or more, and as a high-resolution photoresist, a positive type photoresist is preferable, and as an ultraviolet ray resist, an AZ-based resist (manufactured by Shippray Co., Ltd.), for example, is used.
AZ111, AZ119, AZ1350J, AZ2400, AZ2430,
As far-UV resists, PMMA (polymethyl methacrylate, manufactured by Tokyo Ohka Co., Ltd.), PMIPK
(polymethyl isopropenyl ketone), PBMA (polybutyl methacrylate) and AZ2400,
AZ2430 is suitable.

Incidentally, if the resist thickness is thinner than 5 μm, the thickness of the metal filter will be insufficient and the mechanical strength will be insufficient.

In addition, the uniform electrodeposition of the plating and the size of the particles also affect the pore diameter accuracy, so smooth fine particles with a crystal grain size of 2.5μ or less should be selected, taking into consideration the electrodeposition conditions and the composition of the plating solution. use In the case of the present invention, the pore diameter of the metal filter is determined by the size of the image area of the photoresist, and if the smallest part of the pore is defined as the pore diameter, the diameter of the pore is determined by the size of the plating particles at each part of the cross section of the pore. The pore diameters will be different. In other words, if the radius of the plating particle is r, there will be a part with a larger pore diameter by 2r, which means that the precision of a metal filter with a pore diameter of 25μ or less will be
In the case of production within 10% (within 2.5μ), the size of the plating particles (2r) must be 2.5μ or less, and those larger than 2.5μ cannot be applied to the present invention. Nickel, copper, etc. are used as the metal.

Uniform electrodeposition and smoothness of plating vary depending on metal ion concentration, temperature, pH, buffering agent, brightener, and current density, but an example of the nickel plating bath and electrodeposition conditions according to the method of the present invention is as follows. It is as follows.

Metal bath Nickel sulfate 240g / Nickel chloride 45g / Boric acid 30g / Butyne-1,4-diolnaphthalene-sulfonic acid sodium 5-10g / Formalin 1-2 c.c. / Electrodeposition conditions PH 3.8-4.5 Temperature 40-50 °C Current density 2 to 10 A/dm ² If you want to add chemical resistance to the above metal filter, remove the plating and then chemically activate the plating surface to create a gold layer with a thickness of several thousand Å to several μ. Plating with platinum, rhodium, palladium, indium, ruthenium, etc. may be performed.

In this case, the pore diameter is slightly reduced, but the dimensions of the mask pattern may be corrected in advance by the amount of reduction. Even in this case, since the reduction rate of the pore diameter is small, the uniformity of the pore diameter is superior to that of conventional metal filters.

According to the method of the present invention, a metal filter with a pore size of 25μ or less can be obtained, but it is also possible to obtain a metal filter with a pore size of 1μ or less by setting the substrate surface roughness to 0.1μ or less and the plating crystal particle size to 0.1μ or less. It has the characteristic that it can be obtained.

In the case of the present invention, a smooth conductive substrate is used, a high-resolution material is used as the photosensitive material with a film thickness greater than that required by the filter, and a metal with extremely fine crystal grains is deposited. Therefore, the pore diameter of the manufactured metal filter is fine and uniform, and the pore size is much higher than that of conventional filters. Further, it is not necessary to reduce the pore diameter of the filter by plating.

Hereinafter, the present invention will be explained in more detail with reference to Examples.

Example 1 As a conductive substrate, the surface roughness is approximately 0.1 μ and the plate thickness is 0.3
A copper plate (manufactured by Tamagawa Kikai Kinzoku Co., Ltd.) having a diameter of 1 mm was immersed in a 5% aqueous chromic acid solution and then washed with water to form a release layer. Next, apply PMMA resist (manufactured by Tokyo Ohka Kogyo Co., Ltd.) using a spinner, and after drying, approximately 6μ
The film thickness was obtained. Next, a photomask having a mesh pattern with a line width of 3μ x 3μ and a pitch of 8μ, whose substrate is quartz glass (manufactured by Nippon Quartz Glass Co., Ltd.), is closely attached.
Xenon-mercury lamp light source (manufactured by Ushio Electric Co., Ltd.)
UXM-500MA) for deep UV exposure, then
After development with a 9:1 mixed solution of isoamyl acetate and ethyl acetate and drying, the resist image was observed using an electron microscope to find that it had a square prism structure, and the resist line width was almost the same as the mask pattern line width. Next, nickel plating was performed to a thickness of 5 μm in a bright nickel sulfamic acid bath at a bath temperature of 60° C. and a current density of 5 A/dm ² , and the size of the crystal grains was measured and found to be 0.2 μm at maximum. Next, the plating was peeled off from the substrate, and the pore diameter was 3μ, the pitch was 8μ, and the pore size was approximately 14%.
A metal filter for sieving fine particles having a uniform pore size of .

Example 2 Conductive substrate with surface roughness of approximately 0.1μ and plate thickness of 0.5mm
Using stainless steel plate (manufactured by Nippon Kogyo), degreasing,
Perform pre-treatment consisting of washing with water and drying, then
AZ1350J resist (manufactured by Shippray, USA) was applied using a spinner to obtain a film thickness of approximately 5 μm after drying.
Next, a photomask having a mesh pattern with a line width of 3 μ x 3 μ and a pitch of 8 μ was closely attached and exposed to ultraviolet light using an ultra-high pressure mercury lamp light source (BMD-500D manufactured by Wacom Manufacturing Co., Ltd.). After development and drying, the resist image was observed using an electron microscope, and it was found to have an almost quadrangular pyramidal structure, with a mask pattern line width of 3μ×
3μ, the minimum part of the resist pattern line width is
It was 2.5μ×2.5μ. Next, nickel plating of fine particles with a thickness of 5μ (crystal particle size, maximum 0.2μ) was performed in a bright wax nickel bath at 50℃ and a current density of 5A/ ^dm2 .
Then, the plating was peeled off from the substrate to obtain a metal filter for sieving fine particles having a uniform pore size of 2.5 μm in pore size, 8 μm in pitch, and a pore size of about 9.8%.

[Brief explanation of drawings]

FIGS. 1 and 2 are cross-sectional views schematically showing the manufacturing process of a metal filter by the conventional electroforming method, respectively. FIG. 3 is a cross-sectional view schematically showing each step of an example of a method for manufacturing a metal filter according to the method of the present invention. 20... Ultraviolet rays or deep ultraviolet rays, 21... Conductive substrate, 22... Photoresist layer, 22A... Resist pattern, 23... Metal.

Claims (1)

[Claims] 1 On a smooth conductive base material with a surface roughness of 0.5μ or less,
After applying a photosensitive material to a thickness of 5μ or more, a fine pattern is printed on the photosensitive material layer through a photomask, and then developed to form a resist pattern, and then a resist pattern is formed on the conductive substrate having the resist pattern. A metal for sieving ultrafine particles, characterized in that a metal having a crystal grain size of 2.5 μm or less is deposited by an electroforming method to a thickness equal to or less than the thickness of the resist pattern, and then the deposited metal is peeled off from the substrate. Filter manufacturing method.