JP2000023297A - Production of anisotropic conductive material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method to produce a minute backing member corresponding to a minute composite piezoelectric material that is used for an ultrasonic transducer. SOLUTION: A resist layer 2 is formed on a substrate 1 for the X-ray lithography, and the layer 2 is irradiated by the X-rays via a mask 3. Thus, the layer 2 is developed to obtain a resist pattern 2' where plural minute holes are arrayed with spaces. A metallic material 5 is stacked on the pattern 2', and a metallic body 5' where plural columnar bodies are arrayed with spaces is separated from the pattern 2'. An electrically insulated material 7 is molded with the body 5' used as a mold. The holes of a molded electrically insulated material 7' are filled with a conductive material 9 to obtain a backing member 10 where many conductive columnar bodies 9' are arrayed in the material 7'.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an anisotropic conductive material, and more particularly to a method for producing an anisotropic conductive material useful for wiring to a transducer used in an ultrasonic probe or the like.

[0002]

2. Description of the Related Art A composite piezoelectric material having a structure as shown in FIG. 5 has been used for an ultrasonic probe or the like of an ultrasonic medical diagnostic apparatus. In such a composite piezoelectric material 50, a large number of quadrangular prism-shaped piezoelectric ceramic bodies 51 are regularly arranged in a resin matrix 52 at predetermined intervals. For example, to obtain an ultrasound probe, electrodes including strip electrodes are formed on the major surface of such a composite material. In order to perform wiring for each of the arranged piezoelectric ceramics, the electrodes are divided, and an n × m arrangement is formed according to the arrangement of the piezoelectric ceramics.

A backing material (back load material) having a predetermined acoustic impedance is disposed on the surface of the above-described composite piezoelectric material opposite to the ultrasonic oscillation side to attenuate and absorb ultrasonic waves. Such a backing material is disclosed in U.S. Pat. No. 5,648,942, and comprises a plurality of independent conductive posts and a non-conductive material covering the plurality of posts. ing. The conductive material is, for example, a composite material of a metal powder and an epoxy resin. Such a backing material is manufactured by a process as shown in FIGS. As shown in FIG. 6A, a cut is made in the block of the conductive material using a dicing saw, and a large number of pillars are formed. Next, the formed groove is filled with a non-conductive material, and a structure as shown in FIG. 6B is obtained. Then, the backing material as shown in FIG. 6C is obtained by cutting the front and back surfaces to the level shown by the dotted line.

[0004]

For example, with respect to an ultrasonic probe, the operating frequency tends to increase for the purpose of improving the resolution. When the operating frequency is desired to be increased, the size of the piezoelectric ceramics in the composite piezoelectric material is reduced along with the width of the electrodes formed on the composite piezoelectric material. As the structure of such an ultrasonic transducer becomes finer, the structure of the backing material also needs to be made finer. However, it is difficult for the conventional method using a dicing saw to form a backing material having a finer structure in response to this demand. When forming a groove in a conductive material using a dicing saw, if an attempt is made to reduce the spacing between the grooves, mechanical and thermal effects will cause
This is because the material is easily damaged. Further, a process using a dicing saw takes time for groove processing.

Further, as the ultrasonic transducer becomes finer, the wiring structure becomes finer. If the electrodes are pulled out from the side of the piezoelectric material, it is necessary to arrange a large number of wirings two-dimensionally, and the width of each wiring becomes very small. The formation of such a wiring pattern raises the cost of the device.

An object of the present invention is to provide a method for manufacturing a wiring structure corresponding to a fine electrode structure of an element.

A further object of the present invention is to provide a method capable of manufacturing a backing material having a finer structure in response to the miniaturization of an ultrasonic transducer.

[0008]

According to the present invention, an anisotropic conductive material comprising an electrical insulating material and a plurality of conductive columns arranged in the electrical insulating material without contacting each other is manufactured. A method is provided for: This method includes a step of forming a resist layer for X-ray lithography on a substrate, and a mask having a pattern in which a plurality of figures each corresponding to a cross section of a plurality of pillars are arranged at intervals. Irradiating the resist layer with X-rays, developing the resist layer to obtain a resist pattern in which a plurality of holes are arranged at intervals, depositing a metal material on the resist pattern, Separating the formed metal material from the resist pattern, obtaining a metal body in which a plurality of pillars are arranged at intervals, and forming an electrically insulating material by using the metal body as a mold, Filling the electrically insulating material with a conductive material in portions each having a hole formed by a plurality of pillars of a metal body.

In a mask used for X-ray lithography, the maximum diameter of a figure corresponding to a cross section of a columnar body is 100
μm or less, and more preferably 50 μm or less. The thickness of the resist layer for X-ray lithography can be 100 μm or more, for example, 100 to 1000 μm, preferably 100 to 500 μm.
μm. By lithography with these dimensions, a fine resist pattern having a high aspect ratio can be obtained.

[0010] The step of depositing a metal material on the resist pattern and the step of filling a hole formed in the electrically insulating material with a conductive material can be performed according to a plating method or an electroforming method. As the conductive material, a metal material containing either nickel or copper can be used. Electrical insulating materials are, for example, acrylic resin, epoxy resin,
It can be selected from the group consisting of polyimide resin and glass.

It is preferable to use synchrotron radiation (SR light) for the X-ray lithography according to the present invention.

In the present specification, an anisotropic conductive material refers to a material having anisotropy with respect to conductivity, that is, a material that exhibits conductivity in one specific direction but does not exhibit conductivity in a different direction. Point to.

The present invention is applicable to the manufacture of a backing material for an ultrasonic vibrator.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The manufacturing method according to the present invention will be described below in more detail with reference to the drawings. As shown in FIG. 1A, a resist layer 2 for X-ray lithography is formed on a substrate 1 according to the process of the present invention. As a substrate,
For example, a metal substrate such as copper, nickel, or stainless steel, or a silicon substrate on which a metal such as titanium or chromium is sputter-deposited can be used. A resist material mainly containing a polymethacrylate such as polymethyl methacrylate (PMMA), a chemically amplified resist material sensitive to X-rays, or the like can be applied to the substrate. The thickness of the resist layer can be arbitrarily selected depending on the purpose,
Usually, it can be set to 100 μm to 500 μm.

As shown in FIG. 1B, a mask 3 is arranged above the substrate 1 and the resist layer 2 is formed through the mask 3 by X.
Exposure to lines. SR light is preferably used for X-rays. The mask 3 has an X-ray absorption layer 3a formed in a predetermined pattern. The predetermined pattern includes a pattern in which figures corresponding to the cross section of the columnar body of the anisotropic conductive material to be formed are arranged at intervals. The figure is a square,
It can be a polygon, a circle, or the like. The maximum diameter of the figure (the length of a diagonal line when the figure is a square, and the diameter when the figure is a circle) can be 100 μm or less, and further 50 μm or less. For the light-transmitting base material constituting the mask, for example, silicon nitride, silicon, diamond, titanium, or the like can be used. For the X-ray absorption layer, for example, a heavy metal such as gold, tungsten, tantalum, or a compound thereof is used. be able to. The thickness of the X-ray absorbing layer can be arbitrarily selected depending on the desired thickness of the resist pattern, but can be, for example, 3 to 10 μm. In some cases, a mask without a light-transmitting substrate can be used. Usually, the X-ray absorbing layer has a reverse pattern to the arrangement pattern of the columns of the anisotropic conductive material to be formed.

The wavelength of the SR light to be irradiated on the resist layer is:
For example, it can be 1-10 °, and its energy can be 1-10 keV. The light source of the SR light can be, for example, an industrial small SR device (storage electron energy of 0.6 to 1.5 GeV), a medium-sized SR device (storage electron energy of 1.5 to 3 GeV), or the like.

When the exposed resist layer is developed to remove, for example, a portion altered by SR light, FIG.
The resist pattern 2 'shown in FIG. The resist pattern 2 'has a plurality of holes 2'a. The shape of this hole corresponds to the shape of the columnar body of the anisotropic conductive material to be formed. The maximum diameter of the cross section of the hole can be 100 μm or less, or even 50 μm or less, and the ratio (aspect ratio) of the depth of the hole (thickness of the resist layer) to the maximum diameter of the cross section of the hole is preferably 1 or more, 5 or more is more preferable.

As shown in FIG. 1D, a metal 5 is deposited on the resist pattern 2 '. The metal 5 is deposited with a thickness in the range of 0.5 to 1 mm, for example, exceeding the thickness of the resist pattern 2 '. If plating is performed using the substrate 1 as a plating electrode, a metal can be easily deposited on the resist pattern 2 '. As metal, for example, nickel,
Copper, gold and their alloys, permalloy, and the like can be used, but nickel is more preferable because metal 5 is used later as a mold.

If the substrate is removed by wet etching or the like and the resist is removed by wet etching or plasma etching, a metal body 5 'as shown in FIG. 1 (e) is obtained. The shape of the resist pattern 2 'is transferred to the metal body 5'. That is, the metal body 5 '
Are columnar bodies 5 'corresponding to a plurality of holes in the resist pattern.
a. The maximum diameter of the cross section of the columnar body can be 100 μm or less, and further can be 50 μm or less.

As shown in FIG. 1F, the electrically insulating material 7 is formed by using the metal body 5 'as a mold. Acrylic resin, epoxy resin, polyimide resin, glass, or the like can be used for the electrically insulating material 7.
When the metal body 5 'is separated from the molded body, a molded body 7' made of an insulating material as shown in FIG. 1 (g) is obtained. The molded body 7 'has a hole corresponding to the columnar body 5'a of the metal body 5'.

Next, as shown in FIG. 1 (h), a plate 8 is attached to a molded body 7 'made of an electrically insulating material. As the plate 8,
For example, metal plates such as copper, nickel, stainless steel,
A silicon substrate or the like on which a metal such as titanium or chromium is sputter deposited can be used. A conductive adhesive or tape can be used for attachment. Next, FIG.
As shown in (i), the bottom of the molded body 7 'is shaved or polished to expose holes formed in the molded body 7'.

Next, as shown in FIG. 1 (j), a conductive material 9 such as a metal is deposited on the compact 7 '. In the deposition step, the holes of the molded body 7 'are filled with the conductive material 9. The conductive material 9 is deposited beyond the thickness of the compact 7 '. Board 8
Is used as a plating electrode, metal can be easily filled in the holes of the molded body 7 '. As the metal, for example, nickel, copper, gold and alloys thereof can be used.

Next, the plate 8 is removed by wet etching or the like, and the front and back surfaces of the obtained structure are polished to obtain an anisotropic conductive material 10 as shown in FIG. 1 (k). In the anisotropic conductive material 10, a plurality of pillars 9 'made of a conductive material are arranged substantially in parallel with each other without contacting each other, and the pillars are covered with an electrically insulating material 7'.

By such a process, for example, FIG.
And a structure as shown in FIG. 3 can be obtained. The anisotropic conductive material 20 shown in FIG. 2 includes a large number of conductive columns 21 having a square cross section, and an electric insulating material 22 covering them. Anisotropic conductive material 30 shown in FIG.
Is composed of a number of conductive pillars 31 having a circular cross section and an electrically insulating material 32 covering them. In each material, the conductive pillars are arranged substantially in parallel without contacting each other.

According to the present invention, it is possible to obtain an anisotropic conductive material in which fine and high-aspect-ratio conductive pillars are arranged at high density in an electrically insulating material. According to the present invention,
The aspect ratio of the conductive column (the ratio of the height of the column to the diameter in the cross section of the column) is 5 or more, and more preferably 10 or more.
The above can be considered. The diameter of the cross section of the columnar body is
The thickness can be set to 100 μm or less, or even 50 μm or less. A material having such a fine and high aspect ratio conductive columnar body is suitable as a backing material for an ultrasonic transducer that is being miniaturized. Electrode width is about 100μm
When the thickness of the backing material required to sufficiently attenuate the ultrasonic wave is several hundred μm or more, it is preferable to produce a backing material for an ultrasonic transducer according to the present invention.

In the anisotropic conductive material produced according to the present invention, the conductive columnar body covered with the electrically insulating material penetrates from the front to the back of the material and is used for an element in which minute electrodes are arranged. Wiring. For example, as shown in FIG. 4, an anisotropic conductive material 60 manufactured according to the present invention can be overlaid on a composite piezoelectric material 40 in which a large number of piezoelectric materials 41 are arranged in a resin matrix 42. Each conductive column 61 in the material 60
Can function as wiring corresponding to each of the piezoelectric materials 41. Such a wiring structure facilitates connection between the piezoelectric material and the multi-core cable. In the arrangement as shown in FIG. 4, the anisotropic conductive material 60 having a sufficient thickness can function as a backing material for controlling the acoustic characteristics of the piezoelectric element. The attenuation and absorption characteristics of the ultrasonic wave in the backing material can be controlled by changing the space factor of the conductive column.

[0027]

EXAMPLE 1 According to the process shown in FIG. 1, an anisotropic conductive material having a square cross section of a conductive column was produced. X having a pattern in which many squares each having a diagonal length of 25 μm are arranged
A line mask was used for lithography. In the pattern, adjacent squares were 50 μm apart from each other. In the mask, a large number of square portions are portions that transmit X-rays, and portions between squares are portions that absorb X-rays. The mask was manufactured using lithography and plating using ultraviolet rays. In manufacturing the mask, a resist pattern in which a large number of squares were arranged on a titanium substrate was formed, and then gold plating was performed on titanium not covered with the resist. The plating thickness was 15 μm. The resist was removed to obtain a mask composed of a titanium transmitting material and a gold absorbing material. In the mask, the sum of the square areas transmitting X-rays was about 25% of the area of the entire mask.

A polymethyl methacrylate-based resist for X-ray lithography was applied to a thickness of 300 μm on a silicon substrate on which titanium was deposited by sputtering. The resist layer was covered with a mask, and the resist was irradiated with SR light having a peak wavelength of 0.5 nm. The irradiation dose is 20 absorption at the resist surface.
It was set to be kJ / cm ³ . After the irradiation, the resist was developed with methyl isobutyl ketone for 30 minutes. SR
The portion of the resist irradiated with the light was dissolved by the solvent, and a resist pattern having a large number of holes was obtained.

Using the obtained resist pattern as a mold, nickel was electroplated on a silicon substrate on which titanium was deposited. The substrate was dissolved in an aqueous potassium hydroxide solution, and titanium was removed with hydrofluoric acid to obtain a sword-shaped structure made of plated nickel. An acrylic resin was molded using the obtained nickel structure as a mold. As a result, a resin body having many holes was obtained. Many resin bodies were produced by this molding process. The obtained resin body was attached to a gold-coated Ni plate with an adhesive, and the end of the attached resin body was shaved to expose a hole.
Next, nickel was electroplated on the gold-coated Ni plate to which the resin body was attached. A gold-coated Ni plate is used as a plating electrode, and is placed in a nickel sulfamate bath.
Electroplating was performed under the condition of 0 mA / cm ² to obtain a composite of nickel and an acrylic resin. After polishing the tip of the obtained composite to make the thickness of the composite 200 μm, the composite was separated from the metal plate by mechanical force,
An anisotropic conductive material was obtained.

Example 2 According to the process shown in FIG. 1, an anisotropic conductive material in which the cross section of the conductive column was circular was produced. An X-ray mask having a pattern in which circles each having a diameter of 20 μm were arranged at an interval of 40 μm apart from each other was used. The circle portion is a portion that transmits X-rays, and the remaining portion is a portion that absorbs X-rays.
A mask having such a pattern was produced in the same manner as in Example 1.

On a silicon substrate on which titanium was deposited, a polymethyl methacrylate-based resist for X-ray lithography was applied in a thickness of 500 μm. The resist layer was exposed to SR light having a peak wavelength of 0.5 nm via an X-ray mask. The irradiation amount is 20 kJ / c at the resist surface.
m ³ . After the exposure, the resist was developed with methyl isobutyl ketone for 30 minutes.

Using the obtained resist pattern as a mold, nickel was electroplated on a silicon substrate on which titanium was deposited. The silicon substrate and the titanium film were removed in the same manner as in Example 1 to obtain a nickel body having a fine columnar body. Using this nickel body as a mold, a polyimide resin was molded. After molding, the resin was separated from the mold to obtain a resin body having a large number of cylindrical holes. Many resin bodies were produced by this molding process. The obtained resin body was attached to a metal plate in the same manner as in Example 1, and the tip of the resin was shaved to expose a hole. Using a metal plate as a plating electrode, electroplating was performed in a copper sulfate plating bath under the conditions of 10 mA / cm ² to obtain a composite of copper and a polyimide resin. The tip of the obtained composite was polished to a thickness of 400 μm, and the composite was peeled off from the metal plate in the same manner as in Example 1 to obtain an anisotropic conductive material.

[0033]

According to the present invention, it is possible to obtain a structure in which a large number of fine conductive materials having a high aspect ratio are arranged in an electric insulating material. Such a structure can function as a wiring structure for an element in which fine electrodes are arranged. Such a wiring structure can provide a wiring having a sufficient thickness for each electrode of the element, and also facilitates a wiring process. INDUSTRIAL APPLICABILITY The present invention can be applied not only for providing a wiring structure for various elements, but also for manufacturing a backing material of an ultrasonic element. The wiring structure manufactured according to the present invention can bring about cost reduction and simplification of the wiring of the element. Also, the materials made according to the present invention can improve the acoustic performance of the ultrasonic element.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a specific example of a manufacturing process according to the present invention.

FIG. 2 is a perspective view showing a specific example of an anisotropic conductive material produced according to the present invention.

FIG. 3 is a perspective view showing another specific example of the anisotropic conductive material produced according to the present invention.

FIG. 4 is a schematic cross-sectional view showing how an anisotropic conductive material produced according to the present invention is superimposed on a composite piezoelectric material.

FIG. 5 is a perspective view showing a specific example of a composite piezoelectric material.

FIG. 6 illustrates a conventional method for manufacturing a backing material for a piezoelectric transducer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2, 2 'Resist 3 Mask 5, 5' Metal 7, 7 'Electrical insulating material 9, 9' Conductive material

Claims (8)

[Claims] 1. A method for producing an anisotropic conductive material comprising an electric insulating material and a plurality of conductive columns arranged in the electric insulating material without being in contact with each other, Forming a resist layer for X-ray lithography on a substrate; and forming the resist layer through a mask having a pattern in which a plurality of figures respectively corresponding to the cross sections of the plurality of pillars are arranged at intervals. Irradiating the resist layer with an X-ray; developing the resist layer to obtain a resist pattern in which a plurality of holes are arranged at intervals; and depositing a metal material on the resist pattern. Separating the metal material from the resist pattern to obtain a metal body in which a plurality of pillars are arranged at intervals; and forming the electrical insulating material by using the metal body as a mold. A manufacturing method, comprising: a shaping step; and a step of filling a portion of the formed electrically insulating material, each of which has a hole formed by a plurality of pillars of the metal body, with a conductive material. 2. The method according to claim 1, wherein a maximum diameter of a figure corresponding to a cross section of the columnar body in the mask is 100 μm or less. 3. The method according to claim 1, wherein the thickness of the resist layer is 100 μm or more. 4. The method according to claim 1, wherein the step of depositing the metal material and the step of filling the conductive material are performed according to a plating method or an electroforming method. Manufacturing method. 5. The manufacturing method according to claim 1, wherein the conductive material is a metal material containing any of nickel and copper. 6. The method according to claim 1, wherein the electrical insulating material is selected from the group consisting of an acrylic resin, an epoxy resin, a polyimide resin, and glass. 7. The method according to claim 1, wherein the X-ray is synchrotron radiation. 8. The method according to claim 1, wherein the anisotropic conductive material is used as a backing material for an ultrasonic vibrator.