JP2003277955A - Method for working sheet metal using wet etching process - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wet etching process which improves the anisotropic diffusion speed of an etchant existing on the surfaces of metallic electrodes in order to narrow the pitch of the terminals of the wet etching process and to manufacture lead frames of higher fineness and shadow masks of super-high fineness. <P>SOLUTION: The method for working a sheet metal uses the wet etching process in which a high-frequency electric current is impressed to the etchant in performing spray etching using a ferric chloride solution and the electromagnetic force excited by an induced magnetic field of 1,000 to 4,000 gauss in the magnetic flux density on a sheet substrate improves the anisotropic diffusion speed of the ferric chloride solution near the surface of the sheet metal to be etched, thereby improving the etching rate in the thickness direction of the sheet metal. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for processing a thin metal plate using a wet etching method used for manufacturing an etching component such as a multi-pin lead frame for a semiconductor device or a high definition shadow mask.

[0002]

2. Description of the Related Art In recent years, a lead frame has been required to have a large number of pins because a semiconductor integrated circuit has been highly integrated and highly integrated.

There are two typical methods for manufacturing a lead frame, which are a pressing method and an etching method. However, the pressing method has problems such as warpage distortion due to shear stress, and fine processing for increasing the number of pins. A suitable etching method is used.

An example of the manufacturing process of the lead frame by the etching method will be briefly described. First, the oil content and the organic dust adhering to the thin metal plate as a raw material are removed with an alkaline degreasing liquid. Next, when the photoresist is coated, a surface treatment for acid-treating the surface of the metal thin plate is performed in order to improve the adhesion of the photoresist to the surface of the metal thin plate. Then, both surfaces of the metal thin plate are coated with a water-soluble negative photoresist containing, for example, polyvinyl alcohol and ammonium dichromate as components. Then
A glass mask formed with a predetermined light-shielding pattern is brought into close contact with the metal surface, and pattern exposure is performed by irradiating ultraviolet rays,
The photoresist layer in the region other than the light shielding pattern portion of the glass mask is photopolymerized.

Next, after developing by hot water spray to remove the photosensitive resin in the unexposed area, the remaining photoresist is hardened and burned. Next, an etching solution is sprayed by using the photoresist formed on both sides of the thin metal plate as a mask to dissolve and remove the metal portion exposed from the resist to form a lead frame having a predetermined pattern. Finally, the unnecessary photoresist is immersed and removed in a hot alkaline bath.

The shadow mask is installed inside the glass screen of the color picture tube facing the fluorescent surface formed inside the glass bulb display part. It is made of a thin metal plate and has a large number of through holes regularly formed. I am letting you. This shed mask is
It is also used for forming a fluorescent screen, and is installed so that an electron beam emitted from an electron gun is correctly incident on the fluorescent screen.

Conventionally, in the manufacture of a high-definition shead mask, both sides of a low carbon steel thin metal plate having a thickness of about 0.10 mm are degreased,
After surface conditioning and cleaning treatment, a water-soluble photosensitive solution composed of casein or polyvinyl alcohol and ammonium dichromate is applied on both surfaces and dried to form a photoresist film. Then, it is exposed and baked through an exposure mask having a predetermined pattern and developed to form a resist film on the both surfaces of which the metal thin plate is exposed from the open area. Then, after the resist film is subjected to a hardening treatment and a burning treatment, a first stage etching is performed only on one surface (first surface) of the thin metal plate. A ferric chloride solution is used as the etching solution, and spray etching is usually performed. It is essential that the progress of the etching of the first surface is stopped midway so as not to penetrate the thin metal plate. Next, after washing and drying the thin metal plate with water, a heat-softening resin or a photo-curing resin, for example, is applied and cured on the first surface of the first surface to be etched, and the first surface is formed by the above etching. A corrosion-resistant film that completely fills the recess is formed. The first surface may be on the small hole side or the large hole side, but in most cases, the first surface is formed on the small hole side.

Subsequently, the other surface side (back surface of the first surface) is etched to form a through hole penetrating the recess. Finally, the corrosion resistant film and the photoresist layer are stripped off and unnecessary portions are cut off to obtain a shadow mask.

The through-holes of the above shed mask serve to correctly guide the electron beam to the fluorescent screen when the shed mask is incorporated in the color picture tube. Therefore, the shape of each through-hole to be formed in the sheer mask, especially the hole diameter of the through-hole, is preset in the design stage before the manufacture of the sheer mask, and the hole diameter is a color image when the sheer mask is incorporated into a color picture tube. The tube is designed to provide the desired performance.

In a color picture tube used for reproduction of ordinary color broadcasting, the through-hole diameter of the shear mask is larger than the plate thickness of the metal thin plate, and wet etching can be easily performed.

[0011]

The lead frame and the shear mask produced by the wet etching method as described above usually have a cross-sectional shape as shown in FIG.

Generally, in the case of wet etching, the metal thin film exposed from the resist film is isotropically etched, so that a problem of side etching occurs. Here, the problem of side etching will be described with reference to FIG. As shown in FIG. 5, the etching depth (the depth of the recess formed by etching) is d, and the side etching amount s is a lateral extension more than a predetermined etching width (etching around the lower part of the resist film). ), The etching factor F is defined by the following equation (1). F = d / s ――――― (1)

When wet etching a thin metal plate,
Ideally, it is desirable that the side etching amount s is small and the etching factor F is large in order to improve the pattern accuracy. However, in normal wet etching, the etching factor F is about 1 to 2.

The problem of side etching of the lead frame will be specifically described. As shown in FIG. 4, in the etching shape, adjacent lead portions 5 are formed on the respective lead portion side (breaking) surfaces due to side etching. If such burr portions 5 are present, adjacent burr portions 5 come into contact with each other, causing a short circuit defect. In order to prevent a short circuit from occurring, the interval between adjacent burr parts 5 is at least 5
This requires about 0 μm, which causes a problem that the terminal pitch of the inner leads is limited.

In order to form a lead frame having a pitch width 1 narrower than the penetrating portion to be formed by etching due to the adjacent burr portions 5, the etching factor F is 1 to 2.
Since the etching proceeds isotropically to a certain extent, it is extremely difficult to manufacture the metal plate unless a method such as making the metal plate thinner is taken.

Further, an etching solution is sprayed at high pressure,
Some efforts have been made to reduce the side etching amount s and increase the etching factor F. However, with thinner metal plates, the inner lead part that first comes off in the plane is twisted by the spray pressure, or the adjacent inner lead part comes into contact, so the etching solution does not hit the lead well,
There were also cases where etching was defective. Therefore, the thickness of the metal thin plate is limited so as to maintain a certain level of strength so as not to cause defects frequently, and the pitch of the inner leads cannot be further reduced.

In recent years, there has been a further demand for higher density and higher integration of semiconductor integrated circuits used in semiconductor packages, and in lead frames, there has been a demand for a narrower pitch and a finer terminal pitch of inner leads.

There is also a demand for high definition of TVs and super high definition of monitors for personal computers and the like for the shed mask. Therefore, when manufacturing an ultra-high definition shadow mask, the pitch must be narrowed while securing the strength of the shadow mask as in the lead frame. However, as described above, side etching is inevitable in the conventional manufacturing method, and it has been difficult to achieve the required narrow pitch and miniaturization. The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for processing a metal thin plate using a wet etching method, which enables narrowing of pitch and miniaturization.

Generally, in wet etching of an iron-based thin metal plate material such as a lead frame or a shear mask, a spray etching method using a ferric chloride solution as an etching solution is usually used. This etching is a redox reaction in which ferric ion (Fe ³⁺ ) acts as an oxidizing agent, and goes through the following steps.

The first step is the diffusion of the spray pressure,
Ferric chloride FeCl ₃ (Fe ³⁺ ) is transported to the metal surface.

In the second step, a redox reaction occurs on the metal surface. The redox reaction is shown in the following equation (2).
2FeCl ₃ is ferric chloride, 3FeCl ₂ is ferrous chloride, and 2FeCl ₃ + Fe → 3FeCl ₂ ――――― (2)

Fe ³⁺ is adsorbed on the metal surface, electrons are transferred and the product (FeCl ₂ ) from the metal surface is desorbed.

In the third step, the product of the diffusion (FeCl ₂ ) is transported into the etching solution.

As described above, the diffusion of the etching solution is rate-determining, and in the spray method which is usually used in the wet etching method, the etching solution is forcedly diffused by the striking force of the spray. However, spraying has a problem in that the diffusion speed of the etching solution near the metal surface electrode is slow. Further, it is known that the flow of the etching solution becomes a turbulent flow and the etching proceeds isotropically, so that the side etching is inevitable.

The present invention has been made to solve the above-mentioned problems, and an etching method for improving the etching rate in the thickness direction of a thin metal plate by improving the anisotropic diffusion speed of the etching solution existing on the metal surface. Is provided.

[0026]

The invention according to claim 1 of the present invention comprises the steps of forming a resist film exposing the surface of a thin metal plate according to a predetermined pattern, and spraying ferric chloride solution to form the resist. In a method for processing a metal thin film using a wet etching method that has an etching step of etching a metal thin plate portion exposed from the film to form a penetrating portion, when performing a spray etching process using a ferric chloride solution, an electromagnetic wave is added to the etching solution. A thin metal plate processing method using a wet etching method characterized in that a force is generated and used.

In the invention according to claim 2 of the present invention, when spray etching is performed using the ferric chloride solution, a high frequency current is applied to the inside of the etching chamber, and an electromagnetic force excited by the induced magnetic field is applied. 2. The wet etching method according to claim 1, wherein the etching rate in the thickness direction of the thin metal plate is improved by improving the anisotropic diffusion rate of the ferric chloride solution near the surface of the thin metal plate to be etched. This is the method of processing a thin metal plate used.

The invention according to claim 3 of the present invention is characterized in that the magnetic flux density on the thin plate substrate is 1000 gauss to 4000 gauss when spray etching is performed using the ferric chloride solution. A metal thin plate processing method using the wet etching method according to claim 1 or claim 2.

[0029]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described with reference to FIG. 1 schematically showing an example of a transport roll of an etching apparatus according to the present invention, and FIG. 2 schematically showing an electromagnetic force action which is a feature of the present invention. The details of the metal thin plate processing method will be described.

First, in FIG. 1, the transport roll 8 for transporting the thin metal plate 9 has a structure in which a magnetic material such as iron is used as a core material and the surface of the core material is coated with silicon rubber or the like in order to function as a stator core. Has become. The transport rolls 8 are installed above and below so as to sandwich the thin metal plate 9, and high-frequency currents are applied to the upper and lower transport rolls, respectively. The application direction is the axial direction, and the opposite direction is applied by the upper and lower transport rolls. For example, in the upper transport roll 8a, the roll transport shaft 8a is directed inward in the roll rotation direction (the direction of arrow C in the figure), and conversely, in the lower transport roll 8b, the roll transport shaft 8b is directed in the front direction (in the diagram). Arrow D
Direction) A high frequency alternating current is applied in the opposite direction. In addition,
Although not shown, the etching solution is sprayed onto the metal thin plate from above and below.

FIG. 2 is a schematic view for explaining the force applied to the etching liquid adhering to the cross section 6 of the metal thin plate when the high frequency current is applied during the spray etching.

For example, in FIG. 2, the upper transfer roll 8
When electricity starts to be applied from the upper side to the lower side of the paper in the axial direction of a, a magnetic field is generated in the clockwise direction (Ba direction in the drawing) of the transport roll 8a. Due to the generated magnetic field (Ba direction), an induced current is generated in the iron complex 10 (iron ion) in the etching solution of iron ions on the metal thin plate 6 from the bottom to the top of the paper. A magnetic field (in the Ba direction) and an induced current act on the iron ions 10 to cause the iron ions 1 to move according to Fleming's left-hand rule.
A downward force is generated at 0, and the iron ions 10 move closer to the surface of the thin metal plate. On the contrary, when the electric power printing on the upper transport roll 8a starts to weaken, the induced current is generated from the top to the bottom of the paper. As a result, an upward force is generated in the iron ions 10, and the iron ions 10 move away from the vicinity of the surface of the thin metal plate. By being similarly applied to the lower transport roll 8b, a magnetic field is generated in the counterclockwise direction (Bb direction in the figure), and a vertical force is generated on the iron ions in the etching solution. By printing an alternating current on the upper and lower transport rolls 8 in this manner, it becomes possible to move the iron ions 10 in the etching solution vertically toward and away from the surface of the thin metal plate at the atomic level in the vertical direction. Iron ions in the etching solution near the surface of the thin metal plate diffuse and move in the vertical direction.

FIG. 3 is a graph showing the relationship between the magnetic flux density generated by the upper and lower transport rolls 8 and the etching factor F.

It was found that the etching factor F = 2 was obtained at the magnetic flux density of 1000 gauss and further increased with the increase of the magnetic flux density. Further, the value was increased to 4000 gauss and the value of etching factor F = 4 was confirmed.
As the magnetic flux density was increased, the anisotropic diffusion speed of the etching solution was improved, and the effect was able to improve the etching factor.

[0035]

With the method for processing a thin metal plate by the wet etching method of the present invention, a narrow pitch can be achieved without reducing the thickness of the thin metal plate (while ensuring strength) when manufacturing an etched part such as a lead frame or a shadow mask. it can. In addition, as a function, in the case of spray etching a thin plate, the thin metal plate is conveyed while being sandwiched by upper and lower conveying rolls in order to prevent the thin metal plate from being blown and meandering in the spray chamber. In the conventional processing method, the portion sandwiched by the transport rolls is not directly sprayed, so that the diffusion speed of the etching solution is slowed, which is one of the causes for reducing the productivity. However, in the present invention, since the coil current is applied to the upper and lower transport rolls, it can be expected that the anisotropic etching by the electromagnetic force is most advanced in the portion where the thin metal plate is sandwiched.

As described above, according to the present invention, it is possible to continue the etching even if the thin metal plate is not sprayed when passing through the transport roll, and it is possible to improve the productivity and to narrow the width by anisotropic etching. It became possible to form a pitch pattern.

[0037]

EXAMPLE An example in which the present invention is used for manufacturing a lead frame is shown below.

Example 1 A metal material for a lead frame is an alloy of iron and nickel with a thickness of 150 μm.
A manufacturing process using two materials (metal material name) will be described.

First, degreasing and surface treatment were performed on both surfaces of a strip-shaped metal thin plate material which will be the substrate of the lead frame. Next, a negative photosensitive resin solution (PVA (polyvinyl alcohol) aqueous solution using potassium dichromate as a photosensitizer) is applied to both sides of the thin metal plate material, and after the resist is dried, a mask having a predetermined pattern as a light-shielding portion is formed. Using each mask, both surfaces of the thin metal plate material were brought into close contact with each other, and pattern exposure was performed by simultaneously irradiating ultraviolet rays from both surfaces to photo-cur the areas other than the predetermined pattern portion of the photosensitive resin.

Next, after developing with a hot water spray to remove the unexposed and uncured photosensitive resin, the remaining resin resist was subjected to film hardening treatment and burning treatment. Then
Spray etching was performed with the etching apparatus according to the present invention. At that time, as shown in FIG. 1, spray etching was performed while applying an alternating current to the transport roll 8. The magnetic flux density to the sheet metal material is set to 3500 gauss (etching factor F = 4), and ferric chloride solution (75 ° C, density 1500 g / cm3) is sprayed on both sides of the sheet metal material for the first etching. The process was carried out. In this etching, both surfaces of the thin metal plate material are spray-etched until the surface flat width of the inner lead portion becomes 80 μm.

Next, a varnish for etching prevention was applied so as to fill the concave portion formed by the first etching. In the coating process, 17
A hot-melt resin, which is an ethylene-acrylic acid copolymer resin that softens to 1000 cps at 0 ° C., was applied to a film thickness of 50 μm by a die coater method to obtain an etching preventing varnish.

In this embodiment, the hot melt resin is used in order to further reduce the burrs formed in the constricted portions of the adjacent inner leads and the pitch.
Adopts step etching. The HM varnish used here is an alkali-soluble wax, is resistant to acidic etching solutions, has a softening point of 90 to 100 ° C., but has some flexibility at about 65 ° C. .

Next, as a second etching step, spray etching was performed with the etching apparatus according to the present invention. Also in this case, as shown in FIG. 1, spray etching was performed while applying an alternating current to the transfer roll 8, and the magnetic flux density to the thin metal plate material was set to 3500 gauss (etching factor F = 4), and 75 C, density 1.
Using a ferric chloride solution of 500 g / cm ³ as an etching solution, second etching was performed on the back surface side by a spray method. As a result, a penetrating portion that penetrates the recess formed on the surface by etching is formed. At this time, first, when the etching progresses in the second etching step up to the etching prevention layer filled in the recess formed by etching from the surface side in the first etching step, the hot melt resin forming this etching prevention layer is It softens and pops out to some extent from the penetrating part formed by etching from the back surface to the front surface (first surface).

From there, the etching solution in the second etching step flows into the recesses formed by etching from the surface in the first etching step, and sharply pointed burrs electrochemically concentrate the electric charge to selectively remove the burrs. To be etched. At this time, in the present invention, the burr portion is intensively etched due to the anisotropic etching effect of the etching solution. In this example, when the opening width of the surface formed in the first etching step and the width of the penetrating portion became the same, the second etching step was stopped and the lead frame etching step was ended.

Next, after removing the etching-preventing varnish and the resin resist by a known method, a necessary portion is cut out from the metal thin plate material by a press or the like,
The desired multi-pin lead frame was obtained.

Even in the case of the shear mask, burrs formed in the penetrating portion are also intensively etched, and even if the etching time is short, the same penetrating hole as in the conventional case can be reproduced and the productivity can be improved.

[0047]

In the method for processing a thin metal plate using the wet etching method of the present invention, the anisotropic diffusion speed of the etching solution existing on the metal surface is improved by utilizing the electromagnetic force during the spray etching. However, the etching rate in the thickness direction of the metal thin plate can be improved. Thereby, the etching factor value at the time of wet etching can be improved. As a result, when the present invention is used for manufacturing a lead frame, it is possible to provide a lead frame that can cope with a high pin count and high density, and also improve productivity. Further, even when it is used for manufacturing a shear mask, it is possible to manufacture an ultra-fine pitch and improve productivity.

[Brief description of drawings]

FIG. 1 is a perspective view schematically showing a main part of an etching apparatus according to the present invention.

FIG. 2 is a schematic diagram illustrating an electromagnetic force action that is a feature of the present invention.

FIG. 3 is a graph showing the relationship between etching factor F and magnetic flux density.

FIG. 4 is an enlarged view showing a side sectional view of an etching component obtained by a conventional processing method.

FIG. 5 is a side cross-sectional view for explaining the definition of etching factor F.

[Explanation of symbols]

1 ... Pitch width 2 ... Surface flat width 3 ... Flat width on the back 4 ... Material thickness 5 ... Burr section 6 ... Thin metal plate 7 ... Resist 8, 8a, 8b ... Conveyor rolls 9 ... Thin metal plate 10 ... Iron complex in etching solution

Claims (3)

[Claims] 1. A step of forming a resist film in which the surface of a metal thin plate is exposed according to a predetermined pattern, and a ferric chloride solution is sprayed, and the metal thin plate portion exposed from the resist film is etched to form a penetrating portion. In a method for processing a metal thin film using a wet etching method having an etching step, a wet etching method is used which is characterized in that an electromagnetic force is generated in the etching solution when spray etching is performed using a ferric chloride solution. Metal sheet processing method used. 2. When spray etching is performed using the ferric chloride solution, a high-frequency current is applied in the etching chamber, and the electromagnetic force excited by the induction magnetic field of the ferric chloride causes the chloride near the surface of the thin metal plate to be etched. 2. The method for processing a metal thin plate using the wet etching method according to claim 1, wherein the etching rate in the thickness direction of the metal thin plate is improved by improving the anisotropic diffusion rate of the ferric iron solution. 3. The magnetic flux density on the thin plate substrate is 1000 when spray etching is performed using the ferric chloride solution.
Gauss-4000 gauss is set, The metal thin plate processing method using the wet etching method of Claim 1 or Claim 2 characterized by the above-mentioned.