JPH0548242A - Etching method of metal copper film - Google Patents

Abstract

PURPOSE:To provide an etching method which enables a soldering film to be used as an etching mask and side etching of a metal copper film which is to be etched to be reduced. CONSTITUTION:A copper foil 10 which is formed on a glass epoxy substrate 1 and a metal copper film which consists of a copper plating layer 2 are subjected to etching by using a soldering film 3 which is placed on a surface of the above metal copper film as an etching mask, etching is stopped temporarily when a film thickness of the metal copper film reaches the half, the soldering film 3 is heated and fused and then an end face 15 of the metal copper film is coated by this melted solder, and then etching is restarted, thus enabling the remaining metal copper film to be etched. When this method is used and the etching treatment of a later stage is performed, the end face 15 of the metal copper film which is exposed by the etching treatment at the previous stage is coated by the fused solder, thus preventing that portion from being subjected to side etching and enabling an amount of the side etching to be reduced as compared with a case where an entire film thickness is subjected to etching all at once.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for etching a metallic copper film used for manufacturing a printed wiring board, for example, by using a solder film formed in a pattern on the surface of the metallic copper film as an etching mask. In particular, the present invention relates to improvement of an etching method capable of reducing side etching of a metallic copper film which is an etching target.

[0002]

2. Description of the Related Art This type of etching method is widely used in the production of printed wiring boards, etc., as described above, and the outline thereof will be described below by taking a method called "panel plating method" as an example. Then, as shown in FIG. 9, a glass epoxy substrate b, on which copper foil a having a thickness of about 35 μm is uniformly formed on both surfaces thereof, is drilled at appropriate portions to form through holes c, and After washing the inner wall surface of the through hole c with a high-pressure water washing machine and dissolving and removing the drill residue with a treating agent as appropriate (see FIG. 10), electroless plating with copper is performed to obtain a thickness of 30 μm as shown in FIG. A copper plating layer d of a certain degree is formed on the copper foil a and on the inner wall surface of the through hole c, respectively.

Next, the surface of the copper plating layer d is shown in FIG.
As shown in FIG. 5, a dry film pattern e is formed, a solder plating layer f is formed on a portion exposed from the dry film pattern e (see FIG. 13), and the dry film pattern e is removed (see FIG. 14). rear,
Using the solder plating layer f as an etching mask, the copper plating layer d and the copper foil a exposed from this mask are sequentially removed by etching to form a wiring layer g in a pattern (see FIG. 1).
5 to 16), and the above-mentioned solder plating layer f is heated and melted to complete the eutectic solder structure and the overhang (protruding portion f0 of the solder plating layer f in FIGS. 15 to 16) is eliminated (FIGS. 17)) to obtain a printed wiring board.

[0004]

However, when the wiring layer g is formed by such an etching method as shown in FIG.
As shown in FIG. 16, since the exposed dimension in the thickness direction of the copper plating layer d and the copper foil a sandwiched between the glass epoxy substrate b and the solder plating layer f is large (thickness is 65 μm in this example), When the copper plating layer d and the copper foil a having a thickness of 65 μm are etched, the end faces of the copper plating layer d and the copper foil a are susceptible to side etching, and the line width dimension accuracy is deteriorated. There was a problem that greatly hindered the increase of the.

The present invention has been made in view of such problems, and an object thereof is to provide an etching method capable of reducing side etching of a metallic copper film to be etched.

[0006]

That is, the invention according to claim 1 is a metal for forming a solder film in a pattern on a surface of a metal copper film and etching the metal copper film by using the solder film as an etching mask. Assuming the copper film etching method, the above-mentioned metal copper film is etched, and when the etching process is performed up to the middle of the entire film thickness, the etching is temporarily stopped, and then the solder film on the metal copper film is heated and melted and etched. The invention is characterized in that the end surface of the metal copper film exposed by the treatment is covered with this molten solder and then etching is restarted to etch the remaining metal copper film. Item 1
On the premise of the invention according to (1), the etching process is temporarily stopped when the film thickness of the metallic copper film becomes half of the total film thickness.

The metallic copper film to be etched by such a technical means may be a copper foil laminated appropriately on a substrate with an adhesive or a copper plating layer formed by plating. Often, any metallic copper coating is the target, regardless of its formation means.

As a means for forming a solder film in a pattern on the surface of the metal copper film, a dry film pattern or a photoresist pattern is previously formed on the surface of the metal copper film, and a metal exposed from this pattern is formed. A method of selectively forming on the copper film surface by plating method may be adopted, or a solder film may be uniformly formed on the surface of the metal copper film by an appropriate method and a dry film may be formed on this film. A method of forming a pattern or a photoresist pattern and then selectively removing the solder film exposed from the pattern by dissolving and removing it with an etching agent may be adopted, and the forming means is also arbitrary.

[Solder] that constitutes the above-mentioned solder film
As a Pb-Sn alloy used in the conventional method,
A Pb-Ag alloy, a Bi-Sn alloy, etc. can be applied.

Next, the timing of stopping the etching process of the former stage can be arbitrarily set after the etching of the metal copper film is started and the film thickness thereof starts to decrease. If the difference in the film thickness dimension of the metallic copper film to be etched in the subsequent stage becomes large, the side etching amount becomes large during the etching treatment for the large film thickness, which is not preferable. Therefore, a method of stopping when the film thickness of the metal copper film becomes about half of the total film thickness is desirable.

The invention according to claim 2 is created from such a technical background, and the etching process is temporarily stopped when the film thickness of the metal copper film becomes half of the total film thickness thereof. It is what

Although this technical means can be applied to a method for manufacturing a printed wiring board such as a single-sided printed wiring board, a double-sided printed wiring board, and a multilayer printed wiring board, it can also be applied to an etching method of a metal copper film for other purposes. Of course, it can be applied.

[0013]

According to the first aspect of the invention, the etching of the metallic copper film is stopped once the metallic copper film is etched and the etching treatment is performed up to the middle of the entire film thickness, and then the solder film on the metallic copper film is heated and melted. In addition, since the end surface of the metal copper film exposed by the etching process is covered with this molten solder and then the etching is restarted to etch the remaining metal copper film, the etching process of the first stage is performed during the etching process of the second stage. Since the end surface of the metal copper film exposed at step is covered with molten solder, side etching at that part can be prevented. Therefore, the side etching amount compared to the case where the entire film thickness of the metal copper film is etched at once. Can be reduced.

Further, according to the second aspect of the invention, since the etching process is temporarily stopped when the film thickness of the metallic copper film becomes half of its total film thickness, the etching of the former stage and the latter stage is performed. Since the film thicknesses of the metallic copper films to be formed are the same and the side etching amounts at each etching are substantially equal, it is possible to minimize these side etching amounts.

[0015]

Embodiments of the present invention applied to the manufacture of a double-sided printed wiring board will be described in detail below with reference to the drawings.

First, a copper foil 10 having a thickness of 35 μm is formed on both sides thereof.
Through holes 11 are drilled by a drill machine at appropriate portions of the glass epoxy substrate 1 to which is adhered, and the inner wall surface of the through holes 11 is washed with a high pressure water washing machine, and
After removing the drill residue fused to the inner wall surface with a mixed solvent of potassium permanganate and sodium hydroxide (desmear treatment), electroless plating treatment with copper is applied to the copper foil 10.
Then, a thin copper plating layer was formed on the inner wall surface of the through hole 11, followed by electrolytic plating with copper sulfate to form a copper plating layer 2 having a total thickness of 25 μm (see FIG. 2).

Next, a 30 μm thick solder coating 3 of Pb—Sn alloy is uniformly formed on the surface of the copper plating layer 2 by plating (see FIG. 3), and on this surface. After the dry film 4 having a thickness of 20 μm is laminated by a laminator by a normal process (see FIG. 4), a circuit pattern is exposed on the surface of the dry film 4 and a development process is performed to form a dry film 4 as shown in FIG. A dry film pattern 40 was formed.

Next, the solder film 3 exposed from the dry film pattern 40 is removed by etching using a commercially available solder etching solution, and the dry film pattern 40 is peeled off to leave the solder film remaining as shown in FIG. 3 is exposed, and then the solder coating 3 is used as an etching mask and a copper etching agent is used to form a copper plating layer 2 having a thickness of 25 μm and a copper foil 10 having a thickness of 35 μm.
The metallic copper film having a thickness of μm was etched. The etched film thickness is half of the total film thickness (that is, 30 μm).
When m) is reached, the etching process is temporarily stopped, and the etching site is thoroughly washed with water, and the remaining non-water-soluble impurities are dissolved in dilute sulfuric acid for several seconds, and then washed again. Was used for sufficient washing (see FIG. 7). At this time, since the etching process is temporarily stopped when the film thickness of the metal copper film is halved, the film film of the film to be etched as compared with the case where the entire film thickness of the metal copper film is etched at once. The thickness is relatively thin, and as a result, there is an advantage that side etching can be reduced as shown in FIG.

Next, the solder coating 3 on the metallic copper coating is heated and melted by a far infrared heating device, and the end surface 15 (see FIG. 1A) of the metallic copper coating exposed by the etching treatment is coated with this molten solder. (See Figure 1B). The heat treatment condition was 230 ° C. for 3 minutes in order to surely coat the end surface 15 of the metallic copper film with the molten solder.

Then, the etching process is restarted with the end surface 15 of the metallic copper film covered with the molten solder,
Etching the remaining 30 μm thick copper metal film (see FIG. 8)
Then, the solder coating 3 was peeled off with a commercially available solder peeling liquid to obtain a circuit pattern composed of a copper foil and a copper plating layer.
During the subsequent etching process, since the end surface 15 of the metallic copper film is covered with the molten solder, side etching of this portion is prevented. Then, the portion that undergoes side etching in the latter-stage etching treatment is the remaining 30 μm which is the target of the latter-stage etching.
Since only the end face of the thick metal copper film is formed, it has an advantage that side etching can be reduced as shown in FIG.

Therefore, the copper plating layers 2 and 35 having a thickness of 25 μm are formed.
The total film thickness of the metallic copper film composed of the copper foil 10 having a thickness of μm (60
Since the side etching amount can be reduced as compared with the case where the etching treatment is performed at a time, the line width dimension accuracy is improved and the wiring density can be increased. In fact, the above-mentioned circuit pattern composed of a copper foil and a copper plating layer had a good reproducibility of the dry film pattern 40, and a 50 μm line and space could be formed well with a 35 μm copper foil.

[0022]

According to the first aspect of the present invention, during the subsequent etching process, since the end face of the metallic copper film exposed in the previous etching process is covered with the molten solder, the side etching of that portion is prevented. This can be prevented, and the side etching amount can be reduced as compared with the case where the entire film thickness of the metal copper film is etched at once.

Therefore, since the etching accuracy can be improved as compared with the conventional method, there is an effect that the wiring density can be increased when this method is applied to, for example, the manufacture of a printed wiring board.

Further, according to the second aspect of the invention, since the film thickness dimensions of the metal copper film to be etched in the front and rear stages are the same and the side etching amounts at each etching are substantially equal, these side etching amounts are the same. Can be suppressed to a minimum, and therefore, the etching accuracy can be further improved.

[Brief description of drawings]

FIG. 1A is an explanatory diagram of a first-stage etching process according to an embodiment, FIG. 1B is an explanatory diagram of a heating and melting process of a solder film,
FIG. 1C is an explanatory diagram of a subsequent etching process.

FIG. 2 is a process drawing of an etching method according to an embodiment.

FIG. 3 is a process drawing of an etching method according to an embodiment.

FIG. 4 is a process drawing of an etching method according to an embodiment.

FIG. 5 is a process drawing of an etching method according to an embodiment.

FIG. 6 is a process drawing of an etching method according to an embodiment.

FIG. 7 is a process drawing of the etching method according to the embodiment.

FIG. 8 is a process drawing of the etching method according to the embodiment.

FIG. 9 is a process drawing of the etching method according to the embodiment.

FIG. 10 is a process diagram of a conventional etching method.

FIG. 11 is a process diagram of a conventional etching method.

FIG. 12 is a process diagram of a conventional etching method.

FIG. 13 is a process diagram of a conventional etching method.

FIG. 14 is a process diagram of a conventional etching method.

FIG. 15 is a process diagram of a conventional etching method.

16 is a partially enlarged view of FIG.

FIG. 17 is an explanatory view showing a state in which a solder plating layer is heated and melted.

[Explanation of symbols]

 1 Glass epoxy substrate 2 Copper plating layer 3 Solder film 10 Copper foil 15 Edge surface

Claims (2)

[Claims] 1. A method for etching a metal copper film, comprising forming a solder film in a pattern on a surface of the metal copper film and etching the metal copper film by using the solder film as an etching mask. Then, when the etching process is performed halfway through the entire film thickness, the etching is temporarily stopped,
Next, the solder film on the metallic copper film is heated and melted, and the end surface of the metallic copper film exposed by the etching treatment is covered with this molten solder, and then etching is restarted to etch the remaining metallic copper film. Etching method for metallic copper film. 2. The etching method for a metal copper film according to claim 1, wherein the etching process is temporarily stopped when the film thickness of the metal copper film becomes half of the total film thickness.