JP3147590B2 - Method for manufacturing flexible circuit board for TAB - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a flexible circuit board for TAB comprising a long flexible film having excellent insulation and heat resistance.

[0002]

2. Description of the Related Art A semiconductor element is mounted on a TAB flexible circuit board formed of a polyimide film or the like and having a large number of leads formed of, for example, copper foil on a long flexible film having excellent insulation and heat resistance. The TAB type semiconductor device has many features such as being suitable for mass production, downsizing, fine patterning, etc., and has been widely put into practical use at present.

FIG. 10 is a plan view for explaining a TAB flexible circuit board. In the drawing, reference numeral 1 denotes a device hole 2, 2a, 2b provided at regular intervals in the length direction, a thickness of about 50 to 125 μm, and a length of 200 to 500 m.
It is a strip-shaped flexible film of a degree.

[0004] Reference numeral 3 denotes a large number of leads made of copper foil having a thickness of 15 to 40 µm and a width of about 50 to 300 µm provided on the base film 1, some of which protrude into the device hole 2. Thus, an inner lead 3a is formed. 4 is a base
A sprocket hole for conveying the sfilm 1.

[0005] In such a TAB flexible circuit board, it is necessary to remove irregularities on the back side of the copper foil of the overhang portion to make the surface smooth because of the convenience of mounting. Method was used.

[0006]

SUMMARY OF THE INVENTION There has been a growing demand for a TAB flexible circuit board to have a smooth surface by removing irregularities on the back side of an overhanging copper foil for convenience in mounting. For this reason, etching is performed using a chemical polishing method. However, in the above-described conventional technique, the front side of the copper foil is also etched at the same time. As a practical copper foil thickness standard.

Accordingly, the present invention is to solve such a problem, and an object of the present invention is to provide a method for selectively performing chemical polishing treatment only on the irregularities on the back side of a copper foil.

[0008]

According to a method of manufacturing a flexible circuit board for TAB according to the present invention, an opening is formed in a part of a base film, and a metal foil is provided on the base film including the opening. Preparing a base material of a TAB flexible circuit board in which a resist is coated on a surface of the metal foil opposite to a surface bonded to the base film; and forming the base film in a state where the resist is coated. Chemically polishing an exposed portion of the metal foil located in the opening of the metal foil to flatten the exposed portion of the metal foil. Also,
In addition to the above method, a step of cleaning the base material performed after the step of preparing the base material, a pattern exposure step performed after the flattening step, and the resist after the pattern exposure step A resist coating process performed on a surface opposite to the provided surface, an etching process for removing an unnecessary portion of the metal foil to form a circuit, and a process for removing the resist. It is characterized by.

[0009]

In the past, chemical polishing of a TAB flexible circuit board has generally been performed in a cleaning step before coating a photoresist.

In the present invention, by performing a chemical polishing treatment after the photoresist coating, the front side is completely etched by the photoresist, so that it is not etched, and the uneven portion on the copper foil rear side is selectively etched. Therefore, even if chemical polishing is performed until the unevenness is removed and the surface becomes smooth, a practical copper foil thickness can be secured.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS. The flexible circuit board for TAB includes a cleaning process shown in FIG. 1, a conventional chemical polishing process shown in FIG. 2, a conventional front photoresist coating process shown in FIG. 3, a pattern exposure process shown in FIG. 10, the etching step shown in FIG. 8, and the resist stripping step shown in FIG. 9, whereby the TAB flexible circuit board shown in FIG. 10 is completed.

In the present embodiment, in the present invention, in the conventional chemical polishing process shown in FIG.
An overhang portion 2 is formed on the base material of the TAB flexible circuit board including the hang portion 2, the adhesive 5, and the copper foil 6.
When removing the irregularities on the back side of the copper foil, the problem was how to make the back side of the copper foil a smooth surface without reducing the total thickness of the copper foil.

In the conventional chemical polishing step shown in FIG. 2, when the chemical polishing treatment is performed by dipping (dipping the tape in a chemical polishing liquid), for example, the irregularities on the back surface of the copper foil are reduced by 7%.
If it was about μm, the front side would be polished by 7 μm to remove this, and the copper foil with a total thickness of 40 μm initially would be 26 μm, and the practical copper foil strength as a circuit board would be a problem. become. As a method of selectively performing the chemical polishing treatment on the back side of the copper foil, there is a method using a spray method. And the total thickness of the copper foil was unnecessarily reduced.

In order to solve these problems, according to the present invention, after the cleaning step shown in FIG. 1, the front photoresist coating step of the present invention shown in FIG. Of the present invention is carried out. As a result, at the time of chemical polishing, the copper foil front side is completely covered with the photoresist. Only the foil backside can be selectively chemically polished. The reason that the conventional chemical polishing process was performed before the photoresist coating process was that the photoresist was placed in the chemical polishing solution, the strength became weak, and the patterning quality, which is the original role of the photoresist, was adversely affected. Was thought to be affected. However, in the case of a high-performance photoresist used for manufacturing a flexible circuit board for TAB, remarkable progress has been made in recent years in flexibility and chemical resistance, and in particular, PMER-RF, PMER-RZ, Hoechst manufactured by Tokyo Ohka Co., Ltd. In the case of AZ-8112 manufactured by Nissan, there is no problem at all with respect to the chemical polishing solution which is based on nitric acid and sulfuric acid. Also, in the case of photoresist, there are many cases that are used as an etching resist for a circuit board. Therefore, an acid etching solution of ferric chloride or cupric chloride, which is a general etching solution for a circuit board, is not used. Since the chemical resistance is sufficient, it can be expected that many of the other photoresists are at a level that is practically acceptable for the chemical polishing liquid.

Next, the necessity of the chemical polishing treatment on the back surface side of the copper foil of the overhang portion 2 is largely due to the mounting of the semiconductor element. There are two reasons. The first is to ensure the adhesion of the plating and to ensure the reliability in mounting.

The copper foil used for the TAB flexible circuit board has been rust-proofed over the entire surface. In particular, the rust-preventive layer on the back side of the copper foil is thick and cannot be removed without chemical polishing. If any of the rust-preventive layer remains, the adhesion of the plating deteriorates because a chromium-based compound is used as a rust-preventive agent. The second is to secure the mounting reliability by making the plating deposition amount uniform. That is, since the copper foil rear surface has irregularities, the surface area is several times as large as that of the front surface. Moreover, since the shapes of the irregularities are various, it is considered that there is a considerable difference in the surface area depending on the location. When plating is applied, a certain amount of plating deposition can be obtained by controlling the thickness on the front side, but the amount of plating deposition increases on the back side due to the large surface area, and the amount varies depending on the location. There is also. When the inner lead bonding is performed in such a state, excess plating melts out from the uneven surface on the back surface side of the inner lead portion, and eutectic bumps are generated, thereby significantly lowering the reliability. Some examples have actually occurred.

The above two problems can be solved by flattening the irregularities on the back side of the copper foil by chemical polishing.

[0018]

As described above, according to the present invention, copper polishing is performed by selectively performing chemical polishing, which is indispensable for securing the reliability of a flexible circuit board for TAB, only on the uneven surface on the back side of the copper foil. This has the effect that the thickness of the foil can be kept above the practical thickness and the uneven surface can be made flat.

[Brief description of the drawings]

FIG. 1 is a sectional view of a cleaning step.

FIG. 2 is a cross-sectional view of a conventional chemical polishing process.

FIG. 3 is a cross-sectional view of a conventional front photoresist coating process.

FIG. 4 is a sectional view of a front photoresist coating process of the present invention.

FIG. 5 is a sectional view of a chemical polishing step of the present invention.

FIG. 6 is a sectional view of a pattern exposure step.

FIG. 7 is a sectional view of a developing backside coating process.

FIG. 8 is a sectional view of an etching step.

FIG. 9 is a sectional view of a resist peeling step.

FIG. 10 is a completed plan view of a TAB flexible circuit board.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Base film 2 Overhang part 3 Lead 4 Sprocket hole 5 Adhesive 6 Copper foil 7 Front photoresist 8 Backside resist

Claims (2)

(57) [Claims] An opening is formed in a part of the base film, and a metal foil is provided on the base film including the opening, and a surface of the metal foil opposite to a surface bonded to the base film is provided. Preparing a substrate of a TAB flexible circuit board coated with a resist by applying a resist, and chemically polishing the exposed portion of a metal foil located in an opening of the base film in a state where the resist is coated, thereby forming the metal. Flattening the exposed portion of the foil. A method for manufacturing a flexible circuit board for TAB, comprising: 2. A step of cleaning the base material performed after the step of preparing the base material; a pattern exposure step performed after the flattening step; and the resist being provided after the pattern exposure step. A resist coating process performed on a surface contradictory to the bent surface, an etching process for removing an unnecessary portion of the metal foil to form a circuit, and a process for removing the resist. The method for manufacturing a flexible circuit board for TAB according to claim 1.