JP5051355B2 - Method for manufacturing printed wiring board - Google Patents

Description

  The present invention relates to a method for manufacturing a printed wiring board, and more particularly to a method for manufacturing a printed wiring board in which a method for forming a conductive pattern by etching a conductive metal layer is improved.

  As a method for manufacturing an electronic substrate, a subtractive method is widely used. In the subtractive method, a photosensitive resin layer such as a liquid resist or a dry film is formed on a laminate having a conductive metal layer on a resin substrate, and this photosensitive resin layer is exposed and developed to form a desired resist pattern. This is a method of forming a wiring pattern by peeling the resist pattern after etching and etching the exposed conductive metal layer by an etching process.

In recent years, with the miniaturization of electronic devices, the miniaturization of electronic substrates has rapidly progressed. In particular, in a COF (Chip on Film) used for a liquid crystal driver, a demand for finer wiring pitch is increasing, and a tape having fine area leads with a wiring pitch of 25 μm or less is also made. Further, with the miniaturization of the wiring pitch, improvement in heat dissipation is also an issue, and a wiring shape having a large wiring cross-sectional area is required to improve heat dissipation.

In addition, as a related technology, after etching the copper foil on both sides while transporting the copper clad laminate with copper foil attached on both sides, invert the copper clad laminate and re-etch the copper foil on both sides There is a proposal to uniformly thin the copper foils on both sides (see Patent Document 1).
JP-A-9-92958

  However, when a wiring having a large cross-sectional area is formed using the subtractive method, it becomes more difficult as the wiring pitch becomes finer. This is because the top width of the wiring cannot be secured because the etching with the etching solution is isotropic. That is, as shown in FIG. 3, a resist pattern 14 of the photosensitive resin film 13 is formed on the conductive metal layer 12 formed on the insulating substrate 11 (FIG. 3A), and the conductive metal is etched with an etching solution. The layer 12 is etched (FIGS. 3B to 3D), and after etching, the photosensitive resin film 13 is peeled to form the wiring 15 (FIG. 3E). The top width becomes narrow.

  On the other hand, when a wiring having a large cross-sectional area is formed by performing etching anisotropically, if the resist pattern is removed after the etching, the shape of the top 15a of the wiring 15 having a sharp edge as shown in FIG. (In the figure, Wt is the top width of the wiring 15 and Wb is the bottom width). This wiring shape tends to cause a connection failure when a printed wiring board such as COF and an IC chip are bonded. For example, when a COF tape is flip-chip bonded to an IC chip, a wiring shape with a sharp top edge becomes a problem because it is difficult to form gold bumps and fillets on the IC chip side. The poor connection between the printed wiring board having the wiring shape and the IC chip becomes more prominent as the distance between the wirings becomes finer. For example, when the wiring pitch is as fine as 25 μm or less, a connection failure such as a short circuit is likely to occur because the interval between adjacent leads is narrow. Further, it is difficult to form a fillet, and the surface pressure at the time of bonding becomes high, so that a short circuit between wirings due to the spread of the fillet occurs, resulting in a defect at the time of bonding.

In addition, the wiring formed using the subtractive method may have a rough side wall surface. For example, when tin plating is performed on a wiring formed by COF, if the wiring side wall surface is rough, abnormal precipitation of tin plating may occur. Will occur.

  This invention solves the said subject and provides the manufacturing method of the printed wiring board which can produce the reliable conductor shape and conductor surface.

The first aspect of the present invention includes a step of forming a photosensitive resin film on a conductive metal layer formed on at least one surface of an insulating substrate, and exposing and developing the photosensitive resin film, A step of forming a required resist pattern, a first etching step of forming a conductor pattern by removing the conductive metal layer exposed by an etching solution,
The step of peeling the photosensitive resin film of the resist pattern, and the conductive pattern formed again is treated with an etching solution to smooth the side wall surface of the conductive pattern, or the edge portion of the conductive pattern is A method for manufacturing a printed wiring board having an IC chip bonded thereto, comprising: a second-stage etching step for forming a rounded shape; and a step of flip-chip bonding an IC chip to the conductor pattern.
The printed wiring board includes a so-called printed circuit board (PWB), TAB (Tape Automated Bonding) tape, COF (Chip on Film) tape, FPC (Flexible Printed Circuit), and BGA (Ball Grid Array) wiring tape. included.

A second aspect of the present invention, in the first embodiment, the first stage etching step, were joined IC chip, which is a main etch process for forming the conductive pattern while suppressing the side etching It is a manufacturing method of a printed wiring board.

According to a third aspect of the present invention, in the first or second aspect, the etching solution used in the first stage etching step is a hydrogen peroxide / sulfuric acid solution, a cupric chloride solution, or a ferric chloride solution. This is a method for manufacturing a printed wiring board to which an IC chip is bonded .

According to a fourth aspect of the present invention, in any one of the first to third aspects, the etching solution used in the second-stage etching step is a hydrogen peroxide / sulfuric acid solution, a cupric chloride solution, Or it is a manufacturing method of the printed wiring board which joined the IC chip characterized by being a ferric chloride solution.

A fifth aspect of the present invention, in any of the embodiments of the first to third embodiments, the second stage etching step, bonding the IC chip and performing by electrolytic pickling Print It is a manufacturing method of a wiring board.

  According to the present invention, the conductive metal layer covered with the resist pattern is removed with an etchant to form a conductor pattern, and then the two-step etching is performed in which the conductor pattern from which the resist pattern has been peeled is treated with the etchant again Therefore, it is possible to obtain a conductor shape or a conductor surface such as a desired wiring / land, and to manufacture a reliable printed wiring board.

  Hereinafter, an embodiment of a method for manufacturing a printed wiring board according to the present invention will be described with reference to the drawings. FIG. 1 is a process diagram showing manufacturing steps (a) to (f) in manufacturing a printed wiring board according to this embodiment.

  As shown in FIG. 1 (a), an insulating substrate 1 having a conductive metal layer 2 formed on one side is prepared. The insulating base material 1 is made of an insulating material such as an insulating resin, and the insulating base material 1 may be a flexible material that is flexible or a rigid material that is not flexible. Moreover, what has the conductive metal layer 2 on both surfaces of the insulating base material 1 may be used. The conductive metal layer 2 may be a metal foil such as a copper foil or a metal plating layer such as a copper plating layer.

  First, the photosensitive resin film 3 is formed on the conductive metal layer 2 of the insulating base 1 (FIG. 1B). The photosensitive resin film 3 may be formed by applying a liquid resist on the conductive metal layer 2, or a dry film stuck on the conductive metal layer 2.

  Next, the photosensitive resin film 3 is exposed through a photomask, and a required resist pattern 4 is formed by development (FIG. 1C).

The conductive metal layer 2 not covered with the resist pattern 4 is removed with an etching solution to form a wiring pattern (conductor pattern) 5 (FIG. 1D). This etching process is a first-stage etching process, and the shape of the approximate wiring (conductor) 6 is formed.
Examples of the etching solution used in the first etching step include a hydrogen peroxide / sulfuric acid solution (a mixed aqueous solution of hydrogen peroxide and sulfuric acid), a cupric chloride solution, and a ferric chloride solution. Etching of the conductive metal layer 2 may be performed by spraying an etching solution onto the conductive metal layer 2 or immersing the conductive metal layer 2 in the etching solution.

  After the wiring pattern 5 is formed, the photosensitive resin film 3 of the resist pattern 4 is peeled off with an alkaline aqueous solution or the like (FIG. 1 (e)).

Further, the wiring 6 of the wiring pattern 5 from which the resist pattern 4 has been peeled is treated again with an etching solution (FIG. 1 (f)). This etching process is a second-stage etching step, and the final shape / surface wiring (conductor) 7 is formed.
Examples of the etching solution used in the second etching step include a hydrogen peroxide / sulfuric acid solution, a cupric chloride solution, and a ferric chloride solution. Etching may be performed by spraying an etchant or immersing in an etchant.

The etching solution used in the first and second etching processes may be the same or different in the etching solution base (mixed aqueous solution of hydrogen peroxide and sulfuric acid, cupric chloride, ferric chloride). . However, since the purpose of etching is different between the first and second etching processes, the concentration of the etching solution used as the base (for example, the concentration of hydrogen peroxide, sulfuric acid, iron chloride, copper chloride, etc.) The types of additives to be added to the etching solution are preferably different.
That is, the etching solution for the first etching step is desirably an etching solution that suppresses side etching that can leave a large wiring top width even with a narrow wiring pitch. The etching solution in the second etching process is an etching performed after removing the etching resist pattern of the photosensitive resin layer. In order to maintain the cross-sectional area of the formed wiring as much as possible, the height (thickness of the formed wiring) It is desirable to use an etchant that suppresses the decrease in the number of lines and selectively etches the edge of the wiring top.
Further, as the etchant for the second stage etching process, an etchant for smoothing the side wall surface of the wiring formed in the first stage etching process may be used.

Such two-step etching enables formation of wiring with a large cross-sectional area and rounded edges at the top of the wiring even when the wiring pitch is narrow, and highly reliable printed wiring such as when bonding to an IC chip. A board can be manufactured efficiently.
In addition, a printed wiring board having a smooth side wall surface of the wiring can be obtained. For example, when tin plating is applied to the wiring, an abnormal precipitation of tin plating can be prevented, and a highly reliable printed wiring board can be manufactured.

In the above embodiment, the second etching step may be performed using electrolytic pickling. That is, the surface of the wiring is polished by immersing the stainless steel plate and the printed wiring board in an electrolytic pickling solution and applying a voltage between the stainless steel plate and the wiring of the printed wiring board. In the electrolytic pickling, the current concentrates on the edge portion having a sharp shape, so that only the edge portion of the wiring is selectively dissolved, and the edge portion of the wiring having the sharp shape can be formed into a desired round shape. .

Next, examples of the present invention will be shown and described in more detail.
[Example 1]
A substrate film having a base metal layer made of Ni—Cr on the surface of a polyimide film having an average thickness of 38 μm and having an electrolytic copper layer having an average thickness of 8 μm formed on the base metal layer was used.
A photosensitive resin was applied to the surface of the electrolytic copper layer of the base film, and then exposed and developed to form a photosensitive resin resist pattern having a wiring pitch of 25 μm. The electrolytic copper layer masked with the resist pattern of the photosensitive resin is formed using an etching solution composed of ferric chloride (concentration: 15 g / L) and hydrochloric acid (concentration: 0.1 to 0.2 g / L). Etching was performed by spraying an etching solution at a spray pressure of 0.2 MPa and a solution temperature of 30 ° C. for 25 seconds. Next, the resist pattern formed of the photosensitive resin on the obtained copper wiring was removed by spraying with an aqueous sodium hydroxide solution. After that, the etching is performed by immersing in an etching solution for 120 seconds at a liquid temperature of 40 ° C. using an etching solution made of hydrogen peroxide (concentration: 25 g / L) and sulfuric acid (concentration: 100 g / L). Etched.
The copper wiring pattern formed as described above had a top width of 6.5 μm and a bottom width of 12.5 μm. Moreover, the side wall surface of the formed wiring was smooth.

[Comparative Example 1]
For comparison with Example 1, as Comparative Example 1, wiring was formed by only one etching as in the conventional case. In Comparative Example 1, an etching solution composed of ferric chloride (concentration: 15 g / L) and hydrochloric acid (concentration: 0.1 to 0.2 g / L) was used using the same base film as in Example 1. Then, copper wiring is formed by etching at a liquid temperature of 30 ° C. for 35 seconds, and then the resist pattern formed of the photosensitive resin on the obtained wiring is removed by spraying an aqueous sodium hydroxide solution, and printed wiring A board was produced.
The top width of the wiring of Comparative Example 1 was 5.3 μm, the bottom width was 12.5 μm, and the side wall surface of the formed wiring was rough.

[Example 2]
A substrate film having a base metal layer made of Ni—Cr on the surface of a polyimide film having an average thickness of 38 μm and having an electrolytic copper layer having an average thickness of 8 μm formed on the base metal layer was used.
A photosensitive resin was applied to the surface of the electrolytic copper layer of the base film, and then exposed and developed to form a photosensitive resin resist pattern having a wiring pitch of 25 μm. The electrolytic copper layer masked with the resist pattern of the photosensitive resin is formed using hydrogen peroxide (concentration: 20 g / L), sulfuric acid (concentration: 4 g / L), pyridine (concentration: 0.1 g / L), phenolsulfonic acid. Sodium 1
Etching was performed for about 300 seconds at a spray pressure of 0.1 MPa and a liquid temperature of 40 ° C. using an etching liquid composed of a hydrate (concentration: 1 g / L). As shown in FIG. 4, the formed wiring had a wide wiring top and a sharp edge at the wiring top. The wiring had a top width of 12.5 μm and a bottom width of 12 μm.
The resist pattern formed of the photosensitive resin on the obtained wiring was removed by spraying a sodium hydroxide aqueous solution. Next, second-stage etching was performed using an etching solution composed of hydrogen peroxide (concentration: 80 g / L) and sulfuric acid (concentration: 25 g / L) at a liquid temperature of 30 ° C. for 30 seconds. As a result, as shown in FIG. 2, the edge of the top 7a of the wiring 7 could be rounded (note that 7b is a side wall surface of the wiring 7). The wiring had a top width of 10 μm and a bottom width of 11 μm.

Next, as described above, the COF tape of Example 2 manufactured by the two-stage etching process was flip-chip bonded to the IC chip, and the wiring was performed only by the first stage etching without performing the second stage etching. It was confirmed that the bonding property with the IC chip was improved as compared with the COF tape of Comparative Example 2 in which was formed.
As described above, since the shape of the wiring top can be changed to a desired shape by performing the two-step etching, the surface pressure can be suppressed at the time of bonding with the IC chip, and the wiring is short-circuited due to the expansion of the fillet. It was found that defects during bonding can be reduced.

It is process drawing which shows one Embodiment of the manufacturing method of the printed wiring board which concerns on this invention. It is sectional drawing which shows an example of the wiring shape formed by the manufacturing method of embodiment of this invention. It is process drawing which shows the method of forming wiring using the conventional subtractive method. It is sectional drawing which shows the wiring shape formed by the conventional method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Insulating base material 2 Conductive metal layer 3 Photosensitive resin film 4 Resist pattern 5 Wiring pattern (conductor pattern)
6 Wiring (conductor)
7 Wiring (conductor)
7a Wiring top 7b Wiring side wall surface

Claims (5)

Forming a photosensitive resin film on the conductive metal layer formed on at least one surface of the insulating base;
Exposing and developing the photosensitive resin film to form a required resist pattern;
Removing the conductive metal layer exposed by the etching solution to form a conductive pattern;
Removing the photosensitive resin film of the resist pattern;
A second-stage etching step of smoothing the side wall surface of the conductor pattern by treating the formed conductor pattern again with an etching solution , or making the edge portion of the conductor pattern rounded ,
And a step of flip-chip bonding an IC chip to the conductor pattern. The first stage of the etching process, a manufacturing method of a printed wiring board obtained by bonding an IC chip according to claim 1, characterized in that the main etch process for forming the conductive pattern while suppressing side etching.   3. The IC chip according to claim 1, wherein the etching solution used in the first-stage etching step is a hydrogen peroxide / sulfuric acid solution, a cupric chloride solution, or a ferric chloride solution. Manufacturing method of bonded printed wiring board.   The etching solution used in the second-stage etching step is a hydrogen peroxide / sulfuric acid solution, a cupric chloride solution, or a ferric chloride solution. A method for manufacturing a printed wiring board having an IC chip bonded thereto.   The method for manufacturing a printed wiring board to which an IC chip is bonded according to any one of claims 1 to 3, wherein the second etching step is performed by electrolytic pickling.

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