JP2007220730A - Substrate for flexible wiring board and flexible wiring board using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flexible wiring board formed of a copper layer having good buckling resistance, and also to provide a substrate for flexible wiring board. <P>SOLUTION: A double-layer flexible wiring substrate forming the copper layer for wiring includes adequate amount of sulfur and zinc into a copper-plated layer for wiring of the copper layer to form an electric wiring pattern. The copper layer is a plated substrate formed with the plating method. The flexible wiring board is manufactured using such substrate for flexible wiring board. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a flexible wiring board composed of a copper layer for wiring that is improved in refraction resistance and a substrate for the flexible wiring board.

The flexible wiring board is widely used for a refraction wiring board in an electronic device or a digital camera that requires flexibility such as a read / write head of a hard disk or a printer head.
Here, a flexible wiring board substrate used for manufacturing a flexible wiring board is roughly divided into an insulating film such as a polyimide film, a polyamide film, and a PET film with an electrolytic copper foil or a rolled copper foil. Bonded three-layer substrate (copper layer / adhesive layer / base film layer (insulating layer)) and a polyimide substrate with a copper layer formed directly on the polyimide film by plating etc. A two-layer flexible wiring board (copper layer / base film layer (insulating layer)) such as a wiring board (commonly called a cast board) coated and formed with an insulating layer, and a copper layer provided on both sides of the polyimide film by the same method as described above And double-sided board.

In addition, since flexible wiring boards are used for refractive wirings of electronic devices and the like that require the above-mentioned flexibility, in recent years, it has been desired to improve the resistance to refraction of the flexible wiring boards.
Here, as an evaluation of the refraction resistance of the copper foil used for the electric circuit wiring of the flexible wiring board, a MIT folding endurance test standardized by JIS-P-8115 and ASTM-D2176 is commercially available. Widely adopted. In this test, the refraction resistance of the wiring board is evaluated based on the number of refractions until the copper pattern forming the test piece circuit is broken, and the greater the number of refractions, the better the folding resistance.

As what improves the bending resistance of the copper foil used for such electrical circuit wiring etc., for example, as disclosed in Patent Document 1, a copper foil having a carbon amount of 18 ppm or less is used and the surface of the copper foil is 100 ° C. or higher. To improve the bending resistance and elongation at room temperature and high temperature, and as disclosed in Patent Document 2, using an electrolytic copper foil having an elongation of 20 to 40%, a reduction rate of 40 to 40%. A technique for improving folding resistance by performing 80% rolling has been proposed.
JP-A-8-283886 JP-A-6-269807

However, the techniques described in Patent Document 1 and Patent Document 2 can be applied only to copper foil, and as a flexible wiring board substrate using such copper foil, the three-layer substrate or I had to become a cast substrate.
Therefore, in the plated substrate in which the copper layer is directly plated on the polyimide film, the copper layer alone cannot be heat-treated or rolled, and none of the above prior arts can be employed.
From the background described above, the present situation is that no proposal has been made for a flexible wiring board substrate, particularly a plated substrate, which has a copper layer with good folding resistance.

As a result of intensive studies to solve the above-mentioned problems, the present inventors, as a copper layer of a flexible wiring board substrate, can use a flexible wiring substrate with good refraction resistance if a copper layer containing a predetermined amount of sulfur and zinc is used. The inventors have found that it can be obtained and have reached the present invention.
That is, in the flexible wiring board substrate according to the present invention, the copper layer constituting the substrate has 0.01 wt% to 0.08 wt% sulfur and 0.3 wt% to 1.2 wt% zinc in the copper layer. And the copper layer is a plated substrate formed by a plating method.
Further, the flexible wiring board according to the present invention contains 0.01 wt% to 0.08 wt% sulfur and 0.3 wt% to 1.2 wt% zinc in copper constituting the wiring. It is characterized by being manufactured using the said board | substrate for flexible wiring boards.

As described above, according to the flexible wiring board substrate of the present invention, it is possible to obtain a flexible wiring board having good refraction resistance.
Further, the flexible wiring board of the present invention has good refraction resistance of the copper layer constituting the flexible wiring board, and is optimal for a bent portion of a mobile phone or the like.

The flexible wiring board substrate according to the present invention is a flexible wiring board substrate composed of at least a copper layer and an insulating film, and is made resistant by containing sulfur and zinc in the copper layer forming the electric wiring pattern portion. A two-layer plated substrate with good refraction is obtained.
Specifically, the copper film constituting the substrate has a sulfur element concentration of 0.01 wt% to 0.08 wt% and a zinc element concentration of 0.3 wt% to 1.2 wt% in the film. It has been made.
In addition to the plated substrate of the present invention in which a copper layer is formed by a plating method, the copper film is produced by an electroplating method, and the obtained copper film is used as it is. A three-layer substrate or a cast substrate manufactured in accordance with a conventional method using an electrolytic copper foil or a rolled copper foil after a rolling treatment is also included.
Moreover, when manufacturing a plating board | substrate, what is necessary is just to give a plating by adding a sulfur type additive and zinc ion in a copper plating solution at the plating process for providing a copper layer. At this time, the addition amount of each element is appropriately adjusted so that the concentration of the sulfur element in the plating film is 0.01 wt% to 0.08 wt% and the concentration of the zinc element is 0.3 wt% to 1.2 wt%.
Here, the reason why the sulfur-based additive is added to the plating solution is that there is an effect of making the plated copper plating film finer and smoothing the plating surface. The reason why zinc ions are added to the plating solution is that it is effective in improving the toughness of the plating film.
Furthermore, the addition of both sulfur-based additives and zinc ions in the plating solution does not provide a significant improvement in the bending resistance of the substrate even if the plating is added alone. This is because a good copper plating film can be obtained.
In the present invention, the concentration of the elemental sulfur is set to 0.01 wt% to 0.08 wt%. If the concentration of the elemental sulfur is less than 0.01 wt%, the crystals in the obtained copper plating film become columnar crystals and break. On the other hand, if it exceeds 0.08 wt%, sulfur increases in the crystal grain boundary and becomes a crystal grain boundary that easily undergoes brittle fracture.
Also, the zinc element concentration of 0.3 wt% to 1.2 wt% is preferable because when the zinc element concentration is less than 0.3 wt%, the crystals in the obtained copper plating film become crystals with low toughness. On the other hand, if the content exceeds 1.2 wt%, the electrical conductivity of the copper plating film is reduced to a highly resistive plating film, and even if a printed wiring board is obtained using this, a printed wiring board that can withstand use is obtained. This is because it is not preferable.

As the sulfur-based additive according to the present invention, a hydrophilic organic compound containing sulfur can be used. More specifically, thiourea and saccharin are useful because they are inexpensive. Moreover, the commercially available additive containing a sulfur type additive may be sufficient.
In addition, zinc ions according to the present invention include water-soluble zinc compounds such as zinc sulfate and zinc chloride. However, since zinc chloride contains chlorine, the sulfuric acid bath-based copper plating solution causes the precipitation of copper into the chlorine in the plating solution. Care must be taken because the amount is affected.
The plating bath is preferably a pyrophosphoric acid bath in which the zinc concentration in the coating is easy to operate, but is not particularly limited as long as it is a plating bath in which the contents of sulfur and zinc in the coating can be controlled.

The flexible wiring board of the present invention is characterized in that 0.01 wt% to 0.08 wt% sulfur and 0.3 wt% to 1.2 wt% zinc are contained in copper constituting the wiring. Is. Such a flexible wiring board can be easily produced by a conventional method using the substrate for a flexible wiring board of the present invention described above.
For example, a resist layer is provided on the surface of the copper layer of the flexible wiring board substrate of the present invention, exposed using a mask having a desired wiring pattern, developed to produce an etching mask, and the exposed copper layer is etched. The wiring layer can be obtained by removing and then removing the etching mask.
Also, for example, using a base material provided with an ultrathin conductive layer as an underlayer on the surface of an insulating film such as a polyimide film, providing a resist layer on the underlayer surface, and exposing using a mask having a desired wiring pattern And developing to prepare a plating mask, and the exposed underlayer surface contains 0.01 wt% to 0.08 wt% sulfur and 0.3 wt% to 1.2 wt% zinc in the copper. As described above, a desired amount of copper is deposited by a plating method, and then the plating mask is removed, and then the underlayer is removed by flash etching.
[Example]

  Next, this invention is demonstrated using an Example. In Examples 1 and 2, a copper-polyimide substrate obtained by sputtering copper on the surface of a polyimide film having a thickness of 25 μm so as to have a thickness of 0.2 μm was used, and copper having a thickness of 10 μm was used using a pyrophosphoric acid bath. The refraction resistance of the plated substrate obtained by plating was examined by the MIT folding resistance test. The MIT folding resistance test conditions were R = 0.38 mm, load 500 g, refractive rotation number 175 r.p.m, according to JIS-P-8115. The plating bath composition and plating conditions were as shown in Table 1. Thiourea was used as the sulfur-based additive, and zinc sulfate was used as the zinc additive.

Fig. 1 shows the sulfur content in a copper plating film that is fixed at a zinc concentration of 0.3 wt% in the copper plating film and the sulfur additive concentration in the liquid is changed, and the number of times the copper plating film is refracted. .
From this result, sulfur is about 200 to 400 times in the range of 0.01 wt% to 0.08 wt%, and 2 to 4 times higher refraction resistance than 105 times refraction resistance when sulfur is not added. showed that.

FIG. 2 shows the zinc content in the copper plating film plated with the sulfur concentration in the copper plating film fixed at 0.03 wt% and changing the zinc additive concentration in the solution, and the anti-refractive frequency of the copper plating film. .
From this result, zinc has a high refraction resistance of about 240 to about 470 times in the range of 0.3 wt% to 1.2 wt%, and 2 to 4 times the refraction resistance 121 times when zinc is not added. showed that.

A 15 μm thick photoresist layer (manufactured by Hitachi Chemical Co., Ltd.) on the surface of the copper layer of the plating substrate having a zinc concentration of 0.3 wt% and a sulfur concentration of 0.03% in the copper plating film obtained in the above example. RY3215) was formed by a laminating method, and then the photoresist layer was irradiated with ultraviolet rays through a photomask and developed to obtain an etching mask having a desired circuit pattern. Subsequently, the exposed copper plating film portion of the etching mask was removed by etching with a ferric chloride solution, and then the etching mask was removed to obtain a wiring portion.
When the electrical characteristics of the obtained printed wiring board were examined, it was as good as the conventional product. It was also found that the printed wiring board had good adhesion and good bending resistance.

A photoresist layer (manufactured by Hitachi Chemical Co., Ltd.) having a thickness of 15 μm on the surface of the base layer of a copper-polyimide substrate obtained by sputtering copper as a base layer to a thickness of 0.2 μm on the surface of a polyimide film having a thickness of 25 μm. RY3215) was formed by a laminating method, and then the photoresist layer was irradiated with ultraviolet rays through a photomask and developed to obtain a plating mask having a desired circuit pattern. Subsequently, the surface of the underlying layer exposed in the mask opening was used as a cathode, and copper plating with a thickness of 10 μm with a zinc concentration of 0.3 wt% and a sulfur concentration of 0.03% was applied. Thereafter, the plating mask was removed, and the exposed underlayer was removed using a commercially available sulfuric acid / hydrogen peroxide soft etchant (trade name: CPE800, manufactured by Hiejiang Chemical Co., Ltd.) to obtain a printed wiring board. .
When the electrical characteristics of the obtained printed wiring board were examined, it was as good as the conventional product. It was also found that the printed wiring board had good adhesion and good bending resistance.

  The flexible wiring board substrate according to the present invention is a flexible wiring board substrate composed of at least a copper layer and an insulating film, and is made resistant by containing sulfur and zinc in the copper layer forming the electric wiring pattern portion. A two-layer plated substrate having a good refraction property is obtained, and the flexible wiring board of the present invention using this flexible wiring board substrate has a good refraction resistance of the copper layer constituting the substrate, such as a mobile phone. Ideal for bends.

It is a figure which shows the relationship between the sulfur content rate in the copper plating film in Example 1 of this invention, and the refraction-resistant frequency | count of a copper plating film. It is a figure which shows the relationship between the zinc content rate in the copper plating membrane | film | coat in Example 2 of this invention, and the refraction-resistant frequency | count of a copper plating membrane | film | coat.

Claims (4)

  In a flexible wiring board substrate comprising at least a copper layer and an insulating film, the copper layer constituting the substrate comprises 0.01 wt% to 0.08 wt% sulfur and 0.3 wt% to the copper layer. A substrate for a flexible wiring board, which contains 1.2 wt% zinc.   The flexible wiring board substrate according to claim 1, wherein the copper layer is a plating substrate formed by a plating method.   In a flexible wiring board composed of at least a copper layer and an insulating film, 0.01 wt% to 0.08 wt% sulfur and 0.3 wt% to 1.2 wt% zinc are contained in copper constituting the wiring. A flexible wiring board characterized by being contained. A flexible wiring board produced using the flexible wiring board substrate according to claim 1.

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