JP2008186970A - Substrate for flexible wiring board, its manufacturing method, and flexible wiring board using the substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a substrate for a flexible wiring board having a good flexural resistance. <P>SOLUTION: A shield layer is provided on at least one of surfaces of an insulating film material by dry plating or by electroless plating, and then copper and nickel plating layers are alternately formed on the shield layer at least once by plating. At this time, the copper plating layer is provided by electroplating, and the nickel plating layer is provided by electroplating or by electroless plating. When the nickel plated layers forming the conductive layers has a total thickness T<SB>Ni</SB>and the copper plated layers have a total thickness T<SB>Cu</SB>, the thicknesses of these plated layers are adjusted so that a ratio S (T<SB>Ni</SB>/T<SB>Cu</SB>) is between 0.1 and 0.7. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a flexible wiring board substrate comprising a conductive layer for wiring with improved refraction resistance, a method for manufacturing the same, and a flexible wiring board using the substrate.

  Flexible wiring boards are widely used for read / write heads and printer heads of hard disks that require flexibility, and for refractive wiring boards in digital cameras.

The substrate for a flexible wiring board used for manufacturing a flexible wiring board is roughly divided into an electrolytic copper foil and a rolled copper foil adhered to an insulating film such as a polyimide film, a polyamide film, and a PET film with an adhesive. A layer substrate (copper layer / adhesive layer / base film layer (insulating layer)), a wiring substrate (commonly referred to as a plating substrate) in which a copper layer is directly formed on the surface of the insulating film by plating, or a polyimide varnish directly on a copper foil. 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.
Since such a flexible wiring board is used for a refractive wiring board of the above-described electronic device or the like, in recent years, it has been desired to improve the refraction resistance of the flexible wiring board with respect to the wiring.

  As an evaluation of the refraction resistance of a conductive layer used for wiring of a flexible wiring board, the MIT folding endurance test standardized by JIS-P-8115 and ASTM-D2176 is widely used commercially. . In this test, the refraction resistance of the wiring board is evaluated by the number of refractions until the circuit pattern forming the test piece circuit is disconnected. The larger the number of refractions, the better the refraction resistance.

As for improving the refraction resistance of the copper foil for the conductive layer used for such electric circuit wiring, for example, as disclosed in Patent Document 1, the surface of the copper foil is obtained using a copper foil having a carbon amount of 18 ppm or less. Heat treatment at 100 ° C. or higher to improve bending resistance and elongation at room temperature and high temperature, and as disclosed in Patent Document 2, use an electrolytic copper foil having an elongation of 20 to 40%. There has been proposed a technique for improving the refraction resistance by rolling at a rolling reduction of 40 to 80%.
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 the copper foil itself. As a substrate for a flexible wiring board using such a copper foil, the three-layer substrate is used. And I had to become a cast substrate.
Therefore, in a flexible wiring board substrate (plating substrate) in which a conductive layer is directly plated on an insulating film, the conductive layer on the insulating film cannot be subjected to heat treatment or rolling. Neither could be adopted.
From the background described above, the present situation is that no effective proposal has yet been made to obtain a flexible wiring board substrate, particularly a plated substrate, having a conductive layer with good folding resistance.

  The first invention for solving the above problems comprises an insulating film substrate, a seed layer provided on at least one surface of the insulating film substrate, and a conductive layer provided on the seed layer. The flexible wiring board substrate is characterized in that the conductive layer has a multilayer structure including a copper plating layer and a nickel plating layer.

  The second invention is characterized in that, in the above invention, the copper plating layer is formed by an electrolytic plating method, and the nickel plating layer is formed by an electrolytic plating method or an electroless plating method.

In the third invention, the total thickness T _{Ni of} the nickel plating layers constituting the conductive layer in either of the first or second invention and the total thickness T _Cu of the copper plating layers. The ratio S (T _Ni / T _Cu ) is 0.1 to 0.7.

  And this 4th invention is a manufacturing method of the board | substrate for flexible wiring boards in any one of the said 1st-3rd invention, and seeds at least one surface of the insulating film base material by the dry-type plating method or the electroless-plating method. After providing the layer, a copper plating layer and a nickel plating layer are alternately formed at least once on the seed layer by plating.

  In the fifth aspect of the invention, the copper plating layer is provided by an electrolytic plating method, and the nickel plating layer is provided by an electrolytic plating method or an electroless plating method.

In the sixth aspect of the present invention, the ratio S (T _Ni / T) between the total thickness T _{Ni of} the nickel plating layers constituting the conductive layer and the total thickness T _Cu of the copper plating layers in the above-described invention. _Cu ) is 0.1 to 0.7.

  And this 7th invention is a flexible wiring board manufactured using the board | substrate for flexible wiring boards in any one of the said 1st-3rd invention.

  The substrate for a flexible wiring board of the present invention is obtained by forming a multilayer conductive layer using a copper plating layer and a nickel plating layer on a seed layer formed on at least one surface of a resin film base as described above. is there. By doing so, the stress generated by bending can be dispersed by generating fine cracks in the nickel layer, so that concentration of stress on the copper layer can be avoided, and the resistance of the flexible wiring board substrate of the present invention can be reduced. Refractive properties can be improved.

In addition, according to the method of the present invention, the flexible wiring board substrate of the present invention can be manufactured by combining existing equipment and the completed prior art, so the flexible wiring of the present invention having excellent refraction resistance characteristics. Can be manufactured with high quality and low cost.
Moreover, the reflex resistance of the flexible wiring board produced using the board | substrate of this invention is very high.

In order to obtain the flexible wiring board substrate according to the present invention, first, a seed layer is provided on at least one surface of an insulating resin film substrate such as a polyimide film, a polyamide film, or a PET film. As a method for providing the seed layer, a dry plating method such as a vapor deposition method or a sputtering method, or an electroless plating method can be used. As the material of the seed layer, there is no problem as long as it has conductivity, but from the viewpoint of adhesion with an insulating film, ease of wiring formation, etc., metals such as copper, nickel, chromium, and alloys thereof. It is preferable to do.
It is also possible to form a seed layer by applying conductive oxide powder.
Thereafter, a conductive layer is provided on the seed layer. This conductive layer has a multilayer structure of a copper plating layer and a nickel plating layer.

  Since the copper plating layer constituting the conductive layer is strongly required to have a function as a wiring, it is desired to be dense. In order to provide such a copper layer, it is preferable to apply an electrolytic plating method. This is because a dense copper layer can be easily obtained. At this time, a commercially available plating bath can be applied, and plating is preferably performed according to conditions recommended for the plating bath.

  The nickel plating layer generates fine cracks in the nickel plating layer at the time of refraction, thereby dispersing the stress generated at the time of refraction, delaying the progress of the crack, and sending the generation of cracks in the copper plating layer. Is. Therefore, such a purpose cannot be achieved with an extremely dense nickel layer. Therefore, it is preferable to provide the nickel plating layer by an electrolytic plating method or an electroless plating method, and in particular, an electroless plating method is recommended. Also in this case, a commercially available plating bath can be used, and the plating conditions may be recommended for the plating bath.

  The conductive layer has a multilayer structure composed of a copper plating layer and a nickel plating layer because, as described above, the stress generated at the time of bending generates fine cracks in the nickel layer at the time of bending, thereby dispersing the stress. This is to delay the progress of cracks in the copper layer.

In this case, the ratio of the thickness of the copper plating layer and the nickel plating layer constituting the conductive layer is defined as the ratio S between the total thickness T _Ni of the nickel plating layer and the total thickness T _Cu of the copper plating layer. It is more effective when (T _Ni / T _Cu ) is 0.1 to 0.7. When the ratio S is less than 0.1, the nickel plating layer does not function sufficiently, the stress generated during bending acts directly on the copper plating layer, the crack progresses rapidly in the copper plating layer, and the disconnection is also accelerated. .

  On the other hand, when the ratio S exceeds 0.7, the fine cracks of the nickel plating layer collapse and become large cracks, and stress is directly applied to the copper plating layer, resulting in early disconnection.

  In order to obtain a flexible wiring board using the flexible wiring board substrate of the present invention, a photolithography method can be used as in the prior art.

  Hereinafter, the present invention will be further described with reference to examples.

(Example 1)
Flexible wiring board using a copper-polyimide substrate with a 0.2 μm thick copper layer formed on the surface of a 25 μm thick polyimide film (product name: Kapton, manufactured by Toray DuPont Co., Ltd.) by sputtering. A substrate was made.
The copper layer having a thickness of 0.2 μm was used as a seed layer, and a copper layer having a thickness of 6 μm was provided on the seed layer by performing electrolytic copper plating using a commercially available copper sulfate plating bath.
Next, an electroless nickel plating layer having a thickness of 2 μm was provided on the copper layer using a commercially available electroless nickel plating bath.
The ratio S (T _Ni / T _Cu ) between the layer thickness T _{Ni of the} nickel layer and the total thickness T _Cu of the copper layers constituting the conductive layer obtained was 0.33.

  In order to investigate the refraction resistance of the obtained substrate for flexible wiring, a JIS-P-8115 MIT test method pattern was formed by photolithography, and these were formed using a JIS-P-8115 MIT test machine (Tester Sangyo Co., Ltd.). Company BE-203 Folding Resistance Tester), and the number of refractions until disconnection was determined under the conditions of R = 0.38 mm, a load of 500 g, and a refractive rotation number of 175 rpm. The obtained results are shown in Table 1.

(Example 2)
For flexible wiring boards as in Example 1, except that the thickness of the electrolytic copper plating layer was 4 μm, the thickness of the electroless nickel plating layer was 3 μm, and an electrolytic copper plating layer having a thickness of 1 μm was provided thereon. A substrate was created. The ratio S of the obtained conductive layer was 0.6.

  The obtained flexible wiring board substrate was subjected to an MIT test under the same conditions as in Example 1. The obtained results are also shown in Table 1.

(Example 3)
A flexible wiring board substrate was prepared in the same manner as in Example 1 except that the thickness of the electrolytic copper plating layer was 7 μm and an electric nickel plating layer having a thickness of 1 μm was provided. The ratio S of the obtained conductive layers was 0.1. The plating bath used to obtain the electronickel plating layer was a private bath watt bath.

  The obtained flexible wiring board substrate was subjected to an MIT test under the same conditions as in Example 1. The obtained results are also shown in Table 1.

Example 4
This example corresponds to a conventional example.
A flexible wiring board substrate was prepared in the same manner as in Example 1 except that the conductive layer was an electrolytic copper plating layer having a thickness of 8 μm.

The obtained flexible wiring board substrate was subjected to an MIT test under the same conditions as in Example 1. The obtained results are also shown in Table 1.

  As is apparent from the results in Table 1, the flexible wiring substrate of the present invention has a significantly improved number of refractions until disconnection compared to the conventional product.

Considering this result and the characteristics of the nickel plating layer, in the present invention product, the bending stress received in the MIT folding resistance test is dispersed by forming fine cracks in the nickel plating layer, and cracks in the copper plating layer It can be inferred that the progression of the can be suppressed.
In Example 4, as in the conventional product, the conductive layer is only a copper plating layer, and the bending stress received in the MIT folding resistance test is directly applied directly to the surface of the copper plating layer, so that there is a crack in that portion. It was confirmed by observation of the fracture surface after the test that it was easy to enter, and the crack propagated in the thickness direction, leading to disconnection.

  The flexible wiring board substrate of the present invention is provided with a multilayer plating layer having a multilayer structure formed by sequentially combining a copper plating layer and a nickel plating layer on the seed layer formed on at least one surface of the resin film base as described above. With this configuration, the circuit board has excellent bending characteristics and is excellent as a circuit board having a bent portion and a bent portion. For this reason, the flexible wiring board substrate of the present invention is particularly excellent for wiring boards that require good refraction and bending characteristics, such as hard disk read / write heads and printer heads, and circuit boards for refractive wiring in digital cameras. Demonstrate the effect. Further, according to the method of the present invention, such a high-quality flexible wiring board substrate can be manufactured at low cost. In addition, the flexible wiring board produced using the flexible wiring board substrate of the present invention has high refraction resistance and high reliability. Therefore, the industrial value of the present invention is extremely great.

Claims (7)

In a flexible wiring board substrate comprising an insulating film substrate, a seed layer provided on at least one surface of the insulating film substrate, and a conductive layer provided on the seed layer, the conductive layer is a copper plating layer A substrate for a flexible wiring board, characterized in that it has a multilayer structure comprising a nickel plating layer. 2. The flexible wiring board substrate according to claim 1, wherein the copper plating layer is formed by an electrolytic plating method, and the nickel plating layer is formed by an electrolytic plating method or an electroless plating method. The ratio S (T _Ni / T _Cu ) between the total thickness T _{Ni of the} nickel plating layer and the total thickness T _Cu of the copper plating layer is 0.1 to 0.7. Item 3. The flexible wiring board substrate according to Item 1 or 2. After a seed layer is provided on at least one surface of the insulating film base by dry plating or electroless plating, a copper plating layer and a nickel plating layer are alternately formed at least once on the seed layer by plating. A method for producing a flexible wiring board substrate, comprising: The method for producing a substrate for a flexible wiring board according to claim 4, wherein the copper plating layer is provided by an electrolytic plating method and the nickel plating layer is provided by an electrolytic plating method or an electroless plating method. The ratio S (T _Ni / T _Cu ) between the total thickness T _{Ni of the} nickel plating layer and the total thickness T _Cu of the copper plating layer is 0.1 to 0.7. Item 6. The method for producing a flexible wiring board substrate according to Item 4 or 5. The flexible wiring board manufactured using the board | substrate for flexible wiring boards in any one of Claims 1-3.