JP2009295656A - Substrate for flexible wiring board and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a substrate for a two-layer flexible wiring board, which has a copper film layer on a resin film substrate and which improves a fracture resistance property. <P>SOLUTION: The substrate for the two-layer flexible wiring board is composed of a resin film base material and a wiring copper layer formed at least on one surface of the resin film base material and having [111] preferred orientation. In a method for manufacturing the substrate for the two-layer flexible wiring board, a copper plating laminate obtained by alternately combining a low current density layer and a high current density layer is formed on at least one surface of the resin film base material, and then the copper plating laminate is heat-processed to form the wiring copper layer composed of the copper film having [111] preferred orientation from the copper plating laminate. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a two-layer flexible wiring board substrate having a copper film layer on a resin film substrate and having improved folding resistance, and a method for producing the same.

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 flexible wiring board substrate is commonly known as a three-layer substrate (copper layer / adhesive layer / base film layer (insulating layer)) in which electrolytic copper foil or rolled copper foil is bonded to a resin film substrate with an adhesive, and a resin film. Substrate for wiring board (commonly called plating board) on which a seed layer and a copper plating layer are sequentially formed on a base material, and a wiring board substrate (commonly called cast board) on which an insulating layer is formed by applying a resin film base varnish to copper foil There are two types of two-layer substrates (copper layer / base film layer (insulating layer)).

  In recent years, the MIT folding resistance test (Folding Endurance Test) standardized by JIS-P-8115 and ASTM-D2176 has been industrially used as an evaluation of the refraction resistance of copper foil used for electric circuit wiring of flexible wiring boards. Yes. In this test, the number of refractions until the circuit pattern formed on the test piece is broken is evaluated, and the greater the number of refractions, the better the folding resistance.

By the way, in order to improve the refractive resistance of the copper foil, for example, as disclosed in Patent Document 1, the copper foil surface is heat-treated at 100 ° C. or higher using a copper foil having a carbon content of 18 ppm or less. Improvement in flexibility and elongation at normal temperature and high temperature is performed, and as disclosed in Patent Document 2, rolling with a rolling reduction of 40 to 80% is performed using an electrolytic copper foil with an elongation of 20 to 40%. Thus, a technique for improving the refraction resistance has been proposed.
JP-A-8-283886 JP-A-6-269807

  However, the methods described above are all applied to copper foil before wiring board formation with rolled copper foil or electrolytic copper foil for three-layer substrates, and can be applied to copper foil used for cast substrates with two-layer substrates. However, since the plating substrate targeted by the present invention is provided with a seed layer formed on at least one surface of the resin film substrate, and then a copper plating layer is formed on this seed layer, the copper plating layer It cannot be heat-treated or rolled. Therefore, the proposal about the plating board | substrate excellent in the folding resistance in the plating board | substrate, and its manufacturing method has not been reached.

In view of such a problem, the first invention of the present invention comprises a resin film substrate and a wiring layer [111] preferentially oriented wiring provided on at least one surface of the resin film substrate. It is the board | substrate for 2 layers flexible wiring.
Moreover, it is preferable that this copper layer for wiring is a copper film formed by heat-treating a copper plating laminate in which low current density layers and high current density layers are alternately combined.

According to a second aspect of the present invention, after forming a copper plating laminate in which a low current density layer and a high current density layer are alternately combined on at least one surface of a resin film substrate, the copper plating laminate is then heat treated. [111] A method for producing a substrate for a two-layer flexible wiring board, wherein a copper layer for wiring composed of a preferentially oriented copper film is formed.
The current density of the copper plating when forming the low current density layer is 0.05 to 0.5 A / dm ² , and the current density of the copper plating when forming the high current density layer is 5 to ^{20 A} / dm ^2. dm ² is preferred.

  According to the substrate for a two-layer flexible wiring board of the present invention, a multi-layered laminated plating layer is formed by sequentially combining a plurality of low current density layers and high current density layers on a seed layer formed on at least one surface of a resin film substrate. The laminated plating layer becomes a copper film with [111] priority orientation due to the heat treatment performed after the configuration is provided, and the room temperature dynamic recrystallization occurs during bending in the MIT folding resistance test, which greatly increases the number of refraction resistance. An excellent effect that an improved two-layer flexible wiring board substrate can be obtained can be obtained.

  In the substrate for a two-layer flexible wiring board of the present invention, the method for producing a resin film base material having conductivity on the surface is not particularly limited, and a metal such as copper or nickel is chemically applied to at least one surface of the resin film surface. Conductivity is imparted to the surface of the resin film by using an electroless plating method formed on the substrate or a dry plating method in which a metal such as copper, nickel, or chromium is formed by vapor deposition or sputtering.

The multilayer copper plating layer is formed by alternately forming the copper plating layers of the low current density layer and the high current density layer on the resin film substrate to which conductivity is imparted by using a copper electroplating method. . In that case, the current density range used for forming the low current density layer and the high current density layer is 0.05 to 0.5 A / dm ^{2 for} the low current density layer and 5 to 20 A / dm ^{2 for} the high current density layer. Therefore, it is desirable that the difference in current density is large. If the difference in current density is small, sufficient [111] preferential orientation cannot be obtained even after heat treatment, and the room temperature dynamics at the time of bending in the MIT folding resistance test are not obtained. Recrystallization hardly occurs.
In the formation of the laminated copper plating layer, the low current density layer and the high current density layer are laminated in the order in which the low current density layer is first formed and then the high current density layer is formed. It is preferable to laminate so as to be.

The thickness of each layer of the laminated copper plating layer is preferably 0.5 to 1.0 μm for the low current density layer and 1.5 to 3.0 μm for the high current density layer. Even if it is smaller or larger than these values, good [111] preferred orientation cannot be obtained in the heat treatment after lamination.
In addition, the number of layers in each layer is preferably 1 to 4 layers, and preferably about 2 to 8 layers as a whole, and more preferably 4 to 8 layers are laminated to obtain a good [111] preferential orientation after heat treatment. .

  The bright copper plating solution of the copper electroplating method used for forming this laminated copper plating layer may use a copper plating bath having a known composition, and generally uses a copper sulfate bath. As long as the additive can be used from a low current density to a high current density, a multilayer structure of a low current density layer and a high current density layer can be formed by changing a current value to be passed. Alternatively, the additive for low current density and the additive for high current density may be used separately. Furthermore, the current density can be controlled by plating conditions such as bath temperature and stirring.

The heat treatment after the formation of the laminated copper plating layer is important for [111] preferential orientation. As the conditions, the temperature is preferably 120 to 150 ° C., and the holding time is set to a suitable time depending on the number of layers to be laminated. Select and do.
Hereinafter, it demonstrates in detail using an Example.

A seed layer of a copper film having a thickness of 0.1 μm was formed on one side of a polyimide film having a thickness of 38 μm by sputtering. Using a commercially available copper sulfate plating bath on this conductive polyimide film, a low current density layer (Low) of 0.5 A / dm ² and a high current density layer (High) of 5 A / dm ² are arranged in this order. The laminated copper plating layer adjusted so that the whole film thickness might be set to 8 micrometers was formed by laminating | stacking 4 layers alternately. Next, a heat treatment was performed at 120 ° C. for 90 minutes to prepare a copper polyimide two-layer flexible wiring board substrate having a wiring copper layer composed of a copper film preferentially oriented in [111]. The [111] preferred orientation ratio was determined by the EBSD method (Electron Back Scattering Diffraction Pattern).

  The refraction resistance of the obtained two-layer flexible wiring board substrate is obtained by forming a test piece pattern of the MIT test method of JIS-P-8115 by photolithography and using a MIT test machine of JIS-P-8115. Bending curvature R = 0.38 mm, load 500 g, refractive rotation number 175 r. p. A refraction resistance test was performed under the condition of m, and the number of refractions until disconnection was measured. The results are shown in Table 1.

A copper film having a thickness of 0.1 μm was formed on one side of a polyimide film having a thickness of 38 μm by sputtering. Using this commercially available polyimide film, a commercially available copper sulfate plating bath is used to laminate four layers of 0.1 A / dm ² current density layers and 10 A / dm ² current density layers alternately to form an overall film. A copper polyimide two-layer flexible wiring board substrate was prepared by forming a plating film adjusted to have a thickness of 8 μm and performing heat treatment at 120 ° C. for 90 minutes.
Table 1 also shows the results of a refraction resistance test performed on the obtained two-layer flexible wiring board substrate under the same conditions as in Example 1.

A copper film having a thickness of 0.1 μm was formed on one side of a polyimide film having a thickness of 38 μm by sputtering. Using a commercially available copper sulfate plating bath on this polyimide film provided with conductivity, four current density layers of 0.3 A / dm ² and 8 A / dm ² are alternately laminated to form a whole film. A copper polyimide two-layer flexible wiring board substrate was prepared by forming a plating film adjusted to have a thickness of 8 μm and performing heat treatment at 120 ° C. for 90 minutes.
Table 1 also shows the results of a refraction resistance test performed on the obtained two-layer flexible wiring board substrate under the same conditions as in Example 1.

A seed layer of a copper film having a thickness of 0.1 μm was formed on one side of a polyimide film having a thickness of 38 μm by sputtering. Using a commercially available copper sulfate plating bath on this conductive polyimide film, a low current density layer (Low) of 0.5 A / dm ² and a high current density layer (High) of 5 A / dm ² are arranged in this order. Eight layers were laminated alternately, and a laminated copper plating layer adjusted so that the total film thickness was 8 μm was formed. Next, a heat treatment was performed at 120 ° C. for 90 minutes to prepare a copper polyimide two-layer flexible wiring board substrate having a wiring copper layer composed of a copper film preferentially oriented in [111].
Table 1 also shows the results of a refraction resistance test performed on the obtained two-layer flexible wiring board substrate under the same conditions as in Example 1.

A copper film having a thickness of 0.1 μm was formed on one side of a polyimide film having a thickness of 38 μm by sputtering. Using this commercially available polyimide film, a commercially available copper sulfate plating bath is used to laminate four layers of 0.1 A / dm ² current density layers and 10 A / dm ² current density layers alternately to form an overall film. A plating film adjusted to have a thickness of 8 μm was formed, and a copper-polyimide two-layer flexible wiring board substrate that was heat-treated for 110 minutes at a temperature of 100 ° C. was prototyped.
Table 1 also shows the results of a refraction resistance test performed on the obtained two-layer flexible wiring board substrate under the same conditions as in Example 1.

A copper film having a thickness of 0.1 μm was formed on one side of a polyimide film having a thickness of 38 μm by sputtering. Using this commercially available polyimide film, a commercially available copper sulfate plating bath was used, and a current density layer of 0.3 A / dm ^{2 and} a current density layer of 8.0 A / dm ² were alternately laminated to form a total layer. A copper-polyimide two-layer flexible wiring board substrate was prepared by forming a plating film adjusted to a thickness of 8 μm and heat-treating at 150 ° C. for 70 minutes.
Table 1 also shows the results of a refraction resistance test performed on the obtained two-layer flexible wiring board substrate under the same conditions as in Example 1.

[Comparative Example 1]
A copper film having a thickness of 0.1 μm was formed on one side of a polyimide film having a thickness of 38 μm by sputtering. Using a commercially available copper sulfate plating bath on the polyimide film provided with conductivity, four current density layers of 1 A / dm ² and 3 A / dm ² are alternately laminated, and the total film thickness is A plating film adjusted to 8 μm was formed, and a copper polyimide substrate subjected to a heat treatment at 120 ° C. for 90 minutes was made as a prototype. Table 1 also shows the results of a refraction resistance test performed on the obtained two-layer flexible wiring board substrate under the same conditions as in Example 1.

[Comparative Example 2]
A seed layer of a copper film having a thickness of 0.1 μm was formed on one side of a polyimide film having a thickness of 38 μm by sputtering. Using this commercially available polyimide film, a commercially available copper sulfate plating bath is used, and a low current density layer of 0.5 A / dm ^{2 and} a high current density layer of 5 A / dm ² are alternately arranged in this order to form four layers. Was laminated to form a laminated copper plating layer adjusted so that the total film thickness was 8 μm. Next, a heat treatment was performed at 80 ° C. for 140 minutes to prepare a copper polyimide two-layer flexible wiring board substrate.
Table 1 also shows the results of a refraction resistance test performed on the obtained two-layer flexible wiring board substrate under the same conditions as in Example 1.

[Conventional example]
A seed layer of a copper film having a thickness of 0.1 μm was formed on one side of a polyimide film having a thickness of 38 μm by sputtering. A copper plating layer in which a 0.5 A / dm ² current density layer was adjusted to a thickness of 8 μm was formed on this conductive polyimide film using a commercially available copper sulfate plating bath. Subsequently, the board | substrate for copper polyimide 2 layer flexible wiring boards which has the copper layer for wiring which performed the heat processing for 120 minutes at 120 degreeC was produced.
Table 1 also shows the results of a refraction resistance test performed on the obtained two-layer flexible wiring board substrate under the same conditions as in Example 1.

  As is apparent from Table 1, it can be seen that the number of refractions until disconnection is significantly improved in the two-layer flexible wiring board substrate of the present invention as compared with the conventional example. Further, in Comparative Example 1 in which the current density at the time of forming the plating film layer is out of the range of the present invention, the [111] preferential orientation ratio is low, so that a satisfactory number of bendings cannot be obtained. Further, even in Comparative Example 2 in which the heat treatment conditions were not satisfied, a sufficient [111] preferential orientation ratio could not be obtained, and the number of bendings was not improved.

Claims (4)

  A two-layer flexible wiring board comprising a resin film base material and a wiring layer of [111] priority orientation provided on at least one surface of the resin film base material.   The copper layer for wiring is a [111] preferentially oriented copper film formed by heat-treating a copper plating laminate in which low current density layers and high current density layers are alternately combined. 2 layer flexible wiring board.   After forming a copper plating laminate in which a low current density layer and a high current density layer are alternately combined on at least one surface of the resin film substrate, the copper plating laminate is then heat treated to remove the copper plating laminate from the [111] priority oriented copper film. The manufacturing method of the board | substrate for 2 layer flexible wiring boards characterized by forming the copper layer for wiring which becomes. The current density of the copper plating when forming the low current density layer is 0.05 to 0.5 A / dm ² , and the current density of the copper plating when forming the high current density layer is 5 to 20 A / dm ^2. The method for producing a substrate for a two-layer flexible wiring board according to claim 3, wherein: