JP2006237325A - Production process of film substrate for wiring, and film substrate for wiring - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a film substrate for wiring suitable for transmitting high frequency signal and capable of high density mounting. <P>SOLUTION: The production process of a film substrate for wiring comprises a step for forming a conductor thin film, i.e. a conductor seed layer 3, by electroless plating on the surface of a thermoplastic resin film, i.e. a liquid crystal polymer film 1, through Pd catalyst 2, and a step for hot pressing the conductor seed layer 3 and the liquid crystal polymer film 1 on which the conductor seed layer 3 is formed by the step for forming the conductor thin film. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for manufacturing a wiring film substrate such as a flexible printed circuit board, and more particularly to a method for manufacturing a wiring film substrate suitable for high-frequency signal transmission and capable of high-density mounting.

  In recent years, with the progress of miniaturization of devices incorporating electronic circuits, such as the spread of portable devices, flexible printed wiring boards (film substrates for wiring) using resin films as substrates have come to be widely used. ing. Since the flexible printed wiring board used for such a small device is limited in the space in which it is arranged, it is often used by being bent, and the curvature is different depending on the device used. Moreover, it may be used for a movable part.

  Currently, a polyimide film is widely used as a substrate material for flexible printed wiring boards. This polyimide film has higher heat resistance (up to 500 ° C.) than other organic materials and polymer materials, and also has high performance in terms of mechanical strength and chemical resistance. Further, since it has a low dielectric constant (usually 3.2 to 3.4), is highly ductile, and has an excellent thermal expansion coefficient, it has many advantages as a substrate material for flexible printed wiring boards.

  FIGS. 4A to 4D are views for explaining a manufacturing method for manufacturing a wiring pattern by a subtractive method using polyimide as a substrate material. Here, as shown in FIG. 4A, first, a copper foil 202 having a thickness of, for example, 9 μm is bonded to a polyimide film substrate 201 to form a so-called copper-clad laminate. Thereafter, as shown in FIG. 4B, patterning is performed with a resist 203 on a polyimide film substrate 201 to which the copper foil 202 is bonded. Then, a wiring pattern 202A is formed by etching as shown in FIG. 4C, the resist 203 is peeled off as shown in FIG. 4D, and a wiring pattern 202A is formed on the polyimide film substrate 201. Yes.

Here, with the progress of the information society in recent years, when information transmission and information processing have been speeded up and the signal frequency has been increased, the polyimide film as the substrate material has a high dielectric constant. The problem is that transmission loss increases.
In the formation of the flexible printed wiring board by the subtractive method described above, a copper clad laminate in which a copper foil 202 is bonded to a polyimide film substrate 201 is used. For this reason, the thickness of the copper foil to be etched increases, and the edge of the wiring cannot be formed sharply. Also, the wiring width L1 on the copper film surface side as shown in FIG. 4D and the wiring width L2 on the substrate surface side (bonding side) are greatly different from each other, making it difficult to form fine wiring. There is also a problem of becoming.

Therefore, a method of forming a flexible printed wiring board by a semi-additive method using a liquid crystal polymer film as a substrate material for the next-generation flexible printed wiring board has been studied.
FIGS. 5A to 5E are views for explaining a manufacturing method for manufacturing a wiring pattern by a semi-additive method using a liquid crystal polymer film as a substrate material. First, as shown in FIG. 5A, a thin conductor seed layer 102 is formed on the liquid crystal polymer film 101. Thereafter, a resist 103 is formed on the conductor seed layer 102 as shown in FIG. Next, as shown in FIG. 5C, pattern plating is performed by thickening the copper film 104 only on the wiring forming portion by electroplating using the formed resist 103. Thereafter, the resist 103 is removed (peeled) as shown in FIG. Finally, as shown in FIG. 5E, the conductor seed layer 102 in the non-wiring portion where the resist 103 has been formed is removed by etching to form a wiring pattern.
In the flexible printed wiring board formed in this way, the liquid crystal polymer film 101 has a low dielectric constant, so that transmission loss at high frequencies can be reduced. Further, according to the semi-additive method shown in FIGS. 5A to 5E, high-density wiring (fine wiring) is possible.

Here, in this semi-additive method, since the conductor seed layer 102 must be finally removed by etching, the thinner the conductor seed layer 102 is, the better. However, since it is said that the thickness of the copper foil is about several μm, it is not preferable to form the conductor seed layer 102 with the copper foil.
Further, as a method for forming the conductor seed layer 102, a sputtering method or an electroless plating method can be considered. However, since this sputtering method has to be formed in a vacuum, the manufacturing process becomes complicated and the manufacturing cost increases. Further, the electroless plating method has advantages that the manufacturing process is simple and the cost is low, but it is difficult to form a plating film on the liquid crystal polymer film 101 with sufficient adhesion strength.
Furthermore, in a copper clad laminate of a liquid crystal polymer film that is generally commercially available, the adhesive surface of the copper foil is roughened in advance in order to bond the copper foil to the liquid crystal polymer film with sufficient adhesion strength. This increases transmission loss and reduces the advantages of using a liquid crystal polymer film as a substrate material.

  As a prior art described in the publication, there is one that attempts to obtain sufficient adhesion strength by roughening the film surface when a conductive thin film is formed on a liquid crystal polymer film by an electroless plating method (for example, Patent Document 1). reference.). Moreover, when forming a conductive thin film on a liquid crystal polymer film by an electroless plating method, there is a technique for improving the adhesion strength by devising a catalytic treatment solution used in the electroless plating method (see, for example, Patent Document 2). ). Furthermore, after forming a conductor thin film on the liquid crystal polymer film by electroless plating, the film is heat-treated at a temperature above the glass transition point in nitrogen, oxygen, and air atmosphere to increase the adhesion strength of the conductor thin film to the film. The technique to raise is disclosed (for example, refer patent document 3).

JP 2000-223804 A Japanese Patent Application Laid-Open No. 2004-143587 JP 2004-247425 A

  According to the method proposed in each of the above patent documents, it is possible to form a conductor thin film on the liquid crystal polymer film by an electroless plating method. However, in the method described in Patent Document 1, since the film surface is roughened, transmission loss increases, and the advantage of using a liquid crystal polymer film is reduced. Further, the technique described in Patent Document 2 has a problem that the process becomes complicated and the processing time becomes long. Furthermore, with the technique described in Patent Document 3, sufficient adhesion strength cannot be obtained without roughening the film surface in advance, and as in Patent Document 1, an increase in transmission loss can be avoided. Absent.

  The present invention has been made to solve the technical problems as described above, and an object of the present invention is to provide a wiring film substrate suitable for high-frequency signal transmission and capable of high-density mounting. And it is providing the manufacturing method of this film substrate for wiring.

  Under such an object, the present invention is a proposal made by a method for manufacturing a wiring film substrate as shown in FIG. That is, the method for manufacturing a wiring film substrate to which the present invention is applied includes a conductive thin film forming step of forming a conductive thin film on the surface of a thermoplastic resin film by an electroless plating method, and the conductive thin film is formed by this conductive thin film forming step. And a thermocompression bonding step of thermocompression bonding the thermoplastic resin film and the conductor thin film.

Here, this thermocompression bonding step can be characterized by performing thermocompression bonding at a temperature near the melting point of the thermoplastic resin film. When a thermoplastic resin is heated above its melting point, the viscosity is greatly reduced, and the thermoplastic resin itself becomes an adhesive, and when pressure is applied, it enters fine pores at the interface between the conductor thin film and the film. Therefore, adhesion strength can be improved by performing thermocompression bonding.
The conductor thin film forming step may be characterized in that a conductor thin film is formed by an electroless plating method after imparting metal atoms that serve as catalyst nuclei for electroless plating to the surface of the thermoplastic resin film.

  On the other hand, the present invention is a film substrate used for wiring, which is formed by an electroless plating method on a surface of the thermoplastic resin film and the thermoplastic resin film, and then thermocompression bonded with the thermoplastic resin film. And a conductor thin film to be formed.

Here, the thermoplastic resin film may be a liquid crystal polymer film.
Further, if the unevenness at the interface between the thermoplastic film and the conductor thin film is 2 μm or less in terms of the ten-point average height Rz, high-frequency transmission is performed when wiring is formed using the conductor thin film. This is preferable in that the loss can be reduced. When the unevenness of the interface is 2 μm or more in Rz, the high-frequency transmission loss becomes equal to or higher than that of the product of the copper clad laminate, and the advantage of forming the copper film by the electroless plating method is reduced. In order to further reduce the high-frequency transmission loss, the unevenness of the interface is preferably 500 nm or less in terms of the ten-point average height Rz.

The conductor thin film may be a metal thin film including at least one of Cu, Cu alloy, Ni, and Ni alloy. Furthermore, if the thickness is too thin, the conductor film cannot be satisfactorily laminated by electroplating, and if it is too thick, the etching process at the time of wiring formation takes too much time. 100 nm to 300 nm is more preferable.
Still further, the present invention can be characterized in that metal atoms that serve as catalyst nuclei for electroless plating are contained between the thermoplastic film and the conductive thin film.

  According to the present invention, it is possible to easily provide a wiring film substrate that is suitable for high-frequency signal transmission and can be mounted at high density.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. This embodiment relates to a technique for providing a wiring film substrate itself as shown in FIG.
FIGS. 1A and 1B are diagrams for explaining a method of manufacturing a wiring film substrate to which the present embodiment is applied. First, as shown in FIG. 1A, a conductive seed layer 3 (conductor thin film) having a thickness of, for example, about 200 nm is formed on a liquid crystal polymer film 1 which is a thermoplastic resin by an electroless plating method using a Pd catalyst 2. Form. As the conductor seed layer 3, Cu, Cu alloy, Ni, Ni alloy or the like is preferably used. Further, instead of the Pd catalyst 2, a catalyst such as Pt, Au, or Ag can be used. Next, the conductor seed layer 3 and the liquid crystal polymer film 1 are thermocompression bonded. The thermocompression bonding temperature is higher than the melting point of the liquid crystal polymer film 1. The liquid crystal polymer film 1 is sufficiently adhered to the conductor seed layer 3 by being heated to a temperature higher than the melting point of the liquid crystal polymer film 1 and further applying pressure. In addition, although it is possible to heat from both the liquid crystal polymer film 1 side and the conductor seed layer 3 side, only one of them may be heated.

  FIG. 2 is a configuration diagram illustrating a thermocompression bonding apparatus 20 that performs the thermocompression bonding process illustrated in FIG. The thermocompression bonding apparatus 20 shown in FIG. 2 includes a supply roller 21 for supplying the liquid crystal polymer film 1 on which the conductor seed layer 3 is formed by plating, and a pair of heating processes for thermocompression bonding the conductor seed layer 3 and the liquid crystal polymer film 1. A pressure roller 22 is provided. A heater 23 is provided inside the heat and pressure roller 22. Furthermore, it has a pair of exit roller 24 which conveys the film substrate for wiring after thermocompression bonding to the downstream side. After passing through the exit roller 24, a recovery roller 25 for recovering the liquid crystal polymer film 1 to which the conductor seed layer 3 is heat-welded is provided.

  The liquid crystal polymer film 1 after the formation of the conductor seed layer 3 supplied from the supply roller 21 is sequentially supplied to the contact portions of the pair of heat and pressure rollers 22, and at the contact portions of the pair of heat and pressure rollers 22. , Heated, and pressurized. The heated and pressurized liquid crystal polymer film 1 with the conductor seed layer 3 is conveyed to the exit roller 24 and is recovered by the recovery roller 25 in a cooled state, for example. The sheet collected by the collection roller 25 is used as a wiring film substrate.

Hereinafter, the present embodiment will be specifically described by way of examples. However, this embodiment does not limit the present embodiment unless it exceeds the gist.
[Example 1]
FIG. 3 is a diagram for explaining the steps of the manufacturing method according to the first embodiment. First, a liquid crystal polymer film (manufactured by Kuraray Co., Ltd .: Bexter OC) is prepared (step 101), and a copper plating film is adhered to the surface of the liquid crystal polymer film by the following steps 102 to 106 (electroless plating method). . First, the film surface was chemically activated by atmospheric plasma irradiation (step 102). Then, it was immersed in a silane coupling agent (manufactured by Shin-Etsu Silicone Co., Ltd .: KBM903) for 3 minutes and then washed with water (step 103). Next, it was immersed in a Pd catalyst imparting agent (Okuno Pharmaceutical Co., Ltd .: OPC-80 Catalyst M) for 3 minutes and then washed with water (step 104). Thereafter, it was immersed in hydrochloric acid for 3 minutes and then washed with water (step 105). Then, it was immersed in an electroless copper plating solution (Okuno Pharmaceutical Co., Ltd .: ATS ADKAPPA-IW) at 32 ° C. for 10 minutes, washed with water, and dried in an atmosphere at 100 ° C. for 30 minutes (step 106). As described above, a liquid crystal polymer film having a copper (Cu) plating film formed on the surface was formed. Thereafter, thermocompression bonding was performed with a thermocompression bonding apparatus 20 as shown in FIG. 2 (step 107) to produce a liquid crystal polymer film with a plating film attached (step 108). In this thermocompression bonding, the temperature during thermocompression bonding was 300 ° C. and the pressure was 40 N / cm. According to the result of SEM (Scanning Electron Microscope) observation, the thickness of the plating film formed in this way was about 200 nm, and the unevenness at the interface was 800 nm expressed as the ten-point average height Rz.

[Example 2]
In place of the electroless copper plating solution shown in Step 106, the same operation as in Example 1 was performed except that a Ni-B plating solution (Okuno Pharmaceutical Co., Ltd .: Top Chemialoy B-1) was used. A plating film-attached liquid crystal polymer film having a Ni-B thin film was formed on the liquid crystal polymer film. According to the SEM observation result, the thickness of the plating film was about 200 nm. Further, the unevenness of the interface was 800 nm in terms of the ten-point average height Rz.

[Comparative Example 1]
A copper plating film was formed on the liquid crystal polymer film in the same manner as in Example 1 except that thermocompression bonding was not performed. The unevenness of the interface was 800 nm in terms of ten-point average height Rz.

[Comparative Example 2]
First, the same operation as in Example 1 was performed except that the surface of the liquid crystal polymer film was roughened by chemical treatment. According to the SEM observation result, the unevenness at the interface between the plating film and the film was 5 μm in terms of the ten-point average height Rz.

[Comparative Example 3]
A copper foil having a thickness of 10 μm was thermocompression bonded to the liquid crystal polymer film with a thermocompression bonding apparatus to form a copper clad laminate. According to the SEM observation result, the unevenness of the interface was 6 μm in terms of the ten-point average height Rz.

[Comparative Example 4]
A copper plating film was formed on the liquid crystal polymer film in the same manner as in Example 1 except that the liquid crystal polymer film was heated in a nitrogen atmosphere at 200 ° C. instead of thermocompression bonding. The unevenness of the interface was 800 nm in terms of ten-point average height Rz.

The samples obtained in Examples and Comparative Examples were evaluated as follows, and the results are summarized in Table 1.

  For the samples obtained in Examples 1 and 2 and Comparative Examples 1, 2, and 4, the adhesion strength between the conductor film and the film for the sample obtained by laminating a copper film of about 10 μm by electrolytic plating and the sample for Comparative Example 3 Was measured by a 90 degree peel test. In Example 1 and Example 2, the density strength of the conductor film was 650 N / m, and in Comparative Example 3, the density strength of the conductor film was 670 N / m. However, the adhesion strength of Comparative Example 1 was about 10 N / m, and the adhesion strength of Comparative Example 4 was a very low value of about 50 N / m. That is, it was found that sufficient adhesion strength cannot be obtained in the case of Comparative Example 1 in which thermocompression bonding is not performed or in the case of Comparative Example 4 in which only heating is performed without applying pressure.

  In addition, copper wires having a width / height of 20 μm / 10 μm were formed by the semi-additive method for the samples of Examples 1 and 2 and Comparative Examples 1, 2, and 4 and by the subtractive method for the sample of Comparative Example 3. . And about these samples, the same dimensional relationship as L1 and L2 demonstrated in FIG.4 (d) was grasped | ascertained. That is, L1 / L2 was compared as the wiring width L1 on the copper film surface side and the wiring width L2 on the liquid crystal polymer film surface side (bonding side). As a result, in Example 1 and Example 2, it is clear that the ratio L1 / L2 is as large as 0.98 and 0.97, and it is possible to obtain a wiring film substrate that is preferable for forming fine wiring. became. In Comparative Example 1, Comparative Example 2, and Comparative Example 4, the ratio L1 / L2 was 0.82, 0.87, and 0.97, but in the sample of Comparative Example 3, L1 / L2 was 0.8. 54, which was smaller than the other samples and was found to be inappropriate for microfabrication.

  Furthermore, a current was passed through the wiring formed for the samples of the example and the comparative example, and the transmission loss was measured. As a result, the transmission loss of the samples of Comparative Example 2 and Comparative Example 3 was larger than the loss of the samples of Example 1 and Example 2, Comparative Example 1 and Comparative Example 4. In Comparative Example 2 and Comparative Example 3, it is considered that the transmission loss was also increased due to large irregularities at the interface between the conductor film and the liquid crystal polymer film. Accordingly, the unevenness of the interface is preferably 2 μm or less in terms of the ten-point average height Rz.

(a), (b) is a figure for demonstrating the manufacturing method of the film substrate for wiring to which this Embodiment is applied. It is the block diagram which showed the thermocompression bonding apparatus which performs the thermocompression bonding process shown in FIG.1 (b). FIG. 6 is a diagram for explaining a process of the manufacturing method in Example 1. (a)-(d) is a figure for demonstrating the conventional manufacturing method which manufactures a wiring pattern by a subtractive method, using a polyimide as a board | substrate material. (a)-(e) is a figure for demonstrating the manufacturing method which manufactures a wiring pattern by a semi-additive method using a liquid crystal polymer film as a board | substrate material.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Liquid crystal polymer film, 2 ... Pd catalyst, 3 ... Conductor seed layer, 20 ... Thermocompression bonding apparatus

Claims (8)

A method of manufacturing a wiring film substrate,
A conductor thin film forming step of forming a conductor thin film on the surface of the thermoplastic resin film by an electroless plating method;
The manufacturing method of the film board for wiring including the thermocompression-bonding process of thermocompression-bonding the said thermoplastic resin film in which the said conductor thin film was formed by the said conductor thin film formation process, and the said conductor thin film.   The method for manufacturing a wiring film substrate according to claim 1, wherein the thermocompression bonding is performed by thermocompression bonding at a temperature in the vicinity of a melting point of the thermoplastic resin film.   2. The conductive thin film forming step of forming the conductive thin film by an electroless plating method after imparting metal atoms serving as catalyst nuclei for electroless plating to the surface of the thermoplastic resin film. A method of manufacturing a wiring film substrate. A film substrate used for wiring,
A thermoplastic resin film;
A wiring film substrate comprising: a conductive thin film formed on the surface of the thermoplastic resin film by an electroless plating method, and then formed by thermocompression bonding with the thermoplastic resin film.   5. The wiring film substrate according to claim 4, wherein the thermoplastic resin film is a liquid crystal polymer film.   5. The wiring film substrate according to claim 4, wherein the unevenness at the interface between the thermoplastic film and the conductor thin film is 2 μm or less in terms of a ten-point average height Rz.   5. The wiring film substrate according to claim 4, wherein the conductor thin film is a metal thin film containing at least one of Cu, Cu alloy, Ni, and Ni alloy.   The wiring film substrate according to claim 7, wherein metal atoms serving as catalyst nuclei for electroless plating are contained between the thermoplastic film and the conductive thin film.

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