JP5654205B2 - Manufacturing method of flexible printed circuit board - Google Patents

Description

  The present invention relates to a method for producing a flexible printed circuit board, and more particularly to a method for producing a flexible printed circuit board having a film excellent in adhesive strength between a metal and a polymer film and suitable for high-precision and high-frequency applications.

    As various electronic devices become faster and higher in density, higher functionality of the wiring board is required. In particular, with the development of mobile devices, the flexibility of wiring boards is essential for mobile phone applications, portable music devices, and liquid crystal display applications, and so-called flexible printed circuit boards (hereinafter referred to as “flexible boards”) corresponding to this. Is actively being developed.

    The size of wiring currently mass-produced using a flexible substrate is about 35 μm to 70 μm as a line / space. In addition, for high frequency, materials that can handle pattern miniaturization and materials that do not degrade electrical characteristics at high frequencies are required, and low dielectric constant substrate materials, low moisture absorption materials, and film surface irregularities are few. It is desired. A polyimide film is widely used as the base material of the flexible substrate, but from the background described above, a film made of a material having a low hygroscopic property and an excellent insulating property has begun to be used. (Refer nonpatent literature 1).

    As a method of forming a copper foil film on a film for a flexible substrate, in order to ensure adhesion, a copper thin film containing Ni or Cr is usually formed by sputtering as an adhesive layer, and then electroplated (patent) Reference 1, 2, 3, 4). Subsequently, in the etching process in the patterning of the wiring, there is a problem that not only a process of etching copper but also a process of etching these Ni, Cr and the like are added. (Refer to Patent Documents 5, 6, 7, 8, 9, 10, and 11) Further, since Ni is a magnetic metal, there is a risk of hindrance in high frequency applications.

In addition, a method of forming a copper foil film on a flexible substrate film only by a sputtering method has been proposed. (See Patent Document 12). However, it takes much time to form a copper foil film thickness of up to 12 μm by sputtering alone, which is not practical.
Such a problem in the formation of the seed layer by the sputtering method can be solved to some extent by using the electroless plating method. That is, according to electroless plating, it is possible to increase the process efficiency and form a copper seed layer directly on the flexible substrate film. However, the conventional electroless plating on a plastic film forms irregularities on the surface of the plastic film by pretreatment, and attaches a plating layer by a so-called anchor effect. For example, in the case of a polyimide film, the surface roughening treatment of the flexible substrate film is generally performed by a pretreatment agent called a conditioner. However, surface irregularities cause signal scattering in high frequency applications and are not suitable.

These polymer films have low adhesion of the metal film to the polymer film, and it is difficult to form a seed layer, regardless of which of dry methods such as sputtering and wet methods such as plating. Since the molecules of these polymer films have a structure mainly composed of a benzene ring, the surface stability of the polymer is high despite the high insulation as a high-frequency substrate, resulting in poor surface adhesion. It is thought to do.
In particular, a wiring board using a liquid crystalline polymer (hereinafter referred to as “LCP”) is limited to a copper foil pasting type, and the LCP is a thin film of copper foil despite its excellent insulating properties. However, there is a problem that the form of use as a high-definition substrate for high-frequency applications is restricted. Thus, there is a demand for a method for producing a film substrate for a wiring board and a flexible substrate in which a seed layer is formed by a simple and low-cost process using a polymer film as a substrate.

JP 2006-306209 A JP 2007-247026 A JP 2007-245645 A JP 2007-245646 A JP 9-55575 A JP 2000-165003 A JP 2000-340911 A JP 2002-176242 A JP 2005-15861 A JP 2003-64431 A JP 2002-180157 A JP 2002-094202 A JP 2006-135179 A

Satoshi Onodera, “New Material Technology for Microfabrication-3. Development and Application of Liquid Crystal Polymer Film for Circuit Boards”, Microfabrication Study Group 14th Public Research Society, Japan Institute of Electronics Packaging, September 2004 8th, p16-22

The present invention has been made to solve the technical problems described above.
That is, an object of the present invention is to provide a method for producing a film substrate for a wiring board suitable for high-definition and high-frequency applications using a flexible polymer film as a substrate.

For this purpose, according to the present invention, an evaporated product from a metal oxide containing copper heated and melted is attached on a polymer film heated to 150 ° C. or higher in a vacuum. A step of forming a metal oxide with a thickness of 1 μm or less, a step of forming a conductive metal thin film with copper with a thickness of 1 μm or less by vacuum deposition, a step of plating to a predetermined metal foil thickness, and heat drying A step of producing a film base material for a wiring board.

    In a method for producing a film substrate for a wiring board to which the present invention is applied, a vacuum deposition method is excellent as a method for forming a metal oxide layer and a metal layer for improving adhesion.

    In the method for producing a film substrate for a wiring board to which the present invention is applied, the plating treatment is preferably an electroplating treatment.

    The heat treatment in the method for producing a film substrate for a wiring board to which the present invention is applied heats the resin film at a temperature higher than the glass transition temperature of the underlying polymer film and lower than the decomposition temperature of the polymer film. It is preferable. The heat drying treatment is preferably performed in an atmosphere of an inert gas such as nitrogen or argon in order to prevent damage to the metal foil. By heating the resin film under such conditions, the adhesion between the metal film and the polymer film can be enhanced.

    ADVANTAGE OF THE INVENTION According to this invention, the preparation methods of the film base material for wiring boards suitable for the high-definition and high frequency use which used the polymer film for the base material are provided.

It is a figure for demonstrating the vapor deposition apparatus for preparation of the flexible substrate with which this Embodiment is applied. Example 1

    Hereinafter, the best mode (embodiment) for carrying out the present invention will be described in detail. In addition, this invention is not limited to this Embodiment, It can implement in various deformation | transformation within the range of the summary. The polymer film 11 can be made of one material selected from epoxy resin, polyimide, polyphenylene sulfide (PPS), polyester, Teflon, polyamide, polyimide ether, polyamideimide, polystyrene, aramid, and polycarbonate, or a material made of a mixture thereof. Polyester includes various conventionally known LCPs such as thermotropic liquid crystal, and among them, liquid crystalline polyester is preferable.

    The polymer film is degreased for the purpose of removing impurities adhering to the surface during film production. Usually, the treatment is performed by dipping in a solution of alcohols such as methyl alcohol, ethyl alcohol and isopropyl alcohol, and ketones such as acetone, methyl ethyl ketone and methyl isobutyl ketone. In some cases, it may be wiped with paper, cloth, nonwoven fabric or the like soaked with these liquids. Further, it may be washed with an acid aqueous solution such as dilute hydrochloric acid or a surfactant-containing aqueous solution that is generally widely used in printed circuit boards.

FIG. 1 is a diagram for explaining a vapor deposition apparatus for producing a film substrate for a wiring board to which the present embodiment is applied. The polymer film 11 is fixed above the vapor deposition boat 12 via a fixing jig 16 of the vapor deposition apparatus. A metal oxide 13 serving as an evaporation source is placed on the vapor deposition boat 12. A metal 15 serving as an evaporation source is placed on the vapor deposition boat 14. The fixture has a built- in heater to keep the temperature of the polymer film constant. In order to keep the surface temperature of the polymer film constant, a heater 17 is installed between the evaporation boat and the polymer film.

The metal oxide used at this time is a metal oxide containing copper. Specific examples include copper oxide 1 and copper oxide 2 .

The polymer film 11 is fixed to a fixing jig 16 with a built- in heater, and then fixed above the vapor deposition boat 12. Subsequently, the entire apparatus is evacuated by the vacuum pump 18 and evacuated until the pressure inside the apparatus measured by the vacuum measuring device 19 becomes 10 ⁻¹ Pa or less. At this time, in order to keep the temperature of the polymer film during vapor deposition constant, the temperature is set to 150 ° C. or higher by heating with the fixing jig 16 and the heater 17.

When the pressure of the apparatus reaches 10 ⁻¹ Pa or less, an electric current is applied to the vapor deposition boat 12 to heat it. The metal oxide 13 which is an evaporation source is heated and deposition is started. The amount of metal oxide attached to the polymer film can be achieved as long as it is 0.1 to 10 angstroms per second.

  Subsequently, an electric current is applied to the vapor deposition boat 14 to heat it. The metal 15 which is an evaporation source is melted and deposition is started. The deposition rate of the metal oxide deposited on the polymer film can be achieved if it is 0.1 to 10 angstroms per second.

  At this time, the film thickness of the metal adhering to the polymer film may be 1 μm or less, and it is sufficient that thick film plating can be performed by the plating process in the subsequent process. If the thickness of the metal is excessively less than 0.1 μm, it will dissolve in the plating solution when immersed in the plating treatment solution, and a metal film will not be formed, or the formation of the film in the plating treatment will be insufficient and unevenness will occur. It tends to occur and impair the function as a conductive film or the like. If the thickness of the metal is excessively 1 μm or more, the film quality deteriorates, the distortion of the film increases, and in the worst case, there is a tendency to peel off. Usually, 0.1 μm to 0.5 μm is optimal.

    Also, the polymer film temperature during vapor deposition must be strictly controlled in order to greatly affect the size of metal crystals and the adhesion strength between the polymer film and the metal foil. Usually, the polymer film temperature is set to 100 ° C. or higher, and is preferably lower than the decomposition start temperature of the polymer film. Desirably, it is selected in the range of 150 to 250 ° C.

    Subsequently, the polymer film with the deposited metal is subjected to electroplating in which the plating stress is adjusted with an additive to obtain a necessary film thickness.

    Copper electroplating is a high-throw type copper sulfate basic bath (copper sulfate: 75 g / L, sulfuric acid: 180 g / L, chlorine: 40 ppm), a commercially available additive, Cu-Brite HA-E manufactured by Ebara Eugene Corporation. Alternatively, ST-901 manufactured by Meltex was added and plated with a prepared copper sulfate plating solution to a thickness of 5 to 30 μm.

Gold plating uses a plating bath composed of 2.3 g / L of gold cyanide, 15 g / L of potassium cyanide and 4 g / L of sodium phosphate, and the current density is 0.1 to 0 at 70 ° C. Adjust to 5 A / dm ² and perform electroplating.

Next, the polymer film having a metal film formed by plating is subjected to heat treatment to produce a wiring board film base material having improved adhesion between the metal foil film and the polymer film.
(Heat treatment)
The conditions for the heat treatment are appropriately selected depending on the type of the polymer film, but are usually higher than the treatment temperature of the plating treatment (usually about 15 ° C. to 120 ° C.) and lower than the thermal deformation temperature of the polymer film. It takes place for an appropriate time. For example, heat treatment at a temperature of 200 ° C. for about 30 minutes is preferable.

As described above, after the metal foil film is formed on the surface of the resin film by plating, the polymer film is heated to increase the adhesion between the polymer film and the metal foil film. This is because the heat treatment causes the polymer microstructure that makes up the polymer film to change with temperature, and the interface between the polymer film and the copper foil film is activated. This is thought to be due to stronger bonds.
Usually, the polymer film changes its microstructure (microstructure) if it is below the heat distortion temperature, but it is macroscopic enough to change the practical properties of the film such as electrical properties, water absorption, and dimensional stability. No change will occur. In addition, since the plating treatment is usually performed at a temperature of 100 ° C. or less, the change in the fine structure (microstructure) of the polymer film is slight and no substantial influence is caused.

Hereinafter, the present embodiment will be described in more detail based on examples. Note that this embodiment is not limited to the examples.
(Tape peeling test)
An adhesive tape having a width of 15 mm and a length of 40 mm is applied to the plating film surface of the film base for a wiring board prepared in advance so that the adhesive surface has a length of 20 mm, and then the other end of the adhesive tape is pulled up, The peeling state at the time was visually observed.

Example 1
A 25 μm-thick LCP film 11 (manufactured by Kuraray Co., Ltd .; Vecstar (registered trademark) CT) was prepared, and the surface of this LCP film was rubbed with a non-woven fabric containing isopropyl alcohol to perform a degreasing treatment. Subsequently, the LCP film is fixed to the fixing plate 16 and fixed on the evaporation boat 12 of the vacuum evaporation apparatus. A lump of copper oxide 13 as an evaporation source is deposited on the evaporation boat 12 so that the amount deposited on the LCP film after deposition is 0.01 μm. At the same time, a lump of copper metal 15 as an evaporation source is placed on the evaporation boat 14 so that the amount deposited on the LCP film after deposition is 0.2 μm. The inside of the vacuum apparatus is evacuated by the vacuum pump 18 , and at the same time , the heater of the fixing jig 16 and the heater 17 are energized to heat the LCP film 11. When the temperature of the LCP film reaches 200 ° C., the energization is stopped, and when the pressure in the vacuum deposition apparatus becomes 10 ⁻² Pa, the evaporation boat 12 is heated to start the deposition. When the lump of copper oxide 13 disappears, the energization is stopped. The evaporation boat 14 is heated to start copper deposition. When the lump of metallic copper 15 disappears, the energization is stopped. When it is confirmed that the LCP film 11 can be cooled to 50 ° C. or lower, the exhaust of the vacuum pump 18 is stopped, the leak valve 20 is opened, and the inside of the vacuum apparatus is returned to normal pressure. Subsequently, the LCP film was added to a high-throw type copper sulfate basic bath (copper sulfate: 75 g / L, sulfuric acid: 180 g / L, chlorine: 40 ppm) with a commercially available additive, Cu-Brite HA-E manufactured by Sugawara Eugleite Co., Ltd. The film thickness of the copper foil was 18 μm. Next, heat treatment was performed at a temperature of 200 ° C. for 30 minutes in a nitrogen atmosphere to prepare a film base material for an LCP wiring board.
A tape peeling test of the film substrate for a wiring board thus prepared was conducted, but the copper foil did not adhere to the tape, and high adhesion strength between the LCP film and the copper foil film was confirmed.

(Example 2)
A polyimide film 11 having a thickness of 25 μm (manufactured by Ube Industries, Ltd .; Upilex (registered trademark)) was prepared, and the surface of the polyimide film was rubbed with a non-woven fabric containing isopropyl alcohol for degreasing treatment. Subsequently, the polyimide film is fixed to the fixing plate 16 and fixed on the evaporation boat 12 of the vacuum evaporation apparatus. A lump of copper oxide 13 as an evaporation source is deposited on the evaporation boat 12 so that the amount deposited on the polyimide film after deposition is 0.01 μm. At the same time, a mass of copper metal 15 as an evaporation source is deposited on the evaporation boat 14 so that the amount deposited on the polyimide film after deposition is 0.25 μm. The inside of the vacuum apparatus is evacuated by the vacuum pump 18, and at the same time, the polyimide film 11 is heated by energizing the heater of the fixing jig 16 and the heater 17. When the temperature of the polyimide film reaches 200 ° C., the energization is stopped, and when the pressure in the vacuum vapor deposition apparatus becomes 10 ⁻² Pa, the evaporation boat 12 is heated to start vapor deposition. When the lump of copper oxide 13 disappears, the energization is stopped. The evaporation boat 14 is heated to start copper deposition. When the lump of metallic copper 15 disappears, the energization is stopped. When it is confirmed that the polyimide film 11 can be cooled to 50 ° C. or lower, the exhaust of the vacuum pump 18 is stopped, the leak valve 20 is opened, and the inside of the vacuum apparatus is returned to normal pressure. Next, a commercially available additive, Cu-Brite HA-E manufactured by Sugawara Eugleite Co., Ltd. was added to a high-throw type copper sulfate basic bath (copper sulfate: 75 g / L, sulfuric acid: 180 g / L, chlorine: 40 ppm). The film thickness of the copper foil was 18 μm. Next, a heat treatment was performed at a temperature of 200 ° C. for 30 minutes in a nitrogen atmosphere to prepare a film substrate for a polyimide wiring board.
The tape peeling test of the film substrate for a wiring board thus prepared was conducted, but the copper foil did not adhere to the tape, and high adhesion strength between the polyimide film and the copper foil film was confirmed.

Example 3
A 25 μm thick PPS11 (manufactured by Toray Industries, Inc .; Torelina (registered trademark )) was prepared, and the polyimide film surface was rubbed with a non-woven fabric containing isopropyl alcohol, and degreased. Subsequently, the PPS film is fixed to the fixing plate 16 and fixed on the evaporation boat 12 of the vacuum evaporation apparatus. An evaporation boat 12 is placed so that a mass of copper oxide 13 as an evaporation source adheres to the PPS film after vapor deposition is 0.01 μm. At the same time, a lump of copper metal 15 as an evaporation source is placed on the evaporation boat 14 so that the amount deposited on the PPS film after deposition is 0.15 μm. The inside of the vacuum apparatus is evacuated by the vacuum pump 18, and at the same time , the heater of the fixing jig 16 and the heater 17 are energized to heat the PPS film 11. When the temperature of the PPS film reaches 180 ° C., the energization is stopped, and when the pressure in the vacuum vapor deposition apparatus becomes 10 ⁻² Pa, the evaporation boat 12 is heated to start vapor deposition. When the lump of copper oxide 13 disappears, the energization is stopped. The evaporation boat 14 is heated to start copper deposition. When the lump of metallic copper 15 disappears, the energization is stopped. When it is confirmed that the PPS film 11 can be cooled to 50 ° C. or lower, the exhaust of the vacuum pump 18 is stopped, the leak valve 20 is opened, and the inside of the vacuum apparatus is returned to normal pressure. Next, a commercially available additive, Cu-Brite HA-E manufactured by Sugawara Eugleite Co., was added to a high-throw type copper sulfate basic bath (copper sulfate: 75 g / L, sulfuric acid: 180 g / L, chlorine: 40 ppm). The film thickness of the copper foil was 18 μm. Next, heat treatment was performed at a temperature of 200 ° C. for 30 minutes in a nitrogen atmosphere to prepare a film base material for a PPS wiring board.
The tape peeling test of the film substrate for a wiring board thus prepared was conducted, but the copper foil did not adhere to the tape, and high adhesion strength between the PPS film and the copper foil film was confirmed.

(Comparative example)
A 25 μm-thick LCP film 11 (manufactured by Kuraray Co., Ltd .; Vecstar (registered trademark) CT) was prepared, and the surface of this LCP film was rubbed with a non-woven fabric containing isopropyl alcohol to perform a degreasing treatment. Subsequently, the LCP film is fixed to the fixing plate 16 and fixed on the evaporation boat 14 of the vacuum evaporation apparatus. A lump of copper metal (purity 99.99%) 15 as an evaporation source is placed on an evaporation boat so that the amount deposited on the LCP film after deposition is 0.5 μm. The inside of the vacuum apparatus is evacuated by the vacuum pump 18, and at the same time , the heater of the fixing jig 16 and the heater 17 are energized to heat the LCP film 11. When the temperature of the LCP film reaches 130 ° C., the energization is stopped, and when the pressure in the vacuum deposition apparatus becomes 10 ⁻² Pa, the evaporation boat 14 is heated to start the deposition. When the lump of copper metal 15 disappears, the energization is stopped. When it is confirmed that the LCP film 11 can be cooled to 50 ° C. or lower, the exhaust of the vacuum pump 18 is stopped, the leak valve 20 is opened, and the inside of the vacuum apparatus is returned to normal pressure. The size of the grain boundary of the copper foil formed at this time was observed by SEM, and as a result, it was 1 μm or less. Subsequently, a high-throw type copper sulfate basic bath for LCP film substrates (copper sulfate: 75 g / L, sulfuric acid: 180 g / L, chlorine: 40 ppm), a commercially available additive, ST-901 manufactured by Meltex, was added. The thickness of the copper foil was 12.5 μm. Next, heat treatment was performed at a temperature of 200 ° C. for 30 minutes in a nitrogen atmosphere to prepare a film base material for an LCP wiring board. When the tape peeling test of the film base material for wiring boards prepared as described above was performed, the copper foil adhered to the tape, and the LCP and the copper foil film did not have sufficient adhesion strength for practical use.

    According to the method for producing a wiring board film substrate to which the present invention is applied, a flexible printed board having high adhesion can be produced. This method can be applied to various uses other than the wiring board. For example, an electromagnetic shield film, an antireflection film, and the like are conceivable.

DESCRIPTION OF SYMBOLS 11 Film base material for wiring boards 12 Metal oxide vapor deposition boat 13 Oxide evaporation source 14 Metal vapor deposition boat 15 Metal evaporation source 16 Polymer film fixing jig 17 Heater 18 Vacuum pump 19 Vacuum pressure gauge 20 Leak valve

Claims (4)

On a polymer film that has been heated to 150 ° C. or higher in advance in a vacuum, an evaporant from a metal oxide that has been heated and melted is attached without providing a potential difference between the evaporation source and the film. A first step of providing a metal oxide layer made of a metal oxide by vacuum deposition so as to be 1 μm or less;
A second step of depositing the metal thin film on the metal thin film so that the film thickness of the metal thin film is 1 μm or less;
A third step of forming a metal film with a thickness of 5 μm to 30 μm by electroplating;
A fourth step of drying by heating,
The metal oxide layer includes copper , and the conductive metal of the evaporation source is made of copper . In the fourth step, the flexible print is processed at a temperature not lower than a glass transition temperature of the polymer film and not higher than a decomposition start temperature. A method for manufacturing a substrate.   The method for producing a flexible printed circuit board according to claim 1, wherein in the first step, the metal oxide layer is vacuum-deposited so as to be 0.01 μm or less. 3. The method for manufacturing a flexible printed circuit board according to claim 1, wherein the fourth step is performed in an inert gas such as nitrogen or argon. The polymer film is composed of one selected from epoxy resin, polyimide, polyphenylene sulfide, polyester, Teflon, polyamide, polyimide ether, polyamideimide, polystyrene, aramid, polycarbonate, or a mixture of at least two selected from these. The method for producing a flexible printed circuit board according to any one of claims 1 to 3 .

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