JPH11314310A - Production of fluororesin/thin metal membrane composite sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily produce a composite sheet improved in the bonding strength of a fluororesin sheet and thin metal membrane. SOLUTION: A method for producing a fluororesin/thin metal membrane composite sheet has a process for treating the surface of a fluororesin sheet with remote hydrogen plasma to impart a hydrophilic nature to the same, a process for bonding palladium metal to the surface of the hydrophilic fluororesin sheet and a process for applying nonelectrolytic plating treatment to the fluororesin sheet having palladium metal bonded to the surface thereof to form a thin metal membrane. As the fluororesin sheet, a polytetrafluoroethylene sheet is preferably used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for FPC boards (flexible printed wiring boards), TAB (tape automated bonding) tapes, shielded electric wire covering materials, conductive composite films, films for heating elements, etc. The present invention relates to a method for producing a fluororesin / metal thin film composite sheet that can be used.

[0002]

2. Description of the Related Art In recent years, in the field of electronic technology, which is becoming more and more compact with high functionality and high integration, for example, F
PC board (flexible printed wiring board) is smaller,
Thinner conductors are required, and conductors are narrower and thinner. By the way, copper, which is a conductor, also has an electric resistance, and when an electric current is applied to this, naturally heat is generated. If the generated heat is not dissipated, the temperature rises without limit and destroys the element or insulation, but is usually kept at a certain temperature where heat dissipation and heat generation are balanced. For example,
When a current of 400 mA is applied to a copper foil having a thickness of 35 μm and a width of 0.15 mm, the temperature rises by about 75 ° C. This is for the case of simple conductors, but the temperature of a finer circuit rises to a fairly high temperature. Therefore, materials used for these elements or insulating materials are increasingly required to have heat resistance.

Hitherto, various polymers having excellent heat resistance have been proposed. Among them, polytetrafluoroethylene (hereinafter referred to as "PTFE") has properties such as heat resistance, flame retardancy, and the like. The material is excellent in thermal, chemical, and electrical properties such as chemical resistance and electrical properties, and has high reliability.
That is, PTFE is one of the most stable polymers having heat resistance and chemical resistance while being hydrophobic,
In addition to the above excellent properties, it is an excellent electrical insulating material. Its volume resistance is 10 ¹⁹ Ω-cm at 73 ° F. (22.8 ° C.) under atmospheric pressure, and the relative humidity is 100%.
Is 10 ¹⁶ Ω-cm, and the dielectric constant at 22.8 ° C. in the range of 1 MHz to 1 GHz is 2.1, and the dielectric loss factor is 1 × 10 ⁻⁴ . Therefore, PTF
A composite material of E and copper is a material most suitable for an electrical insulating material for high frequency in the GHz band, for example, a printed wiring board of an integrated circuit, a wire covering material, and the like.

In general, there are many methods for metallizing copper on a polymer material, such as electroless plating, vapor deposition, and sputtering. Of these, electroless plating is the simplest method for metallizing a polymer surface. There is an advantage that no special device is required. By the way, in the process of electroless plating, in order for copper ions to undergo a reduction reaction to copper metal, it is necessary to apply palladium metal particles as a catalyst to the polymer surface. When a polymer material with palladium metal particles attached to the surface is placed in an electroless plating solution containing copper ions, a reduction reaction of the copper ions with formaldehyde is caused by the palladium catalyst, and the reduced copper is reduced to the presence of palladium metal particles. Can be deposited and metallized on the surface of the polymeric material. Therefore, what is important for metallizing is how to attach palladium metal particles to the polymer material surface and how to increase the adhesion between the polymer material surface and the copper thin film deposited by electroless plating. That's what it means.

[0005]

However, when a composite material is formed using a sheet made of a fluororesin, for example, PTFE, as the polymer material, the surface of the fluororesin sheet is inert and hydrophobic, so that the palladium adhered thereto The amount of metal particles was small, and therefore, even when the electroless plating treatment was performed, a copper thin film having a sufficient adhesive force could not be formed.

When a composite material is produced by metallizing a PTFE sheet by metal vapor deposition, sputtering, or the like, the surface of the PTFE sheet is inactive and has low adhesion to other materials. It is essential to pretreat the surface. Conventionally, as a pretreatment method for producing a composite material, there is known a method of roughening the surface of a PTFE sheet in order to increase adhesion by an anchor effect. For example, irradiation of KrF and ArF with an excimer laser, or keV or Me
Ion irradiation in the energy range of V and the like are often employed as a pretreatment method. However, these pretreatment methods have a problem that the processing area is small. These pretreatment methods improve the adhesion between the PTFE sheet and the copper metal by an anchor effect that changes the morphology of the surface of the PTFE sheet. However, there is a problem that the material on the surface of the PTFE sheet is deteriorated. However, it has not yet been fully commercialized.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems in the prior art, and an object of the present invention is to provide an apparatus having improved adhesion between a fluororesin sheet and a metal thin film. It is an object of the present invention to provide a method for easily manufacturing a PTFE / metal thin film composite sheet material capable of coping with high functionality and high integration of components and components.

[0008]

The present inventors have studied the metallization of copper by simple electroless plating. As a result, the important thing in the metallization of the PTFE sheet surface is that the PTFE sheet is first modified. It has been found that remote plasma treatment, in which the sample to be treated is located away from the plasma zone, is effective for surface modification to enhance the surface quality and make the surface of the PTFE sheet wet well with the electroless plating solution. Thus, the present invention has been completed.

The method for producing a fluororesin / metal thin film composite sheet according to the present invention comprises the steps of hydrophilizing the surface of the fluororesin sheet by remote hydrogen plasma treatment and adhering palladium metal to the surface of the hydrophilized fluororesin sheet. And a step of forming a metal thin film by performing an electroless plating process on a fluororesin sheet having a palladium metal adhered to its surface. As a fluororesin sheet,
PTFE sheets are preferably used. Further, after performing the electroless plating, an electrolytic plating may be further performed.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The first step, that is, the step of hydrophilizing the surface of a fluororesin sheet by remote hydrogen plasma treatment will be described. This step is necessary for depositing palladium metal, which serves as a catalyst when a metal thin film is formed by electroless plating. By performing a remote hydrogen plasma treatment, defluorination and oxidation occur, resulting in a fluororesin. The surface of the sheet is modified and made hydrophilic. The remote hydrogen plasma treatment used for the surface modification in the present invention is to perform a plasma treatment with a sample placed at a position away from the plasma zone. Are essentially different.

In the plasma processing, the plasma includes electrons,
It consists of ions and radicals. The radicals promote a chemical reaction on the polymer surface and have a longer life than electrons and ions.
Therefore, if you place a fluororesin sheet at a position away from the normal plasma zone and perform remote hydrogen plasma treatment,
A radical reaction predominantly occurs, and a reaction by electrons or ions hardly occurs. That is, in the remote hydrogen plasma, hydrogen radicals are dominant rather than electrons and hydrogen ions, and the hydrogen radicals mainly promote the hydrophilization reaction. On the other hand, in direct hydrogen plasma, electrons and hydrogen ions coexist with hydrogen radicals.
That is, not only a reforming reaction by hydrogen radicals but also a reaction by electrons and hydrogen ions occur simultaneously. Reactions by electrons and hydrogen ions are mainly caused by etching and erosion (degradation) reactions due to electron and ion bombardment, and as a result, low-molecular-weight reaction products are generated on the surface of the fluororesin sheet by these reactions. WB
The surface is covered with L (Weak Boundary Layer). Since copper plating or the like is applied to the surface of the WBL, the peel strength decreases, and good results cannot be obtained.

In the present invention, preferable conditions for the remote hydrogen plasma treatment are as follows. That is, the output of a high frequency (for example, 13.56 MHz) power supply is 10 W
It is set in the range of 400 W, more preferably in the range of 50 W to 300 W. If the output is greater than 400 W, the output of the remote hydrogen plasma treatment is too strong to deteriorate the fluororesin sheet, while if less than 10 W, no plasma is generated. The remote hydrogen plasma processing pressure was 1.
33 Pa to 133 Pa, preferably 6.7 Pa to
It is set in the range of 26.6 Pa. Processing pressure is 1.33P
If it is less than a and greater than 133 Pa, the plasma processing effect will be weak. The plasma irradiation time is set in a range of 10 seconds to 300 seconds. When the irradiation time is shorter than 10 seconds, the treatment effect is small, while when the irradiation time is longer than 300 seconds, the fluororesin sheet is deteriorated.

The fluororesin sheet (film) used in the present invention includes PTFE, polyvinylidene fluoride, polyvinyl fluoride, polychlorotrifluoroethylene, vinylidene fluoride-tetrafluoroethylene copolymer, tetrafluoroethylene-per Fluoroalkyl vinyl ether copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-hexafluoropropylene-perfluoroalkylvinyl ether copolymer, tetrafluoroethylene-ethylene copolymer, chlorotrifluoroethylene-ethylene copolymer Examples include sheets of polymers and the like. Among these, a PTFE sheet is particularly preferable, and specifically, a film-like sheet and a porous sheet (for example,
(Tomy Filex F, manufactured by Tomoe Paper Mill Co., Ltd.) and the like are used. Generally, the thickness is preferably in the range of 25 to 150 μm.

The remote hydrogen plasma treatment in the present invention can be performed, for example, using the apparatus shown in FIG. In FIG. 1, a reactor is a cylindrical Pyrex glass tube 1 (for example, having a diameter of 45 mm and a length of 1,000 m).
m), and a cylindrical stainless steel chamber 2 (for example, 300 mm in diameter and 300 mm in height). The Pyrex glass tube 1 is provided with gas inlets 3a and 3b for introducing argon gas and hydrogen gas, respectively. The argon cylinder 5a and the hydrogen cylinder 5b are provided via mass flow controllers 4a and 4b, respectively.
It is connected to. A copper tube 6 is wound around the Pyrex glass tube in a coil shape (for example, 9).
Winding), high frequency (RF) power supply 7 (for example, 13.56)
MHz). Stainless steel chamber 2
Is provided with a pressure gauge 8, and an exhaust port 9 is connected to a vacuum system composed of a rotary pump and a diffusion pump. The Pyrex glass tube and the cylindrical stainless steel chamber are connected by a flange using a Viton O-ring 10. 11 indicates a PTFE sheet, A indicates a direct plasma processing position, and B indicates a remote plasma processing position.

The case of processing by this apparatus will be described by way of an example. The PTFE sheet 11 is placed at a position (B) away from the center of the coiled copper tube 6 by about 800 mm and exposed to hydrogen plasma. Next, the air in the reaction system is replaced with argon, and then the inside of the cylindrical stainless steel chamber is evacuated to about 1.3 × 10 ⁻² Pa. Next, hydrogen is introduced into the Pyrex glass tube at a flow rate of 10 cm ³ (room temperature, atmospheric pressure) / min by a mass flow controller. 13. Remote hydrogen plasma processing
The operation is performed at a constant pressure of 3 Pa and under a different pressure while changing the RF output and the irradiation time.

In the present invention, the mechanism of hydrophilization by remote hydrogen plasma treatment will be considered. By the remote hydrogen plasma treatment, defluorination and oxidation occur on the surface of the fluororesin sheet, and oxygen-containing groups are formed. The mechanism for the formation of these oxygen-containing groups is presumed as follows. . Hydrogen radicals in the remote hydrogen plasma extract fluorine atoms from the surface of the fluororesin sheet to form carbon radicals. Carbon radicals recombine with other hydrogen radicals in the hydrogen plasma,
Form a CH bond. This is the mechanism of defluorination by remote hydrogen plasma. However, not all the carbon radicals formed by the fluorine abstraction are recombined with the hydrogen radicals, and some of the carbon radicals remain on the surface of the fluororesin sheet even after the remote hydrogen plasma treatment is completed. As soon as the fluororesin sheet is removed from the plasma reactor, the remaining radicals react with oxygen and moisture in the air to form peroxide groups. The peroxide group is modified to a group with oxygen, such as a hydroxyl, CO or carbonyl group. This is the mechanism for forming a group having oxygen. In the present invention, defluorination and oxidation of the fluororesin sheet surface occur by the remote hydrogen plasma treatment,
The conversion of the defluorination is 25% to 39% (estimated from the concentration of the CF ₂ component and the F / C element ratio), and C—O and C—O formed by oxidation of carbon radicals after remote hydrogen plasma treatment. An oxygen-containing group such as C = O has a role of a site for capturing colloidal palladium metal.

After the fluororesin sheet subjected to the remote hydrogen plasma treatment is subjected to a washing treatment with a solvent such as acetone if desired, palladium metal is adhered to the surface in the next step. The palladium metal attached in this step is
In the following electroless plating process, it acts as a catalyst for reducing metal ions to metal and is essential for forming a metal thin film by electroless plating. Specifically, the fluororesin sheet hydrophilized by remote hydrogen plasma is immersed in a palladium colloid, for example, a colloid solution containing colloidal palladium-tin alloy particles, and then the tin component is dissolved and removed in a sulfuric acid solution. To activate a fluororesin sheet having a colloidal palladium-rich surface. The particle size of the palladium-tin alloy particles in the colloid solution used is preferably from 10 to 400 angstroms. In order to dissolve and remove only the tin component by immersing in a sulfuric acid aqueous solution, appropriate conditions, for example, a concentration of 3.6 at 5 minutes at 40 ° C.
m / l.

The fluororesin sheet having the palladium metal adhered to the surface is then subjected to metal plating using an electroless plating solution. Any known electroless plating solution can be used, and examples of the metal forming the metal thin film include copper, gold, nickel, and cobalt. Specific examples of the electroless plating solution include TMP manufactured by Okuno Pharmaceutical Co., Ltd. Also,
Electroless plating may be performed, for example, at room temperature for about 5 minutes.

Generally, a metal thin film having a thickness of 0.1 to 2.5 μm is formed by electroless plating, but a metal thin film having a larger thickness, for example, a metal thin film having a thickness of 5 to 30 μm is formed. If it is desired, the electroless plating may be performed, and then the electrolytic plating may be further performed. The electrolytic plating can be performed by a known method using a known electrolytic plating solution. For example, a peel strength test requires a copper thin film thickness of about 30 μm,
Generally, a copper sulfate plating method is used. On the sheet surface,
In order to plate uniformly and high-quality copper, a plating solution (for example, a sulfuric acid aqueous solution + copper sulfate + additive) is stirred in an electrolytic plating tank to improve a flowing state, and to improve a current density. It is important to bubble a large amount of air with a small diameter, or to fix the sheet satisfactorily against the water flow of the plating solution. Generally, liquid temperature 20
It is preferable that the cathode current density be in the range of 100 to 500 A / m ^{2 at} a temperature of ° C.

[0020]

EXAMPLES Example 1 PTFE film (Nichias: Teflon 90)
01, width 300 mm, thickness 50 μm) is 10 mm × 30
It was cut into a size of mm to obtain a sample for surface modification.
This PTFE film was subjected to ultrasonic cleaning in acetone and vacuum-dried at room temperature, and then subjected to a remote hydrogen plasma treatment using the apparatus shown in FIG. That is, the PTFE film was placed at a position about 800 mm away from the center of a copper tube wound in a coil shape, and exposed to hydrogen plasma. Next, the air in the reaction system was replaced with argon, and then the inside of the cylindrical stainless steel chamber was evacuated to about 1.3 × 10 ⁻² Pa. Next, the flow rate of hydrogen was reduced to 1 with a mass flow controller.
It was adjusted to 0 cm ³ (room temperature, under atmospheric pressure) / min and introduced into a Pyrex glass tube. The remote hydrogen plasma treatment was performed under a pressure of 13.3 Pa, an RF output of 100 W, and an irradiation time of 10 seconds. Note that a high-purity type gas having a purity of 99.995% was used as hydrogen and argon.

Next, the PTFE film hydrophilized by the remote hydrogen plasma as described above is used to prepare a colloidal solution containing colloidal palladium-tin alloy particles (OPC-80 and OPC-SAL manufactured by Okuno Pharmaceutical Co., Ltd.). The mixture was immersed in the mixture at 25 ° C. for 5 minutes and stirred to allow the colloidal palladium-tin alloy particles to adhere to the PTFE film surface. Next, this PTFE film was immersed in a dilute sulfuric acid solution (3.6 M / l) at 40 ° C. for 5 minutes to dissolve and remove the tin component, thereby obtaining a PTFE film having a surface to which colloidal palladium particles had adhered.

Next, in order to metallize copper on the surface of the PTFE film, two methods of electroless plating and electrolytic plating are used.
Processing was performed by combining the two processes. First, the above-mentioned PTFE film was immersed in an electroless plating solution (TMP, manufactured by Okuno Pharmaceutical Co., Ltd.) at room temperature for 5 minutes to deposit copper on the surface, and a 0.2 μm-thick electroless copper plating layer was formed. Was formed. Next, the PTFE film having the electrical conductivity obtained by the electroless plating was subjected to electrolytic plating to form an electrolytic copper plating layer having a thickness of 30 μm. In the electrolytic plating, a sulfuric acid solution (190 g /
l) to copper sulfate (75 g / l), hydrochloric acid (50 ppm) and additives (Nippon RironalCo.Lt)
d, PCM, 5 ml).
The test was performed at 20 ° C. under the conditions of a current of 10 A (current density of 300 A / m ² ) and a voltage of 8 V. Finally, at 80 ° C., 1
After vacuum drying for 2 hours, a composite film composed of a PTFE film and a copper thin film was obtained.

Example 2 A composite film composed of a PTFE film and a copper thin film was prepared by performing surface treatment in the same manner as in Example 1 except that the irradiation time in the remote hydrogen plasma treatment was changed to 60 seconds. Example 3 A surface treatment was performed in the same manner as in Example 1 except that the irradiation time in the remote hydrogen plasma treatment was changed to 90 seconds, to produce a composite film composed of a PTFE film and a copper thin film. Example 4 A surface treatment was performed in the same manner as in Example 1 except that the irradiation time in the remote hydrogen plasma treatment was changed to 120 seconds, to produce a composite film composed of a PTFE film and a copper thin film.

Example 5 A composite film composed of a PTFE film and a copper thin film was prepared by performing a surface treatment in the same manner as in Example 1 except that the irradiation time in the remote hydrogen plasma treatment was changed to 150 seconds. Example 6 A surface treatment was performed in the same manner as in Example 1 except that the irradiation time in the remote hydrogen plasma treatment was changed to 300 seconds, to produce a composite film composed of a PTFE film and a copper thin film. Example 7 A surface treatment was performed in the same manner as in Example 1 except that the RF output of the remote hydrogen plasma was changed to 50 W and the irradiation time was changed to 150 seconds, to produce a composite film composed of a PTFE film and a copper thin film.

Comparative Example 1 Example 1 was repeated except that the remote hydrogen plasma treatment was not performed.
In the same manner as in the above, a composite film composed of a PTFE film-a copper thin film was produced. Comparative Example 2 A surface treatment was performed in the same manner as in Example 1 except that a direct plasma treatment was performed for an irradiation time of 120 seconds instead of the remote hydrogen plasma treatment in Example 1.
A composite film composed of a TFE film and a copper thin film was produced. The direct plasma treatment was performed using the apparatus shown in FIG. 1 with the PTFE film placed in the plasma zone, that is, at the center of the coiled copper tube.

The following properties of the PTFE film and the composite film composed of the PTFE film and the copper thin film which were treated with the remote hydrogen plasma in Examples 1 to 7 and Comparative Examples 1 and 2 were evaluated.

(1) Contact angle with water The contact angle with water on the surface of the PTFE film treated with the remote hydrogen plasma was set at 20 ° C. within 2-3 minutes after the treatment.
Was measured using a goniometer (Model G-1 manufactured by Elma) under the following environment. Measurements in which the variation in the experimental values was about 3 to 4 ° were performed ten times, and the average value was obtained.

(2) Peel strength between the PTFE film and the copper thin film Regarding the adhesion between the PTFE film and the copper thin film, the T-shaped peel strength (5 mm width) was measured using an Instron type tensile tester (AGS100-, manufactured by Shimadzu Corporation). 10 mm using A)
The peel strength was measured and evaluated at a rate of / min. The average value of the peel strength measured ten times was defined as the peel strength.

Table 1 shows the measurement results together with the plasma irradiation time and the high-frequency output.

[Table 1] From the comparison between Examples 1 to 6 and Comparative Example 1, the contact angle was changed from 118 ° to 8 ° within a short time of plasma irradiation of 10 seconds.
It was found that the contact angle was reduced to 8 °, and the decrease in the contact angle continued until the contact angle became 77 ° at the plasma irradiation time of 120 seconds, and thereafter, the decreasing tendency of the contact angle became negligible. Further, from a comparison between Example 4 and Example 7, it was found that the contact angle of water on the PTFE film surface when the RF output was changed was linearly decreased with an increase in the RF output. These facts indicate that the surface of the PTFE film can be modified by performing the remote hydrogen plasma treatment with a short irradiation time of 120 seconds or less.

Further, from the results of measurement of the peel strength, the effect of surface modification by remote hydrogen plasma was found. That is, in the case of Comparative Example 1, the peel strength between the untreated PTFE and the copper thin film was 7.5 mN / 5 mm, and the plated copper thin film was easily peeled off only by rubbing with a finger. On the other hand, the peel strength between the plasma-treated sheet and the copper thin film increased as the plasma treatment time increased, and reached a maximum value of 92 mN / 5 mm in a plasma irradiation time of 120 seconds. This value was 12 times that of Comparative Example 1. When the irradiation time exceeded 120 seconds, the peel strength did not increase. On the other hand, in the case of Comparative Example 2 in which the direct hydrogen plasma treatment was performed, the peel strength was 15 N / 5 mm.
, And showed a remarkably low degree of adhesion as compared with the case of Example 4.

[0031]

In the method for producing a composite sheet according to the present invention, the surface of the fluororesin sheet is modified by a remote hydrogen plasma treatment, so that the modification causes defluorination and oxidation, thereby making the surface hydrophilic without etching. The adhesion can be improved between the fluororesin sheet and the metal thin film. Therefore, according to the present invention, it is possible to easily produce an excellent composite material having improved adhesion between the fluororesin sheet and the metal thin film by electroless plating.

The composite material produced according to the present invention can be used for various purposes, such as for the space and aircraft industries and as consumer equipment, and particularly as a printed circuit board using a copper thin film. If used,
It has the following advantages: (1) it can be used at a higher temperature; (2) there are few short circuit problems; (3) it becomes easier to form through holes; and (4) the circuit can be made smaller. In addition, cost reduction of products due to downsizing of circuits,
There are also advantages such as saving material costs by not using an adhesive, and eliminating the need for an environmental pollution prevention device because no solvent is used. Further, the composite material sheet according to the present invention is useful as a conductive composite film, particularly in the fields of electronics and information such as transparent electrode films and heating elements, and in the construction industry such as heat ray blocking films and heat insulating films. Material.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an example of a plasma processing apparatus.

[Explanation of symbols]

1: Pyrex glass tube, 2: chamber, 3a, 3
b: gas inlet, 4a, 4b: mass flow controller, 5a: argon cylinder, 5b: hydrogen cylinder, 6: copper tube (electrode), 7: high frequency power supply, 8: pressure gauge,
9: exhaust port, 10: viton O-ring, 11: PTFE
Sheet, A: direct plasma processing position, B: remote plasma processing position.

Claims (6)

[Claims] 1. a step of hydrophilizing the surface of a fluororesin sheet by remote hydrogen plasma treatment, a step of attaching palladium metal to the surface of the hydrophilized fluororesin sheet, and a step of attaching the palladium metal to the surface of the fluororesin sheet. A method for producing a fluororesin / metal thin film composite sheet, comprising a step of forming a metal thin film by performing electroless plating. 2. The method according to claim 1, wherein the fluororesin sheet is a polytetrafluoroethylene sheet. 3. The method for producing a fluororesin / metal thin film composite sheet according to claim 1, wherein the metal thin film is formed by performing an electroplating process after the electroless plating process. 4. The remote hydrogen plasma treatment is performed at a frequency
Using high frequency of 3.56MHz, output 50W to 30
The method for producing a fluororesin / metal thin film composite sheet according to claim 1, wherein the process is performed in a range of 0 W, a pressure of 6.7 Pa to 26.6 Pa, and an irradiation time of 10 seconds to 300 seconds. 5. The method for producing a fluororesin / metal thin film composite sheet according to claim 1, wherein a palladium colloid is used in the step of attaching the palladium metal. 6. The method for producing a fluororesin / metal thin film composite sheet according to claim 1, wherein the metal thin film is a copper thin film.