JP2003198120A - Flexible printed circuit board and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flexible printed circuit board which is suitable for an application for high heat resistance and for fine pitching. <P>SOLUTION: The surface of a polyimide film 1 is formed as a coarse surface 1a through formation of many fine recessed areas 2 where the internal diameter is expanded and an electrically copper plated layer 5 is formed on the surface described above via a sputtered nickel layer 3. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flexible printed circuit board that can cope with both high heat resistance and fine pitch and a method for manufacturing the same.

[0002]

2. Description of the Related Art As electronic devices are becoming lighter, thinner, shorter, and smaller, there is an increasing need for thinning, miniaturization, and high heat resistance of flexible printed circuits (hereinafter referred to as FPCs), which are widely used as such circuits. . Therefore, the flexible printed circuit board used as the material can also withstand higher temperatures than the conventional three-layer base material in which the polyimide film and the copper foil are bonded together by using an adhesive having poor heat resistance. In addition, a two-layer base material of a type in which polyimide and copper are directly laminated has been put into practical use so that the plate thickness can be made thinner to cope with the fine pitch of FPC, and the demand is expanding. There are roughly two methods for producing a two-layer base material without using such an adhesive. The first method is a type in which a polyimide varnish is applied to one side of a copper foil and baked to form a two-layer substrate composed of a copper foil and a polyimide layer. The second method is to sputter one side of a polyimide film. This is a type in which electro-copper plating is performed after making it conductive by vapor deposition or the like.

[0003]

In the first method (varnish coating type method) described above, a commercially available product that has been subjected to surface roughening treatment and high adhesion treatment (for example, surface treatment with a silane coupling agent) in advance. The electrolytic copper foil or rolled copper foil is used, and liquid polyimide is applied to this and baked. Therefore, due to the physical anchoring effect and the chemical affinity effect, the initial adhesive strength of the obtained two-layer base material is high, and the adhesive strength is small even under a high temperature environment for a long time. Suitable for However, commercially available electrolytic copper foils and rolled copper foils have a limit in thickness due to the problem of handleability (currently, the thickness is 12 μm is the lower limit), so the aspect ratio (plate thickness / plate thickness / There is a problem in that the circuit width of the FPC is limited due to the problem of (hole diameter), and it is not suitable for fine pitch applications. In addition, when liquid polyimide is fired to be imidized, stress tends to accumulate between the polyimide and the copper foil, which causes a problem that the rate of dimensional change of the polyimide before and after FPC formation is large.

In the second method (sputtering / plating type method), a commercially available polyimide film is used, and one or both surfaces of the polyimide film is subjected to plasma treatment for roughening it, and then sputtered. Sputtered film of nickel, chromium, etc. (thickness of about 0.02 μm)
After forming a copper sputtered film (thickness: about 0.2 μm) on each of them, electrolytic copper plating is performed to form an electrolytic copper plating layer. Therefore, the thickness (thickness 5 to 8 μm) of the electrolytic copper plating layer can be freely controlled, a fine FPC pattern can be easily produced, and it is suitable for fine pitch applications. Moreover, since a commercially available polyimide film is simply subjected to plasma treatment and sputtering, stress is not accumulated and the dimensional change rate of polyimide before and after FPC formation is small. However, the rough surface formed by the plasma treatment has a tapered shape (see FIG. 12; in FIG. 12, 20a is a rough surface formed on one surface of the polyimide film 20) or a large number of convex concave portions. However, the roughness is low and a physical anchor effect cannot be expected. Therefore, the initial adhesive strength of the obtained two-layer base material is low, and the adhesive strength is remarkably decreased in a high temperature environment for a long time, resulting in insufficient heat resistance for high heat resistance applications. There is.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a flexible printed board suitable for high heat resistance and fine pitch applications and a method for manufacturing the same.

[0006]

In order to achieve the above object, the present invention provides that the surface of an insulating flexible film is
A flexible printed circuit board, which is formed on a roughened surface by forming a large number of minute recesses having an inner diameter and a metal plating layer is formed on the surface via a base metal layer, is defined as a first gist. A flexible film with a copper foil is produced by applying an insulating resin liquid to one of the roughened surfaces and baking it to form an insulating flexible film.
The copper foil of the flexible film is removed by etching the entire surface to transfer the roughened surface of the copper foil to one surface of the flexible film, and then a base metal layer is formed on the transfer surface of the flexible film. A second gist is a method for manufacturing a flexible printed circuit board in which a metal plating process is performed on the base metal layer to integrally form a metal plating layer on the base metal layer.

That is, the inventors of the present invention, in the course of research for obtaining a flexible printed circuit board suitable for high heat resistance and fine pitch applications, use the above-mentioned varnish coating type method and sputtering / plating type method. We thought that it would be possible to obtain a flexible printed circuit board suitable for both of the above-mentioned applications by combining the advantages of both, and we conducted a series of studies on this. As a result, using the above varnish coating type method, after forming the surface of the insulating flexible film on the roughened surface excellent in the physical anchor effect, using the above sputter plating type method, insulation The present invention was found to be able to achieve the intended purpose by forming a metal plating layer on the surface of a flexible film and controlling the thickness of the metal plating layer to produce a fine FPC pattern.

The method for producing a flexible printed circuit board of the present invention utilizes the above-mentioned varnish coating type method, and an insulating resin liquid is applied to one roughened surface of a copper foil and baked to form an insulating flexible film. To produce a flexible film with a copper foil. Then, the copper foil of this flexible film is removed by etching the entire surface to transfer the roughened surface of the copper foil to one surface of the flexible film,
As a result, the transfer surface of the flexible film is formed into a roughened surface having an excellent physical anchor effect. after that,
Using the above-mentioned sputtering / plating type method, form a base metal layer on the transfer surface of the flexible film, perform metal plating treatment on the base metal layer, and laminate the metal plating layer on the base metal layer. To form.

In the thus obtained flexible printed circuit board of the present invention, a roughened surface of one surface of the copper foil (on the roughened surface, a large number of minute convex portions having an enlarged diameter are formed. The surface of the insulative flexible film is formed on the roughened surface due to the formation of a large number of minute recesses with an enlarged inner diameter, resulting in an excellent physical anchoring effect, and after initial and thermal loading. Has very high adhesion.
Moreover, since the thickness of the metal plating layer formed on the surface of the insulating flexible film via the underlying metal layer can be freely controlled, it is possible to deal with a fine FPC pattern. It also has a barrier effect due to the underlying metal layer (the effect of suppressing the diffusion and migration of copper due to heat and preventing the formation of a fragile layer at the interface between the insulating flexible film and the underlying metal layer). The heat-resistant adhesion is further improved by the synergistic effect with. Also,
The dimensional change rate before and after FPC formation is small. in this way,
Since the flexible printed circuit board of the present invention has the advantages of both of the above methods, it can be applied to the applications (high heat resistance application and fine pitch application) which have been conventionally separated by the above methods.

Next, the present invention will be described in detail.

As the copper foil used in the present invention, for example, commercially available electrolytic copper foil or rolled copper foil is preferably used. One or both surfaces of these commercially available electrolytic copper foils or rolled copper foils are formed as roughened surfaces (also referred to as matte surfaces). This roughened surface is, for example, in the case of an electrolytic copper foil, at the time of its production, when the copper particles are deposited on the surface of the drum or the like in an electrolytic bath, the electrolytic copper foil solution (usually copper sulfate solution) side It is formed on one surface and is composed of a large number of minute convex portions. The shape of the minute convex portion may be any shape as long as the diameter of the tip side is increased, and the shape of the mushroom-shaped tip portion of the cylindrical root portion is expanded in a granular shape.
Various shapes such as simple granularity (without a root portion) can be mentioned. Moreover, examples of the above-mentioned particles include spherical particles and hemispherical particles, but are not limited thereto.

The constituent material of the insulating resin liquid applied to the roughened surface of the one surface of the copper foil is not particularly limited and, for example, conventionally known materials such as polyimide, polyester, polycarbonate, polyether sulfone and the like. Is used.

A conventional varnish coating type method is used for producing a flexible film with a copper foil by coating an insulating resin liquid on the roughened surface and baking it to form an insulating flexible film. To be

The roughened surface of the copper foil is transferred to one surface of the insulating flexible film by removing the copper foil of the flexible film with the copper foil by etching the entire surface.
Then, the transfer surface of the insulating flexible film obtained by transferring the roughened surface of the copper foil on which the large number of minute convex portions are formed is a roughened surface by forming a large number of minute concave portions having an inner diameter. It has been formed on the ground and has an excellent physical anchoring effect. Since such minute recesses are formed by transferring a large number of minute protrusions on the roughened surface,
It is formed in various shapes such as a substantially mushroom shape in which the inner end portion of the cylindrical root portion is expanded in a granular shape, a simple granular shape (without a root portion), and the like. Moreover, examples of the granular shape include spherical shapes and hemispherical shapes similar to the minute convex portions, but are not limited thereto.

The surface roughness of the roughened surface of the insulating flexible film is preferably Rz (ten-point average roughness) = 0.
1 to 5.0 μm, preferably Rz = 1.0 μm
set to m. When Rz is smaller than 0.1 μm, the physical anchoring effect on the roughened surface of the insulating flexible film becomes low, and heat resistant adhesion cannot be secured. On the other hand, if Rz is larger than 5.0 μm, the contact area is reduced, the adhesion is lowered, and the formation of the fine FPC pattern is hindered.

Further, the minute recesses on the roughened surface of the insulating flexible film have a hole diameter α of 0.05 at the upper surface opening.
3 to 2 μm, the inner hole diameter β (see both FIGS. 8 and 11) is set to 0.05 to 3 μm, and the depth d (or the height of the protrusion formed between a large number of minute recesses). (See FIG. 8 and FIG. 11) is set to 0.05 to 3 μm. When the hole diameter β and the depth d inside the minute recesses are smaller than 0.05 μm, the physical anchoring effect on the roughened surface of the insulating flexible film is lowered, and the heat resistance is reduced, as in the case of Rz. Adhesion cannot be secured. On the other hand, if it is larger than 3.0 μm, the contact area is reduced, the adhesion is lowered, and the formation of a fine FPC pattern is hindered.

Examples of the etchant used for the above-mentioned entire surface etching include conventionally known ones such as iron chloride solution (ferric chloride aqueous solution) and copper chloride solution (cupric chloride aqueous solution). Further, using the above etching solution, for example, by showering the entire surface of the copper foil of the flexible film with a copper foil at 45 ° C. for about 10 minutes, the entire surface etching is performed.

Conventionally, a base metal layer is formed on the transfer surface of the insulating flexible film, and a metal plating treatment is applied to the base metal layer to form a laminated metal plating layer on the base metal layer. The sputter / plating type method is used.

More specifically, as a method for forming the base metal layer on the roughened surface of the insulating flexible film, there are known conventionally known methods such as sputtering, vapor deposition and ion plating.

As the metal constituting the above-mentioned base metal layer,
Nickel (Ni), Chromium (Cr), Cobalt (C
o), molybdenum (Mo), tungsten (W), zirconium (Zr), titanium (Ti), etc. or alloys thereof are used. Preferably, nickel (this nickel is soluble in the copper etching solution at the time of etching), nickel-chromium alloy (from the viewpoint of the removability of the underlying metal layer by the copper etching solution at the time of etching for forming FPC in the subsequent step). Nichrome) or the like is used.

The above-mentioned base metal layer is not only required for integrally forming a metal plating layer on the transfer surface of the insulative flexible film, but also has a barrier effect (that is, suppresses diffusion and transfer of copper due to heat, and prevents insulation). Of preventing the formation of a brittle layer at the interface between the flexible film and the underlying metal layer)
Has a synergistic effect with the physical anchor effect,
The heat-resistant adhesion between the insulating flexible film and the underlying metal layer is further improved. The thickness of such a base metal layer is set to 20 to 300Å. If the thickness is less than 20Å, diffusion transfer of copper to the interface due to heat cannot be suppressed, and a brittle layer of copper oxide is formed at the polyimide / metal interface, which tends to cause a decrease in adhesion after thermal degradation. On the other hand, when it is larger than 300 Å, not only the etching property deteriorates but also the productivity deteriorates.

When the underlying metal layer is formed on the transfer surface of the insulating flexible film by sputtering, the transfer surface may be subjected to plasma treatment in order to clean the transfer surface. In this plasma treatment, the inside of the sputtering apparatus is set to 10 ^-2 Pa to atmospheric pressure and then 0.05 to 1.0
It is performed at a power density of W / cm ² for about 1 to 60 seconds. A gas such as argon, oxygen, nitrogen or helium is used, and oxygen is preferably used. However, the plasma treatment need not be performed so much as to roughen the transfer surface of the insulating flexible film, and can be omitted. Further, when the plasma treatment is excessively performed, the transfer surface of the insulating flexible film is etched and the shape is broken, and etching residue is generated, which causes a decrease in adhesion due to heat between the polyimide and the base metal layer. Promote.

When an electrolytic copper plating layer is formed as a metal plating layer on the underlying metal layer by electrolytic copper plating, the underlying metal layer is formed and then a copper layer is formed thereon. The thickness of this copper layer may be set to a thickness that does not dissolve in the copper sulfate solution used in the electrolytic copper plating treatment, and is about 0.1 to 0.5 μm. It is preferably set to about 0.2 μm. If this thickness is less than 0.1 μm, it may dissolve during electrolytic copper plating,
If it exceeds 0.5 μm, the productivity becomes poor. Then, in the electrolytic copper plating process, the thickness of the electrolytic copper plating layer is set to a predetermined thickness necessary for forming the FPC. Although it is possible to form only a copper layer as a base metal layer on the roughened surface of the insulating flexible film, the base metal layer +
The adhesive strength is slightly inferior to that in which the copper layer is formed, and the decrease in adhesion due to heat becomes large.

The above-mentioned electrometal plating is performed by a conventionally known method. Further, as the metal forming the metal plating layer, copper, silver (Ag), nickel or the like is used, and preferably copper is used. Further, the thickness of the metal plating layer is preferably set to 5 to 20 μm.

As a method of forming the polyimide film (the insulating flexible film), the surface of the metal (stainless steel, aluminum foil, plate, roll, etc.) whose surface is roughened by a physical or chemical method, ceramic, etc. To the polyamic acid solution (insulating resin solution), then,
There is also a method in which a polyimide film is obtained by mechanically peeling off metal, ceramics, etc. after imidizing (forming an insulating flexible film) by heat treatment. In this case, since it is necessary for the surface to have releasability, it is preferable to apply a coating of titanium, iridium or the like. Also,
As another formation method, 0.05 in the polyimide film
An inorganic or organic filler having a particle diameter of about 3 μm may be dispersed, and only the filler on the surface of the polyimide film may be removed by etching to make the surface uneven. As a method for producing such a polyimide film, a filler is dispersed at the stage of a polyamic acid solution to produce a filler-dispersed polyimide film by imidization, or a dispersion of the filler in a heat-resistant resin solution on a polyimide film. It is applied thinly and solidified. Further, as another method, there is a method of mechanically roughening the surface of the polyimide film by blasting so as to form granular depressions.

[0026]

BEST MODE FOR CARRYING OUT THE INVENTION Next, embodiments of the present invention will be described.

FIG. 1 shows one embodiment of the flexible printed circuit board of the present invention. 1 is a polyimide film (insulating flexible film), one side of which is
Formed on the roughened surface 1a by forming a large number of minute recesses 2 (see FIG. 2) whose inner diameter is expanded, and the sputtered nickel layer (base metal layer) 3 and the sputtered copper layer 4 are provided on the roughened surface 1a. An electrolytic copper plating layer (metal plating layer) 5 is formed.

The above flexible printed circuit board can be manufactured, for example, as follows. That is, first, a commercially available electrolytic copper foil 10 (see FIG. 3) is prepared. One surface of the electrolytic copper foil 10 is formed as a roughened surface 10a, and the roughened surface 10a has a large number of minute projections 11 whose tip portion expands in a granular shape with respect to the root portion (see FIG. 4). )
Are formed to project. Next, a roughened surface of the electrolytic copper foil 10 is obtained by applying a polyimide varnish (insulating resin liquid) to the roughened surface 10a of the electrolytic copper foil 10 and baking it to imidize it (make an insulating flexible film). A flexible film 12 with a copper foil made of a two-layer base material in which a polyimide film 13 is laminated on 10a is produced (see FIGS. 5 and 6). Next, the electrolytic copper foil 10 of the flexible film 12 with the copper foil is entirely etched with an etching solution such as an aqueous solution of cupric chloride to remove all of the electrolytic copper foil 10, and one surface becomes a roughened surface (transfer surface) 1a. The formed polyimide film 1 (see FIGS. 7 and 8) is produced. The roughened surface 1a is formed by transferring the roughened surface 10a of the electro-deposited copper foil 10. By this transfer, the roughened surface 1a has a large number of minute recesses 2 (in which the inside diameter increases). 8) is formed. Next, a sputtering nickel layer 3 (base metal layer) is formed on the roughened surface 1a of the polyimide film 1 by sputtering, and after this formation, the sputtering nickel layer 3 is further formed by sputtering.
A sputtered copper layer 4 is formed thereon (FIGS. 9 and 1).
0). After that, the sputtering copper layer 4 is subjected to electrolytic copper plating treatment, and the electrolytic copper plating layer 5 is laminated and integrally formed on the sputtering copper layer 4. In this way, the flexible printed board shown in FIG. 1 can be obtained.

As described above, in this embodiment, the commercially available electrolytic copper foil 10 is used, and the roughened surface 10 of the electrolytic copper foil 10 is used.
Since one surface of the polyimide film 1 is formed on the roughened surface 1a by the transfer of a, the roughened surface 1a is excellent in the physical anchoring effect. The initial adhesion is high, and the decrease in adhesion is small even in a high temperature environment for a long time. In addition, the roughened surface 1 of the polyimide film 1
Since the thickness of the electrolytic copper plating layer 5 formed on the a through the sputtered nickel layer 3 and the sputtered copper layer 4 can be freely controlled, it can be applied to a fine FPC pattern. Moreover, since the sputtering nickel layer 3 is formed on the roughened surface 1a of the polyimide film 1, a barrier effect (suppresses diffusion and transfer of copper due to heat to form a brittle layer at the interface between the polyimide film 1 and the sputtering nickel layer 3). And the heat-resistant adhesion is further improved by the synergistic effect with the physical anchor effect. Moreover, the dimensional change rate before and after the formation of the fine FPC pattern is reduced.

[0030]

EXAMPLES Next, examples will be described together with comparative examples.

[0031]

Examples 1 to 4 First, a commercially available electrolytic copper foil 10 was prepared,
After applying the polyamic acid solution to the roughened surface 10a of the electrolytic copper foil 10 and drying it, the temperature is changed from 100 ° C. to 4 ° C. in a nitrogen atmosphere.
While heating to 00 ° C., baking for 4 hours to imidize,
A flexible film 12 with a copper foil was produced. Next, the electrolytic copper foil 10 of the flexible film 12 with the copper foil was removed by etching with an etching solution of a 40% ferric chloride aqueous solution.
Shower at 10 ° C for 10 minutes to etch the entire surface,
A polyimide film 1 having one surface formed on the roughened surface 1a was produced.

The above polyamic acid solution contains NMP of pyromellitic dianhydride and diaminodiphenyl ether.
It was obtained by mixing and polymerizing in a (N-methyl-2-pyrrolidone) solvent at 25 ° C.

Further, the hole diameter α of the upper surface opening of the minute recess formed on the roughened surface 1a of the polyimide film 1 and the hole diameter β of the inside (both are average values) are
= 0.15 μm, β = 0.2 μm, in Examples 2 and 3, α = 0.6 m, β = 1.0 μm, and in Example 4,
α = 2.0 μm and β = 3.0 μm were set.

Next, a sputtered nickel layer 3 was formed on the roughened surface 1a of the polyimide film 1 by sputtering, and a sputtered copper layer 4 was formed on the sputtered nickel layer 3 by sputtering. After that, copper sulfate plating 2 is applied to the sputtered copper layer 4.
Performed at a current density of A / dm ² for 45 minutes to obtain a plating thickness of 15
A flexible printed circuit board (see FIG. 1) was manufactured by obtaining the electrolytic copper plating layer 5 having a thickness of μm.

When performing the above-mentioned first sputtering, as a pre-step, plasma treatment was performed for cleaning the roughened surface 1a of the polyimide film 1. That is, after setting the inside of the sputtering apparatus to 10 ^-2 Pa to atmospheric pressure, 0.05 to
The operation was performed at a power density of 1.0 W / cm ² for 10 seconds. Also, oxygen was used as a reactive gas. However, the above Examples 1 to 1
In Example 4, the plasma treatment was not performed.

The sputtering nickel layer 3 was formed at a pressure of 10 ^-2 Pa and a power density of 1.0 W / cm ² for 60 seconds to form a film having a thickness of 0.02 μm. Next, the sputtering copper layer 4 is subjected to the same conditions for 240 seconds to obtain 0.2 μm.
A m-thick film was overlaid on the sputtered nickel layer 3.

[0037]

[Embodiment 5] As in the above embodiments, α = 0.6 μ
Polyimide film 1 with m and β set to 1.0 μm
Was produced. Then, only the sputtered copper layer 4 was formed on the roughened surface 1a of the polyimide film 1 as the base metal layer without forming the sputtered nickel layer 3. When forming the sputtered copper layer 4, plasma treatment and sputtering were performed under the same conditions as those in Examples 1, 2, and 4. After that, under the same conditions as each of the above examples,
Electrolytic copper plating was applied to the sputtered copper layer 4 to manufacture a flexible printed board.

[0038]

[Comparative Example 1] A commercially available polyimide film was used, and plasma treatment was performed to make one side of the polyimide film rough, and then a sputtered nickel film (about 0.02 μm thick) was sputtered on the copper film. After forming each sputtered film (about 0.2 μm in thickness), electrolytic copper plating was performed to obtain an electrolytic copper plating layer.

The flexible printed boards of Examples 1 to 5 and Comparative Example 1 produced as described above were subjected to initial and thermal loading (150 ° C. × 3 days after thermal loading and 150 days).
Adhesion (N / c)
m) was measured. The results are shown in Table 1 below.

[0040]

[Table 1]

From Table 1 above, it can be seen that the products of Examples 1 to 5 are superior to the product of Comparative Example 1 in the adhesive force at the initial stage and after the heat load. Further, the product of Example 2 has a lower adhesion force than the product of Example 3. The reason for this is that when plasma treatment is performed on the roughened surface 1a of the polyimide film 1 as a pre-step of sputtering, the upper surface of each minute recess 2 formed on the roughened surface 1a is scraped by this plasma treatment,
It is considered that this is because the adhesion is reduced. In addition, it can be seen that the product of Example 5 does not have the sputtered nickel layer 3 formed thereon, and therefore the above-mentioned adhesion is reduced. In addition,
The initial adhesion of the product of Example 5 and the product of Comparative Example 1 are not so different, but it can be seen that the product of Example 5 is superior to the product of Comparative Example 1 in terms of adhesion after thermal loading.

In the above-described embodiments and examples, the roughened surface 1a of the polyimide film 1 is provided with a large number of minute recesses 2 in which the tip portion expands in a granular shape with respect to the root portion. The shape is not limited to this, and as shown in FIG. 11, it may be formed in a simple granular shape (without a root portion).

[0043]

As described above, according to the flexible printed circuit board of the present invention, a roughened surface of one surface of a copper foil (on the roughened surface, a large number of minute convex portions having an increased diameter are formed. Exist)
The surface of the insulating flexible film is
Since it is formed on the roughened surface due to the formation of a large number of minute recesses having an enlarged diameter, the physical anchor effect is excellent, and the adhesive force at the initial stage and after the thermal load is very high. Moreover, since the thickness of the metal plating layer formed on the surface of the insulating flexible film via the underlying metal layer can be freely controlled, it is possible to deal with a fine FPC pattern. In addition, the flexible printed circuit board of the present invention also has a barrier effect due to the underlying metal layer (the effect of suppressing diffusion transfer of copper due to heat and preventing the formation of a brittle layer at the interface between the insulating flexible film and the underlying metal layer). Therefore, the heat resistant adhesion is further improved by the synergistic effect with the physical anchor effect. In addition, the dimensional change rate before and after FPC formation is small. In this way, the flexible printed circuit board of the present invention can be applied to the applications (high heat resistance application and fine pitch application) that have been separately segregated by the varnish coating type method and the sputter / plating type method. Become.

In the flexible printed circuit board of the present invention, the surface roughness of the roughened surface is Rz (ten-point average roughness) =
When the thickness is 0.1 to 5.0 μm, the physical anchor effect of the roughened surface of the insulating flexible film is high, heat resistance and adhesion can be secured, and the formation of a fine FPC pattern is hindered. Nor.

The flexible printed circuit board manufacturing method of the present invention can efficiently manufacture the above-described flexible printed circuit board. Moreover, in the method for manufacturing a flexible printed circuit board of the present invention, the base metal layer is formed of a sputtered nickel layer and a sputtered copper layer, the metal plated layer is formed of an electrolytic copper plated layer, and is laminated and integrated with the sputtered copper layer. In that case, the metal plating layer can be reliably laminated and integrally formed on the transfer surface of the insulating flexible film. Moreover, it has a barrier effect (that is, the effect of suppressing the diffusion and transfer of copper due to heat and the effect of preventing the formation of a brittle layer at the interface between the insulating flexible film and the underlying metal layer), and by the synergistic effect with the physical anchor effect. The heat-resistant adhesion between the insulating flexible film and the underlying metal layer is further improved.

[Brief description of drawings]

FIG. 1 is a perspective view showing an embodiment of a flexible printed circuit board of the present invention.

FIG. 2 is a cross-sectional view showing a main part of the flexible printed circuit board.

FIG. 3 is a perspective view showing an electrolytic copper foil.

FIG. 4 is a cross-sectional view showing a main part of the electrolytic copper foil.

FIG. 5 is a perspective view showing a flexible film with a copper foil.

FIG. 6 is a cross-sectional view showing a main part of the copper foil-attached flexible film.

FIG. 7 is a perspective view showing a polyimide film.

FIG. 8 is a cross-sectional view showing a main part of the polyimide film.

FIG. 9 is a perspective view showing a state in which a sputtering nickel layer and a sputtering copper layer are formed on the polyimide film.

FIG. 10 is a cross-sectional view showing a main part of a polyimide film having a sputtered nickel layer and a sputtered copper layer formed thereon.

FIG. 11 is a cross-sectional view of a main part of the polyimide film showing an example of minute recesses.

FIG. 12 is a cross-sectional view showing a conventional example.

[Explanation of symbols]

1 Polyimide film 1a Roughened surface 2 Minute recess 3 Sputtering nickel layer 5 Electrolytic copper plating layer

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Hidei Hotta             Tokai Rubber Works, Higashi 3-chome, Komaki City, Aichi Prefecture             Business F-term (reference) 5E343 AA16 AA18 AA33 AA36 BB22                       BB24 BB25 BB35 BB38 BB39                       BB40 BB44 BB45 BB55 DD23                       DD24 DD25 DD43 GG02 GG16

Claims (4)

[Claims] 1. The surface of the insulating flexible film,
A flexible printed circuit board, characterized in that it is formed on a roughened surface by the formation of a large number of minute recesses having an enlarged inner diameter, and a metal plating layer is formed on the surface through a base metal layer. 2. The flexible printed board according to claim 1, wherein the surface roughness of the roughened surface is Rz (ten-point average roughness) = 0.1 to 5.0 μm. 3. A flexible film with a copper foil is produced by applying an insulating resin liquid to one roughened surface of a copper foil and baking it to form an insulating flexible film. The entire surface of the foil is removed by etching, and the roughened surface of the copper foil is transferred to one surface of the flexible film. Next, a base metal layer is formed on the transfer surface of the flexible film, and metal plating is performed on the base metal layer. A method of manufacturing a flexible printed circuit board, which comprises subjecting a metal plating layer on a base metal layer so as to be integrally laminated. 4. The flexible print according to claim 3, wherein the underlying metal layer comprises a sputtered nickel layer and a sputtered copper layer, the metal plated layer comprises an electrolytic copper plated layer, and is laminated and integrated with the sputtered copper layer. Substrate manufacturing method.