JP6398175B2 - Two-layer flexible wiring board and manufacturing method thereof - Google Patents

Description

  The present invention relates to a flexible wiring board in which a part of a copper layer is deposited by a copper electroplating method to improve folding resistance, and a method for manufacturing the flexible wiring board.

A flexible wiring board is widely used for a portion requiring refraction or bending of an electronic device such as a read / write head of a hard disk or a printer head, or a refraction wiring in a liquid crystal display, taking advantage of its flexibility.
For manufacturing such a flexible wiring board, a method for wiring a flexible wiring board (flexible copper clad laminated board, also referred to as FCCL: Flexible Copper Clad Lamination) in which a copper layer and a resin layer are laminated using a subtractive method or the like. Is used.

This subtractive method is a method in which a copper layer of a copper clad laminate is generally chemically etched to remove unnecessary portions.
That is, a resist is provided on the surface of the copper layer of the flexible wiring board to be left as the conductor wiring, and unnecessary portions of the copper layer are selectively removed through chemical etching treatment and water washing with an etching solution corresponding to copper. Thus, the conductor wiring is formed.

By the way, the flexible wiring board (FCCL) can be classified into a three-layer flexible wiring board (hereinafter referred to as a three-layer FCCL) and a two-layer flexible wiring board (referred to as a two-layer FCCL).
The three-layer FCCL has a structure (copper foil / adhesive layer / resin film) in which an electrolytic copper foil or a rolled copper foil is bonded to a base (insulating layer) resin film. On the other hand, the two-layer FCCL has a structure (copper layer or copper foil / resin film) in which a copper layer or copper foil and a resin film substrate are laminated.

The two-layer FCCL is roughly divided into three types.
That is, FCCL (commonly known as a metalizing substrate) formed by sequentially plating a base metal layer and a copper layer on the surface of a resin film, FCCL (commonly referred to as a cast substrate) in which an insulating layer is formed by applying a resin film varnish to a copper foil, And FCCL (commonly referred to as a laminate substrate) in which a resin film is laminated on a copper foil.

FCCL, which is formed by sequentially plating the base metal layer and the copper layer on the surface of the metalizing substrate, ie, the resin film, can reduce the thickness of the copper layer and has high smoothness at the interface between the polyimide film and the copper layer. Compared with cast substrate, laminate substrate, or three-layer FCCL, it is suitable for fine wiring.
For example, the thickness of the copper layer of the metalizing board can be freely controlled by dry plating and electroplating, whereas the thickness of the cast board, laminate board or three-layer FCCL is limited by the copper foil used. Because it will be done.

On the other hand, with respect to the copper foil used for wiring of the flexible wiring board, for example, a method of performing heat treatment on the copper foil (see Patent Document 1) or a method of performing a rolling process (see Patent Document 2). Improvement of refraction is achieved.
However, these methods relate to the processing of the copper foil itself used for the cast substrate and the laminate substrate of the three-layer FCCL rolled copper foil and the electrolytic copper foil and the two-layer FCCL.

In addition, for evaluation of refraction resistance of copper foil, an MIT refraction resistance test (Folding Endurance Test) standardized by “JIS C-5016-1994” or the like and “ASTM D2176” is industrially used. .
In this test, evaluation is performed based on the number of refractions until the circuit pattern formed on the test piece is disconnected, and the higher the number of refractions, the better the refraction resistance.

JP-A-8-283886 JP-A-6-269807

Since the two-layer flexible wiring board targeted by the present invention is a plating substrate in which a seed layer and a metal layer made of a copper plating layer are sequentially formed on at least one surface of a resin film substrate without using an adhesive, It is difficult to improve the folding resistance by subjecting only the copper plating layer as disclosed in the technical literature to heat treatment or rolling. Therefore, there has been a demand for a method for manufacturing a plated substrate having excellent folding resistance in the plated substrate.
In view of such a situation, the present invention provides a two-layer flexible wiring board excellent in folding resistance and a manufacturing method thereof.

  In order to solve the above-mentioned problems, the present inventors diligently studied the folding resistance of a copper layer formed on a polyimide resin layer by a plating method, and as a result, the change in crystal orientation before and after the folding resistance was tested. The influence on the results was confirmed, and the present invention was achieved.

According to a first aspect of the present invention, a base metal layer made of a nickel alloy is provided on the surface of a resin film substrate without using an adhesive, and a wiring of a metal laminate including a copper layer on the surface of the base metal layer is provided. In the flexible wiring board, the film thickness of the base metal layer is 50 nm or less, and the copper layer includes a copper thin film layer provided on the surface of the base metal layer and a copper electroplating layer provided on the surface of the copper thin film layer. configured, crystal ratio of electron backscatter diffraction (EBSD) by 001 orientation 111 orientation with respect to the crystal fraction OR ₀₀₁ of the crystals contained in the range of from the resin film substrate surface in the metal laminate was measured to 0.4μm the ratio of the oR _{111 (oR} 111 _{/ oR 001)} is 7 or less, with the copper layer (111) crystalline orientation degree index of 1.2 or more, and JIS C-5016-1 The difference [[200] / (111)] in the [(200) / (111)] orientation ratio of the crystal orientation ratio of the copper layer obtained before and after the folding resistance test specified in 94 is 0. 0.03 or more, a two-layer flexible wiring board.

  A second invention of the present invention is a two-layer flexible wiring board, wherein the thickness of the base metal layer in the first invention is 3 nm to 50 nm.

  A third invention of the present invention is a two-layer flexible wiring board characterized in that the film thickness of the copper layer in the first and second inventions is 5 μm to 12 μm.

According to a fourth aspect of the present invention, there is provided a copper thin film layer formed on the surface of the underlying metal layer, and a copper electroplated layer formed on the surface of the copper thin film layer. In the thickness range of 10% or more of the film thickness of the electroplating layer in the direction from the surface of the copper layer to the resin film substrate, the average particle size is 200 nm to 400 nm, and the surface roughness Ra is 0.2 μm or less. This is a two-layer flexible wiring board.

According to a fifth aspect of the present invention, the thickness range in the fourth aspect is 10% of the film thickness of the copper electroplated layer from the surface of the copper layer toward the resin film substrate. It is a flexible wiring board.

  According to a sixth aspect of the present invention, the resin film substrate according to the first to fifth aspects is a polyimide film, a polyamide film, a polyester film, a polytetrafluoroethylene film, a polyphenylene sulfide film, or a polyethylene naphthalate system. It is a two-layer flexible wiring board characterized by being at least one kind of resin film selected from a film and a liquid crystal polymer film.

  According to a seventh aspect of the present invention, a copper thin film layer is formed on a surface of a resin film substrate by a dry plating method without using an adhesive, and a surface of the copper thin film layer. A method for producing a two-layer flexible wiring board according to the first to sixth aspects of the present invention, wherein a copper laminate film is formed by copper electroplating to form a metal laminate to be a wiring. Is an argon / nitrogen mixed gas, and the copper electroplating layer is periodically short in the thickness range of 10% or more of the copper electroplating layer thickness from the surface of the copper electroplating layer toward the resin film substrate. It is a manufacturing method of the two-layer flexible wiring board characterized by forming by the copper electroplating method by Periodic Reverse current which performs electric potential inversion of this.

A metal layer such as Ni, Cr, or Cu and an alloy layer are formed on the surface of the resin film by vapor deposition or sputtering, and then a copper layer is formed by electroplating, electroless plating, or a combination of both. for the wire to become metal laminate provided with an electron backscatter diffraction crystal 001 orientation of the crystal included in the scope of a resin film substrate surface to 0.4μm in the metal laminate was measured by (EBSD) ratio OR ₀₀₁ The ratio (OR ₁₁₁ / OR ₀₀₁ ) with the crystal ratio OR _{111 in the} 111 orientation is 7 or less, the (111) crystal orientation index of the copper layer is 1.2 or more, and a bending resistance test (JIS C- The difference of the [(200) / (111)] orientation ratio d [(20) of the crystal orientation ratio of the copper layer obtained before and after the execution of the folding resistance test specified in 5016-1994). ) / (111)] is According to the flexible wiring board according to the present invention which shows a 0.03 or more, folding endurance is of the substrate is remarkably improved, in which exhibits the industrially remarkable effects.

It is a cross-sectional schematic diagram of the board | substrate for 2 layers flexible wiring produced with the metalining method used by this invention. It is a schematic diagram which shows the roll-to-roll sputtering apparatus which forms the base metal layer and copper thin film layer of the board | substrate for two-layer flexible wiring used for the two-layer flexible wiring board of this invention. It is a schematic diagram which shows the continuous plating apparatus of the roll-to-roll system which performs electroplating in manufacture of the board | substrate for two-layer flexible wiring used for the two-layer flexible wiring board of this invention. It is the figure which showed typically the time and current density of PR current in this invention.

(1) Two-layer flexible wiring board First, a two-layer flexible wiring board used in the two-layer flexible wiring board of the present invention will be described.
The two-layer flexible wiring board has a laminated structure in which a base metal layer and a copper layer are sequentially laminated on at least one surface of a resin film substrate such as a polyimide film without using an adhesive, and the copper layer is It is comprised by the copper thin film layer and the copper electroplating layer.

FIG. 1 is a schematic view showing a cross section of a two-layer flexible wiring board 6 produced by a metalining method, and is also a cross-sectional view of a wiring portion of the two-layer flexible wiring board of the present invention.
A polyimide film is used for the resin film substrate 1, and the base metal layer 2, the copper thin film layer 3, and the copper electroplating layer 4 are sequentially formed and laminated on at least one surface of the polyimide film 1 from the polyimide film 1 side. Yes. In addition, the copper layer 5 is comprised from the copper thin film layer 3 and the copper electroplating layer 4, and the metal laminated body 7 is formed including this copper layer 5 and the base metal layer 2. FIG.

As the resin film substrate 1 to be used, in addition to the polyimide film, a polyamide film, a polyester film, a polytetrafluoroethylene film, a polyphenylene sulfide film, a polyethylene naphthalate film, a liquid crystal polymer film, or the like can be used.
In particular, a polyimide film is particularly preferable from the viewpoint of mechanical strength, heat resistance, and electrical insulation.
Furthermore, the said resin film board | substrate whose film thickness is 12.5-75 micrometers can be used preferably.

  The base metal layer 2 ensures reliability such as adhesion and heat resistance between the resin film substrate and a metal layer such as copper. Therefore, the material of the base metal layer is any one selected from nickel, chromium, or an alloy thereof, but a nickel / chromium alloy is suitable in consideration of adhesion strength and ease of etching during wiring production. ing.

The composition of the nickel-chromium alloy is desirably 15% by weight or more and 22% by weight or less of chromium, and an improvement in corrosion resistance and migration resistance can be expected.
Of these, nickel / chromium alloy of 20% by weight chromium is distributed as a nichrome alloy and is easily available as a sputtering target for the magnetron sputtering method. Further, chromium, vanadium, titanium, molybdenum, cobalt, or the like may be added to the alloy containing nickel.
Furthermore, a plurality of nickel-chromium alloy thin films having different chromium concentrations may be laminated to form a base metal layer having a nickel-chromium alloy concentration gradient.

The film thickness of the base metal layer 2 is desirably 3 nm to 50 nm.
When the film thickness of the underlying metal layer is less than 3 nm, the adhesion between the polyimide film and the copper layer cannot be maintained, and the corrosion resistance and migration resistance are poor. On the other hand, if the thickness of the base metal layer exceeds 50 nm, it may be difficult to sufficiently remove the base metal layer when wiring processing is performed by the subtractive method. If the removal of the underlying metal layer is insufficient, there is a concern about problems such as migration between wirings.

The copper thin film layer 3 is mainly composed of copper, and the thickness of the copper thin film layer is preferably 10 nm to 1 μm.
When the film thickness of the copper thin film layer is less than 10 nm, the conductivity when the copper electroplating layer is formed on the copper thin film layer by the electroplating method cannot be ensured, leading to an appearance defect during electroplating. Even if the film thickness of the copper thin film layer exceeds 1 μm, the quality problem of the two-layer flexible wiring board does not occur, but the productivity is inferior.

The base metal layer 2 and the copper thin film layer 3 can be formed by a dry plating method as described later, and the copper layer 4 can also be formed by a wet plating method.
The obtained flexible wiring board 6 has a 001 orientation of crystals measured by electron beam backscattering diffraction (EBSD) in a film thickness range from the surface of the resin film substrate 1 to 0.4 μm of the metal laminate 7. it is necessary that the ratio of the crystal fraction _{OR 111} of 111 orientation with respect to the crystal fraction _{OR 001 (OR 111 / OR 001} ) of 7 or less.

When the ratio (OR ₁₁₁ / OR ₀₀₁ ) of the crystal ratio OR ₁₁₁ of 111 orientation to the crystal ratio OR ₀₀₁ of the crystal of 001 exceeds 7 (OR ₁₁₁ / OR ₀₀₁ ), the width B of the bottom and the width T of the top of the cross-sectional shape of the wiring pattern From the height C, the etching factor (F _E ) calculated by the following formula (1) is less than 5, the bottom is wide, and the width of the top is narrow. turn into.

In other words, the pitch of the wiring patterns (distance between the centers of the wirings) needs to secure the space between the wiring patterns and take into account the width of the bottom of the cross section of the wiring pattern in order to ensure insulation between adjacent wiring patterns If the cross-sectional shape of the wiring pattern is widened at the bottom, the width of the bottom is taken into consideration, which is not suitable for narrowing the pitch.
The flexible wiring board satisfying the crystal orientation ratio can be processed by a subtractive method to obtain a flexible wiring board with a narrowed wiring pattern.
Even if the resin film substrate provided with the metal laminate as a wiring is etched, the crystal orientation ratio in the film thickness range from the resin film substrate surface of the wiring to 0.4 μm does not change.

(2) Film formation method for base metal layer and copper thin film layer The base metal layer and the copper thin film layer are preferably formed by a dry plating method.
Examples of the dry plating method include a sputtering method, an ion plating method, a cluster ion beam method, a vacuum deposition method, and a CVD method. In the dry plating method, the sputtering method is desirable from the viewpoint of controlling the composition of the seed layer.

  To form a film on a resin film substrate by sputtering, the film can be formed by a known sputtering apparatus. To form a film on a long resin film substrate, it can be formed by a known roll-to-roll sputtering apparatus. . If this roll-to-roll sputtering apparatus is used, a base metal layer and a copper thin film layer can be continuously formed on the surface of a long polyimide film.

FIG. 2 is an example of a roll-to-roll sputtering apparatus.
The roll-to-roll sputtering apparatus 10 includes a rectangular parallelepiped casing 12 that accommodates most of its components.
The casing 12 may have a cylindrical shape, and the shape is not limited as long as it can maintain a reduced pressure in a range of 10 ⁻⁴ Pa to 1 Pa.
Inside this housing 12, a polyimide film F, which is a long resin film substrate, is supplied with an unwinding roll 13, a can roll 14, sputtering cathodes 15a, 15b, 15c, 15d, a front feed roll 16a, and a rear feed roll. 16b, a tension roll 17a, a tension roll 17b, and a winding roll 18.

The unwinding roll 13, the can roll 14, the front feed roll 16a, and the take-up roll 18 are provided with power by a servo motor. The unwinding roll 13 and the winding roll 18 are configured so that the tension balance of the polyimide film F is maintained by torque control using a powder clutch or the like.
The tension rolls 17a and 17b are finished with hard chrome plating and provided with a tension sensor.
The sputtering cathodes 15a to 15d are of a magnetron cathode type and are arranged to face the can roll 14. The width direction dimension of the polyimide film F of the sputtering cathodes 15a to 15d may be wider than the width of the long resin film polyimide film F.

The polyimide film F is transported through a roll-to-roll sputtering apparatus 10 which is a roll-to-roll vacuum film forming apparatus, and is formed by sputtering cathodes 15 a to 15 d facing the can roll 14, with a copper thin film layer. Processed into a polyimide film F2.
The surface of the can roll 14 is finished with hard chrome plating, and a coolant or a heating medium supplied from the outside of the housing 12 circulates inside the can roll 14 to be adjusted to a substantially constant temperature.

When the base metal layer and the copper thin film layer are formed using the roll-to-roll sputtering apparatus 10, the target having the composition of the base metal layer is attached to the sputtering cathode 15a, and the copper target is attached to the sputtering cathodes 15b to 15d. The inside of the apparatus in which the polyimide film is set on the unwinding roll 13 is evacuated, and then the inside of the apparatus is held at about 1.3 Pa by introducing a sputtering gas such as argon.
Further, after forming the base metal layer by sputtering, the copper thin film layer may be formed by vapor deposition.

As an example of the sputtering atmosphere when sputtering the base metal and copper on the resin film substrate, an argon / nitrogen mixed gas is used, and the mixing ratio of nitrogen is preferably 1% by volume or more and 12% by volume or less. It is necessary to determine in consideration that there is a possibility of being influenced by the apparatus such as the shape of the winding type sputtering apparatus.
For example, while confirming the ratio of the crystal ratio OR ₁₁₁ of the 111 orientation to the crystal ratio OR ₀₀₁ of the 001 orientation of the metallized resin film crystal obtained up to the final electroplating on the resin film substrate, the sputtering atmosphere should be appropriately examined. That's fine.

  In addition, if the compounding ratio of nitrogen in the argon / nitrogen mixed gas exceeds 12% by volume, the heat resistance strength of the wiring may be reduced when the obtained metal laminate is used for wiring such as a flexible wiring board. Is not desirable. Note that although an example of a sputtering atmosphere using an argon / nitrogen mixed gas is shown, the sputtering atmosphere is not limited to an argon / nitrogen mixed gas as long as a target crystal state can be realized.

Furthermore, the crystal orientation of the copper thin film layer is also affected by the sputtering atmosphere.
When the sputtering atmosphere is argon only, the (111) plane of the face-centered cubic lattice structure is seen in the Wilson orientation degree index of the crystal by X-ray diffraction of the copper thin film layer, but the (200) plane of the face-centered cubic lattice is in EBSD Little or no surface corresponding to the 001 orientation is observed.
Therefore, when nitrogen is added to argon in the sputtering atmosphere, a (200) plane of a face-centered cubic lattice is observed in the copper thin film layer, and a plane corresponding to the 001 orientation is observed in EBSD.
By such conditions and the electroplating conditions described later, a flexible wiring board with a small difference in the width between the top and bottom of the wiring can be realized.

(3) Copper electroplating layer and film forming method The copper electroplating layer is formed by electroplating. The thickness of the copper electroplating layer is desirably 1 μm to 20 μm.
Here, the electroplating method to be used is one in which electroplating is performed using an insoluble anode in a copper sulfate plating bath, and the composition of the copper plating bath solution to be used is that of a commonly used flexible wiring board. A high-throw copper sulfate plating bath used for through-hole plating may be used.

FIG. 3 is an example of a roll-to-roll continuous electroplating apparatus (hereinafter referred to as a plating apparatus 20) that can be used for manufacturing a two-layer flexible wiring board used in the wiring board of the present invention.
A polyimide film F2 with a copper thin film layer obtained by forming a base metal layer and a copper thin film layer is unwound from the unwinding roll 22 and continuously immersed in the plating solution 28 in the electroplating tank 21. It is conveyed to. Incidentally, 28a indicates the surface of the plating solution.
The polyimide film F2 with a copper thin film layer is formed by depositing a copper layer on the surface of the metal thin film by electroplating while being immersed in the plating solution 28, and after forming a copper layer with a predetermined thickness, the metallized resin The film is wound around a winding roll 29 as a two-layer flexible wiring substrate S which is a film substrate. In addition, the conveyance speed of the polyimide film F2 with a copper thin film layer has the preferable range of several m-several dozen m / min.

If it demonstrates concretely, the polyimide film F2 with a copper thin film layer will be unwound from the unwinding roll 22, and will be immersed in the plating solution 28 in the electroplating tank 21 through the electric power feeding roll 26a. The copper thin film layer-attached polyimide film F2 that has entered the electroplating tank 21 is reversed in the conveying direction through the reversing roll 23, and is drawn out of the electroplating tank 21 by the power supply roll 26b.
Thus, while the polyimide film F2 with a copper thin film layer repeats immersion in a plating solution a plurality of times (20 times in FIG. 3), a copper layer is formed on the metal thin film of the polyimide film F2 with a copper thin film layer. It is.

A power source (not shown) is connected between the power supply roll 26a and the anode 24a.
The power supply roll 26a, the anode 24a, the plating solution, the polyimide film F2 with a copper thin film layer, and the power source constitute an electroplating circuit. The insoluble anode does not require a special one, and may be a known anode whose surface is coated with a conductive ceramic. A mechanism for supplying copper ions to the plating solution 28 is provided outside the electroplating tank 21.

  The copper ions are supplied to the plating solution 28 using an aqueous copper oxide solution, an aqueous copper hydroxide solution, an aqueous copper carbonate solution, or the like. Alternatively, there is a method in which a small amount of iron ions is added to the plating solution to dissolve the oxygen-free copper balls and supply the copper ions. Any of the above methods can be used as a method for supplying copper.

The current density during plating is increased stepwise from the anode 24a toward the downstream in the transport direction so that the maximum current density is reached at 24t from the anode 24o.
Thus, discoloration of the copper layer can be prevented by increasing the current density. In particular, when the current density is high when the thickness of the copper layer is thin, discoloration of the copper layer is likely to occur. Therefore, the current density during plating is 0.1 A / dm ^{2 to} 8 A / except for the reversal current of the PR current described later. dm ² is desirable. When the current density is increased, a poor appearance of the copper electroplating layer occurs.

In order to obtain the two-layer flexible wiring board according to the present invention, it is formed using a PR current in the range of 10% or more from the surface of the film thickness of the copper electroplating layer.
When using a PR current, the reversal current is preferably 1 to 9 times the positive current.
The reversal current time ratio is preferably about 1 to 10%.
Further, the period in which the reversal current next to the PR current flows is desirably 10 milliseconds or more, and more desirably 20 milliseconds to 300 milliseconds.
FIG. 4 schematically shows the time and current density of the PR current.
In addition, what is necessary is just to adjust a plating voltage suitably so that the above-mentioned current density is realizable.

In order to manufacture the two-layer flexible wiring board used in the present invention with a roll-to-roll continuous electroplating apparatus, a PR current may be supplied from one or more anodes from the downstream side of the conveyance path, and a PR current is supplied. The number of anodes is determined by the ratio of the range in which the film is formed with the PR current from the surface of the copper electroplating layer to the polyimide film side. That is, at least the anode 24t causes a PR current to flow, and if necessary, the PR current flows to the anode 24s, the anode 24r, and the anode 24q.
Although a PR current may be supplied to all the anodes, a manufacturing cost increases because a rectifier for PR current is expensive. Therefore, in the two-layer flexible wiring board according to the present invention, if 10% of the film thickness is formed with a PR current in the polyimide direction from the surface of the copper electroplating layer, a fold resistance test (JIS C-5016-1994). The difference d [(200) / (111)] of the crystal orientation ratio [(200) / (111)] of the copper layer is 0.03 or more before and after the execution of the above. (MIT test) can be improved.

  The reason why copper electroplating using a PR current is desirable is that when the current is reversed, the copper crystal grain size of the copper electroplating layer can be about 200 nm or more, and the grain boundaries can be reduced. This is because the starting point of cracking can be reduced.

  In general, in the electroplating method, the deposited copper is affected by the surface of the substrate to be copper-plated, but if a film of 10% or more of the film thickness is formed with a PR current from the surface of the copper electroplating layer, crystal grains The boundary can be controlled, and an effect on the folding resistance of the copper electroplating layer can be obtained. Therefore, if 10% or more of the film thickness from the surface of the copper electroplating layer of the two-layer flexible wiring board is a crystal that matches the folding resistance, an effect on the folding resistance of the copper electroplating layer can be obtained. The object of the present invention can be achieved.

(4) Features of the copper electroplating layer The copper layer in the two-layer flexible wiring board of the present invention is characterized by exhibiting a copper (111) crystal orientation index of 1.2 or more. In the bending resistance test (JIS C-5016-1994), the crystal becomes slippery. The copper layer of the flexible wiring board used in the present invention includes (200), (220), and (311) orientations in addition to the (111) orientation, of which (111) orientation occupies most of the crystal. That is, the degree of orientation index is 1.20 or more.

Furthermore, the difference in crystal orientation ratio [(200) / (111)] before and after the MIT folding resistance test (JIS C-5016-1994) is 0.03 or more. In this state, it is considered that the crystal slipped due to the MIT folding resistance test and recrystallization occurred.
For the glossiness of the surface, a glossy film is preferable so that unevenness on the surface does not cause a notch.

Also, the larger the average crystal grain size, the better. However, it should be noted that it also affects the etching of the copper layer when the copper-clad laminate is processed into a flexible wiring substrate by the subtractive method.
When using an aqueous ferric chloride solution for etching the copper layer in the subtractive method, the crystal grain size of the copper layer may not affect, but when etching the grain boundary of the crystal grain of the copper layer, The crystal grain size also affects the shape of the wiring. The average crystal grain size is preferably about 200 nm to 400 nm. If it is 200 nm or less, there are many crystal grain boundaries, and cracks that are the starting points of fracture are likely to occur, and the reason why it is 400 nm or less is to maintain the smoothness of the metal surface. Furthermore, it is necessary to make Ra 0.2 μm or less from the surface roughness so as not to cause cracks as starting points of fracture.

  That is, the copper layer of the flexible wiring board of the present invention is obtained by the above-described copper layer deposition method, and has a (111) crystal orientation index of 1.2 or more and a crystal orientation ratio before and after the MIT fold resistance test [(200 ) / (111)] is a copper layer having characteristics such as 0.03 or more. The crystal orientation of the copper electroplating layer can be determined from the Wilson orientation degree index of X-ray diffraction.

Furthermore, the copper crystal of the copper layer obtained by the above method has a dynamic recrystallization effect at room temperature during refraction. The average crystal grain size after the bending resistance test tends to be about 100 nm to 200 nm by recrystallization.
In general, it has been considered that a film obtained by electroplating copper does not dynamically recrystallize at room temperature. However, since the flexible wiring board of the present invention is dynamically recrystallized at room temperature, it is difficult to cut the sample when a refraction test such as the MIT test is performed. The average crystal grain size of the copper layer and dynamic recrystallization at room temperature can be observed with a cross-sectional SIM image.

  Further characteristic points of the flexible wiring board according to the present invention are the crystal orientation of the copper thin film layer of the resin film with metal thin film, and 0.4 μm from the resin film substrate surface after copper electroplating of the resin film with metal thin film. Different crystal orientations measured by electron beam backscatter diffraction (EBSD) in the range of film thickness up to, and electron beam backscatter in the film thickness range from the resin film substrate surface after copper electroplating to 0.4 μm That is, the relationship between the bottom width B and the top width T of the cross-sectional shape of the wiring changes depending on the orientation ratio of the crystal measured by the diffraction method (EBSD).

The metal laminate of the flexible wiring board according to the present invention is 111 to the crystal ratio OR ₀₀₁ of the 001 orientation of the crystal measured by electron beam backscattering diffraction (EBSD) in the film thickness range from the resin film substrate surface to 0.4 μm. The ratio of the orientation crystal ratio OR ₁₁₁ (OR ₁₁₁ / OR ₀₀₁ ) is 7 or less.
Then, when wiring processing is performed by the subtractive method in order to use such a metal laminate as a wiring, the cross-sectional shape is an etching determined by the following formula (2) from the bottom width B, the top width T, and the copper film thickness C. The effect represented by the factor (F _E ) can be obtained.

That is, when the etching factor (F _E ) is 5 or more, the bottom width B value and the top width T are close to each other.

In addition, a well-known electron beam backscattering diffraction method (EBSD) can be used for the measurement of the crystal orientation of the metal laminate.
The flexible wiring board according to the present invention has a 111 orientation with respect to the crystal ratio OR ₀₀₁ of the 001 orientation of the crystal by electron beam backscatter diffraction (EBSD) in a metal laminate having a film thickness range from the resin film substrate surface to 0.4 μm. It can be confirmed that the ratio (OR ₁₁₁ / OR ₀₀₁ ) of the crystal ratio OR ₁₁₁ is 7 or less.

Furthermore, the crystal of the 001 orientation of the crystal by the electron beam backscattering diffraction method (EBSD) in the metal laminated body of the film thickness range from the resin film substrate surface to 0.4 micrometer which is one of the characteristics of the flexible wiring board which concerns on this invention. As an example of a method for obtaining a ratio (OR ₁₁₁ / OR ₀₀₁ ) of the crystal orientation OR ₁₁₁ of 111 orientation with respect to the ratio OR ₀₀₁ of 7 or less, the base metal layer and the copper thin film layer are manufactured in the production of the two-layer flexible wiring board. An argon / nitrogen mixed gas containing 1% by volume to 12% by volume of nitrogen in the sputtering film-forming atmosphere and a current in the range of 1 μm to 2.5 μm from the surface of the copper thin film layer of the copper electroplating layer. An example is a film forming method in which the density is 1 A / dm ² .

The result of the MIT fold resistance test of the flexible wiring board becomes worse as the wiring width becomes thinner.
In the bending resistance test according to “JIS C-5016-1994”, the wiring width is 1 mm. However, the flexible wiring board used for the bent wiring in the liquid crystal display has a wiring width of 50 μm or less, and further high definition. The wiring width is 25 μm or less. Even a flexible wiring board that is processed into a flexible wiring board having a wiring width of 1 mm for testing and can realize sufficient folding resistance may not be able to realize sufficient folding resistance when the wiring width is 50 μm or less. Of course, with a flexible wiring board having insufficient folding resistance with a flexible wiring board having a wiring width of 1 mm, even a wiring width of 50 μm or less results in insufficient folding resistance.
Therefore, when the relationship between the cross-sectional shape of the wiring and the bending resistance is examined with a flexible wiring board having a wiring width of 50 μm or less, the etching factor (F _E ) close to the bottom width B and the top width T of the wiring exceeds 5, The improvement of the folding resistance was seen.

The two-layer flexible wiring board according to the present invention is manufactured by wiring a two-layer flexible wiring board by a subtractive method.
Etching solution used for etching process to process copper electroplating layer etc. into wiring is not limited to aqueous solution or special chemical solution containing ferric chloride, cupric chloride and copper sulfate with special blending, general A commercially available etching solution containing a ferric chloride aqueous solution having a specific gravity of 1.30 to 1.45 or a cupric chloride aqueous solution having a specific gravity of 1.30 to 1.45 can be used.

  The surface of the wiring is subjected to tin plating, nickel plating, gold plating, or the like as required by a known plating method, and the surface is covered with a known solder resist or the like. And electronic parts, such as a semiconductor element, are mounted and an electronic device is formed. In the two-layer flexible wiring board according to the present invention, the characteristic crystal structure is not changed by a process such as tin plating or coating with a solder resist.

Hereinafter, the present invention will be described in more detail with reference to examples.
A polyimide film with a copper thin film layer using a polyimide film as a resin film substrate was manufactured using a roll-to-roll sputtering apparatus 10.
A nickel-20 wt% chromium alloy target for forming a base metal layer is attached to the sputtering cathode 15a, and a copper target is attached to the sputtering cathodes 15b to 15d, respectively, and a polyimide film (Kapton: registered trademark) with a thickness of 38 μm is attached to the resin film substrate. / Toray DuPont Co., Ltd.) was evacuated, and the inside of the apparatus was maintained at 1.3 Pa to produce a polyimide film with a copper thin film layer. The film thickness of the base metal layer (nickel-chromium alloy) was 20 nm, and the film thickness of the copper thin film layer was 200 nm.

  The obtained polyimide film with a copper thin film layer was subjected to copper electroplating using a plating apparatus 20 to form a copper electroplating layer. The plating solution is a copper sulfate aqueous solution having a pH of 1 or less, and the anodes 24m to 24t are set to have the maximum current density (excluding the reversal current of the PR current) unless otherwise specified. The current density was adjusted to 8.5 μm.

In the bending resistance test, a test pattern of “JIS-C-5016-1994” is formed by a subtractive method using ferric chloride as an etching solution. Evaluation according to “JIS-5016-1994” was performed except that a test piece having a thickness of 50 μm (hereinafter referred to as a test piece of 50 μm) and a test piece having a wiring width of 20 μm (hereinafter referred to as a test piece of 20 μm) were used. .
The crystal orientation of the copper electroplating layer before and after the fold resistance test was measured by X-ray diffraction using Wilson's orientation degree index.

  For the metal laminate, the orientation and orientation ratio of the copper crystal were measured by the EBSD method. The measurement results were divided into a range from the resin film substrate surface side to a film thickness of 0.4 μm and a range exceeding the film thickness of 0.4 μm.

The measurement conditions of the electron beam backscatter diffraction method (EBSD) used in the examples are as follows.
[Measurement conditions of electron backscatter diffraction (EBSD)]
As a diffractometer, Oxford Instruments (HKL Channel 5) was used, and measurement was performed under the conditions of acceleration voltage: 15 kV, measurement step: 0.05 μm. Further, the (111) plane orientation ratio of the crystal grains was calculated by occupying the area of the measurement range for crystal grains oriented in a range of ± 15 ° in the normal direction of the (111) plane.

The sputtering atmosphere was a mixed gas of 1.3 Pa argon and 5% by volume nitrogen.
The copper electroplating layer has a current density of 1 A / dm ² or less of the anodes 24 a to 24 f that form a film having a thickness of 1.5 μm from the surface of the copper thin film layer in the copper layer, and 10% from the surface of the copper electroplating layer. In order to perform electroplating using a PR current up to the film thickness range, a PR current was passed through the anode 24t to produce a two-layer flexible wiring board of Example 1. The negative current time ratio at this time was 10%.

The crystal ratio of the 001 orientation of the crystal obtained by electron beam backscattering diffraction (EBSD) in the film thickness range from the resin film substrate surface of the metal laminate formed by electrolytic copper plating to 0.4 μm is 111 orientation with respect to OR ₀₀₁ The ratio of the crystal ratio OR ₁₁₁ (OR ₁₁₁ / OR ₀₀₁ ) was 0.7.

The copper electroplating layer (111) crystal orientation index before the MIT folding resistance test was 1.35.
The difference in the crystal orientation ratio [(200) / (111)] represented by the X-ray orientation degree index before and after the MIT folding resistance test was 0.04.

In the MIT fold resistance test, the fold resistance of the sample of Example 1 showing the above characteristics was 545 times when the wiring width was 1 mm, 78 times when the test piece was 50 μm, and 50 times when the test piece was 20 μm and 50 times. .
The etching factor was 6.3 for the test piece of 50 μm and 6.3 for the test piece of 20 μm.

A flexible wiring board was produced in the same manner as in Example 1 except that the sputtering atmosphere was a mixed gas of argon and 1% by volume of nitrogen.
Ratio of crystal ratio OR ₁₁₁ of 111 orientation to crystal ratio OR ₀₀₁ of 001 orientation of crystals obtained by electron beam backscatter diffraction (EBSD) in the film thickness range from the resin film substrate surface of the metal laminate to 0.4 μm (OR ₁₁₁ / OR ₀₀₁ ) was 3.3.

The copper electroplating layer (111) crystal orientation degree index before the MIT folding resistance test was 1.34.
Furthermore, the MIT fold resistance sample of Example 2 in which the difference in crystal orientation ratio [(200) / (111)] expressed by the X-ray orientation degree index before and after the MIT fold resistance test is 0.04 is 1 mm in wiring width. Good results of 851 times, 69 times for the test piece of 50 μm, and 45 times for the test piece of 20 μm were obtained.
The etching factor was 5.3 for the specimen 50 μm and 5.5 for the specimen 20 μm.

(Comparative Example 1)
A flexible wiring board was produced in the same manner as in Example 1 except that argon gas was used only in the sputtering atmosphere.

The ratio (OR ₁₁₁ / OR ₀₀₁ ) of the 111 orientation crystal ratio OR _{111 to} the 001 orientation crystal ratio OR ₀₀₁ of the crystal obtained by measurement by electron beam backscatter diffraction (EBSD) was 7.3.

The copper electroplating layer (111) crystal orientation index before the MIT folding resistance test was 1.20.
The difference in the [(200) / (111)] ratio of the crystal orientation ratio represented by the X-ray orientation degree index before and after the MIT folding resistance test was 0.03.

The fold resistance of the sample of Comparative Example 1 having the above characteristics shows a non-vibrating result of 541 times when the wiring width is 1 mm in the MIT fold resistance test, 27 times when the test piece is 50 μm, and 20 times when the test piece is 20 μm, It was clearly inferior to Example 1 according to the present invention.
The etching factor was 3.9 for a test piece of 50 μm and 4.1 for a test piece of 20 μm.

Table 1 shows wiring shapes (bottom width B, top width T, copper film thickness C), sputter atmosphere, calculated etching factor F _E , and MIT folding resistance test results in Examples and Comparative Examples with wiring widths of 20 μm and 50 μm. Are shown together.

1 Polyimide film (resin film substrate)
DESCRIPTION OF SYMBOLS 2 Base metal layer 3 Copper thin film layer 4 Copper electroplating layer 5 Copper layer 6 Two-layer flexible wiring board 7 Metal laminated body 10 Roll-to-roll sputtering apparatus 12 Case 13 Unwinding roll 14 Can rolls 15a, 15b, 15c , 15d Sputtering cathode 16a Front feed roll 16b Rear feed roll 17a, 17b Tension roll 17b Tension roll 18 Winding roll 20 (Roll-to-roll type continuous electricity) Plating apparatus 21 Electroplating tank 22 Unwinding roll 23 Reversing roll 24a -24t Anode anode 26a-26k Feed roll 28 Plating solution 28a Plating solution level 29 Winding roll F Polyimide film (resin film substrate)
F2 Polyimide film with copper thin film layer (resin film substrate with copper thin film layer)
S 2 layer flexible wiring board

Claims (7)

In a flexible wiring board provided with a base metal layer made of a nickel alloy without using an adhesive on the surface of the resin film substrate and a metal laminate having a copper layer on the surface of the base metal layer,
The thickness of the base metal layer is 50 nm or less, and
The copper layer is composed of a copper thin film layer provided on the surface of the base metal layer and a copper electroplating layer provided on the surface of the copper thin film layer,
A crystal ratio OR ₁₁₁ of 111 orientation with respect to a crystal ratio OR ₀₀₁ of 001 orientation of a crystal included in the range from the resin film substrate surface to 0.4 μm in the metal laminate measured by electron beam backscatter diffraction (EBSD) The ratio (OR ₁₁₁ / OR ₀₀₁ ) is 7 or less,
(111) crystal orientation index of the copper layer is 1.2 or more, and
The difference d [(200) / (111)] of the crystal orientation ratio [(200) / (111)] of the copper layer obtained before and after the execution of the folding resistance test specified in JIS C-5016-1994 is A two-layer flexible wiring board characterized by being 0.03 or more.   2. The two-layer flexible wiring board according to claim 1, wherein the base metal layer has a thickness of 3 nm to 50 nm.   The two-layer flexible wiring board according to claim 1, wherein the copper layer has a thickness of 5 μm to 12 μm. The copper layer is composed of a copper thin film layer provided on the surface of the base metal layer and a copper electroplating layer provided on the surface of the copper thin film layer,
In the thickness range of 10% or more of the film thickness of the copper electroplating layer from the surface of the copper layer toward the resin film substrate, the average particle size is 200 nm to 400 nm, and the surface roughness Ra is 0.2 μm or less. The two-layer flexible wiring board according to any one of claims 1 to 3.   5. The two-layer flexible wiring board according to claim 4, wherein the thickness range is 10% of the film thickness of the copper electroplating layer in the direction from the surface of the copper layer to the resin film substrate.   The resin film substrate is at least one resin selected from a polyimide film, a polyamide film, a polyester film, a polytetrafluoroethylene film, a polyphenylene sulfide film, a polyethylene naphthalate film, and a liquid crystal polymer film. It is a film, The two-layer flexible wiring board of any one of Claim 1 to 5 characterized by the above-mentioned. A base metal layer is formed on the surface of the resin film substrate by a dry plating method without using an adhesive, and a copper thin film layer is formed on the surface of the base metal layer, and a copper plating film is formed on the surface of the copper thin film layer by a copper electroplating method. A method for producing a two-layer flexible wiring board according to any one of claims 1 to 6, wherein
The atmosphere during film formation by the dry plating method is an argon nitrogen mixed gas,
A periodic reverse current in which the copper electroplating layer periodically performs a short-time potential reversal in a thickness range of 10% or more of the copper electroplating layer thickness from the surface of the copper electroplating layer toward the resin film substrate. A method for producing a two-layer flexible wiring board, characterized by being formed by a copper electroplating method.

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