JP2016157752A - Substrate for flexible wiring board and flexible wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a substrate for a flexible wiring board excellent in folding endurance, and also to provide a flexible wiring board that is produced using the substrate for a flexible wiring board and has good folding endurance.SOLUTION: A substrate 6 for a flexible wiring board comprises a laminate film including a substrate metal layer 2 and a copper layer 5 provided on a surface of the substrate metal layer, without providing an adhesive on a surface of a resin film substrate 1. In the substrate for a flexible wiring board, a rapture stress (force per unit cross section) of the laminate film is 280-360 MPa.SELECTED DRAWING: Figure 1

Description

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

Flexible wiring boards are widely used for parts that require bending or bending of electronic devices such as hard disk read / write heads and printer heads, and refractive wiring of IC packages mounted with driver ICs for liquid crystal displays. .
In particular, in an IC package of a liquid crystal display, the liquid crystal display is bent and attached from the end on the front surface side (side on which an image is displayed) to the back surface side of the liquid crystal display.

  For the manufacture of such flexible wiring boards, flexible wiring boards (also referred to as flexible copper clad lamination: FCCL) in which a copper layer and a resin layer are laminated are wired using a subtractive method or a semi-additive method. A processing method is used.

This subtractive method is a method of removing unnecessary portions by chemically etching the copper layer of the flexible wiring board.
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.

On the other hand, the semi-additive method is to form a resist layer on the base metal layer and ultrathin copper layer of the copper clad laminate, pattern the resist layer by photolithography, and remove the resist layer where the wiring is to be formed. Then, copper plating is applied to the open portion where the ultrathin copper layer obtained is exposed to form a wiring. After the wiring is formed, the resist is removed, and the ultrathin copper layer and the base metal layer are chemically etched to remove the ultrathin copper layer and the base metal layer portion.
That is, without forming a resist on the surface of the copper layer of the flexible wiring board where conductor wiring is to be formed, copper is deposited by electrolytic copper plating, and an etching solution corresponding to the ultrathin copper layer and the underlying metal layer is used. Through the chemical etching process and washing with water, unnecessary portions of the ultrathin copper layer and the base metal layer are selectively removed to form a conductor wiring.

By the way, the flexible wiring board (FCCL) is classified into a three-layer flexible wiring board FCCL board (hereinafter referred to as three-layer FCCL) and a two-layer flexible wiring board FCCL board (referred to as two-layer FCCL). Can do.
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.

Among them, FCCL, which is formed by sequentially plating a base metal layer and a copper layer on the surface of a metalizing substrate, that is, a 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. Therefore, it is suitable for forming a fine wiring pattern as compared with a cast substrate, a laminate substrate, or a three-layer FCCL.
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. Will be.

Moreover, about copper foil used for the wiring of a flexible wiring board, for example, the method of performing heat processing to a copper foil (refer patent document 1), or the method of performing a rolling process (refer patent document 2) improves folding resistance. Is planned.
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, the MIT refraction resistance test (Folding Endurance Test) standardized by “JIS C-5016-1994” or “ASTM D2176” is used industrially for the evaluation of the folding resistance of the copper foil.
In this test, evaluation is performed based on the number of refractions until the circuit pattern formed on the test piece breaks, and the greater the number of refractions, the better the folding resistance.

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

The flexible wiring board targeted by the present invention sequentially forms a metal layer that is a laminated film composed of a base metal layer, a copper thin film layer, and a copper electroplating layer formed on at least one surface of a resin film substrate without using an adhesive. Therefore, it is difficult to improve the folding resistance by subjecting only the copper plating layer to heat treatment or rolling as disclosed in the prior art document, and the metalizing substrate itself is not bent. Therefore, it has been desired to produce a metalizing substrate with improved crease resistance and excellent folding resistance.
In view of such circumstances, the present invention provides a flexible wiring board having excellent folding resistance and a flexible wiring board having good folding resistance using the flexible wiring board. .

  1st invention of this invention is the board | substrate for flexible wiring which consists of a laminated film which consists of a copper layer provided in the surface of a resin film board | substrate on the surface of a base metal layer and the said base metal layer without using an adhesive agent, A flexible wiring substrate, wherein the laminated film has a breaking stress (force per unit cross-sectional area) of 280 MPa to 360 MPa.

  According to a second aspect of the present invention, there is provided a flexible wiring board characterized in that the elongation percentage of the laminated film in the first aspect is 5% or more.

  The third invention of the present invention is a copper thin film layer in which the copper layer in the first and second inventions is formed on the surface of the underlying metal layer by a dry plating method, and a wet plating method on the surface of the copper thin film layer. A substrate for flexible wiring, comprising a copper plating layer formed in (1).

  According to a fourth aspect of the present invention, there is provided the flexible wiring board according to any one of the first to third aspects, wherein the copper plating layer has a thickness of 6 μm to 12 μm.

  According to a fifth aspect of the present invention, there is provided the flexible wiring board according to any one of the first to fourth aspects, wherein the base metal layer has a thickness of 3 to 50 nm.

  According to a sixth aspect of the present invention, there is provided the flexible wiring substrate, wherein the underlying metal layer in the first to fifth aspects is nickel, chromium or an alloy thereof.

  A seventh invention of the present invention is a wiring having a width of 50 μm or less comprising a laminated film composed of a base metal layer and a copper layer provided on the surface of the base metal layer without an adhesive on the surface of the resin film substrate The flexible wiring board is characterized in that the breaking stress of the laminated film is 280 MPa to 360 MPa.

  According to an eighth aspect of the present invention, there is provided a copper thin film layer in which the copper layer in the seventh aspect is formed on the surface of the underlying metal layer by a dry plating method and the surface of the copper thin film layer by a wet plating method. It is a flexible wiring board characterized by comprising a copper plating layer.

  According to a ninth aspect of the present invention, there is provided the flexible wiring board according to the seventh and eighth aspects, wherein the base metal layer has a thickness of 3 to 50 nm.

  A tenth aspect of the present invention is a flexible wiring board, wherein the surface of the wiring according to the seventh to ninth aspects is tin-plated.

ADVANTAGE OF THE INVENTION According to this invention, even if wiring width is 50 micrometers or less, the flexible wiring board excellent in the folding resistance improved by the bending resistance test based on "JISC-5016-1994" can be provided.
In particular, since the flexible wiring board according to the present invention has excellent folding resistance, it can be bent with a smaller radius of curvature than conventional products, and even in that case, it is less likely to break at the bent portion.

  When the flexible wiring board according to the present invention is used for a driver IC package of a liquid crystal display, it can be bent with a small radius of curvature, so that the liquid crystal display of an IC package used by being bent around the liquid crystal display. Since the protrusion from the screen can be reduced, it has a design effect of reducing the housing of the liquid crystal display.

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 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 2 layer flexible wiring of this invention. It is the figure which showed typically the time and current density of PR current in this invention.

The breaking stress (force per unit cross-sectional area) of the laminated film of the flexible wiring board and the flexible wiring board according to the present invention needs to be 280 MPa to 360 MPa.
Here, the breaking stress of the laminated film is a breaking stress measured only by the laminated film taken out from the flexible wiring board, and from the viewpoint of fold resistance, there is no decrease in breaking stress due to defects in the laminated film. In the case of a sound laminated film, the lower the breaking stress of the laminated film, the lower is desirable, and the higher the elongation at break is desirable. However, in a practically obtained flexible wiring board, the breaking stress exceeds 280 MPa, In a laminated film having a breaking stress exceeding 360 MPa, the film itself becomes brittle and the problem of poor folding resistance arises.
Therefore, the more desirable breaking stress of the laminated film is in the range of 280 MPa to 320 MPa, and further in the production process of the flexible wiring board, the lamination of the flexible wiring board in a state where a process involving a heat treatment such as an added Sn plating process is not performed. The elongation percentage of the film is desirably 5% or more. In the case of a laminated film of a flexible wiring board that is subjected to a heat treatment such as a Sn plating process, the elongation rate is slightly lowered, but the elongation percentage of the laminated film of the flexible wiring substrate to be used is 5% or more. If this is the case, it will not degrade the folding resistance.

The flexible wiring board according to the present invention is obtained by wiring a two-layer flexible wiring board by a subtractive method or a semi-additive method. If the breaking stress of the laminated film of the two-layer flexible wiring substrate is in the range of 280 MPa to 360 MPa, the method for manufacturing the two-layer flexible wiring substrate is not limited.
Hereinafter, the present invention will be described by way of an example of a manufacturing method in which the breaking stress of the copper layer that is the laminated film of the two-layer flexible wiring board is 280 MPa to 360 MPa.

(1) Two-layer flexible wiring board First, a two-layer flexible wiring board used in the flexible wiring board of the present invention will be described.
The substrate for two-layer flexible wiring according to the present invention is a metalizing substrate that takes a laminated film in which a base metal layer and a copper layer are sequentially laminated on at least one surface of 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 substrate 6 for a two-layer flexible wiring manufactured by a metalining method.
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 from the polyimide film side. The copper layer 5 is composed of a copper thin film layer 3 and a copper electroplating layer 4. Furthermore, the laminated film 7 is composed of a laminated structure in the order of the base metal layer 2 and the copper layer 5.

As the resin film substrate 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. Accordingly, the material of the base metal layer is any one selected from nickel, chromium, or an alloy thereof, but considering the adhesion strength and the ease of etching during wiring production, the nickel-chromium alloy is Is suitable.

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 film thickness of the copper layer is 6 μm to 13 μm. The copper layer is much thicker than the base metal layer, and the breaking stress of the laminated film is almost the breaking stress of the copper layer.
The copper thin film layer 3 is mainly composed of copper, and the film thickness is desirably 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.

(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 evaporation method, a CVD method, and the like. From the viewpoint of controlling the composition of the underlying metal layer, the sputtering method is preferable.
For the sputtering film formation on the resin film substrate, a known sputtering apparatus may be used. For the film formation for a long resin film substrate, a known roll-to-roll sputtering apparatus may be used. It can be carried out. 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 used.
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 only needs to be wider than the width of the 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.

(3) Copper electroplating layer and film forming method The copper electroplating layer is formed by electroplating. The thickness of the copper electroplating layer is preferably 6 μm to 12 μm.

FIG. 3 is an example of a roll-to-roll continuous electroplating apparatus (plating apparatus 20) that can be used for the production of a two-layer flexible wiring board according to 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 electroplated layer on the surface of the copper thin film layer by electroplating while being immersed in the plating solution 28, and forming a copper layer with a predetermined thickness. As a two-layer flexible wiring substrate S that is a plastic resin film substrate, it is wound around a winding roll 29. 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, a copper layer is formed on the metal thin film of the polyimide film F2 with a copper thin film layer.

A power source (not shown) is connected between the power supply roll 26a and the anode 24a.
An electroplating circuit is configured by 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.
Here, the anode used is preferably an insoluble anode.
The insoluble anode does not require a special one, and may be a known insoluble 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.
By increasing the current density in this way, discoloration of the copper electroplating layer can be prevented. In particular, when the current density is high when the thickness of the copper electroplating layer is thin, discoloration is likely to occur on the surface. Therefore, the current density during plating is 0.1 A / dm ² except for the reversal current of Periodic Reverse current described later. 8 A / dm ² is desirable. When the current density is increased, a poor appearance of the copper electroplating layer occurs.

In the production of the two-layer flexible wiring board according to the present invention, the breaking stress can be realized at 280 Pa to 360 Pa by controlling the electroplating conditions of the copper electroplating layer.
A periodic reverse current (hereinafter also referred to as a PR current) can be used as a plating condition for forming a copper electroplating layer for producing the two-layer flexible wiring board according to the present invention. Moreover, as a plating condition for the copper electroplating layer, a PR current and a pulse current may be used in combination.

Furthermore, the range of 10% or more of the film thickness of the copper electroplating layer from the surface of the electroplated copper layer to the polyimide direction (hereinafter also referred to as the depth direction) is obtained by using PR current or PR current and pulse current. If the electroplating layer is formed, the breaking stress of the laminated film can realize the range of 280 Pa to 360 Pa. Moreover, the object of the present invention can be achieved by setting the copper electroplating range with PR current or PR current and pulse current to a range of 70% or less of the film thickness in the depth direction from the surface of the copper layer. .
Note that the PR current is a combination of a positive current and an inverted current whose polarity is inverted, and the inverted 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.
The pulse current is a current that causes no current to flow at a constant cycle with respect to a positive current or performs a current reduction by reducing a current value. The current decrease is desirably a value exceeding 50 amperes of positive current. The period of the next no-current and reduced current in the pulse current is preferably 10 ms or more, and is 20 ms to 300 ms.
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 according to the present invention with a roll-to-roll continuous electroplating apparatus (plating apparatus 20), a PR current may be passed through one or more anodes from the downstream side of the transport path. The number of anodes through which the PR current flows is determined by the ratio of the range in which the PR current is formed from the surface of the copper electroplating layer to the polyimide film side. When a pulse current is not used, a PR current flows through at least the anode 24t, and a PR current flows through the anode 24s, the anode 24r, and the anode 24q as necessary. On the other hand, when the pulse current is not used, a pulse current is applied to at least one of the anode 24s and the anode 24t, and a PR current is applied from the downstream anode disposed immediately after the anode to which the pulse current is applied.
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, the breaking strength of the copper layer occupying most of the laminated film can be obtained. Since it can be controlled, the rupture stress of the laminated film can be realized at 280 Pa to 360 Pa. As a result, it is possible to improve the folding resistance test (MIT test).

  The electroplating method used here is copper electroplating using an insoluble anode in a copper sulfate plating solution containing iron ions, and the composition of the copper plating solution used is usually used. A high-throw copper sulfate plating bath for printed wiring boards may be used, and iron ions are added and used.

In order to set the breaking stress of the laminated film to 280 Pa to 360 Pa, it can also be controlled by an additive of an electroplating solution. Additives such as known levelers and brighteners can be added to the electroplating solution. Many of these additives are organic sulfur compounds. These additives are incorporated into the copper electroplating layer during copper electroplating.
When the sulfur concentration of the copper electroplating layer exceeds 30 ppm, the breaking stress of the laminated film exceeds 360 Pa. Therefore, the folding resistance of the flexible wiring board or the flexible wiring board may be deteriorated. The amount of the leveler or brightener added to the electroplating bath may be appropriately selected from the sulfur content of the copper electroplating layer.

(4) Flexible wiring board The wiring width of the flexible wiring board according to the present invention is 50 μm or less at the narrowest portion. Here, the wiring width is the width of the bottom surface where the wiring is in contact with the popriimide film.
The result of the MIT fold resistance test of the flexible wiring board becomes worse as the wiring width becomes thinner.

That is, in the bending resistance test according to “JIS C-5016-1994”, the wiring width is 1 mm, but in the flexible wiring board used for the bent wiring in the liquid crystal display, the wiring width is 50 μm or less, Furthermore, it has shifted to a high-definition wiring width of 25 μm or less. Even if it is a flexible wiring board that is processed into a flexible wiring board with a wiring width of 1 mm for testing and can realize sufficient folding resistance, it is processed into a flexible wiring board with a wiring width of 50 μm or less that is actually used. Sufficient folding resistance may not be achieved.
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 substrate processed into a flexible wiring board having a wiring width of 50 μm or less results in insufficient folding resistance.

  In the flexible wiring board according to the present invention, the laminated film to be the wiring is a laminated film having a breaking stress of 280 Pa to 360 Pa, so that even if the wiring width is 50 μm or less, such a breaking stress is exerted. The MIT folding resistance is improved as compared with a conventional flexible wiring board that is not provided.

As for the film thickness of the copper layer which consists of a copper thin film layer and a copper electroplating layer of a flexible wiring board, 5 micrometers-12 micrometers are desirable.
If the thickness of the copper layer is less than 5 μm, the conductivity of the wiring becomes insufficient. On the other hand, when the copper layer exceeds 12 μm, it is difficult to form a wiring having a wiring width of 50 μm or less even if the conductivity is sufficient. In particular, in the subtractive method, as the wiring film thickness increases, it becomes difficult to process fine wiring.
The total film thickness of both the copper thin film layer and the copper electroplating layer of the two-layer flexible wiring board (corresponding to the film thickness of the copper layer of the flexible wiring board) may exceed 12 μm. When the total thickness of the copper thin film layer and the copper electroplating layer of the two-layer flexible wiring board exceeds 12 μm, the copper electroplating layer or the like of the two-layer flexible wiring board is made to a predetermined film thickness by chemical polishing or the like. That's fine.

The flexible wiring board according to the present invention is a metallizing substrate manufactured by subjecting the two-layer flexible wiring substrate according to the present invention described above in detail to wiring processing using 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.

In order to obtain the flexible wiring board according to the present invention by the semi-additive method, the same copper plating procedure as that of the above-mentioned two-layer flexible wiring board can be used when copper electroplating is performed on the two-layer flexible wiring board. .
The thickness of the copper layer of the two-layer flexible wiring board to be used may be appropriately determined in consideration of the film thickness of the semi-additive copper plating.

The flexible wiring board subjected to the wiring processing is subjected to tin plating, and thereafter, a known solder resist coating, an IC or the like is mounted via a gold bump, and processed into an IC package component.
By the way, tin plating is performed by immersing a flexible wiring board in a known electroless tin plating solution having a temperature of 50 ° C. to 90 ° C. for 1 minute to 5 minutes. In the solder resist coating, the flexible wiring board is exposed to a temperature of 100 ° C. to 150 ° C. in order to cure the solder resist, and heat is applied to the flexible wiring board even when the element is mounted via the gold bump. Although these chemical loads and thermal loads may adversely affect the bending resistance of the flexible wiring board, the flexible wiring board according to the present invention is a laminate that constitutes the wiring after being exposed to these loads. By setting the rupture stress of the film to 280 Pa to 360 Pa, even after being exposed to these loads, even when tin plating is applied, the folding resistance is improved.

Hereinafter, the present invention will be described in more detail with reference to examples.
The breaking stress of the flexible wiring board without tin plating was obtained by dissolving and removing the polyimide film with an alkaline solution, and cutting a laminated film of the base metal layer and the copper layer into 13 mm × 100 mm, “RTC-1150A” manufactured by Orientec Co., Ltd. ”.
Further, the breaking stress after tin plating was measured in the same manner as the breaking stress of the flexible wiring board without tin plating, except that tin plating and predetermined heat treatment were performed.
The elongation percentage is the elongation percentage of the sample until the laminated film breaks when measuring the breaking stress.

The polyimide film with a copper thin film layer was manufactured using the roll-to-roll sputtering apparatus 10 shown in FIG.
A nickel-20 wt% chromium alloy target for forming a base metal layer was mounted on the sputtering cathode 15a, and a copper target was mounted on the sputtering cathodes 15b-15d, respectively, and a polyimide film (“Kapton” manufactured by Toray DuPont Co., Ltd.). (Registered Trademark) ”) was evacuated and the inside of the apparatus was maintained at 1.3 Pa by introducing argon gas 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 uses a copper sulfate bath, and the anodes 24o to 24t have the maximum current density (excluding the reversal current of the PR current) unless otherwise specified, and finally the thickness of the copper electroplating layer is 8.5 μm. The current density was adjusted so that

  The bending resistance test is a subtractive method using copper chloride as an etching solution, and a test piece with a wiring width of 25 μm and a test piece with a wiring width of 50 μm conforming to “JIS-C-5016-1994” are formed. It evaluated according to.

  In order to perform pulse plating from the surface of the copper electroplating layer to a film thickness range of 1.3 μm, and to perform copper electroplating with a PR current over a film thickness range of 1.3 to 4.5 μm from the surface of the plating layer, FIG. Anodes 24o to 24t (final R is a pulse current and the remaining 3R is a PR current), and a two-layer flexible wiring board used in Example 1 was fabricated. In addition, iron ion was added to the plating solution so that the iron ion concentration was 2 g / liter.

  The obtained two-layer flexible wiring board according to Example 1 was processed into a MIT test wiring having a wiring width of 25 μm (hereinafter also referred to as a wiring width of 25 μm test piece) by a subtractive method, and was commercially available at a temperature of 50 ° C. After being immersed in an alkylsulfonic acid-based electroless tin plating solution and having a tin plating thickness of 0.4 μm, heat treatment was performed at 150 ° C. for 3 hours assuming solder resist curing and device mounting.

The MIT fold resistance test result of the 25 μm test piece was 47 times, and a good result showing an 18% improvement over the conventional product was obtained.
On the other hand, the MIT folding resistance test result of the 50 μm test piece was 48 times. Further, the MIT fold resistance test result of the test piece that was not subjected to tin plating and heat treatment at 150 ° C. for 3 hours on the 50 μm test piece was 95 times.
The measured characteristics are summarized in Table 1.

Pulse plating was performed from the surface of the copper electroplating layer to a film thickness range of 4 μm, and copper electroplating was performed at a film thickness range of 4 to 5 μm from the surface of the plating layer with a PR current.
The MIT fold resistance test result of the 25 μm test piece was 43 times, and a result showing a 13% improvement over the conventional product was obtained.
On the other hand, the MIT folding resistance test result of the 50 μm test piece was 45 times.
The measured characteristics are summarized in Table 1.

A test piece of Example 3 was prepared in the same manner as in Example 1 except that copper electroplating was performed with a direct current without flowing a PR current at any anode of the plating tank.
The result of the MIT folding resistance test of the 25 μm test piece was 38 times, and the result of the MIT folding resistance test of the 50 μm test piece was 37 times.
Table 1 shows the measured characteristics of the 50 μm test piece that was not subjected to tin plating and heat treatment at 150 ° C. for 3 hours.
(Comparative Example 1)

A test piece according to Comparative Example 1 was produced in the same manner as in Example 3 except that the tensile strength was 380 Pa by changing the copper electroplating conditions. As a result, the results of the 50 μm MIT fold resistance test without tin plating and heat treatment held at 150 ° C. for 3 hours were greatly inferior to 40 times, and the subsequent tests were stopped.
The measured characteristics are summarized in Table 1.

  Example 1 and Comparative Example 1 were not subjected to tin plating, and the presence or absence of heat treatment held at 150 ° C. for 3 hours was examined based on the MIT fold resistance test results of 50 μm test pieces. 1 shows a 3% improvement over Comparative Example 1, but when tin plating and heat treatment are applied, Example 1 shows a 30% improvement over Comparative Example 1. . It can be seen that the crystal structure in the copper layer of the wiring of the flexible wiring board according to the present invention is beneficial because it has an excellent effect on the folding resistance of the printed wiring board.

1 Polyimide film (resin film substrate)
DESCRIPTION OF SYMBOLS 2 Underlying metal layer 3 Copper thin film layer 4 Copper electroplating layer 5 Copper layer 6 Two-layer flexible wiring board 7 Laminated film 10 Roll-to-roll sputtering device 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 18 Winding roll 20 (Roll-to-roll type continuous electricity) Plating apparatus 21 Electroplating tank 22 Unwinding roll 23 Reversing rolls 24a-24t Anode 26a ~ 26k Feed roll 28 Plating solution 28a Liquid level of plating solution 29 Winding roll F Resin film substrate (polyimide film)
F2 Polyimide film with copper thin film layer (resin film substrate with copper thin film layer)
S 2 layer flexible wiring board

Claims (10)

In a flexible wiring substrate comprising a laminated film composed of a base metal layer and a copper layer provided on the surface of the base metal layer without using an adhesive on the surface of the resin film substrate,
A flexible wiring board, wherein the laminated film has a breaking stress of 280 MPa to 360 MPa.   The substrate for flexible wiring according to claim 1, wherein an elongation percentage of the laminated film is 5% or more.   The copper layer includes a copper thin film layer formed by a dry plating method on the surface of the base metal layer and a copper plating layer formed by a wet plating method on the surface of the copper thin film layer. Item 3. The flexible wiring board according to Item 1 or 2.   The board | substrate for flexible wiring of any one of Claim 1 to 3 whose film thickness of the said copper plating layer is 6 micrometers-12 micrometers.   The substrate for flexible wiring according to any one of claims 1 to 4, wherein the thickness of the base metal layer is 3 to 50 nm.   The substrate for flexible wiring according to any one of claims 1 to 5, wherein the base metal layer is nickel, chromium, or an alloy thereof. A flexible wiring board in which a wiring having a width of 50 μm or less comprising a base metal layer and a copper layer provided on the surface of the base metal layer is provided on the surface of the resin film substrate without using an adhesive. ,
A flexible wiring board, wherein the laminated film has a breaking stress of 280 MPa to 360 MPa.   The copper layer is composed of a copper thin film layer formed by a dry plating method on the surface of the base metal layer and a copper plating layer formed by a wet plating method on the surface of the copper thin film layer. Item 8. The flexible wiring board according to Item 7.   The flexible wiring board according to claim 7 or 8, wherein the thickness of the base metal layer is 3 to 50 nm.   The flexible wiring board according to claim 7, wherein the surface of the wiring is tin-plated.

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