JP6206724B2 - Manufacturing method of flexible wiring board - Google Patents

Description

  The present invention relates to a method for manufacturing a flexible wiring board in which a two-layer copper-clad laminate in which a base metal layer and a copper layer are laminated on at least one surface of a polyimide film without using an adhesive is processed.

Flexible wiring boards are widely used in wiring parts that require bending of movable parts of electronic devices such as hard disk read / write heads and printer heads, and wiring parts that pass through a slight gap in liquid crystal display devices, taking advantage of its flexible nature. It is used.
The flexible wiring board to be used is generally a subtractive method or semi-solid method for a flexible copper-clad laminate (also referred to as a flexible copper clad lamination) having a laminated structure composed of a copper layer and a resin film layer. It is manufactured by wiring processing using the additive method.

The subtractive method, which is one of the wiring processing methods, is a method of removing unnecessary portions other than wiring by chemically etching the copper layer of the copper-clad laminate.
Specifically, after forming a photoresist layer on the surface of the copper layer of the copper clad laminate, the photoresist layer is subjected to patterning to expose the surface of the copper layer other than the portion to be left as the conductor wiring. The exposed portion of the copper layer is selectively removed using an etching solution that dissolves copper to form a conductor wiring, and then washed with water.

On the other hand, the semi-additive method is a method in which an unnecessary copper layer and a base metal layer are removed by chemical etching after a copper plating layer is provided on the surface of a copper layer of a copper clad laminate so as to have a wiring shape. .
Specifically, after forming a photoresist film having an opening in the shape of a wiring on the surface of the copper layer, copper plating is performed up to the film thickness necessary for the wiring at the opening portion of the copper layer, and a copper plating layer is provided. After removing the photoresist, unnecessary copper layers and underlying metal layers are removed by chemical etching, and then washed with water.

After wiring processing using the subtractive method or semi-additive method, tin plating is applied to the wiring as necessary, and after tin plating, a solder resist is applied and cured at the required location to form a solder resist film and flexible The wiring board is completed.
Electronic components such as semiconductor elements are mounted on the completed flexible wiring board to form a circuit device.

By the way, manufacture of a flexible wiring board is performed in a clean room or the like in which temperature and humidity are controlled. In the process of manufacturing such a flexible wiring board, wet processing such as photoresist development and removal, chemical etching, and tin plating is performed. The humidity is controlled at 45% RH to 65% RH, but the copper-clad laminate used for the production of flexible wiring boards is a laminate of a copper layer and a resin film substrate, of which a resin film The base material, particularly the polyimide film, expands and contracts due to a change in humidity, and dimensional variation due to the expansion and contraction is a problem.
That is, it is related to the alignment of the wiring pattern when connecting the flexible wiring board and the electronic component such as the semiconductor element by miniaturizing the wiring pitch of the flexible wiring board, and the accuracy required as the number of pins of the semiconductor element increases. It is becoming strict to deal with

  Therefore, in Patent Document 1, the reinforcing plate is bonded to one surface of the copper-clad laminate through an organic material layer that can be peeled off, and then a circuit pattern is formed on the surface on which the reinforcing plate is not bonded, and then the flexible plate is formed. A technique for manufacturing a circuit board for peeling a conductive film from a reinforcing plate is disclosed. However, problems such as an increase in manufacturing processes such as a process of attaching a reinforcing plate and a peeling process, and contamination due to organic substances used for adhesion are likely to occur, and a flexible wiring board corresponding to the required accuracy is desired. .

JP 2003-124605 A

  In response to such demands, the present invention suppresses dimensional variation with simple means even if the humidity in the atmosphere to which the copper-clad laminate is exposed in the process of manufacturing a flexible wiring board from the copper-clad laminate is changed. The manufacturing method of the flexible wiring board manufactured is provided.

In view of the above situation, the first invention of the present invention is a long two-layer copper-clad laminate in which a base metal layer and a copper layer are laminated on at least one surface of a long polyimide film without using an adhesive. In the method for manufacturing a flexible wiring board in which a wiring pattern is formed , the long polyimide film is a polyimide containing an imide bond composed of 4,4′-diaminodiphenyl ether and pyromellitic dianhydride, and is a two-layer copper When the humidity in the atmosphere where the tension laminate is exposed in the manufacturing process of the flexible wiring board changes in the range of ± 5% RH, the next process should be performed after leaving it in the changed humidity atmosphere for 6 hours or more. This is a method for manufacturing a flexible wiring board.

  According to a second aspect of the present invention, there is provided a method for manufacturing a flexible wiring board, wherein the underlying metal layer in the first aspect is formed by a dry plating method.

  A third invention of the present invention is a method for producing a flexible wiring board, wherein the base metal layer in the first and second inventions is a nickel-chromium alloy having a thickness of 3 nm to 50 nm.

  According to the present invention, even with a flexible wiring board with a reduced wiring pitch, dimensional fluctuations during wiring processing are suppressed, so that it is possible to produce a flexible wiring board with little dimensional variation and high dimensional accuracy. To do.

It is a schematic cross section of the copper clad laminated board produced using the film processed with the heat processing method of this invention. It is a front view of one specific example of the sputtering film-forming apparatus which can implement suitably the heat processing method of this invention. It is a front view of one specific example of the wet-plating apparatus which can be suitably implemented with respect to the film formed into a film with the sputtering film-forming apparatus.

[1] Copper-clad laminate A copper-clad laminate used for the production of a flexible wiring board is obtained by bonding an electrolytic copper foil or a rolled copper foil to an insulating resin film as a base layer using an adhesive. A copper-clad laminate having a three-layer structure (hereinafter also referred to as a three-layer copper-clad laminate) composed of an “adhesive layer / resin film” and a copper layer or copper foil and a resin film substrate directly bonded to each other. It can be classified into a two-layered copper-clad laminate (hereinafter also referred to as a two-layer copper-clad laminate) composed of “copper foil / resin film”.

  The two-layer copper-clad laminate can be further roughly divided into three types. That is, a copper clad laminate (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, and a copper clad laminate obtained by applying a resin film varnish to a copper foil to form an insulating layer. (Commonly called cast substrate) and copper-clad laminate (commonly called laminate substrate) obtained by laminating a resin film on copper foil.

  Among these, the metallizing substrate can reduce the thickness of the copper layer, and since the smoothness of the interface between the resin film and the copper layer or the base metal layer is high, the cast substrate, the laminate substrate, or the three-layer copper-clad laminate It is suitable for miniaturization of wiring pitch compared to In so-called three-layer copper-clad laminates such as cast substrates and laminate substrates, the surface roughness of the copper foil surface on the resin film side is increased in order to improve the adhesion due to the anchor effect at the interface between the resin film and the copper foil. Therefore, the smoothness of the interface between the resin film and the copper foil cannot be expected. Therefore, in the method for manufacturing a flexible wiring board according to the present invention, it is desirable to process the metalizing substrate.

[2] Metalizing substrate FIG. 1 is a schematic sectional view showing an example of a metalizing substrate (copper-clad laminate 6).
The base metal layer 2, the copper thin film layer 3, and the copper electroplating layer 4 are laminated in order from the resin film base material 1 side on at least one surface of the resin film base material 1 using the polyimide film, and the copper layer 5 is a copper thin film layer. 3 and a copper electroplating layer 4.

  Here, the base metal layer 2 ensures reliability such as adhesion and heat resistance between the resin film substrate 1 and the copper layer 5. Therefore, the material of the base metal layer 2 is preferably nickel, chromium, or any one of these alloys. In particular, a nickel-chromium alloy is suitable in consideration of adhesion strength and ease of etching during wiring production.

  The nickel-chromium alloy used for the base metal layer 2 preferably has a chromium composition of 15% by mass or more and 22% by mass or less, thereby obtaining excellent corrosion resistance and migration resistance. Among these, nickel / chromium alloy of 20% by mass chromium is distributed as a nichrome alloy and can be easily obtained as a sputtering target of the magnetron sputtering method. Further, chromium, vanadium, titanium, molybdenum, cobalt, or the like may be added to the alloy containing nickel. Further, a plurality of nickel-chromium alloy thin films having different chromium concentrations may be laminated to form a base metal layer having a concentration gradient with respect to the nickel-chromium alloy.

  The film thickness of the base metal layer 2 is desirably 3 to 50 nm. If the film thickness of the base metal layer 2 is less than 3 nm, the adhesion between the resin film substrate 1 made of a polyimide film and the copper layer 5 cannot be maintained, and the corrosion resistance and migration resistance may be inferior. On the other hand, if the thickness of the base metal layer 2 exceeds 50 nm, it may be difficult to sufficiently remove the base metal layer 2 when wiring processing is performed by a subtractive method or a semi-additive method. Thus, when the removal of the base metal layer 2 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 film thickness is desirably 10 nm to 1 μm. When the film thickness of the copper thin film layer 3 is less than 10 nm, it becomes difficult to ensure conductivity when a copper electroplating layer 4 described later is formed by an electroplating method, which leads to poor appearance during electroplating. Even if the film thickness of the copper thin film layer 3 exceeds 1 μm, there is no problem in the quality of the two-layer copper-clad laminate, but it may cause a problem in that the productivity is lowered.

  The film thickness of the copper electroplating layer 4 is desirably 12 μm or less. When the film thickness of the copper electroplating layer 4 exceeds 12 μm, chemical etching wiring processing (wiring processing by subtractive method) to a flexible wiring board having a wiring pitch of 50 μm or less is performed. It becomes difficult. When wiring a copper-clad laminate with a two-layer structure using the semi-additive method, the film thickness of the copper layer (the total film thickness of the copper thin film layer and the copper electroplated layer) is the conductivity of the semi-additive process. In order to ensure the property, it may be 1 μm or more.

As the polyimide film used for the resin film substrate 1, an aromatic polyimide film is used.
Since the thermal characteristics of the polyimide film are governed by an imide compound formed from an aromatic acid anhydride and an aromatic diamine, in the method for producing a flexible wiring board according to the present invention, the polyimide film is 4,4′-diaminodiphenyl ether. And an imide compound composed of pyromellitic dianhydride.
As a polyimide film having an imide bond, “Kapton (registered trademark, manufactured by Toray DuPont Co., Ltd.)” is known. “Kapton®” film is readily available on the market.

  The thickness of a polyimide film should just be the thickness which can keep a shape as a softness | flexibility and a film, and thickness 10 micrometers-50 micrometers are desirable.

  Next, as an example of a method for producing a metalizing substrate, a base metal layer is formed on a surface of a base metal layer by dry plating such as sputtering on at least one surface of a polyimide film used as a resin film. A copper thin film layer is formed by the method. On the surface of the copper thin film layer of the resin film substrate with a copper thin film layer on which the base metal layer and the copper thin film layer are formed, copper electroplating is formed in a copper sulfate aqueous solution by a wet plating method such as an electroplating method. Hereinafter, the manufacturing method of a metalizing board | substrate is demonstrated.

[3] Metalizing substrate manufacturing method (dry plating part)
In order to form a base metal layer and a copper thin film layer on a long polyimide film, a roll-to-roll sputtering apparatus shown in FIG. 2 may be used.
The roll-to-roll sputtering apparatus 10 shown in FIG. 2 has a structure in which most of its constituent elements are housed in a rectangular parallelepiped chamber 12. The shape of the chamber 12 is not limited to the rectangular parallelepiped shape of FIG. 2, and may be other shapes such as a cylindrical shape as long as a reduced pressure state of about 10 ⁻⁴ Pa to 1 Pa can be maintained.

  In this chamber 12, unwinding roll 13 from which resin film substrate F1 made of a long polyimide film is drawn, free rolls 11a and 11b rotating following the conveyance of resin film substrate F1, and resin film substrate F1 Can roll 14 wound around the outer peripheral surface and cooled, magnetron cathode type sputtering cathodes 15a, 15b, 15c, 15d, front feed roll 16a and rear feed roll 16b provided adjacent to can roll 14, and a tension sensor A winding roll 18 is provided for winding the tension rolls 17a and 17b, the resin film base material F2 on which the base metal layer and the copper thin film layer are formed into a roll shape.

  Among these, the unwinding roll 13, the can roll 14, the front feed roll 16 a, and the take-up roll 18 are provided with servo motors that are rotation driving means. Furthermore, each of the unwinding roll 13 and the winding roll 18 maintains the tension balance of the resin film substrate being conveyed by torque control using a powder clutch or the like. The outer surfaces of the free rolls 11a and 11b, the can roll 14, and the tension rolls 17a and 17b are finished with hard chrome plating.

  Inside the can roll 14, a coolant and a heating medium supplied from the outside of the chamber 12 circulate, so that the outer peripheral surface of the can roll 14 can be adjusted to a substantially constant temperature. Sputtering cathodes 15 a to 15 d are arranged facing the outer peripheral surface of the can roll 14. The dimensions of the sputtering cathodes 15a to 15d in the width direction of the outer peripheral surface of the can roll 14 are preferably larger than the width of the resin film substrate F1.

  Furthermore, since the polyimide film easily absorbs moisture, it is desirable to heat and dry in a reduced pressure atmosphere before dry plating.

[4] Manufacturing method of metalizing substrate (wet plating part)
Next, the copper electroplating layer is formed on the resin film substrate F2 with a copper thin film layer on which the copper thin film layer is formed by the dry plating method, by a wet plating method.
Examples of the apparatus for performing the wet plating method include an apparatus for performing electroplating using an insoluble anode in a plating bath such as copper sulfate. In addition, the composition of the copper plating bath to be used may be a commonly used high-throw copper sulfate plating bath for printed wiring boards.

FIG. 3 shows a roll-to-roll electroplating apparatus 20 (hereinafter also referred to as electroplating apparatus 20) as a specific example of such an electroplating apparatus.
In the electroplating apparatus 20, the resin film substrate F2 with a copper thin film layer obtained by forming a base metal layer and a copper thin film layer is continuously conveyed by a roll-to-roll process. A copper electroplating layer is formed on the surface of the metal thin film by electroplating while being dipped in the plating solution 28 and repeatedly immersed in the plating solution 28. As a result, a copper clad laminate S having a two-layer structure in which a copper layer having a predetermined thickness is formed can be produced. In addition, the conveyance speed of the resin film base material F2 with a copper thin film layer has the preferable range of several m-several dozen m / min.

  If it demonstrates concretely, the resin film base material 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 resin film base material F2 with the copper thin film layer that has entered the plating solution 28 is pulled up above the plating solution surface 28a after the conveying direction is reversed by the reversing roll 23. An anode 24a and an anode 24b are respectively provided at positions facing the resin film substrate F2 with a copper thin film layer that travels on the conveyance path immediately before and immediately after the reversal by the reversing roll 23. A voltage is applied between each anode and a power supply roll. For example, an electroplating circuit is configured by the power supply roll 26a, the anode 24a, a plating solution, a resin film base material F2 with a copper thin film layer, and a power source. . Thereby, an electroplating process is given to the surface of the resin film base material F2 with a copper thin film layer.

  That is, the 11 power supply rolls 26a to 26k and the 10 reversing rolls 23 cause the resin film substrate F2 with a copper thin film layer to be immersed in the plating solution 28 and in a non-immersed state multiple times (a total of 10 in FIG. 3). This is repeated, whereby a copper layer is gradually formed on the copper thin film layer of the resin film substrate F2 with a copper thin film layer, thereby forming a two-layered copper-clad laminate. The copper-clad laminate S having a two-layer structure whose transport direction has been reversed by the final reversing roll 23 is wound around a winding roll 29 after passing through a power feeding roll 26k. As the insoluble anode constituting each anode, a known one whose surface is coated with a conductive ceramic can be used.

  A mechanism for supplying copper ions to the plating solution 28 is provided outside the electroplating tank 21. It is preferable to supply the copper ions to the plating solution 28 with a copper oxide aqueous solution, a copper hydroxide aqueous solution, a copper carbonate aqueous solution or the like. Or the method of adding a trace amount iron ion in a plating solution, melt | dissolving an oxygen-free copper ball | bowl, and supplying copper ion may be used.

It is preferable that the current density during the electrolytic copper plating is increased stepwise from the anode 24a toward the downstream in the transport direction so that the maximum current density is obtained from the anodes 24q to 24t. Thus, discoloration of the copper layer can be prevented by increasing the current density.
Further, since the color change tends to occur in the current density is high and the copper layer when the thickness of the copper layer is thin, the current density in the plating 0.1~8A / dm ² is preferred. When this current density is higher than 8 A / dm ^2, there is a possibility that a poor appearance of the copper electroplating layer may occur.
A copper electroplating layer is formed to obtain a metallizing substrate of a two-layer copper clad laminate, and the metallizing substrate is cut with a slitter to a width suitable for wiring processing.

[5] Outline of Manufacturing Method of Flexible Wiring Board As a manufacturing method of a flexible wiring board with a fine wiring pitch, the following are known as subtractive methods.
On the metalizing substrate cut to a width suitable for wiring processing, a photoresist film is formed on the surface of the copper layer, and this photoresist film is exposed and developed to form a desired pattern. Next, using the photoresist pattern thus formed as a mask, the exposed copper layer is chemically etched to form a wiring pattern composed of a copper layer and a base metal layer having a shape substantially similar to the photoresist pattern. Next, the photoresist layer is peeled off with an alkaline solution or the like, and then the underlying metal layer remaining between the wiring patterns is removed by etching to form a wiring pattern. After the wiring pattern is formed, tin plating is performed to form a solder resist film, thereby forming a flexible wiring board.

[6] Photoresist film forming step In the photoresist film forming step of forming a photoresist film, a liquid photoresist is applied to the surface of the copper layer by a known coating method such as screen printing, and is heated and dried after coating. The drying conditions for the liquid photoresist are a temperature of 100 ° C. to 150 ° C. and a time of 5 minutes or more.
The photoresist film may be a dry film type photoresist (dry film) laminated on the surface of the copper layer. When laminating a dry film resist, it is pressure-contacted at a temperature of 100 ° C. to 150 ° C. for several seconds or more by a known laminating method. Although it is instantaneous, heat treatment to be heated is performed on the copper clad laminate even when laminating a dry film resist.

[7] Exposure process Next to the photoresist film forming process is an exposure process. In the exposure process, the photoresist film formed on the surface of the copper layer of the copper clad laminate is irradiated with ultraviolet rays through a photomask having a predetermined pattern in order to form a wiring pattern on the copper layer. Then, an exposed portion is formed.

[8] Development process The exposure process is followed by a development process. In the developing process, the exposed photoresist is dissolved and removed with a developing solution to form a photoresist pattern having openings. The developing solution is performed, for example, by spraying an alkaline solution such as a sodium carbonate aqueous solution or a triethanolamine aqueous solution having a temperature of 30 ° C. to 50 ° C.

[9] Chemical etching process The development process is followed by a chemical etching process. After the photoresist pattern is formed, the copper-clad laminate is processed into a wiring pattern in this chemical etching process.
The etchant preferably has a composition that can etch the copper layer and the underlying metal layer. As an etching solution to be used, for example, a cupric chloride aqueous solution or a ferric chloride aqueous solution is used. As the processing conditions, for example, the etching process is performed by spraying an etching solution under the conditions of a temperature of 40 to 50 ° C., a shower pressure of 0.1 to 0.7 MPa, and a processing time of 20 to 120 seconds. At this time, the underlying metal layer is also etched away. Moreover, you may add a base metal layer removal process by shower-injecting base metal layer removal agents, such as permanganate aqueous solution, as needed.

  When the wiring pattern is formed through this chemical etching process, the photoresist pattern is stripped in the photoresist stripping process. In the photoresist stripping step, the photoresist pattern is dissolved and removed with an alkaline solution such as an aqueous sodium hydroxide solution. After the photoresist removal step, the chemical solution is removed by washing with water, and then dried by draining with an air knife or the like. The chemical etching process and the photoresist stripping process are performed continuously. After the photoresist stripping process, the process proceeds to the next tin plating process.

[10] Tin plating step In the tin plating step, a tin plating layer is formed on the surface of the copper layer wiring formed by the chemical etching step by a known electroless tin plating method. After the tin plating step, the chemical solution is removed by washing with water, and then dried by draining with an air knife or the like. After drying, the process proceeds to the next solder resist film forming step.

[11] Solder Resist Film Forming Step The solder resist film forming step prints a predetermined pattern of solder resist on the wiring pattern by screen printing. As the solder resist, polyimide (made by Hitachi Chemical Co., Ltd .: SN-9000) or urethane (made by Nippon Polytech Co., Ltd .: NPR-3300) can be used, both of which are hardened by heating. is there.
After the solder resist printing, the solder resist is heated and cured. The heat curing conditions of the solder resist are heated to a temperature range of 100 ° C to 150 ° C.
After the solder resist curing process, it is completed as a flexible wiring board product. And if necessary, it is cut into a size that facilitates mounting of electronic components.

[12] Humidity management in manufacturing process of flexible wiring board Each of photoresist film forming process, exposure process, developing process, chemical etching process, tin plating process, solder resist film forming process in a series of processes for manufacturing flexible wiring board In this process, a long copper-clad laminate is conveyed by roll-to-roll. Since the processing speed of each process (the number of flexible wiring boards that can be processed per unit time) is different, the photoresist film forming process, exposure process, development process, chemical etching process, tin plating process, solder resist film forming process are separated. It is desirable to do this.

The manufacturing process of a flexible wiring board may be composed of a plurality of processes, and is often manufactured in a plurality of clean rooms. The photoresist film forming process, the exposure process, and the like are often performed in a separate clean room from the etching process and the like because of light shielding.
In this separate clean room, the humidity is not always uniform, and the humidity may vary depending on the location in the same clean room. Furthermore, the humidity of the atmosphere in which the copper clad laminate is placed may change when the copper clad laminate is moved to another clean room or in the clean room during the manufacturing process of the flexible wiring board.

On the other hand, the copper clad laminate expands and contracts when the humidity changes, and the dimensions fluctuate until a certain time elapses after the humidity changes. Such a dimensional variation stops when a certain time elapses, and the dimensional variation stops depending on the type of polyimide film.
From these facts, when the copper clad laminate is moved during the manufacturing process of the flexible wiring board, it is necessary to consider the dimensional variation of the copper clad laminate due to the humidity change before and after the movement.

  However, since the dimensional variation of the copper-clad laminate stops after a certain period of time, the copper-clad laminate may be left at the destination until the dimensional variation stops. At the destination, the copper-clad laminate has a constant dimensional change rate, so if it is processed in consideration of the dimensional change rate, it becomes possible to produce a flexible wiring board with little dimensional variation during mass production and high dimensional accuracy. .

  If the dimensional change rate of the copper-clad laminate is kept constant by leaving the copper-clad laminate for a certain period of time, it can be applied to a method of manufacturing a flexible wiring board. If the resist is heated and dried and left for a certain period of time under a certain humidity before proceeding to the next exposure step, the distance between the photoresist patterns will fluctuate due to the dimensional change (extension of dimensions) of the copper-clad laminate. As a result, the wiring pattern cannot be formed with good reproducibility.

  Also, if the copper clad laminate after humidity change is left at room temperature for a certain time or more, the dimensions of the copper clad laminate will not change, so the residence time between each step after heat treatment should be a certain time. It also means. This means that it is not necessary to hold the process for a long time in order to suppress the dimensional fluctuation of the copper clad laminate.

If the polyimide film of the copper-clad laminate contains an imide compound consisting of 4,4'-diaminodiphenyl ether and pyromellitic dianhydride, the standing time is increased every time the humidity changes within a range of ± 5 RH%. It should be more than time.
That is, 6 hours or more every time the humidity of the environment where the copper-clad laminate using the polyimide film containing the imide compound composed of 4,4′-diaminodiphenyl ether and pyromellitic dianhydride is changed by 5% If left untreated, the dimensional change of the copper clad laminate does not change with a constant dimensional change rate, and this humidity change is the same for humidification and dehumidification.
Further, if the humidity is changed by 10% RH, the dimensional change does not change with a constant dimensional change rate if the humidity is left for 12 hours, which is twice as high as the humidity change of 5 RH%.

In this way, if the dimensional change rate of the copper-clad laminate is stopped, if a photomask used in the exposure process is designed in consideration of the dimensional change rate, a finer wiring with a wiring pitch of 50 μm or less Since a flexible wiring board with high dimensional accuracy can be manufactured, it is possible to correct the alignment problem between the electronic component and the wiring pattern when connecting the electronic component.
In addition, the dimensional accuracy of the flexible wiring board can be increased if the dimensional variation of the copper-clad laminate is stopped even in the processes other than the photoresist film forming process and the exposure process.

  Up to now, the manufacturing method of the flexible wiring board according to the present invention has been described by taking the subtractive method as an example. However, the manufacturing method of the flexible wiring board of the present invention may be applied also when wiring processing is performed by the semi-additive method.

  The present invention will be further described below using examples.

  A long polyimide film “Kapton (registered trademark)” having a thickness of 35 μm containing an imide compound composed of 4,4′-diaminodiphenyl ether and pyromellitic dianhydride using the roll-to-roll sputtering apparatus 10 of FIG. )) A base metal layer made of a nickel-chromium alloy containing 20% by mass of chromium having a thickness of 25 nm on the surface of ENA, and a copper thin film layer having a thickness of 100 nm on the surface of the base metal layer, A resin film substrate with a copper thin film layer was obtained. The copper-clad laminate according to Example 1 is formed by forming a copper electroplating layer having a thickness of 8 μm on the surface of the copper thin film layer of the obtained resin film substrate with a copper thin film layer using the electroplating apparatus 20 of FIG. Was made.

The dimensional change rate in the MD direction (longitudinal direction of the copper-clad laminate) was measured for the obtained copper-clad laminate in accordance with Method A defined by the IPC-TM-650 2.2.4 standard.
Dimensional change measurement at 6 cm intervals in both directions so that the outer dimension of the sample is 20 cm × 16 cm in the MD direction × TD direction (width direction of the copper-clad laminate), and is approximately parallel to the MD direction and the TD direction of the sample. The measurement was performed in accordance with the same standard except that a position hole was opened and the dimensional change rate before and after the humidity change was measured.

  First, after the sample was left under a temperature of 23 ° C. and a humidity of 50% RH, the humidity was changed by 55% RH with the temperature kept constant, and the sample was left for 48 hours for the changed humidity. The dimensional change rate in the MD direction with respect to the humidity before 1, 3, 6, 9, 24, and 48 hours was measured. The results are shown in Table 1.

  The measurement was performed in the same manner as in Example 1 except that the humidity was changed from 55% RH to 60% HR. The results are shown in Table 1.

  The measurement was performed in the same manner as in Example 1 except that the humidity was changed from 60% RH to 65% HR. The results are shown in Table 1.

  The measurement was performed in the same manner as in Example 1 except that the humidity was changed from 65% RH to 60% HR. The results are shown in Table 1.

  Evaluation was performed in the same manner as in Example 1 except that “Kapton (registered trademark) ENC” was used as the polyimide film. The results are shown in Table 1.

  Evaluation was performed in the same manner as in Example 1 except that “Kapton (registered trademark) ENC” was used for the polyimide film and the humidity was changed from 55% RH to 60% HR. The results are shown in Table 1.

  Evaluation was performed in the same manner as in Example 1 except that “Kapton (registered trademark) ENC” was used for the polyimide film and the humidity was changed from 60% RH to 65% HR. The results are shown in Table 1.

  Evaluation was performed in the same manner as in Example 1 except that “Kapton (registered trademark) ENC” was used for the polyimide film and the humidity was changed from 65% RH to 60% HR. The results are shown in Table 1.

From Examples 1 to 8, it can be seen that if the humidity at which the sample is left is changed and left for 6 hours or longer, the dimensional change rate becomes constant. This suggests that if left for more than 6 hours, the dimensions of the copper clad laminate will not change further under that humidity.
From these results, immediately after changing the humidity around the copper-clad laminate within a range of ± 5% RH, the dimension of 0.002% is obtained for the chemically etched flexible wiring board and the chemically etched flexible wiring board after 6 hours. The difference will occur. In the case of a flexible wiring board having a width of 12 cm, the dimension is shifted by 2.4 μm. When the dimension is shifted by 2.4 μm, the flexible wiring board having a wiring pitch of 40 μm has a wiring width of 20 μm. Connection may be difficult.

F1 Resin film base material F2 Resin film base material with copper thin film layer S Two-layered copper clad laminate 1 Resin film base material 2 Underlying metal layer 3 Copper thin film layer 4 Copper electroplating layer 5 Copper layer 6 Copper clad laminate 10 Roll-to-roll sputtering apparatus 11a, 11b Free roll 12 Chamber 13 Unwind roll 14 Can roll 15a, 15b, 15c, 15d Sputtering cathode 16a Front feed roll 16b Rear feed roll 17a, 17b Tension roll 18 Winding roll 20 Roll / roll Two-roll electroplating apparatus 21 Electroplating tank 22 Unwinding roll 23 Reversing roll 24a-24t Anode 26a-26k Feeding roll 28 Plating liquid 28a Plating liquid surface 29 Winding roll

Claims (3)

In the method for producing a flexible wiring board, a wiring pattern is formed on a long two-layer copper-clad laminate in which a base metal layer and a copper layer are laminated without an adhesive on at least one surface of a long polyimide film.
The long polyimide film is a polyimide containing an imide bond composed of 4,4′-diaminodiphenyl ether and pyromellitic dianhydride,
When the humidity in the atmosphere in which the two-layer copper-clad laminate is exposed in the manufacturing process of the flexible wiring board changes in the range of ± 5% RH, after leaving in the changed humidity atmosphere for 6 hours or more, The manufacturing method of the flexible wiring board characterized by performing a process.   The method for manufacturing a flexible wiring board according to claim 1, wherein the base metal layer is formed by a dry plating method.   The method for producing a flexible wiring board according to claim 1, wherein the base metal layer is a nickel-chromium alloy having a thickness of 3 nm to 50 nm.

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