JP2016004844A - Method of manufacturing flexible wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a flexible wiring board that can suppress dimensional variation of a copper clad laminate by simple means under a heat treatment in a process of manufacturing the flexible wiring board from the copper clad laminate.SOLUTION: In a method of manufacturing a flexible wiring board which subjects a copper clad laminate 6 on wiring processing, an elongated polyimide film contains imide bonds comprising aromatic diamine and 3,3'-4,4-diphenyltetracarboxylic acid dianhydride, and a heat treatment is executed at a temperature from 100°C to 150°C while applying tension to an elongated copper clad laminate in a longitudinal direction thereof when wiring processing is executed, and then the copper clad laminate which is cooled to the room temperature is left for 24 hours or more.

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 etchant 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 resist film having an opening in the shape of a wiring on the surface of the copper layer, a copper plating layer is provided on the opening of the copper layer to a necessary film thickness as a wiring, and a copper plating layer is provided. After the removal, 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.

  As described above, in the process of manufacturing the flexible wiring board, heat such as curing of the solder resist is applied to the copper-clad laminate. The copper-clad laminate is a laminate of a copper layer and a resin film layer. In addition, both the copper layer and the resin film layer undergo thermal expansion and contraction due to heat, and dimensional fluctuation due to 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 layer that can be peeled off, and then a circuit pattern is formed on the surface where the reinforcing plate is not bonded, and then the flexible plate is formed. A technology of a circuit board manufacturing method 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 provides a method for manufacturing a flexible wiring board in which dimensional variation can be suppressed by simple means by heat treatment in the process of manufacturing a flexible wiring board from a copper-clad laminate.

  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 producing a flexible wiring board, the long polyimide film is a polyimide containing an imide bond composed of an aromatic diamine and 3,3′-4,4-diphenyltetracarboxylic dianhydride, After performing heat treatment at 100 ° C. to 150 ° C. while applying tension in the longitudinal direction of the long copper clad laminate during wiring processing, the copper clad laminate cooled to room temperature is allowed to stand for 24 hours or more and then It is a manufacturing method of the flexible wiring board characterized by performing processing.

  A second invention of the present invention is a method for producing a flexible wiring board, wherein the base metal layer in the first invention 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.

  A fourth invention of the present invention is a method for producing a flexible wiring board, wherein the heat treatment in the first to third inventions is a step of drying the photoresist.

  According to a fifth aspect of the present invention, there is provided the method for manufacturing a flexible wiring board, wherein the heat treatment in the first to third aspects is a step of curing the solder resist.

  According to the present invention, even with a flexible wiring board with a fine 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. Become.

It is typical sectional drawing 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 layer” in which a copper-clad laminate (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 are directly joined. Alternatively, 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 1 μm or less is desirable because it causes a problem of lowering productivity.

  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 composed of an aromatic diamine and 3, 3 It is necessary to contain an imide compound comprising '-4,4-diphenyltetracarboxylic dianhydride. Examples of the aromatic diamine include diaminobenzene such as paraphenylenediamine.
“Upilex (registered trademark, manufactured by Ube Industries)” is known as a polyimide film having an imide bond. “Upilex®” 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.

[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 deposited to obtain a two-layer copper clad laminate metalizing substrate. The obtained 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 thus formed photoresist pattern as a mask, the exposed copper layer is etched to form a wiring pattern composed of a copper layer having a shape substantially similar to the photoresist pattern and a base metal layer. 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. When the liquid photoresist is heated and dried, the copper clad laminate is also subjected to heat treatment to which heat is applied. 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. Even in the solder resist heat curing, the copper clad laminate is subjected to heat treatment.
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] Heat treatment in manufacturing process of flexible wiring board In each process of a photoresist film forming process, an exposure process, a chemical etching process, a tin plating process, and a solder resist film forming process in a series of processes for manufacturing a flexible wiring board, A long copper-clad laminate is conveyed by roll-to-roll. Since it is conveyed by roll-to-roll and subjected to heat treatment, tension is applied to the copper-clad laminate in the longitudinal direction (MD direction). Moreover, if it does not convey, applying a tension | tensile_strength, a copper clad laminated board will deform | transform by heat processing.

  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, the exposure process, the chemical etching process, the tin plating process, and the solder resist film forming process can be performed separately. desirable.

  In the photoresist film forming step and the solder resist film forming step, heat treatment such as heat drying of the photoresist and heat hardening of the solder resist is performed, so that heat treatment is also applied to the copper clad laminate. If the copper clad laminate heated to 120 ° C. is left at room temperature for 20 minutes after heating, the temperature will drop to room temperature (eg, 20 ° C. to 25 ° C.). As a result of earnest research, the inventor has found that, even after the heat treatment, even if the copper-clad laminate is lowered to room temperature, the dimensional variation is not constant unless it is left at room temperature for a certain time or more. That is, after heat treatment, the dimensions of the copper clad laminate tend to increase, but if left for a certain period of time, the dimensional change rate becomes constant, and the heat treatment does not further increase the dimension of the copper clad laminate. It means that the fluctuation stops at a certain rate of growth. Furthermore, the inventor has also found that the time during which the dimensional change rate is constant varies depending on the type of polyimide film.

  If the copper-clad laminate is heat-treated, lowered to room temperature, and then allowed to stand for a certain period of time, the dimensional change rate of the copper-clad laminate becomes constant. In the photoresist film forming process, after the photoresist is heated and dried, it is left for a certain period of time and then does not proceed to the next exposure process. The wiring pattern cannot be formed with good reproducibility.

  In addition, if the copper clad laminate after heat treatment is allowed to stand at room temperature for a certain time or longer, the copper clad laminate will not be stretched any further by the heat treatment. It also means that it should be. 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 an aromatic diamine and 3,3′-4,4-diphenyltetracarboxylic dianhydride, heat treatment is performed at a temperature range of 100 ° C. to 150 ° C. The remaining time of the subsequent copper-clad laminate at room temperature may be 24 hours or more. That is, a copper clad laminate using a polyimide film containing an imide compound composed of an aromatic diamine and 3,3′-4,4-diphenyltetracarboxylic dianhydride is heat-treated at a temperature range of 100 ° C. to 150 ° C. After that, if left at room temperature for 24 hours or more, the dimensional elongation of the copper clad laminate does not change with a constant dimensional change rate.

  Here, the heat treatment temperature in the method for producing a flexible wiring board according to the present invention is set to 100 ° C. to 150 ° C. The recommended drying temperature range of the liquid photoresist generally used in the production process of the flexible wiring board, Depending on the recommended curing temperature range of the solder resist. Further, since there is no influence of the heat treatment holding time, the heat treatment time necessary for each step may be selected as appropriate. The heat treatment holding time is not specified because the dimensional change of the copper clad laminate after the heat treatment is caused by the expansion and contraction of the copper clad laminate that is exposed to the heat treatment temperature and cooled to room temperature. It is considered that the relaxation of the stress is the elongation of the dimensions of the copper clad laminate when left at room temperature. In addition, what is necessary is just to add tension | tensile_strength suitably in the range by which a wrinkle does not arise in a copper clad laminated board by heat processing.

If it stops at a certain dimensional change rate of the copper-clad laminate, if a photomask used in the exposure process is designed in consideration of the dimensional change rate, it can be applied to a miniaturized wiring pattern with a wiring pitch of 50 μm or less. Since it is possible to produce a flexible wiring board that can cope with the dimensional accuracy, it is possible to correct the problem of alignment 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 having a thickness of 35 μm containing an imide compound comprising an aromatic diamine and 3,3′-4,4-diphenyltetracarboxylic dianhydride using the roll-to-roll sputtering apparatus 10 of FIG. A base metal layer made of a Ni—Cr alloy containing 20 wt% Cr having a thickness of 25 nm is formed on the surface of “UPILEX (registered trademark) V1”, and a copper thin film layer having a thickness of 100 nm is formed on the surface of the base metal layer. Filming was performed to obtain a resin film substrate with a copper thin film layer. 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 the MD direction of the sample and the TD direction are substantially parallel Opening a position hole, holding the heat load condition in air at 120 ° C. for 5 minutes, applying a 9N tension in the MD direction of the sample (longitudinal direction of the copper clad laminate), After the heat treatment, the sample was left to cool for 20 minutes under a temperature of 23 ° C. and a humidity of 50% RH, and then further left to stand under a temperature of 23 ° C. and a humidity of 50% RH for 1 hour, 3 hours, and 6 hours. The measurement was performed in accordance with the same standard except that the dimensional change rate was measured after 24 hours, 48 hours, and 72 hours after cooling in the MD direction. The results are shown in Table 1.

The copper clad laminate produced in Example 1 was cut so that the outer dimension was MD direction × TD direction (width direction of the copper clad laminate) was 20 cm × 16 cm, similar to the sample used in Example 1. An evaluation substrate according to Example 2 in which a position hole for change measurement was formed was produced.
A liquid photoresist was spin-coated on the evaluation substrate, applied with tension as in Example 1, and dried in an oven at 110 ° C. for 15 minutes in the atmosphere. After taking out from the oven, it is left to cool under a temperature of 23 ° C. and a humidity of 50% RH, and after being cooled, the standing time after 24 hours is parallel to the TD direction and 20 μm pitch between the position holes for measuring the dimensional change in the MD direction (wiring) The exposure was performed with a photomask in which stripes of 20 μm and spaces of 20 μm were formed.
Immediately after cooling and after exposure, the dimension of the position hole for dimensional change measurement was measured, and the dimensional change rate was determined. As a result, the dimensional change rate was 0.004%.

Etching was carried out in the same manner as in Example 2 except that the standing time was 72 hours, and a test piece of Example 3 was produced.
When the dimensional change rate immediately after cooling the interval in the MD direction and after exposure was measured, the dimensional change rate of the position hole for measuring the dimensional change was 0.004%.

(Comparative Example 1)
Etching was performed in the same manner as in Example 2 except that the standing time was 6 hours, and a test piece according to Comparative Example 1 was produced.
When the dimensional change rate immediately after cooling the interval in the MD direction and after exposure was measured, the dimensional change rate of the position hole for measuring the dimensional change was 0.002%.

  From Table 1 showing the measurement results of Example 1, it can be seen that the dimensional change rate before heat treatment becomes constant when left at room temperature for 24 hours or more after heat treatment. This means that the dimensional variation stops if left at room temperature for 24 hours or more.

Further, comparing Example 2 with a standing time of 24 hours and Comparative Example 1 with a standing time of 6 hours, Comparative Example 1 has a narrower distance between position holes for measuring the dimensional change in the MD direction by 2.4 μm than Example 2. I understand that.
Such a difference in dimensional change is that when a sample with a different standing time in actual operation moves to the next process, the wiring will be processed with the dimension different, and dimensional accuracy at the time of flexible wiring board production cannot be secured, As a result, it is suggested that there is a high possibility of causing poor connection with electronic components.
In addition, if the dimensional elongation of the wiring is controlled to be constant during mass production, the wiring pattern may be designed in consideration of the dimensional elongation.

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 (5)

In the method for producing a flexible wiring board, in which a long two-layer copper-clad laminate in which a base metal layer and a copper layer are laminated without using 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 an aromatic diamine and 3,3′-4,4-diphenyltetracarboxylic dianhydride,
After performing heat treatment at 100 ° C. to 150 ° C. while applying tension in the longitudinal direction of the long copper clad laminate during wiring processing, the copper clad laminate cooled to room temperature is allowed to stand for 24 hours or more and then 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.   The method of manufacturing a flexible wiring board according to claim 1, wherein the heat treatment is a step of drying the photoresist.   The method for manufacturing a flexible wiring board according to claim 1, wherein the heat treatment is a step of curing the solder resist.

Images