JP6236824B2 - Method for manufacturing printed wiring board - Google Patents

Description

  The present invention relates to a method for manufacturing a printed wiring board, and more particularly to a method for manufacturing a printed wiring board in which undercut is suppressed.

  A printed wiring board in which a wiring pattern is formed on an insulating substrate is widely used for mounting electronic components, semiconductor elements, and the like. With recent demands for downsizing and higher functionality of electronic devices, printed circuit boards are desired to have finer wiring patterns.

  As a wiring pattern forming method, there are a subtractive method, a semi-additive method, and the like. Among these, the semi-additive construction method is used for manufacturing a printed wiring board having a fine wiring pattern because a finer wiring pattern can be formed.

  In the semi-additive construction method, for example, a printed wiring board is manufactured as follows. That is, a base layer such as nickel or Ni—Cr is formed on the surface of the substrate by electroless plating or sputtering. Next, a resist is formed on the underlayer, exposed and developed to form a plating resist layer. Next, electrolytic copper plating is performed to form a copper wiring layer in a portion not covered with the plating resist. Next, the plating resist is peeled and removed, and an unnecessary underlayer between the copper wiring layers is removed by etching. In this way, a printed wiring board is manufactured.

  In the semi-additive method, when the underlayer that is no longer needed is etched away, only the underlayer is selectively used using an etching solution that does not erode the copper wiring layer, as described in Patent Documents 1 and 2. Etching and removal have been conventionally performed.

JP 2001-140084 JP 2003-31927 A

  However, when the wiring pattern is formed by the semi-additive method, when the underlayer that has become unnecessary is removed by etching, conventionally, only the underlayer has been selectively removed by etching, as shown in FIG. Erosion also progressed to the underlayer 2 directly below the copper wiring layer 4, so that the so-called undercut phenomenon in which the line width of the underlayer 2 narrows easily occurred.

  In addition, as the wiring pattern becomes finer, the adhesion between the substrate and the underlayer tends to decrease. For this reason, when using a resin substrate such as a polyimide film as the substrate, the metal component is deposited to a certain depth with respect to the surface of the resin substrate to develop an anchor effect and improve the adhesion between the base layer and the substrate. Has been done. However, when metal components are deposited to a certain depth on the surface of the resin substrate, in order to ensure the insulation reliability of the printed wiring board, the base layer is usually etched when the base layer that has become unnecessary is removed by etching. It was necessary to process more strongly. For this reason, when a fine wiring pattern is formed on the resin substrate, there is a tendency for the possibility of undercut to be further increased.

  When the undercut occurs, the adhesion surface between the substrate and the underlayer is reduced, so that the wiring is easily peeled off from the substrate, and the adhesion reliability is lowered. Further, in the case where an insulating layer is formed as a protective film after the wiring pattern is formed, the insulating layer may not be sufficiently covered on the portion where the undercut occurs, which may reduce the insulation reliability.

  Accordingly, an object of the present invention is to provide a method for manufacturing a printed wiring board that suppresses the occurrence of undercutting in a base layer.

In order to achieve the above object, a method for manufacturing a printed wiring board of the present invention includes:
Step 1 of forming a metal plating layer composed of a metal other than copper by electroless plating on at least one surface of the polyimide film, and forming a base layer including the metal plating layer;
Step 2 of forming a plating resist on a part of the underlayer;
Step 3 of forming a copper wiring layer on the base layer portion not covered with the plating resist by electrolytic copper plating;
Step 4 of peeling and removing the plating resist from the underlayer;
And a step 5 for removing the exposed underlayer by peeling off the plating resist, and a method for manufacturing a printed wiring board,
In the step 5, the underlayer is etched away using an etchant having an etching ability with respect to copper and the metal constituting the metal plating layer, and the side surfaces of the copper wiring layer are simultaneously etched. It is characterized by.

  In the method for manufacturing a printed wiring board according to the present invention, as the etching solution, a rate ratio between an etching rate with respect to a metal constituting the metal plating layer and an etching rate with respect to copper is a metal constituting the metal plating layer: copper = 1. : It is preferable to use what is 0.9-10.

  In the method for producing a printed wiring board according to the present invention, it is preferable that the metal plating layer is a nickel plating layer and the etching solution has an etching ability with respect to copper and nickel.

  In the method for manufacturing a printed wiring board of the present invention, it is preferable to use a material containing sulfuric acid, nitric acid, and hydrogen peroxide as the etching solution.

  In the method for manufacturing a printed wiring board according to the present invention, the thickness of the copper wiring layer when forming the copper wiring layer in step 3 is preferably 1 to 20 μm.

  In the printed wiring board manufacturing method of the present invention, it is preferable that the undercut rate of the underlayer after etching is 0 to 10%, and the width reduction amount of the copper wiring is 0.2 to 5 μm.

  In the method for manufacturing a printed wiring board of the present invention, in the step 1, a base layer may be formed by forming a thin copper layer on the metal plating layer. Thereby, the influence of the resistance of a base layer can be reduced at the time of the electrolytic copper plating in the process 3. In this embodiment, the thickness of the thin copper layer is preferably 0.1 to 1 μm because a sufficient current can be easily secured and subsequent removal is easy.

  According to the method for manufacturing a printed wiring board of the present invention, an etching solution having an etching ability with respect to copper and a metal constituting the metal plating layer is used for the base layer exposed by peeling and removing the plating resist from the base layer. Etching and etching the side surfaces of the copper wiring layer at the same time, there is no or very small shape defect such as undercut, and the line width of the copper wiring layer and the line width of the underlying layer beneath it are Almost equal and substantially rectangular wiring can be formed.

It is a schematic process drawing of the manufacturing method of the printed wiring board of the present invention. It is the schematic which shows the generation | occurrence | production state of an undercut. It is a figure which shows the etching rate with respect to nickel of the etching liquid 1, and the etching rate with respect to copper. It is a figure which shows the etching rate with respect to nickel of the etching liquid 4, and the etching rate with respect to copper.

  An embodiment of a method for producing a printed wiring board of the present invention will be described with reference to FIG.

  First, as shown in FIG. 1 (a), a metal plating layer composed of a metal other than copper is formed on at least one surface of the polyimide film 1 by electroless plating, and an underlayer 2 including the metal plating layer is formed. Form (step 1). By forming a metal plating layer on the surface of the polyimide film by electroless plating, the adhesion between the polyimide film and the metal plating layer is improved, and the circuit (copper plating layer) of the printed wiring board is subjected to a long-term thermal load. It is possible to prevent diffusion and migration of copper to the polyimide film side, which causes a decrease in adhesive strength.

  The polyimide film 1 can be manufactured by a conventionally known method. For example, a polyimide precursor solution containing a polyamic acid and an organic solvent is cast on a support and dried to form a self-supporting film having self-supporting properties. It can be manufactured with complete conversion.

  As the polyimide film 1, a commercially available polyimide film that can be suitably used for various substrates such as a wiring substrate can be used.

Linear expansion coefficient of the polyimide film 1 (50 to 200 ° C.) is preferably close to the linear expansion coefficient of copper to be laminated to the polyimide ^{film, 0.3 × 10 -5 ~2.8 × 10} -5 cm / cm / More preferably, it is ° C.

  As the polyimide film 1, a film having a heat shrinkage rate of 0.05% or less, a small thermal deformation, and excellent heat resistance, electrical insulation and the like can be suitably used.

  As the polyimide film 1, a single layer, a multilayer film in which two or more layers are laminated, or a sheet-like one can be used.

  The thickness of the polyimide film 1 is not particularly limited as long as it can be manufactured and handled without problems and can sufficiently support the metal layer and the wiring pattern layer to be formed. Preferably it is 1-500 micrometers, More preferably, it is 2-300 micrometers, More preferably, it is 5-200 micrometers, Especially preferably, it is 5-175 micrometers, Most preferably, it is 5-100 micrometers.

  Electroless plating can be performed using a conventionally known method. For example, there is an elf seed process manufactured by Sugawara Eugelite Co., Ltd., an SLP process manufactured by Okuno Pharmaceutical Co., Ltd., and the like. The metal plating layer formed by electroless plating may be a pure metal film, but may contain other components such as phosphorus in order to control the film quality.

  The kind of metal used for electroless plating is a metal other than copper, and any film can be formed on the polyimide film by electroless plating without any particular limitation. For example, nickel, tin, silver, cobalt, an indium compound, these alloys, etc. are mentioned. Preferably, it is nickel or a nickel alloy. Nickel and nickel alloy are easy to remove from the underlying layer by uniform etching, the coating of the metal plating layer is stable, easy adhesion strength to the copper wiring layer, relatively good conductivity, and from the copper wiring layer High barrier property against diffusion of copper into polyimide film. Furthermore, nickel and nickel alloys have a high level of electroless plating technology, and various processes are widespread, making it easy to select processes appropriately.

  As an example of a method for producing a metal plating layer laminated polyimide film in which a metal plating layer is laminated on a polyimide film, the polyimide film is treated with an acid solution containing at least a surfactant or an alkaline degreasing solution, and treated with an alkaline solution. Examples of the method include a step, a step of treating with a basic amino acid solution, a step of applying a catalyst, a step of forming a metal plating layer by electroless plating, and a step of heating in this order.

  The above steps will be described in detail below.

  1) In the step of washing with an acid or alkaline degreasing solution containing a surfactant, the surface of the polyimide film is treated with a degreasing solution having a cleaning effect in order to remove oil components on the surface of the polyimide film. For example, in an alkaline solution containing a surfactant such as polyoxyethylene alkyl ether or dipropylene glycol monomethyl ether, sodium hydroxide, monoethanolamine, etc. An example is a method of removing dirt and washing the polyimide film.

  2) In the step of treating with an alkaline solution, the surface of the polyimide film is treated by spraying or immersing the surface of the polyimide film on the alkaline solution. Examples of the alkaline solution include a solution containing potassium hydroxide, sodium hydroxide and the like. For example, a method of immersing in an alkaline aqueous solution containing 10 to 200 g / l of potassium hydroxide or sodium hydroxide at 25 to 80 ° C. for 10 seconds to 10 minutes is an example.

  3) In the step of treating with the basic amino acid solution, the surface of the polyimide film is brought into contact with the basic solution containing the amino acid by a method such as spraying or dipping. For example, a method of immersion treatment at 30 to 60 ° C. for 10 seconds to 10 minutes with an aqueous solution containing 30 to 300 g / l of lysine hydrochloride or arginine hydrochloride adjusted to pH 6 with potassium hydroxide is given as an example. .

  4) In the step of applying a catalyst, in order to form nuclei for electroless base metal precipitation on the surface of the polyimide film, the catalyst is applied to a part or all of the surface of the polyimide film by a method such as adsorption. For example, a method in which palladium ions are adsorbed on the surface of a polyimide film by immersing in an ionic palladium catalyst solution at 30 to 60 ° C. for 1 to 10 minutes, and then immersed in a reducing solution to reduce palladium ions to metallic palladium. Is given as an example.

  5) In the step of forming the metal plating layer, metal is deposited by an electroless plating method to form the metal plating layer. For example, when a nickel plating layer is formed by electroless plating, the nickel plating layer is immersed in a commercially available electroless nickel plating bath at 25 to 45 ° C. for 2 to 20 minutes. Can be formed. In the case of other metals, they can be formed in the same manner.

  The film thickness of the metal plating layer varies depending on the type of metal. For example, in the case of a nickel plating layer, the film thickness is not particularly limited as long as sufficient adhesion is obtained and can be removed later, but it is preferably more than 0.1 μm and 0.3 μm or less. The thickness is more preferably 0.11 μm to 0.28 μm, and more preferably 0.12 μm to 0.27 μm. If the thickness of the nickel plating layer is less than 0.1 μm, it is impossible to prevent diffusion migration of copper to the polyimide film side during a long-term heat load, so that it is possible to suppress a decrease in adhesion strength during a long-term heat load. It can be difficult. That is, it may be difficult to ensure the adhesion between the nickel plating layer and the polyimide film that can withstand both a long-term heat load and a high-temperature heat load. Moreover, when the film thickness of a nickel plating layer exceeds 0.3 micrometer, the adhesiveness of a nickel plating layer and a polyimide film may fall by the heat processing before formation of the copper wiring layer 4 after nickel plating layer formation.

  Moreover, when forming the copper wiring layer 4 described later, in order to efficiently perform electrolytic copper plating, a thin copper layer is formed on the metal plating layer by electrolytic copper plating, electroless copper plating, sputtering, or the like. Also good. That is, the foundation layer 2 may be composed of a lower layer made of a metal plating layer formed by electroless plating of a metal other than copper and an upper layer made of a thin copper layer.

  When the underlayer 2 is composed of a lower layer made of a metal plating layer and an upper layer made of a thin copper layer, the thickness of the thin copper layer is preferably 0.1 to 1.0 μm. If the thickness of the thin copper layer is less than 0.1 μm, the effect of forming the thin copper layer may be hardly obtained. On the other hand, if the thickness of the thin copper layer exceeds 1.0 μm, it takes time to remove the underlayer by etching, and it tends to be difficult to form a fine wiring pattern.

  Next, as shown in FIG. 1B, a resist is formed on the underlayer 2 and exposed, and the resist in a portion that becomes a wiring pattern is developed and removed to form a plating resist 3 (step 2).

  In the present invention, in step 5 to be described later, the base layer 2 is removed by etching using an etchant having an etching ability for copper and the metal constituting the metal plating layer, and the side surface of the copper wiring layer 4 is simultaneously removed. Etch. For this reason, since the line width of the copper wiring layer is reduced in step 5, the length of the copper wiring layer obtained in step 3 is the length corresponding to the amount of reduction in the line width of the copper wiring layer 4 in step 5. It is preferable to form the plating resist 3 so as to increase the width.

  The resist type can be negative or positive. In the case of a negative resist, parts other than the exposed part are removed by development. On the other hand, in the case of a positive resist, the exposed portion is removed by development.

  The method for forming the resist is not particularly limited, and can be performed by a conventionally known method. For example, a method of heat laminating a film-like resist material, a method of applying a liquid type resist material, and drying are exemplified. After forming the resist, exposure is performed through a photomask according to a conventional method.

  The method for developing and removing the resist is not particularly limited and can be performed by a conventionally known method. For example, a method of spraying a developing solution such as a sodium carbonate aqueous solution to develop and remove the resist in a portion that becomes a wiring pattern. Note that the plating resist pattern may be formed by printing or transferring except for a portion to be a wiring.

  Next, as shown in FIG. 1C, a copper wiring layer 4 is formed by electrolytic plating between the plating resists 3, 3, that is, the exposed base portion (step 3).

The electrolytic plating conditions are not particularly limited. Known conditions can be selected as appropriate. For example, the exposed portion of the underlayer 2 is washed with an acid or the like, and electrolytic copper plating is performed at a current density of 0.1 to 10 A / dm ² using copper as a cathode electrode in a solution containing copper sulfate. Thus, the copper wiring layer 4 can be formed. As the plating solution, for example, copper sulfate 180 to 240 g / l, sulfuric acid 45 to 60 g / l, chlorine ions 20 to 80 g / l, and additives can be used. Examples of the additive include thiourea, dextrin, molasses and the like. The thickness of the copper wiring layer 4 may be any thickness, but is preferably 1 to 20 μm.

  Next, as shown in FIG. 1D, the plating resist 3 is peeled off from the underlayer 2 (step 4).

  The peeling removal method of the plating resist 3 is not particularly limited, and can be performed by a conventionally known method. For example, the resist layer can be peeled and removed by spraying an aqueous caustic soda solution (2% by mass or the like).

  Next, as shown in FIG. 1 (e), the plating resist 3 is peeled off and the underlying layer 2 exposed is removed by etching (step 5).

  In the present invention, in step 5, the base layer 2 is removed by etching using an etchant having an etching ability for copper and the metal constituting the metal plating layer, and the side surface of the copper wiring layer 4 is simultaneously etched. To do.

  Conventionally, when the underlayer 2 that has become unnecessary is removed by etching, for example, in the case where the underlayer 2 is made of only a nickel plating layer, an etching solution that selectively etches only nickel is used. Were selectively removed by etching. In the case where the underlayer 2 is composed of an upper layer made of a thin copper layer and a lower layer made of a nickel plating layer, first, using an etching solution that selectively etches only the upper thin copper layer, The copper layer was selectively removed by etching, and then the nickel layer was selectively removed by etching using an etchant that selectively etches only the lower nickel plating layer.

  However, when the nickel plating layer is selectively removed by etching using an etchant that selectively etches only nickel, as shown in FIG. 2, erosion also proceeds to the underlying layer 2 immediately below the copper wiring layer 4. Therefore, the undercut of the underlayer 2 was easy to occur. In particular, when a metal plating layer composed of a metal such as nickel is formed on a resin substrate such as a polyimide film by electroless plating, the metal component diffuses to the inside of the resin substrate. It was necessary to strongly etch the plating layer, and undercut was more likely to occur.

  In the present invention, the base layer 2 is etched away using an etchant having an etching ability with respect to copper and the metal constituting the metal plating layer, and the side surface of the copper wiring layer 4 is simultaneously etched. A substantially rectangular wiring in which the line width W2 of the copper wiring layer 4 is almost equal to the line width W3 of the underlying layer 2 under the copper wiring layer 4 can be formed.

  The mechanism by which the underlayer 2 and the side surface of the copper wiring layer 4 are etched simultaneously is not necessarily clear, but the progress of etching in the line width direction of the underlayer and the progress of etching of the side surface of the copper wiring layer are constant. Estimated to be progressing at a rate. Since the etching of the copper wiring layer does not progress too quickly, the copper wiring layer does not become too thin. Thereby, the printed wiring board of fine wiring can be created.

  Since the underlayer 2 is removed by etching and the side surfaces of the copper wiring layer 4 are simultaneously etched, the line width W2 of the copper wiring layer 4 after etching is shorter than the line width W1 of the copper wiring layer before etching. . However, since the film thickness of the underlayer 2 is extremely thin compared to the film thickness of the copper wiring layer 4, the amount of reduction in the line width of the copper wiring layer 4 is extremely small, and the line width of the copper wiring layer 4 before the etching process is reduced. Can be solved by thickening in advance.

  The line width W2 of the copper wiring layer 4 after etching is, for example, 5 to 25 μm. Furthermore, the line width of the foundation layer 2 located between the substrate 1 after etching and the copper wiring layer 4 is, for example, 4.5 to 22.5 μm. The undercut rate in the present invention is preferably 0 to 10%, and more preferably 0 to 5%. Here, the undercut rate is defined by the following equation.

  Undercut rate (%) = ((line width of the etched copper wiring layer 4) − (line width of the underlying layer 2 after etching)) / (line width of the etched copper wiring layer 4) × 100

  The line width of the copper wiring layer 4 after etching referred to here is the line width of the bottom portion of the copper wiring layer 4.

  Moreover, 0.2-5 micrometers is preferable and, as for the width reduction amount of the copper wiring layer after an etching, 0.3-3 micrometers is more preferable. The amount of reduction in the width of the copper wiring layer referred to here is a value obtained by subtracting the line width of the bottom portion of the copper wiring layer after etching from the line width of the bottom portion of the copper wiring layer before etching.

  In the present invention, the rate ratio between the etching rate of the etching solution for the metal constituting the metal plating layer and the etching rate for copper is preferably metal: copper = 1: 0.9 to 10 constituting the metal plating layer, 1: 0.9 to 5 is more preferable, 1: 0.9 to 2 is particularly preferable, and 1: 1 to 2 is particularly preferable. If the speed ratio of the copper etching rate is less than 0.9, undercut tends to occur easily. If it exceeds 10, the top line width of the wiring becomes thinner than the bottom line width. It tends to be too much. In general, when the wiring becomes extremely thin, it is difficult to perform a sufficient flash etching process when forming a fine pitch, and the metal plating layer cannot be completely removed. Yes. If the ratio of the etching rates of the two is within the above range, undercut will not occur and the wiring will not be remarkably thin. Therefore, it is easy to remove the metal plating layer between the wiring in the case of fine pitch, and electric reliability High printed wiring board can be created. In particular, when the speed ratio is 1: 0.9 to 5, the top line width and the bottom line width of the wiring approach the same, and a wiring closer to a rectangle can be formed.

  Further, when the metal plating layer of the underlayer is a nickel plating layer, the rate ratio of the etching solution to the etching rate with respect to copper is preferably nickel: copper = 1: 0.9 to 10, preferably 1: 0.9 to 5 is more preferable, 1: 0.9 to 2 is particularly preferable, and 1: 1 to 2 is particularly preferable.

  In the present invention, the rate ratio between the etching rate of the etching solution for the metal constituting the metal plating layer and the etching rate for copper is a value measured by the following method.

  In other words, Sample A in which a 200 nm thick metal plating layer was formed by performing electroless plating treatment on a polyimide film, and Sample B in which a 10 μm thick metal copper layer was further formed on Sample A by electrolytic copper plating were prepared. Samples A and B were etched using an etching solution, and the etching rate for the metal constituting the metal plating layer and the etching rate for copper were calculated from the difference between the processing time and the thickness before and after the processing, and the rate ratio was calculated. Asked.

  In the present invention, any etching solution can be preferably used as long as it has an etching ability with respect to copper and the metal constituting the metal plating layer. For example, inorganic acid-hydrogen peroxide system, hydrogen peroxide-fluoride system, ferric chloride and the like can be mentioned. The composition of the etching solution and the like are appropriately adjusted depending on the type of metal constituting the metal plating layer.

  For example, when the metal plating layer is composed of a nickel plating layer, an etchant having an etching ability with respect to copper and nickel is used. Examples of the etching solution having etching ability with respect to copper and nickel include an inorganic acid-hydrogen peroxide etching solution containing an inorganic acid and hydrogen peroxide.

  Moreover, when a metal plating layer is comprised with a cobalt plating layer, what has an etching capability with respect to copper and cobalt is used as etching liquid. Examples of the etching solution having an etching ability for copper and cobalt include an inorganic acid-hydrogen peroxide etching solution containing an inorganic acid and hydrogen peroxide.

  Examples of the inorganic acid include sulfuric acid, nitric acid, phosphoric acid, boric acid and the like, and one or more of these can be used. Preferably, sulfuric acid and nitric acid are used in combination as inorganic acids. That is, in the present invention, a sulfuric acid-nitric acid-hydrogen peroxide etching solution containing sulfuric acid, nitric acid, and hydrogen peroxide is preferably used. A sulfuric acid-nitric acid-hydrogen peroxide etching solution has approximately the same etching rate for copper and nickel.

  In the inorganic acid-hydrogen peroxide etching solution, the hydrogen peroxide concentration is preferably 1 to 30% by mass, more preferably 5 to 20% by mass. If the hydrogen peroxide concentration is less than 1% by mass, a sufficient dissolution rate may not be obtained. If the hydrogen peroxide concentration exceeds 30% by mass, no further improvement in dissolution rate is obtained, which is economically undesirable.

  In the inorganic acid-hydrogen peroxide etching solution, the inorganic acid concentration is preferably 1 to 30% by mass, more preferably 8 to 25% by mass. If the inorganic acid concentration is less than 1% by mass, a sufficient dissolution rate may not be obtained. If the inorganic acid concentration exceeds 30% by mass, no further improvement in dissolution rate is obtained, which is economically undesirable. Moreover, when using together sulfuric acid and nitric acid as an inorganic acid, 0.01-1.0 mass% of sulfuric acid concentration is preferable, More preferably, it is 0.1-0.5 mass%. The nitric acid concentration is preferably 1 to 30% by mass, more preferably 5 to 20% by mass.

  The temperature during etching is preferably 10 to 60 ° C. The etching time is preferably 5 to 180 seconds. Examples of the etching means include an immersion type and a spray type. The spray pressure when the etching means is a spray type is preferably 0.01 to 0.3 MPa.

(Etching solution used)
Etching solution 1:
Etching solution 1 was prepared by mixing 6.84 ml of 95% sulfuric acid, 249.6 ml of 30% hydrogen peroxide, 495 ml of 60% nitric acid, and 3371 ml of pure water. This etching solution had an etching ability with respect to copper and nickel.

Etching solution 2:
An etching solution 2 was prepared by mixing 300 ml of 47% sulfuric acid, 1200 ml of ferric sulfate, 50 g of copper powder, and 3500 ml of pure water. This etching solution has an etching ability with respect to copper, but has substantially no etching ability with respect to nickel.

Etching solution 3:
Nickel selective etching solution (trade name “NC”, manufactured by Nippon Chemical Industry Co., Ltd.) was used as the etching solution 3. This etching solution has an etching ability with respect to nickel, but has substantially no etching ability with respect to copper.

Etching solution 4:
Etching solution 4 was prepared by mixing 6.84 ml of 95% sulfuric acid, 249.6 ml of 30% hydrogen peroxide, 145 ml of 60% nitric acid, and 3854 ml of pure water. This etching solution had an etching ability with respect to copper and nickel.

(Measurement method of etching rate ratio)
Sample A in which a 200-nm-thick nickel plating layer was formed by subjecting a polyimide film (trade name “UPILEX 25SGA” manufactured by Ube Industries) to electroless nickel plating; Sample B in which a layer was formed was prepared.
The samples A and B were etched using etchings 1 and 4, and the etching rate with respect to nickel and the etching rate with respect to copper were calculated from the difference between the processing time and the thickness before and after the processing, and the rate ratio was obtained.

  The rate ratio between the etching rate of the etching solution 1 for nickel and the etching rate for copper was nickel: copper = 1: 1.11. Moreover, the rate ratio of the etching rate with respect to the nickel of the etching liquid 4 and the etching rate with respect to copper was nickel: copper = 1: 4.17.

  FIG. 3 shows the etching rate for nickel and the etching rate for copper of the etching solution 1, and FIG. 4 shows the etching rate for nickel and the etching rate for copper of the etching solution 4.

Example 1
A polyimide film (trade name “UPILEX 25SGA” manufactured by Ube Industries, Ltd.) was subjected to electroless nickel plating by an elf seed process (manufactured by Ebara Eugelite) to form a nickel plating layer having a thickness of 0.13 μm. Next, electrolytic copper plating was performed to form a thin copper layer having a thickness of 0.45 μm on the nickel plating layer, and a base layer composed of a nickel plating layer (lower layer) and a thin copper layer (upper layer) was formed.
Next, a resist was formed on the underlayer, exposed, and the resist at the site that became the wiring pattern was developed and removed to form a plating resist.
Next, electrolytic copper plating was performed to form a copper wiring layer having a line width of 17.5 μm and a thickness of 9 μm at a pitch of 30 μm on the exposed base layer between the plating resists.
Next, the plating resist was peeled off from the underlayer.
Then, using the etching solution 1, spray treatment was performed at 30 ° C. for 20 seconds at a spray pressure of 0.05 MPa to remove the underlayer by etching, and the side surfaces of the copper wiring layer were simultaneously etched to manufacture a printed wiring board.
The line width of the copper wiring layer after the etching process was 13 μm, the line width of the underlying layer immediately below the copper wiring layer was 13 μm, and there was no undercut (the undercut rate was 0%, and the width reduction amount of the copper wiring was 4.5 μm). In addition, the line width of the copper wiring layer decreased before and after the etching process, but the amount of decrease was very small, so that there was no problem in product characteristics.
In addition, in the electrical insulation reliability test, which is a test for confirming the insulation reliability in a state where a comb tooth pattern of 25 μmP is created and a voltage of 52 V is applied under the conditions of 85 ° C. and 85% Rh, from 10 12 A high resistance value of 13th power could be maintained for 1000 hours.

(Example 2)
An electroless nickel plating was performed on a polyimide film (trade name “UPILEX 25SGA” manufactured by Ube Industries) by an elf seed process (manufactured by Ebara Eugelite) to form a nickel plating layer having a thickness of 0.13 μm to form a base layer. .
Next, a resist was formed on the underlayer, exposed, and the resist at the site that became the wiring pattern was developed and removed to form a plating resist.
Next, electrolytic copper plating was performed to form a copper wiring layer having a line width of 17.5 μm and a thickness of 9 μm at a pitch of 30 μm on the exposed base layer between the plating resists.
Next, the plating resist was peeled off from the underlayer and annealed at 150 ° C. for 1 hour.
Then, using the etching solution 1, spray treatment was performed at 30 ° C. for 10 seconds at a spray pressure of 0.05 MPa to remove the underlying layer, and the side surface of the copper wiring layer was simultaneously etched to manufacture a printed wiring board.
The line width of the copper wiring layer after the etching process was 14 μm, the line width of the underlying layer immediately below the copper wiring layer was 14 μm, and there was no undercut (the undercut rate was 0%, and the amount of decrease in the width of the copper wiring was 3.5 μm). In addition, the line width of the copper wiring layer decreased before and after the etching process, but the amount of decrease was very small, so that there was no problem in product characteristics.

(Example 3)
In Example 1, when the exposed underlayer was removed by etching, the underlayer was etched by using the etchant 4 instead of the etchant 1 and spraying at 30 ° C. for 10 seconds with a spray pressure of 0.05 MPa. While removing, the side surface of the copper wiring layer was simultaneously etched to produce a printed wiring board.
As for the line width of the copper wiring layer after the etching treatment, the top line width was 16 μm and the bottom line width was 17 μm. Further, the line width of the underlayer immediately below the copper wiring layer was 17 μm, and there was no undercut (undercut rate was 0%, and the width reduction amount of the copper wiring was 1.5 μm).

(Comparative Example 1)
In Example 1, when the exposed underlayer was removed by etching, two-stage etching was performed using the etching solutions 2 and 3 instead of the etching solution 1. That is, first, the thin copper layer in the upper layer portion of the base layer was removed by etching using the etching solution 2 by spraying at 30 ° C. for 8 seconds with a spray pressure of 0.05 MPa. Next, the printed wiring board was manufactured by immersing in an etching solution 3 maintained at 50 ° C. for 60 seconds, performing manual rocking and stirring with a stirrer, and removing the nickel plating layer in the lower layer portion of the underlying layer by etching.
The line width of the copper wiring layer before the etching process was 16 μm, the line width of the copper wiring layer after the etching process was 14.5 μm, and the width of the underlying layer immediately below the copper wiring layer was 11 μm. There was no reduction in the line width of the copper wiring layer before and after the etching process, but an undercut of the underlayer occurred. The undercut rate was as large as 24%, and the width reduction amount of the copper wiring was 1.5 μm.

1: Polyimide film 2: Underlayer 3: Plating resist 4: Copper wiring layer

Claims (5)

Step 1 of forming a metal plating layer composed of a metal other than copper by electroless plating on at least one surface of the polyimide film, and forming a base layer including the metal plating layer;
Step 2 of forming a plating resist on a part of the underlayer;
Step 3 of forming a copper wiring layer on the base layer portion not covered with the plating resist by electrolytic copper plating;
Step 4 of peeling and removing the plating resist from the underlayer;
And a step 5 for removing the exposed underlayer by peeling off the plating resist, and a method for manufacturing a printed wiring board,
The metal plating layer is a nickel plating layer;
In the step 5 , sulfuric acid, nitric acid, and hydrogen peroxide are contained as the etching solution, and the ratio of the etching rate for nickel and the etching rate for copper is nickel : copper = 1: 0.9-5. A method of manufacturing a printed wiring board, comprising etching and removing the underlayer using a certain etching solution and simultaneously etching side surfaces of the copper wiring layer. The method for manufacturing a printed wiring board according to claim 1 , wherein a film thickness of the copper wiring layer when forming the copper wiring layer in Step 3 is 1 to 20 μm. The manufacturing method of the printed wiring board of Claim 1 or 2 whose undercut rate of the said foundation | substrate layer after an etching is 0-10%, and the width reduction amount of a copper wiring is 0.2-5 micrometers. Wherein in step 1, a manufacturing method of a printed wiring board according to any one of claims 1 to 3 for forming the undercoat layer on the metal plating layer to form a thin copper layer. The method for manufacturing a printed wiring board according to claim 4 , wherein the thin copper layer has a thickness of 0.1 to 1.0 μm.