JP2013060614A - Surface treated copper foil for flexible printed wiring board and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface treated copper foil for a flexible printed wiring board in which a thick film of a chromium-based film is achieved and a ratio of the chromium-based film to the total amount of a base metal film and the chromium-based film is controlled.SOLUTION: The surface treated copper foil for a flexible printed wiring board is obtained by forming the base metal film composed of at least zinc plating and the chromium-based film on a copper foil, wherein the content of chromium metal relative to the total of the content of zinc and chromium metal in the base metal film and the chromium-based film is 50-99 mass%.

Description

  The present invention relates to a surface-treated copper foil for flexible printed wiring boards having high adhesion strength with a polyimide resin and a method for producing the same.

  In recent years, with the downsizing, thinning, lightening, and high functionality of digital home appliances, the miniaturization and high density of FPC (flexible printed wiring boards) used in them have been advanced. In order to meet these requirements, the required characteristics for FPC materials are also strict.

  For copper foils used in FPCs, there is a need to improve the adhesive strength between the copper foil and the resin to which it is attached, improve the chemical resistance used during pattern formation, and improve the resistance to heat applied during processing. .

  In addition, as the pattern becomes thinner, it is particularly important to suppress the adhesion strength between the copper foil and the resin and to prevent the treatment liquid from penetrating during processing between the copper foil and the resin.

  This FPC copper foil is subjected to various surface treatments to improve its properties. In the chromate treatment, one of which is rust prevention and improved adhesion due to the chromium-based film obtained on the substrate surface. Can be expected.

  Conventional chromate treatment is performed according to the following flow.

  First, after applying a base metal plating to the copper foil, it is washed with water. Next, chromate treatment is applied to the substrate surface after washing with water, and this is further washed with water, and finally dried by heating. Thereby, a chromium system coat can be formed on the substrate surface.

Japanese Patent Laid-Open No. 2005-60756

  However, in the conventional method of dissolving the base metal on the substrate surface with the chromate treatment liquid, raising the pH near the base material interface, and depositing the chromium-based film in the chromate treatment liquid, the amount of film formation and the base metal It is difficult to control the ratio change.

  In the chromate treatment, the base metal on the substrate surface is dissolved in the chromate treatment solution, and the pH at the interface rises, so that a chromium-based film containing chromium hydroxide is deposited on the substrate surface.

  At this time, the amount of chromium hydroxide formed can be controlled by the composition, pH, and per solution of the chromate treatment solution. However, in the copper foil for FPC, the base metal film and the chromium-based film are extremely thin. Since the pH in the vicinity of the interface lowers again due to the formation, re-dissolution of the chromium-based film also proceeds at the same time, so it is difficult to increase the thickness of the chromium-based film and control the amount of the film.

  Furthermore, since there is a problem that the production ratio of the chromium-based film cannot be increased compared to the base metal to be dissolved, the thickening of the chromium-based film is necessary to increase the thickness of the base metal according to the final chromium-based film thickness. is necessary. On the other hand, the galvanized surface, which is mainly used as the base, has the property as a chemically active amphoteric metal, so it is easily affected by acid and alkali atmospheres, and thickens the chromium-based film to improve the peel strength. Along with this, the thickened galvanized layer as an underlayer adversely affects various acid and alkali resistance used in the FPC manufacturing process.

  The electrolytic chromate method can be considered as a method of thickening the chromium-based film regardless of the underlying metal film thickness. However, in the electrolytic method, the generation of hexavalent chromium which is an environmentally hazardous substance on the anode side is inevitable due to its characteristics. , Mixing into the product becomes a problem. A method using a diaphragm can be considered to prevent the hexavalent chromium from being mixed into the product by the electrolytic method, but it is not adopted in the present invention because the possibility of the diaphragm being damaged cannot be eradicated.

  Therefore, an object of the present invention is for a flexible printed wiring board in which the chromium-based film is thickened without increasing the thickness of the base metal and the ratio of the chromium-based film to the total amount of the base metal film and the chromium-based film is controlled. It is providing the surface-treated copper foil and its manufacturing method.

  The present invention, which was created to solve the above problems, is a surface-treated copper foil for flexible printed wiring boards in which a base metal film made of at least zinc plating and a chromium-based film are formed on a copper foil. It is a surface-treated copper foil for flexible printed wiring boards in which the content of metal chromium with respect to the total content of zinc and metal chromium in the film is 50% by mass or more and 99% by mass or less.

The underlying zinc metal film is 0.1 [mu] g / cm ² or more 0.8 [mu] g / cm ² or less, the metal chromium of said chromium based coating in is contained 0.4 [mu] g / cm ² or more 2.0 [mu] g / cm ² or less Good.

  Further, the present invention provides a method for producing a surface-treated copper foil for a flexible printed wiring board in which a base metal film made of at least zinc plating and a chromium-based film are formed on a copper foil. It is a manufacturing method of the surface-treated copper foil for flexible printed wiring boards which makes content of metal chromium 50 to 99 mass% with respect to the sum total of content of metal chromium.

  It is preferable to form the chromium-based film by chromate treatment after the base metal film made of galvanizing is formed and subjected to alkali dipping treatment.

  A sodium hydroxide aqueous solution may be used for the alkali immersion treatment.

  ADVANTAGE OF THE INVENTION According to this invention, the surface treatment copper foil for flexible printed wiring boards which controlled the chromium-type film ratio with respect to the total amount of a base metal film and a chromium-type film can be provided, and its manufacturing method. .

It is a figure which shows content of zinc and chromium in each condition, and peel strength.

  Hereinafter, a preferred embodiment of the present invention will be described in detail.

  The surface-treated copper foil for a flexible printed wiring board according to the present embodiment (surface-treated copper foil for FPC) is obtained by forming a base metal film and a chromium-based film made of at least zinc plating on a copper foil. The metal chromium content is 50% by mass or more and 99% by mass or less with respect to the total content of zinc and metal chromium in the metal film and the chromium-based film.

Zinc underlying metal film is 0.1 [mu] g / cm ² or more 0.8 [mu] g / cm ² or less, it is preferable that the metallic chromium chromium based coating in is contained 0.4 [mu] g / cm ² or more 2.0 [mu] g / cm ² or less .

  This surface-treated copper foil for FPC is formed on the copper foil with respect to the total content of zinc and metal chromium in the base metal film and the chromium-based film when the base metal film and chromium-based film made of at least zinc plating are formed. It is manufactured by adjusting the content of metallic chromium to 50 mass% or more and 99 mass% or less.

  Specifically, a base metal film made of galvanization is formed on a copper foil that has been subjected to various surface treatments for improving the characteristics, and the surface of the obtained substrate is washed with water, using an aqueous sodium hydroxide solution. After the alkali immersion treatment, a chromium-based film is formed by chromate treatment. And the surface-treated copper foil for FPC is obtained by further washing with water and heat-drying.

  In the conventional method, the pH of the substrate surface is increased by dissolving the base metal, whereas in the method for manufacturing the surface-treated copper foil for FPC according to the present embodiment, the base material after the base metal plating is made alkaline. By soaking, the pH of the substrate surface was forcibly raised during the subsequent chromate treatment, and chromium hydroxide was deposited efficiently and promptly.

  Therefore, the production | generation ratio of the chromium-type membrane | film | coat with respect to the base metal to melt | dissolve can be enlarged. Further, by changing the concentration of the alkaline solution to be immersed and the chromium concentration in the chromate treatment solution, the amount of the chromium-based film containing chromium hydroxide can be controlled relatively easily.

  The chromate treatment is considered to have a great influence on the improvement of the adhesive strength with the resin, together with the subsequent silane coupling treatment. For this reason, it is expected that the adhesion strength can be improved by optimizing the coating amount according to each resin by making the chromium hydroxide thick and controlling the coating amount.

  Furthermore, conventionally, the base metal is dissolved by the acid contained in the chromate treatment solution in the chromate treatment solution to raise the pH in the vicinity of the substrate interface and promote the deposition of chromium hydroxide. Since the chromate treatment is performed by adhering an alkaline solution to the substrate surface, a chromate film (chromium film) can be formed regardless of the base metal species. Therefore, it is possible to use a metal having higher acid resistance and heat resistance as the base metal.

  In short, according to the present invention, it is possible to increase the thickness of the chromium-based film and to control the ratio of the chromium-based film to the total amount of the base metal film and the chromium-based film.

  Examples, comparative examples, and conventional examples when zinc is used as the base metal plating for chromate treatment are given below.

(Measurement method and evaluation method)
The measurement of zinc and chromium content in the surface treatment layer of copper foil, and the peel strength of a copper foil and a polyimide resin layer were measured or evaluated by the following methods, respectively.
1) Content of zinc and chromium Measured by a calibration curve method using an ICP emission spectrometer.
2) Peel strength between copper foil and polyimide Using a peel strength tester, the polyimide side of a sample patterned to a width of 1 mm was fixed to a metal plate with a double-sided tape, and the copper foil was moved at a speed of 50 mm / min in the 90 ° direction. The peel strength at the time of peeling was measured.

(Processing conditions)
Substrate: A surface-treated rolled copper foil with 2.5 μg / cm ² galvanized on the outermost surface was used.

  Alkaline immersion treatment: Condition (1) No alkali immersion (conventional method), Condition (2) 5 g / L NaOH aqueous solution, Condition (3) 10 g / L NaOH aqueous solution, Condition (4) 15 g / L NaOH aqueous solution It was. Conditions (2) to (3) were all immersed for 5 seconds.

  Chromate treatment: An aqueous solution containing chromium sulfate and nitric acid (as Cr amount: 1.0 g / L, prepared so as to have a pH of 4.0) was used.

A surface-treated copper foil having a zinc plating of 2.5 μg / cm ^{2 on} the outermost surface is subjected to chromate treatment and chromate treatment after alkali immersion at various concentrations to obtain a substrate having a content as shown in FIG. It was.

  Each was subjected to a silane coupling treatment, and then the peel strength was measured as a laminated film with a polyimide resin by a cast method.

  Condition (1) is a conventional example by a conventional construction method, condition (2) is a comparative example, condition (3) is Example 1, and condition (4) is Example 2.

  As shown in Fig. 1, it is possible to drastically increase the chromium content (thickness of chromium-based film) compared to the conventional method by immersion in alkali, and the deposition amount can be controlled by the concentration of alkali to be immersed. I was able to find.

  In addition, the content ratio with the dissolved base metal, which has been difficult in the past, can be greatly changed. According to the above processing conditions, the content of metal chromium with respect to the total content of zinc and metal chromium in the base metal film and the chromium-based film is reduced to 50 by immersing a NaOH aqueous solution of 6 to 7 g / L or more for 5 seconds. It can be made into the mass% or more.

  Further, in Example 2 having the largest chromium-based film thickness, the peel strength was increased by about 20% as compared with the conventional example, and the acid peel strength was similarly improved.

Claims (5)

  In the surface-treated copper foil for flexible printed wiring boards in which a base metal film and a chromium-based film formed of at least zinc plating are formed on a copper foil, the metal with respect to the total content of zinc and metal chromium in the base metal film and the chromium-based film The surface-treated copper foil for flexible printed wiring boards, wherein the chromium content is 50% by mass or more and 99% by mass or less. Claims zinc of the underlying metal film is 0.1 [mu] g / cm ² or more 0.8 [mu] g / cm ² or less, metallic chromium of said chromium based coating in is contained 0.4 [mu] g / cm ² or more 2.0 [mu] g / cm ² or less Item 11. A surface-treated copper foil for a flexible printed wiring board according to Item 1.   In the method for producing a surface-treated copper foil for a flexible printed wiring board, in which a base metal film made of at least zinc plating and a chromium-based film are formed on a copper foil, the zinc and metal chromium content of the base metal film and the chromium-based film The manufacturing method of the surface treatment copper foil for flexible printed wiring boards characterized by making content of metal chromium with respect to a total into 50 mass% or more and 99 mass% or less.   The manufacturing method of the surface treatment copper foil for flexible printed wiring boards of Claim 3 which forms the said chromium-type membrane | film | coat by chromate treatment after forming the said base metal film which consists of galvanization, performing an alkali immersion treatment.   The manufacturing method of the surface-treated copper foil for flexible printed wiring boards of Claim 4 which uses sodium hydroxide aqueous solution for the said alkali immersion treatment.