JPH0259880B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD This invention relates to a copper foil for printed circuits that has oxidation resistance at high temperatures, excellent hydrochloric acid resistance, and is suitable for mass production, and a method for manufacturing the same. Prior Art Printed circuit boards used for wiring electronic devices are made by heating and pressurizing copper foil and a synthetic resin-impregnated base material to form a copper-clad laminate, and then etching the copper in areas other than the circuit forming portion of the copper foil. It was manufactured by dissolving and removing copper and forming a copper circuit on the substrate. When manufacturing copper-clad laminates, in order to strengthen the adhesion between the copper foil and the synthetic resin-impregnated base material, dendritic copper is pre-electrolytically treated on the surface of the copper foil that will be laminated with the base material. It is necessary to let it precipitate. However, if the copper foil in the above state is left in the air, it will gradually oxidize, and a thin copper oxide film will form on the dendritic copper on the side of the copper foil that will be laminated with the base material, resulting in a printed circuit board. When this is done, the peel strength between the copper foil and the substrate decreases. On the other hand, the shiny side of copper foil,
That is, on the printed circuit production side, not only does surface discoloration occur and the appearance is poor, but also solder adhesion to the surface becomes poor, lowering the conductivity of the copper, and making it impossible to use it as a printed circuit board. Therefore, it can be said that improving the antirust ability of copper foil for printed circuits is an extremely important issue in the production of copper foil. Now, as a known technique for improving the rust prevention ability of copper foil, copper foil is treated in an aqueous solution of hexavalent chromium salt,
There is a treatment method that forms a thin chromium film on that surface.
However, this method is not very effective when the printed circuit board is used under severe conditions, particularly when it is used at high temperatures, and an improvement has been desired. As one of the countermeasures, for example, U.S. Patent No. 3,585,010 proposes a copper foil for printed circuits in which a thin layer of indium, zinc, tin, nickel, cobalt, brass, or bronze is formed on the copper foil surface. ing. Among the above metals, zinc has anti-rust ability,
Although it is particularly excellent in oxidation resistance at high temperatures, it is inferior in hydrochloric acid resistance, which is an essential requirement in the production of printed circuits, which poses a practical problem. Further, Japanese Patent Publication No. 7077/1983 discloses a copper foil for printed circuits in which a coating layer of zinc or a mixture of zinc oxide and chromium oxide is formed on at least one surface of the copper foil. The main feature of this method is considered to be that the layer is formed by electrolysis using an alkaline bath. However, in manufacturing copper foil for printed circuits, the process of electrodepositing dendritic copper on the surface of the copper foil and the process of forming a thin film of zinc or the like on the surface of the foil are usually performed using the same processing machine. This is carried out continuously, with the electrodeposition of the dendritic copper being carried out by passing an electric current through the copper foil in a known acidic copper sulfate plating bath. Therefore, when a coating of zinc or the like is created using an alkaline bath in the next process, if these washing effluents are combined, copper hydroxide tends to deposit in the drain, and the momentum is reduced. There is an equipment disadvantage in that a drainage channel is provided separately, and in addition, there is an operational disadvantage in that a large amount of water is required to wash away residual alkali from the copper foil surface. Moreover, although this two-layered copper foil, in which a mixed film of zinc or zinc oxide and chromium oxide is formed on the copper foil surface, has oxidation resistance at high temperatures, it has poor hydrochloric acid resistance required for copper foil. However, when a printed circuit board was manufactured using this copper foil, the method involved practical problems such as side etching. Problems to be Solved by the Invention In terms of oxidation resistance at high temperatures, the present invention has properties equivalent to the above-mentioned known two-layer structure copper foil in which a thin film of zinc or the like is formed on the copper foil surface, and has hydrochloric acid resistance. The purpose of the present invention is to provide a copper foil that exhibits significantly superior properties than those described above, and that does not cause side etching when manufacturing printed circuits, and a manufacturing method that allows mass production of the same. be. Means for Solving the Problems In order to solve the above problems, the present inventors conducted research based on the basic premise of using an acidic bath instead of an alkaline bath for the electrolyte solution for anti-corrosion treatment of copper foil. continued. As a result, after forming a known chromium thin film on at least one side of the copper foil, a mixed thin film of chromium and zinc was subsequently formed thereon using an acidic bath containing hexavalent chromium ions and zinc ions. It was confirmed that the above-mentioned problems could be solved by using a copper foil with a three-layer structure, and thus the present invention was completed. Function Next, the present invention will be explained in more detail. In the present invention, the copper foil to be treated to impart rust prevention ability may be a copper foil produced by either electrolysis or rolling. , electrolytic treatment was performed using a known acidic copper sulfate plating bath, and dendritic copper was electrodeposited on the surface. Conventional rust-prevention treated copper foil has a two-layer structure in which a thin film of zinc or the like is formed on the surface of the copper foil as described above, whereas the one of the present invention has at least A thin chromium film is formed on one side, and a mixed thin film of chromium and zinc is formed on top of that to form a three-layer structure, and all of these thin film formation treatments are performed in an acid bath. To form a chromium thin film, a well-known aqueous solution containing hexavalent chromium ions, such as Na ₂ Cr ₂ O _{7.2H 2} O
Maintain the concentration at 0.5-10g/, the pH of the bath at 4-6,
A thin chromium film is formed by simply energizing the copper foil in this bath at room temperature or by immersing the copper foil in this bath, and then a mixed thin film of chromium and zinc is formed on this thin film using 6.0% as an electrolyte. A mixed aqueous solution containing valent chromium ions, such as Na ₂ Cr ₂ O _{7.2H 2} O, and zinc ions, such as ZnSO _{4.6H 2} O, is used, and if necessary, this mixed solution is added.
A copper foil is used as a cathode and current is applied in a bath to which NaSO ₄ is added. The reason why NaSO ₄ is added here is to improve the electrical conductivity of the aqueous solution when the electrolyte used contains small amounts of chromium ions and zinc ions. Next, regarding the bath temperature, room temperature is sufficient and no particularly strict temperature control is required. Also, Na ₂ Cr ₂ O ₇・
The amounts of 2H ₂ O and ZnSO ₄ .6H ₂ O added do not need to be particularly limited either, but their concentrations are generally in the range of 1 to 10 g/in many cases. Furthermore, the ratio of chromium and zinc in the mixed thin film deposited by electrolysis is correlated with the ratio of chromium ions to zinc ions in the electrolytic solution used. Therefore, it is desirable to take this into consideration when selecting the blending amount. Further, it is preferable that the pH of the electrolytic solution is in the range of 3 to 6. The reason for this is that when the pH is lower than 3, the mixed thin film of chromium and zinc produced as a result of electrolysis becomes more easily dissolved by acid;
This is because when the pH is set to 6 or more, the proportion of zinc deposited by electrolysis decreases. The mixed thin film of chromium and zinc deposited on copper foil according to the present invention may be formed on either the dendritic copper foil surface, that is, the rough surface side of the copper foil or the shiny surface thereof. It may be formed on both sides.
Further, the copper foil after electrolysis is washed with water to remove residual water, so that if it is dried for about 5 minutes in a dryer at 105 to 110° C., a copper foil for printed circuits can be obtained. Hereinafter, the present invention will be explained in more detail with reference to Examples. Example 1 A copper foil with a thickness of 33 μm was immersed at room temperature in an aqueous solution containing Na ₂ Cr ₂ O ₇ .2H ₂ O at a concentration of 5 g/ and a pH between 5 and 6 at a current density of 0.3 A. /d
After forming a thin chromium film on the rough surface of the copper foil by applying current for 5 seconds at m ² , ZnSO ₄ was then applied using the copper foil as a cathode.
6H ₂ O 2 g/, Na ₂ Cr ₂ O ₇・2H ₂ O 5 g/, and current density of 0.15 A/dm ² and 0.3 A/dm ² at room temperature in an aqueous solution with pH maintained between 4 and 5.
type, and the energization time is constant at 5 seconds.
A mixed thin film of chromium and zinc was formed on the chromium thin film of the copper foil. The mixed thin layer of chromium and zinc of the thus obtained three-layer copper foil was layered on a glass-epoxy resin-impregnated base material (using a secondary amine as a hardening agent) at 160℃ and under a pressure of 100Kg/ A copper clad laminate specimen measuring 250 x 250 x 1.2 mm was fabricated by heating and pressurizing it at cm ² for 40 minutes. In addition, in order to compare the performance of the above sample, without forming a thin chromium film on the rough side of a copper foil of the same thickness as above, we directly applied chromium and zinc with the same composition as above, using the copper foil as a cathode. In an aqueous solution of Copper-clad laminates of the same size were trial-produced under different processing conditions, and the peel strength and hydrochloric acid resistance of these trial boards were determined (after immersing the prototype board in an aqueous solution of reagent hydrochloric acid:water = 1:1 for 1 hour at room temperature). (This is the rate of deterioration of peel strength.) and a peel test after heating to evaluate oxidation resistance at high temperatures (a prototype board was heated to 180°C).
This is the peel strength after being allowed to cool after being held for 48 hours. )
At the same time, the amount of chromium and zinc deposited on the copper foil of the prototype board (the weight of these metals deposited per 1 dm ² of copper foil) was measured using atomic absorption spectrometry for reference. The results are shown in Table 1.

[Table] From the table, the three-layer structure copper foil shown in the examples has peel strength and post-heat peel test results that are equal to or higher than the conventional two-layer copper foil, and has a superior hydrochloric acid resistance. We learned that the invented product has extremely superior performance. Example 2 After forming a chromium thin film on the rough side of the same copper foil as described in Example 1 under the same conditions as Example 1,
Subsequently, the copper foil was treated with ZnSO _{4.6H 2} O2g/,
A current density of 0.15 A/dm 2 and 0.5 A/dm ² at room temperature in an aqueous solution consisting of Na ₂ Cr ₂ O ₇・2H ₂ O 1 g/, Na ₂ SO ₄ 2 g/, and the pH was maintained between 4 and ^5. Electrolysis was carried out with the energization time being 5 seconds as in Example 1, and a mixed thin film of chromium and zinc was formed on the chromium thin film of the copper foil, and the mixed thin film surface of the copper foil was Layered with the same resin-impregnated base material as described in Example 1, and using the same molding conditions, 250×
A 250×1.2mm copper-clad laminate specimen was fabricated. Also,
In order to compare the performance with the above specimen, we created a copper foil with a mixed thin film of chromium and zinc directly using the same electrolyte without forming a chromium thin film on the rough side of the same copper foil as above. Copper-clad laminates were also made as prototypes, and the same characteristics as described in Example 1 were obtained for each of these specimens, and for reference, the amount of metal deposited in the thin film formed on the copper foil was also determined. The results are shown in Table 2.

[Table] From the table, it was found that the samples of Examples had the same or better properties than those of Comparative Examples in the post-heating peel test results, and had significantly superior properties in terms of hydrochloric acid resistance. Example 3 A three-layer structure copper foil of the present invention and a conventional two-layer structure copper foil as a comparative example were produced under exactly the same conditions as described in Example 1, and the mixed thin film surface of these copper foils was ,
Copper-clad laminate specimens were produced under the same conditions as in Example 1 by laminating a glass-epoxy resin-impregnated base material using a primary amine as a hardening agent, and the characteristics of these specimens were determined.
The amount of adhesion of the metal thin film formed on the copper foil was measured in the same manner as described in Example 1. The results are in Table 3
As shown.

[Table] From Table 3, it can be seen that the samples of the examples are equivalent to or better than the conventional samples in terms of peeling test results after heating, and can significantly improve hydrochloric acid resistance. In particular, with this example, the three-layer structure is sufficient to overcome the point where the conventional two-layer structure cannot pass the standard of 15% deterioration rate of peel strength, which is a practical certification test value for hydrochloric acid resistance. I learned what it is possible to pass and what I can achieve. Example 4 After producing a three-layer structure copper foil of the present invention and a conventional two-layer structure copper foil under the same conditions as described in Example 2, the same conditions as described in Example 3 were carried out using these prototype copper foils. Test specimens of copper-clad laminates were made, and the characteristics of these specimens and the amount of adhesion of the metal thin film formed on the copper foil were measured under the same conditions as described in Example 1. The results are shown in Table 4.

[Table] From Table 4, the products of the example were found to be equivalent to or better than the conventional products in terms of peeling test results after heating, and were significantly superior to the conventional products in terms of hydrochloric acid resistance. . In particular, according to this example, the conventional two-layer structure was unable to pass the standard of 15% deterioration rate of peel strength, which is a practical certification test value for hydrochloric acid resistance, but the three-layer structure was adopted. I think it is significant that we were able to pass the exam. Example 5 When the three-layer copper foil of the present invention is made into a circuit board,
As an example to demonstrate that side etching does not occur on the circuit board, a thin chromium film was first applied to the shiny side of the copper foil under the same conditions as described in Example 1.
Next, a mixed thin film of chromium and zinc was formed on top of it under the same conditions to create a three-layer structure, while for comparison, only a mixed thin film of chromium and zinc was directly formed on the shiny surface of the copper foil. We also prototyped conventional two-layer copper foils, coated the rough surfaces of these copper foils with butyl rubber and phenolic resin adhesives, and laminated the coated surfaces with paper and phenolic resin-impregnated base materials to create copper-clad laminates. A prototype plate was made. Next, a wiring pattern is printed on the copper foil surface of this sample using a commercially available etching resist, and the copper foil other than the printed circuit portion is dissolved and removed using a known cupric chloride etching solution.
We prototyped a printed circuit board with a circuit width of 1 mm. . Next, whether or not the side etching had occurred in the prototype board was determined by taking a photograph (150x magnification) of the metal structure at the boundary between the circuit of the circuit board and the base material. The photograph shown in FIG. 1 is of the three-layer structure of the present invention, and the photograph shown in FIG. 2 is of the conventional two-layer structure. The continuous linear area (hereinafter referred to simply as the white line) that appears near the center of both photographs is the boundary area, and above it is the copper foil section, and below it is the base material exposed by the etching process. Comparing the two photographs, the metal structure (white line) at the boundary in FIG. 1 is approximately straight, indicating that there is no side etching in the metal structure. On the other hand, in the conventional product shown in FIG. 2, the metal structure (white line) was zigzag, and it was recognized that side etching had occurred. In other words, it has been found that the copper foil of the present invention is extremely effective in preventing the occurrence of side etching during the production of printed circuits. Effects of the invention If the copper foil of the invention is put to practical use in printed circuits,
It is clear that the oxidation resistance at high temperatures is equal to or higher than that of conventional two-layer copper foils, and the hydrochloric acid resistance is significantly superior. Moreover, the product of the present invention does not cause side etching even when used as a printed circuit board. Furthermore, since the copper foil of the present invention uses an acid bath throughout its production, it is suitable for mass production. Therefore, the present invention is considered to provide a copper foil suitable for use in printed circuits and a method for manufacturing the same.

[Brief explanation of drawings]

In order to explain Example 5 of the present invention, FIGS. 1 and 2 show the metal structure of the boundary between the printed circuit and the substrate provided on the copper foil of the present invention and the conventional copper foil at 150°C, respectively.
This is shown in a double enlarged photograph.

Claims (1)

[Claims] 1. A copper foil for printed circuits, characterized in that a mixed thin film of chromium and zinc is further formed on a thin chromium film formed on at least one side of the copper foil. 2. After forming a thin chromium film on at least one surface of the copper foil by immersing it in an aqueous solution containing hexavalent chromium ions or by applying electricity in the aqueous solution, the copper foil is then immersed in an acidic solution containing chromium ions and zinc ions. A method for manufacturing copper foil for printed circuits, which comprises applying electricity in an aqueous solution to form a mixed thin film of chromium and zinc on the chromium thin film.