JPH06103793B2 - Method for treating copper circuit of circuit board for inner layer - Google Patents

Description

Detailed Description of the Invention

[Industrial applications]

The present invention relates to a method of treating a copper circuit of an inner layer circuit board used for manufacturing a multilayer printed wiring board.

[Prior art]

A multilayer printed wiring board is a circuit board for inner layer, which has a circuit formed of copper foil or the like on one or both sides, is overlaid with a circuit board for outer layer or copper foil via a prepreg, and then heat-pressed to form a circuit board for inner layer It is generally manufactured by laminating an outer layer circuit board or a copper foil. In this multilayer printed wiring board, it is necessary to secure the adhesiveness between the copper circuit formed on the inner layer circuit board and the outer layer circuit board or the resin of the prepreg on which the copper foil is laminated. In particular, when the circuit of the inner layer circuit board is formed by electrolytic copper foil, one side of the copper foil is formed as a rough surface, but the other side is formed as a smooth surface. Since the copper foil is adhered with, the surface of the copper circuit of the inner layer circuit board becomes a smooth surface of the copper foil, and the adhesiveness between the copper circuit and the resin of the prepreg is extremely low. It is necessary to devise to improve Therefore, it has been conventionally studied to improve the adhesiveness between the copper circuit and the resin by various methods, and for example, it is generally made to form copper oxide on the surface of the copper circuit to enhance the adhesiveness. Fine protrusions are formed on the surface of the copper oxide obtained by oxidizing copper, and the protrusions can roughen the surface of the copper circuit to improve the adhesiveness. As a method of forming copper oxide on the surface of the copper circuit, it is general to perform treatment by using an alkaline aqueous solution containing potassium persulfate or an alkaline aqueous solution containing sodium chlorite. However, since copper oxide, especially cupric oxide, is easily dissolved in acid, when a through hole is drilled in a multilayer printed wiring board and then plated in a through hole, when immersed in a chemical plating solution or an electroplating solution, The copper oxide layer on the cross-section of the copper circuit exposed on the inner circumference of the through hole dissolves in the acid (hydrochloric acid, etc.) of the plating solution, and the acid penetrates the interface between the copper circuit and the resin from the inner circumference of the through hole. The so-called halo phenomenon in which erosion occurs is likely to occur, and the reliability of the multilayer printed wiring board may decrease. Therefore, the present applicant has previously filed Japanese Patent Application No. 2-69363 (Japanese Patent Publication No. 05-68).
No. 113), etc., proposed a method of reduction treatment with nascent hydrogen. That is, after oxidation treatment to form copper oxide on the surface of the copper circuit of the inner layer circuit board, the surface of the copper circuit is coated with Zn (zinc) powder that is easier to ionize than copper oxide, and then treated with acid. Then, at the same time that Zn is dissolved, nascent hydrogen generated at this time strongly reduces copper oxide while leaving fine irregularities on the surface, and cuprous oxide that is difficult to dissolve copper oxide in acid Alternatively, it is metallic copper. After such reduction treatment, neutralization treatment with an alkali or the like, further washing with water to wash away the acid, and the inner-layer circuit board can be used for molding into a multilayer printed wiring board.

[Problems to be Solved by the Invention]

Neutralizing treatment before washing away the acid by washing with water after reducing the copper oxide as described above is because the unevenness of the copper formed by reducing the copper oxide during the washing with water is the action of the acid. This is to prevent the unevenness from becoming small due to dissolution in the wash water. However, depending on the conditions of the atmosphere in which the circuit board for the inner layer is placed after the reduction treatment of the copper oxide until the neutralization treatment, the reduction-treated coating surface of the copper circuit may be partially dissolved with acid. , Color unevenness occurs on the surface of the copper circuit,
It was the cause of complaints from users. The present invention has been made in view of the above points, and an object of the present invention is to provide a method for treating a copper circuit of an inner layer circuit board capable of preventing the occurrence of color unevenness on the surface of the copper circuit. It is a thing.

[Means for Solving the Problems]

The method for treating a copper circuit of an inner layer circuit board according to the present invention is a method of oxidizing a copper circuit provided on an inner layer circuit board to form copper oxide on the surface of the circuit, and then Zn on the surface of the copper oxide. After coating the powder, dissolve the Zn with acid and reduce the copper oxide with nascent hydrogen generated at this time, then neutralize the surface of the copper circuit with alkali to form a copper circuit. When processing, set the atmospheric conditions for placing the inner layer circuit board between the reduction process and the neutralization process.
The feature is that the temperature is set to 60 ° C x 1 minute or less. Further, the invention is characterized in that the surface temperature of the inner layer circuit board after the reduction treatment and before the neutralization treatment is set to 50 ° C. or lower. The present invention will be described in detail below. As the circuit board for the inner layer, a copper circuit such as a copper clad glass epoxy resin laminated plate and a copper clad glass polyimide resin laminated plate with a copper foil stretched is formed by providing a copper circuit on one side or both sides. In addition to the above, it is also possible to use a laminate having a copper circuit formed on one side or both sides by chemical plating or electroplating. Then, it is preferable to first roughen the surface of the inner layer circuit board. The roughening treatment can be performed by buffing, chemical treatment such as soft etching, electrolytic treatment, liquid honing and the like.
When a copper foil having both surfaces formed with rough surfaces in advance is used, such a roughening treatment can be omitted. Next, the surface of the copper circuit of this inner layer circuit board is oxidized. The oxidation treatment can be performed by using an alkaline aqueous solution containing an oxidizing agent such as an alkaline aqueous solution containing potassium persulfate or an alkaline aqueous solution containing sodium chlorite. By such an oxidation treatment, copper oxide can be formed on the surface of the copper circuit, and the copper oxide is mainly cupric oxide (CuO).
Formed by. By this oxidation treatment, fine projections are formed on the surface of the copper circuit, and it is possible to form irregularities on the surface of the copper circuit to roughen the surface. After the copper oxide is formed on the surface of the copper circuit of the inner layer circuit board in this manner, nascent hydrogen is caused to act on the copper oxide, and the strong reducing action causes the copper oxide to become rough on the surface. It is to be reduced to cuprous oxide or metallic copper while remaining. In the reduction treatment as described above, first, Zn powder, which is more easily ionized than copper oxide (mainly CuO), is attached to the surface of the copper oxide of the copper circuit for coating. To do this coating, for example, in water
It can be carried out by using a liquid in which Zn powder is dispersed, immersing the inner layer circuit board in this liquid, or spraying this solution on the inner layer circuit board. After the Zn powder is attached and coated on the surface of the oxide layer of the copper circuit as described above, the Zn powder is dissolved with acid from the surface of the copper oxide. The acid that dissolves the Zn powder is not particularly limited, but an aqueous solution of sulfuric acid, hydrochloric acid, or the like, which has a low oxidizing power, is preferable from the viewpoint of dissolution of copper oxide and reduction rate.
The Zn powder can be dissolved with an acid by immersing the inner layer circuit board in an acid bath or by spraying the inner layer circuit board with acid. When the Zn powder is dissolved with an acid as described above, the Zn is more easily ionized than the copper oxide, and thus the Zn is preferentially dissolved in the cation state over the copper oxide. As described above, hydrogen is generated when Zn is dissolved in an acid, and this hydrogen acts on the copper oxide in the copper circuit to reduce cupric oxide (CuO) in the copper oxide. C
u ₂ O) and metallic copper (Cu). In particular, the state immediately after generation of hydrogen generated when Zn is dissolved in an acid aqueous solution, that is, hydrogen in the nascent stage is extremely reactive and has a very high reducing action. Since it directly acts on the surface of copper oxide, it can strongly reduce copper oxide. By reducing the copper oxide formed on the surface of the copper circuit in this way, it is possible to make the copper oxide difficult to dissolve in acid, and prevent the halo phenomenon caused by dissolving in acid. It will be possible. Here, when the copper oxide formed on the surface of the copper circuit is dissolved in the acid when the acid is acted as described above, there is a possibility that the uneven rough surface formed by the oxidation of copper may disappear. Since the surface of copper oxide is coated with Zn powder which is dissolved in acid in preference to copper oxide, copper powder can be reduced while protecting copper oxide from acid with this Zn powder, It is possible to reduce the copper oxide to a state in which it is difficult to dissolve in an acid while maintaining the rough surface formed by the oxidation of copper. Further, since a gas such as hydrogen generated when Zn powder dissolves in the acid wraps the surface of the copper oxide, this gas can also protect the copper oxide from the acid. After the treatment with an acid and the reduction treatment in this way, if the acid is washed away immediately by washing with water, the unevenness of the copper formed on the reduced surface of the copper oxide may be dissolved in the washing water. is there. It is presumed that a phenomenon such as a concentration cell of water such as sulfuric acid and water occurs in the reduction treatment surface during washing with water, and copper is dissolved in the washing water. Therefore, instead of the slow method of physically washing the acid with water after treating with acid and reducing it, the chemical method of neutralizing the acid is used to remove it instantly, resulting in a concentration cell and copper dissolution. It is necessary to prevent this, and it is preferable to carry out this neutralization with an alkali, particularly a strong alkali. That is, the inner layer circuit board treated with an acid as described above is dipped in a strong alkaline solution, or the inner layer circuit board is sprayed with a strong alkaline solution. As the strong alkali, an aqueous solution having a pH of 12 or more is preferably used, and an aqueous solution containing a hydroxyl group such as sodium hydroxide or potassium hydroxide is preferably used. Here, as described above, after the reduction treatment of the inner layer circuit board with an acid, the room atmosphere condition in which the inner layer circuit board is placed before the neutralization treatment is set to 60 ° C. × 1 minute or less in the present invention. It is something to set. Here, the atmospheric condition of 60 ° C. × 1 minute or less means that if the atmospheric temperature in the room where the reduction treatment or the neutralization treatment is performed is 60 ° C., the exposure time to this atmosphere is within 1 minute, and if it is 30 ° C. The condition is defined by the product of the ambient temperature and the time of exposure to the ambient temperature, such as within 2 minutes, and it is generally preferable that the ambient temperature does not exceed 60 ° C. At this time, it is also necessary to prevent the surface temperature of the inner layer circuit board from exceeding 50 ° C. as a result of the inner layer circuit board being exposed to this atmosphere. After the inner layer circuit board is reduced with an acid and before the neutralization treatment is performed, the indoor atmosphere condition in which the inner layer circuit board is placed exceeds 60 ° C x 1 minute. If the surface temperature is higher than 50 ° C, the reduced film on the surface of the copper circuit may be dissolved by the acid adhering to the inner circuit board during the reduction treatment, causing uneven color on the surface of the copper circuit. become. Therefore, in the present invention, the neutralization treatment is performed by setting the indoor atmosphere condition in which the inner layer circuit board is placed to 60 ° C. × 1 minute or less and setting the surface temperature of the inner layer circuit board to 50 ° C. or less. Before that, the reduction film on the surface of the copper circuit was prevented from reaching the active point where it started to be dissolved by acid. After neutralizing and removing the acid on the surface of the copper circuit of the inner layer circuit board by neutralizing as described above, immediately wash with water or hot water to dry, then use this inner layer circuit board The multilayer printed wiring board can be manufactured by a normal process. That is, a circuit board for outer layer (or another circuit board for inner layer) or a copper foil is laid on the circuit board for inner layer via a prepreg, and the prepreg is laminated as a bonding layer by heating and pressurizing it to form a multilayer. It is possible to manufacture a multilayer printed wiring board by stacking, providing through holes by drilling, performing through hole plating by chemical plating or the like, and further performing processing such as etching to form an outer layer circuit.

【Example】

Next, the present invention will be described with reference to examples. Example 1 A circuit board for the inner layer was prepared by using a 1.0 mm-thick glass cloth substrate epoxy resin laminated plate formed by lining 35 μm thick copper foil on both sides, and the surface of the copper circuit of the circuit board for the inner layer was buffed. Then, the surface was roughened. Next, adjust the potassium persulfate bath with the composition of K ₂ S ₂ O ₈ … 15g / NaOH… 50g / to 60 ℃ and immerse the inner layer circuit board in this oxidation treatment bath for 3 minutes. Oxidized. Next, 10 liters of zinc powder with a particle size of 5 μm was added to 1 liter of water.
The bath in which g was dispersed was heated to 90 ° C., and the circuit board for the inner layer was immersed in this bath for 3 minutes to coat the surface of the copper circuit with zinc powder in an amount of 20 g / bm ² attached. After coating with zinc powder in this way, the inner layer circuit board was immersed in a 20% H ₂ SO ₄ aqueous solution for 1 minute to dissolve and remove zinc on the surface of the copper circuit. At this time, the copper oxide on the surface of the copper circuit received a reducing action. Next, the circuit board for the inner layer is placed in a room temperature atmosphere of 40 ° C. for 0.5
Place for minutes (the maximum temperature of the surface of the inner layer circuit board at this time is
37 ℃), strong alkaline aqueous solution (p
The circuit board for inner layer was immersed in H13.1) for 1 minute for neutralization. After this, the inner layer circuit board was washed with running water and dried. And both sides of the circuit board for inner layer treated in this way, the thickness of 0.
Three 1mm prepregs are stacked on top of each other, and a copper foil with a thickness of 18μ is further stacked on the outer side of the prepreg, and secondary lamination is performed under a reduced pressure of 6.7 × 10 ³ pascals at 170 ° C, 40 kgf / cm ² , 120 minutes. A multilayer board was obtained by molding. Example 2 After the reduction treatment with an acid, the inner layer circuit board was placed in a room temperature atmosphere of 40 ° C. for 1.0 minute (the maximum temperature of the surface of the inner layer circuit board at this time was 39 ° C.), followed by neutralization treatment. The same procedure as in Example 1 was carried out except that it was carried out. Example 3 After the reduction treatment with an acid, the inner layer circuit board was placed in a room temperature atmosphere of 50 ° C. for 1.0 minute (the maximum temperature of the surface of the inner layer circuit board at this time was 48 ° C.), followed by neutralization treatment. The same procedure as in Example 1 was carried out except that it was carried out. Comparative Example 1 After the reduction treatment with an acid, the inner layer circuit board was placed in a room temperature atmosphere of 60 ° C. for 1.0 minute (the maximum surface temperature of the inner layer circuit board at this time was 56 ° C.), and then neutralized. The same procedure as in Example 1 was carried out except that it was carried out. Comparative Example 2 After the reduction treatment with an acid, the inner layer circuit board was placed in a room temperature atmosphere of 40 ° C. for 2.0 minutes (the maximum temperature of the surface of the inner layer circuit board at this time was 40 ° C.) and then neutralized. The same procedure as in Example 1 was carried out except that it was carried out. The surface of the copper circuit of the inner layer circuit board treated in Examples 1 to 3 and Comparative Examples 1 and 2 was visually inspected. The results of the visual inspection are shown in the following table. As can be seen from the results of each of the examples in the table, the appearance failure was caused by setting the atmosphere condition in which the inner layer circuit board is placed between the reduction treatment and the neutralization treatment to 60 ° C. × 1 minute or less. It is confirmed that can be prevented.

【The invention's effect】

As described above, in the present invention, the atmosphere condition in which the circuit board for the inner layer is placed after the reduction treatment and before the neutralization treatment is set to 60 ° C. × 1 minute or less, and after the reduction treatment, The surface temperature of this inner layer circuit board up to 50
Since the temperature is set below ℃, it is possible to prevent the reduction film on the surface of the copper circuit from reaching the active point where it starts to be dissolved with acid before the neutralization treatment, and the surface of the reduction film on the copper circuit is treated with acid. It is possible to prevent the occurrence of color unevenness on the surface of the copper circuit due to partial melting of the copper circuit.

Claims (2)

[Claims] 1. A copper circuit provided on a circuit board for an inner layer is oxidized to form a copper oxide on the surface of the circuit, and then a Zn powder is coated on the surface of the copper oxide and then immersed in an acid. At the same time as dissolving the Zn powder, the copper oxide was reduced with nascent hydrogen generated at this time, and then the surface of the copper circuit was neutralized with an alkali to reduce the copper circuit. A method for treating a copper circuit of an inner layer circuit board, characterized in that the atmosphere condition in which the inner layer circuit board is placed before the neutralization treatment is set to 60 ° C x 1 minute or less. 2. The method for treating a copper circuit of an inner layer circuit board according to claim 1, wherein the surface temperature of the inner layer circuit board after the reduction treatment and before the neutralization treatment is set to 50 ° C. or lower. .