JPH06103792B2 - 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) proposed a method of reduction treatment with nascent hydrogen. That is, after the oxidation treatment is performed 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 a metal such as zinc powder that is more easily ionized than copper oxide, and then treated with acid. Then, at the same time that the metal is dissolved, the nascent hydrogen generated at this time strongly reduces the copper oxide while leaving the fine irregularities on the surface, and the cuprous oxide is difficult to dissolve in the acid. Alternatively, it is metallic copper. After the reduction treatment as described above, the inner layer circuit board can be washed 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]

However, when the acid resistance of the copper circuit is increased by reducing the copper oxide as described above, the adhesiveness between the copper circuit and the resin of the prepreg tends to be lower than that of the copper oxide not subjected to the reduction treatment. It is considered that this is because, when the acid is washed away by washing with water after the reduction treatment, the unevenness of copper formed by reducing the copper oxide is dissolved in the wash water and the unevenness becomes small. When the adhesiveness between the copper circuit and the resin of the prepreg is reduced in this way, problems such as peeling between the copper circuit and the resin of the prepreg are expected during the molding process as the circuit width becomes narrower. It The present invention has been made in view of the above points, and an object thereof is to provide a method for treating a copper circuit of a circuit board for an inner layer, which can prevent the adhesiveness of the copper circuit from decreasing. is there.

[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 copper on the surface of the copper oxide. After coating a metal that is more easily ionized than an oxide, the metal is dissolved with an acid and at the same time the copper oxide is reduced with nascent hydrogen generated at this time, and then the surface of the copper circuit is treated with a strong alkali. It is characterized in that it is subjected to a washing treatment and then to a washing treatment. 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, a metal that is more easily ionized than copper oxide (mainly CuO), for example, a metal powder such as zinc powder is attached to the surface of the copper oxide of the copper circuit for coating. To perform this coating, for example, a liquid in which a metal powder is dispersed can be used, and the inner layer circuit board can be dipped in this solution or sprayed on the inner layer circuit board. . After depositing and coating the metal powder on the surface of the oxide layer of the copper circuit as described above, the metal powder is dissolved with an acid from the surface of the copper oxide. The acid that dissolves the metal powder is not particularly limited, but an aqueous solution of sulfuric acid, hydrochloric acid, or the like having a low oxidizing power is preferable from the viewpoint of dissolution of copper oxide and reduction rate. The metal 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 metal powder is dissolved with an acid in this manner, the metal is more easily ionized than the copper oxide, and thus the metal is preferentially dissolved in the cation state over the copper oxide. Thus, when the metal powder is dissolved in the acid, hydrogen is generated, and this hydrogen acts on the copper oxide in the copper circuit to reduce cupric oxide (CuO) in the copper oxide. (Cu ₂ O) and metallic copper (Cu). In particular, the state immediately after the generation of hydrogen generated when the metal is dissolved in the aqueous solution of the acid, that is, the 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 the copper oxide is coated with a metal powder that is dissolved in an acid in preference to the copper oxide, the metal powder can be reduced while protecting the copper oxide from the acid, 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. In addition, since gas such as hydrogen generated when the metal powder is dissolved in the acid wraps the surface of the copper oxide, the gas can also protect the copper oxide from the acid. When the product is treated with an acid in this way and subjected to a reduction treatment, and then immediately washed with water to wash away the acid, the copper irregularities formed on the reduced surface of the copper oxide are dissolved in the wash water as described above. There is a risk of doing it. 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, in the present invention, a concentration battery is produced by instantaneously removing the acid by a chemical method of neutralizing the acid, not by a slow method of physically washing the acid with water after reduction by treatment with an acid. To prevent copper from being dissolved, and this neutralization is performed using a strong alkali. That is, the inner layer circuit board treated with an acid as described above is immediately immersed in a solution of a strong alkali,
It can be performed by spraying a strong alkali solution on the inner layer circuit board. 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. 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. Then, the _{K 2 S 2 O 8 ... 15g} / l NaOH ... 50g / l of potassium persulphate bath composition was adjusted to 60 ° C., the copper circuit by dipping the inner-layer circuit board for three minutes in this oxidizing treatment bath The surface was oxidized. Next, add 10 g of zinc powder with an average particle size of 5 μm to water 1.
The dispersed bath was heated to 90 ° C., and the inner layer circuit board was immersed in this bath for 3 minutes to deposit zinc powder on the surface of the copper circuit for coating. 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, a strong alkaline aqueous solution containing 0.4% by weight of NaOH (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 Example 2 was performed in the same manner as in Example 1 except that the neutralization treatment in the step of step 1 was performed using a strong alkaline aqueous solution (pH 14 or more) containing 1% by weight of NaOH. Example 3 Example 3 was performed in the same manner as in Example 1 except that the neutralization treatment in the step of step 1 was performed using a strong alkaline aqueous solution (pH 14 or more) containing 1% by weight of KOH. Comparative Example 1 The procedure of Example 1 was repeated except that the neutralization treatment in the step of Example 1 was omitted. Comparative Example 2 In Example 1, the neutralization treatment step, the Na ₂ CO ₃ 1
The same procedure as in Example 1 was performed except that the weak alkaline aqueous solution added by weight% was used. Comparative Example 3 The procedure of Example 1 was repeated, except that the steps 1 to 3 were not performed. Through holes were processed in the multilayer plates obtained in Examples 1 to 3 and Comparative Examples 1 to 3 by using a 0.4 mmφ drill bit at a rotation speed of 80,000 rpm and a feed rate of 1.6 m / min. The multi-layer board that processed this through hole is 17.5% HC
l It was immersed in an aqueous solution for 10 minutes, and the size of the halo was measured by measuring the size from the inner circumference of the through hole. Further, the interlayer adhesion between the inner layer circuit board and the layer of the prepreg was measured for the above multilayer board. The results are shown in the table below. As can be seen from the results in the above table, in each of the examples in which the reduction treatment was performed using an acid and then the neutralization treatment was performed with a strong alkali, the same as that of the comparative example 3 in which only the oxidation treatment was performed. It is confirmed that the above adhesion is maintained. On the other hand, it is confirmed that the adhesive strength of Comparative Example 2 in which the neutralization treatment is performed with a weak alkali is significantly lower than that of Comparative Example 3.

【The invention's effect】

As described above, in the present invention, the metal coated on the surface of the copper oxide of the copper circuit is dissolved with an acid and at the same time the copper oxide is reduced by nascent hydrogen generated at this time, Since the surface of the circuit is neutralized with a strong alkali and then washed with water, the acid is quickly removed from the surface of the copper circuit by a chemical method of rapidly neutralizing the acid with a strong alkali. The surface of the copper circuit can be prevented from being dissolved by the concentration battery as in the case of removing the acid by washing with water, and the unevenness of the surface of the copper circuit when the acid is removed after the reduction treatment. Can be prevented from being dissolved and the adhesiveness to the prepreg resin is lowered.

Claims (3)

[Claims] 1. A copper circuit provided on an inner layer circuit board is oxidized to form copper oxide on the surface of the circuit, and then the surface of the copper oxide is coated with a metal that is more easily ionized than copper oxide. After that, the metal is dissolved with an acid and at the same time the copper oxide is reduced with nascent hydrogen generated at this time, and then the surface of the copper circuit is neutralized with a strong alkali and then washed with water. A method for treating a copper circuit of an inner layer circuit board. 2. The method for treating a copper circuit of an inner layer circuit board according to claim 1, wherein the strong alkali used for the neutralization treatment is an aqueous solution having a pH of 12 or more. 3. The copper circuit for an inner layer circuit board according to claim 1, wherein the strong alkali used for the neutralization treatment is an aqueous solution containing a hydroxyl group such as sodium hydroxide or potassium hydroxide. Processing method.