JPH02273995A - Treatment of copper circuit on inner layer circuit board - Google Patents

Abstract

PURPOSE:To improve adhesion between a copper circuit and prepreg resin and prevent the development of a halo phenomenon by dissolving and removing an oxide coating on the surface of the copper circuit with warm water after performing oxidation treatment of the copper circuit which is provided on an inner layer circuit board. CONSTITUTION:After electric circuits are formed on the both sides of a laminated board which is a glass cloth base material-epoxy resin laminated board clad with copper foils on the both sides of the above board, both faces are made to become slightly rough by a belt sander. Then the solution of alkaline sodium chlorite is prepared at a temperature of 90 deg.C and an inner layer circuit board is immersed in the above solution for 10min. Then its circuit face is made to become rough still more by performing oxidation treatment of the surface of the copper circuit and a cupric oxide film if formed as well. Subsequently, this circuit board is immersed in warm water for 60min. at a temperature of 50 deg.C to dissolve the cupric oxide film. Then its film is removed and the above board is washed with water and is dried. In this way, surface treatment of the copper circuit not only improves adhesion between the copper circuit and prepreg resin but also prevents the development of a halo phenomenon.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention is applicable to the production of multilayer printed wiring boards used in electronic equipment, electrical equipment, computer communication equipment, etc.
This invention relates to a method for processing copper circuits on circuit boards for use in -.

[Conventional technology 1] A multilayer printed wiring board is made by laminating an outer layer circuit board or copper foil via a prepreg on an inner layer circuit board with a circuit formed on one or both sides using copper foil, etc., and then forming this under heat and pressure. It is generally manufactured by laminating an inner layer circuit board and an outer layer circuit board or copper foil.

It is also necessary to ensure adhesion between the copper circuit formed on the inner layer circuit board and the outer layer circuit board or the prepreg resin on which tMN is laminated.

In particular, when forming circuits on inner layer circuit boards using electrolytic copper foil, one side of the copper foil is formed with a rough surface, while the other side is formed with a smooth surface. Because the copper foil is bonded to the inner layer circuit board, the surface of the copper circuit on the inner layer circuit board becomes a smooth surface of the copper foil, and the adhesion between the copper circuit and the prepreg resin is extremely low. Therefore, it is necessary to devise ways to increase this.

Therefore, various methods have been studied to improve the adhesion between copper circuits and resins, and it is common practice to oxidize the surface of copper circuits to improve adhesion. The surface of the copper circuit is generally oxidized using an alkaline aqueous solution containing potassium persulfate or an alkaline aqueous solution containing sodium chlorite.

[Problems to be Solved by the Invention] By oxidizing the surface of the copper circuit as described above, sufficient adhesion between the copper circuit and the resin can be ensured. However, as reported in JP-A-56-153797 and JP-A-61-176192, copper oxide is easily dissolved in acid, so through-hole plating is not required after drilling through-holes. When it is immersed in a chemical plating solution, the copper oxide on the cross section of the copper circuit exposed on the inner periphery of the through-hole will be dissolved in the acid (hydrochloric acid, etc.) of the plating solution, and the copper circuit and resin will be removed from the inner periphery of the through-hole. The so-called halo phenomenon, in which acid penetrates into the interface between circuits, is likely to occur (resulting in a decrease in the reliability of multilayer printed wiring boards).Furthermore, the copper oxide film formed on the surface of the circuit is Since the physical strength is weak, there is a possibility that the effect of improving the adhesive strength due to the oxide film may be reduced.

The present invention has been made in view of the above points, and an object of the present invention is to provide an inner layer circuit board that has good interlayer adhesion and good halo resistance even when the circuit area becomes large. The present invention provides a method for processing copper circuits.

[Means for Solving the Problems 1] In order to achieve the above object, the method for treating the copper circuit of the inner layer circuit board of the present invention is to oxidize the copper circuit provided on the inner layer circuit board, and then oxidize the copper circuit. The VF feature is the removal of the oxide film on the surface by dissolving it with hot water.

The present invention will be explained in detail below.

For the inner layer circuit board, copper circuits can be formed on one or both sides by etching the vA foil using a copper-clad resin laminate, a copper-clad glass polyimide resin laminate, etc. However, it is also possible to use a laminated board with a copper circuit formed by chemical plating or electroplating.

It is preferable to roughen the surface of this inner layer circuit board, and the roughening treatment can be performed using sandpaper, belt sanding, or the like. If a copper foil with rough surfaces on both sides is used, further roughening treatment can be omitted.

Next, the surface of the copper circuit on the inner layer circuit board is subjected to oxidation treatment (also called blackening treatment). This can be carried out by treatment using an alkaline aqueous solution containing. By performing the oxidation treatment in this manner, a copper oxide layer can be formed on the surface of the copper circuit. The copper oxide layer is formed of cuprous oxide, cupric oxide, or a mixture of both, and a black copper oxide film is formed on the surface of the copper circuit.

After forming the oxide layer on the surface of the copper circuit of the inner layer circuit board in this manner, the oxide film is immersed in warm water to be dissolved and removed.

The temperature of this hot water is 30 to 90°C, preferably 50°C.
The temperature is ~60°C, and the immersion time is 30 minutes to 2 hours. After dissolving and removing the oxide film with this warm water, it is washed with water and dried.

It is not possible to manufacture a multilayer printed wiring board using the inner layer circuit board treated in this way through a normal process. In other words, the outer layer circuit board (
Or other inner layer circuit board) or #! Layer the foil,
This is heated and pressurized and laminated to form multiple layers by adhering with prepreg. This multilayer molding is performed using a multistage press or multiroll, and the molding pressure is 5 to 50.
Kg/c-2, molding temperature is 130 to 220°C, and molding time is 30 to 120 minutes. After multi-layer molding in this way, through-holes are formed by drilling, through-hole plating is performed by chemical plating, etc., and an outer layer circuit is formed by etching, etc.
Multilayer printed wiring boards can be manufactured.

[Function] By oxidizing the surface of the copper circuit of the inner layer circuit board, unevenness can be formed on the surface of the copper circuit, and this unevenness improves the adhesiveness between the copper circuit and the prepreg resin. be able to. In addition, by dissolving and removing the oxide film formed on the surface of the copper circuit with hot water,
It is possible to prevent the halo phenomenon that occurs when the oxide film dissolves in acid during plating.

[Example] Next-2 The present invention will be specifically explained with reference to Examples.

In addition, an electric circuit was formed on both sides using a lath cloth base epoxy tree IIw laminate (Matsushita Electric Works Co., Ltd. product number 176G) with a thickness of 1°01, which was formed by pasting 70μ thick copper foil on both sides,
After forming the electric circuit, the surface was lightly roughened using a belt sander.

Next, NaCa, 02 30g10°NaOH15g
/12°N asP O410g/ Q.

The surface of the copper circuit is oxidized (blackened) by preparing an aqueous solution of alkaline sodium chlorite of Na2c Ov 5 g/IZ at 90°C and immersing the inner layer circuit board in this solution for 10 minutes. Then, the circuit surface was further roughened and a cupric oxide film was formed.

Next, the inner layer circuit board thus formed was crushed in warm water at 50° C. for 60 minutes to dissolve and remove the cupric oxide film, washed with water, and dried.

After treating the surface of the copper circuit in this way, two coats of prepreg (Matsushita Electric Works Co., Ltd.! Z1661JM) with a thickness of 0.1 a + m prepared by impregnating and drying an epoxy resin on a lath cloth base material are applied to both sides of the inner layer circuit board. Layer each sheet one by one, and then layer a 35μ thick copper foil on the outside, 40Kg/am2.
A four-layer printed wiring board was obtained by lamination molding at 165° C. for 60 minutes.

(Using the same inner layer circuit board as in the example, it was oxidized (blackened) in the same manner as in the example, washed with water, dried, and then immediately prepreg and copper foil as in the example. were piled up and molded under heat and pressure to obtain a four-layer printed wiring board.

The four-layer printed wiring boards obtained in the above Examples and Comparative Examples had 0.
Through-hole drilling was performed using a 4 mmφ drill bit at a rotational speed of 80,000 rpm and a feed rate of 1.6 m/win. This was immersed in an acidic solution with a water:HCα volume ratio of 1:1 for 30 minutes, and the state of halo formation was observed using a microscope. The size of the halo (measured by the width of the acid solution entering from the inner circumference of the through-hole) is shown on the barley. In addition, the interlayer adhesion between the copper circuit of the inner layer circuit board and the resin of the prepreg in the four-layer printed wiring board (measured by the peel strength between the inner layer circuit board and the prepreg) was measured. Show the results to barley.

As seen in the table above, the example in which the copper circuit was oxidized and then the oxide film was removed with hot water had a lower halo level than the comparative example in which the oxide film was not removed. It has been confirmed that the occurrence of this phenomenon can be greatly reduced, and it has also been confirmed that interlayer adhesion is further improved.

Therefore, since the comparative example has a slight lack of interlayer adhesion, there is a risk of adhesion failure in circuits with a large circuit area such as fine pattern circuits, but the example has high interlayer adhesion, so fine pattern Adhesion failure does not occur even in the case of the circuit.

[Effect of the invention] As described above, in the present invention, the p
After oxidizing the , @ circuit, the oxide film on the surface of this copper circuit was dissolved and removed with hot water, so the oxidation treatment made it possible to form fine irregularities on the surface of the copper circuit. This unevenness can improve the adhesion between the copper circuit and the prepreg resin, and by dissolving and removing the oxide film formed on the surface of the copper circuit, the oxide film can be removed during plating processing, etc. This eliminates the risk of the product being dissolved in acid and prevents the oxidation phenomenon.Furthermore, since the oxide film is removed by dissolving it with hot water, it is easier and more reliable to remove than physically removing it. It is possible.

Claims (1)

[Claims] [1] A method for treating a copper circuit on an inner layer circuit board, which comprises oxidizing the copper circuit provided on the inner layer circuit board, and then dissolving and removing the oxide film on the surface of the copper circuit with hot water.