JPH06283854A - Surface treating method for copper of circuit board - Google Patents

Abstract

PURPOSE:To stabilize reduced state of a copper oxide layer by making adherence of zinc powder to a surface of copper uniform. CONSTITUTION:The method for surface treating copper of a circuit board comprises the steps of oxidizing copper for forming a circuit provided on a surface of a circuit board to form a copper oxide layer on a surface of the copper, coating the surface of the board with zinc powder to adhere the powder to the surface of the copper, then treating it with acid to dissolve the powder in the acid, and simultaneously reducing the layer with hydrogen generated in this case. In this case, as the powder, powder containing 95wt.% or more of powder of pure zinc having a mean particle size of 4mum or less and less than 5wt.% of powder of zinc oxide having a mean particle size of 5mum or less is used. When the sizes of the pure zinc powder and the zinc oxide powder are set as above, an adhering amount of the zinc powder to the surface of the copper can be stabilized. Further, the zinc oxide powder is mixed to stabilize dissolving velocity of the pure zinc powder in the acid can be stabilized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface treatment method for copper of an inner layer circuit board which is processed into a multilayer printed wiring board.

[0002]

2. Description of the Related Art In a multilayer printed wiring board, an outer circuit board or a copper foil is superposed on a circuit board for an inner layer having a circuit formed of copper foil or the like on one side or both sides through a prepreg, and this is heat-pressed. Then, the circuit board for the inner layer and the circuit board for the outer layer or the copper foil are laminated. The circuit board for the inner layer is formed by, for example, etching a copper-clad laminated board in which copper foils are laminated to form a circuit.

In this multilayer printed wiring board, it is necessary to secure the adhesiveness between the copper circuit formed on the circuit board for the inner layer and the circuit board for the outer layer or the resin of the prepreg on which the copper foil is laminated. is there. Therefore, conventionally, it has been studied to enhance the adhesiveness between the copper circuit and the resin by various methods, and for example, it is generally known that copper oxide is formed on the surface of copper forming the copper circuit to enhance the adhesiveness. Has been done. Fine projections of copper oxide will be formed on the surface of the copper oxide layer obtained by oxidizing copper, and the projections can roughen the surface of the copper circuit and improve the adhesion. Of. And as a method of forming a copper oxide layer on the surface of copper, it is generally performed by treating the surface of copper with an alkaline aqueous solution containing potassium persulfate or an alkaline aqueous solution containing sodium chlorite. Target.

By thus forming the copper oxide layer on the surface of copper, the surface of the copper circuit can be roughened, and sufficient adhesion between the copper circuit and the resin can be ensured. However, since copper oxide (cupric oxide) in the copper oxide layer is easily dissolved in acid, chemical plating liquid or electroplating is used when performing through-hole plating after drilling through-holes in a multilayer printed wiring board. When immersed in the solution, the copper oxide layer on the cross-section of the copper circuit exposed at the inner periphery of the through hole dissolves in the acid (especially hydrochloric acid) of the plating solution, and the interface between the copper circuit and the resin is formed from the inner periphery of the through hole. There is a problem that dissolution erosion due to acid infiltration occurs, so-called halo is likely to occur, and the reliability of the multilayer printed wiring board may decrease.

Therefore, after forming a copper oxide layer on the surface of copper of a circuit board, cuprous oxide (cuprous oxide) which is difficult to dissolve the copper oxide layer in acid while leaving fine protrusions on the surface or Attempts have been made to reduce the halo phenomenon by reducing it to metallic copper. Then, as a method for reducing the copper oxide layer, a method using zinc dust and an acid is provided by the applicant in Japanese Patent Application No. 2-69363. That is, this Japanese Patent Application No. 2
The method of reduction according to No.-69363 is such that zinc dust is attached to the surface of a copper oxide layer formed on copper by coating the surface of the circuit board with zinc dust, and then the circuit board is treated with an acid solution such as an aqueous sulfuric acid solution. When immersed in, the zinc, which is more easily ionized than copper, reacts with the acid and dissolves, and the nascent hydrogen generated at this time acts on the copper oxide layer to reduce the copper oxide. is there.

[0006]

The surface of a circuit board is coated with zinc dust by immersing the circuit board in water in which zinc dust is dispersed. The size of the circuit board and the size of the circuit board Depending on the area of copper left as a circuit on the surface and the copper remaining ratio with respect to the area of the circuit board, the amount of zinc deposited on the copper surface changes subtly and becomes non-uniform, resulting in copper oxide on the copper surface. There is also a problem that the reduced state of the layer also becomes non-uniform, and as a result, the appearance of the surface tone of copper becomes non-uniform and the defective rate increases.

The present invention has been made in view of the above points, and the surface of copper of a circuit board can stabilize the reduced state of the copper oxide layer by making the zinc dust adhere to the surface of copper uniform. It is intended to provide a treatment method.

[0008]

According to the method for surface treatment of copper of a circuit board according to the present invention, copper for forming a circuit provided on the surface of the circuit board is oxidized to form a copper oxide layer on the surface of the copper. After forming, coating the surface of the circuit board with zinc dust and adhering the zinc dust to the surface of copper, then treating with acid to dissolve the zinc dust in acid and at the same time hydrogen generated at this time copper oxide In reducing the layer, the proportion of pure zinc powder having an average particle size of 4 μm or less as the zinc powder exceeds 95% by weight, and the average particle size is 5
It is characterized by using a mixture of zinc oxide powder having a particle size of not more than μm at a ratio of less than 5% by weight.

The present invention will be described in detail below. As the circuit board to be treated in the present invention, a copper-clad glass epoxy resin laminated board on which a copper foil is stretched, a copper foil-clad laminated board such as a copper-clad glass polyimide resin laminated board is subjected to printed wiring processing to form a copper circuit. It is possible to use those provided, or those in which a copper circuit is chemically plated or electroplated on the surface of the resin laminated plate, and the circuit board for the inner layer in which the copper circuit is provided on one side or both sides. It is intended to be used as. Of course, it is not limited to this,
The copper foil before forming the circuit may be used as it is.

First, the copper provided on the surface of the 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. A copper oxide layer can be formed on the surface of copper by such an oxidation treatment, and the copper oxide is mainly formed of copper oxide (cupric oxide: CuO). By this oxidation treatment, fine projections are generated on the surface of copper, and it is possible to roughen the surface of the copper circuit by providing irregularities.

After the copper oxide layer is formed on the copper surface of the copper-clad laminate in this manner, the copper oxide layer is reduced while leaving the surface unevenness. That is, first, by coating the surface of the circuit board with metallic zinc powder, the zinc powder is attached to the surface of the copper oxide layer. For example, wet the surface of the circuit board with water and spray zinc dust, or apply a liquid in which zinc powder is dispersed in water or a solvent to the circuit board with a roll, or in a liquid such as water in which zinc dust is dispersed. The zinc dust can be coated on the surface of the circuit board by dipping the circuit board in.

Here, in the present invention, a mixture of pure zinc powder and zinc oxide powder is used as zinc dust. The pure zinc powder has an average particle size of 4 μm or less, and the range of the average particle size of the pure zinc powder is 3
-4 μm is preferable. The zinc oxide powder has an average particle size of 5
The average particle size of the zinc oxide powder is 0.5 μm.
It is preferable to set to. And the mixing ratio of the pure zinc powder and the zinc oxide powder is such that the pure zinc powder is more than 95% by weight (ie> 95% by weight) and the zinc oxide powder is less than 5% by weight (ie <5% by weight). It is something to set.

Thus, the pure zinc powder has an average particle size of 4
By using one having a thickness of less than μm, the amount of zinc powder deposited on the copper surface can be increased and the deposition can be stabilized,
It can be evenly attached to the surface of copper,
Further, in order to stabilize the adhesion of the zinc powder, it is necessary to set the average particle size of the zinc oxide powder to 5 μm or less. If the average particle size of pure zinc powder or zinc oxide powder exceeds these, the particles are too large and the adhesion to the copper surface deteriorates, and the adhesion becomes unstable and the copper particles evenly adhere to the surface. It will be difficult to do.

After the zinc dust is adhered to the surface of the copper oxide layer formed on the copper surface as described above, an acid such as sulfuric acid or hydrochloric acid is allowed to act on the surface of the circuit board to obtain pure zinc in the zinc dust. The powder is reacted with an acid to dissolve it. The reaction of the acid with the pure zinc powder can be carried out by immersing the circuit board in a bath of an acid solution such as an aqueous solution of the acid, or by spraying the circuit board with the acid solution. When the pure zinc powder is reacted with an acid in this way, the pure zinc powder is more easily ionized than the copper oxide, so that the pure zinc powder is dissolved in the acid solution in a cation state preferentially over the copper oxide. As described above, hydrogen is generated when the pure zinc powder is dissolved in the acid solution, and the hydrogen acts on the copper oxide layer to reduce the hydrogen. In particular, the state immediately after the generation of hydrogen, which is generated when pure zinc powder is dissolved in an acid solution, is extremely reactive, and hydrogen at this generation stage has a very high reducing action, and it has a strong effect on copper oxide. By reducing the copper oxide layer formed on the copper surface in this way, it is difficult to dissolve the copper oxide layer in an acid while retaining the roughened rough surface formed by the oxidation of copper. It can be put into a state.

In the present invention, since the zinc oxide powder is mixed with the pure zinc powder, the mixing rate of the zinc oxide powder can stabilize the dissolution rate of the pure zinc powder in the acid. By mixing the zinc oxide powder, the dissolution rate of the pure zinc powder in the acid can be increased and the dissolution can be stabilized, but if the ratio of the zinc oxide powder is increased, the dissolution rate becomes too high and the treatment is rather rather done. Since the ratio of pure zinc powder decreases and the reducing ability decreases as the amount of zinc oxide powder increases, the ratio of zinc oxide powder is set to less than 5% by weight. It is a thing. The lower limit of the proportion of zinc oxide powder is not particularly limited, but a lower limit of about 0.5% by weight is preferable.

[0016]

The invention will now be illustrated by the examples. A copper foil having a thickness of 35 μm is stretched on both sides to a thickness of 1 mm, 33
Using a glass cloth base epoxy resin laminated board with a size of 0 × 500 mm, a comb-shaped circuit with a circuit distance of 250 μm and a circuit width of 250 μm is formed to form a circuit board for the inner layer, and the surface of this copper circuit is buffed. Polished and roughened.

Next, an oxidation treatment bath having a composition of potassium persulfate 13 g / liter and sodium hydroxide 55 g / liter was adjusted to 60 ° C., and the circuit board was immersed in this oxidation treatment bath for 3 minutes to clean the surface of the copper circuit. Oxidized. The circuit board that has been oxidized as described above has an electrical conductivity of 20.
Immerse in 0 μS, calcium ion 0.15 ppm, chlorion ion 3 ppm, water temperature 50 ° C., agitate and shake air 50 times / minute to wash the circuit board with water and dry within 2 minutes after washing with water. Then, water drops were removed.

Next, 2 parts of zinc powder is added to 1 liter of water.
Disperse at a rate of 5 g, while stirring this zinc dust dispersion water at 80 ° C., immerse the circuit board treated with in this for 2 minutes, and coat the surface of the circuit board with zinc dust to coat the surface of the copper circuit. Zinc dust was attached. After coating the zinc dust on the surface of the copper circuit as described above, the circuit board is immersed in a concentrated sulfuric acid aqueous solution of 28% by weight for 2 minutes for acid treatment to dissolve the zinc dust. At the same time, nascent hydrogen produced by the reaction between zinc and sulfuric acid reduced the copper oxide layer on the surface of the copper circuit.

Then, 50 seconds after the reduction treatment as described above, the circuit board is advanced to the next neutralization step and immersed in an 8% aqueous sodium hydroxide solution for 1 minute for neutralization treatment, and the circuit thus treated. The plate was immediately washed with running water and dried at 100 ° C. for 30 minutes. A mixture of pure zinc powder and zinc oxide powder was used as the zinc powder used in the zinc powder coating step in treating the circuit board as described above. And
The proportion of zinc oxide in the mixture of pure zinc powder and zinc oxide powder was changed, and the relationship between the proportion of zinc oxide and the dissolution rate of zinc was measured. The results are shown in Table 1 and the graph of FIG.

[0020]

[Table 1]

As shown in Table 1 and FIG. 1, when the content of the zinc oxide powder exceeds 5% by weight, the dissolution rate of zinc reaches the maximum level and reaches a saturated state. The content rate is set to less than 5% by weight. Also, various kinds of zinc oxide powders having different average particle diameters were used, and the relationship between the average particle diameter of the zinc oxide powder and the amount of zinc adhered to the copper circuit of the circuit board was measured, and the copper after reduction treatment was used. The appearance of the circuit was inspected. The results are shown in Table 2. In Table 2, the "zinc adhesion amount" is shown as a relative value with the zinc powder adhesion amount being 100 when the average particle size of zinc oxide is 5.0 µm. In addition, in the "processed appearance", "○" means that the appearance is good, "△" means that there is some processing unevenness, and "x".
Indicates that there is uneven processing.

[0022]

[Table 2]

As seen in Table 2, when the average particle size of the zinc oxide powder is 6.0 μm, the amount of zinc dust adhered is greatly reduced, and reduction unevenness is largely generated, resulting in a poor appearance of the treatment. Therefore, in the present invention, the average particle diameter of the zinc oxide powder is set to 5 μm or less. further,
Using various types of pure zinc powder with different average particle diameters, measure the relationship between the average particle diameter of the pure zinc powder and the amount of zinc deposited on the copper circuit of the circuit board, and measure the copper circuit after the reduction treatment. The appearance was inspected. The results are shown in Table 3. In Table 3, "amount of zinc deposited" means that the average particle size of pure zinc powder is 4.0 μm.
It was displayed as a relative value with the amount of zinc powder adhered at that time being 100. In addition, in "processed appearance", "○" means good appearance,
“Δ” indicates that there is some processing unevenness, and “x” indicates that there is processing unevenness.

[0024]

[Table 3]

As shown in Table 3, when the average particle diameter of the pure zinc powder is 8.0 μm, the amount of adhesion is significantly reduced and the reduction unevenness is largely generated, resulting in a poor processed appearance. When the average particle size of the pure zinc powder is 4.0 μm, the amount of adhesion is high and the appearance of the treatment is good. Therefore, in the present invention, the average particle size of the pure zinc powder is set to 4 μm or less.

[0026]

As described above, according to the present invention, the ratio of pure zinc powder having an average particle size of 4 μm or less as the zinc powder is more than 95% by weight, and that of zinc oxide powder having an average particle size of 5 μm or less is 5% by weight. Since the mixture is used in a ratio of less than, it is possible to stabilize the amount of zinc dust adhered to the surface of copper by setting the particle size of pure zinc powder and zinc oxide powder,
Also, by mixing the zinc oxide powder, the dissolution rate of the pure zinc powder in the acid can be increased and the dissolution rate can be stabilized, and the zinc powder adheres to the surface of the copper evenly to reduce the reduced state of the copper oxide layer. Can be stabilized.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the content of zinc oxide and the dissolution rate of zinc.

Claims (1)

[Claims] 1. A circuit forming copper provided on the surface of a circuit board is oxidized to form a copper oxide layer on the surface of the copper, and a zinc powder is coated on the surface of the circuit board to form a copper surface. Pure zinc having an average particle size of 4 μm or less as zinc powder is used in order to dissolve zinc powder in an acid by treating with zinc acid after adhering zinc powder, and at the same time to reduce the copper oxide layer with hydrogen generated at this time. Powder of 95% by weight, average particle size 5μ
A method for surface treatment of copper on a circuit board, characterized in that zinc oxide powder having a particle size of m or less is mixed in a ratio of less than 5% by weight.