JPH0732311B2 - Method for treating copper circuit of circuit board for inner layer - Google Patents

Description

Detailed Description of the Invention

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for 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 applicant has previously filed Japanese Patent Application No. 2-69363 (Japanese Patent Application No.
-68113), 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 zinc (Zn) 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 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.

However, when coating the surface of the copper circuit of the inner layer circuit board with the Zn powder as described above, the circuit board is immersed in a suspension solution in which the Zn powder is dispersed and suspended. Zn on the surface of the copper circuit
Although this is done by depositing the powder, the coating of the Zn powder is uneven, and the reduction of the copper oxide is insufficient, which may cause a halo. Therefore,
There has been a problem that it is necessary to increase the coating amount of the Zn powder in order to prevent defective reduction treatment, resulting in an increase in cost. The present invention has been made in view of the above points, the coating of the Zn powder can be uniformly performed to prevent the occurrence of halo surely and can reduce the processing cost of the copper circuit of the inner layer circuit board It is intended to provide a processing method.

[Means for Solving the Problems]

A 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 a copper oxide on the surface of the circuit, and then in a suspension solution of Zn powder. After coating the Zn powder on the surface of the copper oxide by dipping this circuit board in, to dissolve the Zn powder with acid and reduce the copper oxide with nascent hydrogen generated at this time,
Place the circuit board vertically in a suspension of Zn powder and immerse it.
It is characterized in that the circuit board is swung in the vertical direction in a direction perpendicular to the front and back surfaces with the upper end portion as the swing center. Further, in the present invention, the circuit board is placed horizontally in a suspension solution of Zn powder and immersed, and the circuit board is rotated vertically in a direction perpendicular to the front and back surfaces with the center in the width direction as the center of rotation. You may allow it. Further, in the present invention, the liquid flow may be applied to the front and back surfaces of the circuit board immersed in the suspension solution of Zn powder by alternately switching the strength of the liquid flow. 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 aqueous alkaline 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 this reduction treatment, 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 and coated.
The coating of the Zn powder can be performed by, for example, immersing the circuit board for the inner layer in a suspension solution prepared by dispersing and suspending the Zn powder in water. In the first invention of the present invention, when the circuit board A for the inner layer is thus immersed in the Zn powder suspension B, as shown in FIG. The inner layer circuit board A dipped in is swung in the vertical direction in a direction perpendicular to the front and back surfaces thereof. That is, in the example of FIG.
The circuit board A is dipped vertically in the Zn powder suspension solution B, and the circuit board A is vertically centered on the upper end of the circuit board A in a direction perpendicular to the surface thereof and at a predetermined angle α with respect to the gravity direction. , Β
I try to rock it. α and β are 1 °
The larger the angle is, the more preferable. By swinging the circuit board A in the Zn powder suspension solution B at a predetermined angle in this manner, a liquid flow of the Zn powder suspension B can be generated on the surface of the circuit board A, and The Zn powder can be uniformly applied to the surface to uniformly coat the surface of the copper circuit with the Zn powder. Therefore, it is possible to uniformly coat the Zn powder without increasing the coating amount of the Zn powder, and the processing cost does not increase. Further, in the second invention of the present invention, the circuit board A immersed in the Zn powder suspension solution B is rotated vertically in a direction perpendicular to the front and back surfaces thereof. That is, in the example of FIG.
The circuit board A is immersed in the powder suspension solution B in a horizontal state with one surface facing upward, and then rotated at an angle of 180 ° in the direction of the arrow so that the other surface may be turned upside down. ing. This rotation may be performed intermittently or continuously. By rotating the circuit board A in the Zn powder suspension solution B in this manner, a liquid flow of the Zn powder suspension B is generated on the surface of the circuit board A to uniformly distribute the Zn powder on the surface of the circuit board A. The amount of Zn powder settled in the Zn powder suspension B and deposited on the surface of the circuit board A becomes equal on both front and back surfaces, and as a result, the Zn powder is deposited on the surface of the copper circuit. It can be uniformly coated. Further, according to the third aspect of the present invention, the strength of the liquid flow is alternately switched to both sides of the circuit board dipped in the suspension solution of Zn powder to apply the liquid flow. That is, in the example of FIG. 3, the circuit board A is immersed vertically in the Zn powder suspension solution B, and the propeller 2 is rotationally driven to generate a liquid flow in the treatment tank 1 to generate a liquid flow of the circuit board A. The liquid stream is sprayed on both sides at a right angle. At this time, as shown in FIG. 3 (a), a strong liquid flow (indicated by a double arrow) is applied to one surface of the circuit board A, and at the same time, a weak liquid flow (indicated by a single arrow) is applied to the other surface of the circuit board A. Then, the strength of the liquid flow is switched to weaken the liquid flow applied to one surface of the circuit board A and simultaneously the liquid flow applied to the other surface of the circuit board A as shown in FIG. 3 (b). So that the operation shown in FIGS. 3 (a) and 3 (b) can be repeated. The flow velocity of the liquid is not particularly limited as long as it is strong enough to prevent the set of the circuit board A from coming off, and may be 0 m / sec for weak liquid. In this way, by spraying the liquid flow of the powder suspension solution B on both surfaces of the circuit board A, the Zn powder can be made to uniformly act on the surface of the circuit board A, and the strength of the liquid flow can be improved. Since the liquid flow is applied by alternately switching, the action of the Zn powder can be made more uniform, and as a result, the surface of the copper circuit can be uniformly coated with the Zn powder. It should be noted that the Zn powder may be coated by combining the methods shown in FIGS. 1, 2, and 3 above. In this case, in particular, the combination of the methods shown in FIGS. 1 and 3 and FIG. The combination of the method shown in FIG. 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 from the surface of the copper oxide with an acid. 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 therefore the Zn is preferentially dissolved in the cation state over the copper oxide. Thus, when the Zn powder is dissolved in acid, hydrogen is generated, and this hydrogen acts on the copper oxide in the copper circuit to reduce the cupric oxide (CuO) contained in the copper oxide. (Cu 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 to prevent the halo phenomenon caused by acid dissolution. 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 Zn powder that is dissolved in an acid in preference to the copper oxide, the Zn 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. Further, since a gas such as hydrogen generated when the Zn powder is dissolved in the acid wraps the surface of the copper oxide, this gas can also protect the copper oxide from the acid. After treating with acid in this way and performing reduction treatment, the inner layer circuit board is immediately immersed in a strong alkaline solution, or the inner layer circuit board is sprayed with a strong alkaline solution to form an inner layer circuit board. The acid adhering to is removed by neutralization, and then immediately washed with water, hot water, etc., and dried, and then the inner layer circuit board can be used to produce a multilayer printed wiring board in a usual 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 bath for 3 minutes to clean the surface of the copper circuit. Oxidized. Next, a bath in which 10 g of zinc powder having an average particle size of 5 μm is suspended in 1 liter of water is heated to 90 ° C., the circuit board for the inner layer is immersed in this suspension, and zinc is applied to the surface of the copper circuit. The powder was applied and coated. At this time, 10 circuit boards A for the inner layer were set in a basket rack in parallel, immersed in suspension B so that the circuit board A for the inner layer was vertical as shown in FIG. 1, and shaken. The circuit board A was slowly rocked at a rocking speed of a cycle of 6 times / minute with the dynamic angles α and β set to 10 °, respectively, and the zinc powder was coated for 2 minutes. 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 inner layer circuit board is neutralized by immersing the inner layer circuit board in a strong alkaline aqueous solution (pH 13.1) containing 0.4% by weight of NaOH for 1 minute. After that, the inner layer circuit board is washed with running water and dried. did. And on both sides of the circuit board for inner layer treated in this way,
While stacking three 0.1 mm thick prepregs prepared by impregnating and drying an epoxy resin on a glass cloth base material, further stacking a 18 μm thick copper foil on the outer side of the prepreg under an atmosphere decompressed to 6.7 × 10 ³ pascals, A multi-layer board was obtained by secondary lamination molding under the conditions of 170 ° C., 40 kgf / cm ² and 120 minutes. Example 2 A basket rack 3 containing ten inner layer circuit boards A as in Example 1 is immersed in a suspension B so that the inner layer circuit boards A are horizontal as shown in FIG. The entire basket rack 3 was rotated as indicated by the arrow so that the zinc powder was coated for 2 minutes. Others were the same as in Example 1. Example 3 A basket rack 3 containing ten inner-layer circuit boards A as in Example 1 is immersed in a suspension B so that the inner-layer circuit boards A are horizontal as shown in FIG. After holding the inner circuit board A horizontally for 30 seconds, the entire basket rack 3 is rotated 180 ° as shown by the arrow.
The zinc powder coating treatment was carried out for 2 minutes by repeating the operation of rotating so as to invert at an angle of. Others were the same as in Example 1. Example 4 As shown in FIG. 6, a basket rack 3 containing ten inner layer circuit boards A as in Example 1 is immersed in a suspension B so that the inner layer circuit boards A are vertical, The propeller 2 was operated to alternately spray the suspension B from the left and right at a flow rate of 0.2 m / sec, and the zinc powder coating treatment was performed for 2 minutes. Others were the same as in Example 1. Comparative Example 1 The procedure of Example 1 was repeated, except that the concentration of zinc powder in the suspension in step 1 was set to 50 g / liter and that the treatment was not performed. Comparative Example 2 The same procedure as in Example 1 was carried out except that the zinc powder coating treatment in Example 1 was such that the circuit board A of FIG. The coating amount of the zinc powder in the above Examples 1 to 4 and Comparative Examples 1 and 2 was measured. The results are shown in the following table by the average value () and standard deviation (σ _n-1 ). In addition, the cost of the coating process of this zinc powder is shown in Comparative Example 1 as "1" for relative comparison. Further Examples 1-4
The through holes were processed in the multilayer plates obtained in Comparative Examples 1 and 2 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 with the processed through holes was immersed in a 17.5% HCl aqueous solution for 10 minutes, and the presence or absence of halo was observed. The results are shown by the number of numerator (numerator) generated for 20 (denominator) of the number of observed multilayer boards. As can be seen from the results in the above table, the halo occurrence rate of each of the examples is low, and it is confirmed that the zinc powder is uniformly coated. Also, the processing cost was relatively low.

【The invention's effect】

As described above, in the present invention, the circuit board is vertically arranged and immersed in a suspension solution of Zn powder in a direction perpendicular to the front and back surfaces with the upper end of the circuit board as a swing center. The circuit board should be oscillated vertically or immersed in a suspension of Zn powder with the circuit board placed horizontally, and the circuit board should be placed in a direction perpendicular to the front and back sides with the center in the width direction as the center of rotation. To rotate vertically, or to switch the liquid flow strength alternately between the front and back sides of the circuit board immersed in the suspension solution of Zn powder, so that the liquid flow can be applied to the surface of the circuit board. The Zn powder can be uniformly coated on the surface of the copper circuit by uniformly applying the Zn powder to the Zn powder, and the Zn powder can be uniformly coated without increasing the coating amount of the Zn powder. , Reduction processing without increasing the processing cost The uniformly performed in which it is possible to reliably prevent the occurrence of the halo.

[Brief description of drawings]

FIG. 1, FIG. 2, FIG. 3 (a) (b), FIG. 4 and FIG.
FIG. 6 and FIG. 6 are schematic views showing the method of the present invention. A is a circuit board for the inner layer, and B is a Zn powder suspension.

Claims (3)

[Claims] 1. A copper circuit provided on an inner layer circuit board is oxidized to form a copper oxide on the surface of the circuit, and then the circuit board is immersed in a suspension solution of Zn powder to form the copper oxide. After coating the Zn powder on the surface of the Zn powder, dissolve the Zn powder with an acid and at the same time reduce the copper oxide with the nascent hydrogen generated at this time, put the circuit board vertically in a suspension solution of the Zn powder. A method of treating a copper circuit of an inner layer circuit board, which comprises arranging and immersing the circuit board, and vertically swinging the circuit board about an upper end of the circuit board in a direction perpendicular to the front and back surfaces. 2. A copper circuit provided on an inner layer circuit board is oxidized to form a copper oxide on the surface of the circuit, and then the circuit board is immersed in a suspension solution of Zn powder to form the copper oxide. After coating the Zn powder on the surface of the Zn powder, dissolve the Zn powder with an acid and at the same time reduce the copper oxide with nascent hydrogen generated at this time, place the circuit board horizontally in a suspension solution of the Zn powder. A method for treating a copper circuit of an inner layer circuit board, which comprises arranging and immersing the circuit board, and rotating the circuit board in a vertical direction in a direction perpendicular to the front and back surfaces with a center portion in the width direction as a rotation center. 3. 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 circuit board is immersed in a suspension solution of Zn powder to form the copper oxide. After coating the surface of the Zn powder with the acid to dissolve the Zn powder and reduce the copper oxide with the nascent hydrogen generated at this time, the circuit board immersed in the suspension solution of the Zn powder A method for treating a copper circuit of a circuit board for an inner layer, characterized in that the strength of the liquid flow is alternately switched between the front and back surfaces to apply the liquid flow.