JPH0654829B2 - Method of treating copper foil for printed circuits - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for treating a copper foil for a printed circuit, and in particular, after a copper roughening treatment, a cobalt plating layer or a plating layer composed of cobalt and nickel is formed. The present invention relates to a treatment method for producing a copper foil for a printed circuit, which has alkali etching properties, good heat-resistant peel strength and heat-oxidation resistance, and has a blackened surface tone.

The copper foil of the present invention is particularly suitable, for example, as a fine pattern printed circuit and an FPC (Frexible Printed Circuit) for a magnetic head.

BACKGROUND OF THE INVENTION Copper foil for printed circuits is generally laminated and adhered to a base material such as a synthetic resin under high temperature and high pressure, and after printing a necessary circuit to form a target circuit, an unnecessary portion is removed and etched. Processing is performed. Finally, the required elements are soldered to form various printed circuit boards for electronic devices.

Quality requirements for a copper foil for a printed wiring board are different between a surface bonded to a resin substrate (so-called roughened surface) and a non-bonded surface (so-called glossy surface), and it is important to satisfy both at the same time.

The requirements for the roughened surface are mainly that there is no oxidative discoloration during storage, that the peel strength with the substrate is sufficient even after high temperature heating, wet treatment, soldering, chemical treatment, etc. The absence of so-called laminated stain after the laminating and etching, etc. can be mentioned.

On the other hand, for glossy surface, good appearance, no oxidative discoloration during storage, good solder wettability, no oxidative discoloration at high temperature heating, good adhesion with resist, etc. Is required.

In order to meet these demands, many treatment methods have been proposed for copper foils for printed wiring boards. Although the treatment method is different between the rolled copper foil and the electrolytic copper foil, basically, the roughening treatment is performed on the copper foil after degreasing, the rust prevention treatment is performed if necessary, and further the silane treatment is performed if necessary. Furthermore, the method of performing annealing has been established as one of the useful methods.

2. Description of the Related Art The above-mentioned roughening treatment holds a big key for determining the surface properties of copper foil. As the roughening treatment, a copper roughening treatment in which copper was electrodeposited was initially adopted, but with the progress of electronic circuits, many techniques have been proposed and implemented for the purpose of improving the surface properties thereof. Particularly, the copper-nickel roughening treatment has been established as a typical treatment method for the purpose of improving heat-resistant peel strength, hydrochloric acid resistance and oxidation resistance. The applicant of the present invention has proposed a copper-nickel roughening treatment in Japanese Patent Laid-Open No. 52-145769 and has achieved results.

The copper-nickel treated surface exhibits a black color, and in particular, in the rolled foil for flexible substrates, the black color of the copper-nickel treatment has been recognized as a symbol as a product.

However, while the copper-nickel roughening treatment is excellent in heat-resistant peel strength, oxidation resistance and hydrochloric acid resistance, it is difficult to etch with an alkaline etching solution which has recently become important as a fine pattern treatment, and a 150 μm pitch is required. When the fine pattern with a width less than the circuit width is formed, the processing layer remains as an etching residue.

Therefore, as a fine pattern treatment, the applicant of the present invention has previously proposed that Cu-Co treatment (Japanese Patent Publication No. 63-2158 and Japanese Patent Application No. 1-112227) and Cu-Co-Ni treatment (Japanese Patent Application No. 1-12).
-112226) was developed. These roughening treatments were good in terms of etching property, alkali etching property and hydrochloric acid resistance, but it was found again that the heat-resistant peel strength was reduced when an acrylic adhesive was used, and oxidation resistance was also found. The period was not sufficient and the color tone did not reach black, and it was brown to dark brown.

Problems to be Solved by the Invention With the recent trend toward fine patterning and diversification of printed circuits, heat-resistant peel strength (especially when an acrylic adhesive is used) and hydrochloric acid resistance comparable to those of Cu-Ni treatment The ability to etch printed circuits with a circuit width of 150 μm pitch or less with an alkaline etching solution, and oxidation resistance (180 ° C × 3
It was further required to improve the oxidation resistance in an oven for 0 minutes) and to perform the same blackening treatment as in the Cu-Ni treatment. That is, when the circuit becomes thin, the tendency that the circuit is easily peeled off by the hydrochloric acid etching solution becomes stronger, and it is necessary to prevent it. When the circuit becomes thin, the circuit is likely to peel off due to the high temperature at the time of processing such as soldering, and it is also necessary to prevent it. In the present time when fine patterning is progressing, it is already an essential requirement to be able to etch a printed circuit having a circuit width of 150 μm pitch or less with a CuCl ₂ etching solution, and alkali etching is becoming a necessary requirement as the resists are diversified. The blackening of the surface is also important from the viewpoint of copper foil production and chip mounting in terms of enhancing the alignment accuracy and heat absorption.

Thus, the object of the present invention is not only to have many of the general characteristics described above as a copper foil for printed circuits, but in particular to have the above-mentioned characteristics that are comparable to Cu-Ni treatment, and acrylic. The purpose of the present invention is to develop a copper foil treatment method that does not lower the heat-resistant peel strength when using a system adhesive, has excellent oxidation resistance, is alkali-etchable, and has a color tone close to black.

Means for Solving the Problems To solve the above-mentioned problems, the present inventor solves the above problems by performing a roughening treatment with copper, which is the most basic, on a copper foil surface, and then forming a cobalt plating layer or a plating layer composed of cobalt and nickel thereon. It was found that it is sufficiently effective if formed. Based on this finding, the present invention is characterized in that, in a method for treating a copper foil for a printed circuit, after a copper roughening treatment, a cobalt plating layer or a plating layer composed of cobalt and nickel is formed on the surface of the copper foil. A method for treating a copper foil for a printed circuit is provided. Preferably, after forming the cobalt plating layer or the plating layer consisting of cobalt and nickel,
A rust-preventive treatment typified by a single film treatment of chromium oxide or a mixed film treatment of chromium oxide and zinc and / or zinc oxide is performed.

Detailed Description of the Invention The copper foil used in the present invention may be either an electrolytic copper foil or a rolled copper foil.

Usually, on the surface of the copper foil that is bonded to the resin substrate, that is, the roughened surface, for the purpose of improving the peeling strength of the copper foil after lamination, the surface of the copper foil after degreasing, for example, is made of copper Roughening treatment is performed to perform electrodeposition in the form of strips. Such copper kinky electrodeposition is easily brought about by so-called burn electrodeposition. Normal copper plating or the like may be performed as a pretreatment before roughening, and normal copper plating or the like may be performed as a finishing treatment after roughening. The rolled copper foil and the electrolytic copper foil may have slightly different contents of treatment. In the present invention, including the pretreatment and finishing treatment, known treatments relating to copper roughening are included as necessary, and are collectively referred to as copper roughening treatment.

As an example of the copper roughening treatment, for example, the following conditions can be adopted.

Copper roughening treatment Cu: 10 to 25 g / H ₂ SO ₄ : 20 to 100 g / Temperature: 20 to 40 ° C. D _k : 30 to 70 A / dm ² hours: 1 to 5 seconds The present invention is, after copper roughening treatment, A cobalt plating layer or a plating layer composed of cobalt and nickel is formed as a two-step plating thereon.

Conditions of the cobalt plating or cobalt and nickel plating are as follows: cobalt plating Co 1 to 30 g / Temperature _{30~80 ℃ pH 1.0~3.5 D k 1.0~10.0A /} dm 2 hours 0.5-4 seconds cobalt - nickel plated Co 1 to 30 g / Ni 1 to 30 g / temperature 30 to 80 ° C. pH 1.0 to 3.5 D _k 1.0 to 10.0 A / dm ² hours 0.5 to 4 seconds This cobalt or cobalt-nickel plating improves the adhesive strength between the copper foil and the substrate. It should be carried out to the extent that it does not substantially decrease. That is, according to the present invention, the electrodeposition amount (μg / dm ² ) of cobalt or cobalt-nickel plating is preferably in the range of 200 ≦ Co ≦ 4000 200 ≦ Co + Ni ≦ 4700. If it is less than the lower limit, the desired effect does not occur, the heat-resistant peel strength decreases, and the oxidation resistance and chemical resistance deteriorate. On the other hand, if it exceeds the upper limit, the influence of magnetism becomes large, which is not preferable.

In the case of cobalt-nickel plating, the electrodeposition amount of nickel (μg / dm ² ) is preferably 100 ≦ Ni ≦ 1000. If it is less than the lower limit, the heat resistance will be poor, and if it is more than the upper limit, the etching residue with the alkaline etching solution will increase.

Thus, the cobalt or cobalt-nickel plating is characterized by being extremely thin and exhibiting the desired effect.

After that, rustproofing treatment is carried out if necessary. In the present invention, the preferred rust preventive treatment is a coating treatment of chromium oxide alone or a coating treatment of a mixture of chromium oxide and zinc / zinc oxide. Chromium oxide and zinc / zinc oxide mixture coating treatment means zinc or zinc consisting of zinc oxide and chromium oxide by electroplating using a plating bath containing zinc salt or zinc oxide and chromate. This is a treatment for coating the anticorrosion layer of the chromium-based mixture. As the plating bath, dichromates such as K ₂ Cr ₂ O ₇ , Na ₂ Cr ₂ O ₇ and CrO ₃ are typically used.
And at least one of water-soluble zinc salts such as ZnO and ZnS
A mixed aqueous solution of at least one of O ₄ .7H ₂ O and alkali hydroxide is used. Representative plating bath compositions and examples of electrolysis conditions are as follows: K ₂ Cr ₂ O ₇ (Na ₂ Cr ₂ O ₇ or CrO ₃ ) 2 to 10 g / NaOH or KOH 10 to 50 g / ZnO or ZnSO ₄ · 7H ₂ O 0.05 to 10 g / pH 7 to 13 Bath temperature 20 to 80 ° C Current density 0.05 to 5 A / dm ² hours 5 to 30 seconds Anode Pt-Ti plate, stainless steel plate, etc. Chromium oxide has a chromium content of 15 μg / dm ² Above, zinc is required to have a coating amount of 30 μg / dm ² or more. The rough surface side and the glossy surface side may have different thicknesses. Such rust prevention methods are disclosed in Japanese Examined Patent Publications Sho 58-7077, 61-33908,
62-14040 and the like.

The copper foil thus obtained has heat-resistant peel strength, oxidation resistance and hydrochloric acid resistance comparable to those of the Cu-Ni treatment, and
A printed circuit with a circuit width of 150 μm or less can be etched with CuCl ₂ etching solution, and alkaline etching is also possible. As the alkaline etching solution, for example,
Liquids such as NH ₄ OH: 6 mol /; NH ₄ Cl: 5 mol /; CuCl ₂ ; 2 mol / (temperature 50 ° C.) are known.

More importantly, the resulting copper foil has a dark ash to black color, similar to that of Cu-Ni treatment. Such a blackened color is important in terms of alignment accuracy and high heat absorption rate. More specifically, printed circuit boards including rigid boards and flexible boards are mounted with components such as ICs, resistors, capacitors, etc. in an automatic process, and at that time, they are mounted on a chip while reading a circuit with a sensor. At this time, alignment on the copper foil treated surface may be performed through a film such as Kapton. The same applies to positioning when forming through holes. At this time, the closer the processed surface is to black, the better the light absorption, and the higher the positioning accuracy. Furthermore, when a substrate is produced, the copper foil and the film are often cured and bonded to each other while applying heat. At this time, when heating is performed by using a long wavelength wave such as far infrared rays or infrared rays, the heating efficiency is improved when the color tone of the treated surface is dark.

Finally, if necessary, a silane treatment for applying a silane coupling agent to at least roughening the rust-preventive layer is performed, mainly for the purpose of improving the adhesive force between the copper foil and the resin substrate. The coating method may be spraying of a silane coupling agent solution, coating with a coater, dipping, pouring, or the like. For example, Japanese Examined Patent Publication No. 60-15654 describes that the adhesion between the copper foil and the resin substrate is improved by subjecting the rough surface side of the copper foil to a chromate treatment and then a silane coupling agent treatment. Please refer to this for details.

Thereafter, if necessary, an annealing treatment may be performed for the purpose of improving the ductility of the copper foil.

Next, examples and comparative examples will be presented.

Examples and Comparative Examples Rolled copper foil was subjected to copper roughening treatment under normal conditions to remove copper from copper 2
After adhering 0 mg / dm ^2, it was washed with water to form cobalt plating or cobalt-nickel plating as two-stage plating. In the two-step plating, when cobalt plating alone is used,
Cobalt deposition amount is 1000 μg / dm ² , and cobalt-
In the case of nickel plating, the amount of cobalt deposited is 500 μg / dm
² and the amount of nickel deposited was 540 μg / dm ² . After washing with water, it was rustproofed and dried.

These cobalt plating or cobalt-nickel plating plating conditions were as follows.

Co plating Co: 10 g / pH: 2.5 Temperature: 50 ° C. D _k : 3 A / dm ² hours: 2 seconds Co-Ni plating Co: 10 g / Ni: 20 g / pH: 2.5 Temperature: 50 ° C. D _k : 3 A / dm ² hours: 2 seconds Further, as a sample for comparison, a sample subjected to only copper, copper-nickel (reference sample), copper-cobalt and copper-cobalt-nickel roughening plating treatment was also prepared. These conditions are within the following range and the following adhesion amount (total about 2
It was appropriately selected to be 0 mg / dm ² ): Cu plating As described above.

Cu adhesion amount: 20 mg / dm ² Cu-Ni plating Cu: 5-10 g / Ni: 10-20 g / pH: 1-4 Temperature: 20-40 ° C. D _k : 10-30 A / dm ² hours: 2-5 seconds Cu deposition amount: 10 mg / dm ² Ni deposition amount: 10 mg / dm ² Cu-Co plating Cu: 10-20 g / Co: 1-10 g / pH: 1-4 Temperature: 40-50 ° C. D _k : 20-30 A / dm ² hours: 1 to 5 seconds Cu adhesion amount: 18 mg / dm ² Co adhesion amount: 2000 μg / dm ² Cu-Co-Ni plating Cu: 5 to 25 g / Co: 3 to 15 g / Ni: 3 to 15 g / pH: 1-4 _{temperature: 20~50 ℃ D k: 10~30A /} dm 2 Time: 2-5 seconds Cu deposition amount: 17 mg / dm ² Co deposition amount: 2000μg / dm ² Ni deposition amount: 500 [mu] g / dm ² of these processes The color tone of the latter material was first examined.
The degree of blackening was measured using a digital desitometer Model 144, with the standard sample black being 1.81 and the standard sample white being 0.08.

The results are shown in Table 1. Sample 1 is an example in which copper roughening was only performed and two-step plating was not performed. Samples 2 and 3 are examples of the present invention. Sample 4 is an example of copper-nickel roughening treatment as a reference example. Samples 5 and 6 are prior art examples.

Next, regarding these samples, after heat aging at 150 ° C. for 10 days, heat-resistant peel strength characteristics (deterioration rate%) using a polyimide film such as Kapton and an acrylic adhesive, 180 ° C. for 30 minutes, copper in an oven was used. The foil was put in and the oxidation resistance test for examining the oxidative discoloration of the surface and the alkali etching property were evaluated. For heat-resistant peel strength, samples are laminated and bonded, and normal (room temperature) peel strength (kg / cm)
Was measured and shown as the deterioration rate (%) of the peel strength after aging. The oxidation resistance is the result of visual observation of the oxidation state. The alkali etching is the result of visual observation of the etching state using the above-mentioned alkali etching solution.

The results are summarized in Table 2.

It should be noted that the higher the value of the blackening degree, the darker it is. It is necessary that the blackening degree is 1.0 or more from the color tone.

From the above Tables 1 and 2, it can be seen that by performing the two-step plating of the present invention, the color tone of the copper foil surface becomes black and the degree of blackening approaches 1.210 of copper-nickel plating. The deterioration rate of heat-resistant peel strength is also improved. Both oxidation resistance and alkali etching resistance are good.

Effects of the Invention The present invention provides a method for treating a copper foil capable of accommodating high density and high number of layers for a printed circuit accompanying the recent rapid development of semiconductor devices. The copper foil produced by this method should have heat-resistant peel strength (especially when an alkaline adhesive is used) and hydrochloric acid resistance that are comparable to those of the Cu-Ni treatment. Satisfies the requirements of being able to etch, improving the oxidation resistance as in the case of Cu-Ni treatment, and being the same blackening treatment as in the case of Cu-Ni treatment. The present invention can be used particularly as a fine pattern and as an FPC for a magnetic head.

Claims (3)

[Claims] 1. A method for treating a printed circuit copper foil, comprising forming a cobalt plating layer or a plating layer composed of cobalt and nickel on the surface of the copper foil after copper roughening treatment. Processing method. 2. The method for treating a copper foil for a printed circuit according to claim 1, wherein a rust preventive treatment is performed after the cobalt plating layer or the plating layer composed of cobalt and nickel is formed. 3. The rust preventive treatment is a single coating treatment of chromium oxide or a mixed coating treatment of chromium oxide and zinc and / or zinc oxide.
A method for treating a copper foil for a printed circuit according to the item.