JPH0654831B2 - Method of treating copper foil for printed circuits - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for treating a copper foil for a printed circuit, and in particular, to a surface of a copper rough surface after a roughening treatment by plating comprising copper-cobalt-nickel, A copper foil for a printed circuit having a black surface color tone, which has alkali etching property, good heat-resistant peel strength and heat-oxidation resistance by forming a cobalt plating layer or a plating layer made of cobalt and nickel The present invention relates to a processing method for generating.

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-described roughening treatment holds a big key for determining the surface properties of a copper foil. As the roughening treatment, copper roughening treatment in which copper was initially electrodeposited was adopted, but with the progress of electronic circuits, a number of techniques have been proposed and implemented for the purpose of improving the surface properties thereof, but in particular, A 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 application filed JP-A-52-1457.
In No. 69, a copper-nickel roughening treatment was proposed and the results were paid.

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 processing, the applicant of the present invention has previously proposed that Cu-Co processing (Japanese Patent Publication No. 63-2158 and Japanese Patent Application No. 1-112227) and Cu-Co-Ni processing (Japanese Patent Application No.
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 black surface is also important from the viewpoint of copper foil fabrication and chip mounting in terms of enhancing alignment accuracy and heat absorption.

Thus, the problem of the present invention is, of course, to have many of the general characteristics described above as a printed circuit copper foil,
In particular, a copper foil treatment method that has the above-mentioned characteristics that are comparable to those of Cu-Ni treatment, yet does not lower the heat-resistant peel strength when using an acrylic adhesive, has excellent oxidation resistance, and has a black surface color tone. Is to develop.

Means for Solving the Problems The present inventor has conducted research to make use of the usefulness of roughening treatment with copper-cobalt-nickel, which is one of the conventionally proposed methods, and as a result, copper-cobalt-nickel on the copper foil surface. It was found that it is effective to form a cobalt plating layer or a plating layer composed of cobalt and nickel thereon after the roughening treatment by.

Based on this finding, in the method for treating a copper foil for a printed circuit, the present invention provides a surface of a copper foil after a roughening treatment by plating comprising copper-cobalt-nickel and then a cobalt plating layer or a plating layer comprising cobalt and nickel. The present invention provides a method for treating a copper foil for a printed circuit, which comprises forming

Preferably, after forming the cobalt plating layer or the plating layer composed of cobalt and nickel, a coating treatment of chromium oxide alone or a coating treatment of chromium oxide and zinc and / or zinc oxide is representative. Rust treatment is applied.

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, the surface of the copper foil that is bonded to the resin substrate, that is, the roughened surface, has the purpose of improving the peeling strength of the copper foil after lamination, and for the purpose of improving the peeling strength of the copper foil after degreasing. A roughening process is carried out for the coating. In the present invention, this roughening treatment is performed by copper-cobalt-nickel alloy plating.
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, the known treatments related to the copper foil roughening, including such pretreatment and finishing treatment, are collectively referred to as the roughening treatment, if necessary.

According to the invention, this alloy plating is carried out by electroplating to form 15-40 mg / dm ² copper-100-2000 μg / dm ² cobalt-100-1000 μg / dm ² nickel ternary alloy. .

In addition, Co and Ni in the Cu-Co-Ni ternary alloy layer
The contents are 1-4 wt% Co and 0.5-1.5 wt% Ni.

The general bath and plating conditions for forming such a ternary alloy plating are as follows.

Bath composition and plating conditions Cu: 10 to 20 g / Co: 1 to 10 g / Ni: 1 to 10 g / pH: 1 to 4 Temperature: 40 to 50 ° C. Current density D _k : 20 to 30 A / dm ² hours: 1 to 5 Second In the present invention, after the 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 ≦ 1700 200 ≦ Co + Ni ≦ 2300. 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 obtained copper foil has a black color as in the case of Cu-Ni treatment. Such black 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 the roughened surface of 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.

Hereinafter, examples and comparative examples will be presented.

Copper range of conditions described above in the Examples and Comparative Examples rolled copper foil - cobalt - is subjected to nickel plating roughening treatment, copper 17 mg / dm ^2, after the cobalt 2000 [mu] g / dm ² and the nickel was 500 [mu] g / dm ² deposited After washing with water, cobalt plating or cobalt-nickel plating as two-step plating was formed. If the cobalt adhesion amount of the cobalt plating alone 1000 [mu] g / dm ^2, and Cobalt - For nickel plating, cobalt coating weight 500 [mu] g / dm ^2, the nickel coating weight was 540μg / dm ^2. After washing with water, it was rustproofed and dried.

The cobalt plating and cobalt-nickel 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 reference samples for comparison, copper, copper-nickel (reference sample), copper-cobalt and copper-cobalt-nickel roughening plating. A product that was only processed was also prepared.
These conditions were appropriately selected from the following ranges so as to obtain the following adhesion amount (total about 20 mg / dm ² ): Copper roughening treatment Cu: 10 to 25 g / H ₂ SO ₄ : 20 to 100 g / temperature : 20 to 40 ° C _Dk : 30 to 70 A / dm ² hours: 1 to 5 seconds Copper adhesion amount: 20 mg / dm ² Cu-Ni plating Cu: 5 to 10 g / Ni: 10 to 20 g / pH: 1 to 4 temperature : 20 to 40 ° C. D _k : 10 to 30 A / dm ² hours: 2 to 5 seconds Copper adhesion amount: 10 mg / dm ² Nickel adhesion amount: 10 mg / dm ² Cu-Co plating Cu: 10 to 20 g / Co: 1 to 10 g / pH: 1 to 4 Temperature: 40 to 50 ° C. D _k : 20 to 30 A / dm ² hours: 1 to 5 seconds Copper deposition amount: 18 mg / dm ² Cobalt deposition amount: 2000 μg / dm ² Cu-Co-Ni plating As above.

Copper coverage: 17 mg / dm ² Cobalt coverage: 2000 μg / dm ² Nickel coverage: 500 μg / dm ² The color tone of these treated materials 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, heat-resistant peel strength characteristics (deterioration rate%) using a polyimide film such as Kapton and an acrylic adhesive after aging at 150 ° C. for 10 days, copper foil in an oven at 180 ° C. for 30 minutes Then, an oxidation resistance test for examining the oxidative discoloration of the surface and an 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.

The higher the degree of blackening, the darker it is, and the degree of blackening needs to be 1.0 or more according to 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 significantly improved as compared with Comparative Examples 5 and 6. 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 according to this method should have heat-resistant peel strength (especially when using an acrylic adhesive) and hydrochloric acid resistance comparable to those in the case of Cu-Ni treatment. Use a printed circuit of 150 μm pitch circuit width or less with an alkaline etching solution. 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 copper foil for a printed circuit, comprising forming a cobalt plating layer or a plating layer comprising cobalt and nickel on the surface of the copper foil after roughening treatment by plating comprising copper-cobalt-nickel. A characteristic method of treating a copper foil for a printed circuit. 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.