JPH0650795B2 - 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, it has a relatively good peel strength property and alkali etching property, and has a magnetic property. The present invention relates to a processing method for producing a small copper foil for a printed circuit. INDUSTRIAL APPLICABILITY The copper foil of the present invention is used, for example, in a fine pattern printed circuit, an FPC (Frexib) for a magnetic head.
Especially suitable as a le Printed Circuit).

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. The treatment method is different between rolled copper foil and electrolytic copper foil, but after degreasing, the copper foil is subjected to pretreatment including plating and roughening treatment, if necessary, and then alloy plating to form the required copper foil surface. It has been established that one of the useful methods is to perform rust prevention treatment, silane treatment, and if necessary silane treatment.

2. Description of the Related Art The alloy plating treatment described above holds a major key in determining the surface properties of a copper foil. As a typical processing method for alloy plating, the applicant of the present invention has already proposed Cu-Co processing (Japanese Patent Publication No. 63-2158) and has achieved results.

The CU-Co treatment can etch printed circuits with a copper chloride (CuCl ₂ ) etchant of less than 150μ pitch circuit width, enables alkaline etching, and has relatively good peel strength characteristics. Copper foil for future printed circuits Is expected to be useful.

Problems to be Solved by the Invention With the recent trend toward fine patterning and diversification of printed circuits, it is no longer essential to be able to etch printed circuits with a circuit width of 150 μpitch or less with CuCl ₂ etching solution. With the diversification of the above, alkali etching is becoming a necessary requirement.

More importantly, in view of higher performance of the printed circuit and expansion of its application, especially application as an FPC for a magnetic head, the printed circuit is often arranged close to the magnetic medium. There is a new interest in.
Alloys with large magnetic susceptibility as found in conventional Cu-Co alloys cannot be used, and the saturation magnetization, remanent magnetization and coercive force must be regulated to below a predetermined level.

OBJECT OF THE INVENTION The object of the present invention is not only to have many of the general characteristics described above as a printed circuit copper foil, but also to maintain good peel strength characteristics, while using a CuCl ₂ etching solution of 150 μm.
It is an object of the present invention to provide a copper foil for a printed circuit, which can etch a printed circuit having a pitch circuit width or less, can also be alkali-etched, and has a magnetic susceptibility of an acceptable level or less.

SUMMARY OF THE INVENTION As a result of repeated studies aimed at the above objects, the present inventors found that a copper-cobalt binary alloy having a smaller cobalt content than the conventionally used Cu-Co alloy fulfills the above objects. I came to find out again. Further, the subsequent rust-prevention treatment is also important, and it has been found that the coating treatment of chromium oxide alone or the coating treatment of a mixture of chromium oxide and zinc / zinc oxide is suitable for the purpose of the present invention on the alloy plating layer.

It has been found that by using a binary alloy having a controlled cobalt content, the magnetic susceptibility can be reduced to an allowable level or lower while maintaining the advantages of the conventional Cu-Co alloy. This was an unexpected finding.

Based on these findings, the present invention provides (1) a method for treating a copper foil for a printed circuit, wherein the surface of the copper foil to be treated has 20 to 40 mg / dm ² of copper and 100 to 100 cobalt.
A method for treating a copper foil for a printed circuit, which comprises forming an electroplating layer of 3000 μg / dm ² , and (2) a rustproofing treatment after the formation of the electroplating layer. 1) A method for treating a copper foil for a printed circuit according to 1) is provided.

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 A roughening treatment for performing electrodeposition is performed. Such copper kinky electrodeposition is easily brought about by so-called burn electrodeposition.
Conventional copper plating may be performed as a pretreatment before roughening and as a finishing treatment after roughening. Roughening treatment by other known methods can also be carried out. The rolled copper foil and the electrolytic copper foil have different processing contents.
The roughening treatment itself may be omitted in some types of rolled copper foil. In the present invention, such processing is generically called preprocessing.

The present invention relates to the treatment of copper foil after pretreatment. After pretreatment, an alloy surface is formed by plating on at least one side of the copper foil, which provides many of the properties required for a printed circuit surface.

According to the invention, this alloy plating is performed by electroplating 20-40 mg / dm ² copper-100-3000 μg / dm ²
Conducted to form a cobalt binary alloy. If the cobalt content is less than 100 μg / dm ² , the peeling characteristics (heat deterioration and hydrochloric acid resistance) and heat resistance deteriorate, and the etching property deteriorates. On the other hand, when the cobalt content exceeds 3000 μg / dm ² , the influence of magnetism becomes large, which is not preferable.

It is difficult to uniquely determine the thickness of the Cu—Co binary alloy layer because the surface of the copper foil has irregularities and the true specific gravity of the alloy is unknown.

Therefore, if the true specific gravity of Cu and Co alone is used and the unevenness is ignored and the average thickness is calculated, it is 0.2
.About.0.5 .mu.m, preferably 0.3 to 0.4 .mu.m. If it is less than 0.2 μm, the peel strength is lowered and the heat resistance and chemical resistance are deteriorated. On the other hand, if it exceeds 0.5 μm, the treated layer becomes brittle and etching residue tends to remain.

Similarly, the Co content in the Cu—Co binary alloy layer is as follows. Co content is 1 to 10% by weight
% Is preferable, and if it is less than 1%, the heat resistance tends to be poor.
If it exceeds 0%, the effect of magnetism becomes large.

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

Bath composition and plating conditions Cu: 10 to 20 g / Co: 1 to 10 g / pH: 1 to 4 Temperature: 40 to 50 ° C. Current density D _x : 20 to 30 A / dm ² hours: 1 to 5 seconds Processing is performed. In the present invention, the anticorrosion treatment is carried out as 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. The plating bath is typically K ₂ Cr ₂ O ₇ , at least one dichromate such as Na ₂ Cr ₂ O ₇ or CrO _3, and a water-soluble zinc salt such as ZnO or ZnSO _4.
A mixed aqueous solution of at least one such as 7H ₂ O and alkali hydroxide is used.

Typical plating solution composition and 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 0.05-10 g / pH 7-13 Bath temperature 20-80 ° C. Current density 0.05-5 A / dm ² hours 5-30 seconds Anode Pt-Ti plate,
Stainless steel plates, etc. Chromium oxides are required to have a chromium content of 15 μg / dm ² or more, and 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 and 61-3390.
8, 62-14040 and the like. However, this Cu
-Not known for compatibility with Co alloys.

The copper foil thus obtained retains peel strength characteristics (heat deterioration and hydrochloric acid resistance) comparable to that of the conventional Cu-Co alloy, even though the content of cobalt is greatly reduced, and the CuCl ₂ etching solution is used. In this way, it is possible to etch a printed circuit having a circuit width of 150 μ pitch or less, and further, it is possible to reduce the magnetic susceptibility without impairing the excellent feature that alkali etching is possible.

Examples of the alkaline etching solution here include NH
Liquids such as ₄ OH: 6 mol /; NH ₄ Cl: 5 mol /; CuCl ₂ : 2 mol / (temperature 50 ° C.) are known.

Despite containing cobalt, the magnetic susceptibility is below the allowable level. Here, "the magnetic susceptibility is equal to or lower than the allowable level" means that the saturation magnetization M _s is 160 emu / cc or lower and the residual magnetization M _{r is}
Is 70 emu / cc or less, and the coercive force H _c is 3000 e or less.

In the present invention, the saturation magnetization M _s is 50 emu / cc or less,
The residual magnetization _{M r} 40 emu / cc or less and 2 the coercive force _{H c}
It is possible to easily realize 200e or less.

Further, preferably, for the main purpose of improving the adhesive force between the copper foil and the resin substrate, a silane coupling agent is applied to at least the roughened surface of the anticorrosion layer to perform a silane treatment to form a thin film. 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. Annealing is performed, for example, in an oxygen-free atmosphere (O ₂ ≦ 10 ppm or less, 10 ⁻³ Torr + N ₂ gas injection)
In the case of rolled copper foil, at a temperature of 150 to 200 ° C., 5 to 9
Will be carried out for hours. In the case of electrolytic copper foil, the temperature is 300-50.
Increased to 0 ℃.

Examples and Comparative Examples After subjecting the rolled copper foil to pretreatment including ordinary roughening treatment,
For the purpose of the present invention and comparative purposes, the alloy plating treatment according to the present invention and the conventional example was performed.

The conditions for the copper roughening treatment were as follows.

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 Conventional Cu-Co plating (Japanese Patent Publication No. 63-2158) Cu: 2.5 g / Co: 20 g / pH: H ₂ SO ₄ 5 g / Temperature: 30 ° C. D _k : 7 A / dm ² hours: 60 seconds Cu-Co plating Cu: 5 of the present invention -25 g / Co: 3-15 g / pH: 1-4 Temperature: 20-50 ° C _Dk : 10-30 A / dm ² hours: 2-5 seconds After rust-proofing these materials, surface layer component analysis and peel strength The properties, magnetic properties and etching properties were evaluated.

The magnetic characteristics were measured as follows.

Samples 5.5 mm diameter samples were punched with punched punches, 20 plies were stacked and VSM measured. Processing surface area S
Was 0.0475 dm ² .

Evaluation item Saturation magnetization M _s (emu / cc) Remanent magnetization M _r (emu / cc) Coercive force H _c (0e) Measurement Use a VSM made by Toei Industry Co., Ltd. to draw a hysteresis curve and read each characteristic value. It was Maximum applied magnetic field is 10 kOe
And Regarding the remanent magnetization and the coercive force, both values were read and the average value was adopted.

Regarding the peel strength, the sample was laminated and adhered to a glass cloth base epoxy resin plate, and the normal (room temperature) peel strength (kg /
cm), and the heat resistance deterioration is shown as the deterioration rate (%) of the peel strength after heating at 180 ° C. for 48 hours, and the hydrochloric acid resistance deterioration is the peel strength after dipping in 18% hydrochloric acid for 1 hour. Deterioration rate (%) when measured by.

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 the table below.

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 obtained by this method has peeling characteristics including heat-resistant peel strength and hydrochloric acid resistance of acceptable levels, and it can etch printed circuits with a circuit width of 150 μ pitch or less with CuCl ₂ etching solution, and can also be etched with alkali. Is also possible. Moreover, with regard to magnetic properties that will become more important in the future, we succeeded in keeping the magnetic susceptibility below the allowable level. The present invention can be used particularly as a fine pattern and as an FPC for a magnetic head.

Claims (2)

[Claims] 1. A method for treating a copper foil for a printed circuit, comprising: 20-40 mg / dm ² of copper and 1 cobalt on the surface of the copper foil to be treated.
A method for treating a copper foil for a printed circuit, which comprises forming an electroplating layer comprising 0 to 3000 μg / dm ² . 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 electroplated layer is formed.