JPH051384A - Electroless plating bath - Google Patents

Abstract

PURPOSE:To stably form a semihard magnetic film having large saturation magnetization and coersive force by plating with high productivity by using this electroless plating bath. CONSTITUTION:The citrate group and malate group as the complexing agent for a metal ion are added to an aq. soln. contg. cobalt ion as the metal ion and the dimethylamine borane or diethylamine borane as the reducing agent for the metal ion as the additive to obtain the electroless plating bath.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electroless plating bath for producing a semi-hard magnetic film such as an underlayer of a magnetic recording medium used for perpendicular recording.

[0002]

2. Description of the Related Art Conventionally, in a magnetic recording device such as a general magnetic disk device or a magnetic tape device, recording has been performed by magnetizing in the longitudinal direction of a magnetic recording medium.
In this method, there is a drawback that the demagnetizing field in the medium increases with the increase of the recording density, the residual magnetization is attenuated and rotated, and the reproduction output is significantly reduced. Therefore, the demagnetizing field becomes smaller as the recording density increases, and a perpendicular recording method that enables high-density recording and a CoCr sputtered film that is easy to magnetize in the direction perpendicular to the film thickness are proposed as a magnetic recording medium suitable for this perpendicular recording. (Japanese Patent Application Laid-Open No. 52-134706). In order to efficiently perform such perpendicular recording, a magnetic recording body having a two-layer magnetic film has been proposed (Japanese Patent Publication No. 58-91). The two-layer magnetic film is composed of a perpendicular magnetic recording layer (magnetic recording medium) and an underlayer having a low coercive force. This underlayer acts to cancel the magnetic pole on the back surface of the perpendicular magnetic recording layer, so that the demagnetizing action is reduced. It is possible to increase the reproduction output. The underlying layer of the two-layer magnetic film is mainly a FeNi film (permalloy) by sputtering, MoFe
Ni film (molybdenum permalloy), CoZr film, CoZ
A soft magnetic film such as rNb film is used. However, when a soft magnetic film is used as an underlayer of the perpendicular magnetic recording layer (magnetic recording medium), the reproduction output is improved, but the domain wall movement is likely to occur due to the low coercive force, and noise is likely to occur. For this reason, it has been proposed to use a semi-hard magnetic film of cobalt or cobalt-nickel alloy instead of the soft magnetic film (JP-A-2-18710). If the coercive force of this semi-hard magnetic film is smaller than 30 Oe, it causes spike noise, and if it is larger than 300 Oe, recording on the underlayer becomes difficult (because the effect of canceling the magnetic pole on the back surface is reduced). It is said that it is preferably in the range of up to 300 Oe.

[0003]

Such a base layer is
It is produced by a dry film forming method such as sputtering, vapor deposition, and ion plating. In this case, there is a problem in mass productivity because it is performed in a vacuum system. Therefore, application of an underlayer formed by an electroless plating method that is excellent in mass productivity by improving manufacturing problems is being studied. This includes electroless N
iFeP plated film, electroless NiP plated film, electroless Ni
The WP plating film and the like are applied, but the largest reproduction output can be obtained when the NiFeP film having a relatively large saturation magnetization of 400 emu / cc is used.
IEEE Transaction on Magnetics No. Mag-
23, pp. 2356-2358, 1987). However, since the coercive force of these electroless plated films is a soft magnetic film of 20 Oe or less, it has the above-mentioned problem of noise. As a plating bath for obtaining a NiFeP film, the Metal Surface Technology Association, 65th Lecture Meeting, Proceedings, 138-139,
In 1983, a NiFeP plating bath using iron alum as a source of iron ions, and Tohoku University Institute of Scientific Measurement, Vol. 33, pp. 1-13, 1984, was used as a source of iron ions. An example of a NiFeP plating bath using salt is given. However, the coercive force of these NiFeP films could not exceed 30 Oe even if the bath conditions were changed.

In the electroless plating method, the saturation magnetization is 14
A CoB film as large as about 00 emu / cc (a value about 3.5 times that of the NiFeP film) can be produced, and a further output increasing effect is expected. However, the plating film obtained from the conventional electroless CoB plating bath using tartaric acid as a complexing agent is a soft magnetic film, and its coercive force is as small as several Oe or less (typically 1.9 Oe) (Japan). Applied Magnetics Society Academic Lectures, 483, 1989). An object of the present invention is to improve the conventional problems as described above, and to make a semi-hard alloy made of CoB alloy having a coercive force of 30 Oe or more and a large saturation magnetization.
An object of the present invention is to provide an electroless plating bath capable of stably producing a demagnetic film.

[0005]

The present invention is an aqueous solution containing cobalt ions as metal ions and at least dimethylamine borane or diethylamine borane as a reducing agent for the metal ions as an additive. The electroless plating bath is characterized by containing a citric acid group and a malic acid group as an agent. The main components of the electroless plating bath used in the present invention include cobalt ions as metal ions, dimethylamine borane or diethylamine borane as a reducing agent for the metal ions, and citric acid groups and malic acid groups as complexing agents for the metal ions. However, the purpose of the present invention, as long as the effect is not impaired, pH buffer, brightener, smoothing agent, stimulant,
Additives such as pinhole inhibitors and surfactants can be used.

Cobalt ions are supplied by dissolving a soluble salt of cobalt sulfate, chloride or acetate in an electroless plating bath. The cobalt ion concentration is in the range of 0.0003 to 1.1 mol / l, preferably 0.02 to 0.3 mol / l. The metal ions used in the present invention include:
Cobalt is the main component, but a small amount of Ni, Fe, Be,
Mg, Al, Ru, Si, Co, Sr, Y, Zn, Z
r, Nb, Cd, In, Sb, Ta, Ir, Hg, T
l, Nb, Gd, Tb, Ti, V, Cr, Cu, Ga,
Ge, Mn, W, Mo, Rh, Pd, Ag, Au, P
t, Sn, Te, Ba, Ce, Sm, Os, Pb, R
Ions such as e and Bi may be contained in a range that does not impair the effects of the present invention. As the reducing agent, dimethylamine borane or diethylamine borane or a derivative thereof is used in the range of 0.0001 to 0.5 mol / l, preferably 0.01 to 0.1 mol / l.

The citric acid group as a complexing agent is supplied by citric acid or a soluble salt such as sodium citrate or potassium citrate. These are 0.001-1m
Used in the range of ol / l, 0.01-0.3mo
A range of 1 / l is preferred. The malic acid group as a complexing agent is supplied by malic acid or a soluble salt such as sodium malate, potassium malate and the like. They are,
It is used in the range of 0.001 to 2 mol / l, but 0.
The range of 05-1.2 mol / l is preferable. Other complexing agents include formic acid, acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, isovaleric acid, oxalic acid, glutaric acid, maleic acid, tartaric acid, fumaric acid, citraconic acid, itaconic acid, tricarballylic acid. , Succinic acid, malonic acid, glyco-
Acid, thioglycolic acid, lactic acid, β-hydroxypropionic acid, pyruvic acid, oxalacetic acid, diglycolic acid,
Carboxylic acids such as thiodiglycolic acid, mercaptosuccinic acid, dimercaptosuccinic acid, benzoic acid, mandelic acid, phthalic acid, salicylic acid, ascorbic acid, sulfosalicylic acid, tropolone, 3-methyltropolone, tyrone, etc.
Amine and its derivatives such as ethylenediamine, diethylenetriamine, triethylenetetraamine, pyridine, iminodiacetic acid, iminodipropionic acid, nitrilotriacetic acid, nitrilotripropionic acid, ethylenediaminediacetic acid, ethylenediaminetetraacetic acid, ethylenediaminetetrapropionic acid, diethylenetriaminepentaacetic acid, etc. Aminopolycarboxylic acid, alanine, sarcosine,
Amino acids such as valine, norleucine, tyrosine, cysteine, glutamic acid, glycine, aspartic acid, asparagine, and histidine, hexonic acid such as gluconic acid, alloic acid, idonic acid, galactonic acid, gulonic acid, taronic acid, and mannonic acid, pyrophosphoric acid, etc. One or a combination of two or more of the weak acids or their soluble salts may be used within a range that does not impair the effects of the present invention.

As the pH buffer, ammonium sulfate,
Ammonium salts such as ammonium chloride and boric acid are used. The concentration range is 0.001 to 2 mol / l, preferably 0.03 to 0.7 mol / l. p
As the H regulator, ammonia, caustic alkali such as NaOH, LiOH, KOH, RbOH, CsOH,
FrOH, Be (OH) ₂ , Mg (OH) ₂ , Ca (O
H) ₂ , Sr (OH) ₂ , Ba (OH) ₂ , Ra (OH) ₂
Hydroxides of metals such as the above are used alone or in combination of two or more. It is also possible to use ammonia and caustic together. Usually, the plating solution before adding a bath without adding a pH adjuster is in a neutral or acidic region, and the pH is adjusted to alkaline by adding the hydroxide. Required pH
When it exceeds the above, acids such as hydrochloric acid, sulfuric acid, nitric acid and acetic acid are used for pH reduction. The pH range used is between 4 and 13, preferably between 7.5 and 11.

[0009]

[Function] The center of the electroless plated film is Co particles.
It is considered that the element becomes rich, and the mixed elements such as B and P are distributed to the outside to form a layer close to non-magnetic and have a structure that encloses the Co-rich portion. If such a non-magnetic layer is thick, the Co particles are magnetically isolated and a high coercive force is obtained. 2 for electroless CoP alloy film
Since about 5% of P can be co-deposited, 10
A hard magnetic film exceeding 00 Oe can be obtained. In addition, the magnetic characteristics of the magnetic plating film also depend largely on the crystal structure.
In the electroless plated CoB alloy film, the amount of B eutectoid is as small as 1% or less, which is a CoB alloy film close to pure Co, so that a soft magnetic film is easily obtained. Therefore, conventionally, for the purpose of producing a soft magnetic film of about 1 Oe or less,
Efforts have been made to minimize the coercive force of CoB alloy films. However, even if the amount of B eutectoid of the electroless plated CoB alloy film is small, it is possible to obtain the coercive force of about 30 to 300 Oe of the semi-hard magnetic film, which is the object of the present invention, depending on the manufacturing conditions (plating bath conditions). I was wondering. For this reason, the inventors have found that electroless CoB
As a result of extensively experimentally examining the plating bath conditions of the plating bath, it is possible to increase the coercive force depending on the type and combination of complexing agents. Saturation is achieved by using citric acid groups and malic acid groups as complexing agents. It has been found that a semi-hard magnetic film having a large magnetization can be stably obtained and can be applied to the object of the present invention. The detailed mechanism of this is unknown, but the metal addition agent in the bath and the complexing agent that makes it complex are deeply involved in the deposition reaction of electroless plating, and when a citric acid group and a malic acid group are combined. It is considered that the plating film structure is suitable for obtaining a semi-hard magnetic film. The present invention has been brought about by obtaining such knowledge.

[0010]

EXAMPLES Next, examples of the present invention will be described. Example 1 A nonmagnetic NiP layer was plated on an aluminum alloy and the surface was mirror-polished to obtain a substrate. A CoB film having a thickness of 0.05 μm was formed on this substrate by using the electroless plating bath described below. Electroless plating bath (1) Bath composition cobalt sulfate 0.10 mol / l dimethylamine borane 0.015 mol / l ammonium sulfate 0.1 mol / l sodium malate 0-1.5 mol / l sodium citrate 0.04 mol / l Plating condition Bath temperature 70 ° C. pH of plating bath 8.0 (pH adjustment with ammonia water at room temperature) The magnetic characteristics of the CoB film obtained by changing the sodium malate concentration were measured using a vibrating sample magnetometer. The result is shown in Figure 1.
Shown in. Coercive force (Hc) is sodium malate 0mo
In the case of 1 / l, it is as small as 10 Oe. Hc increased with the concentration of sodium malate, and sodium malate 0.
It becomes 31 Oe at 05 mol / l, 0.4 mol / l
The maximum value is 188 Oe. After that, Hc gradually decreased to 30 O at 1.2 mol / l of sodium malate.
It became e. The saturation magnetization (Ms) was 1395 emu / cc at 0 mol / l sodium malate, decreased slightly to 1340 emu / cc at 0.4 mol / l sodium malate, and was 1 at 1.5 mol / l sodium malate.
It takes a value of 400 emu / cc. Thus, 1340
While maintaining a high saturation magnetization of emu / cc or more,
A semi-hard magnetic film with a coercive force of 188 Oe was obtained.

Example 2 A CoB film having a thickness of 0.05 μm was formed in the same manner as in Example 1, but the following electroless plating bath was used in this example. Electroless plating bath (2) bath composition cobalt sulfate 0.10 mol / l dimethylamine borane 0.015 mol / l ammonium sulfate 0.1 mol / l sodium malate 0.4 mol / l sodium citrate 0-0.4 mol / l Plating conditions Bath temperature 70 ° C. pH of plating bath 8.0 (pH adjusted with aqueous ammonia at room temperature) The CoB film magnetic properties obtained by changing the sodium citrate concentration are shown in FIG. Hc is as small as 1 Oe when sodium citrate is 0 mol / l. Hc increased with the sodium citrate concentration, reaching 30 Oe at 0.01 mol / l sodium citrate,
The maximum value is 188 Oe at 04 mol / l. Then Hc
Gradually decreases, sodium citrate 0.3 mol /
It became 32 Oe at l. Ms is sodium citrate 0
1340 to 1400 emu in the range of up to 0.4 mol / l
It was / cc. Thus, a semi-hard magnetic film having a coercive force of 30 to 188 Oe was obtained while maintaining a high saturation magnetization of 1340 emu / cc or more.

Example 3 A CoB film having a thickness of 0.05 μm was formed in the same manner as in Example 1, but the following electroless plating bath was used in this example. Electroless plating bath (3) Bath composition Cobalt sulfate 0.10 mol / l Dimethylamine borane 0.015 mol / l Ammonium sulfate 0.1 mol / l Sodium malate 0.4 mol / l Sodium citrate 0.04 mol / l Plating conditions Bath temperature 70 ° C. pH of plating bath 10.0 (pH adjusted with aqueous ammonia at room temperature) The magnetic properties of the obtained CoB film were measured. Hc is 235
Oe, which was increased by about 50 Oe from Hc = 188 Oe obtained under the condition of sodium malate concentration of 0.4 mol / l of Example 1 by increasing pH. Ms
Was 1345 emu / cc, which was a large value.

Example 4 A CoB film having a thickness of 0.05 μm was formed in the same manner as in Example 1, but the following electroless plating bath was used in this example. Electroless plating bath (4) Bath composition Cobalt sulfate 0.10 mol / l Dimethylamine borane 0.02 mol / l Ammonium sulfate 0.1 mol / l Sodium malate 0.4 mol / l Sodium citrate 0.04 mol / l Plating conditions Bath temperature 70 ° C. pH of plating bath 8.0 (pH adjusted with aqueous ammonia at room temperature) The magnetic properties of the obtained CoB film were measured. Hc is 242
Oe, and increasing the dimethylamine borane concentration, the sodium malate concentration of Example 1 was 0.4 mo
About 50 from Hc = 188 Oe obtained under the condition of 1 / l
Oe increased. Ms was 1343 emu / cc and maintained a large value.

Example 5 A CoB film having a thickness of 0.05 μm was formed in the same manner as in Example 1. In this example, however, the following electroless plating bath was used. Electroless plating bath (5) Bath composition Cobalt sulfate 0.11 mol / l Dimethylamine borane 0.02 mol / l Ammonium sulfate 0.3 mol / l Sodium malate 0.45 mol / l Sodium citrate 0.045 mol / l Plating conditions Bath temperature 65 ° C. pH of plating bath 10.0 (pH adjusted with aqueous ammonia at room temperature) The magnetic properties of the obtained CoB film were measured. Hc is 300
It was Oe, and Hc increased by selecting bath conditions. Ms was 1340 emu / cc and maintained a large value.

Example 6 A CoB film having a thickness of 0.05 μm was formed in the same manner as in Example 1, but the following electroless plating bath was used in this example. Electroless plating bath (6) Bath composition Cobalt sulfate 0.08 mol / l Diethylamine borane 0.017 mol / l Ammonium sulfate 0.2 mol / l Sodium malate 0.35 mol / l Sodium citrate 0.035 mol / l Plating conditions Bath temperature 75 ° C. pH of plating bath 8.5 (pH adjusted with aqueous ammonia at room temperature) The magnetic properties of the obtained CoB film were measured. Hc is 110
Oe and Ms maintained a large value of 1370 emu / cc.

In Examples 1 to 6, on aluminum plywood,
Although a substrate plated with a non-magnetic NiP layer was used, an electroless Cu plating layer, an electrolytic Cu plating layer, an electroless NiCuP plating layer, an electroless NiSnP plating layer, an electroless NiWP
The same applies when a substrate on which a plating layer other than NiP such as a plating layer or an electroless NiWP plating layer is formed, or a substrate such as a copper substrate, a brass substrate, a plastic that has been subjected to an appropriate catalyst treatment, or a non-metal substrate such as glass is used. The characteristics of the semi-hard magnetic film were obtained. Further, the film thickness of the CoB plating film is not limited to 0.05 μm in the embodiment, but 0.005-1
It was possible to obtain the characteristics of the semi-hard magnetic film in the range of 0 μm.

[0017]

As described above, according to the present invention, a semi-hard magnetic film having a large saturation magnetization of 1340 to 1400 emu / cc and a coercive force of 30 to 300 Oe can be formed.

[Brief description of drawings]

FIG. 1 is a CoB obtained by the electroless plating bath of the present invention.
It is a figure which shows the relationship between the coercive force (Hc) and saturation magnetization (Ms) of an example of a semi-hard magnetic film, and the sodium malate concentration in a plating bath.

FIG. 2 CoB obtained by the electroless plating bath of the present invention
It is a figure which shows the relationship between the coercive force (Hc) and saturation magnetization (Ms) of an example of a semi-hard magnetic film, and the sodium citrate concentration in a plating bath.

Claims (1)

1. An aqueous solution containing cobalt ions as metal ions and at least dimethylamine borane or diethylamine borane as a reducing agent for the metal ions as an additive, which is a complexing agent for metal ions. An electroless plating bath, characterized in that it contains a citric acid group and a malic acid group.