JPH05247659A - Etching liquid for pretreatment of aluminum substrate for magnetic disk and pretreatment of this substrate by using this etching liquid - Google Patents

Abstract

PURPOSE:To omit a polishing stage after plating and to stably produce magnetic disks having excellent quality without having defects, such as micropits, by improving acidic etching soln. as a pretreatment for electroless plating of an Ni-P alloy on the surface of an Al substrate. CONSTITUTION:The surface of the Al substrate as a ground surface substrate for the magnetic disks is subjected to the pretreatment etching by the etching liquid prepd. by incorporating a fluoride, such as acidic ammonium fluoride, at 10 to 40g/l concn. into a sulfuric acid liquid of 600 to 1350g/l concn. contg. phosphoric acid at 15 to 60g/l concn. and incorporating nitrate, such as sodium vitrate at 10 to 100g/l prior to electroless plating of the N-P alloy on the surface of the above-mentioned substrate. The Ni-P alloy is then electroless plated and an Ni-P alloy plating layer free from the defects, such as micropits and nodule is formed on the surface and, therefore, the need for the subsequent polishing target is eliminated. The Al substrate for the magnetic disks having the excellent surface is thus obtd. easily at low cost.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electroless Ni-based aluminum substrate used as a base substrate for a magnetic disk.
More specifically, it relates to a pretreatment method and an etching solution used therefor.

[0002]

2. Description of the Related Art In recent years, miniaturization of magnetic disk drives,
The demand for higher quality and lower cost of magnetic disks, which are the main components, is becoming strict as the price is rapidly increasing at the same time as the capacity is increased. The manufacturing process of this metal thin film magnetic disk is shown in FIG. Among them, the polishing process is a process for correcting plating defects (nodules, micropits, etc.) on the surface of the substrate after the electroless Ni-P plating process, but automation is difficult and is the biggest cost reduction. The biggest challenge is to omit this step.

In the magnetic disk manufacturing process,
To describe the electroless Ni-P plating process in more detail, this process includes alkali degreasing, acid etching,
Treatments are carried out in the order of nitric acid dipping, first zinc substitution, zinc nitrate stripping, second zinc substitution, and electroless Ni-P plating, and a washing step with pure water is performed between each step. However, in the case of acid etching, the conventional method has been used.
170, a method using a treatment liquid containing sodium persulfate as a main component, and a method using a treatment liquid containing boric acid in phosphoric acid as disclosed in JP-A-62-177191.
A method using a treatment liquid containing nitric acid and ammonium hydrogen fluoride as disclosed in JP-A-62-192331, or a treatment liquid containing a mixed acid of nitric acid and hydrofluoric acid, a mixed acid of sulfuric acid and phosphoric acid, and the like has been proposed. .. However, the composition of these treatment liquids does not solve the fundamental problem even if the concentration and treatment temperature treatment time are variously changed, and the plating surface nodules, which is a condition necessary for omitting the polishing step,
It was impossible to suppress defects such as micropits to 0.1 μm or less. Therefore, as described above, a polishing process for removing this defect after the plating process is indispensable, which is a major obstacle to labor saving and cost reduction.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to improve the pretreatment method for electroless Ni-P plating, in particular, to improve the acid etching so as to save labor in the polishing step of the magnetic disk manufacturing process. , To provide a smooth plated substrate having no micropit defects.

[0005]

Means for Solving the Problems The present inventors have conducted extensive research on the mechanism of generation of nodules and micropits, which are plating defects on the plating surface in the above-mentioned conventional electroless Ni-P plating process. The intermetallic compound generated during the reaction in the etching treatment solution, the insoluble foreign matter (smut) that is generated and the crystallized product is the core, and (b) the acidic etching solution has a specific composition. Smut (insoluble foreign substance) that is generated at the same time as intermetallic compounds and crystallized substances do not selectively dissolve, uniform etching is performed, and microscopic depressions that cause micropits are not created
It has been found that the metal can be dissolved to prevent nodules from being generated on the plating surface, and the present invention has been completed based on this finding.

That is, the present invention provides an etching solution for pretreatment of an aluminum substrate for a magnetic disk, which contains sulfuric acid or an acid containing sulfuric acid and phosphoric acid, a fluoride and a nitrate. .. In the etching solution of the present invention, examples of the fluoride contained in an acid selected from sulfuric acid or a mixed acid of sulfuric acid and phosphoric acid include ammonium acid fluoride, sodium acid fluoride, and potassium acid fluoride. Examples of nitrates include ammonium nitrate, sodium nitrate, potassium nitrate and the like.

In the etching solution of the present invention, the total concentration of sulfuric acid or sulfuric acid and phosphoric acid is not particularly limited, but preferably 600 to 1350 g / liter, more preferably 100.
It is 0 to 1250 g / liter. If this amount is too small, the surface roughness after plating becomes large and the depth of the micropits becomes deep, making it difficult to omit the polishing step. Also, if this acid is too much, nodules will be generated.

Sulfuric acid may be used alone, but it is preferable to add it appropriately because the addition of phosphoric acid tends to suppress the generation of micropits. The concentration of phosphoric acid in this case is preferably 15 to 60 g / liter. The pretreatment method for an aluminum substrate for a magnetic disk using the etching solution of the present invention is a usual method except that the above etching step is carried out, which comprises the following steps in order.

The degreasing step is usually performed with a non-etching type treatment liquid for aluminum (as an alkali degreasing agent, preferably 10 to 50 g / liter). The etching process is as described above. The first zinc substitution step is performed with a treatment liquid containing 200 g / liter of caustic soda, 40 g / liter of Roussel salt, 20 g / liter of zinc oxide, and 2 g / liter of ferrous chloride. The zinc nitrate stripping step is performed with a treatment liquid containing 50 g / liter of nitric acid. In the second zinc replacement step, the same treatment liquid as in the first zinc replacement step is used. The time and temperature of each treatment in these pretreatment steps are not particularly different from those of the usual method.

[0010]

EXAMPLES The present invention will be described in more detail based on examples.

Example 1 An aluminum substrate substrate (3.5 inch FP-3 material manufactured by Furukawa Electric Co., Ltd.) was used, and an acid etching solution having the composition shown in Table 1 below was used.
X 5 minutes), acidic etching treatment (20 ° C x 1 minute), nitric acid treatment (25 ° C x 1 minute), first zinc substitution treatment (22 ° C x 1 minute)
Min), nitric acid stripping treatment (25 ° C. × 1 minute), and second zinc substitution treatment (22 ° C. × 30 seconds), and then a film having a thickness of about 12 μm is formed by electroless Ni-P plating. A film was formed.

After plating, using an optical microscope,
The occurrence of micropits was observed and evaluated according to the criteria described below. That is, the number of nodules and the number of micropits in the field of view of the microscope are counted at a magnification of 300 times,
The maximum and minimum values of 5 in-plane × 5 plated substrates were measured, and the average value was determined. The results are shown in Table 2 below.
Also, without polishing this plated substrate,
As a result of texturing under a predetermined condition and observing under a microscope, it became clear that no surface defect remained and the polishing step could be omitted.

Examples 2 to 7 After pretreatment was performed in exactly the same manner as in Example 1 except that the concentrations of sulfuric acid, ammonium acid fluoride and ammonium nitrate in the etching solution were set as shown in Table 1, Similarly, electroless Ni-P plating was performed. With respect to the plated substrate sample thus obtained, the occurrence of nodules and micropits was observed in the same manner as in Example 1.
The results are shown in Table 2. Further, this plating substrate was capable of omitting the polishing step as in Example 1.

Comparative Example 1 An aluminum substrate substrate (3.5 inch FP-3 material manufactured by Furukawa Electric Co., Ltd.) was used as in Example 1 and sulfuric acid 1 was used.
Degreasing treatment (50 ° C. × 5 minutes) using an acidic etching solution consisting of 00 g / liter and phosphoric acid 50 g / liter
Acid etching treatment (70 ° C x 1 minute), nitric acid treatment (25
℃ × 1 minute), first zinc replacement treatment (22 ℃ × 1 minute), nitric acid stripping treatment (25 ℃ × 1 minute), second zinc replacement treatment (22 ℃
× 30 seconds) was pretreated. Under the same conditions as the example,
About 12 μm of electroless Ni-P plating was deposited.

After plating, the film was observed and evaluated in the same manner as in the example. The results are shown in Table 2, but nodules and micropits frequently occur, and the surface is rough and the smoothness is poor. Further, when the plated substrate was subjected to texturing and microscopic observation without polishing as in the example, it was confirmed that micropits and surface roughness remained and polishing could not be omitted.

Comparative Example 2 An aluminum substrate substrate (3.5 inch FR-3 material manufactured by Furukawa Electric Co., Ltd.) was added with 30 g of phosphoric acid in the same manner as in Example.
/ L, 30 g / L boric acid, an acid etching solution is used. Degreasing treatment (50 ° C. × 5 minutes), acidic etching treatment (30 ° C. × 2 minutes), nitric acid treatment (25 ° C. × 1)
Min), first zinc substitution treatment (22 ° C x 30 seconds), nitric acid stripping treatment (25 ° C x 1 minute), second zinc substitution treatment (22 ° C x 3)
0 second) pretreatment was performed. Under the same conditions as in Example 1, electroless Ni-P plating of about 12 μm was formed. The results are shown in Table 2, but as in Comparative Example 1, it was confirmed that the surface was rough and the smoothness was poor, and polishing could not be omitted.

[0017]

[Table 1]

[0018]

[Table 2]

[0019]

As a result of the pretreatment process of the present invention, it is possible to prevent the metallic defects, which are the cores of nodules and micropits, and the formation of insoluble foreign matter from being prevented in the acid etching process, which is defect-free and has good smoothness. A plated surface is obtained. As a result, the polishing process in the magnetic disk manufacturing process can be omitted, and the manufacturing cost can be significantly reduced. Further, since the surface sagging and the like that occurs in the polishing process can be eliminated, it leads to a technological advance toward higher capacity.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a magnetic disk manufacturing process.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Mitsuo Masuda 2-6-1, Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd.

Claims (3)

[Claims] 1. An etching solution for pretreatment of an aluminum substrate for a magnetic disk, which contains sulfuric acid or an acid containing sulfuric acid and phosphoric acid, a fluoride and a nitrate. 2. Sulfuric acid or a combination of sulfuric acid and phosphoric acid is 600.
The etching solution according to claim 1, which contains ˜1350 g / liter, 10 to 40 g / liter of fluoride and 10 to 100 g / liter of nitrate. 3. A pretreatment method for an aluminum substrate for a magnetic disk, which comprises an etching step in the pretreatment step and uses the etching solution according to claim 1 or 2 as an etching solution.