JP7718962B2 - Metal replacement treatment solution, aluminum or aluminum alloy surface treatment method - Google Patents

Description

The present invention relates to a metal replacement treatment solution and a method for treating the surface of aluminum or aluminum alloys.

Aluminum easily forms an oxide film in the air or water. It is known that this oxide film causes poor adhesion of the plating film when plating aluminum or aluminum alloys. Therefore, prior to plating, a zinc substitution treatment (zincate treatment) is carried out to remove the oxide film from the aluminum or aluminum alloy surface and ensure adhesion of the plating film formed on the aluminum (see, for example, Patent Documents 1-3 and Non-Patent Documents 1-3).

Japanese Patent Application Laid-Open No. 2000-256864 Japanese Patent Application Laid-Open No. 2020-196914 JP 2009-127101 A

Surface Technology Vol. 64 (2013), No. 12, p. 645-649 Surface Technology Vol. 66 (2015), No. 12, p. 658-665 Surface Technology Vol. 47 (1996), No. 9, p. 802-807

As a result of extensive research, the inventors have found that there is room for improvement in the adhesion of conventional technologies to plating films.

The present invention aims to solve the above-mentioned problems newly discovered by the inventors and to provide a metal replacement treatment liquid that can impart good adhesion to plating films (metal films), and a surface treatment method for aluminum or aluminum alloys using this metal replacement treatment liquid.

As a result of extensive research, the present inventors have discovered that by using a metal substitution treatment solution with a specific composition, good adhesion to a plating film (metal film) can be imparted, and have completed the present invention.
That is, the present invention relates to a metal substitution treatment solution containing a zinc compound, a nickel compound, a germanium compound, and a fluorine compound.

The metal replacement treatment solution preferably contains a zinc compound at a zinc concentration of 0.2 to 5.0 g/L.

The metal replacement treatment solution preferably contains a nickel compound at a nickel concentration of 0.2 to 10 g/L.

The metal replacement treatment solution preferably contains a germanium compound at a germanium concentration of 0.2 to 5.0 g/L.

The metal replacement treatment solution preferably contains a fluorine compound at a fluorine concentration of 5.0 to 50 g/L.

It is preferable that the ratio of zinc concentration to germanium concentration in the metal replacement treatment solution be 1:5 to 5:1.

The metal replacement treatment solution preferably has a pH of 4.0 to 6.5.

The metal replacement treatment liquid is preferably for use on aluminum or aluminum alloys.

The present invention also relates to a surface treatment method for aluminum or aluminum alloys, which involves contacting a workpiece having aluminum or an aluminum alloy on its surface with the metal replacement treatment solution, removing an oxide film on the aluminum or aluminum alloy, and performing a metal replacement treatment to replace the aluminum with a metal contained in the metal replacement treatment solution, thereby forming a replacement metal film containing the metal on the surface of the workpiece.

After forming the replacement metal film, it is preferable to form a plating film on the surface of the replacement metal film.

According to the present invention, the metal replacement treatment solution contains zinc compounds, nickel compounds, germanium compounds, and fluorine compounds, which can impart good adhesion to the plating film (metal film).

FIG. 1 is a schematic diagram illustrating an outline of a folding and breaking test. (a) is a photograph showing an example of a case where no Al spikes are observed, and (b) is a photograph showing an example of a case where Al spikes are observed.

The metal replacement treatment solution of the present invention contains a zinc compound, a nickel compound, a germanium compound, and a fluorine compound. This allows it to provide good adhesion to the plating film (metal film).

The reason why the metal substitution treatment solution provides the above-mentioned effects is presumed to be as follows.
A metal substitution treatment is performed by bringing a workpiece having aluminum or an aluminum alloy on its surface into contact with the metal substitution treatment liquid, removing an oxide film on the aluminum or aluminum alloy, and substituting the aluminum with a metal contained in the metal substitution treatment liquid. As a result, nickel (Ni) and germanium (Ge) are co-deposited with zinc (Zn), and a substituted metal film containing Zn, Ni, and Ge can be formed on the aluminum or aluminum alloy surface.
When aluminum or an aluminum alloy having such a substituted metal film containing Zn, Ni, or Ge on its surface is plated to form a plated film (metal film, for example, a nickel film), the Zn, Ni, and Ge present in the substituted metal film act synergistically between the aluminum or aluminum alloy and the plated film (metal film, for example, a nickel film), and good adhesion between the aluminum or aluminum alloy and the plated film (metal film) can be imparted to the aluminum or aluminum alloy.
The synergistic effect of Zn, Ni, and Ge is evident from the fact that good adhesion to the plating film (metal film) cannot be imparted when Zn, Ni, or Ge is used alone, when a combination of Zn and Ni (without Ge), when a combination of Zn and Ge (without Ni), or when a combination of Ni and Ge (without Zn) is used.

<Metal replacement treatment liquid>
The metal substitution treatment liquid of the present invention contains a zinc compound, a nickel compound, a germanium compound, and a fluorine compound.

<<Zinc compounds>>
The zinc compound is not particularly limited as long as it is a water-soluble zinc compound. Specific examples include zinc sulfate, zinc nitrate, zinc chloride, zinc acetate, zinc oxide, and zinc gluconate. These may be used alone or in combination of two or more. Of these, zinc sulfate is preferred.

The metal replacement treatment solution preferably contains a zinc compound with a zinc (metallic zinc (Zn)) concentration of 0.1 to 7.0 g/L, more preferably 0.2 to 5.0 g/L, and even more preferably 0.2 to 4.0 g/L. If the concentration is less than 0.1 g/L, the amount of Zn precipitated will be small and sufficient adhesion will not be ensured. If the concentration is more than 7.0 g/L, the amount of Zn precipitated will be excessive and sufficient adhesion will not be ensured.

<<Nickel compounds>>
The nickel compound is not particularly limited as long as it is a water-soluble nickel compound. Specific examples include nickel sulfate, nickel nitrate, nickel chloride, nickel acetate, and nickel gluconate. These may be used alone or in combination of two or more. Of these, nickel sulfate is preferred.

The metal replacement treatment solution preferably contains a nickel compound at a nickel (metallic nickel (Ni)) concentration of 0.1 to 12 g/L, and more preferably 0.2 to 10 g/L. If the concentration is less than 0.1 g/L, the amount of co-deposited Zn decreases, and sufficient adhesion tends to be insufficient. If the concentration is more than 12 g/L, the amount of co-deposited Zn becomes excessive, and sufficient adhesion tends to be insufficient.

<<Germanium Compounds>>
The germanium compound is not particularly limited as long as it is a water-soluble germanium compound. Specific examples thereof include germanium dioxide, germanium sulfate, germanium sulfide, germanium fluoride, germanium chloride, and germanium iodide. These compounds may be used alone or in combination of two or more. Among these, germanium dioxide is preferred.
In this specification, when a compound corresponds to both a germanium compound and a fluorine compound, such as germanium fluoride, it is treated as a germanium compound. Similarly, when a zinc compound or a nickel compound corresponds to both a zinc compound and a nickel compound, it is treated as a zinc compound or a nickel compound.

The metal replacement treatment solution preferably contains a germanium compound at a germanium (metallic germanium (Ge)) concentration of 0.1 to 7.0 g/L, and more preferably 0.2 to 5.0 g/L. If the concentration is less than 0.1 g/L, the amount of co-deposited Zn decreases, and sufficient adhesion tends to be insufficient. If the concentration is more than 7.0 g/L, the amount of co-deposited Zn becomes excessive, and sufficient adhesion tends to be insufficient.

The ratio of zinc concentration to germanium concentration (zinc concentration:germanium concentration) is preferably 1:5 to 5:1.

<<Fluorine compounds>>
Fluorine compounds dissolve aluminum in the oxide film on the surface of aluminum or aluminum alloys, and facilitate the replacement with metals such as zinc.
Specific examples of fluorine compounds include fluoroboric acid, sodium fluoride, potassium fluoride, ammonium hydrogen fluoride, ammonium fluoride, hydrogen fluoride, and lithium fluoride. These may be used alone or in combination of two or more. Among these, fluoroboric acid, sodium fluoride, potassium fluoride, ammonium hydrogen fluoride, ammonium fluoride, and hydrogen fluoride are preferred, and fluoroboric acid, sodium fluoride, potassium fluoride, ammonium hydrogen fluoride, and ammonium fluoride are more preferred.

The metal replacement treatment solution preferably contains a fluorine compound at a fluorine (F) concentration of 1.0 to 100 g/L, more preferably 5.0 to 50 g/L. If the concentration is less than 1.0 g/L, the aluminum dissolving effect is weak, and sufficient adhesion tends to be insufficient. If the concentration is more than 100 g/L, aluminum dissolves excessively, and sufficient adhesion tends to be insufficient.
In this specification, the zinc (metallic zinc (Zn)) concentration, nickel (metallic nickel (Ni)) concentration, and germanium (metallic germanium (Ge)) concentration in the metal substitution treatment solution are measured by ICP (manufactured by Horiba, Ltd.).
In this specification, the fluorine (F) concentration in the metal substitution treatment solution is measured using a fluorine ion electrode.

<<pH>>
The pH of the metal substitution treatment solution is preferably 1.0 to 12.0, more preferably 2.0 to 10.0. That is, the metal substitution treatment solution of the present invention can be used in either alkaline or acidic conditions. Here, in a typical zincate treatment, when the solution is alkaline, aluminum may be excessively eluted (for example, Figure 9 of Non-Patent Document 3), which tends to cause aluminum spikes. When the solution is acidic, although aluminum does not excessively elute, sufficient adhesion tends to be difficult to ensure.
On the other hand, the metal replacement treatment solution of the present invention can ensure sufficient adhesion even when it is acidic, and when used in an acidic state, a more significant improvement in adhesion can be achieved. Furthermore, when it is acidic, aluminum is not excessively eluted and aluminum spikes can be reduced. However, if the pH is less than 3.5, there is a risk of excessive aluminum elution.
Therefore, the pH of the metal replacement treatment solution is more preferably 3.5 to 6.5, particularly preferably 4.0 to 6.5, and most preferably 4.5 to 6.5. As described above, this not only achieves a more significant improvement in adhesion, but also prevents excessive aluminum elution and reduces aluminum spikes. If excessive aluminum elution results in aluminum spikes, numerous wedge-shaped depressions form on the aluminum surface. In the subsequent plating film formation process, nickel plating, for example, penetrates into these depressions, resulting in the formation of a plating film with poor smoothness, which affects conductivity and significantly impairs the appearance. Therefore, reducing aluminum spikes allows the formation of a plating film with high smoothness and excellent plating appearance.
In this specification, the pH of the metal replacement treatment solution is a value measured at 25°C.

The pH of the metal substitution treatment solution can be adjusted by selecting the type of zinc compound, nickel compound, germanium compound, or fluorine compound.Alkaline components and acidic components may also be added as needed.
The alkaline component is not particularly limited, but examples thereof include sodium hydroxide, ammonium, etc. The acid component is not particularly limited, but examples thereof include sulfuric acid, phosphoric acid, etc. These alkaline components and acid components may be used alone or in combination of two or more.

The metal substitution treatment solution may contain a buffering agent to enhance pH buffering properties.
The buffering agent is not particularly limited as long as it has buffering properties, and examples of compounds that have buffering properties around pH 4.0 to 6.5 include acetic acid, malic acid, succinic acid, citric acid, malonic acid, lactic acid, oxalic acid, glutaric acid, adipic acid, formic acid, etc. These may be used alone or in combination of two or more.
The concentration of the buffer in the metal replacement treatment solution is preferably 1.0 to 50 g/L, more preferably 5.0 to 30 g/L.

<<Others>>
The metal replacement treatment liquid may contain, in addition to the above components, components commonly used in metal replacement treatment liquids, such as surfactants and brighteners. It may also contain water-soluble salts of metals other than those mentioned above, such as iron, copper, silver, palladium, lead, bismuth, and thallium. These may be used alone or in combination of two or more.

The metal replacement treatment solution can be produced by appropriately mixing each component using a solvent (preferably water). From the perspective of operational safety, the metal replacement treatment solution is preferably prepared as an aqueous solution, but other solvents such as methanol, ethanol, ethylene glycol, diethylene glycol, triethylene glycol, glycerin, IPA, etc. can also be used, or a mixed solvent with water can be used. These solvents may be used alone, or two or more types may be used in combination.

The metal replacement treatment liquid can be suitably used as a metal replacement treatment liquid for aluminum or aluminum alloys.

<Surface treatment method for aluminum or aluminum alloy>
Next, the method for surface treatment of aluminum or aluminum alloys of the present invention using the metal substitution treatment liquid of the present invention will be described.
The method for surface treatment of aluminum or an aluminum alloy of the present invention involves bringing a workpiece having aluminum or an aluminum alloy on its surface into contact with the metal substitution treatment liquid of the present invention, removing an oxide film on the aluminum or aluminum alloy, and performing a metal substitution treatment to replace the aluminum with a metal contained in the metal substitution treatment liquid, thereby forming a substituted metal film containing the metal on the surface of the workpiece.
This surface treatment method is a pretreatment method for applying a plating film, such as a nickel plating film or a palladium plating film, to a workpiece, and involves bringing the metal substitution treatment solution of the present invention into contact with the workpiece, which has aluminum or an aluminum alloy at least on its surface, to remove the oxide film adhering to the surface and form a substitution metal film, thereby increasing the adhesion of the nickel plating film or the like to be applied later.

In the aluminum or aluminum alloy surface treatment method of the present invention, the metal substitution treatment solution of the present invention is used to remove an oxide film adhering to a workpiece having at least aluminum or an aluminum alloy on its surface (hereinafter also referred to as an aluminum substrate), and zinc particles, nickel particles, and germanium particles are precipitated on the surface of the workpiece through a substitution reaction caused by the electrode potential difference between a metal such as zinc and aluminum.

Generally, in the plating pretreatment of an aluminum substrate using a zincate treatment solution, a double zincate treatment process is performed in which two zincation treatments are performed: (1) the aluminum substrate is subjected to a first zincation treatment, (2) pickling, and then (3) a second zincation treatment is performed. After this double zincate treatment, (4) a plating treatment such as electroless nickel plating is performed.
On the other hand, in the surface treatment method for aluminum or aluminum alloys of the present invention using the metal substitution treatment solution of the present invention, very good adhesion can be obtained, so that double zincate treatment is not necessary, and good adhesion can be imparted by single zincate treatment. Therefore, in the surface treatment method for aluminum or aluminum alloys of the present invention, it is preferable to (1) subject the aluminum substrate to metal substitution treatment, and after this single zincate treatment, to (4) a plating treatment such as electroless nickel plating. In other words, it is preferable not to perform (2) pickling treatment between the metal substitution treatment and the plating treatment, or (3) a second metal substitution treatment after the pickling treatment.

<<(1) Metal Replacement Treatment>>
The aluminum substrate, which is the object to be plated, need only have aluminum or an aluminum alloy on at least its surface. Examples of aluminum substrates include various articles made of aluminum or aluminum alloys, as well as articles in which an aluminum or aluminum alloy coating is formed on a non-aluminum material (e.g., various substrates such as ceramics and wafers), articles subjected to hot-dip aluminum plating, castings, die-cast products, etc. The shape of the aluminum substrate is not particularly limited, and may be any of ordinary plate-like articles (including thin-film articles such as films and sheets) and molded articles formed into various shapes. Furthermore, the plate-like articles are not limited to plate-like articles made of aluminum or aluminum alloys alone, but also include aluminum coatings (integrated with the substrate) formed on substrates such as ceramics or wafers by conventional methods such as sputtering, vacuum deposition, and ion plating.

The aluminum alloy is not particularly limited, and various alloys containing aluminum as the main metallic component can be used. Examples of applicable alloys include A1000 series quasi-aluminum alloys, A2000 series aluminum alloys containing copper and manganese, A3000 series aluminum-manganese alloys, A4000 series aluminum-silicon alloys, A5000 series aluminum-magnesium alloys, A6000 series aluminum-magnesium-silicon alloys, A7000 series aluminum-zinc-magnesium alloys, and A8000 series aluminum-lithium alloys.

From the viewpoint of plating smoothness, the aluminum purity of the aluminum or aluminum alloy is preferably 98% or more, more preferably 98.5% or more, and even more preferably 99% or more.

The aluminum substrate, which is the workpiece to be plated, can be produced by coating a non-aluminum material, such as a silicon plate, with an aluminum layer using well-known methods, such as sputtering. The aluminum layer may cover the entire non-aluminum material, or only a portion of it, and is typically 0.5 μm or thicker, preferably 1 μm or thicker. Furthermore, the method for forming this aluminum substrate is not limited to sputtering; vacuum deposition, ion plating, and other methods can also be used.

First, the aluminum substrate is subjected to a cleaning process such as degreasing using a well-known method, and after being appropriately rinsed with water, it is subjected to a well-known etching process using alkali or acid. Specifically, the degreasing process is carried out by immersing the substrate in a degreasing solution for aluminum or by electrolytic degreasing. The etching process is carried out by immersing the substrate in a solution of, for example, about 1 to 10% alkali or about 1 to 20% acid at a temperature of about 25 to 75°C for about 1 to 15 minutes.

Next, to remove any smut residues (residues) from alkaline or acid etching, the substrate is immersed in an acidic solution for a predetermined period of time. Specifically, the etched aluminum substrate is immersed for approximately 30 seconds to 2 minutes in an aqueous solution of nitric acid with a concentration ranging from approximately 10 to 800 ml/L, preferably from approximately 100 to 600 ml/L, at a temperature of approximately 15 to 35°C, to remove smut.

Then, after rinsing with water, the aluminum substrate that has been subjected to the desmutting treatment and other processes is immersed in the metal substitution treatment liquid (zincate treatment liquid) of the present invention to perform the metal substitution treatment. Specifically, for example, the aluminum substrate is immersed in a zincate treatment liquid having the composition described above and a liquid temperature of 10 to 50°C, preferably 15 to 30°C. If the temperature of the zincate treatment liquid is 10°C or higher, the substitution reaction does not slow down too much, allowing a metal coating to be formed without unevenness. On the other hand, if the temperature is 50°C or lower, the substitution reaction does not accelerate too much, preventing the surface of the substituted metal coating from becoming rough. Therefore, the above-mentioned temperatures are preferred.

There are no particular restrictions on the immersion time, which can be set appropriately taking into account factors such as the thickness of the aluminum oxide film to be removed. For example, it is usually at least about 5 seconds, preferably at least 10 seconds, with an upper limit of 5 minutes. If the immersion time is too short, the substitution will not progress and the oxide film will not be sufficiently removed. On the other hand, if the immersion time is too long, the treatment liquid may seep through small holes in the substituted metal layer, causing the aluminum or aluminum alloy to dissolve. Therefore, the conditions must be set taking these points into consideration.

By immersing an aluminum substrate in this zincate treatment solution, the oxide film adhering to the substrate surface can be removed, and by further coating the aluminum surface with a substitution metal film containing Zn, Ni, and Ge, it is possible to form a plating film with good adhesion to the substrate.

The metal replacement treatment is not particularly limited as long as it is possible for the metal replacement treatment solution of the present invention to come into contact with the surface of the aluminum substrate. In addition to immersion, other contact methods such as coating and spraying can also be used.

<<(4) Plating Treatment>>
The plating is carried out on the zincated aluminum substrate by electroless or electrolytic plating with a suitable metal plating solution, such as an electroless nickel, electroless palladium, or copper plating bath, to the desired final film thickness.

Specifically, electroless nickel plating will be described as an example. Electroless nickel plating solutions provide nickel ions using water-soluble nickel salts, such as nickel sulfate, nickel chloride, and nickel acetate. The nickel ion concentration is, for example, approximately 1 to 10 g/L. Furthermore, electroless nickel plating solutions contain organic acid salts, such as acetates, succinates, and citrates, or nickel complexing agents, such as ammonium salts and amine salts, at concentrations ranging from approximately 20 to 80 g/L. They also contain hypophosphites, such as hypophosphorous acid or sodium hypophosphite, as reducing agents at concentrations ranging from approximately 10 to 40 g/L. The inclusion of hypophosphites or other reducing agents enhances the stability of the plating solution, enabling the formation of inexpensive nickel-phosphorus alloy coatings. The plating solution containing these compounds is prepared to have a pH of approximately 4 to 7, and the temperature of this plating solution is adjusted to 60 to 95°C. The aluminum substrate is immersed in the plating solution for approximately 15 seconds to 120 minutes to perform the plating process. The thickness of the plating film can also be altered by changing the plating time as needed.

As mentioned above, the plating process is not limited to electroless plating, and electrolytic plating may also be used. Furthermore, in addition to the types of plating metals exemplified above, plating metals such as Cu and Au may also be used. Furthermore, plating may be performed to form two or more layers using a displacement plating method, etc.

The processing conditions and various concentration settings for the zincate treatment and plating treatment described above are not limited to those described above, and can, of course, be changed as appropriate depending on the thickness of the coating to be formed, etc.

In the surface treatment method for aluminum or an aluminum alloy of the present invention, a workpiece having aluminum or an aluminum alloy on its surface is brought into contact with the metal substitution treatment liquid of the present invention to perform a metal substitution treatment in which an oxide film on the aluminum or aluminum alloy is removed and the aluminum is substituted with a metal contained in the metal substitution treatment liquid. As a result, Ni and Ge are co-deposited with Zn, and a substituted metal film containing Zn, Ni, and Ge can be formed on the aluminum or aluminum alloy surface.
When aluminum or an aluminum alloy having such a substituted metal film containing Zn, Ni, or Ge on its surface is plated to form a plated film (metal film, for example, a nickel film), the Zn, Ni, and Ge present in the substituted metal film act synergistically between the aluminum or aluminum alloy and the plated film (metal film, for example, a nickel film), and good adhesion between the aluminum or aluminum alloy and the plated film (metal film) can be imparted to the aluminum or aluminum alloy.

The aluminum or aluminum alloy coated with the plating film (metal film) obtained by the present invention can be used in a variety of electronic components, including, for example, electronic components used in home appliances, in-vehicle equipment, power transmission systems, transportation equipment, and communication equipment, and more specifically, air conditioners, elevators, electric vehicles, hybrid vehicles, trains, power modules such as power control units for power generation devices, general home appliances, and personal computers.
In the present invention, by adjusting the pH of the metal substitution treatment liquid to 4.0 to 6.5, aluminum spikes can also be reduced, and pre-plating surface treatment can be performed to form a plating film with high smoothness and excellent plating appearance. Therefore, the present invention is suitable for use in semiconductor applications, preferably wafer applications, and is particularly suitable as a metal substitution treatment liquid on aluminum or aluminum alloys that is effective for pretreatment when forming under-bump metal or bumps on a wafer, and as a surface treatment method for aluminum or aluminum alloys using this metal substitution treatment liquid.

The present invention will be specifically explained based on examples, but the present invention is not limited to these examples.

Plating films were formed by subjecting aluminum substrates to various treatments under the conditions shown in Tables 1 to 3. A 1 cm x 2 cm Al-Cu TEG wafer was used as the aluminum substrate. The resulting plating films and the substrates on which the plating films were formed were evaluated using the following methods. The evaluation results are shown in Tables 2 and 3.
In Tables 2 and 3, the numerical values (concentrations) in the tables, except for succinic acid, are fluorine (F) or metal element equivalent concentrations (g/L).

<Adhesion evaluation: folding test>
The substrate with the resulting plating film was air-dried, and cellophane tape was applied to the plated surface. The wafer was then scratched in the center where the tape was applied, and split in half. The tape was peeled from the center of the split, and the amount of peeling between the Al substrate and the Ni film was calculated as a percentage. An overview of the folding test is shown in Figure 1.
0% means that none of the plating film peels off when the tape is peeled off, and 100% means that the plating film peels off from the entire surface when the tape is peeled off.

<Aluminum (Al) Spike Evaluation>
The obtained plating film was subjected to cross-sectional observation using a focused ion beam (FIB) using an XVision 210DB manufactured by Hitachi High-Technologies Corporation. Figure 2(a) shows an example of a case where no Al spikes were observed, and Figure 2(b) shows an example of a case where Al spikes were observed. When no Al spikes were observed, as in Figure 2(a), the film was judged to be good.

Degreasing/etching: Epitas MCE-31 (Uemura Industries Co., Ltd.)
Electroless Ni: Epitas NPR-18 (Uemura Industries Co., Ltd.)

Tables 2 and 3 show that the metal replacement treatment solutions of the examples, which contain a zinc compound, a nickel compound, a germanium compound, and a fluorine compound, can provide good adhesion to plating films (metal films). Furthermore, it was found that aluminum spikes can be reduced by adjusting the pH of the metal replacement treatment solution to 3.5 to 6.5. While Tables 2 and 3 show results when an Al-Cu TEG wafer was used as the aluminum substrate, similar results were obtained when an Al-Si TEG wafer was used as the aluminum substrate.

Claims (9)

zinc compounds, nickel compounds, germanium compounds, and fluorine compounds ,
A metal replacement treatment solution for aluminum or an aluminum alloy, which contains a zinc compound at a zinc concentration of 0.1 to 7.0 g/L, a nickel compound at a nickel concentration of 0.1 to 12 g/L, a germanium compound at a germanium concentration of 0.1 to 7.0 g/L, and a fluorine compound at a fluorine concentration of 1.0 to 100 g/L, and has a pH of 3.5 to 6.5 . The metal replacement treatment solution for aluminum or aluminum alloys according to claim 1, containing a zinc compound at a zinc concentration of 0.2 to 5.0 g/L. The metal replacement treatment solution for aluminum or aluminum alloys according to claim 1 or 2, containing a nickel compound at a nickel concentration of 0.2 to 10 g/L. The metal replacement treatment solution for aluminum or aluminum alloys according to any one of claims 1 to 3, containing a germanium compound at a germanium concentration of 0.2 to 5.0 g/L. The metal replacement treatment solution for aluminum or aluminum alloys according to any one of claims 1 to 4, containing a fluorine compound at a fluorine concentration of 5.0 to 50 g/L. A metal replacement treatment solution for aluminum or aluminum alloys according to any one of claims 1 to 5, wherein the ratio of zinc concentration to germanium concentration is 1:5 to 5:1. The metal replacement treatment solution for aluminum or aluminum alloys according to any one of claims 1 to 6, having a pH of 4.0 to 6.5. A surface treatment method for aluminum or aluminum alloys, comprising contacting a workpiece having aluminum or an aluminum alloy on its surface with the metal replacement treatment solution for aluminum or aluminum alloys described in any one of claims 1 to 7, removing an oxide film on the aluminum or aluminum alloy, and performing a metal replacement treatment to replace the aluminum with a metal contained in the metal replacement treatment solution, thereby forming a replacement metal film containing the metal on the surface of the workpiece. 9. The method for treating the surface of aluminum or an aluminum alloy according to claim 8, wherein after forming the displacement metal film, a plating film is formed on the surface of the displacement metal film.