JP2023069841A - Metal replacement process liquid, surface treatment method for aluminum or aluminum alloy - Google Patents

Abstract

To provide a metal replacement process liquid which provides excellent adhesion with a plating film (metallic film), and a surface treatment method for aluminum or aluminum alloy using the metal replacement process liquid.SOLUTION: A metal replacement process liquid includes a zinc compound, a nickel compound, a germanium compound, and a fluorine compound.SELECTED DRAWING: Figure 2

Description

The present invention relates to a metal displacement treatment liquid and a method for surface treatment of aluminum or aluminum alloys.

Aluminum easily forms an oxide film in air and water. It is known that due to this oxide film, the adhesion of the plating film is low when plating aluminum or an aluminum alloy. Therefore, prior to plating, a zincate treatment is performed for the purpose of removing the oxide film on the surface of aluminum or aluminum alloy and ensuring adhesion with the plating film formed on aluminum ( For example, Patent Documents 1 to 3, Non-Patent Documents 1 to 3).

JP-A-2000-256864 JP 2020-196914 A 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 intensive studies by the present inventors, it has been found that there is room for improvement in the adhesion to the plating film in the conventional technique.

The present invention solves the problems newly found by the present inventors, and provides a metal replacement treatment solution capable of imparting good adhesion to a plating film (metal film), aluminum using the metal replacement treatment solution, or aluminum It is an object of the present invention to provide a surface treatment method for alloys.

As a result of intensive studies, the present inventors have found that good adhesion to a plating film (metal film) can be imparted by using a metal displacement treatment solution having a specific composition, and have completed the present invention.
That is, the present invention relates to a metal replacement processing solution containing a zinc compound, a nickel compound, a germanium compound and a fluorine compound.

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

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

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

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

The metal substitution treatment liquid preferably has a ratio of zinc concentration to germanium concentration of 1:5 to 5:1.

The metal substitution treatment liquid preferably has a pH of 4.0 to 6.5.

The metal replacement treatment liquid is preferably for aluminum or an aluminum alloy.

In the present invention, an object to be treated having aluminum or an aluminum alloy on its surface is brought into contact with the metal replacement treatment liquid to remove the oxide film on the aluminum or aluminum alloy, and the aluminum is contained in the metal replacement treatment liquid. The present invention relates to a method for surface treatment of aluminum or an aluminum alloy, comprising performing a metal substitution treatment for substituting a metal to be treated to form a substitution metal film containing the metal on the surface of the object to be treated.

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

According to the present invention, since the metal displacement treatment liquid contains a zinc compound, a nickel compound, a germanium compound, and a fluorine compound, good adhesion to the plating film (metal film) can be imparted.

It is a schematic diagram which shows the outline|summary of a folding-splitting test. (a) is a photograph showing an example when Al spikes are not seen. (b) A photograph showing an example in which Al spikes are observed.

The metal substitution treatment liquid of the present invention contains a zinc compound, a nickel compound, a germanium compound and a fluorine compound. This makes it possible to impart good adhesion to the plating film (metal film).

The reason why the above-mentioned effects are obtained with the metal-substitution treatment liquid is presumed as follows.
An object to be treated having aluminum or an aluminum alloy on its surface is brought into contact with the metal replacement treatment liquid to remove the oxide film on the aluminum or aluminum alloy and replace the aluminum with the metal contained in the metal replacement treatment liquid. Nickel (Ni) and germanium (Ge) co-deposit together with zinc (Zn) by performing a metal substitution treatment to form a substitution metal film containing Zn, Ni and Ge on the aluminum or aluminum alloy surface.
When a plating film (a metal film, for example, a nickel film) is formed by performing a plating treatment on aluminum or an aluminum alloy having such a substitution metal film containing Zn, Ni, and Ge on the surface, aluminum or an aluminum alloy and plating Between films (metal films, for example, nickel films), Zn, Ni, and Ge present in the substituted metal film act synergistically, so that aluminum or aluminum alloys have a good relationship with the plating film (metal film). Adhesion can be imparted.
The fact that Zn, Ni, and Ge act synergistically is that Zn, Ni, and Ge alone; , and Ge (without Zn) cannot provide good adhesion to the plating film (metal film).

<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 compound>>
The zinc compound is not particularly limited as long as it is a water-soluble zinc compound. Specific examples thereof 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. Among them, zinc sulfate is preferred.

The metal substitution treatment liquid preferably contains a zinc compound (zinc metal (Zn)) at a concentration of 0.1 to 7.0 g/L, more preferably 0.2 to 5.0 g/L. More preferably, it contains 2 to 4.0 g/L. If it is less than 0.1 g/L, there is a tendency that the amount of Zn precipitated is small and sufficient adhesion cannot be ensured. If it exceeds 7.0 g/L, the amount of precipitated Zn tends to be excessive and sufficient adhesion cannot be ensured.

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

The metal replacement treatment liquid preferably contains a nickel compound at a nickel (metallic nickel (Ni)) concentration of 0.1 to 12 g/L, more preferably 0.2 to 10 g/L. If it is less than 0.1 g/L, the amount of co-precipitation with Zn tends to decrease and sufficient adhesion cannot be ensured. If it exceeds 12 g/L, the amount of eutectoid with Zn becomes excessive and there is a tendency that sufficient adhesion cannot be ensured.

<<Germanium compound>>
The germanium compound is not particularly limited as long as it is a water-soluble germanium compound. Specific examples include germanium dioxide, germanium sulfate, germanium sulfide, germanium fluoride, germanium chloride, and germanium iodide. These may be used alone or in combination of two or more. Among them, germanium dioxide is preferable.
In this specification, germanium compounds and fluorine compounds, such as germanium fluoride, are handled as germanium compounds. Zinc compounds and nickel compounds are similarly treated as zinc compounds and nickel compounds in the same case.

The metal substitution treatment liquid preferably contains a germanium compound at a germanium (metal germanium (Ge)) concentration of 0.1 to 7.0 g/L, more preferably 0.2 to 5.0 g/L. If it is less than 0.1 g/L, the amount of co-precipitation with Zn tends to decrease and sufficient adhesion cannot be ensured. If it exceeds 7.0 g/L, the amount of eutectoid with Zn becomes excessive and there is a tendency that sufficient adhesion cannot be ensured.

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

<<fluorine compound>>
A fluorine compound dissolves aluminum in an oxide film on the surface of aluminum or an aluminum alloy, and smoothly progresses substitution with a metal such as zinc.
Specific examples of fluorine compounds include hydroboric 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, preferred are fluoroboric acid, sodium fluoride, potassium fluoride, ammonium hydrogen fluoride, ammonium fluoride and hydrogen fluoride. ammonium chloride is more preferred.

The metal substitution treatment liquid 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 it is less than 1.0 g/L, the action of dissolving aluminum tends to be weak and sufficient adhesion cannot be ensured. If it exceeds 100 g/L, there is a tendency that aluminum is excessively dissolved and sufficient adhesion cannot be ensured.
In this specification, the zinc (metallic zinc (Zn)) concentration, nickel (metallic nickel (Ni)) concentration, and germanium (metallic germanium (Ge)) concentration in the metal replacement treatment solution are defined as ICP (Horiba Ltd.) manufactured by).
Further, in this specification, the fluorine (F) concentration in the metal substitution treatment liquid 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 liquid of the present invention can be used in either alkaline or acidic conditions. Here, in the normal zincate treatment, when alkaline, aluminum may be excessively eluted (for example, FIG. 9 of Non-Patent Document 3), and aluminum spikes tend to occur, and when acidic, aluminum is excessive. However, there is a tendency that sufficient adhesion cannot be secured.
On the other hand, the metal substitution treatment liquid of the present invention can ensure sufficient adhesion even in the case of acidity, and by using it in acidity, a more remarkable effect of improving adhesion can be obtained. Furthermore, in the case of acidity, excessive elution of aluminum does not occur, and aluminum spikes can also be reduced. However, if the pH is less than 3.5, aluminum may be excessively eluted.
Therefore, the pH of the metal substitution 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 a result, as described above, a more remarkable effect of improving adhesion can be obtained, aluminum can be prevented from being excessively eluted, and aluminum spikes can be reduced. Here, when aluminum is excessively eluted and aluminum spikes are generated, a large number of wedge-shaped dents are formed on the aluminum surface. A poor plating film is formed, which affects the conductivity and greatly impairs the appearance. Therefore, by reducing aluminum spikes, it is possible to form a plated film with high smoothness and excellent plating appearance.
In addition, in this specification, the pH of the metal substitution treatment liquid is a value measured at 25°C.

The pH of the metal substitution treatment solution can also be adjusted by selecting the type of zinc compound, nickel compound, germanium compound, and fluorine compound. Moreover, you may add an alkali component and an acid component as needed.
Alkaline components are not particularly limited, but examples include sodium hydroxide, ammonium hydroxide, and the like. Examples of the acid component include, but are not limited to, sulfuric acid, phosphoric acid, and the like. These alkaline components and acid components may be used alone, or two or more of them may be used in combination.

The metal-displacement treatment liquid may contain a buffering agent in order to enhance pH buffering properties.
The buffering agent is not particularly limited as long as it has a buffering property. Lactic acid, oxalic acid, glutaric acid, adipic acid, formic acid and the like. These may be used alone or in combination of two or more.
The concentration of the buffering agent in the metal replacement treatment solution is preferably 1.0-50 g/L, more preferably 5.0-30 g/L.

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

The metal substitution treatment liquid can be produced by appropriately mixing each component using a solvent (preferably water). The metal-substitution treatment liquid is preferably prepared as an aqueous solution from the viewpoint of operational safety. It is also possible to use a mixed solvent with These solvents may be used alone, or two or more of them 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.

<Method for surface treatment of aluminum or aluminum alloy>
Next, the method for surface treatment of aluminum or aluminum alloy of the present invention using the metal displacement treatment liquid of the present invention will be described.
The method for surface treatment of aluminum or aluminum alloy of the present invention comprises contacting an object to be treated having aluminum or aluminum alloy on its surface with the metal displacement treatment liquid of the present invention to remove an oxide film on the aluminum or aluminum alloy, A metal replacement treatment is performed to replace the aluminum with a metal contained in the metal replacement treatment liquid, thereby forming a replacement metal film containing the metal on the surface of the object to be treated.
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 an object to be treated. By contacting the metal replacement treatment liquid to remove the oxide film adhering to the surface and forming a replacement metal film, the adhesion of the nickel plating film or the like to be treated later is enhanced.

In the method for surface treatment of aluminum or aluminum alloy of the present invention, an oxide film deposited on an object to be treated (hereinafter also referred to as an aluminum substrate) having at least aluminum or an aluminum alloy on its surface by the metal displacement treatment solution of the present invention. is removed, and zinc particles, nickel particles, and germanium particles are deposited on the surface of the object to be treated by a substitution reaction caused by an electrode potential difference between a metal such as zinc and aluminum.

In general, the pre-plating treatment of an aluminum substrate using a zincating solution is performed by a double zincating process in which zinc substitution is performed twice. That is, it is a process of (1) subjecting an aluminum substrate to a first zinc substitution treatment, (2) after pickling, (3) then subjecting it to a second zinc substitution treatment, and after this double zincate treatment, (4) electroless Plating such as nickel plating is performed.
On the other hand, in the method for surface treatment of aluminum or aluminum alloy of the present invention using the metal substitution treatment solution of the present invention, very good adhesion can be obtained, so there is no need to perform double zincate treatment, and single zincate treatment is performed. Good adhesion can be imparted. Therefore, in the aluminum or aluminum alloy surface treatment method of the present invention, it is preferable that (1) the aluminum substrate is subjected to metal substitution treatment, and after this single zincate treatment, (4) plating treatment such as electroless nickel plating is performed. That is, it is preferable not to perform (2) the pickling process and (3) the second metal replacing process after the pickling process between the metal replacement process and the plating process.

<<(1) Metal replacement treatment>>
The aluminum substrate, which is the object to be plated, should have at least aluminum or an aluminum alloy on its surface. Aluminum substrates include, for example, various articles made of aluminum or aluminum alloys, as well as articles in which aluminum or aluminum alloy films are formed on non-aluminum materials (for example, various substrates such as ceramics and wafers), Articles subjected to hot-dip aluminum plating, castings, die castings, etc. can be used. The shape of the aluminum substrate is also not particularly limited, and it may be an ordinary plate (including thin films such as films and sheets) or a molded article molded into various shapes. In addition, the plate-like material is not limited to a plate-like material made of aluminum or an aluminum alloy alone. Aluminum coatings (integrated with the substrate) are also included.

The aluminum alloy is not particularly limited, and for example, various alloys containing aluminum as a main metal component can be used. For example, A1000 series quasi-aluminum, A2000 series aluminum alloy containing copper and manganese, A3000 series aluminum-manganese alloy, A4000 series aluminum-silicon alloy, A5000 series aluminum-magnesium alloy, A6000 series aluminum-magnesium- Silicon alloys, A7000 series aluminum-zinc-magnesium alloys, A8000 series aluminum-lithium alloys, etc. can be applied.

The purity of aluminum or aluminum alloy is preferably 98% or higher, more preferably 98.5% or higher, and still more preferably 99% or higher, from the viewpoint of plating smoothness.

The aluminum substrate, which is the object to be plated, can be prepared by coating a non-aluminum material such as a silicon plate with an aluminum layer by a known method such as sputtering. The coating of the aluminum layer may cover the entire non-aluminum material or may cover only a part of it, and the aluminum layer is usually coated with a thickness of 0.5 μm or more, preferably 1 μm or more. Further, the method for forming this aluminum substrate is not limited to the sputtering method, and it can be produced using a vacuum vapor deposition method, an ion plating method, or the like.

First, the aluminum substrate is subjected to cleaning treatment such as degreasing treatment by a well-known method, washed with water as appropriate, and then subjected to well-known etching treatment with alkali or acid. Specifically, the degreasing treatment is performed by immersion in a degreasing solution for aluminum or electrolytic degreasing. Further, the etching treatment is performed by using, for example, about 1 to 10% alkaline solution or about 1 to 20% acidic solution, at a liquid temperature of about 25 to 75° C., and immersing in the solution for about 1 to 15 minutes. .

Next, it is immersed in an acidic solution for a predetermined time for the purpose of removing etching residues (smut) caused by alkali or acid. Specifically, for example, an aluminum substrate having a concentration range of about 10 to 800 ml/L, preferably about 100 to 600 ml/L and a solution temperature of about 15 to 35° C. is etched in an aqueous nitric acid solution. Allow to soak for about 30 seconds to 2 minutes to remove smut.

After being washed with water, the aluminum substrate thus subjected to the desmutting treatment or the like is immersed in the metal replacement treatment liquid (zincate treatment liquid) of the present invention to carry out the metal replacement treatment. Specifically, for example, the aluminum substrate is immersed in the zincate treatment liquid having the composition described above and having a liquid temperature of 10 to 50.degree. C., preferably 15 to 30.degree. If the temperature of the zincate treatment solution is 10°C or higher, the substitution reaction does not become too slow, and a metal film can be formed without unevenness. The temperature described above is preferable because it is possible to prevent the surface of the metal film from becoming rough.

The conditions for the immersion time are not particularly limited, and can be appropriately set in consideration of the thickness of the aluminum oxide film to be removed. 5 minutes or less. If the immersion time is too short, the replacement will not progress and the oxide film will not be removed sufficiently. On the other hand, if the immersion time is too long, the treatment solution will enter through small holes in the replacement metal layer, and aluminum or aluminum alloy will be eluted. Therefore, it is necessary to set the conditions in consideration of these points.

By immersing the aluminum substrate in the zincate treatment solution in this manner, the oxide film adhering to the substrate surface can be removed, and the aluminum surface is further coated with a substitution metal film containing Zn, Ni, and Ge. Activation makes it possible to form a plating film having good adhesion to the object to be treated.

The metal replacement treatment is not particularly limited as long as the metal replacement treatment solution of the present invention can come into contact with the surface of the aluminum substrate. As the contact method, other than immersion, for example, a method such as coating or spraying can be adopted.

<<(4) Plating treatment>>
This plating treatment is performed by electroless plating or electrolytic plating on the zincate-treated aluminum substrate. For example, a suitable metal plating solution such as an electroless nickel, electroless palladium or copper plating bath is plated to the desired final film thickness.

Specifically, electroless nickel plating will be described as an example. The electroless nickel plating solution is provided with nickel ions by using a water-soluble nickel salt such as nickel sulfate, nickel chloride, or nickel acetate, and the concentration of the nickel ions is, for example, about 1 to 10 g/L. . Further, the electroless nickel plating solution contains, for example, organic acid salts such as acetates, succinates, and citrates having a concentration range of about 20 to 80 g/L, and nickel complexes such as ammonium salts and amine salts. and hypophosphite such as hypophosphorous acid or sodium hypophosphite having a concentration range of about 10-40 g/L as a reducing agent. By containing hypophosphite or the like as a reducing agent, the stability of the plating solution is enhanced, and an inexpensive nickel-phosphorus alloy film can be formed. The plating solution comprising these compounds is used after being adjusted to have a pH of about 4 to 7. This plating solution is further adjusted to a solution temperature of 60 to 95° C., and the aluminum substrate to the plating solution. As for the immersion time of , the plating treatment is performed by immersing for about 15 seconds to 120 minutes. Moreover, the thickness of the plating film can be changed by appropriately changing the plating treatment time.

In addition, as described above, the plating treatment is not limited to the electroless plating treatment, and electrolytic plating may be performed. In addition to the types of plating metals exemplified above, plating metals such as Cu and Au may be used, and furthermore, plating is performed by displacement plating or the like so as to form two or more layers. you can go

It goes without saying that the treatment conditions and various concentration settings in the zincate treatment and plating treatment described above are not limited to the conditions described above, and can be appropriately changed depending on the thickness of the film to be formed.

In the aluminum or aluminum alloy surface treatment method of the present invention, an object to be treated having aluminum or an aluminum alloy on its surface is brought into contact with the metal replacement treatment liquid of the present invention to remove the oxide film on the aluminum or aluminum alloy, By performing a metal substitution treatment for substituting the aluminum with the metal contained in the metal substitution treatment solution, Ni and Ge are co-deposited together with Zn, and the substitution metal film containing Zn, Ni and Ge is formed of aluminum or aluminum. It can form on the alloy surface.
When a plating film (a metal film, for example, a nickel film) is formed by performing a plating treatment on aluminum or an aluminum alloy having such a substitution metal film containing Zn, Ni, and Ge on the surface, aluminum or an aluminum alloy and plating Between films (metal films, for example, nickel films), Zn, Ni, and Ge present in the substituted metal film act synergistically, so that aluminum or aluminum alloys have a good relationship with the plating film (metal film). Adhesion can be imparted.

Aluminum or an aluminum alloy provided with a plating film (metal film) obtained by the present invention can be used for various electronic components. Examples of electronic components include electronic components used in home appliances, in-vehicle equipment, power transmission systems, transportation equipment, communication equipment, etc. Specific examples include air conditioners, elevators, electric vehicles, hybrid vehicles, trains, and power generators. power modules such as power control units for electronic devices, general home appliances, personal computers, and the like.
In the present invention, by setting the pH of the metal replacement treatment solution to 4.0 to 6.5, aluminum spikes can be reduced, and the surface before plating for forming a plated film with high smoothness and excellent plating appearance. Since it can be processed, it can be suitably used for semiconductor applications, preferably wafer applications, and is particularly effective for pretreatment when forming underbump metal or bumps on a wafer. And it is suitable as a surface treatment method of aluminum or aluminum alloy using this metal replacement treatment liquid.

EXAMPLES The present invention will be specifically described based on Examples, but the present invention is not limited to these.

Under the conditions shown in Tables 1 to 3, aluminum substrates were subjected to various treatments to form plating films. Here, a 1 cm×2 cm Al—Cu TEG wafer was used as the aluminum substrate. The resulting plated film and the substrate provided with the plated film were evaluated by the following methods. Tables 2 and 3 show the evaluation results.
In addition, in Tables 2 and 3, the numerical values (concentrations) in the tables are fluorine (F) or each metal element conversion concentration (g/L) except for succinic acid.

<Adhesion evaluation: folding test>
The obtained substrate provided with the plated film was air-blown dried, and a cellophane tape was attached to the plated surface. Then, the center portion of the wafer to which the tape was pasted was scratched and split in half. The tape was peeled off from the center of the split, and the amount of peeling between the Al substrate and the Ni coating was determined as 100%. In addition, the outline|summary of a folding-splitting test was shown in FIG.
0% means that the plating film is not peeled off at all when the tape is peeled off, and 100% means that the plating film is peeled off over the entire surface when the tape is peeled off.

<Aluminum (Al) spike evaluation>
FIB (Focused Ion Beam) cross-sectional observation of the obtained plating film was performed using XVision 210DB manufactured by Hitachi High-Technologies Corporation. FIG. 2(a) shows an example in which no Al spike is observed, and FIG. 2(b) shows an example in which an Al spike is observed. It was judged to be good when no Al spike was observed as shown in FIG. 2(a).

脱脂／エッチング：エピタスＭＣＥ－３１（上村工業（株）製）
無電解Ｎｉ：エピタスＮＰＲ－１８（上村工業（株）製）

Degreasing/etching: Epitas MCE-31 (manufactured by Uemura Kogyo Co., Ltd.)
Electroless Ni: Epitas NPR-18 (manufactured by Uyemura & Co., Ltd.)

From Tables 2 and 3, it was found that the metal replacement treatment liquids of Examples containing zinc compounds, nickel compounds, germanium compounds, and fluorine compounds can impart good adhesion to plating films (metal films). It was also found that aluminum spikes can be reduced by adjusting the pH of the metal replacement treatment solution to 3.5 to 6.5. Tables 2 and 3 show the results when an Al--Cu TEG wafer was used as the aluminum substrate, but similar results were obtained when an .Al--Si TEG wafer was used as the aluminum substrate.

Claims (10)

A metal replacement treatment liquid containing a zinc compound, a nickel compound, a germanium compound, and a fluorine compound. 2. The metal replacement treatment liquid according to claim 1, which contains a zinc compound at a zinc concentration of 0.2 to 5.0 g/L. 3. The metal replacement treatment liquid according to claim 1, which contains a nickel compound with a nickel concentration of 0.2 to 10 g/L. 4. The metal replacement treatment liquid according to any one of claims 1 to 3, which contains a germanium compound with a germanium concentration of 0.2 to 5.0 g/L. 5. The metal substitution treatment liquid according to any one of claims 1 to 4, which contains a fluorine compound at a fluorine concentration of 5.0 to 50 g/L. 6. The metal replacement treatment solution according to claim 1, wherein the ratio of zinc concentration to germanium concentration is 1:5 to 5:1. 7. The metal substitution treatment liquid according to any one of claims 1 to 6, which has a pH of 4.0 to 6.5. 8. The metal replacement treatment liquid according to any one of claims 1 to 7, which is for aluminum or an aluminum alloy. An object to be treated having aluminum or an aluminum alloy on its surface is brought into contact with the metal replacement treatment liquid according to any one of claims 1 to 8, the oxide film on the aluminum or aluminum alloy is removed, and the aluminum is replaced with the metal. A method for surface treatment of aluminum or an aluminum alloy, comprising performing a metal substitution treatment for substituting a metal contained in a substitution treatment liquid to form a substitution metal film containing the metal on the surface of the object to be treated. 10. The method for surface treatment of aluminum or aluminum alloy according to claim 9, wherein after forming the substitution metal film, a plating film is formed on the surface of the substitution metal film.

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