JP5937086B2 - Electroless metal deposition using highly alkaline plating bath - Google Patents

Description

Related Applications This application is a U.S. provisional application 61 / 344,800 filed on Oct. 13, 2010, U.S. provisional application 61 / 457,446 filed on March 30, 2011. No. and US Provisional Application No. 61 / 457,590, filed April 26, 2011, claim the benefit of 35 USC 119 (e).

TECHNICAL FIELD The present invention relates to a method for electroless deposition or plating of a metal on a substrate. Specifically, it relates to methods for plated metals and plated metal alloys that are soluble at high pH above 11.5, most preferably pH 13.5-14.

In the electroless coating method, it is generally known that an alkaline plating bath having a pH of 11 or more is harmful. This is because the deposition rate rapidly decreases and the pot life of the electroless plating bath solution decreases. Thus, the use of a highly alkaline electroless plating solution has been considered commercially impossible so far because the solution pot life is reduced. Furthermore, tests using highly alkaline plating solutions often show that metal deposition stops at pH 13 and above.

The Applicant has a very light and readily available metal material as a more reactive substrate, and magnesium with good structural and mechanical properties is the optimal substrate to replace other heavier metals I realized that. A major problem with magnesium plating is that when magnesium and another metal are in mechanical contact, electrical conductivity is created between them and the magnesium can be rapidly oxidatively corroded by the galvanic effect.

In the case of a more reactive substrate such as magnesium, the coating formed tends to be non-uniform when conventional electroless deposition solutions are used. This is because the electroless deposition action is inhibited by the surface oxidation and / or corrosion of the substrate. For this reason, conventional electroless plating bath solutions have the disadvantage that they do not prevent oxidation and / or corrosion of the surface of the reactive metal substrate but also promote them, and sparsely deposit the desired coating. It can only be made.

At present, as a means for preventing oxidative corrosion of magnesium, it is most effective to electrically insulate magnesium from other metals. However, the field where such an insulating plating system can be applied is limited, and as a result, the use of magnesium is limited.

In order to overcome at least some of these difficulties associated with conventional electroless plating methods, the present invention contemplates a plating method using an electroless plating bath comprised of two separate prepared component solutions. The two component solutions are preferably made separately and then mixed immediately before the plating operation, preferably within about 5 days. This provides a highly alkaline plating solution having a pH higher than about 11.5. The pH is preferably higher than about 13, and most preferably about 13.5-14.

One of the component solutions of this two-component plating bath contains a metal salt or a plating ion source and is initially separated from the other second preparation component solution containing formaldehyde and paraformaldehyde. The formaldehyde and paraformaldehyde are used to reduce the metal salt to the metal desired to be deposited on the substrate. Each component solution further contains sodium hydroxide, the concentration of which when mixed in a ratio of about 0.5: 1 to 1.5: 1, preferably 0.7: 1 to 1: 1. The resulting mixture is selected to be a final alkaline plating bath solution having a pH higher than 11.5. The pH is preferably higher than 13, most preferably about 13.5-14.

It is preferable that each component solution is prepared as a pre-preparation solution and physically separated up to 7 days before the plating operation, preferably up to 3.5 days.

Applicant has developed a method for preparing a plating bath solution by mixing two pre-prepared component solutions, increasing the shelf-life of the bath components, increasing the stability of the solution, and a large-scale commercial electroless plating method. It has been found that the solution can be used in Specifically, when using a conventional highly alkaline plating solution with a pH higher than 11.5, sodium hydroxide in the plating bath may cause precipitation of the plating metal, thereby reducing the storage time of the bath. I found. By separating the plating bath component solutions from each other, both component solutions are prepared in advance. By mixing these later, a high pH plating bath can be prepared as one step of a batch method or a commercial continuous plating method.

Applicants have found that with the method of the present invention, in one embodiment, magnesium can be advantageously plated with a given metal in a highly alkaline plating bath having a pH of about 13.5-14. Thereby, the galvanic effect at the time of magnesium contacting mechanically with another metal can be prevented. For this reason, the method of the present invention makes it possible to prevent the formation of a galvanic couple while maintaining the conductivity of the entire magnesium structure. Thus, the electroless deposition method of the present invention envisions that magnesium can be used in a variety of structures or assemblies in which dissimilar materials are mechanically joined.

The Applicant has also found that electroless cladding of plated metals such as copper is not limiting in highly alkaline precipitation baths established for magnesium, magnesium alloys, and other reactive metals. In another embodiment, the method of the present invention is also suitably used when a metal plating such as copper is applied on a silicon substrate. Unlike the case of magnesium, when electrolessly depositing a metal on silicon, a highly alkaline bath for reducing corrosion is not necessary. However, in the case of an environment containing an excessive formaldehyde derivative reducing agent such as paraformaldehyde, it is possible to improve electroless copper deposition with high alkalinity exceeding pH 11.5, more preferably around pH 13.5.

The high pH electroless coating bath of the present invention can also be advantageously used to apply films of other metals and alloys to various substrates. Additional examples of substrates include, but are not limited to beryllium, vanadium, and titanium. High pH electroless coating methods are useful for various plating or coating metals and alloys. Examples of these metals and alloys include silver, copper, nickel / tungsten, nickel, boron, which are soluble at a pH higher than 11.5, preferably higher than 13, most preferably pH 13.5-14. And other metals and alloys, but are not limited to these.

The electroless coating system using the two-part plating bath of the present invention may also include a doped hybrid solution containing non-metallic particles. Non-metallic particles include, but are not limited to, diamond, Teflon ^™ , ceramic, and / or molybdenum.

That is, one aspect of the present invention is a method for electroless plating of a plated metal on a substrate, which includes 10 to 50 g / L sodium hydroxide, 40 to 120 g / L potassium sodium tartrate, and a metal salt. Preparing a first bath solution; and a second bath solution physically separated from said first bath solution comprising 40-75 g / L paraformaldehyde and 30-50 g / L sodium hydroxide. A step of preparing, a step of mixing the first bath solution and the second bath solution to produce a mixed plating bath solution having a pH higher than 11.5, and dipping a substrate to be plated in the mixed solution And the metal salt includes a plating metal selected from the group consisting of Cu, Al, Ni, Au, Ag, and alloys thereof.

Another aspect of the present invention is a method for electroless plating of a nickel or nickel alloy plated metal onto a magnesium metal substrate, wherein a first bath solution containing 25-60 g / L nickel chloride hexahydrate is provided. A first step physically separated from said first bath solution comprising 40-75 ml / L ethylenediamine, 30-50 g / L sodium hydroxide, and 3-8 g / L sodium borohydride. A step of preparing a second bath solution, a step of mixing the first and second bath solutions to prepare a mixed plating solution having a pH of 12 or more, and a step of immersing a substrate in the mixed solution It is the method which has.

Yet another aspect of the present invention is a method of electroless copper plating on a substrate comprising 15-25 g / L sodium hydroxide, 60-100 g / L potassium sodium tartrate, and 35-40 g / L. CuSO ₄ · 5H ₂ preparing a first bath component solution containing O, the first bath component solution and the physical containing sodium hydroxide paraformaldehyde and 20~45g / L of 50~65g / L of Preparing a second separated bath solution component and mixing the first and second bath solutions in a ratio of 0.5: 1 to 1.5: 1 and having a pH of 13 or greater The method includes a step of preparing a plating solution, and a step of setting the use temperature of the bath to about 17 to 32 ° C. and immersing a substrate to be plated in the mixed solution.

Yet another aspect of the present invention is a method for electroless copper plating on a substrate, comprising 10-30 g / L sodium hydroxide, 40-120 g / L potassium sodium tartrate, and 20-45 g / L. Preparing a first bath component solution containing 5 mg of copper sulfate pentahydrate, and physical and said first bath component solution comprising 40-75 g / L paraformaldehyde and 20-50 g / L sodium hydroxide Preparing a second separated bath component solution, mixing the first and second bath solutions to produce a mixed plating solution having a pH higher than 13, and a base to be plated Dipping a material in the mixed solution, and the base material includes a metal selected from the group consisting of magnesium, aluminum, and alloys thereof.

Yet another aspect of the present invention is a method for electroless plating of nickel-boron plating metal on a magnesium substrate, wherein a first bath solution containing 25-50 g / L nickel chloride hexahydrate is prepared. A first physically separated solution from said first bath solution component comprising 50-75 ml / L ethylenediamine, 30-50 g / L sodium hydroxide, and 3-8 g / L sodium borohydride. Preparing a second bath solution component and mixing the first and second bath solution components in a ratio selected to obtain a mixed plating solution having a pH of 13 or more, preferably about 14. And a step of immersing the magnesium substrate in the mixed solution.
In this method, the time for immersing the magnesium substrate in the mixed solution is about 1 to 60 minutes, preferably 10 to 30 minutes.
In this method, the first bath solution component and the second bath solution component are physically separated for 5 hours or more, preferably 72 hours or more.

The highly alkaline plating bath solution for metal deposition is prepared from two components, a first component (solution A) that is a metal salt solution and a second component (solution B) that is a solvent component of the final bath solution. All component solutions contain sodium hydroxide. The concentration of sodium hydroxide maintains the stability of each component, and the mixed solution of the two component solutions is suitable for use as a substrate when plating either a reactive metal substrate or a silicon-based substrate. Select to be the final highly alkaline plating bath. The two component solutions are prepared separately and stored separately until just before use in the manufacturing process. Specifically, a final electroless metal deposition bath for a processing member is prepared by mixing two component solutions in a desired ratio, preferably after 84 hours before plating work, more preferably after 72 hours. To do.

By using separately prepared and stored component solutions, a highly alkaline electroless copper deposition bath having a pH higher than about 13, preferably a pH of about 13.5 to about 14, can be obtained. This final solution also has a very low hydrogen content. It is more preferable that the solvent component solution contains paraformaldehyde (minimum polyoxymethylene) instead of formaldehyde which has been conventionally used as an active material for the anode reaction.

The method of the present application is not limited, but is believed to have various advantages, particularly in the plating of magnesium and magnesium alloys. According to the method of the present application, it is considered that the magnesium substrate is completely encapsulated in another metal that is not galvanically oxidized, and galvanic oxidation of the magnesium nucleus of the member can be prevented.

In addition, each of the two-component solution combined to produce a plating bath for a high pH electroless plating method maintains stability and can be stored for a long time.

Moreover, if a high pH precipitation bath is used, it is possible to prevent the highly reactive metal substrate to be plated from being oxidized before the desired metal is deposited on the surface. Therefore, if the plating bath has a high pH, an environment in which the surface of the highly reactive material can be completely covered before significant surface oxidation that may hinder the formation of a desired film occurs.

An experimental high alkaline electroless plating bath was prepared as follows using the two-component solution.

Example 1-Copper cladding of magnesium / magnesium alloy

In the case of directly electroless copper cladding a magnesium alloy from a highly alkaline precipitation bath, a component metal salt solution and a solvent solution were prepared and mixed to prepare a precipitation bath. The solution was prepared generally as follows.

注：基材がマグネシウムのように析出浴内で腐食しないので、浴内では様々な成分を用いてよい。

Note: Since the substrate does not corrode in the precipitation bath like magnesium, various components may be used in the bath.

Preparation of test piece

AZ91D and AM50 magnesium alloy (composition is shown in Table 2) were used as the base material, and these were cut into metal specimens of 2 cm × 3 cm × 0.5 cm. A hole was made in the upper end of the 2 × 3 cm surface of the test piece, and it was hung in the precipitation bath with a nonconductive nylon wire. In order to ensure the uniformity of the initial surface, the test specimens were wet-polished with SiC emery abrasive paper of Grit 240 and rinsed with distilled water.

Precipitation bath for testing

High alkaline precipitation baths for electroless copper precipitation tests were prepared according to Tables 3-4.

Solution A
In solution A, the following was added to 1 liter of deionized water.

Solution B
In solution B, the following was added to 1 liter of deionized water.

Solution components A and B both showed high stability, and the storage time at room temperature was long. After the preparation, component solutions A and B were mixed to obtain a mixed electroless plating solution. The obtained mixed electroless plating solution had a high pH of about 13.5 to 14, and the pot life was 48 hours or more at room temperature. However, it has been found that the storable time of the mixed plating solution used depends on the solution temperature, the amount of treatment performed with the solution, and the ratio of solution A to solution B. The effects of these variables on pot life are as follows.
1. 1. The higher the temperature, the shorter the active time of the solution. The higher the processing load, the shorter the solution active time.
3. The greater the ratio of solution B to solution A, the shorter the activity time of the solution.

Precipitation procedure

While the test piece was exposed to the outside air, it was dry-polished using a SiC emery abrasive paper of grit 240 to remove the rapidly formed oxidation / hydroxide film. Polishing was performed so that the heat generated on the test piece was minimized so as not to further promote the formation of the insulating oxide film. Then, the test piece was thrown into the electroless deposition bath (Bath A and B mixed 1: 1) of the temperature shown in Table 1.

After allowing sufficient precipitation time, the specimen was removed, rinsed with distilled water, hung and dried. In order to increase the drying speed, it has been found that it is effective to bring the base of the test piece into contact with a non-conductive wire so that the flow of adsorbed water is away from the test piece.

result

First, several sets of precipitations were performed on the AZ91DMg alloy to identify the function of the oxide. Two test pieces were put into the electroless Cu plating bath at the same time. The temperature of the two plating baths was the same room temperature. However, first, both test pieces were wet-polished with SiC paper of grit 240 and dried by exposure to the outside air for 3 weeks. One of the subsequent specimens was polished and placed in the precipitation bath as quickly as possible according to this procedure. The other specimen was not treated. Finally, both test pieces were left in the precipitation bath for 20 minutes and removed. No precipitation occurred on the oxidized test piece. On the other hand, the deposited layer on the coated specimen was of better quality and was more continuous both visually and by EDS observation.

If the above-mentioned two-component solution is used, a commercial magnesium / magnesium alloy plating method in which the component solutions A and B are mixed as one step of a batch method or a continuous electroless plating system as described below can be obtained.

1. The oxidized surface film is removed and the surface of the magnesium alloy to be coated is treated. The surface oxide may be mechanically removed by various polishing processes, or a chemical immersion method may be used. Alternatively, it may be removed by plasma.
2. Thereafter, the surface of the alloy base material to be coated is washed.
3. Once the oxide film is removed, the exposed magnesium alloy touches the air and begins to oxidize immediately. Therefore, it is highly preferable that the alloy base material whose surface has been treated is immersed in the coating bath within less than 30 minutes after the removal of the oxide.
4). The surface of the magnesium to be coated is preferably completely immersed in the precipitation bath for 15 to 30 minutes depending on the desired thickness of the copper film.
The rate of copper deposition on magnesium depends on the cumulative effects of the following factors and variables.

a. The film formation rate increases as the bath temperature increases. At present, the full effective temperature range has not been accurately verified. However, due to the nature of the material, there is an upper temperature limit that may be determined by further experimentation. Furthermore, there appears to be an ideal temperature range that provides the maximum amount of film deposition per bath in the shortest time.
b. The size of the surface area to be coated affects the deposition rate. The greater the surface area in a given volume of bath, the lower the overall deposition rate.
c. The amount of copper remaining in the solution that can be used in subsequent coatings. The copper concentration decreases by the amount of copper coating the surface of the member through the solution, and also decreases with time. That is, copper naturally precipitates from solution due to various factors, and the copper content in the solution decreases with time.

5. After soaking in the plating bath for a desired time, the plated substrate is removed from the bath. The removed copper-coated magnesium alloy member is rinsed with water or sodium hydroxide solution. In general, rinsing with water results in a bright copper finish. When it is desired to finish the copper plating product with a dark appearance, a hydroxide-based cleaning solution may be used.

Example 2-Pretreatment-(AM50 and AZ91D) Removal of oxide film on Mg alloy with acid

In metal plating, it is more preferable to perform acid etching on the substrate as a pretreatment. Thereby, electroless copper precipitation and its adhesiveness improve. It has already been confirmed that acid etching can remove insulating oxides from various metal surfaces including aluminum [Al] and magnesium [Mg]. It has also been confirmed that some acids are not suitable for removing oxides during secondary deposition because they cause corrosion of the substrate.

In the case of an Mg alloy, it is known that corrosion occurs in the presence of a chlorine [Cl ⁻ ] anion and a sulfuric acid [SO ₄ ²⁻ ] anion, and this may form a selective corrosion region. In electroless copper [Cu] precipitation, since the amorphous Cu precipitation layer has a quasicrystalline structure, it is difficult to plate the region where corrosion has started due to the anionic component.

In order to improve plating characteristics, tartaric acid [C ₄ H ₆ O ₆ ] Table 5 and sulfuric acid [H ₂ SO ₄ ] (Table 6) were verified for oxide removal from the Mg alloy surface. The test piece was dry-polished with a SiC emery cloth of Grit 240, oxidized by exposure to the outside air for 48 hours or more, and then deoxidized. Both acids were found to remove oxides and improve precipitation. In the verification example, the sample was exposed to the acid for only a few seconds, and no treatment with a rinsing bath was performed between the oxide removal step and the precipitation step. This is because distilled water baths can lead to surface reoxidation.

Furthermore, an attempt was made to add copper sulfate pentahydrate [CuSO ₄ .5H ₂ O] to the C ₄ H ₆ O ₆ bath according to Table 7. In this case, a simple substitution reaction occurred and a black discontinuous copper film appeared to be formed on the Mg-based substrate. The black deposited layer by this treatment did not adhere very strongly, but the subsequent copper deposition appeared to adhere very well. However, the pot life has decreased.

The pretreatment including removal of the oxide film by acid and the bath used for the subsequent electroless copper plating were prepared as follows according to Table 4.

注：酒石酸は濃度５３ｇ／Ｌにおける溶解性に難点があり、３０ｇ／ＬのＣｕＳＯ_４・５Ｈ_２Ｏと組み合わせて用いた場合容器の底に白色の沈殿物が生じる。

Note: Tartaric acid has a difficulty in solubility at a concentration of 53 g / L, and when used in combination with 30 g / L of CuSO ₄ .5H ₂ O, a white precipitate is formed at the bottom of the container.

The results strongly indicate that most acids are not sufficient to activate the silicon oxide surface, and nitric acid [HNO ₃ ] and sulfuric acid [H ₂ SO ₄ ] at a concentration of 20 mL / L remain after 5 minutes. No changes could be made to the surface.

Once the magnesium substrate is encapsulated with a metal alloy film, the metal film itself becomes the basis for the coating and deposition of the film formed thereafter. Therefore, the initial film is selected according to the desired film to be subsequently formed. Furthermore, magnesium encapsulated with metal maintains electrical conductivity and can be mechanically joined to dissimilar metals without causing galvanic effects or corrosion at the joint.

Example 3-Magnesium / magnesium oxide nickel-boron (Ni-B) cladding

An electroless deposition coating solution for nickel-boron metal coating on a magnesium substrate was prepared from a two-component solution (component solutions A and B) shown in Table 8. The two-part solution was mixed immediately before coating the substrate. Since nickel itself does not dissolve at high pH, a nickel-boron salt solution was prepared as a separate bath solution A that was kept at a pH much lower than the final bath. The bath solution A constitutes component A shown in the following table.

The nickel-boron deposition solution was prepared as a two-part system mixed with deionized water.

The solvent component solution B contained a borohydride compound that was very easily oxidized in a solution having a neutral or acidic pH. Therefore, when the solutions A and B are mixed for final use, the addition of the solution A to the solution B can advantageously prevent oxidation of the borohydride compound. Furthermore, the ethylenediamine contained in the compound solution B promotes the solubility of nickel in the high pH solution, and nickel is likely to be deposited on the magnesium surface. On the other hand, boron is deposited on the same surface by an anodic reaction.

It should also be noted that ethylenediamine is extremely reactive with copper. For this reason, it is preferable to avoid copper during the nickel-boron coating. However, it is possible to coat the nickel-boron film with copper using the electroless coating method described herein.

Electroless nickel-boron deposition as a plating on a magnesium substrate is performed as follows.
1. Component solutions A and B are prepared as physically separated solutions.
2. Subsequently, solutions A and B are mixed at room temperature. At this time, the solution A is poured into the solution B. Then, it heats to 80-95 degreeC as a single plating bath.
3. The magnesium substrate to be coated is cleaned mechanically, chemically or by plasma to remove the oxide surface from the magnesium.
4). After removing the oxide, secondary cleaning is performed by washing the non-oxide surface portion of the magnesium base with deionized water.
5. The washed magnesium substrate is submerged in the prepared plating bath, and the solution is brought into contact with the entire surface area of the member for a maximum of 30 minutes (not limited to this time), depending on the desired film thickness.
6). After the desired thickness of film has been deposited on the magnesium member, the member is rinsed with water or sodium hydroxide solution.
7). If cobalt ions and / or zinc ions are added to the bath, additional favorable effects may be obtained.

In a magnesium nickel-boron coating, the deposition rate depends on the following factors and the cumulative effect of variables.
a. Ratio of component solution A to solution B. The volume of the metal salt present is adjusted with the solution A.
b. Bath temperature (ie 80-95 ° C.)

Preparation of test piece

Even in a test conducted using an Ni-B precipitation bath at 85 to 90 ° C. for 5 minutes, a precipitation layer could be obtained on the AZ91D magnesium alloy. In the case of Ni-B, the temperature is one important factor in film formation, and the deposition rate is significantly reduced at low temperatures. It was observed by scanning electron microscopy (SEM) and energy dispersive X-rays (EDS) that the continuous coverage was microscopically discontinuous when viewed with the naked eye, but discontinuities observed with EDS. This is thought to be due in part to the lack of film thickness. However, if the precipitation layer has such a degree of continuity, it is sufficient to be a minimum foundation for the secondary precipitation layer formed at a high pH thereafter. Note that a high pH is necessary to alleviate the intense reaction during acid electrolysis when magnesium is exposed.

A secondary electroless Cu thin film was deposited on Ni-B, and it was observed that the film was almost continuous in both the naked eye and SEM. The first Ni—B precipitation layer was formed on the AZ91DMg alloy for about 5 minutes or more at about 87 ° C., and was expected to be a somewhat discontinuous precipitation layer. The specimen was rinsed with distilled water, suspended by exposure to air for 15 minutes, dried, and then placed in an electroless copper bath at room temperature for 5 minutes. Thereafter, the test piece was rinsed with distilled water, again exposed to the outside air, hung and dried. When the test piece after the secondary deposition step was observed, limited corrosion occurred on the test piece, suggesting that the Ni-B coating was actually somewhat discontinuous. This is confirmed by SEM showing an initial discontinuous film that has just begun to form on the Ni-B “nucleation” site.

In a further similar test, a Ni—B deposited layer was obtained at about 80 ° C. for 15 minutes, rinsed with distilled water and dried for 7 minutes, and then placed in an electroless copper bath at room temperature for 22 minutes. This gave a better film with almost no defects observed with SEM and EDS. When the specimen during the secondary deposition was observed, the Cu deposition layer was not glossy, and a relatively thin deposition layer was obtained even after 7 minutes of deposition in the electroless copper bath. It is suggested that the film was discontinuous. In this second specimen, the continuity is clearly increased, and the SEM image of the surface clearly shows that the wear traces due to the polishing treatment are covered.

In order to compare the morphology of the first layer and the second layer, a test piece was prepared in which only the lower half was exposed to a secondary Cu precipitation bath. The first electroless Ni—B deposited layer was formed on a polished AZ91D alloy specimen over 89 ° C. for 5 minutes or more. Although EDS still showed a small peak due to Mg, when viewed by SEM, the deposited layer was continuous with only slight defects. The specimen was rinsed with distilled water, hung and exposed to the outside air, and dried for 25 minutes. After drying, the lower part of the test piece was exposed to an electroless Cu bath at room temperature for an additional 5 minutes, rinsed and dried. During the secondary deposition process, the film was hydrated from below to above one third by exposure to a deposition bath. Since this deposition was achieved in about one-fourth of the time required for the first specimen, the continuity of the primary coating is an important factor for the quality of the secondary deposition layer, but the initial coating It became clear that a good secondary precipitation layer could be obtained even if it was not completely continuous. In addition, SEM analysis of secondary Cu cladding showed that magnesium sequestration was improved. Although corrosion may be observed near the Ni-B / Cu interface with the naked eye, it is appropriate to view this as galvanic corrosion due to incomplete immersion of the specimen.

If the electroless deposition method in a highly alkaline environment is used, particularly when a secondary layer is deposited, a deposited layer having excellent adhesion can be formed satisfactorily. Here, the secondary precipitation bath is also highly alkaline. This is to prevent a gullback battery from being easily formed or starting corrosion even if there are pinholes, gaps, or defects in the coating that is expected to be continuous. Gaps that occur in the initial cladding of magnesium can be due to the formation of insulating surface oxides by one or both of the following possible actions, especially when using copper.

1) The alloys that have been tested so far are AZ91D and A50 magnesium alloys, which contain nominally about 9% and about 5% aluminum, respectively. Since aluminum is easily oxidized in a highly alkaline environment, it is considered that the Al—Mg intermetallic compound is oxidized in the precipitation bath, leading to the formation of an insulating oxide. In this case, a non-aluminum alloyed magnesium alloy is considered to exhibit better properties in a highly alkaline precipitation bath. This also leads to a significant development of magnesium alloy cladding since there is currently no single cladding process sufficient to coat a wide variety of magnesium alloys.

2) When a magnesium alloy is polished by exposure to the outside air, the surface, particularly the unevenness, may be heated, and this heat contributes to oxidation. Verification of the insulating ability of oxides has confirmed that such electroless deposition techniques are not useful for electroless cladding on oxidized magnesium. This problem can be easily solved by cooling the test piece or polishing it under an inert gas atmosphere to prevent oxidation. However, the present method can form an insulating oxide if appropriate measures are taken. Indicates that it can be managed.

It is a highly alkaline precipitation bath that can deposit copper despite the clear difference between copper (+0.340 vs. SHE) and magnesium (-2.372 vs. SHE) at the standard electrode potential. Because. High alkaline deposition baths help prevent substrate corrosion and prevent the formation of active galvanic cells. This is observed because the deposited layer formed at a slightly acidic pH value (pH≈12) causes corrosion of the substrate. For these reasons, the solubility of copper in a high pH environment was an important factor when selecting copper as the cladding metal.

More importantly, it has been observed that when a polished Mg alloy specimen is exposed to bath A of a copper precipitation bath, copper with good adhesion is formed on the specimen surface even in the absence of a reducing agent. .

Example 4-Electroless copper deposition on an aluminum alloy substrate

In another embodiment, the method of the present invention can be used in the electroless deposition of a coating layer of a metal such as copper on an aluminum or aluminum alloy substrate.

The copper precipitation bath was prepared as follows from component solutions A and B as a two-component bath.

Copper deposition bath

In the copper coating on the aluminum alloy substrate, the following method is used.
1) The oxide film is removed from the Al alloy using conventional means. In order to improve the adhesion, it is most preferable to remove the oxide by a method that also increases the surface roughness, such as dry polishing.
2) The Al alloy is put into a room temperature electroless copper deposition bath for about 5 to 10 minutes. In order to increase the deposition rate and / or film thickness, the deposition time may be increased and the temperature may be increased.
3) After the copper layer is formed, the plated specimen is removed from the deposition bath and rinsed with distilled water to remove excess electrolyte.
4) With these, an electroless copper cladding with gloss, flatness / uniformity, continuousness and good adhesion is applied to the Al alloy.

Polishing was necessary for the test pieces on which electroless Cu deposition was performed according to the most preferred method. Almost no precipitation occurred on the unpolished surface.

In the other Al alloy test pieces, precipitation was performed on both the oxidized surface and the polished surface, but a low-adhesion and / or powder-like deposited layer was obtained. As a test for examining whether a deposited layer with good adhesion can be obtained by polishing, it is considered to use the characteristics of the deposited layer.

Aluminum is generally, as the positive standard electrode potential E ^0, rapidly (spontaneously) under hydroxide environment is understood as oxidation. Therefore, it is considered counterintuitive to perform electroless deposition from a high pH precipitation bath on an Al alloy.

[Equation 1]
^{_{Al (s) + 3OH - (}} aq) → Al (OH) 3 (s) + 3e - E 0 = + 2.31V

According to the present invention, the electroless deposition of copper is performed in an electroless copper bath with a maximum pH of 13.5, using a high concentration formaldehyde reducing agent as the AlN substrate.

Other electroless copper deposition methods suitable for Al plating include a method in which a copper dip coating is applied on a 3003-Al alloy and then electroless Ni-P deposition is performed. The copper immersion film is formed by placing in a 25 ° C. bath containing CuSO ₄ .5H ₂ O (30 g / l) and C ₄ H ₆ O ₆ (tartaric acid) (53 g / l) for 3 minutes. This coating is performed to prevent direct contact between Al and the electroless nickel deposition solution and to increase the stability of the electroless deposition bath.

Applicants have found that with the present invention, dip coating can be a means of extending electroless copper deposition to a wider range of aluminum alloys. In this connection, the subsequent electroless Ni-P coating is formed at a conventional pH level of about 4.5, so that the subsequent electroless copper layer may be acidic, It may be alkaline.

In the experimental example, electroless copper cladding can be realized and adhered to the Al alloy specimen. Al in the test piece was a considerably recycled metal, and a large amount of impurities were mixed. In a test conducted with 12% Si and a 6061 Al alloy, a precipitate layer having a powdery shape and poor adhesion was obtained on the surface of the test piece. Therefore, the properties of the alloy itself can also be a contributing factor for performing advanced precipitation.

In other specimens, precipitation occurred on the oxidized surface as well as the polished area, and precipitation was not independent of polishing.

A preferred method is to immerse in an electroless copper deposition bath having a pH of over 13.5, preferably pH 13.5 to 14, but a lower pH depending on the specific composition of the aluminum alloy and the presence or absence of adhesive strength. It seems possible to realize electroless deposition of copper. Electroless Cu at lower pH is also probably feasible for alloys that do not have adhesion.

As one example of commercial use, within a solar cell, an electroless copper method may be applied to form a conductive backing used to recombine “electrons” and “holes”. Conventionally, the conductive backing is generally made of an aluminum paste. It is more important that the electroless deposition method of the present invention may be applied to a copper layer that forms a grid electrode that contacts the battery front surface. In general, the electrodes are formed by screen-printing silver paste on both the front and back surfaces of the solar cell. If the electroless copper plating method is used, it is cheaper than using a silver paste, and at the same time the surface area usually covered by the grid is reduced, so that the solar cell efficiency can be further increased in place of the conventional printing method.

Example 5-Electroless copper deposition on silicon substrate-

The electroless technique is also expected to be effective in integrated circuit manufacturing, particularly in processor assemblies.

In addition to silicon test pieces that are considered to be substantially pure silicon in the experimental results, copper deposition is verified on an n-type silicon substrate using the method of the present invention. Assuming that silicon is doped for n-type and p-type silicon fabrication, the deposition technique is expected to be effective on all silicon substrates used in the assembly of electronic devices. In addition, it should be noted that a copper deposition layer is observed at the edge of the substrate, that is, where the test piece is cut from the large plate. This indicates that it is not caused by an abnormality caused by the polishing method.

It is possible to adjust the optimal bath conditions by measuring whether the deposition bath promotes oxide growth and an oxidation intermediate film is formed between the silicon substrate and the copper cladding, and the thickness of the deposited coating. Become. Preliminary measurements indicate that some resistive contact exists between the cladding and the substrate, but its accuracy needs to be verified by thin film four-terminal measurement.

The electroless deposition of the coating layer would allow the use of a variety of silicon and metal substrates in a vast number of fields and applications that have been impractical to date. Non-limiting examples include the use of coated magnesium / magnesium alloy substrates, computer hard drives, naval warships, aircraft and aerospace applications, internal combustion engine heads and blocks, transmission and gear housings, automobile frame assemblies Examples include but are not limited to bodies.

Also, the amount of metal deposited on the surface of a given substrate does not affect its reuse. Specifically, the surface film can be formed by adjusting the amount so that “impurities” are within an allowable range. Furthermore, a highly wear-resistant or hardened film may be used for more flexible metal substrates such as magnesium. This would make it possible to use such metals in fields where good surface wear properties are required.

This specification describes, but is not limited to, the use of the method of the invention in coating magnesium, aluminum, and silicon substrates with copper and nickel-boron. It has been found that the two-part coating method of the present invention may be used to form a variety of coating layers that are soluble in highly alkaline plating baths.

Although various preferable numerical values in the plating method are described in the present specification, the present invention is not limited thereto. Many variations will appear soon. For the scope of the invention, reference should be made to the appended claims.

Claims (16)

A method of electroless plating nickel or nickel alloy plating metal on a magnesium metal substrate,
Preparing a first bath solution at pH 5 containing 25-60 g / L nickel chloride hexahydrate;
Ethylenediamine of 40~75m l / L,
And preparing 30 to 50 g / L of sodium hydroxide, and the second bath solution wherein are first bath solution and physically separating containing hydrogen sodium borohydride of 3 to 8 g / L,
Mixing the first and second bath solutions to produce a mixed plating solution having a pH of 12 or higher;
Immersing the magnesium metal substrate in the mixed plating solution within 84 hours after mixing the first and second bath solutions . The method of claim 1, wherein the plating metal is a nickel-boron alloy. The method according to claim 1 or 2, wherein the mixed plating solution has a pH of 13 or more, and the time for immersing the magnesium metal substrate in the mixed plating solution is 1 to 60 minutes. The method according to claim 3, wherein the magnesium metal substrate is immersed in the mixed plating solution for 10 to 30 minutes. The method according to any one of claims 1 to 3, wherein the temperature of the mixed plating solution is maintained at 80 to 95 ° C while the magnesium metal substrate is immersed. The method according to any one of claims 1 to 5, wherein the first and second bath solutions are mixed in a volume ratio of 1 : 1 by a continuous batch method. A method of electroless plating a nickel-boron plating metal on a magnesium substrate,
Preparing a first bath solution component of pH 5 comprising 25-50 g / L nickel chloride hexahydrate;
50-75 ml / L ethylenediamine,
Preparing a second bath solution component physically separated from said first bath solution component comprising 30-50 g / L sodium hydroxide and 3-8 g / L sodium borohydride;
Mixing the first and second bath solution components in a ratio selected to obtain a mixed plating solution having a pH of 13 or higher;
Immersing the magnesium substrate in the mixed plating solution within 84 hours after mixing the first and second bath solution components . The method of claim 7, wherein the ratio is a ratio selected to obtain a mixed plating solution having a pH of 14 . The method according to claim 7 or 8, wherein a use temperature of the mixed plating solution is maintained at 80 to 95 ° C while the magnesium substrate is immersed. The method according to any one of claims 7 to 9, wherein a time for immersing the magnesium substrate in the mixed plating solution is 1 to 60 minutes. The method according to claim 10, wherein the time for immersing the magnesium substrate in the mixed plating solution is 10 to 30 minutes. The method according to claim 10 or 11, wherein the time for immersing the magnesium substrate in the mixed plating solution is a maximum of 30 minutes. The method according to any one of claims 7 to 12 for separating the first bath solution component and the second bath solution and the five hours or more physical components. 14. The method of claim 13, wherein the first bath solution component and the second bath solution component are physically separated for at least 72 hours. The method according to any one of claims 1 to 6, wherein a magnesium metal substrate is immersed in the mixed plating solution within 72 hours after mixing the first and second bath solutions. The method according to any one of claims 7 to 14, wherein a magnesium substrate is immersed in the mixed plating solution within 72 hours after mixing the first and second bath solution components.