KR20010112499A - Palladium electroplating bath and process for electroplating - Google Patents

Abstract

The present invention relates to an electroplating bath comprising a noble metal-sulfonic acid complex and a free sulfonic acid. The precious metals include Pd, Au, hard Au (containing Ni or Co as hardener), Pt, Rh, Ru, Ag and alloys thereof.

Description

Palladium Electroplating Bath and Electroplating Method {PALLADIUM ELECTROPLATING BATH AND PROCESS FOR ELECTROPLATING}

The present invention relates to electroplating, more particularly to electroplating salts, electroplating baths and electroplating methods.

Precious metals are used in a variety of industrial applications, including electrical circuits such as electrical contact surfaces, conductive paths, and heat sinks. Precious metals can be very advantageously used for such applications due to various properties. Such advantageous properties include physicochemical stability, high electrical conductivity, low porosity and high thermal conductivity. Precious metals are often used in high density circuits such as integrated circuits due to one or more of the above mentioned properties.

In the precious metal electroplating process, there are problems associated with the selection of suitable compounds for initially supplying the electroplating metal to the plating bath. This compound should be easily prepared in a stable, fairly pure form and easily dissolved in an electroplating bath. This problem is particularly difficult when a large amount of palladium plating must be performed rapidly. In this case, a relatively large amount of palladium metal is plated, and therefore a large amount of palladium must be added to the plating bath. Under these circumstances, high solubility and fast dissolution rate are extremely important.

In addition, the complexity of the plating bath as well as the compatibility of the components of the palladium compound (complexes, anions, etc.) can not only provide contaminants to the main plating tank, but can also limit the life of the electroplating bath and electroplating of the plating bath. It is very important for practical use because it can change the characteristics.

1 shows a flowchart of the general method of the present invention for synthesizing a metal-sulfonic acid complex or salt or electrolyte for use in supplying a plating metal to a plating bath or plating solution for electroplating precious metals.

2 shows a flow chart of the general method of the present invention using a plating bath or plating solution containing a metal-sulfonic acid complex to electroplat a precious metal.

3A to 3D are photographs taken using a scanning electron microscope of Pd layers deposited in various thicknesses on a substrate or a plated body by the method of FIGS. 1 and 2.

According to one embodiment the electroplating bath comprises a noble metal-sulfonic acid complex and a free sulfonic acid. The term "noble metal" herein encompasses Pd, Au, hard Au (adding Ni or Co as hardener), Pt, Rh, Ru, Ag and alloys thereof.

Sulfonic acid may be an acid having the structure:

R [SO ₃ ] -X

Where

R is an alkyl or aryl group and X is a cationic compound.

The sulfonic acid can be for example methane sulfonic acid (MSA). The resulting plating bath may have a pH of less than 2.5, in particular less than 1.0.

The electroplating bath may comprise only one additive, such as a brightener.

When the noble metal alloy is plated, the electroplating bath may also include an alloying metal-sulfonic acid complex. For example, the plating bath for plating Pd-Ni alloys may include Pd-sulfonic acid complexes and Ni-sulfonic acid complexes. The concentration of the two metal complexes depends largely on the percent desired composition of the alloy.

In another embodiment, a method of electroplating a metal to a plated body (e.g., a substrate) comprises applying a current to the plating bath to a solution comprising a metal-sulfonic acid complex having a noble metal and a free sulfonic acid. Maintenance. The plated body may be presoaked in sulfonic acid.

In one example, the precious metal may be Pd immersed on a substrate such as copper or a copper alloy.

In another embodiment, a metal salt is provided for use in an electroplating bath to electroplat Pd or Pd alloy. The chemical formula of the Pd salt can be represented by the formula:

Pd (NH ₃ ) _x MSA ₂

Where

x is 0-4.

In a further embodiment, a method of synthesizing a metal salt for use in providing a plated metal to an electroplating bath is provided. The method includes mixing a source of sulfonic acid and a noble metal ion to form a slurry; Filtering the slurry to collect precious metal-sulfonic acid salts; Washing the collected salt with alcohol; And drying the washed salt. Mixing can be performed at approximately room temperature.

Other additional aspects of the present invention will become apparent from the following detailed description with reference to the accompanying drawings.

The present invention relates to metal compositions for supplying plated metal to an electroplating bath, in particular metal complexes of methane sulfonic acid (MSA), and methods of synthesizing metal-MSA complexes.

The invention also relates to an electroplating bath comprising a metal complex of sulfonic acid, and a method of using the plating bath to electroplat a precious metal onto a plated body (eg a substrate). The term "noble metal" herein includes Pd, Au, hard Au (containing Ni or Co as hardener), Pt, Rh, Ru, Ag and alloys thereof.

It has been found that metal complexes of sulfonic acid can generally be used to supply the plating metal to the electroplating bath to electroplate the precious metal on the surface of the plated body. Provided herein is a method of forming a metal-sulfonic acid complex that enables metal salts to be obtained in high yields while minimizing waste of underlying metals.

By using the metal-sulfonic acid complex, a strong acid plating bath for precious metal electroplating can be obtained which is particularly suitable for plating strikes or underlayers on the plated body. In addition, metal-sulfonic acid complexes require smaller amounts of chemicals and additives, reduce the risk of contamination or contamination of the main plating tank, produce high quality plating products, and reduce the total cost of maintenance of the main plating tank. It provides an electrolyte plating bath or plating solution that can be.

According to the first embodiment, an electrolytic plating bath or plating liquid is provided for plating a noble metal on the surface of the plated body. Plating baths or plating solutions include noble metal-sulfonic acid complexes or salts, and free sulfonic acids. The plating bath may also include an additive metal-sulfonic acid complex or salt for plating the noble metal alloy. This arrangement is provided for acidic plating baths of less than pH 2.5, preferably less than pH 1.0.

In one example, the plating bath or plating liquid may be limited to only one additive, such as brighteners or other known plating additives. For example, additive systems used for Pd plating can typically be divided into the following two types.

Brighteners of the first type are generally unsaturated sulfone compounds having an unsaturated group in the alpha- or beta-position of the sulfone group. The compound has the formula A-SO ₃ -B wherein A is a substituted or unsubstituted aryl or alkylene group, B may be OH, OR, OM, NH _2, or the like.

Organic brighteners of the second type are generally unsaturated or carbonyl organic compounds. Examples are compounds containing> C = O,> C = C <,> C = N-, (-N = N-) and the like.

Therefore, by reducing or minimizing chemicals in the plating bath or the plating liquid, it is possible to reduce the contamination or the possibility of contamination of the main plating tank.

According to another embodiment, provided herein is a method for plating a noble metal. The plating method generally includes applying a current to pass through the plating bath while maintaining the plated body (eg, a substrate) in a plating bath or a plating solution containing a noble metal-sulfonic acid complex. To plate the noble metal alloy, the plating bath may further comprise an additive metal-sulfonic acid complex.

The method can be used to deposit strikes or underlying layers of precious metals.

In another embodiment, electrolytes or salts for use in plating precious metals such as Pd and methods of making them are provided. The Pd electrolyte or salt may comprise a palladium-amine methane sulfonic acid complex of formula

Pd (NH ₃ ) _x MSA ₂

Where

x is from 0 to 4,

MSA is methane sulfonic acid.

Pd complexes of sulfonic acids can generally be formed by mixing free sulfonic acids (MSA in this example) with a solution containing an ion source of Pd, such as a Pd salt.

The use of metal-sulfonic acid salts has many effects and advantages over conventional methods. For example, using Pd-MSA salts at least pH for plating of strikes (e.g., layers having an approximate thickness of 3 to 4 microinches) as well as plating of other types of metal layers having an approximate thickness of 10 to 20 microinches. It is particularly useful to provide a strongly acidic plating bath of less than 2.5, preferably less than pH 1.0. If the plating bath is strongly acidic, the surface layer (eg oxide layer) of the substrate to be plated is cleaned without the need for additional chemicals or additives that typically increase the complexity and cost of the plating bath. The plating bath may be limited to one additive.

Since the required amount of chemicals and additives is reduced, the possibility of contamination or contamination of the main plating tank caused by substrate corrosion and / or metal salts entering the tank in conventional plating operations can be substantially reduced. Reducing contamination of the main plating tank ensures the production of high quality plating products and reduces the total maintenance cost of the main plating tank.

The Pd-MSA salt also provides a plating bath that is particularly suitable for depositing strikes. This provides additional advantages, including improved adhesion on easily passivated surfaces such as Ni, and reduced porosity of subsequent deposits, and further prevents substrate corrosion and contamination with the introduced metal salt during conventional plating operations. .

Pd-MSA salts also provide plating baths, such as non-halide and halide-based compounds, which are also suitable for other plating operations that can be performed in the main plating tank.

Schemes relating to the preparation of Pd-MSA salts, for example Pd (NH ₃ ) _x [MSA] ₂ , can be represented by the following scheme 1:

[Pd (NH ₃ ) _x ] A + excess MSA-> [Pd (NH ₃ ) _x ] [MSA] ₂ + MSA + HA

Where

x is preferably 0 to 4,

A is an anion.

In this example, the sulfonic acid is methane sulfonic acid and the source of Pd metal ions is the Pd (NH ₃ ) A salt and the anion A is for example sulfates, halides (e.g. fluorine, chlorine, bromine and iodine), nitrates, nitrites , Acetate, phosphate or sulfamate. In Scheme 1, NH ₃ can be removed to provide pure metal-sulfonic acid complexes or substituted with other organic amines to provide complexes of Pd-MSA salts.

Although a reaction scheme involving one embodiment of the Pd-MSA salt is described above, the same or similar anion exchange reaction can generally be applied to obtain additional metal-sulfone salts as well as to obtain other precious metal-sulfonic acids.

For example, the scheme of the additive metal-MSA salt is generally represented by Scheme 2:

[M] [A] + MSA (excess)-> [M] [MSA] + MSA + HA

Where

M is an additive metal such as Ni, Co, Ag, Sn,

MSA is methane sulfonic acid.

Like Scheme 1, Anion A can be sulfate, halides (eg fluorine, chlorine, bromine and iodine), nitrate, nitrite, acetate, phosphate or sulfamate. M can be any desired additive metal, such as Ni, Co, Ag or Sn, and can be selected according to the desired use. The additive metal M may initially be in the form of an additive metal ion source, such as a metal salt comprising the additive metal. The concentration of the additive metal depends on the alloy composition to be deposited (10 wt% to 95 wt% Pd).

When plating an alloy, a plating bath or plating solution can be prepared by mixing an additive metal-MSA complex solution with Pd-MSA complex and free MSA.

In order to facilitate plating of the alloy, mixed ligand systems may also be used if necessary. The appropriate ligand can be selected depending on the metal in the desired alloy. For example, the ligand of Pd is ammonia.

Although the above has been described for methane sulfonic acid, other sulfonic acids in the group having the structure R [SO ₃ ] -X (R is an alkyl or aryl group and X is a cationic species such as H ⁺ or Na ^+, etc.) are metals. -Sulfonic acid complexes, and precious metal electroplating baths comprising the same.

In Figure 1, a general method of synthesizing a noble metal complex of sulfonic acid for use in supplying a noble metal plated metal to a plating bath is to (a) add a sulfonic acid to a solution containing a source of precious metal ions (e.g. (B) stirring the slurry from which the precipitate has been produced for a suitable time, (c) filtering the slurry to collect the metal-sulfonic acid salt, (d) washing the salt with an alcohol such as isopropanol, and (e) air drying the washed metal-sulfonic acid salt.

Residual filtrate and alcohol are collected and properly recycled.

The method provides an efficient process for producing metal-sulfonic acid salts, in particular Pd-MSA salts, with significantly higher yields with minimal metal waste. This is especially important when dealing with expensive precious metals.

Example 1

Examples of methods for synthesizing Pd-MSA salts are provided herein. In this example, 250 ml of methane sulfonic acid (70% v / v solution) was slowly added to 1 L of [Pd (NH ₃ ) ₄ ] [SO ₄ ] containing 70 g / L of Pd (metal form) at room temperature. Stirred. After complete addition of MSA, the resulting pale yellow suspension was stirred continuously for an additional 30 minutes. The entire contents of the reaction vessel were poured into a large Buchner funnel. The slightly greyish white microcrystalline product was washed three times with 40 ml portions of isopropanol (IPA) and air dried. This gave 220 g of Pd-MSA salt (91% based on 70 g / L of Pd of [Pd (NH ₃ ) ₄ ] [SO ₄ ] solution).

The remaining filtrate was collected and recycled for Pd recovery. If necessary, the alcohol used to wash the product can also be recycled by evaporation and condensation using standard equipment.

In Fig. 2, a general method of electroplating a noble metal on a plated body (e.g., a substrate) using a plating bath comprising metal-sulfonic acid to supply the noble metal includes (a) a noble metal or a noble metal alloy such as palladium Or pre-immersing the plated body to which the surface portion to be plated with the palladium alloy is exposed in sulfonic acid compatible with the plating metal-sulfonic acid salt; (b) rinsing the plated body; (c) applying a current density greater than 5 mA / cm ² to the plating bath depending on the type of treatment (eg, rack or continuous); And (d) maintaining the plated body in the plating bath for a time sufficient to cause the noble metal layer of desired thickness to develop on the exposed surface portion.

The electroplating method can be used to immerse and deposit Pd on a substrate such as Cu or Cu alloy.

Examples of plating baths or plating solutions for Pd or Pd alloys are provided below. Plating baths come with several plating methods, such as low speed plating typical for rack mounted articles, or high speed plating typical for open reel continuous supply for electrical components such as connectors, printed circuit boards, and printed wiring boards. Can be used.

Example 2

In this embodiment, the composition of the plating bath or plating solution for Pd electroplating is provided in Table 1 below. The single additive may be a first type or a second type of brightener as discussed above. Pd may be deposited below pH 1.

Reaction conditions shame [Pd (NH ₃ ) ₄ ] MSA ₂ Pd 0.5 to 20 g / L Single additive 0.5 to 10 mL / L Yuri MSA 50 to 300 mL / L pH Less than 1 Temperature Room temperature Current density 5 to 50 ASF rotation 100 to 500 rpm

Example 3

In this embodiment, the composition of the plating bath or plating solution for electroplating Pd-Ni alloy is provided in Table 2 below. The single additive may be a first type or a second type of brightener as discussed above. Pd-Ni alloys may be deposited below pH 1.

Reaction conditions shame [Pd (NH ₃ ) ₄ ] MSA ₂ Pd 0.5 to 20 g / L Ni [MSA] Ni 0.5-20 g / L Single additive 0.5 to 10 mL / L Yuri MSA 50 to 300 mL / L pH Less than 1 Temperature Room temperature Current density 5 to 50 ASF rotation 100 to 500 rpm

Various tests have been conducted to study the use of Pd-MSA for electroplating Pd, for example, on a substrate or substrate formed from Cu, the results of which are described below.

3A-3D are photographs taken using a scanning electron microscope at 2200 × of Pd layers of different thickness levels deposited on a substrate or plated body using the method of FIGS. 1 and 2. As shown, no microcracks appeared in the deposited layer.

Immersion deposition on a copper substrate using a Pd-MSA bath resulted in a bright white Pd layer. This phenomenon will be particularly useful in the electrical industry. More specifically, it will be useful in the manufacture of printed wiring boards (PWB), printed circuit boards (PCB) and plating on plastics.

To test metallic contamination of the main plating tanks, both Ni and Cu were increased to around 50 ppm without adversely affecting the deposition quality. Concerning the problem of inflow during other plating operations, amounts up to 20 ml / l were carefully added to both halide and non-halide systems without causing problems.

As those skilled in the art can readily make various changes and modifications to the present invention, it is not intended that the present invention be strictly limited to the configurations and operations described and described herein, so that all suitable changes and equivalents are claimed herein. It should be construed as being included in the scope of the scope.

Using the electroplating salts, electroplating baths and electroplating methods of the present invention, it is possible to stably perform precious metal electroplating characterized by physicochemical stability, high electrical conductivity, low porosity and high thermal conductivity without wasting precious metals. Can be.

Claims (25)

Precious metal-sulfonic acid complexes; And an electroplating bath comprising free sulfonic acid. The method of claim 1, Electroplating bath further comprising only one additive. The method of claim 1, An electroplating bath further comprising an alloying metal-sulfonic acid complex. The method of claim 2, An electroplating bath wherein the precious metal is Pd and the additive metal is selected from the group consisting of Ni, Co, Ag and Sn. The method of claim 1, Electroplating baths with a pH of less than 2.5. The method of claim 5, Electroplating baths with a pH of less than 1.0. The method of claim 1, An electroplating bath wherein the sulfonic acid is an acid having the structure of Formula 1: Formula 1 R [SO ₃ ] -X Where R is an alkyl group or an aryl group and X is a cationic species. The method of claim 1, An electroplating bath wherein one additive is one of the first or second type brighteners as defined herein. The method of claim 1, An electroplating bath wherein the sulfonic acid comprises methane sulfonic acid and the metal-sulfonic acid complex comprises a metal-methane sulfonic acid complex. A method of electroplating a metal on a plated body, the method comprising: maintaining the plated body in a solution comprising a noble metal containing metal-sulfonic acid complex and free sulfonic acid while applying a current through a plating bath. The method of claim 10, The method of electroplating further comprising the step of pre-soaking the plated body in sulfonic acid. The electroplating bath according to claim 10, wherein the plating bath comprises only one additive. The electroplating bath according to claim 10, wherein the plating bath further comprises an additive metal-sulfonic acid salt. The method of claim 13, An electroplating bath wherein the precious metal is Pd and the additive metal is selected from the group consisting of Ni, Co, Ag and Sn. The electroplating bath according to claim 10 which is less than pH 2.5. The method of claim 15, Electroplating baths with a pH of less than 1.0. An electroplating bath according to claim 10 wherein the sulfonic acid is an acid of the formula: Formula 1 R [SO ₃ ] -X Where R is an alkyl group or an aryl group and X is a cationic species. The electroplating bath according to claim 10, wherein the sulfonic acid comprises methane sulfonic acid and the metal-sulfonic acid complex comprises a metal methane sulfonic acid complex. The electroplating bath according to claim 10, wherein the precious metal is Pd immersed and deposited on a substrate. The method of claim 19, An electroplating bath wherein the body to be plated comprises at least one of Cu or a Cu alloy. A metal salt comprising a salt of formula (2), used in an electroplating bath to electroplat Pd or Pd alloy: Formula 2 Pd (NH ₃ ) _x MSA ₂ Where x is 0-4. Mixing the sulfonic acid with a source of precious metal ions to form a slurry; And collecting the precious metal-sulfonic acid salt by filtration of the slurry. The method of claim 22, Washing the collected salt with alcohol; And drying the washed salt. The method of claim 22, Method for synthesizing metal salts mixed at about room temperature. The method of claim 22, A method for synthesizing metal salts wherein the noble metal is Pd and the sulfonic acid is methane sulfonic acid.