CN111485262A - Indium electroplating composition and method of electroplating indium on nickel - Google Patents

Abstract

The indium electroplating composition electroplates a substantially defect-free, whisker-free, uniform layer of indium having a smooth surface morphology on nickel. The indium electroplating compositions are environmentally friendly and comprise selected amino acids to provide smooth, uniform and defect free indium deposits.

Description

Indium electroplating composition and method of electroplating indium on nickel

technical field

The present invention relates to indium electroplating compositions and methods for electroplating indium on nickel layers wherein the indium deposits are uniform, substantially void-free, whisker-free, and have a smooth surface morphology. More particularly, the present invention relates to an acid indium electroplating composition and a method of electroplating indium on a nickel layer, wherein the indium deposit is uniform, substantially void-free, whisker-free and has a smooth surface morphology, wherein the indium electroplating composition is Indium deposits that are environmentally friendly and contain selected amino acids to provide a uniform matte, substantially void-free, whisker-free and smooth surface morphology.

Background technique

Electrolytic indium is very attractive for press fit applications in the connector industry. Indium can be used as an alternative metal to tin. Tin normally grows whiskers under stress conditions. As electronic components become smaller, it is important to eliminate the risk of whisker formation, which can cause electrical shorts. The advantage of indium over tin is that indium is less prone to whisker formation even after reflow.

Connector pins (copper alloys) for press fit applications are first coated with nickel, followed by indium flash adjacent to the nickel. The thickness of the indium layer is usually 0.2-1 μm. The problem is that many electrolytic indium processes are not capable of plating thin layers with uniform thickness distribution and good adhesion on nickel without the use of a strike layer (adhesion promoter coating). Such primer layers may have a thickness of 1-100 nm.

The ability to reproducibly deposit void-free uniform matte indium with target thickness and smooth surface morphology on nickel layers is challenging. Indium reduction occurs at a more negative potential than that for proton reduction, and the surface roughness increases due to the large amount of hydrogen bubbling at the cathode. Indium( ¹⁺ ) ions formed during indium deposition, stabilized by the inert electron pair effect, catalyze proton reduction and participate in disproportionation reactions to regenerate indium( ³⁺ ) ions. In the absence of a complexing agent, indium ions begin to precipitate out of solution above pH > 2. Plating indium on nickel is challenging because nickel is a good catalyst for proton reduction and is more inert than indium, so nickel may cause corrosion of indium in galvanic interactions. Indium may also form undesired intermetallic compounds with nickel. Another problem with indium plating is the generation of hydrogen gas. Such hydrogen generation can result in rough and irregular indium deposits that are not suitable for use in electronic components and devices.

Additionally, many conventional indium plating baths contain environmentally harmful additives such as certain inhibitors, many levelling agents, grain refiners, certain buffers, and Compounds that evolve hydrogen during plating. Many governments around the world are passing stricter environmental laws and regulations on how chemical waste is handled and the types of chemicals that industry may use in development and manufacturing processes. For example, in the European Union, the Registration, Evaluation, Authorization and Restriction of Chemicals Regulations (known as REACh) have banned many chemicals or are in the process of banning chemicals used in plating baths for industrial use in large quantities.

Therefore, there is a need for improved indium compositions that are useful for electroplating indium metal layers on nickel substrates and that are environmentally friendly.

SUMMARY OF THE INVENTION

The present invention relates to an indium electroplating composition consisting of: water; one or more sources of indium ions; one or more acids selected from the group consisting of inorganic acids, alkane sulfonic acids, and salts of said acids , wherein the inorganic acid is selected from the group consisting of sulfamic acid and sulfuric acid; and one or more amino acids selected from the group consisting of alanine, arginine, aspartic acid, asparagine, glutamic acid , glycine, glutamine, histidine, leucine, lysine, threonine, isoleucine, serine, and valine; optionally one or more alloying metals; and any Optionally one or more pH adjusting agents.

The present invention also relates to a method for electroplating indium on nickel, comprising:

a) providing a substrate comprising a nickel layer adjacent to the copper or copper alloy layer;

b) contacting the substrate comprising the nickel layer adjacent to the copper or copper alloy layer with an indium electroplating composition consisting of: water; one or more a source of indium ions; one or more acids selected from the group consisting of inorganic acids, alkane sulfonic acids, and salts of said acids, wherein said inorganic acids are selected from the group consisting of sulfamic acid and sulfuric acid; and one or Multiple amino acids selected from alanine, arginine, aspartic acid, asparagine, glutamic acid, glycine, glutamine, histidine, leucine, lysine, threonine, the group consisting of isoleucine, serine, and valine; optionally one or more alloying metals; and optionally one or more pH adjusting agents; and

c) Electroplating an indium layer adjacent to the nickel layer of the substrate using the indium electroplating composition.

The aqueous acidic indium electroplating compositions and methods of the present invention can be used to plate indium metal layers having a thickness of >0.1 μm on nickel without the use of a primer. The aqueous acidic indium electroplating composition is highly current efficient and the indium deposit is uniform and matte, substantially void-free, whisker-free, has a smooth surface morphology and exhibits good adhesion on nickel. Post-annealing of substrates with indium deposits showed slight to essentially no dewetting. During indium electroplating, hydrogen evolution is substantially suppressed to achieve smooth and uniform matte indium deposits. The indium electroplating composition contains only registered and REACh compliant compounds.

Detailed ways

As used throughout this specification, unless the context clearly dictates otherwise, the following abbreviations have the following meanings: °C = Celsius; g = grams; mg = milligrams; L = liters; A = amperes; dm = decimeters; ASD = A/dm ² = current density; μm = micron = micrometer; indium ion = In ³⁺ ; nm = nanometer = 10 ⁻⁹ meters; μm = micrometers = 10 ⁻⁶ meters; M = moles; min .=min; IC=integrated circuit; XRF=X-ray fluorescence; and eg=eg.

Throughout the specification, the terms "depositing", "plating" and "electroplating" are used interchangeably. The term "aqueous" means that the solvent of the water-based or composition is water. The term "adjacent" refers to direct contact or that two separate surfaces or planes have a common interface. The term "interface" refers to one or more points of contact between two surfaces or planes. The term "plane" refers to a substantially flat surface such that a straight line connecting any two points thereon lies entirely therein. The term "surface" refers to the outer or uppermost region of an article or structure. The term "copolymer" is a compound composed of two or more different monomers or oligomers. The term "dewetting" refers to the retraction of the indium plating at a location on the nickel surface after reflow, where this location of the nickel is referred to as a non-wettable area, and occurs when adhesion is poor. The term "matte" refers to a dull and flat appearance without gloss. Unless otherwise indicated, all plating baths are aqueous solvent based, ie water based plating baths. All amounts are weight percentages and all ratios are in moles unless otherwise indicated. All numerical ranges are inclusive and combinable in any order unless it is logical that such numerical ranges be limited to add up to 100%.

The aqueous acidic indium compositions of the present invention comprise one or more sources of indium ions that are soluble in an aqueous environment. These sources include, but are not limited to, indium salts of alkanesulfonic acids such as methanesulfonic acid, ethanesulfonic acid, and butanesulfonic acid, indium salts of sulfamic acid, indium sulfate salts, indium chloride and bromide salts, Nitrates, hydroxide salts, indium oxide, fluoroborates, carboxylic acids (such as citric acid, acetoacetic acid, glyoxylic acid, pyruvic acid, glycolic acid, malonic acid, hydroxamic acid, iminodiacetic acid, Indium salts of salicylic acid, glyceric acid, succinic acid, malic acid, tartaric acid, hydroxybutyric acid, amino acids such as arginine, aspartic acid, asparagine, glutamic acid, glycine, glutamine, leucine amino acid, lysine, threonine, isoleucine and valine). Preferably, the source of indium ions is one or more indium salts of sulfuric acid, sulfamic acid, and alkanesulfonic acid. More preferably, the source of indium ions is one or more indium salts of sulfuric acid, sulfamic acid, and methanesulfonic acid. Most preferably, the source of indium ions is indium sulfate.

Indium ions from a water-soluble salt of indium are included in the composition in an amount sufficient to provide an indium deposit of the desired thickness. Preferably, indium ions from water-soluble indium salts are included in the composition in an amount of 5 g/L to 70 g/L, more preferably 10 g/L to 50 g/L, most preferably 10 g/L to 40 g/L.

selected from alanine, arginine, aspartic acid, asparagine, glutamic acid, glycine, glutamine, histidine, leucine, lysine, threonine, isoleucine, One or more amino acids from the group consisting of serine and valine are contained in the indium plating composition of the present invention. Preferably, the indium electroplating compositions of the present invention are free of sulfur and sulfur functional amino acids. Preferably, the one or more amino acids are selected from the group consisting of arginine, aspartic acid, asparagine, glycine, glutamine, lysine, serine and histidine, more preferably, the one The one or more amino acids are selected from the group consisting of arginine, asparagine, glycine, aspartic acid, lysine and serine, even more preferably, the one or more amino acids are selected from glycine, lysine and serine groups. Most preferably, the amino acid is glycine. Inclusion of one or more of these amino acids in the indium electroplating compositions of the present invention inhibits hydrogen evolution during indium electroplating and stabilizes the indium ions such that substantially no indium occurs at relatively high pH > 1.5 ion precipitation.

One or more of the aforementioned amino acids may be included in the indium plating composition of the present invention in an amount of 5 g/L or more. Preferably, one or more amino acids of the present invention may be included in an amount of 10g/L to 200g/L, more preferably, the amino acid may be included in an amount of 25g/L to 150g/L (eg 30g/L to 120g/L, 30g/L /L to 100g/L or 25g/L to 75g/L) is included, even more preferably, the amino acid may be 25g/L to 100g/L (eg 30g/L to 100g/L or 40g/L to 100g) /L) is included, most preferably the amino acid is included in an amount of 50 g/L to 100 g/L (eg 50 g/L to 90 g/L).

One or more acids selected from the group consisting of inorganic acids, alkane sulfonic acids, and salts of these acids, wherein the inorganic acids are selected from the group consisting of sulfamic acid and sulfuric acid. Alkane sulfonic acids include, but are not limited to, methane sulfonic acid, ethane sulfonic acid, and butane sulfonic acid. Preferably, the one or more acids are selected from the group consisting of sulfuric acid, sulfamic acid and methanesulfonic acid, more preferably the one or more acids are selected from the group consisting of sulfuric acid and sulfamic acid, most preferably , the acid is sulfamic acid.

One or more of the aforementioned acids or their salts are included in the indium electroplating composition of the present invention in an amount of 10 g/L or more. Preferably, the one or more acids are present at 10 g/L to 300 g/L, more preferably 50 g/L to 250 g/L, even more preferably 50 g/L to 200 g/L, most preferably 50 g/L to 100 g/L The amount of L is included in the indium plating composition.

The pH of the aqueous acidic indium electroplating composition of the present invention is in the range of 5 or less, preferably 1-4, more preferably 1-3, even more preferably 1.5-3, most preferably 1.5-2.5.

Optionally, one or more pH modifiers may be included in the indium electroplating composition to provide and maintain the desired acidic pH. The pH adjusting agent may comprise buffering agents including an acid and its conjugate base salts. The acid is selected from glyoxylic acid, pyruvic acid, hydroxamic acid, iminodiacetic acid, salicylic acid, succinic acid, hydroxybutyric acid, acetic acid, acetoacetic acid, tartaric acid, phosphoric acid, oxalic acid, carbonic acid, ascorbic acid, butyric acid, sulfuric acid acetic acid, glycolic acid, malic acid, formic acid, heptanoic acid, caproic acid, hydrofluoric acid, lactic acid, nitrous acid, octanoic acid, valeric acid, uric acid, nonanoic acid, capric acid, sulfurous acid, sulfuric acid, alkanesulfonic acid and aromatic sulfonic acid, such as methanesulfonic acid, ethanesulfonic acid, benzenesulfonic acid, toluenesulfonic acid, sulfamic acid. Bases such as potassium hydroxide and sodium hydroxide can also be used as pH adjusters, alone or in combination with one or more of the foregoing acids. Preferably, the one or more pH modifiers are selected from the group consisting of sulfamic acid, sulfuric acid, potassium hydroxide and sodium hydroxide, more preferably, the one or more pH modifiers are selected from sulfamic acid, Sulfuric acid and potassium hydroxide.

Optionally, the aqueous acidic indium electroplating composition may include one or more alloying metals. Preferably, the one or more alloying metals are selected from the group consisting of tin, copper, bismuth and silver, more preferably the one or more alloying metals are selected from the group consisting of tin, copper and silver, most preferably , the alloy metal is tin. These alloying metals can be added to the indium composition as water-soluble metal salts. Such water-soluble metal salts are well known to those skilled in the art. Many are commercially available or can be prepared as described in the literature. One or more sources of alloying metals may be added to the indium electroplating composition in amounts such that the indium alloy has 1 wt% to 3 wt% of the one or more alloying metals. Preferably, alloying metals are excluded from the indium composition. Preferably, only indium metal is plated.

Optionally, one or more sources of chloride ions can be added to the indium electroplating compositions of the present invention. Sources of chloride ions include, but are not limited to, sodium chloride and potassium chloride. Preferably, when one or more sources of chloride ions are added to the indium electroplating composition, the concentration of chloride ions may be in the range of 1-50 g/L.

Conventional hydrogen suppressors, such as copolymers of epihalohydrin and nitrogen-containing organic compounds, are excluded from the indium electroplating compositions of the present invention. Preferably, many conventional additives, such as levelers, inhibitors, brighteners, grain refiners, alloying metals, and surfactants, are also excluded from the indium electroplating compositions of the present invention.

Preferably, in the aqueous acidic indium electroplating composition of the present invention, the water is at least one of deionized water and distilled water to limit incidental impurities.

Preferably, the aqueous acidic indium electroplating composition of the present invention consists of: water; one or more sources of indium ions, including indium (In ³⁺ ) cations and counter anions; one or more acids selected from inorganic The group consisting of acids, wherein these inorganic acids are selected from the group consisting of sulfamic acid, sulfuric acid, and alkane sulfonic acid (including salts of sulfamic acid, sulfuric acid, and alkane sulfonic acid); one or more amino acids, selected from alanine , arginine, aspartic acid, asparagine, glycine, glutamine, histidine, leucine, lysine, threonine, isoleucine, serine and valine; optionally one or more sources of chloride ions; and optionally one or more pH adjusting agents.

More preferably, the aqueous acidic indium electroplating composition of the present invention consists of: water; one or more sources of indium ions, including indium (In ³⁺ ) cations and counter anions; one or more acids selected from The group consisting of sulfamic acid, sulfuric acid, methanesulfonic acid, and salts of the foregoing acids; one or more amino acids selected from the group consisting of arginine, aspartic acid, asparagine, glycine, glutamine, lysine, and the group consisting of serine; one or more sources of chloride ions; and optionally one or more pH adjusting agents.

Most preferably, the aqueous acidic indium electroplating composition of the present invention consists of: water; one or more sources of indium ions, including indium (In ³⁺ ) cations and counter anions; one or more acids selected from The group consisting of sulfamic acid and sulfuric acid, wherein the most preferred acid is sulfamic acid; one or more amino acids selected from the group consisting of arginine, asparagine, glycine, lysine and serine, wherein glycine, Lysine and serine are more preferred amino acids, and glycine is most preferred; and optionally one or more pH adjusting agents.

Preferably, the aqueous acidic indium electroplating compositions of the present invention are useful for electroplating indium metal or indium alloys directly adjacent to a nickel layer that is directly adjacent to copper or copper alloys. More preferably, the aqueous acidic indium electroplating compositions of the present invention are useful for electroplating indium metal directly adjacent to a nickel layer that is directly adjacent to copper or copper alloys. The thickness of the nickel layer is preferably in the range of 0.1-5 μm. Conventional indium or silver undercoats with thickness values of 1-100 nm, more typically 1-40 nm, are excluded from the nickel surface, allowing indium metal or indium alloys to be electroplated directly adjacent to the nickel, and providing a matte, uniform >100 nm , void-free, substantially whisker-free indium deposits with good adhesion to nickel. This adhesion can be tested by cross-hatch testing, lead bend testing, and reflow testing followed by dehumidification control.

The thickness of the indium layer is in the range >0.1 μm, preferably 0.2 μm to 10 μm, more preferably 0.2 μm to 5 μm, most preferably 0.2 μm to 1 μm.

Equipment for depositing indium metal or indium alloys directly adjacent to nickel is conventional. Preferably, a conventional soluble indium electrode is used as the anode. The current density can vary depending on the concentration of indium ions in the electroplating composition and the agitation of the bath. Preferably, the current density is in the range of 0.1 ASD or greater (eg 0.1-50 ASD, 0.1-30 ASD or 0.1-20 ASD), more preferably 0.5 ASD to 50 ASD (eg 0.5-40 ASD, 1-20 ASD or 1-10 ASD) ).

The temperature of the indium composition during indium metal or indium alloy electroplating may range from room temperature to 60°C. Preferably, the temperature is in the range of room temperature to 55°C, more preferably room temperature to 50°C, most preferably, 30°C to 45°C.

The indium plating speed of the aqueous acidic indium electroplating composition of the present invention can be > 0.2 μm/min, > 0.5 μm/min, > 1 μm/min, > 2.3 μm/min at 1, 2, 4, 8 or 10 ASD, respectively or >3μm/min.

Optionally, the indium or indium alloy plated nickel and copper or copper alloy substrates are reflowed. The reflow test is preferably performed at a temperature of > 150°C, more preferably a temperature of > 200°C, most preferably a temperature of 200°C to 350°C. Reflow can be performed in conventional reflow ovens for metal substrates. The reflowed indium plated nickel substrate showed little or no dewetting.

Although the aqueous acidic indium electroplating compositions of the present invention are preferably used for depositing indium metal or indium alloys directly adjacent to a nickel layer that is directly adjacent to copper or copper alloys, such as for connector pins in IC electronics, However, it is envisaged that the aqueous acidic indium electroplating compositions of the present invention may be used to deposit indium metal or indium alloys directly adjacent to other metals such as copper and copper alloys. Preferably, the indium metal is deposited directly adjacent to other metals such as nickel, copper or copper alloys, and most preferably, the indium metal is deposited directly adjacent to nickel, wherein nickel is directly adjacent to copper or copper alloys.

The following examples are intended to illustrate the invention, but are not intended to limit the scope of the invention.

Example 1-10

Hull cell electroplating performance of the aqueous acidic indium electroplating compositions of the present invention

The following aqueous acidic indium electroplating compositions were prepared:

Table 1

The solvent of the aforementioned indium electroplating composition is water, and potassium hydroxide is used to adjust the pH of the indium electroplating composition.

250 mL of each indium composition was placed in a separate Hull cell. A nickel-coated brass (copper-zinc alloy) panel was used as the cathode. Indium metal is used as the soluble anode. The rectifier is set to 2A. During the plating process, the indium composition was stirred using a common laboratory paddle stirrer. Indium plating was performed for 3 min. The current density is in the range of 0.1-10 ASD. Indium metal deposits were measured using a Fischerscope X-Ray XDV-SD XRF device at current densities of 1, 2, 3, 4, 6, 8, and 10 ASD. The plating rate was determined by dividing the thickness at each current density by the plating time in minutes.

As the current density increases, the plating rate for depositing indium on nickel also increases. Plating rates ranged from a low rate of 0.5 μm/min at 1 ASD to a high rate of 3.2 μm/min at 10 ASD. After plating is complete, check the deposit quality of the indium deposit. All indium deposits appeared smooth, matte and uniform. No deposit defects were observed.

Example 11-12

Reflow Test of Indium Metal on Nickel

The following aqueous acidic indium electroplating compositions were prepared:

Table 2

¹ LUGALVAN ^™ IZE from BASF (IZE contains 48-50 wt% copolymer).

Each aqueous acidic indium electroplating composition was used to plate indium on nickel-coated brass (copper-zinc alloy). The counter electrode is an indium soluble anode. Indium was plated on the nickel of the substrate for 3 min at a current density of 5 ASD. The indium electroplating composition is agitated throughout the plating process.

After plating, the indium plated substrates were rinsed with DI water, dried and observed for plating properties. Indium deposits on nickel appeared uniform, matte and smooth on both substrates.

The substrate is then reflowed/heated using a conventional reflow oven. Reflux for 3 min at 200°C. The reflowed substrate was removed from the furnace and the quality of its surface was analyzed. The substrate plated with the indium composition of Example 11 showed no signs of dewetting. In contrast, the substrate plated with the indium composition of Example 12 showed significant dewetting: prior to reflow, the nickel was exposed on certain areas covered by indium.

Example 13-14

Hull Cell Plating Properties of Aqueous Acidic Indium Plating Compositions Containing Amino Acid Cysteine or Amino Acid Glycine

The following aqueous acidic indium electroplating compositions were prepared:

table 3

250 mL of each aqueous acidic indium composition was placed in a Hull cell. A nickel-coated brass (copper-zinc alloy) substrate was used as the cathode. Plating was carried out at a current of 2 A for 3 min with paddle stirring. The counter electrode is a soluble indium anode. The appearance and thickness of the coatings were evaluated at current densities of 0.1-10 ASD. For Comparative Example 13, there is no evidence of indium plating because of the lower current density of 0.1-3 ASD. At current densities above 3ASD, the indium deposits are very thin (less than 0.4 μm) and non-uniform. A large amount of gas evolution was observed during plating (bubbling was observed from the cathode with the naked eye).

In contrast, the indium deposit of Example 14 appeared uniform, matte and smooth at 0.1-10 ASD. The plating rates were comparable to those of Examples 1-5 above.

Example 15-17

Hull Cell Plating Properties of Aqueous Acidic Indium Plating Compositions

The following aqueous acidic indium electroplating compositions were prepared:

Table 4

¹ LUGALVAN ^™ IZE from BASF (IZE contains 48-50 wt% copolymer).

250 mL of each aqueous acidic indium composition was placed in a Hull cell. A nickel-coated brass (copper-zinc alloy) substrate was used as the cathode. Plating was performed with a current of 2A. Plating was carried out with paddle stirring for 3 min. The counter electrode is an indium soluble anode. The appearance and thickness of the indium coatings were evaluated at current densities of 0.1-10 ASD.

The indium plated substrate of Example 15 had a uniform, matte and smooth indium deposit. In the current density range of 0.1-10 ASD, the plating rate was good and substantially the same as Examples 1-5 above. No observable defects.

In contrast, the indium composition-coated substrates of Examples 16-17 did not exhibit significant amounts of indium deposited on the substrates. XRF analysis of the substrates of Examples 16-17 showed 0.1-0.6 μm indium clusters in certain regions of the substrates. A large amount of gas evolution was observed during the plating of the substrates of Examples 16-17. It has been determined that imidazole/epihalohydrin copolymers are not suitable for indium metal plating.

Example 18

Hydrogen generation and reflow testing of indium on nickel

The indium plating compositions of Examples 15, 16, and 17 of Table 4 above were added to a separate one-liter glass beaker. Two indium soluble anodes were placed in each beaker. Nickel-coated brass coupons were used as cathodes in each beaker. Connect the electrodes to the rectifier. A current density of 4 ASD was applied to each composition. Plating was completed within 2 minutes. A magnetic stirrer was used to stir the indium electroplating composition throughout the plating process. After plating, each coupon was removed from the beaker, rinsed with DI water, dried and analyzed for indium plating performance.

The coupon of Example 15 had a 2.2 μm thick uniform, matte and smooth indium deposit. In contrast, the indium deposits from the plating compositions of Examples 16-17 were very thin. XRF analysis determined that the indium deposits of the indium composition coated coupons of Example 16 were only 0.2 μm thick, and the indium deposits of the composition of Example 17 were 0.1 μm thick. For Examples 16-17, substantial gas evolution was observed during plating.

The above experiment was repeated using a current density of 8 ASD with a plating time of 1 minute 30 seconds. The indium deposit of Example 15 was uniform, matte and smooth in appearance, with a 3.7 μm thick indium deposit. The indium deposits from the compositions of Examples 16-17 had indium thicknesses of 0.55 μm and 0.35 μm, respectively.

Examples 19-21

Hydrogen generation and reflow testing of indium on nickel

The following aqueous acidic indium electroplating compositions were prepared:

table 5

¹ LUGALVAN ^™ IZE from BASF (IZE contains 48-50 wt% copolymer).

Each of the indium plating compositions of Examples 19-20 was added to a separate one-liter glass beaker. Two indium anodes were placed in each beaker, and a nickel-coated coupon was used as the cathode in each beaker. Connect the electrodes to the rectifier. A current density of 4 ASD was applied for 2 min of plating. The plating composition is stirred throughout the plating process. During indium plating, significant hydrogen evolution was observed for Examples 20-21. In contrast, for Example 19, trace amounts of hydrogen gas evolution were observed.

After plating, the indium plated substrates were rinsed with DI water, dried and observed for plating properties. The indium deposits on nickel plated with the indium composition of Example 19 appeared uniform, matte and smooth. The average indium thickness was 2.2 μm.

In contrast, with the indium compositions of Examples 20 and 21, substantially no indium was deposited on the nickel. The average thickness of indium on nickel plated with the indium composition of Example 20 was only 0.55 μm, and the average thickness on nickel plated with the indium composition of Example 21 was only 0.35 μm.

The substrate with the indium deposit adjacent to the nickel is then reflowed using a conventional reflow oven. Reflux for 3 min at 200°C. The reflowed substrate was removed from the furnace and the quality of its surface was analyzed. The substrate plated with the indium composition of Example 19 showed no signs of dewetting. In contrast, the substrates plated with the indium compositions of Examples 20-21 exhibited several dewetting spots distributed on the surface of the indium layer.

Example 22-27

Stability of Aqueous Acidic Indium Electroplating Compositions

The following aqueous acidic indium electroplating compositions were prepared:

Table 6

All of the foregoing indium plating compositions appeared colorless after initial make-up at room temperature. All indium plating compositions were left at room temperature for one day. The indium plating composition of Example 22 was noticeably cloudy. A white precipitate was observed at the bottom of the glass beaker. A white precipitate indicates the indium salt precipitated from the composition.

In contrast, the indium plating compositions of Examples 23-27 remained colorless, indicating good stability. The compositions of Examples 23-27 remained colorless for several weeks, indicating that the indium compositions were stable. No turbidity or precipitation was observed after one month.

Claims (10)

1. An indium electroplating composition consisting of: water; one or more sources of indium ions; one or more acids selected from the group consisting of inorganic acids, alkane sulfonic acids, and salts of said acids group, wherein the inorganic acid is selected from the group consisting of sulfamic acid and sulfuric acid; and one or more amino acids selected from the group consisting of alanine, arginine, aspartic acid, asparagine, glutamic acid, the group consisting of glycine, glutamine, leucine, histidine, lysine, threonine, isoleucine, serine, and valine; optionally one or more alloying metals; and optionally one or more pH modifiers. 2. The indium electroplating composition of claim 1, wherein the one or more amino acids are selected from the group consisting of glycine, arginine, lysine, glutamine, serine, histidine, and asparagine group. 3. The indium electroplating composition of claim 1, wherein the one or more amino acids are present in an amount of at least 5 g/L. 4. The indium electroplating composition of claim 3, wherein the one or more amino acids are in an amount of 10 g/L to 200 g/L. 5. The indium electroplating composition of claim 1, wherein the one or more acids are inorganic acids selected from the group consisting of sulfamic acid and sulfuric acid. 6. The indium electroplating composition of claim 1, wherein the one or more alloying metals is selected from the group consisting of tin, silver, bismuth, and copper. 7. A method of electroplating indium on nickel, comprising: a. Provide a substrate including a nickel layer adjacent to the copper or copper alloy layer: b. contacting the substrate including the nickel layer adjacent to the copper or copper alloy layer with an indium electroplating composition consisting of: water; one or more a source of indium ions; one or more acids selected from the group consisting of inorganic acids, alkane sulfonic acids, and salts of the acids, wherein the inorganic acids are selected from the group consisting of sulfamic acid and sulfuric acid; and a or amino acids selected from the group consisting of alanine, arginine, aspartic acid, asparagine, glutamic acid, glycine, glutamine, histidine, leucine, lysine, threonine , isoleucine, serine, and valine; optionally one or more alloying metals; and one or more pH adjusting agents; and c. Electroplating an indium layer adjacent to the nickel layer of the substrate using the indium electroplating composition. 8. The method of electroplating indium on nickel as claimed in claim 7, wherein the indium layer is larger than 0.1 μm. 9. The method for electroplating indium on nickel according to claim 8, wherein the indium layer is 0.2-1 μm. 10. The method of electroplating indium according to claim 7, wherein the one or more amino acids are selected from the group consisting of glycine, lysine, glutamine, histidine, serine, asparagine and arginine group.