JP5583896B2 - High-speed plating method of palladium and palladium alloy - Google Patents

Description

  The present invention relates to a method for rapid plating of palladium and palladium alloys using ammonia-based palladium and palladium alloy plating compositions. More particularly, the present invention relates to a method for high speed plating of palladium and palladium alloys using ammonia-based palladium and palladium alloy plating compositions with reduced amounts of free ammonia.

The dramatic rise in gold prices over the past few years has resulted in new methods and equipment in the field of metal plating and attempts to use alternative metals such as palladium and its alloys, for example by open reel plating. ing. The use of such plating methods requires high speed plating, and high speed requires a current density of 10 amps / dm ² or higher. Furthermore, the industry desires high speed plating that achieves metal deposition in the shortest possible time so that it is more efficient in manufacturing metal plated articles. The high-speed plating apparatus can use a jet plating principle in which a plating solution is jetted in a jet flow onto a substrate to be plated to bring about vigorous stirring. Vigorous agitation can be achieved by using a pump to move the solution past the substrate to be plated very quickly, or by moving the substrate through the solution quickly, without using a jet stream. Can also be supplied. Another form of high speed plating is selective plating. Such selective plating uses special plating equipment, such as a chemical or mechanical mask that limits metal deposition to specific required areas while leaving other areas free of metal deposition.

Attempts have been made to plate palladium and its alloys in high speed plating equipment using various baths, but the deposits are burnt or matte gray, or the deposits are glossy to semi-glossy and high It is stressed and shows surface microcracks that are visible only under a high power microscope. Such cracks may be visible in the deposit as soon as it leaves the plating bath, or they become visible after the deposit has been at room temperature for more than a day. There is a lot of literature on this crack. This is because hydrogen co-deposits with palladium. After hydrogen is removed from the deposit, cracks appear. The industry desires crack-free palladium and palladium alloy deposits with usable current densities in high speed plating at 10-100 amps / dm ² and higher. In addition, the industry desires palladium and palladium alloys that have high wear resistance, high corrosion resistance, low electrical resistance, and good solderability such as for use as a coating for electrical contacts.

  In order to achieve a palladium or palladium alloy deposit having the desired properties from the plating process, a number of process parameters must be specified. Such parameters include, but are not limited to, bath composition, bath temperature, stirring rate during plating, and bath pH. The specific parameters to achieve the optimum process can vary widely depending on whether the process is slow or fast plating. Many palladium and palladium alloy plating processes use ammonia as a ligand for metals. Ammonia-based processes have many advantages over processes that do not contain ammonia. These advantages include: 1) no harmful degradation products from organic ligands compared to other types of ligands such as polyamide-type ligands; 2) highly ductile deposits; and 3) ammonia Palladium-ammonia salts are more economical and readily available than many foreign palladium salts required for processes that do not contain.

  Such ammonia-based processes function from a low acidic pH to a high alkaline pH range, for example, pH 6 and above. During the bath function, free ammonia escapes the bath as ammonia vapor. This changes the pH of the bath, destabilizes the bath and greatly degrades the performance of the bath. This is a particular problem in high speed plating where the plating rate is faster than the low speed plating and the bath agitation is more intense, thus increasing the rate of loss of free ammonia. Also, the elevated temperature during plating or high temperature plating, typical of high speed plating, causes loss of ammonia from the bath, thereby destabilizing the plating process. Ammonia-based plating processes require periodic replenishment of ammonia to maintain process stability and optimal drive. Typically, the amount of free ammonia is maintained between 50 g / L and 150 g / L, more typically 100 g / L. However, ammonia replenishment is difficult. Ammonia is often replenished by adding ammonium sulfate, eg, sulfate-based solutions, to the plating bath; this results in the accumulation of anions in the plating bath, which is the bath. As a result of salting out the ingredients, the life of the bath is shortened dramatically. Ammonia gas and ammonium hydroxide can also be added to the bath; such components are inconvenient and problematic to handle. Both the current potentially serious harm and toxicity pose a danger to workers using it. As more free ammonia is added to the bath, the loss of ammonia is also greater, thus posing a danger to the environment. Therefore, the industry desires a high speed plating method in which the amount of free ammonia is reduced.

  In high speed plating such as open reel plating, the loss of ammonia is greater, thus requiring a higher proportion of ammonia replenishment, increasing the difficulty of maintaining a stable plating process. Also, the high bath temperature and rapid agitation during high speed plating further increases ammonia loss and bath instability. The quick loss of ammonia results in an unstable bath and poor process performance. This reduces the overall efficiency of the process and increases the cost of plating.

US Pat. No. 5,415,685 discloses ammonia-based palladium plating compositions and methods. This patent claims that the ammonia-based palladium plating composition provides a whiter palladium deposit over a wide range of plating thicknesses and is more stable than conventional methods. The method described in this patent is a low speed method with a current density range of 0.1 amp / ft ² to 50 amp / ft ² (0.01 amp / dm ^{2 to} 5 amp / dm ² ).

US Pat. No. 5,415,685

  In industries where high speed plating is essential to achieving economic efficiency, such methods are not appropriate. Thus, there is a need for a high speed method for plating palladium and palladium alloys from ammonia based baths.

In some embodiments, the method provides a) a composition consisting essentially of one or more palladium sources, ammonium ions and urea; b) contacting the substrate with the composition; and c) at least 10 amps / dm. Generating a current density of ² to deposit palladium on the substrate.
In another aspect, the method provides a composition consisting essentially of a) one or more of a palladium source, one or more of an alloying metal source, ammonium ions and urea; b) contacting the substrate with the composition And c) generating a current density of at least 10 amperes / dm ² to deposit a palladium alloy on the substrate.

This high speed method provides a stable palladium and palladium alloy bath, eliminating the need to add ammonium sulfate, ammonium hydroxide, ammonia gas or other ammonium compounds to replenish the amount of free ammonia in the bath. Thus, the danger and other disadvantages of adding such compounds to the plating bath are eliminated. This high speed method also reduces the amount of free ammonia in the bath compared to many conventional high speed palladium and palladium alloy methods. Therefore, the amount of ammonia vapor can also be reduced.
This high speed method provides palladium and palladium alloy deposits on the substrate at high current densities that are glossy, ductile and crack free. This high speed method can be used to plate palladium and palladium alloys on any substrate where a palladium and palladium alloy coating is desired. Such substrates include electronic components and jewelry. Electronic components can include electrical contacts where high wear resistance, high corrosion resistance, and low electrical contact resistance and good solderability are desired.

  As used herein, unless the text clearly indicates otherwise, the following abbreviations have the following meanings: ° C = degrees Celsius; g = grams; mg = milligrams; L = liters; mL = milliliters Amp = Amp; dm = Decimeter; μm = Micron = Micrometer; rpm = Number of revolutions per minute.

  The terms “deposition”, “plating” and “electroplating” are used interchangeably herein. The term “burnt” means a dull finish or a rough finish. The term “gloss” means an optical reflective finish. The term “ductile” or “ductility” is the resistance of a metal deposit to crack formation during deformation such as bending or stretching. “Metal Turnover (MTO)” = all deposited palladium (in grams) divided by the palladium content in solution (in grams). All amounts are percent by weight unless otherwise indicated. All numerical ranges include boundary values and can be combined in any order, except where it is logical that such numerical ranges are constrained to add up to 100%.

  The method is a high speed electroplating method for depositing palladium and palladium alloys with a small amount of free ammonia, thereby reducing the generation of ammonia vapor during high speed electroplating and vigorous bath agitation. Typically, free ammonia in the electroplating bath is less than 50 g / L. Since less ammonia vapor is generated during electroplating compared to many conventional ammonia-based baths, the reduction of free ammonia also provides a more environmentally friendly bath. The unpleasant and troublesome odor of ammonia is eliminated or at least reduced. Also, the constantly evaporating ammonia causes significant difficulty in controlling the pH value. In conventional ammonia-based baths, ammonia is continuously added in measured amounts to maintain an optimum pH. Typically, ammonium sulfate, ammonium hydroxide and ammonia gas are used. Such compounds are difficult to handle, toxic and dangerous to workers. Furthermore, the addition of such compounds to the bath often results in salting out of the bath components, thus degrading the performance of the bath. This high speed method eliminates the need to add such compounds to the plating bath.

  Urea is included in the bath to stabilize the bath by supplementing the reduced free ammonia and preventing changes in pH due to ammonia loss. High speed electroplating baths have a pH in the range of 6-10, typically 7-8. Including urea in the bath eliminates the need to replenish ammonia by the addition of ammonium compounds or ammonia. Urea is easier to handle than ammonia or ammonium compounds. Urea is a weak complexing agent and the addition of large amounts of urea to the ammonia-based plating bath does not adversely affect the microstructure of palladium and palladium alloy deposits. Furthermore, there is no accumulation of degradation products that limit the bath life. In addition, one of the hydrolysis products of urea is ammonia, which is used to supplement the loss of free ammonia and help maintain the desired pH and bath stability. Urea is included in the bath in an amount such that the total amount of urea and free ammonia in the bath is between 100 g / L and 150 g / L.

  A wide range of palladium compounds can be used as a palladium source in high speed electroplating methods, although they are compatible with the high speed methods and other bath components. Such palladium compounds include, but are not limited to, palladium complex ion compounds with ammonia as a complexing agent. Such compounds include, but are not limited to, dichlorodiammine palladium (II), dinitrodiammine palladium (II), tetraammine palladium (II) chloride, tetraammine palladium (II) sulfate, tetraammine palladium tetrachloroparadate, Examples include tetraamine palladium carbonate and tetraamine palladium hydrogen carbonate. Additional sources of palladium include, but are not limited to, palladium dichloride, palladium dibromide, palladium sulfate, palladium nitrate, palladium monooxide-hydrate, palladium acetate, palladium propionate, palladium oxalate and palladium formate. . One or more palladium sources can be mixed together in a bath. Typically, an ammonia palladium complex is used in the bath. One or more sources of palladium are added to the bath in an amount sufficient to provide 10 g / L to 50 g / L of palladium or, for example, 20 g / L to 40 g / L of palladium for deposition.

  Ammonia can be added to the bath by a water soluble ammonium salt. Such ammonium salts include, but are not limited to, ammonium halides such as ammonium chloride and ammonium bromide, ammonium sulfate and ammonium nitrate. The ammonia source is added to the bath in an amount less than 50 g / L, or for example, sufficient to provide free ammonia in an amount of 10 g / L to 45 g / L, or such as 15 g / L to 35 g / L.

  Alloying metals that can be added to the high speed electroplating bath to form a palladium alloy include, but are not limited to, one or more of nickel, cobalt, iron and zinc. The alloy can be a binary alloy or a ternary alloy. Typically, the alloy is a binary alloy such as palladium / nickel, palladium / cobalt, and palladium / zinc. More typically, the binary alloy is palladium / nickel. Typically the ternary alloy is palladium / nickel / zinc. One or more alloying metals may be added to the bath as a water soluble salt. Such salts include, but are not limited to, halides, sulfates, lead sulfites, phosphates, pyrophosphates, nitrates and salts with organic acids such as acetates, propionates, oxalates and formic acid. Salt. Typically halides and sulfates are used. One or more alloying metal salts are added to the bath in an amount sufficient to provide alloying metal ions in an amount of 0.1 g / L to 15 g / L, or such as from 1 g / L to 10 g / L.

  Palladium alloys produced by high speed methods are stable. Stable means that the alloy composition remains substantially constant over a wide range of current densities and changes in bath pH, temperature fluctuations and bath agitation speed. The weight range of palladium in the binary alloy is in the range of 50% to 90% by weight with the balance being the alloy-forming metal. An example of such a binary alloy used to coat electrical contacts is palladium / nickel (80 wt% / 20 wt%). The weight range of palladium in the ternary alloy is in the range of 40 wt% to 80 wt%, the balance being the two alloying metals, in equal or unequal proportions.

  The palladium electroplating bath used in the high speed process consists essentially of one or more of the palladium sources, ammonium ions, free ammonia and urea. If the bath is used to deposit a palladium alloy, one or more of the alloying metal ions are added to the bath. Palladium and palladium alloys deposited by high speed methods are glossy, free of cracks and adhere to the substrate.

  One or more existing additives may also be added to the bath. Such existing additives include, but are not limited to, buffering agents, brighteners, surfactants, and mixtures thereof. Such additives can be included in the bath in conventional amounts.

  One or more surfactants that do not degrade the performance of the bath may be included. Typically, such surfactants include, but are not limited to, nonionic surfactants, cationic surfactants and anionic surfactants. Examples of such surfactants are polyethylene glycol, alkyl quaternary ammonium salts and sulfopropylated alkyl alkoxylates.

  Buffering agents include, but are not limited to, one or more of acetic acid, boric acid, carbonic acid, citric acid, tetraboric acid, maleic acid, itaconic acid, and salts thereof. Other conventional water soluble acids may also be included as buffering agents.

  Mineral acids and bases can also be added to the bath to help maintain the pH. Such mineral acids include sulfuric acid, hydrochloric acid and nitric acid. Bases include but are not limited to sodium hydroxide and potassium hydroxide. Typically, sulfuric acid or sodium hydroxide is used.

  Suitable brighteners are compounds that result in bright palladium or palladium alloy deposits. Such brighteners include existing organic brighteners. Such organic brighteners include, but are not limited to, succinimide, maleimide, quinoline, substituted quinoline, phenanthroline, and substituted phenanthroline and their quaternized derivatives, pyridine and its derivatives, such as pyridinecarboxylic acid, pyridinecarboxylic acid amine And polypyridines such as bipyridine, nicotinic acid and derivatives thereof, pyridinium alkyl sulfobetaines, piperidine and derivatives thereof, piperazine and derivatives thereof, pyrazine and derivatives thereof, and mixtures thereof. Typically, brighteners used in high speed baths are organic brighteners with nitrogen-containing heterocyclic rings, but exclude aromatic sulfonamides. More typically, the brightener used is a pyridine derivative, a pyrazine derivative or a mixture thereof.

  Since palladium and palladium alloys deposited by high speed methods are typically crack free, stress reducing agents are generally removed from the bath. An example of such a stress reducing agent is an aromatic sulfonamide. A typical aromatic sulfonamide used as a stress reducing agent is saccharin.

  The bath temperature can be maintained by conventional heating equipment. The bath temperature is in the range of 40-70 ° C, or for example 50-60 ° C. It is highly desirable to maintain the bath temperature within that range, particularly at the upper end of the range, as the amount of ammonia vapor exiting the bath increases as the temperature increases. Therefore, maintaining the temperature is important.

High speed electroplating methods use a current density of 10 amps / dm ² or higher. Typically, the current density ranges from 10 amps / dm ^{2 to} 100 amps / dm ² , or such as from 20 amps / dm ² to 80 amps / dm ² . Such current density is controlled using a conventional rectifier.

  Conventional high speed plating equipment can be used to electroplate palladium metal and palladium metal alloys. Typically, palladium and palladium alloys are electroplated using a reel-to-reel plating apparatus, although any apparatus that maintains a high plating rate can be used.

  Conventional insoluble anodes can be used in a high speed manner. Examples of insoluble anodes include, but are not limited to, platinized titanium, mixed oxide coated titanium and stainless steel. Also, anodes of the above materials with shield designs as described in US Patent Application Publication No. 2006/0124451 can be used.

  The cathode includes any material that can be plated with palladium or a palladium alloy. Generally, palladium or palladium alloys are deposited on copper, copper alloys, or nickel plated copper substrates. Such a substrate can be an electrical contact that requires high wear resistance, high corrosion resistance, low electrical contact resistance, high ductility and good solderability. Examples of electrical contacts are lead frames and electrical connectors. Electronic devices including such electrical contacts include, but are not limited to, printed circuit boards, semiconductor devices, optoelectronic devices, electrical components, and automotive components. In addition, the high speed method can be used to deposit palladium or palladium alloys on solar cell component parts and jewelry and any article that can accept palladium or palladium alloy coatings.

  The thickness of palladium and palladium alloy coatings deposited by high speed methods can vary depending on the function of the substrate. In general, the thickness ranges from 0.1 μm to 100 μm. Typically, the thickness is in the range of 0.5 μm to 20 μm.

The rate of deposition depends on the current density used. In general, the speed can range from 1 μm / min to 30 μm / min. For example, a palladium / nickel alloy can be plated at 10 ampere / dm ^{2 at} 3 μm / min and 60 ampere / dm ^{2 at} 18 μm / min.

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

Example 1 (comparison)
The following conventional palladium / nickel alloy aqueous ammonia-based compositions were prepared for depositing palladium / nickel alloys (80/20% weight / weight).

The ammonia-based palladium / nickel alloy composition was added to a 1000 ml beaker and the composition was kept stirring with a magnetic stirrer during electroplating. The anode was a platinized titanium insoluble anode and the cathode was a brass substrate.
The temperature of the composition was maintained at 50 ° C. and the initial pH was 7.2. Electroplating was done at a high current density of 10 amperes / dm ^2. The experiment was conducted until 20 MTO was achieved for palladium metal.

Free ammonia in the bath was analyzed for each MTO for the first 5 MTO and then reduced to a frequency of every 3-5 MTO. The ammonia content in the bath was monitored by a pH titration method using 809 Titlando (trade ^name ) from Metrohm. It was observed that the bath was chemically unstable when deposition began at an initial low free ammonia concentration of 35 g / L. Bath destabilization could be observed by the formation of a white precipitate at the bottom of the beaker. In order to maintain the stability and functionality of the bath and achieve a glossy and ductile deposit, the white precipitate is removed from the bath by filtration and the free ammonia content is increased to 100 g / L by adding ammonium sulfate. It was. A strong odor of ammonia was detected during electroplating. Furthermore, free ammonia loss during electroplating had to be replenished to maintain a stable pH. In addition to the amount of ammonia added through the Pd (NH ₃ ) ₄ SO ₄ replenishment, 3-4 g of ammonia was added to the bath as ammonia gas and NH ₄ OH per gram of palladium to be plated. An ammonia concentration of 100 g / L was required to maintain bath stability. A bright, ductile deposit was plated, but the stability varied over 20 MTO, adding 3-4 g of ammonia per g of palladium to be plated to replenish the bath and maintain bath stability. In addition to removing white precipitate was required.

Example 2
The following palladium / nickel alloy aqueous ammonia-based composition was prepared to deposit a bright and ductile palladium / nickel alloy (80/20% weight / weight).

The ammonia-based palladium / nickel alloy composition was added to a 1000 ml beaker and the composition was kept stirring with a magnetic stirrer during electroplating. The anode was a platinized titanium insoluble anode and the cathode was a brass substrate.
The temperature of the composition was maintained at 50 ° C. and the pH was 7.2. Electroplating was done at a high current density of 10 amperes / dm ^2. The experiment was conducted until 20 MTO was achieved for palladium metal.
Free ammonia in the bath was analyzed per MTO for the first 5 MTO, and then the analysis was reduced to a frequency of every 3-5 MTO. The ammonia content in the bath was monitored by a pH titration method using 809 Titlando (trade ^name ) from Metrohm. The amount of urea was analyzed using the Genesis II FTIR spectrometer ^trademark from Mattson Instruments. Electroplating bath analysis showed that the ammonia / ammonium amount and pH remained stable throughout electroplating (20 metal turnover with palladium). There was no detectable white precipitate. The urea replenishment was 0.7-0.8 g per gram of palladium metal deposited.

The use of an ammonia-based / urea electroplating composition eliminated the need for ammonia replenishment with undesirable hazardous compounds such as NH ₄ OH and ammonia gas during electroplating. Compared to the bath of Example 1, a small amount of free ammonia was easily maintained during electroplating. Also, toxic vapors were reduced due to low free ammonia. Furthermore, the frequency and amount of urea replenishment was less than ammonia replenishment using NH ₄ OH and ammonia gas in Comparative Example 1, thus providing a more economical and cost effective method than conventional methods.
This process was repeated except that the pH of the bath was 8. The result was substantially the same as at pH 7.2.

Example 3
The palladium / nickel method described in Example 2 was repeated except that the amount of urea added to the electroplating composition was 80 g / L. The rate of urea replenishment was 0.7-0.8 g per gram of palladium metal deposited on the brass substrate. The bath was stable throughout electroplating. The performance of this method was the same as in Example 2. A glossy and ductile palladium / nickel alloy was deposited on the brass substrate.

Example 4
The following palladium / nickel alloy aqueous ammonia-based composition was prepared to deposit a bright and ductile palladium / nickel alloy (80/20% weight / weight).

The ammonia-based palladium / nickel alloy composition was added to a 1000 ml beaker. The cathode was a rotating cylinder pre-plated with bright nickel. During plating, the cathode was rotated at 1000 rpm. The pH of the ammonia-based composition was maintained at 7.2 during electroplating and the temperature was 50 ° C. Electroplating was done at a current density 20 amp / dm ^2. The bath was stable during the electroplating process. The palladium / nickel deposit was bright and ductile and adhered to the bright nickel.
The above method was repeated twice with the same parameters except that it was performed at current densities of 40 amps / dm ² and 60 amps / dm ² . The result was the same as at 20 amps / dm ² . A bright and ductile palladium / nickel deposit was deposited on and adhered to the nickel at a high current density.

Example 5
Four bright nickel-coated brass substrates were electroplated with an aqueous ammonia-based palladium / nickel composition as described in Example 4. Each substrate was plated with the composition at a different current density. The current densities were 20 amps / dm ² , 40 amps / dm ² , 60 amps / dm ² and 80 amps / dm ² . The pH of the plating composition was 7.2, and the temperature was 50 ° C. A high-speed method was performed using a jet plating apparatus designed for laboratory testing. The plating composition was applied to the substrate at a flow rate of 800 liters / hour. All of the palladium / nickel deposits on the bright nickel-coated brass substrate were bright and ductile and adhered to the substrate.

Example 6
The following aqueous ammonia-based palladium metal composition is produced to deposit a palladium coating on a copper substrate.

An aqueous ammonia-based palladium composition is deposited on a copper substrate using the jet plating apparatus described in Example 5. The pH of the composition is maintained at 8, and the temperature of the composition is maintained at 40 ° C. Current density is 20 Amps / dm ^2. The bath is expected to be stable during electroplating. The palladium coating obtained on the substrate is semi-glossy and is not expected to crack.

Example 7
The following aqueous ammonia-based palladium / cobalt alloy composition is produced to deposit a palladium / cobalt alloy on a copper substrate.

An aqueous ammonia-based palladium alloy composition is deposited on a copper substrate using the jet plating apparatus described in Example 5. The bath pH is maintained at 7.5 and the temperature is maintained at 60 ° C. Current density is 90 Amps / dm ^2. The bath is expected to be stable during electroplating. The palladium / cobalt deposit is glossy and is expected to be free of cracks.

Example 8
The following aqueous ammonia-based palladium / zinc alloy composition is prepared for depositing a palladium-zinc alloy on a copper / tin alloy substrate.

An aqueous ammonia-based palladium alloy composition is deposited on a copper / tin alloy substrate using the jet plating apparatus described in Example 5. The pH of the composition is maintained at 7, and the temperature of the composition is maintained at 60 ° C. Current density is 30 Amps / dm ^2. The bath is expected to be stable during electroplating. A shiny and crack-free palladium / zinc alloy is deposited on the copper / tin alloy.

Example 9
The following aqueous ammonia-based palladium / nickel / zinc alloy composition is used to deposit a palladium / nickel / zinc alloy on a copper substrate.

An aqueous ammonia-based palladium alloy composition is deposited on a copper substrate using the jet plating apparatus described in Example 5. The pH of the composition is maintained at 7, and the temperature of the composition is maintained at 60 ° C. Current density is 85 Amps / dm ^2. The bath is expected to be stable during electroplating. The palladium / nickel / zinc alloy is expected to be glossy and free of cracks.

Claims (5)

a) a composition consisting essentially of one or more palladium ion sources, one or more alloying metal ion sources selected from nickel, cobalt and zinc , ammonium ions , free ammonia and urea , comprising free ammonia and Providing a composition wherein the total concentration of urea is between 100 g / L and 150 g / L ;
b) contacting the substrate with the composition; and c) generating a current density of at least 10 amps / dm ² to deposit a palladium alloy on the substrate;
A method involving that. The method of claim 1 , wherein the current density ranges from 10 amperes / dm ^{2 to} 100 amperes / dm ² . The method of claim 1 , wherein the composition further comprises one or more acids or salts thereof. The method of claim 1 , wherein the composition further comprises one or more brighteners. The method of claim 1 , wherein the composition has a free ammonia concentration of less than 50 g / L.