JP2016117946A - Environmentally friendly gold electroplating compositions and methods - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide pure gold electroplating solutions substantially free of environmentally toxic substances such as lead and free cyanide.SOLUTION: A gold electroplating composition free of free cyanide comprises gold cyanide, a phosphate ion, a phosphonic acid ion, sodium potassium tartrate, and trivalent antimony. The phosphonic acid ion is a compound represented by formula (I).SELECTED DRAWING: None

Description

  The present invention is directed to environmentally friendly gold electroplating compositions and methods. More specifically, the present invention provides an environmentally friendly gold electroplating composition that can electroplate soft gold over a wide current density range to provide a bright soft gold deposit even under jet and pulse current plating conditions. Intended for objects and methods.

  Electrolytic gold is typically used in the finishing of connectors and electronics because of the extraordinary performance of gold for these specific uses. Gold is one of the most reliable materials for electronic components because of its corrosion resistance, electrical conductivity, and thermal stability. Substantially pure gold is typically electroplated from a cyan electroplating bath containing several additives and a metallic brightener. Some of those additives, such as hydrazine, are toxic and are now regulated by many national and international regulations. Most commercial pure gold baths contain free cyanide and one or more grain refiners such as arsenic, thallium, and lead that are known to be harmful to the environment, so such gold plating The treatment of waste from the bath must be separated and is time consuming and expensive for the industry. In addition, such gold electroplating baths pose excessive danger to workers using the baths.

US Pat. No. 5,277,790 to Morrissey discloses a cyan-free gold electroplating bath in which gold is provided as a soluble sulfite complex. This gold electroplating bath does not contain cyan, but unnecessarily produces sulfur dioxide at high temperatures. Sulfur dioxide is a toxic gas with an irritating odor. To solve this problem, more sulfite is added to the plating solution. In addition, gold is plated with a relatively low plating rate near zero ~30mA / cm ^2. Therefore, there is a need for an improved gold electroplating bath that is environmentally friendly and can be plated over a wide current density range.

  One or more gold ion sources derived from a gold cyanide salt, one or more phosphate ion sources, one or more phosphonic acid sources or salts thereof, potassium sodium tartrate, and one or more antimony (III) ion sources A gold electroplating composition comprising: a gold electroplating composition substantially free of free cyanide.

  The method of electroplating gold includes one or more gold ion sources derived from a gold cyanide salt, one or more phosphate ion sources, one or more phosphonic acid sources or salts thereof, potassium sodium tartrate, and one or more A gold electroplating composition comprising a source of antimony (III) ions substantially free of cyanide and contacting the substrate with the gold electroplating composition And electroplating gold onto the substrate using direct current or pulsed current at a current density of 0.03 ASD or higher.

  The gold electroplating composition is environmentally friendly and can plate bright soft gold deposits over a wide current density range, including high speed jet plating conditions. The soft gold deposit also has a particulate structure. The electroplated gold composition can be used to plate a gold strike layer on electronic components, and is used to electroplate a soft gold layer in the formation of contacts for connectors and gold layers on switches or printed circuit boards. Can be done. The gold electroplating composition can also be used to deposit a soft gold layer on a decorative article. The gold deposit also has a particulate structure. Small particle size reduces porosity within the thin film. The luminous intensity of the deposit is also a direct result of this small particle size. In general, the roughness of a matte or semi-gloss deposit is high compared to a smooth gloss deposit.

1 is a SEM at a magnification of 20,000 showing the microstructure of a soft gold deposit electroplated with a gold electroplating composition containing antimony (III) ions. 1 is a SEM at a magnification of 20,000 showing the microstructure of a gold deposit electroplated with a conventional gold electroplating bath containing lead as a grain refiner.

As used throughout this specification, the following abbreviations shall have the following meanings unless the context clearly indicates otherwise: ° C = Celsius temperature, g = grams, mg = milligrams, L = liters, mL = Milliliter, cm = centimeter, mm = millimeter, μm = micron = micrometer, ppb = parts per billion, ms = millisecond, DC = direct current, ASD = ampere / decimeter square = A / dm ² , and ASTM = US standard test method.

  The terms “electroplating” and “plating” are used interchangeably throughout this specification. The terms “composition”, “solution”, “bath” are used interchangeably throughout this specification. The terms “a” and “an” refer to both singular and plural.

  All percentages are by weight unless otherwise stated. All numerical ranges are inclusive and combinable in any order, except where it is logical that such numerical ranges are constrained to add up to 100%.

  The composition comprises one or more gold cyanide derived gold ions, such as an alkaline gold cyanide compound such as potassium gold cyanide, sodium gold cyanide, and ammonium gold cyanide. Preferably, the alkali gold cyanide compound is potassium gold cyanide. Gold ions are provided by a gold cyanide salt, but no free cyanide is added to the gold electroplating composition, such as a cyanogen alkali metal salt or any salt, except gold salts that can provide a free cyan ligand.

  In addition to the gold cyanide salt, additional gold ions include thiosulfated alkali gold compounds such as trisodium thiosulfate gold and tripotassium gold thiosulfate, gold halides such as gold chloride, hydrogen tetrachloroaurate, and May be provided by gold trichloride. Preferably, gold ions are provided only from a gold cyanide salt. Such gold compounds are generally commercially available from various suppliers or can be prepared by methods well known in the art.

  The amount of gold salt added to the composition is that amount that provides gold ions at the desired concentration. In general, gold ions are in an amount of 4 g / L to 20 g / L, preferably 8 g / L to 20 g / L, more preferably 15 g / L to 20 g / L. The amount of gold ions in the electroplating composition depends on the type of plating such as jet, rack, or barrel plating.

  Conductive inorganic acids and salts thereof are included in the gold electroplating composition. Such conductive acids include, but are not limited to, phosphoric acid, sulfuric acid, and hydrochloric acid, and salts thereof. Preferably, the conductive inorganic acid and its salt are selected from phosphoric acid and potassium dihydrogen phosphate, sodium dihydrogen phosphate, potassium phosphate, sodium phosphate, and mixtures thereof. Preferably, phosphoric acid is added when using potassium phosphate.

Alkaline compounds can also be added to maintain the pH of the composition at the desired level of 5 to 6.8, preferably 5.8 to 6.7, more preferably 6 to 6.3. Such alkaline compounds include, but are not limited to hydroxides, carbonates, and other salts of sodium, potassium, and magnesium. For example, NaOH, KOH, K ₂ CO ₃ , Na ₂ CO ₃ , NaHCO ₃ , and mixtures thereof are suitable alkaline compounds. Typically, the alkaline material is included in an amount of 1 g / L to 100 g / L.

  An organophosphorus compound is included in the gold electroplating composition as a chelating agent for gold ions. They are deprotonated and chelated with gold ions within the pH range of the gold electroplating composition, the chelating ability of these compounds is that no free cyanide from potassium cyanide or sodium cyanide is added and the gold composition is It is good enough to stabilize.

  The organophosphorus compounds include those compounds having the formula:

Where n is an integer from 2 to 3 (including 2 and 3), M ₁ and M ₂ may be the same or different and are hydrogen, ammonium, 1 to 9 carbon atoms, preferably 1 Selected from lower alkyl amines having ˜5 carbon atoms, or alkali metal cations such as sodium, potassium, lithium, etc., preferably the alkali metal cation is potassium or sodium, Z is a valence of n and Are equal radicals, straight or branched chain substituted or unsubstituted (C ₁ -C ₁₂ ) alkyl, or N-substituted (C ₂ -C ₃ ) alkyl, and the Z radical is a phosphorus atom of formula (I) Has a carbon atom bonded to. Preferably Z is a linear or branched substituted or unsubstituted (C ₁ -C ₄ ) alkyl, wherein the substituent is hydroxyl. Such compounds are included in amounts of 5 g / l to 200 g / L, preferably 20 g / L to 150 g / L, more preferably 50 g / l to 120 g / L.

  A group of compounds falling within the general formula above includes aminotris (lower alkylidene phosphonic acids). Examples of such compounds include aminotri (methylenephosphonic acid), aminotri (ethylidenephosphonic acid), aminotri (isopropylidenephosphonic acid), aminodi (methylenephosphonic acid) mono (ethylidenephosphonic acid), aminodi (methylenephosphonic acid) Mono (isopropylidenephosphonic acid), aminomono (methylenephosphonic acid) di (ethylidenephosphonic acid), and aminomono (methylenephosphonic acid) diisopropylidenephosphonic acid.

  Lower alkylidene diphosphonic acid compounds within the above formula are methylene diphosphonic acid, ethylidene diphosphonic acid, isopropylene diphosphonic acid, isopropylidene diphosphonic acid, 1-hydroxyethylidene diphosphonic acid, 1-hydroxypropylidenedi Phosphonic acid and butylidene diphosphonic acid.

  Particularly preferred organophosphorus compounds are tetrapotassium 1-hydroxyethylidene diphosphonate, tetrasodium 1-hydroxyethylidene diphosphonate, and hydroxyethylene-1,1-diphosphonic acid.

  Antimony (III) ions are included as potassium antimony tartrate in combination with potassium sodium tartrate. Antimony (III) ions can be added as antimony chloride or antimony sulfate, but antimony (III) is preferably added as antimony tartrate. The salt of antimony (III) is added to the gold electroplating composition in an amount that provides 1 mg / L to 20 mg / L, preferably 5 mg / L to 15 mg / L of antimony (III) ions. Sodium potassium tartrate is added to the gold electroplating composition in an amount of 10 g / l to 50 g / L, preferably 15 g / l to 35 g / L. Additional tartaric acid can be added to the gold electroplating composition in the amounts specified for sodium potassium tartrate as tartaric acid, potassium tartrate, or other water soluble tartrate salts and compounds, although the most preferred tartaric acid source Is sodium potassium tartrate for preventing antimony (III) ions from oxidizing to antimony (V) ions. Without being bound by theory, the presence of antimony (III) ions can provide bright gold deposits even under jet plating conditions. In addition, antimony can provide a soft gold deposit.

  Optionally, the gold plating composition may include one or more organic acids such as citric acid, malic acid, oxalic acid, formic acid, or polyethyleneaminoacetic acid, or an inorganic acid such as phosphoric acid. Such acids help maintain the pH of the composition in the desired range. Typically, the acid is included in an amount of 1 g / L to 200 g / L.

  Optionally, a wide variety of additional gold chelates or complexing agents can be included in the composition. Suitable gold complexing agents include thiosulfates such as thiosulfuric acid, sodium thiosulfate, potassium thiosulfate, potassium sorbate, and ammonium thiosulfate, ethylenediaminetetraacetic acid and its salts, iminodiacetic acid, and nitrilotriacetic acid. However, it is not limited to these.

  One or more additional chelates or complexing agents may be added in conventional amounts, such as in amounts of 1 g / L to 100 g / L, or in amounts of 10 g / L to 50 g / L. One or more complexing agents are generally commercially available or can be prepared by methods well known in the art.

The composition may also include one or more surfactants. Any suitable surfactant can be used in the composition. Such surfactants include, but are not limited to, alkoxyalkyl sulfuric acid (alkyl ether sulfuric acid) and alkoxyalkyl phosphoric acid (alkyl ether phosphoric acid). Alkyl and alkoxy groups typically contain from 10 to 20 carbon atoms. Examples of such surfactants are sodium lauryl sulfate, sodium capryl sulfate, sodium myristyl sulfate, sodium ether sulfate of C ₁₂ -C ₁₈ linear alcohols, sodium lauryl ether phosphate, and the corresponding potassium salts.

Other suitable surfactants that can be used include, but are not limited to, N-oxide surfactants. Such N-oxide surfactants include cocodimethylamine N-oxide, lauryldimethylamine N-oxide, oleyldimethylamine N-oxide, dodecyldimethylamine N-oxide, octyldimethylamine N-oxide, bis- (hydroxy Ethyl) isodecyloxypropylamine N-oxide, decyldimethylamine N-oxide, cocamidopropyldimethylamine N-oxide, bis (hydroxyethyl) C ₁₂ -C ₁₅ alkoxypropylamine N-oxide, lauramine N-oxide, laurami - de propyldimethylamine N- _oxide, C 14 _{-C 16} alkyldimethylamine N- oxides, N, N- dimethyl (hydrogenated tallow alkyl) amine N- oxides, isostearamide propyl morpholine N- Oki De, and including isostearamide propyl pyridine N- oxides thereof.

  Other suitable surfactants include, but are not limited to, betaines and alkoxylates such as ethylene oxide / propylene oxide (EO / PO) compounds. Such surfactants are well known in the art.

  Many of the surfactants can be obtained commercially or can be made by methods described in the literature. Typically, the surfactant is included in the composition in an amount of 0.1 g / L to 20 g / L.

  The components of the composition can be combined by any suitable method known in the art. Typically, the components are mixed in any order and the composition is brought to the desired volume by adding sufficient water. Some heating may be required to solubilize certain composition components. The gold electroplating composition is substantially free of arsenic, lead, thallium, hydrazine, and sulfite. In general, substantially free means that metals, hydrazine, and sulfites are not readily detectable with most conventional analyzers, or if they are detectable, they are at a level of 100 ppb or less. means.

  In general, the current density can range from 0.03 ASD to higher using DC or pulse plating. For barrel plating applications, the current density can be 0.05 ASD to 2.5 ASD using DC current. The gold ion concentration preferably ranges from 4 g / L to 8 g / L. For rack plating applications, the current density can range from 0.05 ASD to 4 ASD using DC current. The gold ion concentration preferably ranges from 8 g / L to 12 g / L, but the applicable current density is 6 ASD for rack plating when using a pulsed current with an on: off time of 1: 3 milliseconds. Can be expanded. In the case of jet plating with a jet plating facility, the gold ion concentration preferably ranges from 12 g / L to 20 g / L. The glossy deposit is obtained from a pulse peak current of 2 ASD to 70 ASD and an on: off pulse parameter of 1: 1 to 1: 4 milliseconds. Jet agitation can vary from 100 L / hr to 1000 L / hr depending on the applied current density. It is preferred to use high agitation at higher pulse peak currents. The present soft gold electroplating composition can be used in rack plating, barrel plating, and high speed jet plating by adjusting the gold concentration and plating parameters. Unlike many conventional pure gold electroplating compositions, the gold electroplating composition can be used with jet plating equipment for high speed gold deposition. Jet plating or high current density plating provides faster and higher electroplating efficiency in the production line than low current density plating. Such a high speed jet plating process is highly desirable for mass production.

  In addition to providing a bright deposit at a high current density, the present soft gold electroplating composition deposit is a substantially uniform soft gold deposit. Gold hardness is typically expressed as a Knoop hardness value and represents the average of a number of tests using a 25 gram indenter. The Knoop hardness value, when plated, is a gold grade B of 91-129 according to ASTM B488-11. After annealing, the Knoop hardness value is 78 or gold grade A. The purity of the gold deposit is 99.9%, which is type III purity.

  The plating time can vary. The amount of time depends on the desired thickness of gold on the substrate. Typically, the gold thickness is from 0.01 microns to 50 microns, such as from 0.1 microns to 2 microns, or from 0.2 microns to 0.5 microns.

  Conventional gold plating equipment can be used to electroplate gold onto the substrate. The anode is an insoluble anode such as stainless steel, platinum, platinum-clad tantalum, platinized titanium, and graphite. Preferably, the anode is a platinized titanium anode.

  The soft gold electroplating composition may be used to electroplate gold layers on metals such as nickel, nickel alloys, copper, copper alloys, tin, and tin alloys. Preferably, the gold electroplating composition is used to electroplate gold on nickel and nickel alloys such as contacts, connectors, switches, and printed circuit boards. The gold electroplating composition can also be used to plate a gold layer on decorative articles such as jewelry. The gold electroplating composition can also be used to plate a strike layer on a substrate to enhance adhesion between metal layers.

  The present soft gold electroplating composition is environmentally friendly and can deposit bright gold deposits over an applicable current density range using DC or pulsed current and under barrel, rack or jet plating conditions. The gold deposit also has a particulate structure. Small particle size reduces porosity within the thin film. The luminous intensity of the deposit is also a direct result of this small particle size. In general, the roughness of a matte or semi-gloss deposit is high compared to a smooth gloss deposit.

  The following examples are intended to illustrate the invention and are not intended to limit its scope.

Example 1
A water-soluble soft gold electroplating bath having the following composition was prepared.

Five test panels of copper pre-plated with 15 × 20 mm ² on both sides with nickel were immersed in a 500 mL bath of this soft gold electroplating bath for 3 minutes, and gold was plated on nickel. The anode was a platinized titanium electrode. The bath was stirred for 3 minutes using a magnetic stirrer. The bath had a pH of 6.2 and the bath temperature was 55 ° C. DC current was applied at a current density of 1 ASD. After 3 minutes, the coupon was removed from the bath, rinsed with deionized water and allowed to air dry. The gold deposit was glossy. The thickness of the gold deposit was measured with a FISCHERSCOPE ™ X-ray instrument, model XDV-SD, and determined to be 1.7 microns. The panel was then analyzed for the microstructure of the gold deposit using a SEM microscope at a magnification of 20,000. FIG. 1 shows one of the SEMs obtained with this microscope. SEM showed a small grain structure.

Example 2 (comparison)
A water-soluble gold electroplating bath having the following formula was prepared.

Five copper test panels pre-plated with nickel on both sides of 15 × 20 mm ² were immersed in a 500 mL gold electroplating bath for 3 minutes, and gold was plated on nickel. The anode was a platinized titanium electrode. The bath was stirred for 3 minutes using a magnetic stirrer. The bath had a pH of 6.2 and the bath temperature was 55 ° C. DC current was applied at a current density of 1 ASD. After 3 minutes, the coupon was removed from the bath, rinsed with deionized water and allowed to air dry. The gold deposit thickness was 1.7 microns. The panel was then analyzed for the microstructure of the gold deposit using a SEM microscope at a magnification of 20,000. FIG. 2 shows one of the SEMs obtained with this microscope. SEM showed a coarse grain structure. This microstructure was consistent with the optical appearance of the deposit that was semi-glossy. The grain structure and optical appearance of the gold plated from Table 2 includes the antimony (III) derived from potassium antimony tartrate together with sodium potassium tartrate, and electroplating the test panel with gold derived from an electroplating bath that does not contain lead. It was inferior to that of the gold electroplating composition of Example 1.

Example 3
Eight copper test panels pre-plated with 15 × 20 mm ² of nickel on both sides were separately immersed in a 500 mL bath containing a gold electroplating bath having the formulation in Table 1 of Example 1. The anode was a platinized titanium electrode. Electroplating of gold on nickel was performed for 3 minutes in each bath. The bath was stirred using a magnetic stirrer for the entire plating time. The bath had a pH of 6.2 and the bath temperature was 55 ° C. DC current was applied at various current densities by each panel. The current densities were 0.5 ASD, 1.2 ASD, 1.5 ASD, 2 ASD, 2.5 ASD, 3 ASD, 3.5 ASD, and 4 ASD. After plating, the panel was removed from the bath, rinsed with deionized water and allowed to air dry. All gold deposits had a glossy appearance.

  The electroplating process described above was repeated except that the gold electroplating bath of Table 2 of Example 2 was used. After plating, gold deposits electroplated at 0.5 ASD to 3 ASD had semi-gloss deposits, while gold plated at 3.5 ASD and 4 ASD had a hazy matte appearance. The results showed that the gold electroplating baths in Table 1 have improved plating performance over the lead containing the gold electroplating baths in Table 2 with respect to applicable current density and appearance.

Example 4
A soft gold electroplating bath as shown in the table below was prepared.

A copper test panel pre-plated with nickel on both sides of 15 × 20 mm ² was installed in a jet plating facility including 1000 mL of the soft gold electroplating bath shown in Table 3. The anode was a platinized titanium electrode. The bath had a pH of 6.2 and the bath temperature was 60 ° C. The pulse current was applied at a peak current density of 50 ASD with an on: off time of 1: 3 milliseconds. This corresponded to an average current density of 12.5 ASD. Jet agitation or flow rate was set at 800 L / hour. After a 10 second plating period, the panel was removed from the bath, rinsed with deionized water, and allowed to air dry. All panels had a shiny gold deposit.

  This process was repeated with the gold electroplating baths in Table 2 except that the amount of gold ions was 20 g / L gold. The same jet agitation and plating parameters described above were used. The appearance of the gold deposit was quite matte or burnt. This test was repeated except that the pulse peak current density was 30 ASD at the same flow rate as above. This corresponded to an average current density of 7.5 ASD. All deposits were matte. The electroplating baths in Table 2 do not provide high current density, bright or semi-glossy gold deposits under jet agitation and therefore this gold bath performs better than the gold plating baths in Table 3. Was inferior.

Claims (14)

  One or more gold ion sources derived from a gold cyanide salt, one or more phosphate ion sources, one or more phosphonic acid sources or salts thereof, potassium sodium tartrate, and one or more antimony (III) ion sources A gold electroplating composition comprising, wherein the gold electroplating composition does not contain free cyanide.   The gold electroplating composition according to claim 1, wherein the gold cyanide salt is selected from potassium gold cyanide, sodium gold cyanide, and ammonium gold cyanide.   The gold electroplating composition of claim 1, wherein the one or more phosphate ion sources are selected from phosphoric acid, sodium dihydrogenate, and potassium dihydrogen phosphate. The one or more phosphonic acids have the formula:
Wherein n is an integer from 2 to 3, M ₁ and M ₂ may be the same or different and are selected from hydrogen, ammonium, lower alkylamine, or alkali metal cation, and Z is A radical having a valence equal to n, a linear or branched substituted or unsubstituted (C ₁ -C ₁₂ ) alkyl, or N-substituted (C ₂ -C ₃ ) alkyl, wherein the Z radical is The said gold electroplating composition of Claim 1 which has the carbon atom couple | bonded with the phosphorus atom of Formula (I).   2. The gold electroplating composition of claim 1, wherein the one or more antimony (III) ion sources are selected from potassium antimony tartrate, antimony sodium tartrate, antimony sulfate, and antimony chloride.   The gold electroplating composition of claim 1, wherein the gold electroplating composition is substantially free of lead, arsenic, thallium, hydrazine, and sulfite. A method of electroplating gold,
a. One or more gold ion sources derived from a gold cyanide salt, one or more phosphate ion sources, one or more phosphonic acid sources or salts thereof, potassium sodium tartrate, and one or more antimony (III) ion sources A gold electroplating composition comprising: a gold electroplating composition substantially free of free cyanide;
b. Contacting a substrate with the gold electroplating composition;
c. Electroplating gold onto the substrate using direct current or pulsed current at a current density of 0.03 ASD or higher.   The method of electroplating the gold according to claim 7, wherein the current density is 1 ASD to 50 ASD.   The method of electroplating gold according to claim 7, wherein the gold cyanide salt is selected from potassium gold cyanide, sodium gold cyanide, and ammonium gold cyanide.   8. The method of electroplating gold according to claim 7, wherein the one or more phosphate ion sources are selected from phosphoric acid, sodium dihydrogen phosphate, and potassium dihydrogen phosphate. The one or more phosphonic acids have the formula:
Wherein n is an integer from 2 to 3, M ₁ and M ₂ may be the same or different and are selected from hydrogen, ammonium, lower alkylamine, or alkali metal cation, and Z is A radical having a valence equal to n, a linear or branched substituted or unsubstituted (C ₁ -C ₁₂ ) alkyl, or N-substituted (C ₂ -C ₃ ) alkyl, wherein the Z radical is The method of electroplating gold according to claim 7, wherein the gold atom has a carbon atom bonded to a phosphorus atom of formula (I).   8. The method of electroplating gold according to claim 7, wherein the one or more antimony (III) ion sources are selected from potassium antimony tartrate, antimony sodium antitartrate, antimony sulfate, and antimony chloride.   8. The method of electroplating gold according to claim 7, wherein the gold electroplating composition is substantially free of free cyanide, lead, arsenic, thallium, hydrazine, and sulfite.   8. The method of electroplating gold according to claim 7, wherein the substrate is a printed circuit board, a contact for a connector, a switch, or a decorative article.