阅读说明：本技术 用于制备金和银的层的水性制剂 (Aqueous preparation for producing gold and silver layers ) 是由 洛塔尔·迪特里希 莫滕·布林克 赫尔曼·奥佩尔曼 于 2020-03-03 设计创作，主要内容包括：本发明涉及无氰化物制剂,其用于在导电基材上电沉积金和银的层,其中所述制剂分别包含选自亚硫酸盐和硫代硫酸盐的络合剂,其特征在于,添加至少一种来自第5副族或第6副族的过渡金属的可溶含氧酸形式以提高镀液稳定性。(The invention relates to cyanide-free preparations for the electrodeposition of gold and silver layers on electrically conductive substrates, wherein the preparations each contain a complexing agent selected from the group consisting of sulfites and thiosulfates, characterized in that at least one soluble oxyacid form of a transition metal from the 5 th or 6 th subgroup is added in order to increase bath stability.)

1. A cyanide-free, metal salt-containing aqueous formulation for electrodeposition of layers of gold and silver on electrically conductive substrates, the formulation comprising or consisting of:

at least one gold salt and at least one silver salt,

at least one first complexing agent selected from thiosulfate salts,

at least one second complexing agent selected from sulfites, and

at least one soluble oxo acid of a transition metal selected from groups 5 (vanadium group) and 6 (chromium group) of the periodic Table of the elements.

2. The formulation of claim 1, wherein the group 5 and group 6 transition metals are selected from the group consisting of vanadium, chromium, molybdenum, and tungsten.

3. Formulation according to any one of the preceding claims, characterized in that at least one oxoacid of a transition metal is contained in the form of its soluble salt, preferably Vanadate (VO)₃ ^-) Orthovanadate (VO)₄ ^3-) Chromate (CrO)₄ ^2-) Or dichromate (Cr)₂O₇ ^2-) Molybdate (MoO)₄ ^2-) Or tungstate (WO)₄ ^2-) (ii) a Andor in its independent metal acid form, preferably molybdic acid (H)₂MoO₄) Or tungstic acid (H)₂WO₄) (ii) a And/or in the form of their anhydrides, preferably vanadium (V) pentoxide₂O₅) Chromium trioxide (CrO)₃) Molybdenum trioxide (MoO)₃) Or tungsten trioxide (WO)₃)。

4. Formulation according to any one of the preceding claims, characterized in that the concentration of the oxoacid of at least one transition metal comprised is between 0.1 and 1000mmol/l, preferably between 1 and 50 mmol/l.

5. The formulation according to any one of the preceding claims,

the gold is contained in the form of monovalent gold cations, preferably gold sodium sulfite (Na)₃Au(SO₃)₂) Gold ammonium sulfite ((NH)₄)₃Au(SO₃)₂) Or a combination thereof, and/or

The silver is in the form of monovalent silver cation, preferably silver chloride (AgCl), silver bromide (AgBr), silver iodide (AgI), silver carbonate (Ag)₂CO₃) Silver acetate (Ag (CH)₃COO)), silver thiosulfate (Ag₂S₂O₃) Or a combination thereof.

6. The formulation according to any one of the preceding claims,

the gold is contained in a concentration of 2g/l to 60g/l, preferably 8g/l to 24g/l, and/or

The silver is contained in a concentration of 2g/l to 60g/l, preferably 6g/l to 18 g/l.

7. Formulation according to any one of the preceding claims, characterized in that the first complexing agent comprised from the group of thiosulfates is a salt of thiosulfuric acid, preferably an ammonium, sodium or potassium salt.

8. Formulation according to any one of the preceding claims, characterized in that the first complexing agent chosen from thiosulfates is included in excess with respect to the total amount of gold and silver, preferably in a concentration of 0.2 to 1.5mol/l, more preferably 0.5 to 1.0 mol/l.

9. Formulation according to any one of the preceding claims, characterized in that the second complexing agent comprised from the group of sulfites is a salt of sulfurous acid or of metabisulfite, preferably an ammonium, sodium or potassium salt.

10. Formulation according to any one of the preceding claims, characterized in that the second complexing agent chosen from sulphites is comprised in a concentration of 0.1 to 1mol/l, preferably 0.2 to 0.5 mol/l.

11. Formulation according to any one of the preceding claims, characterized in that it comprises at least one buffer substance chosen from aliphatic polycarboxylic acids, preferably oxalic acid, malonic acid or succinic acid; hydroxycarboxylic acids, preferably malic acid, tartaric acid, glycolic acid, gluconic acid, lactic acid or citric acid; polyprotic weak mineral acids, preferably phosphoric acid or carbonic acid, wherein the buffer substance is contained in a concentration preferably ranging from 1g/l to 100g/l, more preferably from 5g/l to 25 g/l.

12. Formulation according to any one of the preceding claims, characterized in that it comprises at least one substance chosen from polymeric carboxylic acids, preferably acrylic polymers (I), methacrylic polymers (II) or acrylic-maleic copolymers (III) of the general formula,

wherein, for the acrylic polymer (I), R₁、R₂And R₃Are each a hydrogen ion, and are,

for the methacrylic acid polymer (II), R₁And R₃Are each a methyl group,R₂is a hydrogen ion, and

for the acrylic acid-maleic acid copolymer (III), R₁And R₃Are each a hydrogen ion, R₂Is a carboxyl group.

13. Formulation according to any one of the preceding claims, characterized in that the concentration of said at least one substance is between 1 and 100g/l, preferably between 5 and 50 g/l.

14. Formulation according to any one of the preceding claims, characterized in that it comprises at least one substance chosen from ketocarboxylic acids in acid or salt form, preferably acetoacetic acid, oxaloacetic acid, α -ketoglutaric acid, 2-ketobutyric acid or levulinic acid, wherein the concentration of said at least one substance is preferably comprised between 1 and 100g/l, preferably between 5 and 25 g/l.

15. Formulation according to any one of the preceding claims, characterized in that its pH is between 6.5 and 12, preferably between 7 and 9.

16. A formulation according to any preceding claim, comprising at least one grain refining additive which inhibits metal deposition and prevents crystal growth.

17. Formulation according to any one of the preceding claims, characterized in that it comprises at least one surfactant additive chosen from anionic, cationic, amphoteric or nonionic surfactants.

18. A method for electrodepositing a layer of gold and silver on an electrically conductive substrate using a formulation according to any one of the preceding claims, wherein the substrate is fully or partially immersed in the formulation and a voltage is applied between the cathodically polarised substrate and at least one anodically polarised counter electrode.

19. Method according to the preceding claim, characterized in that the substrate is directly exposed to the solution, at least in the area of the surface to be coated, using a suitable nozzle or paddle-like device.

20. Method according to either of the two preceding claims, characterized in that the substrate comprises a substantially sheet-like metallic or metallized workpiece, such as a printed circuit board, a semiconductor substrate, a film substrate or a ceramic plate, and the surface to be coated is partly masked or unmasked by the non-conductive layer.

21. A method according to any one of claims 18 to 20, characterised in that the deposition of gold and silver is carried out simultaneously and the gold content of the deposited layer or deposited deposit is 15 to 85 wt.%, preferably 25 to 50 wt.%.

Technical Field

The invention relates to cyanide-free preparations for the electrodeposition of gold and silver layers on electrically conductive substrates, wherein the preparations each contain a complexing agent from the group of sulfites and thiosulfates, characterized in that at least one soluble oxyacid form of a transition metal from transition group 5 or 6 is added for increasing bath stability.

The invention also relates to an electroplating method for producing an alloy deposit using the formulation according to the invention, which is carried out by immersing a substrate to be coated in a process solution and applying an electric field between a cathodically polarized substrate and at least one anodically polarized counter electrode while reducing gold and silver ions on the substrate surface.

SUMMARY

The present invention relates to the field of aqueous electrolytes for the electrodeposition of metals, in particular cyanide-free electrolytes for the electrodeposition of alloys of gold and silver. Depending on the type of substrate used, the deposition can be carried out as follows: in the form of a layer in the case of full-face coating or in the form of a separate deposit in the case of partial coating on a masked surface.

Such galvanically produced deposits are particularly suitable for use in assembly and connection technology in microelectronics, and in microsystems technology. In this field of application, thin metal layers are used in the form of conductor circuit planes for the construction of semiconductors, in the form of contact structures for connecting active and passive semiconductor components, but also in the form of defined rigid or movable microstructures for producing actuators and sensors.

The deposited gold deposit is peculiar in that it is capable of chemically or electrochemically rendering porous gold to have a skeletal structure by selective etching of silver. The formation of the open-porous structure by alloying takes place on a gold alloy with a silver content of about 20 to 50% by weight and is based on the surface diffusion of gold atoms. Gold deposits produced in this way have a low density and a large active surface, which not only allow applications in novel chip connection technology, but also provide diverse substrate surfaces for use in sensor technology applications, for example for chemisorption and physisorption processes, or for biotechnological applications, for example for connecting living organic materials.

In contrast to other manufacturing processes, electroplating methods are characterized by the precise patterning of the mask openings, for example by forming photoresist through photolithography structures. Side opening sizes of less than 1 micron and opening sizes of a few millimeters can be molded. Depending on the application, layer thicknesses from tens of nanometers up to tens of micrometers are required. The pH of the electrolyte is from weakly to weakly acidic to facilitate the specific purpose of electrodeposition in pre-fabricated masks made with aqueous alkaline developable photoresist systems.

Background

Stable aqueous electrolytes for depositing gold and silver are typically cyanide-based, with gold bound as a cyanoaurate complex and silver bound as a cyanoargentate complex. Such baths are described, for example, in WO 02/101119 or CH 629259.

For conducting properties, such electrolytes contain inorganic and/or organic acids and their salts. The formulation described in CH 629259 contains potassium pyrophosphate as the conducting salt.

In order to retard the time-dependent and light-induced mechanisms of silver deposition, other stabilizers such as amino acids or large amounts of free cyanide are generally added. In WO 02/101119 a large amount of free cyanide in the form of a potassium salt is added to the electrolyte.

In order to be able to deposit closed and fine-grained layers from such electrolytes at direct voltage, the solutions are usually mixed with certain organic compounds as gloss additives or leveling agents. Such inhibitors expand the range of current densities available for the manufacture of homogeneous and fine crystal layers and/or shift this range towards higher current densities. The use of higher current densities may in turn enable higher deposition rates. WO 02/101119 describes mixtures of dithiocarbamyl dithiohydrazines and xanthates which can be used as gloss-forming additives, in particular in cyanide gold and silver electrolytes. CH 629259 proposes the use of alkylene polyamines and alkylene imine polymers as bath additives to achieve a glossy alloy layer of gold and silver.

The use of toxic cyanide in aqueous process solutions is known to pose potentially high risks to manufacturers and users, particularly in the transportation of hazardous cargo, operational safety protection and waste disposal. To overcome these difficulties, great efforts have been made in the past decades to develop cyanide-free formulations for the electrodeposition of gold and silver. Although suitable complexing agents have been found only for the deposition of gold or silver, no stable formulation has been developed for technical use to simultaneously deposit gold and silver to make an alloy layer. None of these new systems enter into practical electroplating technology and have not been implemented industrially to date. As an alternative to the thiosulfate and sulfite based electrolyte systems according to the invention, the other organic complexing agents do not show either a sufficiently strong noble metal complexing action or a sufficiently high electrolytic stability.

Disclosure of Invention

Based on this, it was therefore an object of the present invention to find an improved formulation for stable aqueous solutions which, owing to the toxicity described above, does not contain cyanide and which makes it possible to achieve galvanic deposition of alloys of gold and silver in as large a concentration range as possible. The stability of the solution must take into account the effects of air, light, heat and current so that during use the solution does not exhibit cloudiness and as little as possible deposition of elemental silver or other reaction products in the form of particles or deposits.

Furthermore, it is an object of the present invention to provide a method for depositing an alloy of gold and silver on a substantially plate-like or foil-like substrate, with which closed layer or isolated alloy deposits can be produced using the formulation according to the invention. In this case, a uniform, fine-grained and pore-free structure with a thickness of as low as 100 μm is required in the range of the maximum possible current density. Furthermore, the gold content in the alloy should be selectively adjusted over an extended concentration range of 15 to 85 wt.%.

This object is achieved on the basis of a cyanide-free, metal salt-containing aqueous formulation having the features of claim 1 and with a method for the electrodeposition of gold and silver layers on electrically conductive substrates having the features of claim 18. The respective dependent claims represent advantageous developments.

The invention therefore relates to cyanide-free, aqueous preparations containing metal salts for the electrodeposition of gold and silver layers on electrically conductive substrates, comprising at least one gold salt and at least one silver salt; and at least two types of complexing agents, namely at least one first complexing agent selected from thiosulfates and at least one second complexing agent selected from sulfites. Furthermore, the preparation comprises at least one soluble oxoacid of a transition metal of group 5 (vanadium group) and group 6 (chromium group) of the periodic table of the elements.

A cyanide-free system is therefore selected in which monovalent gold ions and monovalent silver ions are preferably present in a mixed alkaline solution, preferably in a weakly alkaline solution, together with sulfite and thiosulfate.

For this purpose, gold is used in the form of a metabisulphite aurate complex, preferably gold sodium sulfite (Na)₃Au(SO₃)₂) Gold ammonium sulfite ((NH)₄)₃Au(SO₃)₂) Or a combination thereof.

Silver and one of its ligands as silver thiosulfate (Ag)₂S₂O₃) Or in the form of a silver (I) salt, preferably silver chloride (AgCl), silver bromide (AgBr), silver iodide (AgI), silver carbonate (Ag)₂CO₃) Silver acetate (Ag (CH)₃COO)) or combinations thereof, dissolved as a dithiosulfate silver salt complex by adding thiosulfate to an aqueous solution in a stoichiometric ratio of at least 1 part thiosulfate to 1 part silver.

Since the mixed complexes of noble metals formed in the presence of sulfite and thiosulfate alone do not have sufficient stability and decompose spontaneously in a relatively short time frame, other effective stabilizers must be found and added to extend the useful life of the aqueous solution.

In a first development of the formulation, an excess of further thiosulfate ions is added to the aqueous solution containing the complexed gold and silver ions. The free thiosulfate ion changes the equilibrium of the complex reaction with gold and silver, favoring the activity of the complex. Salts of thiosulfuric acid, preferably ammonium, sodium or potassium salts, can be added as thiosulfates in this process. Advantageous concentrations for the use of these compounds in the gold/silver electrolyte according to the invention are in the range from 0.2mol/l to 1.5mol/l, preferably from 0.5mol/l to 1 mol/l.

In a second development of the formulation, an excess of further sulfite ions is added to the aqueous solution containing complexed noble metal ions and free thiosulfate ions. The free sulfite ions stabilize the thiosulfate and prevent sulfur deposition in the noble metal complex. In this process, the sulfite may be added as a salt of sulfurous acid or a salt of metabisulfite, preferably an ammonium, sodium or potassium salt. Advantageous concentrations for the use of these compounds in the gold/silver electrolyte according to the invention are in the range from 0.1mol/l to 1mol/l, preferably from 0.2mol/l to 0.5 mol/l.

It has surprisingly been found that further improvements in the formulation are achieved if soluble oxo acids of transition metals of transition groups 5 and 6 of the periodic table, in particular soluble oxo acids of vanadium, chromium, molybdenum and tungsten, which have the function of stabilizers which extend the service life, are added to cyanide-free electrolytes based on thiosulfates and sulfites for the deposition of alloys of gold and silver. The transition metal oxoacids can be added in the form of their soluble salts, preferably Vanadates (VO)₃ ^-) Orthovanadate (VO)₄ ^3-) Chromate (CrO)₄ ^2-) Or dichromate (Cr)₂O₇ ^2-) Molybdate (MoO)₄ ^2-) Or tungstate (WO)₄ ^2-) And/or may be added in the form of its separate metal salt, preferably molybdic acid (H)₂MoO₄) Or tungstic acid (H)₂WO₄) Or in the form of anhydrides of these metal acids, preferably vanadium pentoxide (V)₂O₅) Chromium trioxide (CrO)₃) Molybdenum trioxide (MoO)₃) Or tungsten trioxide (WO)₃). The concentration of these substances contained in the preparations according to the invention may be from 0.1mmol/l to 1000mmol/l, preferably from 1mmol/l to 50mmol/l, but up to the limit of their solubility.

It has also been discovered, by chance, that polymeric carboxylates have a beneficial effect on bath stability. These additions can achieve buffering of free hydroxide ions and dispersion of elemental silver in a synergistic manner, resulting in improved pH stability of the solution and further reduced tendency to form precipitates. Accordingly, the formulations according to the invention may comprise at least one substance selected from the group consisting of polymeric carboxylic acids, in particular acrylic polymers (I), methacrylic polymers (II) or acrylic-maleic copolymers (III) of the general formula (IV):

wherein in the substance (I), R₁、R₂And R₃Respectively, is a hydrogen ion, in the substance (II), R₁And R₃Are each methyl, and R₂Is a hydrogen ion, and in substance (III), R₁And R₃Are each a hydrogen ion, and R₂Is a carboxyl group. The multiples "x" and "y" are determined by the average chain length of the polymer and can take any value. The bath additive according to formula (IV) has sufficient water solubility and the required electrochemical resistance. Advantageous concentrations for the use of these polymers in the gold/silver electrolytes according to the invention are in the range from 1g/l to 100g/l, preferably from 5g/l to 50 g/l.

In aqueous solution, free sulphite is oxidized to sulphate by dissolved air oxygen over time and temperature. In addition, free sulfite is also forced to oxidize during the electroplating coating process due to anodic reaction. It is well known that hydrocarbon compounds having functional aldehyde or ketone groups can counteract these undesirable reactions. Accordingly, at least one substance selected from the group consisting of ketocarboxylic acids, preferably acetoacetic acid, oxaloacetic acid, α -ketoglutaric acid, 2-ketobutyric acid or levulinic acid in its acid or salt form, can be added to the gold/silver electrolyte for delaying sulfite oxidation. Advantageous concentrations for the use of these compounds in the gold/silver electrolytes according to the invention are in the range from 1g/l to 100g/l, preferably from 5g/l to 25 g/l.

In order to buffer the pH of the aqueous solution and to maintain the alkalinity of the anodic film during electrodeposition, the formulation according to the invention may also comprise at least one buffer substance selected from aliphatic polycarboxylic acids, preferably oxalic acid, malonic acid or succinic acid; hydroxycarboxylic acids, preferably malic acid, tartaric acid, glycolic acid, gluconic acid, lactic acid or citric acid; preferably a polyprotic weak mineral acid of phosphoric acid or carbonic acid. Advantageous concentrations for the use of these compounds in the gold/silver electrolytes according to the invention are in the range from 1g/l to 100g/l, preferably from 5g/l to 25 g/l.

In order to specifically regulate the particle size, so-called grain refiners or so-called brighteners can be added to the preparations according to the invention. These substances inhibit crystal growth and generally lead to an increase in the polarization of the cathodic metal reduction.

To improve wetting, the preparations according to the invention may comprise further surface-active substances, as so-called wetting agents or surfactants, to reduce the surface tension of the solution. These organic substances may be present in solution as anionic, cationic, amphoteric or non-ionic molecules.

In order to set the desired gold content in the deposited alloy in the range of 15 to 85 wt.%, the formulation according to the invention may comprise gold in a concentration of 2 to 60g/l, preferably 8 to 24g/l, and silver in a concentration of 1 to 60g/l, preferably 3 to 15 g/l.

In addition to the precious metal content, other coating parameters, in particular variations in plating solution temperature, current density and inflow strength, can also affect the resulting alloy ratio. By varying the gold and silver ion concentrations in the process solution, the desired gold content in the deposited layer or the deposited deposit can be specifically adjusted. By varying at least one other coating parameter, preferably the current density, the temperature or the fluid flow, the alloy ratio is also influenced in the following manner: an increase in current density alone increases the gold content, and an increase in temperature or an increase in the inflow strength decreases the gold content. In the case of electroplating coated masked substrates, the resulting alloy fraction is also influenced by the design of the electroplating mask, where larger sized structures tend to have a gold-rich alloy, an increase in the density of the deposit results in a local gold enrichment inside the compressed regions, and an overall increase in the area fraction of the photo-etched open regions in the mask also results in an overall gold-richer deposit.

Because thiosulfate salts tend to decompose in acidic solutions, electroplating baths with formulations according to the present invention can operate in neutral or alkaline pH ranges. The pH of the aqueous solution may suitably be from 6.5 to 12, preferably from 7 to 9.

Furthermore, the invention relates to a method for electrodepositing a layer of gold and silver on a conductive substrate using the aforementioned formulation according to the invention. In the method according to the invention, the substrate is completely or partially immersed in the formulation and layers of gold and silver are deposited by applying a voltage between a cathodically polarized substrate and at least one anodically polarized counter electrode.

In the technical process, the substrate to be treated is brought into contact with the process solution according to the invention, so that the surface to be coated is completely wetted with liquid and flowed through by means of suitable devices to achieve uniform mass transport. This can be done, for example, by completely or partially immersing the substrate in a bath containing the liquid, or by fixing the substrate on the bath and exposing the liquid from below to the surface to be coated.

Suitable means for uniformly exposing the plate-like or sheet-like substrate are, for example, paddles or laminae which are moved parallel to the substrate surface. In other embodiments, the inflow may be achieved by one or more nozzles through which the electrolyte with increased liquid pressure is directed onto the substrate surface. In the case of an additional relative movement between nozzle and substrate, the static flow distribution can be counteracted and an improvement in the flow distribution can be achieved. In the simplest embodiment, the movement of liquid over the substrate surface is effected by circulation of a liquid reservoir in the electroplating bath by means of a stirrer or pump circuit.

For the purpose of galvanic metal deposition, an electric field is applied between the wetted substrate and at least one counter electrode located in an electrolyte, wherein noble metal ions are forced to reduce on the cathodically polarized substrate and oxidation reactions are forced to proceed on the anodically polarized counter electrode to achieve charge neutrality of the solution. The electric field may be in the form of a static, pulsed dc voltage or in the form of a pulsed rectification.

The counter electrode body used in the method according to the invention consists of a material that is insoluble in the electrolyte and has a low overvoltage for water decomposition, preferably of platinum, platinized titanium or a mixed metal oxide coated titanium-based material. In principle, almost any form of electrode body can be used, but preferably a flat anode or a mesh anode is used.

For the aforementioned gold and silver layers, many technical application areas can be envisaged. The layer can be used in surface technology for corrosion protection against oxidation-sensitive alkaline metals such as nickel or copper. Furthermore, the deposits produced with the formulations according to the invention can be used as electrical contact elements for connecting components of semiconductor and printed circuit board technology.

Another feature of the electrodeposited alloy deposits already mentioned is that porous gold sponges with nanometer-scale pore sizes can be produced by selective etching to remove the silver content. The low-density metal structures formed here can prove advantageous in various fields of application, for example as permeable supports in filtration technology, as compressive contact metals in chip connection technology, or in bionics and sensor technology. The use of gold sponge is also advantageous when the catalytic reaction takes place on the gold surface, since the metal surface is very large compared to the occupied substrate surface.

Detailed Description

The aqueous formulations according to the invention for the electrodeposition of gold and silver alloys are described in detail in the examples below.

Comparative example 1:

an aqueous solution having the following is prepared accordingly in a stoichiometric ratio of 1 part thiosulfate ion to 1 part noble metal ion:

4.7g/l gold in the form of sodium metabisulphite

Silver in the form of 6g/l silver chloride

19.7g/l sodium thiosulfate pentahydrate

And the pH was set to 7.9. First the solution was clear. If a conductive substrate and a platinum-plated counter electrode were immersed in the solution with the formulation according to example 1 and a voltage was applied at 40 ℃ so that a cathodic current density of 0.5A/dm was generated²The solution immediately turns brown.

Comparative example 2:

an aqueous solution was prepared with the same formulation as in example 1 and the pH was set to 7.9. First the solution was clear. After 12 days at 21 ℃ in a closed container under artificial light, a powdery black precipitate appeared.

Comparative example 3:

preparing an aqueous solution having:

7.5g/l gold in the form of sodium metabisulphite

Silver in the form of 7.5g/l silver chloride

90g/l sodium thiosulfate pentahydrate

30g/l sodium sulfite

And the pH was set to 8.0. First the solution was clear. After 12 days in a closed container at 21 ℃ under artificial light, only few black particles were deposited, while the solution remained clear.