CN108754553B - Trivalent gold cyanide-free gold plating solution based on heterocyclic alkaloid coordination and its application - Google Patents

Abstract

The invention discloses a trivalent gold cyanide-free gold plating electroplating solution based on the coordination of heterocyclic alkaloids and an application thereof. The electroplating solution includes a trivalent gold salt, a complexing agent, a pH buffer, an antifungal agent and additives. Among them, the chloroauric acid that provides trivalent gold is used as the main salt, the heterocyclic alkaloid is used as a complexing agent, the mixture of anhydrous potassium carbonate and dipotassium hydrogen phosphate trihydrate is used as a pH buffer, and sodium tetraborate or benzene Sodium formate or formaldehyde is an antifungal agent, and sulfur-containing organic matter is used as an additive. The gold salt of the cyanide-free gold plating solution of the present invention has convenient sources and outstanding comprehensive performance; the plating solution has good throwing ability; strong displacement resistance, and the fresh nickel-plated sheet is placed in the plating solution for 3 minutes without displacing the gold layer; Under the wide current density of ^0.1-1.2A /dm2, the obtained gold-plated layer has good bonding force with nickel and copper substrates, high brightness and uniform golden color; in addition, it also has the characteristics of simple preparation of plating solution and convenient and controllable gold-plating process.

Description

Trivalent gold cyanide-free gold plating solution based on heterocyclic alkaloid coordination and its application

technical field

The invention belongs to the technical field of cyanide-free gold plating, and specifically relates to a trivalent gold cyanide-free gold plating solution based on heterocyclic alkaloid coordination and an application thereof.

Background technique

Gold electroplating is widely used in electrical appliances, connectors, printed circuit boards, integrated circuits and decoration fields.

Common oxidation states of gold are trivalent and monovalent. During the reduction process of trivalent gold, first two electrons are obtained to reduce to monovalent gold, and then one electron is obtained to reduce to elemental gold. The reduction overpotential of simple and uncoordinated trivalent gold ions is small, and the resulting gold deposit particles are relatively coarse and may cause the inclusion of monovalent gold. In an aqueous solution without a complexing agent, monovalent gold is extremely prone to disproportionation reaction, turning into trivalent gold and elemental gold, which is difficult to exist stably.

In the cyanide gold plating solution, the cyanide ion is stably coordinated with the monovalent gold ion, so the plating solution is stable and the quality of the plating layer is good. Cyanide is highly toxic. Sodium gold sulfite solution is often used as the main salt of the cyanide-free monovalent gold plating solution. Gold sodium sulfite solution is not only poor in stability, it can usually only be stored for six months, and gold sodium sulfite is not sold in solid state, so it needs to be prepared by itself. In addition, when the concentration of sodium sulfite in the plating solution is too high, the gold plating layer is easy to contain sulfur and the stress increases and becomes brittle.

Trivalent gold ions have a higher positive charge and coordinate with ligands containing N, O, and S that can provide lone pairs of electrons. Due to the addition of the complexing agent, the reduction overpotential of gold is increased, and a finer gold plating layer can be obtained.

Chinese patent (CN 105420771 A) discloses a kind of with cysteine as the main ligand of gold, 2-thio-5,5-dimethylhydantoin, triethylamine, citric acid, cyclohexyl The monovalent gold cyanide-free gold-plating electroplating solution using hexaol as an auxiliary complexing agent improves the stability of the plating solution to a certain extent. In the existing research, in the cyanide-free gold plating process using cysteine as a complexing agent, a strong coordination bond is formed between cysteine and monovalent gold, and a plating layer of a certain thickness can be obtained. However, the above-mentioned cyanide-free gold plating process is all monovalent gold plating, and the main salt added is still a self-made sodium gold sulfite solution.

Chinese patent (CN 105112953 A) discloses a sodium gold sulfite as the main salt, and one or more of potassium sulfite, sodium metabisulfite, sodium dithionite, sodium thiosulfate and potassium thiosulfate as the main ingredient. Agents, ethylenediamine, organic phosphonic acid, pyridine, pyridine-3-sulfonic acid, aminopyridine, quinoline, quinolinic acid, quinoline-2-sulfonic acid, hydroxyquinoline, ethylenediaminetriacetic acid, ethylenediamine A cyanide-free gold plating solution in which one or more of amine diacetic acid, nitrotriacetic acid and iminodiacetic acid is used as an auxiliary complexing agent. Chinese patent (CN 105316718 A) discloses a sulfite cyanide-free pulse electroplating solution and an electroplating method with sulfite as the main complexing agent and alkali metal mercaptopropanesulfonate as the auxiliary complexing agent. Chinese patent (CN105937028 A) discloses a kind of sodium gold sulfite as main salt, sodium thiocyanate, thiosemicarbazide, ethylene thiourea, 2-amino-5-mercapto-1,3,4thiazole, 6 - One or more than two of mercaptopurine as soft base complexing agent, potassium pyrophosphate, melamine, sulfamate, iminodiacetic acid, glycine, tetraethylenepentamine, uridine, caffeine A compound cyanide-free gold plating solution in which one or more of ammonium citrate and tartaric acid are used as non-soft base complexing agents and a preparation method thereof. In the above-mentioned monovalent gold cyanide-free gold plating process, the main salt or complexing agent contains sulfur, and the total amount used is relatively large, so the obtained coating is likely to contain sulfur and may become brittle.

In addition, due to the lack of stability of monovalent gold, some studies have used chloroauric acid as the main salt source, hypoxanthine as a complexing agent, and polyethyleneimine as an additive to a cyanide-free gold plating system. Although the stability of the electroplating solution has been improved, the The pH value of the system is high, which is easy to cause corrosion of electroplating equipment.

In short, the current cyanide-free gold plating process or insufficient stability of the electroplating solution, or harsh electroplating conditions, or low-quality coatings, and easy-to-corrosion equipment all have defects that cannot meet the needs of electroplating processing. Therefore, it is of great practical significance to invent a trivalent gold cyanide-free gold plating process with outstanding comprehensive performance.

Contents of the invention

The purpose of the present invention is to overcome the deficiencies of the prior art, provide a trivalent gold cyanide-free gold plating solution based on heterocyclic alkaloid coordination and its application, and solve the problems in the above-mentioned background technology.

The technical solution adopted by the present invention to solve its technical problems is: trivalent gold cyanide-free gold plating electroplating solution based on heterocyclic alkaloid coordination, including trivalent gold salt, complexing agent, pH buffering agent, antifungal agent and additives ;

The trivalent gold salt is chloroauric acid containing trivalent gold;

The coordinating agent includes a first coordinating agent and a second coordinating agent, and the first coordinating agent and the second coordinating agent are mixed in a mass ratio of 2 to 4:1; the first coordinating agent The agent includes at least one of theobromine, aminophylline, theophylline and its alkali metal salt, ammonium salt, and the second complexing agent includes caffeine, 8-azaguanine, xanthine, 2,6-di At least one of aminopurine, thioguanine, 6-benzylaminopurine and their alkali metal salts and ammonium salts;

The pH buffering agent is a mixture of anhydrous potassium carbonate and dipotassium hydrogen phosphate trihydrate, and the anhydrous potassium carbonate and dipotassium hydrogen phosphate trihydrate are mixed in a mass ratio of 1:3 to 6;

Described antifungal agent comprises the one in sodium tetraborate, sodium benzoate, formaldehyde;

The additive includes a first additive and a second additive, the first additive includes one of pyridine-3-sulfonic acid and 3-mercaptopropionic acid, and the second additive includes methionine, thiophene carboxylic acid, mercaptobutane At least one of acid and taurine, the mass ratio of the first additive to the second additive is 1-3:1.

In a preferred embodiment of the present invention, the mass concentration of the trivalent gold salt in the electroplating solution is 1-8.4 g/L, and the mass concentration of the trivalent gold ion is 0.5-4 g/L.

In a preferred embodiment of the present invention, the mass concentration of the complexing agent is 2-55 g/L, and the molar ratio to the concentration of the trivalent gold salt is 4.5-15:1.

In a preferred embodiment of the present invention, the mass concentration of the pH buffering agent is 20-110 g/L.

In a preferred embodiment of the present invention, the antifungal agent is one of sodium benzoate or formaldehyde, and its mass concentration is 0.5-5.5 g/L.

In a preferred embodiment of the present invention, the antifungal agent is sodium tetraborate with a mass concentration of 25-65 g/L.

In a preferred embodiment of the present invention, the electroplating solution further includes hydrochloric acid and potassium hydroxide for adjusting the pH value of the electroplating solution, and the pH value of the electroplating solution is 8.4-12.1.

The present invention also provides an electroplating method, using the electroplating solution as above, the electroplating process parameters include current density 0.1-1.2A/dm ² , the pH value of the plating solution is 8.4-12.1, the temperature of the plating solution is 30-70°C, and the thickness of the coating is 0.1～0.6μm, the anode is a platinum-plated titanium mesh, and the plating solution is stirred or circulated and filtered during electroplating.

In a preferred embodiment of the present invention, 20% hydrochloric acid or 20% potassium hydroxide aqueous solution is used to adjust the pH value of the electroplating solution.

In a preferred embodiment of the present invention, the temperature of the plating solution is 35-60°C.

Compared with monovalent gold ions, the advantage of choosing trivalent gold is that the electroplating solution will not deteriorate during long-term use, and trivalent gold ions can exist stably. According to density functional theory calculations, under the condition of aqueous solution, the total energy of the complex formed by the combination of trivalent gold and ligand is much lower than the total energy of the complex formed by the combination of monovalent gold and ligand. Stablize.

At present, the main salt of the monovalent gold cyanide-free electroplating solution on the market comes from the self-made sodium gold sulfite solution. During the storage process, sulfite will inevitably be oxidized or decomposed in contact with air, resulting in the deterioration of the solution. In addition, the process of preparing sodium gold sulfite is extremely cumbersome, which easily causes the loss of gold salt. The trivalent gold salt chloroauric acid is stable and can be purchased directly.

The heterocyclic alkaloid complexing agent has a heterocyclic aromatic structure, and the N atom in it has a large electronegativity and a bare lone pair of electrons. It can not only coordinate with trivalent gold, but also be adsorbed on the surface of the cathode, preventing the three The electro-reduction of valent gold increases the reduction overpotential of the trivalent gold cathode, thereby refining the coating grains and improving the coating quality. When the mass concentration of the heterocyclic alkaloid complexing agent is lower than 2g/L, gold hydroxide precipitation is prone to occur in the plating solution; when the mass concentration is higher than 55g/L, the cathodic hydrogen evolution reaction is intensified.

The addition of a mixture of anhydrous potassium carbonate and dipotassium hydrogen phosphate (trihydrate) can stabilize the pH value at 8.4 to 12.1 during the gold plating process. If the pH value is too high, it is easy to corrode the electroplating equipment; if the pH value is too low, the heterocyclic The alkaloids will precipitate out in solution.

Since the heterocyclic alkaloids are organic matter, the electroplating solution is prone to mold after standing for a long time, which can be significantly improved after adding an antifungal agent, and will not affect the quality of the plating layer. Sodium tetraborate not only has anti-mildew effect, but also has pH buffering effect.

The additive will be adsorbed on the surface of the cathode, and act as an electronic bridge to coordinate with trivalent gold, thereby inducing the reduction deposition of trivalent gold. In addition, additives can also make the coating brighter and the grains more compact.

If the current density is lower than 0.1A/dm ² , the coating brightness will be low and the deposition speed will be slow; if the current density is higher than 1.2A/dm ² , the coating will be burnt; if the temperature is lower than 35°C, the nucleation speed will be slower and the coating brightness will be low , the temperature is higher than 60 ° C, the heterocyclic alkaloids are easy to decompose.

Compared with the background technology, this technical solution has the following advantages:

1. The electroplating solution of the present invention has convenient sources, outstanding comprehensive performance, good throwing ability, and is suitable for thin gold electroplating with a thickness of 0.1 to 0.6 μm; it has strong anti-displacement ability, and fresh nickel-plated sheets are placed in the plating solution for 3 minutes. There will be a phenomenon of replacing the gold layer;

2. Heterocyclic alkaloids are coordinated with trivalent gold ions, combined with pH buffers, antifungal agents and additives of specific composition and content, to ensure the environmental protection and stability of the electroplating solution;

^3. Under the wide current density of 0.1～1.2A/dm2, the obtained gold plating layer has good bonding force with nickel and copper substrates, high brightness and uniform golden color;

4. Trivalent gold salt can be purchased directly, the preparation of electroplating solution is simple, and the gold plating process is convenient and controllable.

Description of drawings

Fig. 1 is the SEM topography figure (magnification 10000 times) of the coating of embodiment 1 of the present invention;

Fig. 2 is the EDS spectrogram and elemental composition of the coating of Example 1 of the present invention.

Detailed ways

The trivalent gold cyanide-free gold plating electroplating solution based on the coordination of heterocyclic alkaloids of the present invention comprises a trivalent gold salt, a complexing agent, a pH buffer, an antifungal agent and an additive; Hydrochloric acid, potassium hydroxide, the pH value of the electroplating solution is 8.4-12.1.

The trivalent gold salt is chloroauric acid containing trivalent gold; the mass concentration of the chloroauric acid in the electroplating solution is 1-8.4 g/L, and the mass concentration of trivalent gold ions is 0.5-4 g/L.

The complexing agent is a heterocyclic alkaloid complexing agent, including a first complexing agent and a second complexing agent, and the mass ratio of the first complexing agent and the second complexing agent is 2 to 4:1 Mixing ratio; the mass concentration of the complexing agent is 2-55g/L, and the molar ratio to the concentration of the trivalent gold salt is 4.5-15:1. The first complexing agent includes at least one of theobromine, aminophylline, theophylline and its alkali metal salt, ammonium salt, and the second complexing agent includes caffeine, 8-azaguanine, xanthine , at least one of 2,6-diaminopurine, thioguanine, 6-benzylaminopurine and their alkali metal salts and ammonium salts;

The pH buffer is a mixture of anhydrous potassium carbonate and dipotassium hydrogen phosphate trihydrate, and the anhydrous potassium carbonate and dipotassium hydrogen phosphate trihydrate are mixed in a mass ratio of 1:3 to 6; the pH buffer The mass concentration of the agent is 20-110g/L.

The antifungal agent includes one of sodium tetraborate, sodium benzoate and formaldehyde; when one of sodium benzoate or formaldehyde is selected, its mass concentration is 0.5-5.5g/L; when sodium tetraborate is selected, its mass concentration 25~65g/L, sodium tetraborate not only has anti-mold effect, but also has pH buffering effect.

The additive includes a first additive and a second additive, the first additive includes one of pyridine-3-sulfonic acid and 3-mercaptopropionic acid, and the second additive includes methionine, thiophene carboxylic acid, mercaptobutane At least one of acid and taurine, the mass ratio of the first additive to the second additive is 1-3:1.

The concrete preparation process of electroplating solution of the present invention is (taking preparation 1000mL as example):

① Accurately weigh the heterocyclic alkaloid complexing agent with a mass of 2-55g, add 20% potassium hydroxide aqueous solution, stir and dissolve;

② Add 1-8.4g of chloroauric acid containing trivalent gold ions to ①, stir to dissolve, and add deionized water to 500ml;

③Accurately weigh the pH buffer agent with a total mass of 20-110g, add it to ①, and adjust the pH value within the range of 8.4-12.1;

④Add 0.5-5.5g of antifungal agent sodium benzoate or formaldehyde, or 25-65g of sodium tetraborate to ①, and stir to dissolve evenly;

⑤ Continue to add 25-830 mg of additives to ①, and stir to dissolve evenly;

⑥Use 20% hydrochloric acid or 20% potassium hydroxide aqueous solution to adjust the pH value in the range of 8.4 to 12.1, and add an appropriate amount of deionized water to 1000ml.

The electroplating method of the present invention adopts the above-mentioned electroplating solution, and the electroplating process parameters include a current density of 0.1-1.2A/dm ² , a pH value of the plating solution of 8.4-12.1, a temperature of the plating solution of 30-70°C, and a coating thickness of 0.1-0.6 μm, the anode is a platinum-plated titanium mesh, and the plating solution is stirred or circulated and filtered during electroplating. Adjust the pH value of the electroplating solution with 20% hydrochloric acid or 20% potassium hydroxide aqueous solution.

With copper sheet as the base material, the process flow is: ultrasonic degreasing (50-70°C, time 3-5min) → water washing → pickling (dilute sulfuric acid with a mass concentration of 5%, 20-40s) → water washing → deionized water washing → Nickel electroplating → water washing → deionized water washing → gold electroplating.

Adopt electroplating solution of the present invention and above-mentioned operation condition, take platinum-plated titanium mesh as anode, nickel-plated copper sheet is negative electrode, and plating solution is stirred during electroplating, adopts three kinds of different electroplating solution composition and electroplating process parameter respectively, all can To obtain an ideal gold-plated layer, the specific implementation conditions and the performance of the obtained coating are shown in the following table:

Table 1 Electroplating solutions with different components and their electroplating effects (1000mL electroplating solution)

The appearance color of the gold coating was observed visually, and the coating was lemon yellow within the allowable range of the process; the thickness of the coating was obtained by an X-Ray thickness gauge; the microscopic morphology of the coating was observed through a scanning electron microscope (SEM).

Those skilled in the art will know that when the technical parameters of the present invention vary within the following ranges, the same or similar technical effects as those of the above-mentioned embodiments can be expected: when the substrate is made of clean copper, copper-nickel alloy, clean electroplated copper layer, Electroplated nickel layer, or clean electroless copper layer, electroless nickel layer, the result that obtains is identical with above-mentioned embodiment result.

The above is only a preferred embodiment of the present invention, so the scope of the present invention cannot be limited accordingly, that is, the equivalent changes and modifications made according to the patent scope of the present invention and the content of the specification should still be covered by the present invention within range.

Claims (9)

1. The trivalent gold cyanide-free gold plating solution based on the coordination of heterocyclic alkaloids is characterized in that: comprising trivalent gold salt, complexing agent, pH buffering agent, antifungal agent and additive; The trivalent gold salt is chloroauric acid containing trivalent gold; The coordinating agent includes a first coordinating agent and a second coordinating agent, and the first coordinating agent and the second coordinating agent are mixed in a mass ratio of 2 to 4:1; the first coordinating agent The agent includes at least one of theobromine, aminophylline, theophylline and its alkali metal salt, ammonium salt, and the second complexing agent includes caffeine, 8-azaguanine, xanthine, 2,6-di At least one of aminopurine, thioguanine, 6-benzylaminopurine and their alkali metal salts and ammonium salts; the mass concentration of the complexing agent is 2 to 55g/L, and the molar ratio of the concentration of the trivalent gold salt 4.5～15:1; The pH buffering agent is a mixture of anhydrous potassium carbonate and dipotassium hydrogen phosphate trihydrate, and the anhydrous potassium carbonate and dipotassium hydrogen phosphate trihydrate are mixed in a mass ratio of 1:3 to 6; Described antifungal agent comprises the one in sodium tetraborate, sodium benzoate, formaldehyde; The additive includes a first additive and a second additive, the first additive includes one of pyridine-3-sulfonic acid and 3-mercaptopropionic acid, and the second additive includes methionine, thiophene carboxylic acid, mercaptobutane At least one of acid and taurine, the mass ratio of the first additive to the second additive is 1-3:1. 2. The trivalent gold cyanide-free gold-plating electroplating solution based on heterocyclic alkaloid coordination according to claim 1, characterized in that: the mass concentration of the trivalent gold salt in the electroplating solution is 1 to 8.4 g/ L, the mass concentration of trivalent gold ions is 0.5-4g/L. 3. The trivalent gold cyanide-free gold plating solution based on heterocyclic alkaloid coordination according to claim 1, characterized in that: the mass concentration of the pH buffer is 20-110 g/L. 4. the trivalent gold cyanide-free gold-plating electroplating solution based on heterocyclic alkaloid coordination according to claim 1, is characterized in that: described antifungal agent is a kind of in sodium benzoate or formaldehyde, and its mass concentration is 0.5～5.5g/L. 5. The trivalent gold cyanide-free gold plating solution based on the coordination of heterocyclic alkaloids according to claim 1, characterized in that: the antifungal agent is sodium tetraborate, and its mass concentration is 25 ~ 65g/L . 6. the trivalent gold cyanide-free gold-plating electroplating solution based on heterocyclic alkaloid coordination according to claim 1, is characterized in that: also comprise hydrochloric acid, potassium hydroxide for regulating the pH value of electroplating solution, described electroplating The pH value of the solution is 8.4-12.1. 7. The electroplating method, characterized in that: the electroplating solution as claimed in any one of claims 1 to 6 is used, the electroplating process parameters include a current density of 0.1 to 1.2A/dm ² , the pH of the plating solution is 8.4 to 9.7, and the plating solution The temperature is 30-70°C, the thickness of the coating is 0.1-0.6 μm, the anode is a platinum-plated titanium mesh, and the plating solution is stirred or circulated and filtered during electroplating. 8. The electroplating method according to claim 7, characterized in that: the pH value of the electroplating solution is adjusted with 20% hydrochloric acid or 20% potassium hydroxide aqueous solution. 9. The electroplating method according to claim 7, characterized in that the temperature of the plating solution is 35-60°C.