A kind of gold immersion liquid for chemical gold plating and preparation method thereof

Abstract

The invention discloses a gold-plating solution for chemical gold plating and a preparation method thereof. The gold-plating solution comprises the following raw materials in parts by weight: 30-50 parts of a polymer corrosion inhibitor, 0.1-0.2 parts of a water-soluble gold salt, 0.4-0.8 parts of a complexing agent and 90-110 parts of deionized water. The gold-plating solution enhances the shielding and corrosion inhibition effects on material corrosion by selectively adsorbing on the surface of a metal and forming a barrier film for preventing corrosive ions from entering the interior of the metal; and partially quaternizes the corrosion inhibitor to compensate for the poor solubility of the polymer corrosion inhibitor; and further enhances the corrosion inhibition effect by the synergistic effect of the complexing agent and the corrosion inhibitor.

Description

Technical Field

[0001] The invention belongs to the field of chemical plating, and in particular relates to a gold immersion liquid used for chemical gold plating and a preparation method thereof. Background Art

[0002] As electronic products develop towards high frequency and high speed, the design of printed circuit boards (PCBs) used for signal transmission is also increasingly tending towards high frequency, high speed, high density and miniaturization. This dense and complex circuit working environment poses new challenges to the stability and reliability of the printed circuit board surface treatment process.

[0003] In order to ensure the reliability of the connection between the circuit board and electronic components and external circuits, the bare copper wire on the PCB surface usually requires final surface treatment. The process flow is to first perform chemical nickel plating on the surface of the exposed copper line, and then gold plating to obtain a Ni / Au composite coating.

[0004] Chemical gold plating is generally divided into reduction gold plating and displacement gold plating. Reduction gold plating is to reduce and deposit gold ions on the surface to be plated through the oxidation reaction of the reducing agent in the plating solution; displacement gold plating is to utilize the potential difference between the Ni layer and the gold ions to spontaneously carry out chemical displacement deposition in the absence of current. However, excessive corrosion of the nickel substrate during the gold plating process will cause welding failure problems on the treated circuit board, which is often manifested as brittle fracture and gray or black on the surface of the substrate nickel. Nickel layer corrosion has become a key factor affecting the quality of high-quality circuit boards. Patent CN113005437B discloses a chemical gold precipitation solution for printed circuit boards, including a variety of raw materials such as water-soluble gold salts, complexing agents, complexing stabilizers, pH buffers and corrosion inhibitors, which solves the palladium corrosion problem of conventional chemical palladium gold plating, but the selection of complexing agents in the invention is not environmentally friendly enough. Summary of the invention

[0005] The invention provides a gold immersion liquid for chemical gold plating and a preparation method thereof, which enhances the shielding and corrosion inhibition of material corrosion by forming a barrier film on the metal surface to prevent corrosive ions from entering the interior of the metal, and compensates for the poor solubility of the polymer corrosion inhibitor by partially quaternizing the corrosion inhibitor. In addition, the corrosion inhibition effect is enhanced by the synergistic effect of the complexing agent and the corrosion inhibitor.

[0006] To achieve the above object, the technical solution adopted by the present invention is:

[0007] On one hand, the present invention provides a gold immersion solution for chemical gold plating, which comprises the following raw materials by weight: 30-50 parts of a polymer corrosion inhibitor, 0.1-0.2 parts of a water-soluble gold salt, 0.4-0.8 parts of a complexing agent and 90-110 parts of deionized water.

[0008] In some embodiments, the preparation steps of the polymer corrosion inhibitor are as follows:

[0009] A1. Prepare a dopamine solution by mixing dopamine hydrochloride and deionized water, adjust the pH to 7.4-7.8, shake at room temperature, and introduce nitrogen for 10-20 minutes to obtain liquid A;

[0010] A2, adding dimethyl sulfate and anhydrous ethanol to the liquid A in step A1, reflux at 80-90° C. for 1-3 h, to obtain a liquid B containing reactant 1 and reactant 2;

[0011] A3. Cool the liquid B in step A2 to room temperature, adjust the pH to 8.5-9.5 and continue to shake for 6-8 hours to obtain a polymer corrosion inhibitor.

[0012] In some embodiments, the concentration of the dopamine solution in step A1 is 1.8-2.2 mg / mL.

[0013] In some embodiments, the shaking standard in step A1 is to stop shaking when the dopamine solution changes from colorless to light black liquid.

[0014] In some embodiments, the mass ratio of liquid A, dimethyl sulfate and anhydrous ethanol in step A2 is 1:(0.4-0.5):(4-8).

[0015] In some embodiments, the structural formula of reactant 1 in liquid B in step A2 is as follows:

[0016]

[0017] In some embodiments, the water-soluble gold salt is one or more of sodium gold sulfite, tetrachloroauric acid, and sodium gold thiosulfate.

[0018] In some embodiments, the preparation steps of the complexing agent are as follows:

[0019] Stir diethylenetriaminepentaacetic acid and anhydrous ethanol at 20-30°C for 20-30 minutes, then add allyl chloride, raise the temperature to 40-50°C, stir for 1-3 hours, rotary evaporate, wash and dry to obtain the complexing agent.

[0020] In the preparation step, the mass ratio of diethylenetriaminepentaacetic acid, anhydrous ethanol and allyl chloride is 1:(4-6):(0.58-0.64).

[0021] Another aspect of the present invention provides a method for preparing a gold immersion solution for chemical gold plating, comprising the following steps:

[0022] A water-soluble gold salt is added to deionized water and stirred until no solid is present to form a gold solution. A complexing agent is then added to the gold solution and stirred at 300-400 rpm for 1-2 hours. Finally, a polymer corrosion inhibitor is added and stirred for 1-3 hours to obtain the gold precipitation solution.

[0023] The Au in the gold solution + The concentration is 0.0045-0.0055mol / L.

[0024] Chemical gold plating is currently widely used in the surface treatment of PCBs. The prepared coating has excellent corrosion resistance, conductivity and solderability. However, the Ni layer is prone to over-corrosion during the gold plating process, resulting in welding failure problems on the PCB circuit board, which often manifests as fractures. Such situations can usually only be discovered after welding, thus causing huge losses to the processing party.

[0025] In order to avoid excessive corrosion of the nickel substrate during the gold plating process, there are generally two methods to solve the problem: surface modification of the nickel layer or adding corrosion inhibitors to the corrosive environment. Among them, corrosion inhibitors have the advantages of simple operation, quick effect and low cost. The present invention uses a self-made polymer corrosion inhibitor, the basic skeleton of which is polydopamine, which has a large number of functional adsorption centers, such as amino groups, hydroxyl groups, N heteroatoms and aromatic rings, etc. These effective sites, on the one hand, combine the ionic charge on the corrosion inhibitor with the charged metal surface through electrostatic attraction adsorption; on the other hand, through the presence of π electrons in heteroatoms and aromatic rings in the corrosion inhibitor, the lone pair of electrons and π electrons in the molecule share free electron pairs with the metal or charge transfer occurs, thereby generating a strong chemical bond and enhancing the adsorption capacity of the corrosion inhibitor on the metal surface. The two aspects work together to form a barrier film on the surface of the metal to prevent corrosive ions from entering the interior of the metal to enhance the shielding and corrosion inhibition of material corrosion.

[0026] In the process of preparing polymer corrosion inhibitors, compared with other traditional polymerization reactions, the reaction conditions of dopamine polymerization reaction are mild and green and environmentally friendly, and no initiator is required. Oxidative self-polymerization can occur in aqueous solution, but the solubility of polydopamine is poor, which makes it unable to play an ideal corrosion inhibition effect in gold sinking liquid. After studying the polymerization process of dopamine, it was found that dopamine will first be oxidized to dopamine-quinone, and then undergo intramolecular cyclization through Michael addition reaction, and then further oxidative rearrangement will form 5,6-dihydroxyindole. The present invention chooses to quaternize part of 5,6-dihydroxyindole by sulfate method after the second step oxidation of dopamine, making full use of the good solubility of quaternary ammonium salts to make up for the poor solubility of current polymer corrosion inhibitors.

[0027] Since 5,6-dihydroxyindole is easily oxidized to 5,6-indolequinone, the reaction solution needs to be passivated before the quaternization reaction to ensure that part of the 5,6-dihydroxyindole is successfully quaternized, and the remaining 5,6-dihydroxyindole and the generated 5,6-indolequinone are covalently connected between aromatic rings. Finally, during the oscillation process, the three are reversed by catechol and quinone to form a multi-crosslinked polymer. This method improves the water solubility of polydopamine and makes it easy to be adsorbed by negatively charged metal surface active atoms, thereby enhancing the corrosion inhibition effect of polydopamine.

[0028] Since the present invention adopts a cyanide-free gold plating system, the stability of the plating solution is slightly inferior to that of the cyanide gold plating system, and the plating solution is often manifested as gold precipitation and turbidity. Therefore, the present invention generates a complexing agent with a large number of vinyl groups and carboxyl groups through a nucleophilic reaction of diethylenetriaminepentaacetic acid and allyl chloride, and avoids the occurrence of gold precipitation in the plating solution through complexation.

[0029] In the nucleophilic reaction, the nitrogen atom of diethylenetriaminepentaacetic acid carries a lone pair of electrons and can act as a nucleophilic reagent. The polarization of the carbon-chlorine bond in allyl chloride makes the carbon atom carry a partial positive charge. Under the attack of the nucleophilic reagent, an ionic chloride ion is obtained. The chloride ion can form an intermediate bridge between the positively charged gold ion and the positive end of the corrosion inhibitor. Due to this ion pair interaction between the corrosion inhibitor and the chloride ion, the continuous dissolution of the metal is reduced, resulting in a synergistic corrosion inhibition effect.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] 1. The present invention provides a gold plating solution with corrosion inhibition effect, which avoids the excessive corrosion of the nickel substrate during the gold plating process.

[0032] 2. The present invention provides a corrosion inhibitor having a polymer skeleton and a large number of functional adsorption centers, which enhances the shielding and corrosion inhibition effects on material corrosion by selectively adsorbing on the surface of the metal and forming a barrier film that prevents corrosive ions from entering the interior of the metal.

[0033] 3. The present invention partially quaternizes the corrosion inhibitor to make up for the poor solubility of the polymer corrosion inhibitor, so that it can play an ideal corrosion inhibition effect in the gold precipitation liquid.

[0034] 4. The present invention generates a complexing agent having a large number of vinyl groups and carboxyl groups through the nucleophilic reaction of diethylenetriaminepentaacetic acid and allyl chloride, thereby improving the stability of the complex in the gold sinking solution.

[0035] 5. The present invention enhances the corrosion inhibition effect through the synergistic effect of the complexing agent and the corrosion inhibitor. DETAILED DESCRIPTION

[0036] The present invention will be described below in conjunction with specific embodiments. It should be noted that the following embodiments are examples of the present invention and are only used to illustrate the present invention, but not to limit the present invention. Other combinations and various modifications within the concept of the present invention may be performed without departing from the spirit or scope of the present invention.

[0037] Preparation Example 1

[0038] The preparation steps of polymer corrosion inhibitor-A are as follows:

[0039] A1. Prepare a dopamine solution by mixing 1 g of dopamine hydrochloride with 500 mL of deionized water. Adjust the pH to 7.8 with aqueous ammonia. Shake at room temperature. When the solution changes from colorless to light black liquid, stop shaking. Pass nitrogen gas for 15 minutes to obtain liquid A.

[0040] A2, adding 225g of dimethyl sulfate and 3000g of anhydrous ethanol to the liquid A in step A1, reflux at 85°C for 2h to obtain a liquid B containing reactant 1 and reactant 2;

[0041] A3. Cool the liquid B in step A2 to room temperature, adjust the pH to 9 with a 1 mol / L sodium hydroxide solution, and continue to shake for 6 hours to obtain a polymer corrosion inhibitor-A.

[0042] Preparation Example 2

[0043] The preparation steps of polymer corrosion inhibitor-B are as follows:

[0044] The difference between this preparation example and preparation example 1 is that 0.85 g of dopamine hydrochloride is used in step A1.

[0045] Preparation Example 3

[0046] The preparation steps of polymer corrosion inhibitor-C are as follows:

[0047] The difference between this preparation example and preparation example 1 is that 1.15 g of dopamine hydrochloride is used in step A1.

[0048] Preparation Example 4

[0049] The preparation steps of polymer corrosion inhibitor-D are as follows:

[0050] 1 g of dopamine hydrochloride and 500 mL of deionized water were prepared into a dopamine solution, the pH was adjusted to 9 with a 1 mol / L sodium hydroxide solution, and the solution was shaken at room temperature for 6 h to obtain a polymer corrosion inhibitor-D.

[0051] Preparation Example 5

[0052] The preparation steps of complexing agent-A are as follows:

[0053] 100 g of diethylenetriaminepentaacetic acid and 500 g of anhydrous ethanol were stirred at 30°C for 25 min, and then 61 g of allyl chloride was added. The temperature was raised to 45°C, and stirred for 2 h. The complexing agent A was obtained by rotary evaporation, washing, and drying.

[0054] Preparation Example 6

[0055] The preparation steps of complexing agent-B are as follows:

[0056] The difference between this preparation example and preparation example 5 is that 57 g of allyl chloride is added.

[0057] Preparation Example 7

[0058] The preparation steps of nucleating agent-C are as follows:

[0059] The difference between this preparation example and preparation example 5 is that 65 g of allyl chloride is added.

[0060] Example 1

[0061] A gold immersion liquid for chemical gold plating comprises the following raw materials in parts by weight: 40 parts of a polymer corrosion inhibitor-A, 0.15 parts of a water-soluble gold salt, 0.6 parts of a complexing agent-A and 100 parts of deionized water.

[0062] In this embodiment, a method for preparing a gold immersion solution for chemical gold plating comprises the following steps:

[0063] A water-soluble gold salt was added to deionized water and stirred until no solid was present to form a gold solution. Then, a complexing agent-A was added to the gold solution and stirred at a speed of 350 rpm for 1.5 hours. Finally, a polymer corrosion inhibitor-A was added and stirred for 2 hours to obtain the gold precipitation solution.

[0064] Example 2

[0065] A gold immersion liquid for chemical gold plating comprises the following raw materials in parts by weight: 35 parts of a polymer corrosion inhibitor-A, 0.12 parts of a water-soluble gold salt, 0.4 parts of a complexing agent-A and 95 parts of deionized water.

[0066] In this embodiment, a method for preparing a gold immersion solution for chemical gold plating comprises the following steps:

[0067] A water-soluble gold salt was added to deionized water and stirred until no solid was present to form a gold solution. Then, a complexing agent-A was added to the gold solution and stirred at 300 rpm for 2 hours. Finally, a polymer corrosion inhibitor-A was added and stirred for 1.2 hours to obtain the gold precipitation solution.

[0068] Example 3

[0069] A gold immersion liquid for chemical gold plating comprises the following raw materials in parts by weight: 45 parts of a polymer corrosion inhibitor-A, 0.18 parts of a water-soluble gold salt, 0.7 parts of a complexing agent-A and 105 parts of deionized water.

[0070] In this embodiment, a method for preparing a gold immersion solution for chemical gold plating comprises the following steps:

[0071] A water-soluble gold salt was added to deionized water and stirred until no solid was present to form a gold solution. Then, a complexing agent-A was added to the gold solution and stirred at a speed of 400 rpm for 1 hour. Finally, a polymer corrosion inhibitor-A was added and stirred for 2.5 hours to obtain the gold precipitation solution.

[0072] Example 4

[0073] This embodiment provides a gold immersion solution for chemical gold plating and a preparation method thereof. The specific implementation method is the same as that of Example 1, except that the polymer corrosion inhibitor-A in the raw material is replaced by an equal portion of polymer corrosion inhibitor-B.

[0074] Example 5

[0075] This embodiment provides a gold immersion solution for chemical gold plating and a preparation method thereof. The specific implementation method is the same as that of Example 1, except that the polymer corrosion inhibitor-A in the raw material is replaced by an equal portion of polymer corrosion inhibitor-C.

[0076] Example 6

[0077] This embodiment provides a gold immersion solution for chemical gold plating and a preparation method thereof. The specific implementation method is the same as that of Example 1, except that the polymer corrosion inhibitor-A in the raw material is replaced by an equal portion of polymer corrosion inhibitor-D.

[0078] Example 7

[0079] This embodiment provides a gold immersion solution for chemical gold plating and a preparation method thereof. The specific implementation method is the same as that of Example 1, except that: the complexing agent-A in the raw material is replaced by an equal amount of complexing agent-B.

[0080] Example 8

[0081] This embodiment provides a gold immersion solution for chemical gold plating and a preparation method thereof. The specific implementation method is the same as that of Example 1, except that: the complexing agent-A in the raw material is replaced by an equal amount of complexing agent-C.

[0082] Example 9

[0083] This embodiment provides a gold immersion solution for chemical gold plating and a preparation method thereof. The specific implementation method is the same as that of Example 1, except that the complexing agent-A in the raw material is replaced by an equal portion of diethylenetriaminepentaacetic acid.

[0084] Performance Test:

[0085] 1. Corrosion inhibition effect test

[0086] The nickel-plated sample was immersed in the gold immersion solution for 10 minutes and then taken out. After the sample was cleaned and dried, the morphology of the sample cross section was observed using a Hitachi SU1510 scanning electron microscope. The maximum corrosion depth of the nickel-plated layer was used to characterize the corrosion inhibition effect of the corrosion inhibitor.

[0087] The nickel-plated sample is a 5 cm × 5 cm copper-based circuit board test piece as the sample to be plated, which is plated in 120 mL / L HDQ-209M chemical nickel plating solution at 84 ° C for 25 minutes, wherein the HDQ-209M chemical nickel plating solution is purchased from Ji'an Hongdaqiu Technology Co., Ltd.

[0088] 2. Stability test

[0089] 30 mL of the gold precipitation solution provided in each embodiment was placed in a test tube and placed in an oven at 60° C. for 96 hours. The stability level was determined by observing whether there was turbidity or gold precipitation. The judgment criteria were as follows:

[0090] Level 1: no turbidity, no gold precipitation;

[0091] Level 2: slightly turbid, no gold precipitation;

[0092] Level 3: obvious turbidity, slight precipitation of gold;

[0093] Level 4: Obvious turbidity and obvious gold precipitation.

[0094] The above test results are shown in Table 1.

[0095] Table 1 Performance test results of different embodiments

[0096]

[0097]

[0098] It can be seen from the data in Table 1 that the gold immersion liquid of Examples 1-3 has a light corrosion on nickel and the system is stable; it can be seen from Examples 1 and 4-6 that the adjustment of the raw material ratio of the polymer corrosion inhibitor has a certain influence on the corrosion inhibition effect and stability. The possible reason is that the active sites on the polydopamine skeleton are insufficient, resulting in a decrease in the adsorption capacity on the nickel surface, or the solubility of the polydopamine skeleton is insufficient, resulting in the inability to exert the corrosion inhibition effect in the gold immersion liquid; it can be seen from Examples 1 and 7-9 that the complexing agent with a large number of vinyl, carboxyl and chlorine bridges can effectively ensure the stability and corrosion inhibition effect of the gold immersion liquid, wherein the change in the number of active sites related to the complexing agent may affect the dissociation process of the ions, thereby affecting the stability and corrosion inhibition effect of the gold immersion liquid.

[0099] The embodiments described above do not impose any form of limitation on the present invention. Although the present invention has been disclosed as a preferred embodiment as above, it is not intended to limit the present invention. Any technician familiar with the profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the scope of the technical solution of the present invention.

Claims

1. A gold immersion solution for chemical gold plating, characterized in that: The raw materials are as follows: 30-50 parts of polymer corrosion inhibitor, 0.1-0.2 parts of water-soluble gold salt, 0.4-0.8 parts of complexing agent and 90-110 parts of deionized water. The preparation steps of the polymer corrosion inhibitor are as follows: A1. Prepare a dopamine solution by mixing dopamine hydrochloride and deionized water, adjust the pH to 7.4-7.8, shake at room temperature, and introduce nitrogen for 10-20 minutes to obtain liquid A; A2, adding dimethyl sulfate and anhydrous ethanol to the liquid A in step A1, reflux at 80-90° C. for 1-3 h, to obtain a liquid B containing reactant 1 and reactant 2; A3, cool the liquid B in step A2 to room temperature, adjust the pH to 8.5-9.5 and continue to shake for 6-8 hours to obtain a polymer corrosion inhibitor; The preparation steps of the complexing agent are as follows: Stir diethylenetriaminepentaacetic acid and anhydrous ethanol at 20-30°C for 20-30 minutes, then add allyl chloride, raise the temperature to 40-50°C, stir for 1-3 hours, rotary evaporate, wash and dry to obtain the complexing agent.

2. The gold immersion solution for chemical gold plating according to claim 1, characterized in that: The concentration of the dopamine solution in step A1 is 1.8-2.2 mg / mL.

3. The gold immersion liquid for chemical gold plating according to claim 1, characterized in that: The shaking standard in step A1 is to stop shaking when the dopamine solution changes from colorless to light black liquid.

4. The gold immersion liquid for chemical gold plating according to claim 1, characterized in that: In the step A2, the mass ratio of liquid A, dimethyl sulfate and anhydrous ethanol is 1:(0.4-0.5):(4-8).

5. The gold immersion liquid for chemical gold plating according to claim 1, characterized in that: The water-soluble gold salt is one or more of sodium gold sulfite, tetrachloroauric acid and sodium gold thiosulfate.

6. The gold immersion solution for chemical gold plating according to claim 1, characterized in that: In the preparation step, the mass ratio of diethylenetriaminepentaacetic acid, anhydrous ethanol and allyl chloride is 1:(4-6):(0.58-0.64).

7. A method for preparing a gold immersion solution for chemical gold plating according to any one of claims 1 to 6, characterized in that: The method comprises the following steps: adding water-soluble gold salt to deionized water, stirring until no solid is present to form a gold solution, then adding a complexing agent to the gold solution, stirring at a speed of 300-400 rpm for 1-2 hours, and finally adding a polymer corrosion inhibitor and stirring for 1-3 hours to obtain the gold precipitation solution.

8. The method for preparing a gold immersion solution for chemical gold plating according to claim 7, characterized in that: The Au in the gold solution + The concentration is 0.0045-0.0055mol / L.

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