CN104342644B - A kind of chemical plating liquid and silver-coating method - Google Patents

Abstract

The invention provides an electroless silver plating solution, which comprises a silver salt, a complexing agent, a pH regulator, and a surfactant; the complexing agent comprises ammonium citrate, ammonium sulfate and cysteine; The weight ratio of the ammonium citrate, ammonium sulfate and cysteine is 1:0.5-1.5:0.002-0.02, and the pH of the electroless silver plating solution is 8.2-10.2. The invention also provides a method for performing chemical silver plating with the chemical silver plating solution. The appearance of the products plated by the electroless silver plating solution of the present invention is dense and uniform, while the appearance of products plated by similar silver plating solutions on the market has prominent and uneven particles and even partial missing plating phenomenon. Moreover, the chemical silver plating solution of the present invention begins to decompose longer and more stable than that of similar silver plating solutions on the market.

Description

A kind of electroless silver plating solution and silver plating method

technical field

The invention belongs to the field of electroless plating, in particular to an electroless silver plating solution and a silver plating method.

Background technique

Since silver has good solderability, weather resistance and electrical conductivity, the use of electroless silver plating to protect copper substrates has been widely used in the printed circuit board industry. At present, there are two methods of copper-based electroless silver plating commonly used: 1. Redox chemical silver plating method; 2. Displacement chemical silver plating method. Due to redox silver plating, an additional reducing agent needs to be added, which makes the electroless silver plating solution easily unstable, and when used, it is necessary to carry out corresponding sensitization pretreatment on the metal substrate, and the production cost is high, which hinders its industrial application. Because of its wide application, displacement electroless silver plating is superior to redox electroless silver plating, which requires the use of reducing agents. Moreover, in order to increase the stability of the silver plating solution, potassium cyanide is added as a complexing agent in some electroless silver plating solutions. Potassium cyanide is highly toxic and pollutes the environment. The replacement electroless silver plating method utilizes that the metal activity of copper is stronger than that of silver, directly uses copper as a reducing agent, and achieves the purpose of direct silver plating on the copper surface through the replacement reaction of copper and silver ions. However, the similar potion products currently on the market are mainly strong acid potions. Its strong acidity will corrode the copper substrate, and its plating layer is rough, which cannot meet the needs of the current electronics industry.

The Chinese patent with the publication number CN101182637A discloses a slightly alkaline electroless silver plating solution, which contains the following components: silver ions or silver complex ions 0.01-20g/L, amine complexing agents 0.1-150g/L, amino acids Type complexing agent 0.1-150g/L, polyhydroxy acid complexing agent 0.1-150g/L. The slightly alkaline electroless silver plating solution has poor stability and low utilization rate, and the plating layer is easily oxidized and yellowed.

Contents of the invention

In order to solve the technical problem of unstable chemical silver plating solution in the prior art, the invention provides a stable chemical silver plating solution and a silver plating method thereof.

The invention provides an electroless silver plating solution, which comprises a silver salt, a complexing agent, a pH regulator, and a surfactant; the complexing agent comprises ammonium citrate, ammonium sulfate and cysteine; The weight ratio of the ammonium citrate, ammonium sulfate and cysteine is 1:0.5-1.5:0.002-0.02, and the pH of the electroless silver plating solution is 8.2-10.2.

The present invention also provides an electroless silver plating method, which includes placing the workpiece to be plated in an electroless silver plating solution for electroless plating; wherein, the electroless silver plating solution is the electroless silver plating solution described in the present invention.

In the electroless silver plating solution of the present invention, ammonium citrate, ammonium sulfate, and cysteine have the same complexing ability as silver ions, and they are 1:0.5- 1.5: Mixing at a ratio of 0.002-0.02 is prone to clustering effect, forming a mixed complex and increasing the stability of the electroless silver plating solution.

Description of drawings

Fig. 1 is the topography photograph of the silver-plated product of embodiment 1 under the magnifying glass of 400 times;

Figure 2 is a photo of the appearance of the silver-plated product of Comparative Example 1 under a magnifying glass of 400 times.

detailed description

In order to make the technical problems, technical solutions and beneficial effects solved by the present invention clearer, the present invention will be further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention.

The invention provides an electroless silver plating solution, which comprises a silver salt, a complexing agent, a pH regulator, and a surfactant; the complexing agent comprises ammonium citrate, ammonium sulfate and cysteine; The weight ratio of the ammonium citrate, ammonium sulfate and cysteine is 1:0.5-1.5:0.002-0.02, and the pH of the electroless silver plating solution is 8.2-10.2. Keeping the complexing agent within the above range can maintain the good stability of the plating solution, make the plating uniform, and the product has good brightness.

In the present invention, in order to obtain good coating performance, preferably, the content of the silver salt is 0.5-5g/L, the content of the complexing agent is 1-10g/L; the content of the surfactant 13-30 ppm.

According to the electroless silver plating solution provided by the present invention, the silver salt, pH regulator and surfactant are not particularly limited, and may be various silver salts, pH regulator and surfactant commonly used in the art. In the present invention, the silver salt is at least one of silver nitrate, silver iodide and silver eicosanoate; the pH regulator is at least one of sodium hydroxide, potassium hydroxide and sulfuric acid; the surface active The agent is at least one of sodium dodecyl sulfate, PEG-1000, PEG-300, sodium dodecylbenzenesulfonate and PEG-6000.

In the present invention, preferably, the electroless silver plating solution further includes ceric sulfate, and the concentration of the ceric sulfate is 1-10 ppm. The electroless silver plating solution also contains lanthanum oxide; the concentration of the lanthanum oxide is 5-50ppm.

The cerium sulfate can be co-deposited with the silver plating layer to make the plating layer more delicate and whitish. It is better to add lanthanum oxide at the same time.

In the present invention, the electroless silver plating solution further includes benzotriazole, and the concentration of the benzotriazole is 0.2-3ppm. Benzotriazepam prevents oxidation or corrosion of the silver layer during electroless plating.

The present invention also provides an electroless silver plating method, which includes placing the workpiece to be plated in an electroless silver plating solution for electroless plating; wherein, the electroless silver plating solution is the electroless silver plating solution described in the present invention.

In the present invention, the workpiece to be plated can be a metal whose metal activity is stronger than that of silver, such as copper, nickel, iron and aluminum.

In order to make the effect of electroless silver plating better, preferably, the temperature of the electroless silver plating solution is 41-48° C., and the time of the electroless silver plating is 5-9 minutes.

In order to better protect the silver-plated layer, preferably, the method further includes a step of protecting the silver layer after electroless silver-plating. The protection treatment method is to use benzotriazole, tetrazole, and dodecanethiol to form a complex protection layer with silver to achieve the purpose of protecting the silver plating layer.

In order to improve the bonding force of the silver plating layer, preferably, the method further includes a pretreatment step before the electroless silver plating. The pretreatment includes degreasing and acid etching. Multiple water washes are required after degreasing and acid etching.

Electroless silver plating liquid of the present invention and chemical silver plating method thereof are suitable for SBID (super beam induceddeposition super laser induced deposition, is a kind of plastic composition and its surface selective metallization process. Specifically is to bombard material surface with high-energy particle beam, The metal nucleus is reduced, and then a layer of metal copper is plated on the surface bombarded by high-energy particle beams by electroless copper plating, and then traditional electroplating is used to thicken the copper layer to produce circuit boards) and LDS process The demand for silver plating of 3D mobile phone antennas and related products, because the chemical silver plating solution is weakly alkaline, to avoid acid corrosion on copper plating wires, and due to the addition of ammonium citrate, ammonium sulfate and cysteine, and citric acid The weight ratio of ammonium, ammonium sulfate and cysteine is 1:0.5-1.5:0.002-0.02, which makes the electroless silver plating solution stable and the silver plating speed is fast. It can replace the silver plating by more than 0.5 microns in 5 minutes. This complexing agent is not used. The system is 0.25 micron, and the production efficiency is high. Moreover, the copper ion replacement content of the electroless silver plating solution of the present invention can reach more than 3g/L, which is more convenient to use than the existing chemical silver plating solution, has higher utilization rate of active components, and more stable maintenance of the chemical silver plating solution.

The present invention will be described in detail below in conjunction with specific embodiments.

Example 1

Electroless silver plating solution: silver nitrate 0.5g/L; ammonium citrate 0.5g/L; ammonium sulfate 0.5g/L; cysteine 1ppm; sodium lauryl sulfate 3ppm; benzotriazole 1ppm; PEG- 1000 10ppm; use sodium hydroxide solution to adjust the pH value to 9.0 to obtain electroless silver plating solution A1;

Electroless silver plating:

1. Degreasing: Ultrasonic degreasing of the copper workpiece to be plated;

2. Acid etching: soak the workpiece to be plated obtained in step 1 with dilute acid solution to remove the oxide layer;

3. Electroless silver plating: Heat the electroless silver plating solution A1 to 45°C, and then place the workpiece to be plated obtained in step 2 in the heated chemical silver plating solution to react for 9 minutes;

4. Protection treatment: place the plated piece obtained in step 3 in a silver protectant for treatment for 3 minutes, and then dry to obtain the silver-plated product S1.

Multiple washes are required between the above steps.

Example 2

Electroless silver plating solution: silver nitrate 4g/L; ammonium citrate 5g/L; ammonium sulfate 2.5g/L; cysteine 50ppm; cerium sulfate 1ppm; lanthanum oxide 5ppm; sodium lauryl sulfate 10ppm; PEG- 300-40ppm; , with sodium hydroxide solution, adjust the pH value to be 9.0 to obtain chemical silver plating solution A2;

Electroless silver plating:

1. Degreasing: Ultrasonic degreasing of the copper workpiece to be plated;

2. Acid etching: soak the workpiece to be plated obtained in step 1 with dilute acid solution to remove the oxide layer;

3. Electroless silver plating: Heat the electroless silver plating solution A2 to 45°C, and then place the workpiece to be plated obtained in step 2 in the heated chemical silver plating solution for 9 minutes;

4. Protection treatment: place the plated piece obtained in step 3 in a silver protectant for treatment for 3 minutes, and then dry to obtain a silver-plated product S2.

Multiple washes are required between the above steps.

Example 3

Electroless silver plating solution: silver iodide 1g/L; ammonium citrate 0.5g/L; ammonium sulfate 0.75g/L; cysteine 10ppm; ceric sulfate 5ppm; lanthanum oxide 50ppm; benzotriazole 0.2ppm; Alkyl sodium sulfate 30ppm; PEG-6000 70ppm; use sodium hydroxide solution to adjust the pH value to 9.0 to obtain chemical silver plating solution A3;

Electroless silver plating:

1. Degreasing: Ultrasonic degreasing of the copper workpiece to be plated;

2. Acid etching: soak the workpiece to be plated obtained in step 1 with dilute acid solution to remove the oxide layer;

3. Electroless silver plating: Heat the electroless silver plating solution A3 to 48°C, and then place the workpiece to be plated obtained in step 2 in the heated chemical silver plating solution to react for 5 minutes;

4. Protection treatment: place the plated piece obtained in step 3 in a silver protectant for treatment for 3 minutes, and then dry to obtain a silver-plated product S3.

Multiple washes are required between the above steps.

Example 4

Electroless silver plating solution: silver eicosanoate 2g/L; ammonium citrate 2g/L; ammonium sulfate 2g/L; cysteine 4ppm; ceric sulfate 4ppm; benzotriazole 0.8ppm; Sodium benzenesulfonate 12ppm; PEG-1000 40ppm; use potassium hydroxide solution to adjust the pH value to 8.6 to obtain chemical silver plating solution A4;

Electroless silver plating:

1. Degreasing: Ultrasonic degreasing of the copper workpiece to be plated;

2. Acid etching: soak the workpiece to be plated obtained in step 1 with dilute acid solution to remove the oxide layer;

3. Electroless silver plating: Heat the electroless silver plating solution A4 to 41°C, and then place the workpiece to be plated obtained in step 2 in the heated chemical silver plating solution for 9 minutes;

4. Protection treatment: place the plated piece obtained in step 3 in a silver protectant for treatment for 3 minutes, and then dry to obtain the silver-plated product S4.

Multiple washes are required between the above steps.

Example 5

Electroless silver plating solution: silver nitrate 5g/L; ammonium citrate 5g/L; ammonium sulfate 5g/L; cysteine 25ppm; cerium sulfate 10ppm; lanthanum oxide 30ppm; benzotriazole 3ppm; dodecyl Sodium sulfate 30ppm; PEG-1000 100ppm;, use sodium hydroxide solution to adjust the pH value to 8.6 to obtain chemical silver plating solution A5;

Electroless silver plating:

1. Degreasing: Ultrasonic degreasing of the copper workpiece to be plated;

2. Acid etching: soak the workpiece to be plated obtained in step 1 with dilute acid solution to remove the oxide layer;

3. Electroless silver plating: Heat the electroless silver plating solution A5 to 45°C, and then place the workpiece to be plated obtained in step 2 in the heated chemical silver plating solution to react for 7 minutes;

4. Protection treatment: place the plated piece obtained in step 3 in a silver protectant for treatment for 3 minutes, and then dry to obtain a silver-plated product S5.

Multiple washes are required between the above steps.

Comparative example 1

The electroless silver plating solution and method of Example 1 of CN101182637A were used to carry out electroless silver plating to obtain product CS1.

Test method and data

1. Salt spray test

Neutral salt spray test conditions: In the salt spray corrosion test chamber, use a salt solution with a sodium chloride content of 5±1%: when the temperature is 35°C, the pH value of the collected solution after spraying is 6.5~7.2. Allow pH adjustment with diluted hydrochloric acid or sodium hydroxide. The temperature of the test space is 35°C; the continuous spray test time is 48H; then return to normal atmospheric conditions in the box, and keep it for 2H after stabilization. Perform visual inspection. Standard: no rust, discoloration, and coating peeling off. The results are shown in Table 1.

2. Product appearance

(1) Use an optical magnifying glass to magnify the corresponding product to 400 times to observe its surface morphology. The results are shown in Table 1.

The appearance of the products plated by this potion is dense and uniform, while the appearance of products plated by similar potions on the market has prominent and uneven particles and even partial missing plating.

(2) Use an optical magnifying glass to magnify the product S1 of the embodiment and the product CS1 of the comparative example 1 to 400 times to observe, observe the surface morphology of the silver-plated product, and take pictures of the morphology as shown in Figure 1 and Figure 2 respectively.

Table 1

As can be seen from Table 1, the salt spray resistance of the silver-plated product prepared by the chemical silver-plating solution of the present invention is better than the salt spray resistance of the silver-plated product of the comparative example, and the chemical silver-plating solution of the present invention The appearance of the obtained silver-plated product is dense and uniform, while the appearance of the silver-plated product obtained in the comparative example obviously has prominent and uneven particles and even partially lacks plating.

From the comparison of Fig. 1 and Fig. 2, it can be clearly seen that the appearance of the silver-plated product of Example 1 is dense and uniform; while the appearance of the silver-plated product of Comparative Example 1 obviously has prominent and uneven particles and even partially lacks plating. .

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention should be included in the protection of the present invention. within range.

Claims (12)

1. a kind of chemical plating liquid, it is characterised in that the chemical plating liquid includes silver salt, complexing agent, pH adjusting agent, surface-active Agent；The complexing agent includes ammonium citrate, ammonium sulfate and cysteine；The weight of the ammonium citrate, ammonium sulfate and cysteine Amount is than being 1：0.5-1.5：0.002-0.02, the pH of the chemical plating liquid is 8.2-10.2.

2. chemical plating liquid as claimed in claim 1, it is characterised in that the content of the silver salt is 0.5-5g/L, the network The content of mixture is 1-10g/L；The content of the surfactant is 13-130 ppm.

3. chemical plating liquid as claimed in claim 1, it is characterised in that the silver salt is silver nitrate, silver iodide and eicosane At least one in sour silver；The pH adjusting agent be NaOH and potassium hydroxide in one or two；The surface-active Agent is at least one in lauryl sodium sulfate, PEG-1000, PEG-300, neopelex and PEG-6000.

4. chemical plating liquid as claimed in claim 1, it is characterised in that the chemical plating liquid also includes ceric sulfate, institute The concentration for stating ceric sulfate is 1-10ppm.

5. chemical plating liquid as claimed in claim 4, it is characterised in that also contain lanthana in the chemical plating liquid；Institute The concentration for stating lanthana is 5-50ppm.

6. the chemical plating liquid as described in claim 1-4 any one, it is characterised in that the chemical plating liquid also includes benzene And triazole, the concentration of the BTA is 0.2-3ppm.

7. a kind of chemical silver plating method, it is characterised in that the method includes being placed into workpiece to be plated in chemical plating liquid carrying out Chemical plating；Wherein, the chemical plating liquid is the chemical plating liquid described in claim 1-6 any one.

8. chemical silver plating method according to claim 7, it is characterised in that the temperature of the chemical plating liquid is 41-48 DEG C, the time 5-9min of the chemical silvering.

9. chemical silver plating method according to claim 7, it is characterised in that the method is additionally included in after chemical silvering to silver The step of layer carries out protection treatment.

10. chemical silver plating method according to claim 9, it is characterised in that the method for protection treatment is to utilize complexing agent With silver-colored Absorptive complex wave, organic protective film is formed.

11. chemical silver plating methods according to claim 7, it is characterised in that before the method is additionally included in chemical silvering The step of carrying out pre-treatment.

12. chemical silver plating methods according to claim 11, it is characterised in that the pre-treatment includes oil removing, acid etching.