Double-pulse silver plating method

Abstract

The invention belongs to the technical field of electrochemical silver plating, and particularly relates to a double-pulse silver plating method. The double-pulse silver plating method provided by the invention comprises the following steps: (1) feeding; (2) electrolytic degreasing; (3) washing; (4) acid activation; (5) washing; (6) copper plating; (7) washing; (8) pre-plating silver; (9) washing; (10) double-pulse silver plating; (11) washing with water; (12) passivating; (13) washing with water; (14) drying; and (15) collecting the material. According to the double-pulse silver plating method, the product performance is effectively improved, the consumption of metal silver is reduced, and compared with direct current electroplating, a silver plating product plated through the double-pulse technological process is finer and smoother in plating layer crystallization, good in wear resistance, high in hardness, capable of bearing large high-current impact, high in dynamic load bearing capacity and high in working temperature. And the problem of poor wear resistance of a traditional direct-current silver plating layer is solved. And meanwhile, the double-pulse silver plating can ensure that the color is not changed within 10 minutes in a K2S solution with the temperature of 28 DEG C and the concentration of 5%, and the plating density of the double-pulse silver plating is better than that of the traditional direct-current silver plating.

Description

Technical Field

[0001] The invention belongs to the technical field of electrochemical silver plating, and in particular relates to a double-pulse silver plating method. Background Art

[0002] Electroplating is the process of using electrolysis to deposit metal or alloy on the surface of a workpiece to form a uniform, dense, and well-bonded metal layer.

[0003] As a precious metal, silver has stable physical and chemical properties, and its coating has good corrosion resistance, oxidation resistance, conductivity and ductility. It is widely used in the production and manufacturing of connectors, relays, semiconductor components, precision instruments, optoelectronic devices, high-frequency components, etc. At present, the silver plating methods in the industry are mainly divided into DC silver plating and pulse silver plating. DC silver plating of general products can basically meet their quality requirements. With the expansion of market demand for high-power and high-frequency connectors, traditional DC silver plating cannot overcome the concentration polarization and electrochemical polarization phenomena in the electroplating reaction, which easily leads to uneven distribution of coating film thickness. The coating cannot meet the quality requirements of such products, such as large coating porosity, poor bonding strength, poor wear resistance, etc. Compared with DC electroplating, pulse electroplating has better effect in producing dense and uniform silver layer. Summary of the invention

[0004] The purpose of the present invention is to provide a double-pulse silver plating method, which aims to solve the technical problems in the prior art that the silver-plated terminals required for new energy connectors and high-frequency and high-conductivity communications in traditional ordinary DC electroplating have poor wear resistance, low hardness, low resistance to current impact and low ability to withstand dynamic loads.

[0005] To achieve the above object, the double pulse silver plating method provided by the embodiment of the present invention comprises the following steps:

[0006] (1) Loading;

[0007] (2) Electrolytic degreasing;

[0008] (3) Washing with water;

[0009] (4) Acid activation;

[0010] (5) Washing with water;

[0011] (6) Copper plating;

[0012] (7) Washing with water;

[0013] (8) Pre-silvering;

[0014] (9) Washing with water;

[0015] (10) Double pulse silver plating;

[0016] (11) washing;

[0017] (12) Passivation;

[0018] (13) washing;

[0019] (14) drying;

[0020] (15) Collect materials.

[0021] As an optional scheme of the present invention, the electrolytic degreasing formula in step (2) includes the following components: 25-30 g / L sodium carbonate, 25-30 g / L sodium phosphate and 25-30 g / L sodium silicate, wherein the current density is 10-20 ASD.

[0022] As an optional solution of the present invention, the acid activation formula in step (4) includes the following components: 160-180 mL / L sulfuric acid, 50-70 mL / L ethanol, 140-160 mL / L hydrogen peroxide, and 30-40 mL / L acetic acid.

[0023] As an optional solution of the present invention, the copper plating in step (6) adopts a copper plating electrolyte, and the copper plating electrolyte comprises the following components: 80-120 g / L of copper sulfate, 180-220 g / L of sulfuric acid and 0.01-0.02 g / L of brightener, wherein the brightener is sodium polydisulfide dipropane sulfonate, wherein the anode is a copper ball and the current density is 15-25 ASD.

[0024] As an optional solution of the present invention, the pre-silver plating formula in step (8) includes the following components: 6-8 g / L silver cyanide and 80-120 g / L potassium cyanide, wherein the anode is a silver plate and the current density is 1-3 ASD.

[0025] As an optional solution of the present invention, the double pulse silver plating in step (10) adopts a plating solution, and the plating solution comprises the following components: 35-70 g / L potassium silver cyanide, 90-150 g / L free potassium cyanide, 5-10 g / L potassium hydroxide and 15-20 mL / L brightener, wherein the brightener is a sulfonated fatty acid amine, and the silver ion concentration is analyzed by atomic absorption spectrometer.

[0026] As an optional solution of the present invention, in the double pulse silver plating process of step (10), the pulse period is set to 0.8-2.0 ms, the frequency is between 500-1000 Hz, the forward peak current is set to 90-180 A, the negative peak current is set to 90-180 A, the forward duty cycle is set to 65%-90%, the negative duty cycle is set to 5%-12.5%, the forward conduction time is 0.7-1.8 ms, the negative conduction time is 0.1-0.5 ms, and the average current (I m) is 60~100A, and electroplating is carried out at a temperature of 20~25℃.

[0027] As an optional scheme of the present invention, a passivating agent is used for passivation in step (12), and the preparation method of the passivating agent is as follows: add 200 ml of polyethylene glycol 600 to 400 ml of pure water, heat and stir to 60° C., add 300 ml of OP-10 emulsifier, stir evenly, then add 32 g of octadecyl mercaptan and 3.2 g of hexadecanethiol, stir to dissolve, add the remainder of water, and stir at 60° C. for 1 hour.

[0028] The above one or more technical solutions in the double pulse silver plating method provided by the embodiment of the present invention have at least one of the following technical effects:

[0029] The double-pulse silver plating method provided in the present application adopts DOE experiment to design the double-pulse silver plating process parameters, adopts the silver plating formula as the above silver plating formula and double-pulse rectifier, can effectively improve product performance and reduce the consumption of metallic silver, and the silver-plated products plated by the double-pulse process flow are more delicate in crystallization, good in wear resistance, high in hardness, can withstand high current impact, strong in dynamic load bearing capacity and high in working temperature compared with direct current electroplating. By observing the microstructure of the coating, wear resistance experiment, hardness experiment and sulfurization discoloration experiment, it is proved that double-pulse silver plating can improve the problems of low hardness, poor wear resistance, insufficient resistance to current impact and dynamic load capacity of the silver plating layer of traditional direct current silver plating.

[0030] By comparing the traditional direct current silver plating with the double pulse silver plating of the present invention, it is found that the film thickness distribution of the double pulse silver plating is more uniform, which can greatly flatten the high and low film thickness areas, and the crystallization of the coating is more delicate. The hardness of the traditional direct current silver plating layer is between 90 and 100 HV under the load of 50g. The double pulse silver plating layer of the present invention is tested under the same conditions, and its hardness is 120-130 HV. The hardness of the silver layer is significantly improved, which improves the problem of poor wear resistance of the traditional direct current silver plating layer; at the same time, the traditional direct current silver plating and the double pulse silver plating of the present invention are compared. The products made under the same process conditions are tested in terms of corrosion resistance and anti-sulfurization of the silver-plated products. The double pulse silver plating can ensure that it does not change color for 10 minutes in a K2S solution with a temperature of 28°C and a concentration of 5%, while the traditional direct current silver plating product starts to change color in a K2S solution with a temperature of 28°C and a concentration of 5% for 5 minutes, indicating that the density of the double pulse silver plating layer is better than that of the traditional direct current silver plating layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0032] Figure 1 A square wave diagram of a double pulse of the double pulse silver plating method provided in an embodiment of the present invention.

[0033] Figure 2 A double-pulse sine wave diagram of the double-pulse silver plating method provided in an embodiment of the present invention.

[0034] Figure 3 A double-pulse step waveform diagram of the double-pulse silver plating method provided in an embodiment of the present invention.

[0035] Figure 4 A sawtooth wave diagram of a double pulse of the double pulse silver plating method provided in an embodiment of the present invention.

[0036] Figure 5 A double-pulse periodic commutation wave diagram of the double-pulse silver plating method provided in an embodiment of the present invention.

[0037] Figure 6 A double-pulse commutation wave diagram of a double-pulse silver plating method provided in an embodiment of the present invention.

[0038] Figure 7 A silver plating process flow chart of the double pulse silver plating method provided in an embodiment of the present invention.

[0039] Figure 8 A double pulse electroplating formula for a double pulse silver plating method provided in an embodiment of the present invention.

[0040] Among them, the reference numerals in the figure are:

[0041] 1. Steel pipe; 2. Dust cover; 3. Dust seal; 4. Main oil seal; 5. Step seal; 6. Oil-free bearing; 7. Outer sealing ring; 8. Support ring; 9. Shock absorber oil. DETAILED DESCRIPTION

[0042] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the embodiments of the present invention, and should not be construed as limiting the present invention.

[0043] In the description of the embodiments of the present invention, it should be understood that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside" and "outside" etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the embodiments of the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0044] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the embodiments of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0045] In the embodiments of the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the embodiments of the present invention can be understood according to specific circumstances.

[0046] Embodiment 1:

[0047] In one embodiment of the present invention, Figure 7 As shown, a double pulse silver plating method is provided, comprising the following steps:

[0048] (1) Loading;

[0049] (2) Electrolytic degreasing;

[0050] (3) Washing with water;

[0051] (4) Acid activation;

[0052] (5) Washing with water;

[0053] (6) Copper plating;

[0054] (7) Washing with water;

[0055] (8) Pre-silvering;

[0056] (9) Washing with water;

[0057] (10) Double pulse silver plating;

[0058] (11) washing;

[0059] (12) Passivation;

[0060] (13) washing;

[0061] (14) drying;

[0062] (15) Collect materials.

[0063] The double pulse silver plating method provided by the present invention adopts double pulse silver plating, wherein the waveform of the double pulse is a square wave ( Figure 1 As shown), sine wave ( Figure 2 As shown), step wave ( Figure 3 As shown), sawtooth wave ( Figure 4 As shown), periodic commutation wave ( Figure 5 shown) and double pulse commutation wave ( Figure 6 As shown in the figure, the present invention adopts a periodic commutation wave. The waveform of the periodic commutation wave is not a theoretical waveform. In practice, it will produce different degrees of deformation with the positive conduction time (Ton+), positive turn-off time (Toff+), negative conduction time (Ton-), negative turn-off time (Toff-), frequency (T) and the properties of different electroplating solutions. The square wave deformation is too serious, resulting in a rough coating and failing to achieve the effect of double-pulse electroplating. It is particularly important to ensure the square wave waveform. The double electric layer existing at the electrode / electrolyte interface and the capacitance effect generated in the pulse state directly affect the selection of the pulse period. Only when the pulse width is much larger than the double electric layer charging time and the pulse interval time is much larger than the double electric layer discharging time can the ideal square wave be output. However, it is difficult to achieve the above two conditions by using a pulse period that is too short.

[0064] Compared with traditional DC electroplating, double pulse electroplating has multiple reaction parameters that can be adjusted, such as the forward peak current (I p+ ), negative peak current (I p- ) and the positive conduction time (Ton+), negative conduction time (Ton-), positive turn-off time (Toff+), negative turn-off time (Toff-), the key parameters involved in double pulse electroplating are defined as follows (see formula 1-6 for details): the pulse period (T) is the sum of the conduction time (Ton) and the turn-off time (Toff), the ratio of Ton+ to the entire period is the positive duty cycle (γ + ), the ratio of Ton-to the entire cycle is the negative duty cycle (γ - ), the pulse frequency (f) is the inverse of the period. By controlling the forward peak current (I p+ ), negative peak current (I p-) and the ratio of the forward conduction time (Ton+), the negative conduction time (Ton-), the forward turn-off time (Toff+), and the negative conduction time (Toff-) to achieve the purpose of improving the coating performance and improving the coating quality.

[0065] When the pulse plating is turned on (Ton), the peak current density of the cathode is equivalent to several times or even more than ten times the normal DC current density. High current density will cause the cathode reaction to produce strong electrochemical polarization and high overpotential, so that a large number of silver ions are quickly reduced to crystal nuclei on the cathode. Since the metal crystal nucleus formation rate is greater than the crystal growth rate, a fine-grained silver plating layer is obtained. At the same time, the high current density reaction will quickly consume the silver ions near the cathode interface, causing the metal ion concentration near the cathode interface to rapidly decrease or even zero, resulting in concentration polarization. At this stage, the electroplating process is timely regulated to enter the shutdown (Toff), and the reaction is interrupted in time to promote the transfer of silver ions in the electrolyte to the vicinity of the cathode, replenishing metal ions for the next conduction period reaction. In general, when the current is turned on, the metal ions in the area near the cathode are fully reduced and deposited under strong electrochemical polarization; when the current is turned off, the metal ion concentration in the area near the cathode gradually recovers, and the concentration polarization is eliminated; based on the periodic on and off operations, the silver plating layer gradually forms.

[0066] In another embodiment of the present invention, the electrolytic degreasing formula in step (2) of the double pulse silver plating method includes the following components: 25-30 g / L sodium carbonate, 25-30 g / L sodium phosphate and 25-30 g / L sodium silicate, wherein the current density is 10-20 ASD.

[0067] In another embodiment of the present invention, the acid activation formula in step (4) of the double pulse silver plating method comprises the following components: 160-180 mL / L of sulfuric acid, 50-70 mL / L of ethanol, 140-160 mL / L of hydrogen peroxide, and 30-40 mL / L of acetic acid.

[0068] In another embodiment of the present invention, in step (6) of the double pulse silver plating method, copper plating adopts a copper plating electrolyte, and the copper plating electrolyte comprises the following components: 80-120 g / L of copper sulfate, 180-220 g / L of sulfuric acid and 0.01-0.02 g / L of brightener, wherein the brightener is sodium polydisulfide dipropane sulfonate, wherein the anode is a copper ball and the current density is 15-25 ASD.

[0069] In another embodiment of the present invention, the pre-silver plating formula in step (8) of the double pulse silver plating method includes the following components: 6-8 g / L silver cyanide and 80-120 g / L potassium cyanide, wherein the anode is a silver plate and the current density is 1-3 ASD.

[0070] In another embodiment of the present invention, in step (10) of the double pulse silver plating method, the double pulse silver plating adopts a plating solution, and the plating solution comprises the following components: 35-70 g / L potassium silver cyanide, 90-150 g / L free potassium cyanide, 5-10 g / L potassium hydroxide and 15-20 mL / L brightener, the brightener is a sulfonated fatty acid amine, and the silver ion concentration is analyzed by atomic absorption spectrometer.

[0071] In another embodiment of the present invention, in the double pulse silver plating process of step (10) of the double pulse silver plating method, the pulse period is set to 0.8-2.0 ms, the frequency is between 500-1000 Hz, the forward peak current is set to 90-180 A, the negative peak current is set to 90-180 A, the forward duty cycle is set to 65%-90%, the negative duty cycle is set to 5%-12.5%, the forward conduction time is 0.7-1.8 ms, the negative conduction time is 0.1-0.5 ms, and the average current (I m ) is 60~100A, and electroplating is carried out at a temperature of 20~25℃.

[0072] In another embodiment of the present invention, a passivating agent is used for passivation in step (12) of the double pulse silver plating method, and the preparation method of the passivating agent is as follows: 200 ml of polyethylene glycol 600 is added to 400 ml of pure water, heated and stirred to 60° C., 300 ml of OP-10 emulsifier is added, and after stirring evenly, 32 g of octadecyl mercaptan and 3.2 g of hexadecanethiol are added, stirred to dissolve, the remainder is supplemented with water, and stirred at 60° C. for 1 hour.

[0073] The process flow of double pulse silver plating is the same as that of direct current silver plating, which mainly includes pre-plating treatment, copper plating, pre-silver plating, double pulse silver plating and post-treatment. Figure 7 Among them, the electrolytic degreasing process aims to remove oil stains and some oxides on the surface of the product. The temperature is 60-80℃, the cathode moving time is 30-60S, and the electrolytic degreasing formula is: sodium carbonate (Na2CO3) 25-30g / L, sodium phosphate (Na3PO4) 25-30g / L, sodium silicate (Na2SiO3) 25-30g / L, and the current density is 10-20ASD; the next step is activation. The purpose of activation is to remove the passivation film or very thin oxide film on the surface to facilitate the strong bonding between the coating and the substrate. The temperature is 20-45℃, the cathode moving time is 10-60S, and the activation formula is: sulfuric acid (H2SO4) 160-180mL / L, ethanol (C2H5OH) 50-70mL / L, hydrogen peroxide (H2O2) 140-160mL / L, acetic acid (CH3COOH) 30-40mL / L. After the product is washed, it enters the metal electroplating stage.

[0074] The electroplating substrate is pure copper and its copper alloy. The product is copper plated at a temperature of 30-60°C, a cathode movement time of 20-30S, and a copper plating electrolyte formula of 80-120g / L copper sulfate (CuSO4), sulfuric acid (H2 S O4)180~220g / L, brightener 0.01~0.02g / L, brightener is sodium polydisulfide dipropane sulfonate, the anode is a copper ball, and the current density is 15~25ASD; after copper plating, it is washed with water and enters the pre-silver plating process, the cathode moves for 10~20S, and the pre-silver plating formula is: silver cyanide (AgCN) 6~8g / L, potassium cyanide (KCN) 80~120g / L, the anode is a silver plate, and the current density is 1~3ASD. After pre-silver plating, the double pulse silver plating process is directly entered. The plating solution temperature is 20-25°C, the cathode movement time is 60-120S, and the plating solution formula is: potassium silver cyanide (K[Ag(CN)2]) 35-70g / L, free potassium cyanide (KCN) 90-150g / L, potassium hydroxide 5-10g / L, brightener is 15-20mL / L, and the brightener is sulfonated fatty acid amine.

[0075] Embodiment 1 The specific scheme is as follows:

[0076] Pulse silver plating parameter selection, double pulse silver plating has multiple parameters to choose from, forward peak current (I p+ ) is set to 90A, and its negative peak current (I p- ) is set to 90A, its single double pulse period (T) is set to 1.0ms, its forward conduction time (Ton+) is 0.8ms, its negative conduction time (Ton-) is 0.1ms, its turn-off time (Toff) is 0.1ms, its double pulse frequency (f) is 1000HZ, and the product is double-pulse electroplating within this parameter range.

[0077] The coating of this embodiment has good bonding strength with the substrate, good density of the coating, and high wear resistance.

[0078] Embodiment 2:

[0079] Embodiment 2 The specific scheme is as follows:

[0080] Pulse silver plating parameter selection, double pulse silver plating has multiple parameters to choose from, forward peak current (I p+ ) is set to 90A, and its negative peak current (I p- ) is set to 162A, its single double pulse period (T) is set to 1.0ms, its forward conduction time (Ton+) is 0.8ms, its negative conduction time (Ton-) is 0.1ms, its turn-off time (Toff) is 0.1ms, its double pulse frequency (f) is 1000HZ, and the product is double-pulse electroplating within this parameter range.

[0081] The coating of this embodiment has good bonding strength with the substrate, good density of the coating, high wear resistance, and uniform film thickness distribution.

[0082] The rest of this embodiment is the same as that of Embodiment 1. The features not explained in this embodiment are all based on the explanations of Embodiment 1 and will not be described in detail here.

[0083] Embodiment 3:

[0084] Embodiment 3 The specific scheme is as follows:

[0085] Pulse silver plating parameter selection, double pulse silver plating has multiple parameters to choose from, forward peak current (I p+ ) is set to 90A, and its negative peak current (I p- ) is set to 162A, its forward conduction time (Ton+) is 1.0ms, its negative conduction time (Ton-) is 0.15ms, 0.1ms, 0.3ms, 0.5ms, 0.8ms, 1.0ms, and its turn-off time (Toff) is 0.2ms. Double-pulse electroplating is performed on the product within this parameter range.

[0086] The uniformity and density of the silver on the coating of this embodiment are good, and the bonding strength with the substrate is good. As the negative conduction time increases, the uniformity of the coating increases first and then decreases, reaching an extreme value when the negative conduction time is 0.3ms.

[0087] In order to obtain a coating with uniform film thickness distribution, high hardness, good wear resistance, resistance to high current impact and ability to withstand dynamic loads, the negative peak current can be set to 1.0 to 1.5 times the positive peak current. The conduction ratio is the ratio of the forward conduction time (Ton+) to the negative conduction time (Ton-). Experiments have shown that a silver coating with finer crystals can be obtained when the conduction ratio is 8:1 to 15:1.

[0088] The rest of this embodiment is the same as the first embodiment. The features not explained in this embodiment are all based on the explanations in the first embodiment and will not be described in detail here.

[0089] The double-pulse silver plating method provided in the present application adopts DOE experiment to design the double-pulse silver plating process parameters, adopts the silver plating formula as the above silver plating formula and double-pulse rectifier, can effectively improve product performance and reduce the consumption of metallic silver, and the silver-plated products plated by the double-pulse process flow are more delicate in crystallization, good in wear resistance, high in hardness, can withstand high current impact, strong in dynamic load bearing capacity and high in working temperature compared with direct current electroplating. By observing the microstructure of the coating, wear resistance experiment, hardness experiment and sulfurization discoloration experiment, it is proved that double-pulse silver plating can improve the problems of low hardness, poor wear resistance, insufficient resistance to current impact and dynamic load capacity of the silver plating layer of traditional direct current silver plating.

[0090] By comparing the traditional direct current silver plating with the double pulse silver plating of the present invention, it is found that the film thickness distribution of the double pulse silver plating is more uniform, which can greatly flatten the high and low film thickness areas, and the crystallization of the coating is more delicate. The hardness of the traditional direct current silver plating layer is between 90 and 100 HV under the load of 50g. The double pulse silver plating layer of the present invention is tested under the same conditions, and its hardness is 120-130 HV. The hardness of the silver layer is significantly improved, which improves the problem of poor wear resistance of the traditional direct current silver plating layer; at the same time, the traditional direct current silver plating and the double pulse silver plating of the present invention are compared. The products made under the same process conditions are tested in terms of corrosion resistance and anti-sulfurization of the silver-plated products. The double pulse silver plating can ensure that it does not change color for 10 minutes in a K2S solution with a temperature of 28°C and a concentration of 5%, while the traditional direct current silver plating product starts to change color in a K2S solution with a temperature of 28°C and a concentration of 5% for 5 minutes, indicating that the density of the double pulse silver plating layer is better than that of the traditional direct current silver plating layer.

[0091] The above examples illustrate the present invention in detail, but do not mean that the present invention is limited to these three examples. Without departing from the technical principle of the present invention, improvements and modifications thereof are within the scope of the claims and techniques of the present invention and should also fall within the protection scope of the present invention.

[0092] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A double pulse silver plating method, characterized in that: The following steps are involved: (1) Loading; (2) Electrolytic degreasing; (3) Washing with water; (4) Acid activation; (5) Washing with water; (6) Copper plating; (7) Washing with water; (8) Pre-silvering; (9) Washing with water; (10) Double pulse silver plating; (11) washing; (12) Passivation; (13) washing; (14) drying; (15) Collect materials.

2. A double pulse silver plating method according to claim 1, characterized in that: The electrolytic degreasing formula in step (2) includes the following components: 25-30 g / L sodium carbonate, 25-30 g / L sodium phosphate and 25-30 g / L sodium silicate, wherein the current density is 10-20 ASD.

3. A double pulse silver plating method according to claim 1, characterized in that: The acid activation formula in step (4) includes the following components: 160-180 mL / L of sulfuric acid, 50-70 mL / L of ethanol, 140-160 mL / L of hydrogen peroxide, and 30-40 mL / L of acetic acid.

4. A double pulse silver plating method according to claim 1, characterized in that: In the step (6), copper plating adopts a copper plating electrolyte, which comprises the following components: 80-120 g / L of copper sulfate, 180-220 g / L of sulfuric acid and 0.01-0.02 g / L of a brightener, wherein the brightener is sodium polydisulfide dipropane sulfonate, wherein the anode is a copper ball and the current density is 15-25 ASD.

5. A double pulse silver plating method according to claim 1, characterized in that: The pre-silver plating formula in step (8) includes the following components: 6-8 g / L of silver cyanide and 80-120 g / L of potassium cyanide, wherein the anode is a silver plate and the current density is 1-3 ASD.

6. A double pulse silver plating method according to claim 1, characterized in that: In the step (10), the double pulse silver plating adopts an electroplating solution, which comprises the following components: 35-70 g / L potassium silver cyanide, 90-150 g / L free potassium cyanide, 5-10 g / L potassium hydroxide and 15-20 mL / L brightener, wherein the brightener is a sulfonated fatty acid amine, and the silver ion concentration is analyzed by atomic absorption spectrometer.

7. A double pulse silver plating method according to claim 1, characterized in that: In the double pulse silver plating process of step (10), the pulse period is set to 0.8-2.0 ms, the frequency is between 500-1000 Hz, the forward peak current is set to 90-180 A, the negative peak current is set to 90-180 A, the forward duty cycle is set to 65%-90%, the negative duty cycle is set to 5%-12.5%, the forward conduction time is 0.7-1.8 ms, the negative conduction time is 0.1-0.5 ms, and the average current (I m ) is 60~100A, and electroplating is carried out at a temperature of 20~25℃.

8. A double pulse silver plating method according to claim 1, characterized in that: In the step (12), a passivating agent is used for passivation, and the preparation method of the passivating agent is as follows: 200 ml of polyethylene glycol 600 is added to 400 ml of pure water, heated and stirred to 60° C., 300 ml of OP-10 emulsifier is added, and after stirring evenly, 32 g of octadecyl mercaptan and 3.2 g of hexadecanethiol are added, stirred to dissolve, the remainder is supplemented with water, and stirred at 60° C. for 1 hour.

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