Surface pretreatment method for cold drawing of tungsten filament

Abstract

The invention provides a tungsten filament cold drawing surface pretreatment method, and relates to the technical field of diamond wire bus electroplating, the pretreatment method comprises the following steps: S1, providing a tungsten filament, and carrying out alkali washing and acid washing on the tungsten filament; s2, sequentially electroplating a nickel layer, a copper layer and a zinc layer on the acid-washed tungsten filament; s3, performing thermal diffusion on the tungsten filament subjected to zinc layer electroplating to obtain a tungsten filament with a copper-zinc alloy layer; and S4, the tungsten filament with the copper-zinc alloy layer is subjected to acid pickling, water washing and air drying, and the tungsten filament subjected to the pretreatment method can adapt to the cold drawing process.

Description

Technical Field

[0001] This invention relates to the field of diamond wire busbar electroplating technology, specifically to a surface pretreatment method for cold-drawn tungsten wire. Background Technology

[0002] In recent years, the photovoltaic industry has developed rapidly, and costs have been decreasing. Among these changes, the diameter of the diamond wire used for silicon wafer cutting has become increasingly finer, from 95μm to 45μm. The diameter of the main wire used has also decreased from 80μm to 35μm. However, the demand for cost reduction continues. When the diameter of high-carbon steel wire is below 35μm, the breakage rate increases exponentially, which can no longer meet the requirements of diamond wire for photovoltaic wafer cutting. Therefore, tungsten wire is used to replace high-carbon steel wire to make ultra-fine diamond wire. Currently, 30μm tungsten wire main wire is being used in batches to make diamond wire, which has high cutting efficiency, low breakage rate, low silicon loss, and lower overall wafer cutting cost.

[0003] The existing problem is that hot-drawn tungsten wire is drawn at a high temperature of 1200℃, and graphite is required as a lubricant during the drawing process. This process is more suitable for drawing tungsten wires with larger diameters, as it is efficient and stable. However, the diamond wire used for fine wires in photovoltaic wafers is less than 30μm, and the disadvantages of the hot-drawing process become more obvious, specifically including the following defects:

[0004] High cost: Hot-drawn fine wires require more precise temperature control equipment (to maintain local high temperature while avoiding overall overheating) and higher purity protective gas (to prevent oxidation), resulting in higher energy consumption; in addition, the yield of fine wires is low, and production efficiency is reduced due to frequent breakage, ultimately leading to a higher cost per unit length of hot-drawn fine wire; at the same time, after the drawing is completed, an additional electrolysis is required to remove the graphite on the surface of the tungsten wire, making the entire processing process complex and costly.

[0005] Poor precision and straightness: When hot-drawn tungsten wires are in a high-temperature environment, recrystallization can lead to uneven microstructure and chaotic internal stress distribution due to uneven temperature, resulting in poor dimensional accuracy during drawing. At the same time, factors such as control precision and thermal expansion and contraction can cause local "diameter shrinkage" or "side bending" of the wire, resulting in large diameter variations and poor straightness.

[0006] Cold drawing of tungsten wire can effectively avoid the disadvantages of hot drawing, allowing for finer diameters, higher and more uniform diameter accuracy, and better straightness. However, the high tensile force during the drawing process can easily damage the die or cause the tungsten wire to break. Therefore, it is necessary to pre-treat the surface of the tungsten wire raw material to reduce the friction between the surface and the die, thereby reducing damage to the die and improving the yield of drawn products. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the prior art and provide a surface pretreatment method for cold drawing of tungsten wire.

[0008] To achieve the above and other objectives, the present invention is implemented through the following technical solution: The present invention provides a surface pretreatment method for cold drawing of tungsten wire, the pretreatment method comprising the following steps:

[0009] S1: Provide a tungsten wire, and subject the tungsten wire to alkaline washing and acid washing;

[0010] S2: The acid-washed tungsten wire is sequentially electroplated with nickel, copper and zinc layers;

[0011] S3: Thermal diffusion is performed on the tungsten wire after electroplating with zinc to obtain a tungsten wire with a copper-zinc alloy layer;

[0012] S4: Pickling, washing and air drying are performed on tungsten wires with copper-zinc alloy layers.

[0013] In one embodiment, in step S1, the diameter of the tungsten wire is 45~60μm.

[0014] In one embodiment, in step S1, the conditions for alkaline washing include: the alkaline washing solution is 70±5 g / L sodium hydroxide, the temperature is 60±2℃, and the electrolysis voltage is 4V; after alkaline washing, the water is washed with water, and the pH of the water used for washing is less than or equal to 9.

[0015] In one embodiment, in step S1, the pickling conditions include: the pickling solution is 30±5 g / L of aminosulfonic acid, and the temperature is room temperature; the pickling is followed by water washing, and the pH of the water used for washing is greater than or equal to 4.

[0016] In one embodiment, in step S2, the conditions for electroplating the nickel layer include: the electroplating solution is a nickel sulfamate system, wherein the nickel ion concentration is 100±5 g / L, the boric acid concentration is 40±3 g / L, the nickel chloride concentration is 5±2 g / L, the pH is 3.80±0.20, and the temperature is 50±2℃; after electroplating the nickel layer, it is washed with water, wherein the pH of the water used for washing is greater than or equal to 4.

[0017] In one embodiment, in step S2, the conditions for electroplating the copper layer include: the electroplating solution is a copper pyrophosphate system, wherein the copper ion concentration is 27±3 g / L, the pyrophosphate concentration is 200±20 g / L, the pyrophosphate ratio is 7.5±0.5, the pH is 8.30±0.20, the temperature is 50±2℃, and the copper layer is washed with water after electroplating, and the pH of the wash water is required to be less than or equal to 8.

[0018] In one embodiment, in step S2, the conditions for electroplating the zinc layer include: the electroplating solution is a zinc sulfate system, wherein the concentration of zinc sulfate heptahydrate is 220±30 g / L, the zinc ion concentration is 47±3 g / L, the pH is 1.80±0.20, the temperature is 40±2℃, and the zinc layer is washed with water after electroplating, and the pH of the wash water is required to be greater than or equal to 4.

[0019] In one embodiment, in step S3, the temperature of the heat diffusion is 550±50℃, and the heat diffusion time is 0.8-1.5 seconds.

[0020] In one embodiment, in step S4, the pickling conditions include: the pickling solution is a sulfuric acid solution, the pH of the pickling solution is 1.20±0.20, the zinc oxide on the surface is removed, the zinc ion concentration in the pickling solution is required to be less than or equal to 5g / L, and the pickling solution is replaced if the concentration exceeds the standard.

[0021] In one embodiment, the thickness ratio of the copper layer to the zinc layer is 4:1.

[0022] Compared with existing technologies, this invention provides a surface pretreatment method for cold drawing tungsten wire. The method involves plating the surface of the tungsten wire raw material with nickel, copper, and zinc, forming an alloy at high temperature. Nickel increases bonding strength, while the copper-zinc alloy reduces friction with the die during cold drawing, thereby reducing die damage during tungsten wire cold drawing, decreasing the breakage rate, significantly improving cold drawing yield, and substantially reducing production costs. Tungsten wire treated using this pretreatment method exhibits the following beneficial effects:

[0023] 1. When pre-treated tungsten wire raw materials are cold drawn, the wear of the die is reduced by 50%, which greatly reduces the use of drawing dies and thus reduces the drawing cost.

[0024] 2. When pretreated tungsten wire raw materials are drawn, the wire breakage rate is reduced by more than 30%, and the final yield rate is increased from 60% to 90%, which contributes to the reduction of tungsten wire cost and its widespread use.

[0025] 3. The tungsten wires drawn from the pretreated tungsten raw materials can be finer. Tungsten wires with a diameter of 22μm have been successfully drawn. At the same time, the straightness of the drawn tungsten wires is better, and the coil diameter has been increased from 50mm to 70μm. Attached Figure Description

[0026] Figure 1 The diagram shown is a process flow chart of the pretreatment method of the present invention;

[0027] Figure 2 The image shown is of the tungsten wire obtained in Example 1 of the present invention.

[0028] Figure 3 The image shown is of the tungsten wire obtained in Comparative Example 2 of this invention. Detailed Implementation

[0029] Please see Figures 1 to 3The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0030] This invention provides a surface pretreatment method for cold-drawn tungsten wire, which may specifically include the following steps:

[0031] 1. This invention is a continuous electroplating production process in which raw materials are produced in one go after passing through various processes from the production line.

[0032] 2. From the start of the wire feeding process, the tungsten wire undergoes sodium hydroxide electrolytic alkaline washing to remove any residual graphite. It is then washed with water to remove the sodium hydroxide solution from the surface. Next, the tungsten wire is activated by aminosulfonic acid pickling, followed by water washing to remove any residual aminosulfonic acid from the surface. This process is called pretreatment cleaning.

[0033] 3. The pre-treated and cleaned tungsten wire is placed in a nickel plating bath for nickel plating to a thickness of 0.2μm to increase the adhesion between the plating layer and the substrate. Then, the surface plating solution is washed off with water. Next, it is placed in a copper plating bath for copper plating to a thickness of 0.8μm. After washing off the copper plating solution, it is placed in a zinc plating bath for zinc plating to a thickness of 0.2μm. After washing off the zinc plating solution, the copper and zinc plating are used to form a copper-zinc alloy, with a brass-colored surface.

[0034] In some embodiments, the thickness of the copper layer is 0.6~1.0 μm, and the thickness of the zinc layer is 0.15~0.25 μm. Further, the thickness ratio of the copper layer to the zinc layer is 4:1. Within this ratio range, the pretreated tungsten wire can be guaranteed to have a good drawing yield, and the wire diameter after pretreatment can be controlled within a reasonable range.

[0035] 4. After being plated with nickel, copper, and zinc, the mixture is placed in a thermal diffusion furnace and formed into a copper-zinc alloy in 0.8 seconds at a high temperature of 500°C.

[0036] 5. After the copper-zinc alloy is formed, there is a small amount of zinc oxide on the surface. Therefore, it is then placed in a sulfuric acid bath to react with sulfuric acid to remove the zinc oxide on the surface of the copper-zinc alloy. This coating is more conducive to drawing.

[0037] 6. After that, wash off the sulfuric acid solution on the surface with hot water, blow dry with air, and finally reel in the wire to make the finished product. The copper content of the pretreated tungsten wire can be greater than or equal to 20g / kg.

[0038] The preprocessing method of the present invention will be illustrated below through specific embodiments.

[0039] Example 1

[0040] Using the technical solution of this invention, 60μm tungsten wire raw material is used, and its surface is subjected to alloying pretreatment. The specific process is as follows:

[0041] (1) The tungsten wire is placed in an alkaline washing tank for cleaning. The alkaline washing solution used is 70±5g / L sodium hydroxide, the temperature is 60±2℃, and the electrolysis voltage is 4V. After cleaning, the sodium hydroxide solution on the surface of the tungsten wire is washed off with water. The pH of the water washing is ≤9.

[0042] (2) Tungsten wires are put into the pickling tank for cleaning and activation. The pickling solution is 30±5g / L aminosulfonic acid, and the temperature is room temperature. After pickling, the aminosulfonic acid solution on the surface is washed off with water. The pH of the wash water is required to be ≥4.

[0043] (3) The acid-washed and activated tungsten wire is then placed in a nickel plating bath. The plating solution used is a nickel sulfamate system, with a nickel ion concentration of 100±5 g / L, a boric acid concentration of 40±3 g / L, a nickel chloride concentration of 5±2 g / L, a pH of 3.80±0.20, a temperature of 50±2℃, and a nickel plating thickness of 0.2 μm. After nickel plating, the surface is rinsed with water to remove any residual plating solution. The rinse water must have a pH ≥ 4.

[0044] (4) The nickel-plated tungsten wire enters the copper plating bath. The electroplating solution used is a copper pyrophosphate system, with a copper ion concentration of 27±3 g / L, a pyrophosphate concentration of 200±20 g / L, a coke ratio of 7.5±0.5, a pH of 8.30±0.20, a temperature of 50±2℃, and a copper plating thickness of 0.8 μm. After copper plating, the surface is rinsed with water to remove any residual plating solution. The rinse water must have a pH ≤ 8.

[0045] (5) The copper-plated tungsten wire enters the zinc plating bath. The electroplating solution used is a zinc sulfate system, with a zinc sulfate heptahydrate concentration of 220±30 g / L, a zinc ion concentration of 47±3 g / L, a pH of 1.80±0.20, a temperature of 40±2℃, and a zinc plating thickness of 0.2 μm. After zinc plating, the surface is rinsed with water to remove any residual plating solution. The rinse water must have a pH ≥ 4.

[0046] (6) The galvanized tungsten wire enters the thermal diffusion furnace, which requires a temperature of 550±50℃ and a thermal diffusion time of 0.8-1.5 seconds to form a copper-zinc alloy with a brass color.

[0047] (7) The alloyed tungsten wire enters the sulfuric acid washing process. The solution is sulfuric acid solution with a pH of 1.20±0.20 to remove zinc oxide from the surface. The zinc ion concentration in the solution is required to be ≤5g / L. If the concentration exceeds the standard, the sulfuric acid solution should be replaced.

[0048] (8) Finally, the surface is washed with hot water to remove the residual zinc sulfate solution, then dried by air, and finally the thread is collected to make the finished product.

[0049] Example 2: The difference from Example 1 is that 50μm tungsten wire raw material is used, while the other steps are the same as in Example 1.

[0050] Example 3: The difference from Example 1 is that 45μm tungsten wire raw material is used, while the other steps are the same as in Example 1.

[0051] Comparative Example 1: The difference from Example 1 is that the copper plating thickness is 0.6 μm and the zinc plating thickness is 0.2 μm, while the other steps are the same as in Example 1.

[0052] Comparative Example 2: The difference from Example 1 is that the copper plating thickness is 0.4 μm and the zinc plating thickness is 0.4 μm, while the other steps are the same as in Example 1.

[0053] Performance Evaluation

[0054] (1) Appearance evaluation: Observe the color of the tungsten wire coating after pretreatment. If the color is brass, it is considered qualified.

[0055] (2) Copper content test: The copper content of the electroplated tungsten wire is determined by corrosion dissolution. The qualified standard for copper content is ≥20g / kg. The copper content of the pretreated tungsten wire should be greater than or equal to 20g per kilogram. Only when the copper content is greater than or equal to 20g can the yield of the cold-drawn tungsten wire in the subsequent process be greater than 90%. When the copper content is low, the drawing yield is low, the toughness is poor, and it is easy to break the die and the wire breaks.

[0056] Determination method: Take a piece of plated tungsten wire and weigh it as A. Then dissolve the plating of the tungsten wire with nitric acid. Then measure the weight B of copper in the solution by titration. The copper content is B*1000 / A (g / kg).

[0057] The results of the above tests on the above embodiments and comparative examples are shown in Table 1.

[0058] Table 1 Performance Comparison of Examples and Comparative Examples

[0059] Exterior color Copper content Example 1 brass 24.95g / kg Example 2 brass 30.19g / kg Example 3 brass 33.41g / kg Comparative Example 1 light brass color 18.65g / kg Comparative Example 2 silver-gray 12.39g / kg

[0060] Table 1 shows that when the copper layer to zinc layer thickness ratio is 4:1 in Examples 1-3, the copper content meets the qualified standard. However, in Comparative Examples 1-2, the small copper-zinc thickness ratio results in an excessively low copper content, making them unqualified products.

[0061] A comparison of Examples 1-3 reveals that as the diameter of the tungsten wire decreases, the copper content gradually increases. This is because the weight A decreases after the diameter of the tungsten wire decreases, leading to an increase in the copper content.

[0062] Therefore, this invention effectively overcomes the various shortcomings of the prior art and has high industrial applicability. The above embodiments are merely illustrative of the principles and effects of this invention and are not intended to limit the invention. Any person skilled in the art can modify or change the above embodiments without departing from the spirit and scope of this invention. Therefore, all equivalent modifications or changes made by those skilled in the art without departing from the spirit and technical concept disclosed in this invention should still be covered by the claims of this invention.

Claims

1. A surface pretreatment method for cold-drawn tungsten wire, characterized in that, The surface pretreatment method includes the following steps: S1: Provide a tungsten wire, and subject the tungsten wire to alkaline washing and acid washing; S2: The acid-washed tungsten wire is sequentially electroplated with nickel, copper and zinc layers; S3: Thermal diffusion is performed on the tungsten wire after electroplating with zinc to obtain a tungsten wire with a copper-zinc alloy layer; S4: Pickling, washing and air drying are performed on tungsten wires with copper-zinc alloy layers.

2. The surface pretreatment method according to claim 1, characterized in that: In step S1, the diameter of the tungsten wire is 45~60μm.

3. The surface pretreatment method according to claim 1, characterized in that: In step S1, the conditions for alkaline washing include: the alkaline washing solution is 70±5 g / L sodium hydroxide, the temperature is 60±2℃, and the electrolysis voltage is 4V; after alkaline washing, the water is washed with water, and the pH of the water used for washing is less than or equal to 9.

4. The surface pretreatment method according to claim 1, characterized in that: In step S1, the pickling conditions include: the pickling solution is 30±5 g / L of aminosulfonic acid, and the temperature is room temperature; the pickling is followed by water washing, and the pH of the water used for washing is greater than or equal to 4.

5. The surface pretreatment method according to claim 1, characterized in that: In step S2, the conditions for electroplating the nickel layer include: the electroplating solution is a nickel sulfamate system, wherein the nickel ion concentration is 100±5 g / L, the boric acid concentration is 40±3 g / L, the nickel chloride concentration is 5±2 g / L, the pH is 3.80±0.20, and the temperature is 50±2℃; after electroplating the nickel layer, it is washed with water, and the pH of the water used for washing is greater than or equal to 4.

6. The surface pretreatment method according to claim 1, characterized in that: In step S2, the conditions for electroplating the copper layer include: the electroplating solution is a copper pyrophosphate system, wherein the copper ion concentration is 27±3 g / L, the pyrophosphate concentration is 200±20 g / L, the pyrophosphate ratio is 7.5±0.5, the pH is 8.30±0.20, the temperature is 50±2℃, and the copper layer is washed with water after electroplating, and the pH of the wash water is required to be less than or equal to 8.

7. The surface pretreatment method according to claim 1, characterized in that: In step S2, the conditions for electroplating the zinc layer include: the electroplating solution is a zinc sulfate system, wherein the concentration of zinc sulfate heptahydrate is 220±30 g / L, the zinc ion concentration is 47±3 g / L, the pH is 1.80±0.20, the temperature is 40±2℃, and the zinc layer is washed with water after electroplating, and the pH of the wash water is required to be greater than or equal to 4.

8. The surface pretreatment method according to claim 1, characterized in that: In step S3, the temperature of the heat diffusion is 550±50℃, and the heat diffusion time is 0.8-1.5 seconds.

9. The surface pretreatment method according to claim 1, characterized in that: In step S4, the pickling conditions include: the pickling solution is a sulfuric acid solution, the pH of the pickling solution is 1.20±0.20, the zinc ion concentration in the pickling solution is required to be less than or equal to 5g / L, and the pickling solution should be replaced if the concentration exceeds the standard.

10. The surface pretreatment method according to claim 1, characterized in that: The thickness ratio of the copper layer to the zinc layer is 4:1.

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