Tungsten filament gradient synergistic electrolytic polishing solution, preparation method and electrolytic polishing method

Abstract

The invention discloses a tungsten filament gradient synergistic electrolytic polishing solution, a preparation method and an electrolytic polishing method. The electrolytic polishing solution comprises the following components of, by mass concentration, 9-12 g / L of sodium hydroxide, 3-6 g / L of sodium carbonate, 4-6 g / L of sodium citrate and 0.5-1.5 g / L of polyethylene glycol 600. The electrolytic polishing solution is alkaline, an alkaline electrolysis system avoids the common over-corrosion problem of an acidic system by dynamically controlling dissolution balance, and the alkaline system is wide in operation window, stable in electrolyte and suitable for continuous production.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electroplated diamond wire preparation, and particularly relates to a tungsten wire gradient synergistic electrolytic polishing solution, a preparation method and an electrolytic polishing method. BACKGROUND

[0002] At present, crystalline silicon cells continue to dominate the photovoltaic technology route with a mature process system and a market share of up to 90%. Under this background, as the core process of silicon wafer manufacturing, the diamond wire cutting technology has become an industry standard due to its high cutting efficiency (wire speed up to 30-40 m / s) and low material loss (silicon loss reduced from 40% in traditional mortar cutting to below 15%).

[0003] As the core consumable for photovoltaic silicon wafer cutting, the performance of the busbar material of the electroplated diamond wire directly affects the cutting efficiency and the quality of the silicon wafer. With the development of silicon wafers towards large size and thinning, traditional carbon steel busbars face bottlenecks due to the limit of thinning (close to 38-42 μm) and insufficient strength, while tungsten wire busbars, with higher tensile strength (6000-6500 N / mm²) and thinner wire diameter (as low as 27 μm), have become an important direction to replace carbon steel. Under this background, tungsten wire electrolytic polishing, as a key process for busbar pretreatment, has high compatibility with the performance requirements of electroplated diamond wire and broad application prospects.

[0004] Tungsten wire electrolytic polishing can significantly reduce the surface roughness of tungsten wire, reduce microscopic defects, provide a uniform substrate for subsequent nickel plating and diamond particle consolidation, and improve the adhesion of the plating layer. The tungsten wire electrolytic polishing process (three-stage electrolytic polishing → water washing → drying) has been integrated into the existing gold wire downstream processing production line, and does not require additional equipment, with strong compatibility with carbon steel busbar processes.

[0005] At present, most tungsten wire electrolytic polishing solutions are acidic systems. For example, Chinese Patent CN201010155303 discloses a polishing solution for molybdenum grid electrolytic polishing, which is prepared from 400-450 ml of phosphoric acid, 150-200 ml of sulfuric acid, 40-60 g of nickel sulfate, and 150-200 ml of water; and Chinese Patent CN104962857A discloses a polishing solution for molybdenum heating element electrolytic polishing, which is prepared from 5-10 vol.% hydrofluoric acid, 10-20 vol.% nitric acid, and water. Both of the above-mentioned acidic polishing solutions have strong corrosive properties and generate polluting gases such as SO 2 and NO 2 during the polishing process. In particular, hydrogen fluoride has strong irritation to the skin, eyes, respiratory tract, and digestive tract mucosa, and is highly toxic to the human body.

[0006] Therefore, some electrolytic polishing solutions using alkaline systems have also been developed at this stage, such as: Chinese patent CN104060320A discloses a tungsten spiral line electrolytic polishing polishing liquid, the polishing liquid is prepared from sodium phosphate, sodium hydroxide, glycerol and water; but in its technical solution, viscous liquid film is difficult to remove from the diamond abrasive grain gap, leading to micro area corrosion; Chinese patent CN105887179B discloses a tungsten alloy or molybdenum alloy electrolytic polishing liquid and electrolytic polishing method, which is prepared by mixing sodium hydroxide, sodium carbonate, sodium molybdate and water; but in its technical solution, molybdenum will be co-deposited on the tungsten surface, reducing the diamond coating adhesion (XPS detects Mo-C hybrid peak). SUMMARY

[0007] In order to solve the problems existing in the prior art, the purpose of the present application is to provide a tungsten wire gradient synergistic electrolytic polishing liquid, a preparation method and an electrolytic polishing method.

[0008] In order to achieve the above-mentioned purpose of the application, the technical solution adopted by the present application is as follows: A tungsten wire diamond wire gradient synergistic electrolytic polishing liquid, comprising the following components with the following mass concentrations: sodium hydroxide 9-12 g / L, sodium carbonate 3-6 g / L, sodium citrate 4-6 g / L, polyethylene glycol 600 0.5-1.5 g / L.

[0009] Further, the molar concentration ratio of polyethylene glycol 600 to sodium citrate is 1:(8-12).

[0010] Further, the conductivity of the electrolytic polishing liquid is 15-25 mS / cm.

[0011] Further, the mass ratio of sodium hydroxide to sodium carbonate is 3:1.

[0012] Further, the molar concentration ratio of polyethylene glycol 600 to sodium citrate is 1:10.

[0013] A preparation method of a tungsten wire diamond wire gradient synergistic electrolytic polishing liquid, comprising the following steps: Step one: premix sodium hydroxide and sodium carbonate in 50-60℃ deionized water to form a basic electrolyte; Step two: after the electrolyte of step one is cooled to below 30℃, add sodium citrate and polyethylene glycol 600 in sequence; Step three: filter the solution obtained in step two through a 0.22μm microporous filter membrane to prepare the electrolytic polishing liquid, and store it under nitrogen protection.

[0014] A method for electrolytic polishing of tungsten wire using the above-mentioned electrolytic polishing liquid, spraying the electrolytic polishing liquid onto the tungsten wire through a nozzle, and applying a constant current between the nozzle and the tungsten wire.

[0015] Further, the constant current is 0.3A.

[0016] Due to the above technical solutions, the application has the following advantages: 1. The electrolytic polishing solution of the application is alkaline. The alkaline electrolytic system controls the dissolution balance dynamically, avoids the over-corrosion problem commonly seen in acid systems, and has a wide operating window. The stability of the alkaline system is >200 hours, which is suitable for continuous production, reduces maintenance costs, and compared with the acid system, the alkaline electrolytic polishing solution does not volatilize strong acid, the waste liquid treatment cost is reduced by 40-60%, and meets the green manufacturing trend of the photovoltaic industry.

[0017] 2. By adjusting the ratio of sodium hydroxide and sodium carbonate, a dynamic buffer system can be formed, which can stabilize the pH value of the electrolytic polishing solution at 10.8-11.0.

[0018] 3. By adjusting the molar concentration ratio of polyethylene glycol 600 and sodium citrate, the oxidation product can be promoted to separate, and the diamond interface can be protected by steric hindrance effect.

[0019] 4. During the electrolytic polishing process, a constant current of 0.3A is applied between the nozzle and the tungsten wire, so that the components in the electrolytic polishing solution can effectively cooperate. Sodium hydroxide and sodium carbonate can maintain the pH stability. Sodium citrate can complex tungsten ions to prevent the accumulation of passivation layer. Polyethylene glycol 600 acts as a surfactant to reduce surface tension, promote uniform distribution of electrolyte, and timely remove bubbles and impurities. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 The tungsten wire before electrolytic polishing; Figure 2 The tungsten wire after electrolytic polishing with a constant current of 0.2A; Figure 3 The tungsten wire after electrolytic polishing with a constant current of 0.3A; Figure 4 The tungsten wire after electrolytic polishing with a constant current of 0.4A. DETAILED DESCRIPTION

[0021] The technical solutions of the application will be further described in detail through specific embodiments.

[0022] A tungsten wire diamond wire gradient synergistic electrolytic polishing solution, comprising the following mass concentration of components: sodium hydroxide 9-12g / L, sodium carbonate 3-6g / L, sodium citrate 4-6g / L, polyethylene glycol 600 0.5-1.5g / L; the conductivity of the electrolytic polishing solution is 15-25mS / cm.

[0023] In the present application, the mass concentration and the ratio of each component are strictly required, that is, when the mass concentration of sodium hydroxide is greater than 12 g / L, the dissolution rate of tungsten changes abruptly (>0.8 μm / min), which causes damage to the diamond coating; when the mass concentration of sodium carbonate is less than 3 g / L, the buffer capacity of the solution decreases (pH fluctuation > ± 0.5), and etch pits are generated on the surface.

[0024] As a preferred embodiment of the present application, the molar concentration ratio of polyethylene glycol 600 to sodium citrate is 1: (8-12).

[0025] When the molar ratio of sodium citrate to polyethylene glycol 600 is greater than 12:1, the complex is oversaturated and precipitates, and when the molar ratio of sodium citrate to polyethylene glycol 600 is less than 8:1, the wettability deteriorates.

[0026] As a preferred embodiment, the mass concentration ratio of sodium hydroxide to sodium carbonate is 3:1, forming a buffer system of [CO3^2−] / [OH−]=0.17, which can stabilize the pH value at 10.8-11.0.

[0027] The molar concentration ratio of polyethylene glycol 600 to sodium citrate is 1:10, which can promote the separation of oxidation products and protect the diamond interface through steric hindrance effect.

[0028] A preparation method of a tungsten wire diamond wire gradient synergistic electrolytic polishing solution, comprising the following steps: Step one: mixing sodium hydroxide and sodium carbonate in 50-60℃ deionized water to form a basic electrolyte; Step two: after the electrolyte in step one is cooled to below 30℃, sodium citrate and polyethylene glycol 600 are added in sequence; Step three: filtering the solution obtained in step two through a 0.22 μm microporous filter to obtain an electrolytic polishing solution, and storing it under nitrogen protection.

[0029] A method for electrolytic polishing of tungsten wire using the above-mentioned electrolytic polishing solution, spraying the electrolytic polishing solution onto the tungsten wire through a nozzle, and applying a constant current between the nozzle and the tungsten wire.

[0030] During the electrolytic polishing of the tungsten wire, the current intensity directly affects the core mechanism and surface reaction kinetics balance of the polishing effect, and as a preferred embodiment of the present application, the constant current is 0.3 A.

[0031] The present application takes 0.2 A, 0.3 A and 0.4 A per root as a control, and 0.3 A current shows the best polishing effect, as shown in Figure 3 , compared with Figure 1The rough tungsten-based bus in the electrolyte has obvious improvement; it is shown that the components in the electrolyte can effectively cooperate when the current is moderate, sodium hydroxide and sodium carbonate can maintain the pH stability of the electrolytic polishing solution, sodium citrate can complex tungsten ions to prevent the accumulation of passivation layer, and polyethylene glycol 600 can reduce the surface tension, promote the uniform distribution of the electrolyte, and timely discharge bubbles and impurities.

[0032] When the current is too large (0.4A), it will cause the local current density to be too high, and excessive electrolysis will be caused, as shown in Figure 4 , bubbles and etch pits are generated. At the same time, the temperature rise will accelerate the side reaction, destroy the stability of the electrolyte, such as the decomposition of sodium carbonate, the fluctuation of pH value, and affect the polishing effect.

[0033] When the current is too low (0.2A), the electrolysis reaction is insufficient, which leads to poor effect, as shown in Figure 2 , because the oxide layer cannot be effectively dissolved, which leads to more surface residues and higher roughness, and at the same time, insufficient current will lead to insufficient polarization, and the metal dissolution rate is not enough, and a uniform polished surface cannot be formed. Embodiment

[0034] A tungsten wire diamond wire gradient synergistic electrolytic polishing solution, comprising the following mass concentration of components: sodium hydroxide 10.5g / L, sodium carbonate 3.5g / L, sodium citrate 5g / L, polyethylene glycol 600 0.5g / L; The above electrolytic polishing solution of the present application is used for electrolytic polishing processing of 32μm tungsten wire, and the ellipticity representing the range of wire diameter fluctuation is reduced from 0.77μm to 0.15μm (infrared diameter instrument measurement data), and after continuous electrolytic polishing processing for 72 hours, the produced tungsten wire is still very smooth.

[0035] The electrolytic polishing solution of the present application is suitable for tungsten wire with a wire diameter of 27-35μm, and through long-term production practice, the polishing tungsten wire qualified rate is improved from 90% to 98%.

[0036] In the present application, sodium citrate has an activation effect, and the carboxyl group can form a Ni-citrate composite transition layer with the subsequent nickel plating layer to enhance the bonding force; and polyethylene glycol has a self-stripping property, and the adsorbed film automatically dissociates after electrolysis stops, without additional cleaning.

Claims

1. A tungsten wire diamond wire gradient synergistic electrolytic polishing solution, characterized by: comprising the following components: sodium hydroxide 9-12 g / L, sodium carbonate 3-6 g / L, sodium citrate 4-6 g / L, polyethylene glycol 600 0.5-1.5 g / L.

2. The wire electrochemical discharge grinding fluid of claim 1, wherein: The molar concentration ratio of polyethylene glycol 600 to sodium citrate is 1:(8-12).

3. The wire electrochemical discharge grinding fluid of claim 2, wherein the tungsten wire is made of tungsten wire having a diameter of 0.1 mm to 0.3 mm. The molar concentration ratio of polyethylene glycol 600 to sodium citrate is 1:

10.

4. The wire electrochemical discharge grinding fluid of tungsten wire according to claim 1, wherein: The conductivity of the electrolytic polishing solution is 15-25 mS / cm.

5. The wire electrochemical discharge grinding fluid of tungsten wire according to claim 1, wherein: The mass ratio of sodium hydroxide to sodium carbonate is 3:

1.

6. A method for preparing the tungsten wire diamond wire gradient synergistic electrolytic polishing solution according to any one of claims 1-5, characterized by: comprising the following steps: Step one: premixing sodium hydroxide and sodium carbonate in 50-60℃ deionized water to form a basic electrolyte; Step two: after the electrolyte of step one is cooled to below 30℃, adding sodium citrate and polyethylene glycol 600 in sequence; Step three: filtering the solution obtained in step two through a 0.22μm microporous filter to obtain the electrolytic polishing solution, and storing it under nitrogen protection.

7. A method of electrolytically polishing a tungsten wire using the electrolytic polishing solution according to any one of claims 1 to 5, characterized by: The electrolytic polishing solution is sprayed onto the tungsten wire through a nozzle, and a constant current is applied between the nozzle and the tungsten wire.

8. The method of claim 7, wherein the electrolytic polishing solution is used to electrolytically polish tungsten wire. The constant current is 0.3A.

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