Deoxidant and oxidation film removal process

Abstract

The invention discloses a technology for removing a deoxidant and an oxidation film, the deoxidant comprises sulfuric acid and sodium thiosulfate, in a deoxidant solution, the concentration of the sulfuric acid is 5-90 g / L, and the concentration of the sodium thiosulfate is 5-50 g / L. Sulfuric acid and sodium thiosulfate are adopted as deoxidants, the sulfuric acid is used for removing oxides or sulfides on the surface of a base material, the sodium thiosulfate can inhibit oxidation reaction, and the sodium thiosulfate is a weak reducing agent and can reduce Cu < 2 + > into Cu under the acidic condition; sodium thiosulfate can play a catalytic role in the reduction process, and the reaction speed is increased; sodium thiosulfate can inhibit oxidation reaction, and thiosulfate ions (S2O3 < 2->) can react with oxygen molecules to prevent oxygen from further reacting with other substances.

Description

Technical Field

[0001] The invention relates to a surface pretreatment process, in particular to a process for removing a deoxidizer and an oxide film. Background Art

[0002] After being plastic-sealed, electronic components on the market will form an oxide film on the surface due to high temperature or copper oxidation itself, which will hinder the electroplating process or cause the adhesion of the electroplating layer to decrease. Currently, the market mainly uses dilute acid (mainly sulfuric acid or nitric acid) to remove it, and the deoxidation ability is relatively weak.

[0003] Silver electroplating is a technology that uses the principle of an electrolytic cell to deposit a metal coating with good adhesion but different properties on a mechanical product. Through silver electroplating, a decorative protective and functional layer can be obtained on mechanical products such as rectifier bridges. This layer of silver plating can not only effectively prevent corrosion, but also increase conductivity. At the same time, the gloss and reflectivity of the silver plating also improve the aesthetics of the product. In addition, the silver electroplating layer is more uniform than the hot-dip layer, and is generally thinner, ranging from a few microns to tens of microns. It is widely used in manufacturing enterprises such as household appliances, instruments and lighting equipment. For example, when copper or copper alloy materials are electroplated with silver, they will first be degreased and rusted, and then pre-plated with thin silver or immersed in a solution composed of mercuric chloride and other solutions for mercurization treatment, so that a layer of mercury film is plated on the surface of the workpiece, and then the workpiece is used as the cathode and the pure silver plate is used as the anode. It is immersed in a potassium silver cyanide electrolyte composed of silver nitrate and potassium cyanide for electroplating. Products such as rectifier bridges treated in this way have multiple effects such as good corrosion resistance, conductivity, reflection and beauty.

[0004] However, after electroplating, the silver layer will easily react with oxygen or sulfur in the air to form silver oxide or silver sulfide, which will cause the metal surface to be discolored, hinder the electroplating process or cause the adhesion of the electroplated layer to decrease, affecting the customer's welding use, so the oxide layer needs to be removed. However, the conventional method of removing the oxide layer with dilute acid (mainly sulfuric acid or nitric acid) cannot effectively remove the silver oxide layer or silver sulfide layer. Summary of the invention

[0005] In view of the problem that the above conventional methods cannot effectively remove the oxide film and silver oxide layer on the copper surface, the present invention provides a deoxidizer and an oxide film removal process. The process uses sodium thiosulfate to enhance the deoxidation ability of the deoxidation solution, which can effectively remove severe oxide films and ensure the adhesion of the electroplating layer.

[0006] In order to achieve the above object, the present invention provides a deoxidizer, which includes sulfuric acid and sodium thiosulfate. In the deoxidizer solution, the concentration of sulfuric acid is 5-90 g / L, and the concentration of sodium thiosulfate is 5-50 g / L.

[0007] In one embodiment of the present invention, in the deoxidizer solution, the concentration of sulfuric acid is 5-90 g / L, and the concentration of sodium thiosulfate is 5-40 g / L.

[0008] In another embodiment of the present invention, in the deoxidizer solution, the concentration of sulfuric acid is 5-30 g / L, and the concentration of sodium thiosulfate is 5-50 g / L.

[0009] A second aspect of the present invention provides a process for removing an oxide film on a copper surface, comprising the following steps: A. Soak the oxidized product in a strong alkaline solution with a concentration of 10-50 g / L for 1-15 minutes, and use the alkaline saponification reaction to hydrolyze the oil on the surface of the material; B. Wash the product treated in step A with water at room temperature and hot water in turn. The water at room temperature uses overflow to remove most of the alkaline agents on the surface of the material. The hot water is used to completely remove the alkaline agents. If cold water is omitted, the hot water will be seriously polluted after several rounds, affecting the cleaning effect. C. Soak the product treated in step B in a solution containing 5-40 g / L sodium thiosulfate and 5-90 g / L sulfuric acid for 1-10 min; D. Wash the product treated in step C with water.

[0010] In the above technical solution, a mixed solution of sodium thiosulfate and sulfuric acid is used to remove the oxide film on the copper surface. The principle is: Sulfuric acid reacts with oxides (mainly copper oxide) to remove the oxide layer: CuO + H2SO4 → CuSO4 + H2O; Sodium thiosulfate is a weak reducing agent that can reduce Cu 2+ Reduced to Cu; sodium thiosulfate can play a catalytic role in the reduction process and accelerate the reaction rate; Sodium thiosulfate can inhibit oxidation reactions, in which thiosulfate ions (S2O3 2- ) can react with oxygen molecules, preventing oxygen from further reacting with other substances.

[0011] The above process can effectively and thoroughly remove copper oxide and grease on the surface, so that the coating and the substrate fit perfectly without the addition of an oxide layer, thus ensuring adhesion.

[0012] Preferably, in step A, the temperature of the strong alkaline solution is 40-80°C.

[0013] In the above technical solution, at this temperature, dirt and grease on the surface can be effectively removed. The strong base is potassium hydroxide or sodium hydroxide.

[0014] Preferably, in step B, the washing with water at room temperature is performed at least twice.

[0015] In the above technical solution, residual dirt and grease can be effectively removed by washing with water at room temperature for multiple times.

[0016] Preferably, in step B, the temperature of the hot water for washing with hot water is 50-80° C. to completely remove the strong alkaline agent.

[0017] Preferably, in step C, the solution is at room temperature.

[0018] A third aspect of the present invention provides a process for removing an oxide film of a silver-plated layer, comprising the following steps: S1. Soak the oxidized silver-plated product in a solution containing 5-50 g / L sodium thiosulfate and 5-30 g / L sulfuric acid for 0.5-3 min; S2, washing the product treated in step S1 with water at room temperature and with hot water in sequence; S3. Bake the product processed in step S2 at 150±10° C. for 1 hour.

[0019] In the above technical solution, 1. Sulfuric acid: Reacts with oxides (mainly silver oxide) to remove the oxide layer: Ag2O+H2SO4→Ag2SO4+H2O Reacts with sulfides (mainly silver sulfide) to remove sulfides: Ag2S + H2SO4 = Ag2SO4 + H2S 2. Sodium thiosulfate: Antioxidant property: Sodium thiosulfate can inhibit oxidation reaction, among which thiosulfate ion (S2O3 2- ) can react with oxygen molecules, preventing oxygen from further reacting with other substances.

[0020] Catalytic effect: Sodium thiosulfate can play a catalytic role in the reduction process and accelerate the reaction rate.

[0021] Preferably, in step S1, the temperature of the solution is 30-45°C.

[0022] In the above technical solution, at this temperature, the deoxidation and desulfurization reactions can be accelerated.

[0023] Preferably, in step S2, the normal temperature water washing is performed at least twice.

[0024] In the above technical solution, by performing multiple normal temperature water washings, Preferably, in step S2, the temperature of hot water for hot water washing is (≥60°C).

[0025] In the above technical solution, the purpose of normal temperature water washing is to remove the residual agent on the surface of the material. The purpose of hot water washing is: 1. Completely remove the residual agent on the surface; 2. When the material is baked after being soaked in hot pure water, the surface moisture is more likely to evaporate, because the temperature of the residual water on the surface of the material after hot water washing is higher, which helps to accelerate the evaporation of water.

[0026] Through the above technical solution, the present invention achieves the following beneficial effects: The present invention uses sulfuric acid and sodium thiosulfate as deoxidizers. Sulfuric acid is used to remove oxides or sulfides on the surface of the substrate. Sodium thiosulfate can inhibit oxidation reactions. Sodium thiosulfate is a weak reducing agent that can reduce Cu under acidic conditions. 2+ Reduced to Cu; Sodium thiosulfate can play a catalytic role in the reduction process and accelerate the reaction rate; Sodium thiosulfate can inhibit the oxidation reaction, in which the thiosulfate ion (S2O3 2- ) can react with oxygen molecules, preventing oxygen from further reacting with other substances. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Schematic diagram of the locations of five points on the surface of the copper substrate after treatment in Example 1; Figure 2 is the eZAF intelligent quantitative result of EDS point 1 on the surface of the copper substrate treated in Example 1; Figure 3 is the eZAF intelligent quantitative result of EDS point 2 on the surface of the copper substrate treated in Example 1; Figure 4 is the eZAF intelligent quantitative result of EDS point 3 on the surface of the copper substrate treated in Example 1; Figure 5 is the eZAF intelligent quantitative result of EDS point 4 on the surface of the copper substrate treated in Example 1; Figure 6 is the eZAF intelligent quantitative result of EDS point 5 on the surface of the copper substrate treated in Example 1; Figure 7 Schematic diagram of the locations of 5 points on the surface of the copper substrate after treatment in Example 1; Figure 8 is the eZAF intelligent quantitative result of EDS point 1 on the surface of the copper substrate after treatment in comparative example 1; Fig. 9 is the eZAF intelligent quantitative result of EDS point 2 on the surface of the copper substrate treated in comparative example 1; Fig.10 is the eZAF intelligent quantitative result of EDS point 3 on the surface of the copper substrate after treatment in comparative example 1; Fig.11is the eZAF intelligent quantitative result of EDS point 4 on the surface of the copper substrate treated in comparative example 1; Fig.12 is the eZAF intelligent quantitative result of EDS point 5 on the surface of the copper substrate treated in comparative example 1; Fig.13 This is the result of the constant temperature and humidity treatment of the silver surface treated in Example 4; Fig.14 This is the result of the constant temperature and humidity treatment of the silver surface treated in Example 2. DETAILED DESCRIPTION

[0028] The specific implementation of the present invention is described in detail below in conjunction with the examples. It should be understood that the specific implementation described herein is only used to illustrate and explain the present invention, and is not used to limit the present invention.

[0029] In the following Examples 1-2 and Comparative Example 1, the treated products are GBJ series rectifier bridge products, which are moderately oxidized (the oxide film thickness is about 5 microns).

[0030] Example 1 Removal of oxide film on copper surface: A. Soak the oxidized product in a strong alkaline solution with a concentration of 10 g / L for 15 minutes; B. Wash the product treated in step A twice with normal temperature water and once with hot water; C. Soak the product treated in step B in a solution containing 5 g / L sodium thiosulfate and 90 g / L sulfuric acid for 1 min; D. Wash the product treated in step C with water.

[0031] Example 2 Removal of oxide film on copper surface: A. Soak the oxidized product in a strong alkaline solution with a concentration of 50 g / L for 1 minute; B. Wash the product treated in step A twice with normal temperature water and once with hot water; C. Soak the product treated in step B in a solution containing 40 g / L sodium thiosulfate and 5 g / L sulfuric acid for 10 min; D. Wash the product treated in step C with water.

[0032] Comparative Example 1 Other conditions were the same as in Example 1, except that sodium thiosulfate was not used.

[0033] Verify the removal effect of the oxide film of Example 1, Example 2 and Comparative Example 1: 1. EDX detects whether there is oxide on the surface of copper Determination of Example 1 ( Figure 1 ) and Comparative Example 1 ( Figure 7 ) at 5 points on the copper substrate surface after treatment (conditions: kV: 20, magnification: 600, take-off angle: 12.6, live time (s): 50, amplifier time constant (µs): 7.68, resolution: (eV) 131.9), the eZAF intelligent quantitative results of Example 1 are as follows Figure 2-Figure 6 As shown in Table 1, the results show that there is no oxygen residue on the surface of the copper substrate after being treated in Example 1. Figure 8-Figure 12 As shown in Table 2, the results show that oxygen remains on the surface of the copper substrate after being treated in Comparative Example 1.

[0034] Table 1 EDX test results of copper surface treated in Example 1

[0035] Table 2 EDX test results of copper surface after treatment in Comparative Example 1

[0036] A coating was prepared on the substrate treated by Example 1, Example 2 and Comparative Example 1: Plating solution ingredients: methanesulfonic acid 120-180g / L, stannous methanesulfonate 9-16g / L, 310A 50ml / L, 310B 20-30ml / L.

[0037] Bath temperature: 10-25°C Plating time: 40-60A Electroplating time: 30-40min.

[0038] 2. HTHH (constant temperature and humidity) temperature 85°C, humidity 85%, test time 168h, the coatings of Examples 1 and 2 have no discoloration, and the coating of Comparative Example 1 begins to change color after 48h.

[0039] 3. Bending test 5 pieces of copper-based tin-plated materials processed by Example 1, Example 2 and Comparative Example 1 were subjected to a 90-degree bending test, and no cracks or coating shedding occurred on the surface.

[0040] In the following Examples 3-4 and Comparative Example 2, the processed product is a KBPCW rectifier bridge product, and the oxide film is silver oxide and silver sulfide with a thickness of about 0.2 microns.

[0041] Example 3 The method for removing the oxide film is: S1. Soak the oxidized silver-plated product in a solution containing 5 g / L sodium thiosulfate and 30 g / L sulfuric acid for 3 min; S2, washing the product treated in step S1 twice with normal temperature water and once with hot water; S3. Bake the product processed in step S2 at 150±10° C. for 1 hour.

[0042] Example 4 The method for removing the oxide film is: S1. Soak the oxidized silver-plated product in a solution containing 50 g / L sodium thiosulfate and 5 g / L sulfuric acid for 0.5 min; S2, washing the product treated in step S1 twice with normal temperature water and once with hot water; S3. Bake the product processed in step S2 at 150±10° C. for 1 hour.

[0043] Comparative Example 2 Use the current silver oxide rework process on the market: The ingredients of the deplating solution are: 20% sulfuric acid, 40% hydrogen peroxide, and the time is 90 seconds.

[0044] Verify the removal effect of the oxide film of Example 3, Example 4 and Comparative Example 2: HTHH (constant temperature and humidity): temperature 85℃, humidity 85%, test time 168h. Fig.13 and Fig.14 As shown, through Example 3 and Example 4 ( Fig.13 ) treated silver without oxidation, compared with Comparative Example 2 ( Fig.14 ) The treated silver starts to oxidize and change color after 26 hours.

[0045] The preferred implementation modes of the present invention are described in detail above in combination with the embodiments; however, the present invention is not limited to the specific details in the above implementation modes. Within the technical concept of the present invention, a variety of simple modifications can be made to the technical scheme of the present invention, and these simple modifications all belong to the protection scope of the present invention.

[0046] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0047] In addition, various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A deoxidizer, characterized in that: The deoxidizer comprises sulfuric acid and sodium thiosulfate. In the deoxidizer solution, the concentration of sulfuric acid is 5-90 g / L, and the concentration of sodium thiosulfate is 5-50 g / L.

2. The deoxidizer according to claim 1, characterized in that In the deoxidizer solution, the concentration of sulfuric acid is 5 to 90 g / L, and the concentration of sodium thiosulfate is 5 to 40 g / L.

3. The deoxidizer according to claim 1, characterized in that In the deoxidizer solution, the concentration of sulfuric acid is 5 to 30 g / L, and the concentration of sodium thiosulfate is 5 to 50 g / L.

4. A process for removing oxide film on copper surface, characterized in that: The steps include: A. Soak the oxidized product in a strong alkaline solution with a concentration of 10-50g / L for 1-15 minutes; B. Wash the product treated in step A with water at room temperature and with hot water in sequence; C. Soak the product treated in step B in a solution containing 5-40 g / L sodium thiosulfate and 5-90 g / L sulfuric acid for 1-10 min; D. Wash the product treated in step C with water.

5. The removal process according to claim 4, characterized in that: In step A, the temperature of the strong alkaline solution is 40-80°C.

6. The removal process according to claim 4, characterized in that: In step B, the normal temperature water washing is performed at least twice.

7. The removal process according to claim 4, characterized in that: In step B, the temperature of the hot water for hot water washing is 50-80°C.

8. The removal process according to claim 4, characterized in that: In step C, the solution is at room temperature.

9. A process for removing an oxide film from a silver-plated layer, characterized in that: The steps include: S1. Soak the oxidized silver-plated product in a solution containing 5-50 g / L sodium thiosulfate and 5-30 g / L sulfuric acid for 0.5-3 min; S2, washing the product treated in step S1 with water at room temperature and with hot water in sequence; S3, baking the product processed in step S2 at 140-160°C.

10. The removal process according to claim 9, characterized in that: In step S1, the temperature of the solution is 30-45°C.

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