A method for electrodepositing Sn-Ag-Cu ternary alloy solder in a deep eutectic solvent

Abstract

The application relates to a method for preparing Sn-Ag-Cu ternary alloy solder through electrodeposition in a eutectic solvent, and belongs to the technical field of electrodeposition. A tin source, a silver source and a copper source are dissolved in a eutectic solvent prepared from choline chloride and ethylene glycol to obtain an electrolyte. In the electrolyte system, Sn-Ag-Cu ternary alloy solder is obtained through constant-potential electrodeposition. The Sn content of the alloy solder is 90.0-99.0 wt.%, the Ag content is 0.2-8.0 wt.%, the Cu content is 0.1-2.0 wt.%, and the melting point is 210-225 DEG C. The method is simple, safe and reliable, no side reactions such as hydrogen evolution and oxygen evolution occur in the electrodeposition process, the current efficiency is high, the composition and crystal structure of the solder can be adjusted and controlled, the solder has good solder wetting performance and high welding strength, the electrolyte can be recycled and reused, and the method is a green and environment-friendly method for preparing Sn-Ag-Cu ternary alloy solder.

Description

TECHNICAL FIELD

[0001] The application relates to a method for preparing a Sn-Ag-Cu ternary alloy solder through an electrodeposition method in a eutectic solvent, and belongs to the technical field of electronic materials, in particular to the technical fields of electrodeposition and surface treatment, and is mainly applied to the fields of electronics, chemical industry, aerospace, petroleum and the like. BACKGROUND

[0002] At present, tin-based lead-free binary alloy solders still have a high melting point and poor wettability, resulting in poor solderability, electrical conductivity and mechanical properties. In order to solve these problems, researchers direct their attention to ternary, quaternary and even multi-component alloys to seek a solder that has the advantages of Pb-based alloy solder and environmental friendliness. Sn-Ag-Cu (SAC) ternary alloys with stable IMC (intermetallic compound) Ag3Sn and additional strengthening phase Cu6Sn5 distribution, such as SAC305 alloy containing 3.0wt.% of silver and 0.5wt.% of copper, SAC0307 alloy containing 0.3wt.% of silver and 0.7wt.% of copper, etc., gradually enter the public's field of vision as a popular choice to replace Sn-Pb binary alloy solder due to their low eutectic melting point (217.00-227.00 DEG C), good mechanical properties and acceptable wettability.

[0003] Traditional melting and metallurgical methods for preparing SAC alloy solder are usually accompanied by the following problems: 1. In order to achieve the condition of melting three metals, a large amount of energy is consumed, and the cost is increased; 2. In the preparation process, it is difficult to avoid the doping of Fe, Zn, Al and other elements that have an impact on the wettability of solder welding and the mechanical properties of solder, as well as Pb, As, Cd, Sb and other elements limited in RoHS and RECH standards, so that the purity of the obtained product is not high and the performance is not good; 3. In the process flow, the environmental pollution caused by the discharge of waste water and waste gas cannot be recovered.

[0004] The purity and quality of SAC alloy solder obtained by the method of electrodeposition are high, but due to the initial reduction potential of Ag + in water system is 0.35V, the initial reduction potential of Cu 2+ is 0.00V, and the initial reduction potential of Sn 2+ is-0.46V, the potential difference between the three is huge, and the potential difference is as high as 0.94V. In the absence of additives, the electrodeposition of SAC alloy solder in aqueous solution system also faces the following challenges: 1. Due to the large potential difference between H + and OH -The presence of ions, inevitable hydrogen evolution and oxygen evolution can affect the morphology of the coating and further affect the performance of the coating. In addition, the occurrence of hydrogen evolution and oxygen evolution can seriously reduce the current efficiency. 2. The intermediate product produced in the traditional aqueous solution system can pose a threat to human health and the environment. 3. The use of additives in the aqueous solution system can increase the difficulty of post-treatment of the plating solution and increase the risk of environmental pollution. In addition, He et al. (Surface & Coatings Technology, 2012(206), 4310-4315) found that the reduction potential of Sn-Ag-Cu alloy deviated greatly during the electrodeposition process, making it difficult to co-deposit the ternary alloy. In order to narrow the reduction potential of the three metals, He et al. added N-(2-hydroxyethyl) ethylenediamine-N,N',N'-triacetic acid (HEDTA), thiourea and other additives to the aqueous electrolyte. The results showed that the crystal phase structure of the coating was affected by the additives, the performance of the solderable coating was affected, and the difficulty of post-treatment of the plating solution was increased, which posed a potential risk to the environment. Although the system also obtained Sn-Ag-Cu alloy, the alloy composition range was uncontrollable, and the performance in the solder field was poor.

[0005] Organic solutions are considered as a possible alternative to traditional aqueous solutions, showing higher controllability of alloy composition. In the framework of non-aqueous solutions, the eutectic solvent (DESs) based on choline chloride is an ideal solvent to replace the traditional electrodeposition system. Although there are existing technologies for the preparation of alloys by electrodeposition in eutectic solvents, there are few studies on Sn-Ag-Cu ternary alloy solder in the field of electrodeposition. The current process for electrodeposition of alloys in eutectic solvents cannot be directly applied to Sn-Ag-Cu ternary alloy solder, for example, CN201610378714.5 A method for electroplating Ni-Cr-Sn alloy coating in ionic liquid, which still needs to add benzene and ammonium chloride as additives to adjust the electrodeposition process of nickel, chromium and tin, and the operation is complex. CN201510335144.7 A method for electrochemical co-deposition of CZTS(Se) film in deep eutectic solution adds deionized water as an additive in the plating solution to reduce the viscosity of the system and improve the deposition rate, but the addition of water will inevitably cause the quality problems of the plating solution and the coating caused by hydrogen evolution and oxygen evolution. At present, constant current method is mostly used to prepare metal single elements or alloys. Due to the relatively high viscosity and low conductivity of non-aqueous systems, especially eutectic solvents, the ion mobility is small, which leads to large fluctuation of deposition potential under certain current density, and deposition is difficult.

[0006] The technical problem to be solved by the present application is how to realize controllable deposition of Sn-Ag-Cu ternary alloy in eutectic solvent without adding additives by constant potential, and the deposition process is free of hydrogen evolution and oxygen evolution, and the current efficiency is high. SUMMARY

[0007] The application provides a green and environment-friendly process and method for preparing Sn-Ag-Cu ternary alloy solder by electrodeposition in a eutectic solvent, the method uses a eutectic solvent as a solvent and electrolyte, the plating solution system does not need to add complexing agents, stabilizers, grain refiners and the like, and the electrodeposition process is free of hydrogen evolution and oxygen evolution, and has high current efficiency. Through preparation of the plating solution system and control of the electrodeposition process conditions, the obtained Sn-Ag-Cu ternary alloy solder composition is adjustable and controllable, the eutectic melting point is relatively low, the solder wettability is excellent, and the welding strength is high.

[0008] The application provides a method for preparing Sn-Ag-Cu ternary alloy solder by electrodeposition in a eutectic solvent, and the specific steps are as follows:

[0009] (1) alkali cleaning and oil removal: the substrates polished and polished by 800, 1200 and 2000 mesh metallographic sandpaper respectively are placed in an alkali cleaning and oil removal solution, the oil and organic contaminants on the surface of the substrates are removed, and then the substrates are washed with deionized water. Alkali cleaning temperature: 25-45 DEG C; alkali cleaning time: 2-5 min.

[0010] (2) acid cleaning and activation: the substrates cleaned by alkali in step (1) are placed in an acid cleaning solution to remove the surface oxide film and metal impurities, and then the substrates are washed with deionized water. Acid cleaning temperature: 20-35 DEG C; acid cleaning time: 1-3 min.

[0011] (3) dehydration: the substrates after acid cleaning and activation in step (2) are placed in anhydrous ethanol for dehydration, the dehydration time is 1-3 min, and the treated substrates are ready for use.

[0012] (4) preparation of eutectic solvent: choline chloride and ethylene glycol are vacuum dried at 120 DEG C for 24 h respectively, after cooling to 20 DEG C, the two are mixed in a certain molar ratio, and heated and stirred at 60-90 DEG C to form a clear and transparent eutectic solvent.

[0013] (5) preparation of electrolyte: tin source, silver source and copper source are added to the eutectic solvent at a certain temperature and stirred and dissolved, mixed and stirred uniformly in proportion to obtain the electrolyte.

[0014] (6) plating: the plating solution is heated to the plating temperature, the anode is an insoluble oxide coating electrode, the cathode is the pretreated substrate, the distance between the cathode and the anode is adjusted, the stirring rate is adjusted, and continuous plating is carried out at a certain deposition potential and temperature.

[0015] (7) post-plating treatment: after the plating is completed, the plated piece is placed in anhydrous ethanol for ultrasonic cleaning for 1-5 min, and then placed in deionized water for washing and cold air drying.

[0016] Further, the alkali cleaning oil-removing solution of step (1) comprises: NaOH 10-20 g / L, Na2CO3 40-60 g / L, Na2SiO3 5-10 g / L, and sodium dodecyl benzene sulfonate 0.1-0.5 g / L.

[0017] Further, the acid cleaning activation solution of step (2) comprises: H2SO4 5-15 mL / L and Na2S2O8 10-20 g / L.

[0018] Further, the eutectic solvent of step (4) is prepared by heating and stirring choline chloride and ethylene glycol at a molar ratio of 1:1-1:5 at 60-90°C for 2-4 h.

[0019] Further, the tin source of step (5) is any one of stannous chloride, stannous sulfate, stannous sulfamate and the like, and the concentration ranges from 15 to 40 g / L; the silver source is any one of silver sulfate, silver chloride, silver oxide and silver nitrate, and the concentration ranges from 0.2 to 2.0 g / L; and the copper source is any one of copper chloride and copper sulfate and the like, and the concentration ranges from 0.10 to 1.0 g / L. The DESs system can well dissolve metal salts and oxides, and the DESs can quickly and conveniently dissolve silver chloride and silver oxide as well as silver sulfate, and such dissolving capacity and stability cannot be achieved by water systems and organic solvent systems, and can effectively prevent hydrogen embrittlement of the substrate caused by hydrogen evolution in the electrodeposition process.

[0020] Further, the preparation method of the electrolyte of step (5) is to add a certain amount of tin source, silver source and copper source into the eutectic solvent, and then stir and dissolve completely at 60-90°C, and then mix the three in proportion to obtain the Sn-Ag-Cu ternary alloy solder electrolyte. Dissolving the three kinds of metal salts in the DESs respectively can help to fully dissolve the metal ions and complex with the DESs. After complete dissolution of the three kinds of metal sources, mixing and preparation can effectively prevent precipitation and decomposition of the metal ions caused by mutual influence, thereby improving the stability of the plating solution. At the same time, the catalytic and induced co-deposition of silver can promote the deposition of tin and copper at a lower overpotential, thereby more easily realizing the co-deposition of the three kinds of metals. Excessive copper content in the low-temperature solder can cause excessive growth of Cu6Sn5 phase, thereby increasing the melting point of the alloy solder. Excessive silver content in the solder can increase the number of lamellar alloy phase Ag3Sn and increase the melting point, and also increase the cost. The present application regulates the tin-silver-copper ratio within a certain range to obtain the Sn-Ag-Cu ternary alloy solder with low eutectic melting point, good solder flow performance, good wetting performance and high welding strength.

[0021] Further, the insoluble oxide coating electrode in step (6) is a titanium-based lead oxide coating electrode, a titanium-based iridium-tantalum oxide electrode and a platinum-based iridium-tantalum oxide electrode. The platinum-based iridium-tantalum oxide electrode is preferred, and the oxide coating electrode has the advantages of small side reaction and high current efficiency compared with conventional platinum, titanium, graphite and other insoluble electrodes, and the platinum-based iridium-tantalum oxide electrode has the advantages of strong corrosion resistance, high conductivity and high electron conduction efficiency, and can avoid the pollution of electrolyte and solder caused by the dissolution of the electrode matrix.

[0022] Further, the electrochemical workstation is used in step (6) to perform electrodeposition in a constant potential mode, the potential range is -0.8 to -1.4 V, the anode-cathode distance is 10 to 40 mm, the electrodeposition temperature is 60 to 90 DEG C, the stirring speed is 100 to 600 rpm, and the electrodeposition time is 10 to 60 min, so that the Sn-Ag-Cu ternary alloy solder can be continuously deposited. The electrochemical workstation CHI660E can provide accurate potential control to achieve the purpose of accurately controlling the alloy composition; the convection of the electrolyte is promoted by external stirring to improve the mass transfer efficiency, so as to improve the electrodeposition rate, refine the grain size and improve the flatness of the coating. The alloying of the co-deposited elements can be realized by accurately controlling the deposition potential, and the formation and quantity of Ag3Sn and Cu6Sn5 intermetallic compounds can be controlled.

[0023] The Sn-Ag-Cu ternary alloy solder obtained in the application has the Sn content of 90.0 to 99.0 wt.%, the Ag content of 0.2 to 8.0 wt.%, the Cu content of 0.1 to 2.0 wt.%, the melting point of 210 to 225 DEG C, good wettability and weldability, high welding strength and long service life of the solder joint.

[0024] Compared with the prior art, the application has the following advantages:

[0025] The metal selection range of the application is wide, and silver chloride and silver oxide which cannot be used in water systems and organic systems can be used as silver sources. The plating solution is simple to prepare, and does not need to add complexing agents and stabilizers, and the plating solution can be used for a long time and repeatedly. The electrodeposition conditions are mild and the operation is simple, the plating solution is stable, the current efficiency is high when using the platinum-based oxide coating electrode, and there is no harmful intermediate product in the electrodeposition process, the solution after plating can be degraded and recycled, and is friendly to human health and the environment.

[0026] The Sn-Ag-Cu ternary alloy solder eutectic obtained by the method of electrodeposition in the eutectic solvent has low eutectic melting point, good wettability and weldability, high welding strength and long service life of the solder joint, and can be widely used in printed circuit boards, electronic components, aerospace materials and petroleum fields. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1is the surface morphology and EDS diagram of Sn-Ag-Cu ternary alloy solder prepared by electrodeposition in the eutectic solvent in Example One.

[0028] Figure 2 is the surface morphology and EDS diagram of Sn-Ag-Cu ternary alloy solder prepared by electrodeposition in the eutectic solvent in Example Two.

[0029] Figure 3 is the surface morphology and EDS diagram of Sn-Ag-Cu ternary alloy solder prepared by electrodeposition in the eutectic solvent in Example Three.

[0030] Figure 4 is the surface morphology and EDS diagram of Sn-Ag-Cu ternary alloy solder prepared by electrodeposition in the eutectic solvent in Example Four.

[0031] Figure 5 is the surface morphology and EDS diagram of Sn-Ag-Cu ternary alloy solder prepared by electrodeposition in the eutectic solvent in Example Five.

[0032] Figure 6 is the surface morphology and EDS diagram of Sn-Ag-Cu ternary alloy solder prepared by electrodeposition in the eutectic solvent in Comparative Example One.

[0033] Figure 7 is the surface morphology and EDS diagram of Sn-Ag-Cu ternary alloy solder prepared by electrodeposition in the methanesulfonic acid solution in Comparative Example Two.

[0034] Figure 8 is the surface morphology and EDS diagram of Sn-Ag-Cu ternary alloy solder prepared by electrodeposition in the eutectic solvent in Comparative Example Three.

[0035] Figure 9 is the XRD pattern of Sn-Ag-Cu ternary alloy solder prepared by electrodeposition in the eutectic solvent in Examples One to Five.

[0036] Figure 10 is the differential scanning calorimetry (DSC) curve of Sn-Ag-Cu ternary alloy solder prepared by electrodeposition in the eutectic solvent in Example One. DETAILED DESCRIPTION

[0037] Example One:

[0038] (1) A copper foil (purity greater than 99.9%) with a model number of CF-004, a size of 50 mm x 10 mm x 0.03 mm, was subjected to alkaline cleaning to remove oil, acid cleaning to remove rust and impurities, and desorption of water on the surface of the substrate, and was ready for use.

[0039] (2) Choline chloride and ethylene glycol were dried in a vacuum drying oven at 120 °C for 24 h, and then cooled to 20 °C. The two were mixed at a molar ratio of 1:2 at 80 °C for 4 h to form a clear transparent solution, which was cooled to room temperature and used as prepared.

[0040] (3) The eutectic solvent prepared in step (2) was added with 35.0 g / L stannous chloride, 1.0 g / L silver sulfate, and 0.5 g / L copper chloride, and stirred until the solution was clear and transparent.

[0041] (4) Electrodeposition: the anode was a platinum-based iridium-tantalum oxide coated electrode, the cathode was a copper foil, the distance between the anode and the cathode was 10 mm, the stirring speed was 300 rpm, the deposition potential was -1.2 V, the deposition temperature was 80 °C, and the electrodeposition time was 60 min.

[0042] (5) After the electrodeposition, the plated piece was ultrasonically cleaned in anhydrous ethanol for 1 min, then washed with deionized water for 3 min, and dried with cold air and stored for use.

[0043] The surface morphology of the Sn-Ag-Cu (SAC) ternary alloy solder coating obtained by electrodeposition at a potential of -1.2 V in the DESs electrolyte system of Example One for 1 h is shown in Figure 1 As can be seen from Figure 1 , the surface of the SAC alloy solder coating is flat, and the grains are uniform and dense. The composition of the alloy solder is shown in the polar chart in Figure 1 , wherein the Sn content is 96.5 wt.%, the Ag content is 2.9 wt.%, and the Cu content is 0.6 wt.%. The XRD analysis results are shown in Figure 9 , and the main phases of the coating are Cu6Sn5 and Ag3Sn. The differential scanning calorimetry (DSC) analysis results are shown in Figure 10 , and the melting point of the Sn-Ag-Cu ternary alloy solder is 215.02 °C, and the melting range is 212.15-224.50 °C. The Sn-Ag-Cu ternary alloy solder of Example One has good wetting performance, and the soldering strength meets the requirements after peak soldering, as detected by a SKC-8H solderability tester.

[0044] Example Two:

[0045] (1) A copper foil with a model number of CF-004 (purity greater than 99.9%) and a size of 50 mm x 10 mm x 0.03 mm was used as prepared after alkaline cleaning to remove oil, acid cleaning to remove rust and impurities, and removal of water from the surface of the substrate.

[0046] (2) Choline chloride and ethylene glycol were dried in a vacuum drying oven at 120°C for 24 h, and then heated and stirred at 80°C for 4 h at a molar ratio of 1:2 after cooling to 20.0°C to form a clear and transparent solution, and then cooled to room temperature for standby.

[0047] (3) 20.0 g / L stannous chloride, 0.5 g / L silver chloride, and 0.2 g / L copper chloride were added to the DES in step (2) and stirred until the solution was clear and transparent.

[0048] (4) Electrodeposition: the anode was a platinum-based iridium-tantalum oxide coated electrode, the cathode was a copper foil, the distance between the anode and the cathode was 15 mm, the stirring speed was 200 rpm, the deposition potential was -1.0 V, the temperature was 90°C, and the electrodeposition time was 60 min.

[0049] (5) After the electrodeposition was completed, the plated piece was ultrasonically cleaned in anhydrous ethanol for 1 min, then washed with deionized water for 3 min, and then air-dried and stored for standby.

[0050] The surface morphology of the Sn-Ag-Cu ternary alloy solder obtained by electrodeposition at a potential of -1.0 V in the DES electrolyte system of Example Two for 1 hour is shown in Figure 2 As can be seen from Figure 2 , the morphology of the SAC alloy solder is more uniform and dense than that of Example One. The composition of the alloy solder is shown in the polar chart in Figure 2 , wherein the Sn content is 96.8 wt.%, the Ag content is 2.7 wt.%, and the Cu content is 0.5 wt.%. The XRD analysis result is shown in Figure 9 , and the phases of the plated layer are mainly Cu6Sn5 and Ag3Sn phases. The melting point of the Sn-Ag-Cu ternary alloy solder is 218.30°C, and the melting range is 215.80-227.30°C. The solder has good wetting performance, and the solder joint strength meets the requirements after wave soldering.

[0051] (1) A copper foil with a model number of CF-004 (purity greater than 99.9%) and a size of 50 mm x 10 mm x 0.03 mm was used after alkaline cleaning to remove oil, acid cleaning to remove rust and impurities, and removal of water from the surface of the substrate.

[0052] (2) Choline chloride and ethylene glycol were dried in a vacuum drying oven at 120°C for 24 h, and then heated and stirred at 80°C for 4 h at a molar ratio of 1:2 after cooling to 20.0°C to form a clear and transparent solution, and then cooled for standby. (3) 30.0 g / L stannous sulfate, 0.5 g / L silver oxide, and 0.15 g / L copper sulfate were added to the DES in step (2) and stirred until the solution was clear and transparent.

[0053] (4) Electrodeposition: the anode for electrodeposition is platinum-based iridium-tantalum oxide coating electrode, the cathode is copper foil, the distance between anode and cathode is 20 mm, the stirring speed is 100 rpm, the deposition potential is -1.3 V, the temperature is 90 ℃, and the electrodeposition time is 60 min.

[0054] (5) After the electrodeposition is completed, the plated piece is ultrasonically cleaned in anhydrous ethanol for 1 min, then washed with deionized water for 3 min, dried by cold air, and stored for standby use.

[0055] The surface morphology diagram of the Sn-Ag-Cu ternary alloy solder obtained by electrodeposition at a potential of -1.3 V in the DES electrolyte system of Example Three for 1 hour is shown in Figure 3 As can be seen from Figure 3 , the SAC alloy solder is uniform and dense, and the grain size is slightly large. The composition of the alloy solder is shown in the angular diagram in Figure 3 , wherein the Sn content is 95.7 wt.%, the Ag content is 3.3 wt.%, and the Cu content is 1.0 wt.%. The XRD analysis result is shown in Figure 9 , and the phases of the plated layer are mainly Cu6Sn5 and Ag3Sn phases. The melting point of the Sn-Ag-Cu ternary alloy solder is 217.14 ℃, and the melting range is 214.02-226.40 ℃. The solder has good wetting performance, and the solder joint strength meets the requirements after peak welding.

[0056] Example Four:

[0057] (1) A carbon steel piece with a model of Q235-B is used as a substrate, the substrate size is 50 mm x 10 mm x 1 mm, the substrate is subjected to alkaline cleaning to remove oil, acid cleaning to remove rust and impurities, and surface moisture removal, and is ready for use.

[0058] (2) Choline chloride and ethylene glycol are respectively placed in a vacuum drying box at 120 ℃ and dried for 24 h, cooled to 20.0 ℃, and then heated and stirred at 80 ℃ for 4 h according to a molar ratio of 1:3 to form a clear and transparent solution, and cooled for standby use.

[0059] (4) Electrodeposition: the anode for electrodeposition is platinum-based iridium-tantalum oxide coating electrode, the cathode is carbon steel piece, the distance between anode and cathode is 20 mm, the stirring speed is 300 rpm, the deposition potential is -1.3 V, the temperature is 90 ℃, and the electrodeposition time is 60 min.

[0060] (5) After the electrodeposition is completed, the plated piece is ultrasonically cleaned in anhydrous ethanol for 1 min, then washed with deionized water for 3 min, dried by cold air, and stored for standby use.

[0061] Example Four: The surface morphology of Sn-Ag-Cu ternary alloy solder obtained by electrodeposition at a potential of -1.3 V for 1 hour in the DESs electrolyte system is shown in Figure 4 Figure 4 It can be seen from Figure 9 that the SAC alloy solder is uniform and dense. The XRD analysis results are shown in

[0062] Example Five:

[0063] (1) An aluminum sheet (purity greater than 99.99) with a size of 50 mm x 10 mm x 1 mm was used as the substrate, which was subjected to alkaline cleaning to remove oil, acid cleaning to remove rust and impurities, and removal of moisture on the surface of the substrate, and was ready for use.

[0064] (2) Choline chloride and ethylene glycol were dried in a vacuum drying oven at 120°C for 24 h. After cooling to 20.0°C, they were heated and stirred at 80°C for 4 h at a molar ratio of 1:1.5 to form a clear and transparent solution, which was cooled and ready for use.

[0065] (4) Electrodeposition: The anode electrode was an iridium-tantalum oxide coated electrode, and the cathode was a pure aluminum sheet. The distance between the anode and cathode was 10 mm. The deposition potential was -1.4 V, the temperature was 80°C, and the electrodeposition time was 60 min.

[0066] (5) After the electrodeposition was completed, the plated sheet was ultrasonically cleaned in absolute ethanol for 1 min, then washed with deionized water for 3 min, and then blown dry with cold air. It was stored for use.

[0067] Example Five: The surface morphology of Sn-Ag-Cu ternary alloy solder obtained by electrodeposition at a potential of -1.4 V for 1 hour in the DESs electrolyte system is shown in Figure 5 Figure 5 It can be seen from Figure 9 ​​The phase of the plating layer is mainly Cu6Sn5 and Ag3Sn phase. The Sn content of the Sn-Ag-Cu ternary alloy solder is 96.2 wt.%, the Ag content is 3.1 wt.%, and the Cu content is 0.7 wt.%. The melting point of the alloy solder is 219.46°C, and the melting range is 215.80-227.50°C. The SKC-8H solderability tester test result shows that the alloy solder has good wettability and meets the requirements of solderability; the wave solder test result shows that the solder has good flowability, the tin is full, and the welding strength meets the requirements.

[0068] Comparative Example One:

[0069] (1) The copper foil with the model of CF-004 was used as the substrate, the size was 50mmx10mmx0.03mm, and the substrate surface was cleaned by alkaline cleaning, acid cleaning, and removing water, and was prepared for use.

[0070] (2) The choline chloride and ethylene glycol were respectively placed in a vacuum drying box at 120°C for 24h, and after cooling to room temperature, they were heated and stirred at 80°C for 4h at a molar ratio of 1:2 to form a clear and transparent solution.

[0071] (3) 35.0g / L stannous chloride, 1.0g / L silver sulfate, and 0.5g / L copper chloride were added to the eutectic solvent in step (2), and the solution was stirred until it was clear and transparent.

[0072] (4) Electrodeposition: the anode was a platinum-based iridium-tantalum oxide coated electrode, the cathode was a copper foil, the distance between the anode and the cathode was 10mm, the deposition potential was-0.6V, the stirring speed was 300rpm, the temperature was 80°C, and the electrodeposition time was 60min.

[0073] (5) After the electrodeposition was completed, the plated piece was ultrasonically cleaned in anhydrous ethanol for 1min, then washed with deionized water for 3min, and then air-dried and stored for use.

[0074] Comparative Example One is the Sn-Ag-Cu ternary alloy solder obtained by electrodeposition at a temperature of 80°C for 1h in a DESs electrolyte system at a potential of-0.6V and a distance of 10mm between the anode and the cathode. The main difference from Example One is that the deposition potential is more positive than that of Example One. It can be seen from Figure 6 that the morphology of the SAC alloy solder is unevenly distributed and the grain size is inconsistent. The Sn content of the alloy solder is 88.8wt.%, the Ag content is 4.7wt.%, and the Cu content is 6.5wt.%, which does not meet the requirements of the SAC alloy solder. The melting point of the alloy solder is relatively high, which is 240.50°C. The wave solder test result shows that the solder has poor wettability and the tin is not full.

[0075] Comparative Example Two:

[0076] (1) The copper foil with model CF-004 was used as the substrate, the size of which was 50mm x 10mm x 0.03mm, and the substrate was prepared by alkali washing to remove oil, acid washing to remove rust and impurities, and removing water on the surface of the substrate.

[0077] (2) 20.0g / L stannous methanesulfonate, 0.5g / L silver methanesulfonate, 0.2g / L copper sulfate, 25.0g / L methanesulfonic acid, and 10g / L thiourea, and 30g / L EDTA were respectively stirred and dissolved in deionized water, and then mixed uniformly to obtain an aqueous electrolyte.

[0078] (3) Electrodeposition: the anode was a platinum-based iridium-tantalum oxide coated electrode, the cathode was a copper foil, the distance between the anode and the cathode was 10mm, the stirring speed was 200rpm, the deposition potential was -1.0V, the temperature was 90℃, and the electrodeposition time was 30min.

[0079] (4) After the electrodeposition was completed, the substrate was washed with deionized water for 3min, and then dried by cold air to be stored for use.

[0080] In Comparative Example 2, Sn-Ag-Cu ternary alloy solder was obtained by electrodeposition in an aqueous electrolyte at a potential of -1.0V and a distance of 10mm between the anode and the cathode for 0.5h at a temperature of 90℃. The main difference between Comparative Example 2 and Example 2 is that the electrolyte in Comparative Example 2 is an aqueous electrolyte. During the electrodeposition in Comparative Example 2, hydrogen was severely generated on the surface of the cathode, and the Sn-Ag-Cu ternary alloy solder obtained in Comparative Example 2 was not uniform in shape and had a large amount of hydrogen on the surface. Figure 7 It can be seen that the alloy solder obtained in the system has a more uneven distribution and an irregular shape compared with Example 2. In Comparative Example 2, the Sn content in the SAC alloy solder is 80.9wt.%, the Ag content is 10.7wt.%, and the Cu content is 8.4wt.%. The XRD analysis result shows that when electrodeposition is performed in an aqueous methanesulfonic acid solution, Sn, Ag, and Cu are deposited in the form of elements, no Cu6Sn5 and Ag3Sn phases are generated, and there is tin oxide (SnO2) on the surface of the solder. The plating solution has poor stability, and the plating solution becomes turbid after plating. The melting point of the alloy solder is 290.80℃, and the wave peak solder test result shows that the solder has a long melting time and poor wettability.

[0081] Comparative Example 3:

[0082] (1) The copper foil with model CF-004 was used as the substrate, the size of which was 50mm x 10mm x 0.03mm, and the substrate was prepared by alkali washing to remove oil, acid washing to remove rust and impurities, and removing water on the surface of the substrate.

[0083] (2) Choline chloride and ethylene glycol were respectively dried in a vacuum drying oven at 120℃ for 24h, and then heated and stirred at 80℃ for 4h after being cooled to room temperature at a molar ratio of 1:2 to form a clear and transparent solution.

[0084] (3) To the eutectic solvent in step (2), 30.0 g / L of stannous chloride, 0.5 g / L of silver oxide, 0.15 g / L of copper chloride dihydrate were added, and stirring was performed until the solution was clear and transparent.

[0085] (4) Electrodeposition: the anode for electrodeposition was a platinum-based iridium-tantalum oxide coated electrode, the cathode was a copper foil, the distance between the anode and the cathode was 20 mm, the stirring speed was 100 rpm, the current density for constant current electrodeposition was 1.0 ASD, the temperature was 90°C, and the electrodeposition time was 60 min.

[0086] (5) After the electrodeposition was completed, the plated piece was placed in anhydrous ethanol for ultrasonic cleaning for 1 min, then washed with deionized water for 3 min, dried by cold air, and stored for standby use.

[0087] In Comparative Example Three, insoluble graphite sheets were used as the anode, the current density was 1.0 A / dm 2 , the constant current mode was used, the distance between the anode and the cathode was 20 mm, the electrodeposition temperature was 90°C, and the electrodeposition time was 60 min, and the obtained Sn-Ag-Cu ternary alloy solder. The main difference between Comparative Example Three and Example Three is the difference in the electrodeposition mode. It can be seen from Figure 8 that the morphology of the SAC alloy solder is unevenly distributed, and the shape of the deposit is irregular.

[0088] In Comparative Example Three, the Sn content in the SAC alloy solder was 88.2 wt.%, the Ag content was 8.3 wt.%, and the Cu content was 3.5 wt.%. The melting point of the alloy solder was 235.06°C, and the peak soldering test results showed that the solder had a long melting time and poor wettability. It was found by comparison that the morphology, composition, and solder performance of the solder obtained by constant current electrodeposition were all inferior to those of the Sn-Ag-Cu ternary alloy solder obtained by constant potential electrodeposition.

[0089] The above examples and drawings are further illustrations of the technical solutions of the present application, but are not limited to the above examples and drawings. Any modification or equivalent replacement to the technical solutions of the present application without departing from the spirit and scope of the technical solutions of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing Sn-Ag-Cu ternary alloy solder by electrodeposition in a eutectic solvent, characterized in that: Includes the following steps: (1) Electrolyte preparation: Add tin source, silver source and copper source to the eutectic solvent prepared with choline chloride and ethylene glycol respectively and stir until completely dissolved. Mix them in proportion and stir evenly to obtain the electrolyte for electrodeposition of Sn-Ag-Cu ternary alloy solder; the concentration of tin salt in the electrolyte is 15-40 g / L, the concentration of silver salt or silver oxide is 0.2-2.0 g / L, and the concentration of copper salt is 0.1-1.0 g / L. The eutectic solvent is prepared by stirring choline chloride and ethylene glycol in a molar ratio of 1:1 to 1:5 at 60 to 90°C for 2 to 4 hours. In the electrolyte preparation, tin, silver, and copper sources are added to the eutectic solvent and stirred at 60 to 90°C until completely dissolved. The three sources are then mixed uniformly in the specified proportions to obtain the Sn-Ag-Cu ternary alloy solder electrolyte. The tin source is any one of stannous chloride, stannous sulfate, stannous sulfamate, or other stannous salts. The silver source is any one of silver sulfate, silver chloride, silver oxide, silver nitrate, or silver methanesulfonate. The copper source is any one of copper chloride, copper sulfate, or copper oxide. (2) The electrodeposition anode is an insoluble oxide coating electrode, and the cathode is the substrate to be electrodeposited after pretreatment; The insoluble oxide-coated electrodes are titanium-based lead oxide electrodes, titanium-based iridium-tantalum oxide electrodes, and platinum-based iridium-tantalum oxide electrodes; the substrate is one of copper, aluminum, aluminum alloy, or steel. (3) Electrodeposition: The substrate is placed in the electrolyte and Sn-Ag-Cu ternary alloy solder is prepared by constant potential electrodeposition; the Sn content of the alloy solder is 90.0~99.0wt.%, the Ag content is 0.2~8.0wt.%, the Cu content is 0.1~2.0wt.%, and the melting point is 210.00~225.00℃; the cathode-anode distance is 10~40mm, the potential range of constant potential electrodeposition is -0.8~-1.4V; the electrodeposition temperature is 70~90℃, the electrodeposition time is 10~60min, and the stirring speed is 100~600rpm.

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