Method for producing core-shell tin-based antioxidant solder alloy

Abstract

The application discloses a preparation method of a core-shell structure tin-based anti-oxidation solder alloy, and has the characteristics that an anti-oxidation intermediate alloy block is taken as a base body, a high-softening-point rosin is coated on the anti-oxidation intermediate alloy block, then tin foil is coated as a secondary outer layer, and boron nitride hollow mould is coated as an outermost layer, so that an anti-oxidation intermediate alloy-robin-tin foil-boron nitride coating hollow mould core-shell structure is formed; the anti-oxidation intermediate alloy block is a SnPGa anti-oxidation intermediate alloy block or a SnPGe anti-oxidation intermediate alloy block, the mass ratio of P to Ga in the SnPGa anti-oxidation intermediate alloy is 1:5, the mass ratio of P to Ge in the SnPGe anti-oxidation intermediate alloy is 1:2, the mass ratio of the high-softening-point rosin to the anti-oxidation intermediate alloy is 0.02:1, and the volume ratio of the anti-oxidation intermediate alloy block to the boron nitride coating hollow mould is 1:1.3. The core-shell structure tin-based anti-oxidation solder alloy prepared by the method can significantly improve the alloy element yield, improve the static melt surface anti-oxidation performance, and improve the dynamic melt surface mirror surface maintaining state.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of solder alloy preparation methods for electronic packaging, and particularly relates to a preparation method of a tin-based anti-oxidation solder alloy with a core-shell structure. BACKGROUND

[0002] Tin-based solder alloys are widely used in electronic welding such as wave soldering and dip soldering due to their low melting point and good comprehensive performance. Compared with reflow soldering and selective soldering, the large-area molten pool of double-peak wave soldering and dip soldering exposes the solder surface to atmospheric conditions, causing serious oxidation of the solder surface and an increase in dross, which easily leads to a decrease in the reliability of the solder joint and poor appearance after soldering. Therefore, it is crucial to add a sufficient amount of micro-alloying elements with anti-oxidation properties during the preparation and use of tin-based solder.

[0003] During the preparation of solder alloy samples, from the perspective of alloying elements, the addition of anti-oxidation elements is in the form of simple substances or intermediate alloys due to low solubility or high melting points. If the anti-oxidation metal elements are directly added to the tin alloy melt as disclosed in Chinese patent CN106271187A, the melting point of Ge is close to 938℃, which requires a high smelting temperature and high energy consumption. P is flammable, which poses a safety risk and is prone to burning loss. The melting point of Ga (about 30℃) is much lower than the melting point of mainstream lead-free solder alloys (210-230℃), which is prone to burning loss. Moreover, P, Ge, and Ga elements are easily enriched on the surface of the solder melt. Direct addition in the form of simple substances can cause composition segregation on one hand and the anti-oxidation elements can be easily wrapped in tin slag on the other hand, resulting in a much lower content of anti-oxidation elements in the alloy matrix than the designed value. In addition, if the anti-oxidation intermediate alloy Sn-P-Ge-Ga is simply added to the tin pool as disclosed in Japanese patent JP4445046B2 and Chinese patent CN112322929A, the density of the anti-oxidation alloy is close to that of the solder alloy melt, and the anti-oxidation elements are easily enriched on the surface and prone to oxidation and burning loss at high temperatures, which results in a lower content of anti-oxidation elements in the actual alloy matrix than the initial addition amount, and the expected static and dynamic anti-oxidation performance of the solder is significantly reduced.

[0004] In actual solder production, to improve the oxidation resistance of solder, ammonium chloride (see Chinese Patent CN106271187A) and fluoride (see Chinese Patent CN114833490A) are usually added to the solder alloy melt and stirred to prepare the solder alloy product. However, chlorine- and fluorine-containing chemical materials are prone to volatilizing and releasing pungent or toxic gases at the high temperature of solder melting, which not only affects the health of operators but also has adverse effects on the environment. Adding an intermediate alloy and coating the alloy surface with rosin (see Chinese Patent CN115383349A) is another way to reduce solder oxidation and improve metal yield, but it has limitations such as insufficient rosin selection and unsuitable dosage leading to flue gas diffusion, excessive carbides on the alloy surface affecting melt purification, or poor solder oxidation resistance. Another method is to use stainless steel and graphite bell jars to press the metal into the bottom of the melt and hold it for a period of time until it is completely melted. However, elements such as Fe and Cr in stainless steel and carbon impurities in graphite are easily trapped in the solder alloy, affecting the reliability of the solder joint. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of the existing technology and provide a method for preparing a core-shell structured tin-based antioxidant solder alloy. This method improves the problems caused by directly placing the alloy on the surface of the antioxidant alloy melt during the preparation process, which leads to insufficient dissolution of alloy elements, easy oxidation and failure of elements, resulting in low antioxidant element yield, excessive slag production, and failure of the antioxidant performance to meet expectations during solder use. It effectively improves the antioxidant performance of the static melt surface and enhances the mirror-like retention state of the dynamic melt surface.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] The preparation method of the core-shell structured tin-based antioxidant solder alloy involves using an antioxidant intermediate alloy block as the matrix, coating the antioxidant intermediate alloy block with high softening-point rosin, then wrapping it with tin foil as the second outermost layer, and finally wrapping it with a boron nitride perforated mold as the outermost layer, forming a core-shell structure of antioxidant intermediate alloy-rosin-tin foil-boron nitride coating perforated mold. The antioxidant intermediate alloy block is either a SnPGa antioxidant intermediate alloy block or a SnPGe antioxidant intermediate alloy block. To enhance the synergistic antioxidant effect of P, Ga, and Ge elements, the mass ratio of P to Ga in the SnPGa antioxidant intermediate alloy is 1:5; the mass ratio of P to Ge in the SnPGe antioxidant intermediate alloy is 1:2. The mass ratio of the high softening-point rosin to the antioxidant intermediate alloy is 0.02:1, which can reduce the amount of fumes generated during rosin volatilization while eliminating the oxide layer and promoting wetting. The volume ratio of the antioxidant intermediate alloy block to the boron nitride coating perforated mold is 1:1.3. It facilitates the placement of antioxidant intermediate alloys and protective molds, thereby obtaining a core-shell structured multi-component tin-based antioxidant solder intermediate alloy.

[0008] The preparation method of the core-shell structured tin-based antioxidant solder alloy includes the following steps:

[0009] (1) Under argon protection, an antioxidant intermediate alloy block was prepared in a closed melting furnace;

[0010] (2) Using a stainless steel die with a lid, a boron nitride coating is evenly sprayed onto the stainless steel surface. The die is then baked at 80°C for 2 hours to obtain a boron nitride coated die. The boron nitride coated die not only has high thermal stability against corrosion, but also, due to gravity, it can overcome the density of the tin alloy melt and automatically sink to the bottom of the alloy melt, eliminating the need for manual pressing.

[0011] (3) Heat high softening point KE604 rosin to 150°C in a beaker, immerse the antioxidant intermediate alloy block in the molten rosin, hold for 2 seconds, and then quickly lift the antioxidant intermediate alloy block. At this time, the surface of the antioxidant intermediate alloy block is coated with a rosin layer, which can remove the oxide on the surface of the antioxidant intermediate alloy. Wrap a layer of tin foil around the rosin layer, then open the lid of the boron nitride coated hollow mold, put the rosin and tin foil-coated antioxidant intermediate alloy block into the boron nitride coated hollow mold, and then close the lid to obtain a core-shell structured multi-element tin-based antioxidant intermediate alloy; finally, add the core-shell structured multi-element tin-based antioxidant intermediate alloy into tin alloy melt at 280°C, and cast it into a mold to prepare the tin-based antioxidant solder alloy.

[0012] The present invention has the following advantages:

[0013] Compared with the direct addition of elemental Ge metal and SnP / SnGe binary master alloys, the core-shell structure of the present invention significantly improves the antioxidant element yield, exceeding 90%. This means that the gap between the nominal and actual antioxidant element content is further narrowed, and the accuracy of antioxidant element addition is significantly improved.

[0014] The multi-element antioxidant intermediate alloy of the present invention is added to the solder in the form of a core-shell structure, which significantly improves the antioxidant properties of the solder. This includes a significant improvement in the static melt surface maintaining a mirror-like state, static oxidation weight gain, dynamic mirror-like retention time, and dynamic slag production during cyclic scraping.

[0015] (3) The core-shell structure multi-tin-based antioxidant intermediate alloy of the present invention, compared with the addition of elemental Ge metal and SnP, SnGe binary intermediate alloy at a tin-based alloy melt temperature higher than 320°C, requires a tin alloy melt temperature of only 280°C for the core-shell structure multi-tin-based antioxidant alloy, further reducing the alloy melting temperature and reducing the energy consumption of solder alloy preparation.

[0016] (4) When the shell structure of the present invention is added to the solder, it sinks to the bottom of the melt due to gravity, which can effectively reduce oxidation and burn-off and fully dissolve the antioxidant intermediate alloy, shorten the stirring time and melting time, and improve the preparation efficiency of antioxidant solder.

[0017] (5) When the core-shell structure multi-tin-based antioxidant alloy of the present invention is added to the solder, it will not generate irritating gases such as chlorine, improve the operating environment, and effectively reduce the amount of tin dross generated, thereby reducing the production cost of enterprises. Attached Figure Description

[0018] Figure 1 This is a static oxidation surface image of the solder in Embodiment 1 of the present invention;

[0019] Figure 2 This is a static oxidation surface image of the solder in Embodiment 2 of the present invention;

[0020] Figure 3 This is a static oxidation surface image of the solder in Comparative Example 1 of the present invention;

[0021] Figure 4 This is a static oxidation surface image of the solder in Comparative Example 2 of the present invention;

[0022] Figure 5 This is a static oxidation surface image of the solder in Comparative Example 3 of the present invention;

[0023] Figure 6 This is a static oxidation surface image of the solder in Comparative Example 4 of the present invention;

[0024] Figure 7 The graphs show the static oxidation weight gain curves of the solder in Examples 1-2 and Comparative Examples 1-4 of this invention.

[0025] Figure 8 This is an image of the dynamic oxidation surface of the solder in Embodiment 1 of the present invention;

[0026] Figure 9 Images of the dynamic oxidation surface of the solder in Embodiment 2 of the present invention;

[0027] Figure 10 This is an image of the dynamic oxidation surface of the solder in Comparative Example 3 of the present invention;

[0028] Figure 11 This is an image of the dynamic oxidation surface of the solder in Comparative Example 4 of the present invention;

[0029] Figure 12 This is an image of the dynamic oxidation surface of the solder in Comparative Example 1 of the present invention;

[0030] Figure 13 This is an image of the dynamic oxidation surface of the solder in Comparative Example 2 of the present invention;

[0031] Figure 14 This is a statistical chart of the dynamic oxide slag amount during solder circulation scraping in Examples 1-2 and Comparative Examples 1-4 of the present invention;

[0032] Figure 15 This is an etching curve of the solder oxide surface in Embodiment 1 of the present invention;

[0033] Figure 16 This is an etching curve of the solder oxide surface in Embodiment 2 of the present invention;

[0034] Figure 17 This is a solder oxide surface etching curve diagram of Comparative Example 1 of the present invention;

[0035] Figure 18 This is a solder oxide surface etching curve diagram of Comparative Example 2 of the present invention;

[0036] Figure 19 This is a solder oxide surface etching curve diagram of Comparative Example 3 of the present invention;

[0037] Figure 20 This is a solder oxide surface etching curve diagram of Comparative Example 4 of the present invention;

[0038] Figure 21 Schematic diagram of a boron nitride coated cage-type hollow mold;

[0039] Figure 22 yes Figure 21 View from direction A;

[0040] Figure 23 Schematic diagram of a boron nitride coated frame-type hollow mold;

[0041] Figure 24 yes Figure 23 View B. Detailed Implementation

[0042] The present invention will be further described in detail below through embodiments, but the scope of protection of the present invention is not limited to the contents described in the embodiments.

[0043] The technical effects of the present invention were analyzed by testing the antioxidant element composition and surface oxidation resistance of the solder alloys obtained in the following embodiments and comparative examples. The cage-like or frame-like hollow mold used in the present invention was obtained by welding stainless steel strips. Figure 21 , Figure 22 The cage-like perforated mold shown in the embodiment has an outer diameter of 55 mm, an inner diameter of 50 mm, and an internal volume of 65.45 cm³. 3 Cage-type hollow molds can be used as follows: Figure 21 , Figure 22As shown, the structure is composed of two hemispherical hollow half-molds 1, one on each side. The two half-molds are connected by a hinge 2 on one side, and fastened by a buckle 3 on the other side. The buckle structure can utilize existing technology. The upper half-mold serves as the lid, which can be opened and closed by rotating along the hinge 2. After the lid is closed, the buckle 3 secures the upper and lower half-molds together. Other opening structures can also be used for the cage-like hollow mold. Figure 23 , Figure 24 The frame-like hollow mold shown in the embodiment has an inner side length of 50 mm and an internal volume of 125 cm³. 3 Frame-type hollow molds can be used as Figure 23 , Figure 24 As shown, the device consists of a square hollow frame 4 and a cover 5 placed on top of the hollow frame. One side of the cover is connected by a hinge 2, and the other side can be fastened by a buckle 3. The cover can be opened and closed by rotating along the hinge 2. After the cover is closed, it is fastened to the hollow frame by the buckle 3. Other hollow frame and opening structures can also be used for the frame-type hollow mold. The alloy composition testing equipment used in this invention is a SPECTROLABM10 direct-reading spectrometer. The test sample is a solder alloy cylinder with a diameter of 30 mm and a height of 10 mm. The composition testing standard refers to YS / T747-20108 standard, and there are no less than 3 parallel samples. The oxidation resistance of the solder is comprehensively reflected by the surface of the alloy melt under static atmospheric conditions, the weight gain of TG oxidation, the slag production of dynamic cyclic slag scraping, the surface state of the dynamically oxidized melt, and the oxidation thickness of the solder surface. The static and dynamic surface states of the solder alloy melt were tested using a solder alloy melt surface oxidation state testing device according to Chinese patent application number 2024215083379. The heating temperature for both static and dynamic oxidation was 300℃, and the cyclic slag scraping time for both was 2 hours, with a cyclic slag scraping rate of 1 minute / cycle. The amount of dynamic oxidation slag was weighed using a METTLER TOLEDO ME204E analytical balance. The solder oxidation weight gain was tested using a STA449F5 calorimeter. The test sample consisted of 300 mg solder alloy spheres. The temperature was raised to 300℃ under Ar atmosphere, then held at that temperature for 2 hours under O2 atmosphere, and subsequently cooled to room temperature under Ar atmosphere. The heating and cooling rates were both 20 K / min, and the temperature range was between 30 and 300℃. The oxide layer on the solder surface was measured using a Thermofisher K-Alpha X-ray photoelectron spectroscopy (XPS) instrument with a monochromatic Al target (1486.7 eV) as the X-ray source. The sputtering ion source was an Ar single-ion beam with an energy resolution ≤0.5 eV (based on the Ag3d full width at half maximum) and an etching rate of 0.54 nm / s. Example 1

[0044] A core-shell structured tin-based antioxidant alloy was prepared and added as an intermediate alloy to SnCu0.7 solder to obtain the SnCu0.7P0.0032Ga0.016 antioxidant solder alloy. The specific steps are as follows:

[0045] (1) Under argon protection, approximately 393.19 g of Sn0.32PGa1.6 antioxidant intermediate alloy blocks were prepared in a closed melting furnace, with a P to Ga mass ratio of 1:5;

[0046] (2) Design and prepare such as Figure 21 The cage-type stainless steel hollow mold shown has an inner diameter of approximately 50 mm. A boron nitride coating is uniformly sprayed onto the surface of the stainless steel mold, with the coating thickness controlled at 20 μm. The mold is then baked at 80℃ for 2 hours to obtain a boron nitride coated cage-type hollow mold.

[0047] (3) Heat the high softening point KE604 rosin (softening point is 124~134℃) in a beaker to 150℃, immerse the antioxidant intermediate alloy block in the molten rosin, hold for 2 seconds, and then quickly lift out the antioxidant intermediate alloy. The alloy surface is coated with a thin layer of rosin, the amount of rosin coating is about 7.86 g, and the mass ratio of rosin to antioxidant intermediate alloy is about 0.02:1. A 10 μm thick tin foil is wrapped around the solidified rosin layer. The rosin and tin foil-wrapped antioxidant intermediate alloy block is then placed into a boron nitride-coated hollow mold with a volume ratio of approximately 1:1.3, resulting in a core-shell structured ternary tin-based antioxidant intermediate alloy. This core-shell structured ternary tin-based antioxidant intermediate alloy is then added to SnCu0.7 alloy melt at 280°C to form approximately 39.32 kg of antioxidant solder. After holding at this temperature for 1 hour, the solder is cast into a mold to obtain the SnCu0.7P0.0032Ga0.016 antioxidant solder alloy.

[0048] SnCu0.7P0.0032Ga0.016 solder, prepared by adding a core-shell structure to a ternary tin-based antioxidant master alloy, exhibits excellent antioxidant properties. Its P element recovery is approximately 90.62%, and its Ga element recovery is approximately 93.12%. Furthermore, under oxidation conditions of 300℃ for 2 hours, the TG oxidation weight gain is 0.36 mg, the dynamic oxidation slag amount is 3.16 g, and the surface of the alloy melt maintains a mirror-like finish in both static and dynamic conditions (see...). Figure 1 The central spherical mirror solder and Figure 8 The oxide layer clearly reflects the surface of the handheld mobile phone (the surface of the oxide layer is only 1.29 wt.%), and the oxygen concentration decreases to 0.67 wt.% after 300 s etching. See Tables 1-3 and attached figures for details. Example 2

[0049] A core-shell structured tin-based antioxidant alloy was prepared and added as an intermediate alloy to SnCu0.7 solder to obtain a SnCu0.7P0.005Ge0.01 antioxidant solder alloy. The preparation method and addition steps are described below.

[0050] (1) Under argon protection, approximately 750.96 g of SnP0.5Ge1 antioxidant intermediate alloy block was prepared in a closed melting furnace, with a mass ratio of P to Ge of 1:2.

[0051] (2) Design and prepare such as Figure 22 The frame-type stainless steel hollow mold shown has an inner side length of approximately 50 mm. A boron nitride coating is uniformly sprayed onto the surface of the stainless steel mold, with the coating thickness controlled at 20 μm. The mold is then baked at 80℃ for 2 hours to obtain a boron nitride coated frame-type hollow mold.

[0052] (3) Heat the high softening point KE604 rosin in a beaker to 150°C, immerse the antioxidant intermediate alloy block in the molten rosin, hold for 2 seconds, and then quickly lift out the antioxidant intermediate alloy. The surface of the alloy is coated with a thin layer of rosin. The mass ratio of rosin to antioxidant intermediate alloy is about 0.02:1, and the amount of rosin coating is about 15.02 g. A layer of tin foil with a thickness of 10 μm is wrapped around the solidified rosin layer. The rosin and tin foil-wrapped antioxidant intermediate alloy block is then placed into a boron nitride-coated hollow mold with a volume ratio of approximately 1:1.3, resulting in a core-shell structured ternary tin-based antioxidant intermediate alloy. This core-shell structured ternary tin-based antioxidant intermediate alloy is then added to SnCu0.7 alloy melt at 280°C to form approximately 75.10 kg of antioxidant solder. The melt is held at this temperature for 1 hour and then cast into a mold to obtain the SnCu0.7P0.005Ge0.01 antioxidant solder alloy.

[0053] Solder prepared by adding a core-shell structure to a ternary tin-based antioxidant master alloy exhibits excellent antioxidant properties. Its phosphorus (P) yield is approximately 94%, and its gemine (Ge) yield is approximately 92%. Furthermore, under oxidation conditions of 300°C for 2 hours, the TG oxidation weight gain is 0.38 mg, the dynamic oxide slag content is 2.97 g, and the surface of both static and dynamic alloy melts maintains a mirror-like finish (see...). Figure 2 The central spherical mirror solder and Figure 9 The surface of the oxide layer clearly reflects the handheld mobile phone (the oxygen content is only 1.96 wt.), and the oxygen concentration decreases to 0.98 wt. after 300 s etching. Comparative Example 1

[0054] A SnP1 master alloy was prepared and directly added with metallic Ga to SnCu0.7 solder to obtain an antioxidant solder alloy of SnCu0.7P0.0032Ga0.016. The steps are as follows: The SnP1 master alloy was melted in a closed melting furnace. SnP1 and metallic Ga were placed in SnCu0.7 solder melt at 330℃, held for 2 hours, and stirred. The mixture was then cast into a mold to obtain the antioxidant solder.

[0055] An antioxidant solder prepared using a SnP1 binary master alloy with added metallic Ga showed a P element yield of only 75% and a Ga element yield of approximately 73.75%. Under oxidation conditions of 300°C for 2 hours, the TG oxidation weight gain was 0.44 mg, and the dynamic oxide slag amount increased to 8.51 g. The static and dynamic alloy melt surfaces were covered with a large number of yellow oxide film streaks, and the oxygen content on the oxide layer surface was as high as 43.97 wt.%. After etching for 300 s, the oxygen concentration was still 26.04 wt.%. Comparative Example 2

[0056] An antioxidant solder alloy, SnCu0.7P0.005Ge0.01, was prepared by directly adding a SnP1 master alloy and metallic Ge to SnCu0.7 solder. The steps are as follows: The SnP1 master alloy was melted in a closed melting furnace. SnP1 and metallic Ga were placed in SnCu0.7 solder melt at 400℃, held for 2 hours, and stirred. The mixture was then cast into a mold to obtain the antioxidant solder.

[0057] An antioxidant solder prepared using SnP1 binary master alloy with added metallic Ga had a P element recovery rate of approximately 80% and a Ga element recovery rate of approximately 75%. Under oxidation conditions of 300℃ for 2 hours, the TG oxidation weight gain was 0.45 mg, and the dynamic oxide slag amount increased to 7.27 g. Large gray and yellow oxide film streaks were distributed on the surface of the static and dynamic alloy melts, respectively. The oxygen content on the oxide layer surface was as high as 45.37 wt.%, and the oxygen concentration was still 29.64 wt.% after etching for 300 s. Comparative Example 3

[0058] A SnP1 master alloy was prepared and directly added to SnCu0.7 solder along with SnGa1 to obtain an antioxidant solder alloy of SnCu0.7P0.0032Ga0.016. The steps are as follows: The SnP1 and SnGa1 master alloys were melted in a closed melting furnace. The SnP1 and SnGa1 master alloys were then placed in SnCu0.7 solder melt at a temperature of 310℃, held at that temperature for 2 hours, and stirred. The mixture was then cast into a mold to obtain the antioxidant solder.

[0059] An antioxidant solder prepared by directly adding SnP1 and SnGa1 binary intermediates showed a P element recovery of approximately 78.12% and a Ga element recovery of approximately 74.38%. Under oxidation conditions of 300℃ for 2 hours, the TG oxidation weight gain was 0.41 mg, the dynamic oxide slag amount increased to 5.86 g, and a small amount of gray oxide film streaks appeared on the surface of both static and dynamic alloy melts. The oxygen content on the oxide layer surface increased to 32.73 wt.%, and the oxygen concentration was still 13.83 wt.% after etching for 300 s. Comparative Example 4

[0060] An antioxidant solder alloy, SnCu0.7P0.005Ge0.01, was prepared by directly adding SnP1 master alloy and SnGe1 to SnCu0.7 solder. The steps are as follows: The SnP1 and SnGe1 master alloys were melted in a closed melting furnace. The SnP1 and SnGe1 master alloys were then placed in SnCu0.7 solder melt at 330℃, held for 2 hours, and stirred. The mixture was then cast into a mold to obtain the antioxidant solder.

[0061] An antioxidant solder prepared by directly adding SnP1 and SnGa1 binary intermediates had a P element recovery rate of approximately 88% and a Ga element recovery rate of approximately 83%. Under oxidation conditions of 300℃ for 2 hours, the TG oxidation weight gain was 0.42 mg, the dynamic oxide slag amount increased to 4.49 g, and a small amount of gray oxide film streaks appeared on the surface of both static and dynamic alloy melts. The oxygen content on the oxide layer surface increased to 34.92 wt.%, and the oxygen concentration was still 15.28 wt.% after etching for 300 s.

[0062] Table 1 lists the results of direct-reading spectral analysis of the antioxidant elements in Examples 1-2 and Comparative Examples 1-4. Table 2 lists the results of static TG oxidation weight gain tests of the solders in Examples 1-2 and Comparative Examples 1-4. Table 3 lists the results of dynamic oxidation slag content tests of the solders in Examples 1-2 and Comparative Examples 1-4.

[0063] Figures 1-6 Images of the static oxidation surface of the solder in Examples 1, 2, and Comparative Examples 1 to 4 are shown.

[0064] Figure 7 The graphs show the static oxidation weight gain curves of solder in Examples 1, 2, and Comparative Examples 1 to 4.

[0065] Figures 8-13 Images of the dynamic oxidation surface of solder in Examples 1, 2, and Comparative Examples 1 to 4 are shown.

[0066] Figure 14The graph shows the dynamic oxidation slag amount statistics of solder circulation scraping in Examples 1, 2, and Comparative Examples 1 to 4.

[0067] Figure 15 ~for Figure 20 The above are etching curves of the solder oxide surface of Examples 1, 2 and Comparative Examples 1 to 4.

[0068] Table 1. Results of direct-reading spectral analysis of antioxidant elements in solders of Examples 1-2 and Comparative Examples 1-4

[0069]

[0070] Table 2. Results of static TG oxidation weight gain test of solder in Examples 1-2 and Comparative Examples 1-4

[0071]

[0072] Table 3. Test results of dynamic oxide slag content in solder for Examples 1-2 and Comparative Examples 1-4.

[0073]

[0074] From Table 1, Table 2, Table 3 and Figures 1-20 As can be seen, the method of the present invention can significantly improve the recovery rate of alloying elements, with the recovery rate of antioxidant elements exceeding 90%, effectively improving the oxidation resistance of the static melt surface, with static oxidation weight gain as low as 0.36~0.38mg, and the oxygen content at an etching depth of 300s from the surface is only 0.67~0.98 wt.%, greatly improving the mirror-like state of the dynamic melt surface, reducing the amount of dynamic oxidation slag, and maintaining the mirror-like state of the dynamic melt for more than 2 hours after cyclic slag scraping, with a dynamic slag weight gain of only 6.40 wt.%, thus comprehensively improving the oxidation resistance of the solder alloy. Figure 1 , Figure 2 and Figures 3-6 In comparison, it is obvious that the static mirror surface of the solder in Examples 1 and 2 is very bright, while the static mirror surface of the solder in Comparative Examples 1 to 4 is obviously dull and the oxidation is more serious. Figure 8 , Figure 9 and Figures 10-12 In comparison, it is evident that the dynamic mirror surface of the solder in Examples 1 and 2 is very bright, clearly reflecting the image from the handheld camera, while the dynamic mirror surface of the solder in Comparative Examples 1-4 is very blurry and severely oxidized. The preparation method of this invention can also be used to prepare solder sheets, tin powder, tin balls, solder paste, and tin bars with antioxidant properties.

[0075] The sealed smelting furnace described in this invention is existing technology and will not be described in detail here.

Claims

1. A method for preparing a core-shell structured tin-based antioxidant solder alloy, characterized in that, Using an antioxidant intermediate alloy block as the matrix, the antioxidant intermediate alloy block is coated with KE604, a high softening point hydrogenated rosin derivative, then wrapped with tin foil as the second outer layer, and finally coated with a boron nitride-coated perforated mold as the outermost layer, forming a core-shell structure of antioxidant intermediate alloy-rosin-tin foil-boron nitride-coated perforated mold, forming a multi-element tin-based antioxidant intermediate alloy; the antioxidant intermediate alloy block is a SnPGa antioxidant intermediate alloy block or a SnPGe antioxidant intermediate alloy block, wherein the SnPGa antioxidant intermediate alloy contains... The mass ratio of P to Ga is 1:5; in the SnPGe antioxidant master alloy, the mass ratio of P to Ge is 1:2; the mass ratio of the high softening point hydrogenated rosin derivative KE604 to the antioxidant master alloy is 0.02:1; the volume ratio of the antioxidant master alloy block to the boron nitride coated hollow mold is 1:1.3; the core-shell structured multi-element tin-based antioxidant master alloy is then added to tin alloy melt at 280°C and cast into a mold to prepare a tin-based antioxidant solder alloy.

2. The method for preparing the core-shell structured tin-based antioxidant solder alloy according to claim 1, characterized in that, The preparation method includes the following steps: (1) Under argon protection, an antioxidant intermediate alloy block was prepared in a closed melting furnace; (2) Design and prepare a cage-type or frame-type stainless steel hollow mold with a cover, spray a boron nitride coating evenly on the stainless steel surface, and bake the hollow mold at 80°C for 2 hours to obtain a boron nitride coated hollow mold. (3) Heat the high softening point hydrogenated rosin derivative KE604 in a beaker to 150°C, immerse the antioxidant intermediate alloy block in the molten hydrogenated rosin derivative KE604, keep it for 2 s, lift the antioxidant intermediate alloy block, the surface of the antioxidant intermediate alloy block is coated with rosin layer, wrap a layer of tin foil on the outer layer of rosin, open the lid of the boron nitride coated hollow mold, put the antioxidant intermediate alloy block coated with rosin and tin foil into the boron nitride coated hollow mold and close the lid to obtain the core-shell structure multi-component tin-based antioxidant intermediate alloy; continue to add the core-shell structure multi-component tin-based antioxidant intermediate alloy into the tin alloy melt at 280°C, and cast it into the mold to prepare the tin-based antioxidant solder alloy.

3. The method for preparing the core-shell structured tin-based antioxidant solder alloy according to claim 2, characterized in that, The covered cage-type stainless steel hollow mold consists of a hollowed-out upper hemisphere and a hollowed-out lower hemisphere.

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