Tin-silver-copper alloy, preparation method thereof and solder

Abstract

The invention discloses a tin-silver-copper alloy, a preparation method thereof and solder, and belongs to the technical field of alloy materials, the tin-silver-copper alloy comprises, by mass, 2.8%-3.1% of Ag, 0.3%-0.7% of Cu, 0.01%-0.5% of B, 0.03%-1.0% of P and the balance Sn and impurity elements, and the content of Pb and the content of Fe in the impurity elements are both smaller than or equal to 0.001%. According to the embodiment of the invention, the content of impurity elements in the tin-silver-copper alloy is controlled, the B and P elements are added on the basis of the tin-silver-copper basic elements, the alloy is refined, an oxidation film is formed on the surface of the liquid solder, and the corrosion to a titanium alloy part is reduced.

Description

Technical Field

[0001] The present application relates to the technical field of alloy materials, and in particular to a tin-silver-copper alloy and a preparation method and solder thereof. Background Art

[0002] With the widespread use of tin-based wave solders, the problem of high-tin solders corroding wave soldering equipment components has become increasingly prominent. Tin solders of different nominal values ​​have a certain degree of corrosion on wave soldering components, resulting in a shortening of the component life of the soldering equipment by more than 70% and an increase of more than 10% in wave soldering operating costs. Tin-silver-copper alloy is the main raw material for wave soldering. The development of corrosion-resistant tin-silver-copper alloy for wave soldering is of great significance to the development of wave soldering technology. Summary of the invention

[0003] The main purpose of the present application is to provide a tin-silver-copper alloy and a preparation method and solder thereof, aiming to solve the technical problem that the currently commonly used solder is highly corrosive to the components of welding equipment.

[0004] To achieve the above-mentioned purpose, an embodiment of the present application provides a tin-silver-copper alloy, which includes, by mass percentage, 2.8%-3.1% Ag, 0.3%-0.7% Cu, 0.01%-0.5% B, 0.03%-1.0% P, and the remainder is Sn and impurity elements, among which the contents of Pb and Fe are both less than or equal to 0.001%.

[0005] The present application also provides a method for preparing a tin-silver-copper alloy, which is used to prepare the tin-silver-copper alloy as described above, and the preparation method comprises the following steps:

[0006] Pure tin, tin-silver alloy, tin-copper alloy, tin-phosphorus alloy, tin-boron alloy, tin-titanium alloy, tin-chromium alloy and rare earth elements are taken according to mass percentage;

[0007] Putting the pure tin into a crucible and heating it to melt;

[0008] Adding the tin-silver alloy, tin-copper alloy, tin-phosphorus alloy, tin-boron alloy, tin-titanium alloy, tin-chromium alloy and rare earth elements into the crucible and continuing to heat and melt;

[0009] Add covering agent to cover the molten tin liquid surface, control the temperature within the range of 350-450℃, and keep warm for 5-30min;

[0010] After sedation for 20 minutes, the molten tin is cast into a tin-silver-copper alloy in the form of tin ingots or tin bars.

[0011] The embodiment of the present application also provides a solder, wherein the material of the solder is the tin-silver-copper alloy as described above.

[0012] The embodiment of the present application discloses a tin-silver-copper alloy, which includes 2.8%-3.1% Ag, 0.3%-0.7% Cu, 0.01%-0.5% B, 0.03%-1.0% P in terms of mass percentage, and the remainder is Sn and impurity elements, among which the contents of Pb and Fe are both less than or equal to 0.001%. On the basis of SAC305, which is widely used as solder, the content of impurity elements in the alloy is strictly controlled to reduce the reaction of Pb and Fe with titanium alloy equipment parts during welding, and the P element is added to form a thin and dense oxide film on the surface of the liquid solder to prevent further oxidation of the internal solder. The addition of the B element can inhibit the abnormal growth of the alloy structure and improve the strength of the alloy. Through the synergistic effect of the added alloy elements and the control of the content of impurity elements, the corrosion resistance of the tin-silver-copper alloy is comprehensively improved, and the corrosion to the welding equipment parts is reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a schematic flow chart of the method for preparing tin-silver-copper alloy involved in the embodiment of the present application.

[0014] The realization of the purpose, functional features and advantages of this application will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0015] It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0016] With the widespread use of tin-based wave solders, the problem of high-tin solders corroding wave soldering equipment components has become increasingly prominent. Tin-silver-copper alloy is the main raw material for wave soldering. At present, the tin-silver-copper alloys used for wave soldering mainly include SAC305, SAC387, SAC405, SAC0307, ​​etc., among which SAC305 is the most widely used. SAC305 alloy is highly corrosive to wave soldering equipment, which seriously affects the market promotion of tin alloy solder.

[0017] The embodiment of the present application provides a tin-silver-copper alloy. In terms of mass percentage, the tin-silver-copper alloy includes 2.8%-3.1% Ag, 0.3%-0.7% Cu, 0.01%-0.5% B, 0.03%-1.0% P, and the remainder is Sn and impurity elements. Among the impurity elements, the contents of Pb and Fe are both less than or equal to 0.001%.

[0018] SAC305 indicates a soft solder containing about 3% Ag, about 0.5% Cu, and the remainder Sn, which meets the technical requirements of ANSI / J-STD-006 solder alloys, flux and non-flux solid solders for electronic soldering. In the embodiment of the present application, 2.8-3.1% Ag and 0.3-0.7% Cu are added to Sn to form a standard SAC305 alloy, maintaining the composition ratio of the main system of the solder alloy and providing basic properties for use as a solder. Lead has better wettability than tin, but it is toxic, and solders with high lead content have been gradually eliminated. Copper can lower the melting point, improve thermal cycle fatigue resistance, and improve the wetting properties of molten solder. Silver can provide mechanical strength and improve resistance to fatigue from thermal cycles in the absence of lead. Therefore, tin-silver-copper system alloys can also provide better wetting properties and be used as solder.

[0019] The embodiment of the present application controls the content of impurity elements in the tin-silver-copper alloy, and the content of the Pb element is less than or equal to 0.001%, and the content of the Fe element is less than or equal to 0.001%. The control of the content of the Pb element improves the safety of the alloy and reduces damage to human health on the one hand, and on the other hand, avoids the reaction between the Pb element and the titanium alloy parts during the welding process, which corrodes the titanium alloy parts. For the Fe element, in the tin bath processing scenario, Sn and oxides will react with Fe, affecting the corrosion resistance of the titanium alloy parts. Therefore, the Fe content has a greater impact on the corrosion resistance of the titanium alloy, and should also be strictly controlled at a lower level to reduce corrosion to the titanium alloy parts.

[0020] 0.01%-0.5% B is added to the tin-silver-copper alloy, for example, 0.01%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%. The B element can promote grain refinement, limit the diffusion of grain boundaries and the growth rate of grains, maintain a finer grain size and a higher grain boundary area, inhibit the abnormal growth of the alloy structure, and improve the strength and toughness of the alloy. Exemplarily, the B content is in the range of 0.03%-0.3%. Adding too little B element to the alloy will not play a strengthening role, and adding too much will affect the performance of the alloy.

[0021] No more than 0.03%-1.0% P is added to the tin-silver-copper alloy, for example, 0.03%, 0.05%, 0.07%, 0.09%, 1.0%. The P element can effectively prevent the generation of oxides on the surface of the liquid solder, because the P element has a skin effect, which can form a thin and dense oxide film on the surface of the liquid solder to prevent the internal liquid solder covered by the oxide film from oxidizing. Exemplarily, the content of the P element is in the range of 0.03-0.05%. When the P element content is greater than 1%, too much P element will deteriorate the performance of the tin-silver-copper alloy. If the P content is too small, it will not have an anti-oxidation effect. The titanium alloy parts are in direct contact with the liquid solder, reducing the oxidation inside the solder can also reduce the possibility of the titanium alloy parts being oxidized by contact with oxygen, thereby reducing the corrosion of the titanium alloy parts.

[0022] Exemplarily, 0.1%-0.6% Ti can also be added to the tin-silver-copper alloy, for example, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%. The Ti element can form a concentration gradient between the Ti alloy component and the liquid solder, reducing the corrosion rate of the solder on the titanium alloy component. At the same time, the titanium element can form titanium oxide to cover the surface of the liquid solder, preventing the internal liquid solder from oxidizing. Exemplarily, the amount of Ti element added is 0.1-0.3%. Too little Ti element content cannot form an effective concentration gradient, and an oxide film that can cover the surface of the solder. Too much Ti element affects the performance of the tin-silver-copper alloy.

[0023] Exemplarily, less than 0.03%-0.1% Cr can be added to the tin-silver-copper alloy, for example, 0.03%, 0.05%, 0.07%, 0.09%, 0.1%. The Cr element can form an extremely thin Cr2O3 oxide film on the surface of the liquid solder to prevent the liquid solder from oxidizing and slow down the corrosion of Sn on titanium alloy parts. Exemplarily, the Cr element content can be in the range of 0.03-0.05%. Too little Cr element content cannot form an oxide film that can cover the surface of the liquid solder, and too much Cr element content affects the performance of the tin-silver-copper alloy.

[0024] Exemplarily, 0.05%-1.0% of rare earth elements RE (Rare Earth) can also be added to the tin-silver-copper alloy, for example, 0.05%, 0.1%, 0.3%, 0.5%, 0.7%, 0.9%, 1.0%. Rare earth elements can not only purify the alloy, refine the structure, eliminate the harmful effects of impurity oxygen in the alloy, but also improve the fatigue performance of the solder joint. Exemplarily, the rare earth element RE selects lanthanide rare earths, such as La and Ce, and its content is in the range of 0.05-0.5%. Rare earth elements are active in nature, and adding a small amount can purify the alloy and improve the performance of the alloy, while adding too much will lead to the deterioration of the performance of the tin-silver-copper alloy.

[0025] The tin-silver-copper alloy provided in the embodiment of the present application can be regarded as SAC305 as the basis. By more strictly controlling the impurity elements such as Fe and Pb, and adding trace alloying elements such as Ti, Cr, B, P and lanthanide rare earths, the corrosion problem of tin alloy solder on titanium alloy equipment parts for welding is solved. Accelerated corrosion experiments have proved that the corrosion degree of the solder alloy with the improved formula is more than 70% lower than that of the pure SAC305 alloy on the same titanium alloy parts. Using the improved solder, the corrosion degree of wave soldering parts is reduced by more than 80%, which prolongs the service life of the parts, reduces the downtime for maintenance, and reduces the cost of purchasing spare parts.

[0026] The present application also provides a method for preparing a tin-silver-copper alloy. Figure 1 The preparation method of the tin-silver-copper alloy is used to prepare the above tin-silver-copper alloy, and the preparation method of the tin-silver-copper alloy comprises the following steps:

[0027] Step S10, taking pure tin, tin-silver alloy, tin-copper alloy, tin-phosphorus alloy, tin-boron alloy, tin-titanium alloy, tin-chromium alloy and rare earth elements according to mass percentage;

[0028] Sn element and rare earth element can be supplied by single substance raw material, and other added alloy elements can be added in the form of master alloy. Exemplarily, the master alloy can be selected from Sn-10% Ag master alloy, Sn-10% Cu master alloy, Sn-30% P master alloy, Sn-10% B master alloy, Sn-3% Cr master alloy and Sn-3% Ti master alloy. Among them, Sn-10% Ag master alloy provides silver source, Sn-10% Cu master alloy provides copper source, Sn-30% P master alloy provides phosphorus source, Sn-10% B master alloy provides boron source, Sn-3% Cr master alloy provides chromium source, Sn-3% Ti master alloy provides titanium source.

[0029] The above master alloys can be prepared by vacuum melting, and the vacuum degree during the preparation process is greater than 1.0×10 -3 Pa. Vacuum melting includes vacuum induction melting, vacuum arc melting and electron beam melting. In this embodiment, any of the above vacuum melting methods can be selected. Vacuum melting can produce an intermediate alloy with less impurities and high purity.

[0030] Impurity elements in alloys should be strictly controlled. The purity of raw materials has a great influence on the properties of the final alloy, so the selection of raw materials is also very important. Raw materials from different origins may have different impurity contents. Low impurity content and high purity can be maintained by selecting raw materials with high purity.

[0031] Step S20, putting pure tin into a crucible and heating it to melt;

[0032] As the base metal in the tin-silver-copper alloy, the tin element accounts for the largest proportion in the alloy and can be first put into a crucible to heat and melt to form tin liquid.

[0033] A medium frequency furnace is a power supply device that converts 50HZ industrial frequency alternating current into medium frequency (300HZ to 1000HZ). It converts three-phase industrial frequency alternating current into direct current after rectification, and then converts direct current into adjustable medium frequency current, which is supplied to the medium frequency alternating current flowing through the capacitor and the induction coil, generating high-density magnetic lines of force in the induction coil. The magnetic lines of force cut the metal material contained in the induction coil, generating eddy currents in the metal material for heating. In one feasible implementation, the crucible can be placed in a medium frequency furnace for heating, and the voltage of the medium frequency furnace is set to 0.4kV and the current is set to 150A. The medium frequency furnace has the advantages of high thermal efficiency, short smelting time, less alloy element burnout, wide smelting material, low environmental pollution, and the ability to accurately control the temperature and composition of the molten metal.

[0034] Step S30, adding tin-silver alloy, tin-copper alloy, tin-phosphorus alloy, tin-boron alloy, tin-titanium alloy, tin-chromium alloy and rare earth elements into the crucible and continuing to heat and melt;

[0035] When pure tin is completely melted to form tin liquid, tin-silver alloy, tin-copper alloy, tin-phosphorus alloy, tin-boron alloy, tin-titanium alloy, tin-chromium alloy and other master alloys, as well as rare earth elements, are put into a crucible, heated and melted, and dissolved in the tin liquid. Among the alloying elements added, the input amount difference between different elements may be large. In a feasible implementation, when feeding, a master alloy with a high content of alloying elements can be first put in, and then a master alloy with a low content of elements can be put in to promote the melting of the raw materials in the tin liquid and form a metal melt with a relatively uniform distribution. The above-mentioned master alloy can also be put into the crucible at one time.

[0036] In another feasible implementation, the order of feeding can be determined according to the properties of the master alloy. The alloy elements that are easily evaporated or oxidized are left to be fed last, and the metals that can produce a large thermal effect when melted are not fed as the last material to prevent the melt from overheating.

[0037] Step S40, adding a covering agent to cover the molten tin liquid surface, controlling the temperature within the range of 350-450° C., and keeping the temperature for 5-30 minutes;

[0038] Under the condition that the metal melt has a certain fluidity and the casting can be carried out normally, a lower casting temperature can be selected as much as possible. In a feasible embodiment, the temperature can be controlled within the range of 350-450°C, and in order to reduce the evaporation and oxidation loss of the metal and prevent the inhalation of gas, a covering agent can be used on the surface of the tin liquid. Exemplarily, the covering agent can be selected from charcoal powder or molten salt. The tin liquid can be stirred within 5-30 minutes of insulation. In a feasible embodiment, a titanium rod is used for stirring every 3-5 minutes from the starting time, and the number of stirrings is at least once. Stirring can accelerate the melting of the intermediate alloy added to the tin liquid and promote the uniform distribution of alloy elements. The melting point of titanium is high, and the rod used for stirring will not be excessively melted in the tin liquid, and titanium is also one of the elements added to the tin-silver-copper alloy, and a trace amount of melting will not have too much impact on the performance of the alloy.

[0039] Step S50, calming for 20 minutes, casting the molten tin into a tin-silver-copper alloy in the form of a tin ingot or a tin bar.

[0040] Ingots and bars are the most common alloy shapes, suitable for use, transportation and storage. The molten tin is poured into a mold with a special shape, and the alloy after cooling and solidification has a shape corresponding to the mold.

[0041] In this embodiment, a tin-silver-copper alloy including 2.8%-3.1% Ag, 0.3%-0.7% Cu, 0.01%-0.5% B, 0.03%-1.0% P, and the remainder being Sn and impurity elements, wherein the content of Pb and Fe in the impurity elements is less than or equal to 0.001% is prepared by using appropriate raw materials and casting processes. On the basis of SAC305, which is widely used as solder, the content of impurity elements in the alloy is strictly controlled to reduce the reaction of Pb and Fe with titanium alloy equipment parts during the welding process, and the P element is added to form a thin and dense oxide film on the surface of the liquid solder to prevent further oxidation of the internal solder. The addition of the B element can inhibit the abnormal growth of the alloy structure and improve the strength of the alloy. Through the synergistic effect of the added alloy elements and the control of the content of impurity elements, the corrosion resistance of the tin-silver-copper alloy is comprehensively improved, and the corrosion to the welding equipment parts is reduced.

[0042] The embodiment of the present application also provides a solder, and the material of the solder is the tin-silver-copper alloy disclosed in the above embodiment. It is used in the scenes of tin bath processing such as wave soldering, selective soldering and module soldering of circuit boards in the manufacture of electronic products, and is a very important general production basic material used in processes such as wave soldering, selective soldering and module soldering. It is used to form solder joints to achieve mechanical connection and circuit conduction between components and printed circuit pads. In the processing scenarios of wave soldering, selective soldering, module soldering and other welding methods, the solder provided by the embodiment of the present application can be used, which can reduce the corrosion of titanium alloy parts under the condition of direct contact with titanium alloy parts at an operating temperature of 260-270°C. On this basis, the phenomenon of liquid solder overflow caused by tin bath dissolution is effectively reduced to ensure safe production; reduce the time of downtime for maintenance, improve equipment utilization; reduce the frequency of replacement of spare parts, and save spare parts procurement costs.

[0043] Example 1

[0044] Ingredients are prepared according to the following mass percentages:

[0045] Sn+2.8%Ag+0.5%Cu+0.3%Ti+0.5%B+1.0%P+0.5%RE, the contents of Pb and Fe are both not more than 0.001%.

[0046] Preparation method:

[0047] Pure tin, tin-silver alloy, tin-copper alloy, tin-phosphorus alloy, tin-boron alloy, tin-titanium alloy and rare earth elements are taken according to the above mass percentages;

[0048] Put pure tin into a crucible and heat it to melt;

[0049] Add tin-silver alloy, tin-copper alloy, tin-phosphorus alloy, tin-boron alloy, tin-titanium alloy and rare earth elements into the crucible and continue to heat and melt;

[0050] Add covering agent to cover the molten tin liquid surface, control the temperature within the range of 350-450℃, and keep warm for 5-30min;

[0051] After sedation for 20 minutes, the molten tin is cast into a tin-silver-copper alloy in the form of tin ingots or tin bars.

[0052] Example 2

[0053] Ingredients are prepared according to the following mass percentages:

[0054] Sn+3.1%Ag+0.7%Cu+0.1%Cr+0.02%B+0.03%P, the contents of Pb and Fe are both not more than 0.001%.

[0055] Preparation method:

[0056] Pure tin, tin-silver alloy, tin-copper alloy, tin-phosphorus alloy, tin-boron alloy and tin-chromium alloy are taken according to the above mass percentages;

[0057] Put pure tin into a crucible and heat it to melt;

[0058] Add tin-silver alloy, tin-copper alloy, tin-phosphorus alloy, tin-boron alloy and tin-chromium alloy into the crucible and continue to heat and melt;

[0059] Add covering agent to cover the molten tin liquid surface, control the temperature within the range of 350-450℃, and keep warm for 5-30min;

[0060] After sedation for 20 minutes, the molten tin is cast into a tin-silver-copper alloy in the form of tin ingots or tin bars.

[0061] Example 3

[0062] Ingredients are prepared according to the following mass percentages:

[0063] Sn+3.0%Ag+0.3%Cu+0.6%Ti+0.05%Cr+0.01%B+0.03%P+1.0%RE, the contents of Pb and Fe are both not more than 0.001%.

[0064] Preparation method:

[0065] Pure tin, tin-silver alloy, tin-copper alloy, tin-phosphorus alloy, tin-boron alloy, tin-titanium alloy, tin-chromium alloy and rare earth elements are taken according to the above mass percentages;

[0066] Put pure tin into a crucible and heat it to melt;

[0067] Add tin-silver alloy, tin-copper alloy, tin-phosphorus alloy, tin-boron alloy, tin-titanium alloy, tin-chromium alloy and rare earth elements into the crucible and continue to heat and melt;

[0068] Add covering agent to cover the molten tin liquid surface, control the temperature within the range of 350-450℃, and keep warm for 5-30min;

[0069] After sedation for 20 minutes, the molten tin is cast into a tin-silver-copper alloy in the form of tin ingots or tin bars.

[0070] Example 4

[0071] Ingredients are prepared according to the following mass percentages:

[0072] Sn+2.9%Ag+0.5%Cu+0.4%Ti+0.07%Cr+0.04%B+0.08%P+0.5%RE, the content of Pb and Fe is not more than 0.001%.

[0073] Preparation method:

[0074] Pure tin, tin-silver alloy, tin-copper alloy, tin-phosphorus alloy, tin-boron alloy, tin-titanium alloy, tin-chromium alloy and rare earth elements are taken according to the above mass percentages;

[0075] Put pure tin into a crucible and heat it to melt;

[0076] Add tin-silver alloy, tin-copper alloy, tin-phosphorus alloy, tin-boron alloy, tin-titanium alloy, tin-chromium alloy and rare earth elements into the crucible and continue to heat and melt;

[0077] Add covering agent to cover the molten tin liquid surface, control the temperature within the range of 350-450℃, and keep warm for 5-30min;

[0078] After sedation for 20 minutes, the molten tin is cast into a tin-silver-copper alloy in the form of tin ingots or tin bars.

[0079] Comparative Example

[0080] Commercially available Yunxi SAC305 tin bars.

[0081] Performance Testing

[0082] The alloys of Examples 1-4 and the comparative example were subjected to corrosion resistance tests, that is, the titanium alloy samples were placed in a wave soldering accelerated corrosion tester at 280° C. for 200 hours and the corrosion rates were measured. The specific test results are shown in Table 1 below.

[0083] Table 1

[0084]

[0085] Corrosion rate = (original weight - remaining weight) / original weight, the higher the corrosion rate, the worse the corrosion resistance. As can be seen from Table 1: compared with the traditional commercially available SAC305, the corrosion rate of the tin-silver-copper alloy on the titanium alloy in Examples 1-4 is significantly reduced.

[0086] The serial numbers of the above-mentioned embodiments of the present application are for description only and do not represent the advantages or disadvantages of the embodiments.

[0087] The above are only preferred embodiments of the present application, and are not intended to limit the patent scope of the present application. Any equivalent structure or equivalent process transformation made using the contents of the present application specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. A tin-silver-copper alloy, characterized in that: In terms of mass percentage, the tin-silver-copper alloy includes 2.8%-3.1% Ag, 0.3%-0.7% Cu, 0.01%-0.5% B, 0.03%-1.0% P, and the remainder is Sn and impurity elements, among which the contents of Pb and Fe are both less than or equal to 0.001%.

2. The tin-silver-copper alloy according to claim 1, characterized in that: The tin-silver-copper alloy also includes 0.1%-0.6% Ti.

3. The tin-silver-copper alloy according to claim 1, characterized in that: The tin-silver-copper alloy further comprises 0.03%-0.1% Cr.

4. The tin-silver-copper alloy according to claim 1, characterized in that: The content of P in the tin-silver-copper alloy is 0.03%-0.05%.

5. The tin-silver-copper alloy according to claim 1, characterized in that: The content of B in the tin-silver-copper alloy is 0.03%-0.3%.

6. The tin-silver-copper alloy according to claim 1, characterized in that: The tin-silver-copper alloy also includes 0.05%-1.0% of rare earth elements.

7. A method for preparing a tin-silver-copper alloy, characterized in that: For preparing the tin-silver-copper alloy according to any one of claims 1 to 6, the preparation method comprises the following steps: Pure tin, tin-silver alloy, tin-copper alloy, tin-phosphorus alloy, tin-boron alloy, tin-titanium alloy, tin-chromium alloy and rare earth elements are taken according to mass percentage; Putting the pure tin into a crucible and heating it to melt; Adding the tin-silver alloy, tin-copper alloy, tin-phosphorus alloy, tin-boron alloy, tin-titanium alloy, tin-chromium alloy and rare earth elements into the crucible and continuing to heat and melt; Add covering agent to cover the molten tin liquid surface, control the temperature within the range of 350-450℃, and keep warm for 5-30min; After sedation for 20 minutes, the molten tin is cast into a tin-silver-copper alloy in the form of tin ingots or tin bars.

8. The method for preparing the tin-silver-copper alloy according to claim 7, characterized in that: The covering agent is charcoal powder or molten salt.

9. The method for preparing the tin-silver-copper alloy according to claim 7, characterized in that: During the insulation process, a titanium rod was used for stirring every 3-5 minutes starting from the starting time.

10. A solder, characterized in that: The material of the solder is the tin-silver-copper alloy as described in any one of claims 1-6.

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