Sn-zn-al-pt-cu-based lead-free solder and method for manufacturing the same

Abstract

The application discloses a Sn-Zn-Al-Pt-Cu series lead-free solder and a preparation method thereof, and belongs to the technical field of electronic packaging soft soldering. The lead-free solder comprises the following components in percentage by mass: Zn 9%, Al 0.4%-0.5%, Cu 0.1%, Pt 0.5%-0.8%, and the rest is Sn, and the total percentage by mass of the above components is 100%. The application further discloses a preparation method, wherein Sn and Zn are weighed according to a mass ratio of 4:1, Sn and Cu are weighed according to a mass ratio of 1:1, and Sn and Al are weighed according to a mass ratio of 9:1, and then the three kinds of intermediate alloys are respectively put into a vacuum induction melting furnace for melting, and then are poured into a mold to obtain the three kinds of intermediate alloys; the three kinds of intermediate alloys and Pt and Sn are put into the vacuum induction melting furnace for melting, and then are poured into the mold to obtain the Sn-Zn-Al-Pt-Cu series lead-free solder. The solder has a low melting point, the problem of contradiction between wettability and oxidation resistance of the Sn-Zn-Al series lead-free solder is overcome by adding Pt elements and Cu elements, the wettability and oxidation resistance of the solder can be simultaneously improved, and the excessive growth of interfacial compounds of a soldered joint in an aging stage can be inhibited.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of electronic packaging soldering, and relates to a Sn-Zn-Al-Pt-Cu system lead-free solder and a preparation method thereof. BACKGROUND

[0002] Traditional Sn-Pb solder is widely used in the field of electronic packaging soldering due to its low cost, low melting point and good wettability. However, with the enhancement of people's environmental awareness and the deepening of the understanding of Pb element, countries and organizations around the world have legislated to restrict the application of lead and its alloys in electronic packaging. Under the trend of "lead-free", domestic and foreign scholars have devoted themselves to the research of new lead-free packaging solder, and have developed a variety of Sn-based lead-free solders. Among them, Sn-Zn solder is considered to be the most likely to replace traditional Sn-Pb solder due to its superior mechanical properties, similar melting point to Sn-Pb solder and higher solder joint reliability. However, Zn element is easily oxidized during soldering, and the formed oxide film hinders the wetting and spreading of the solder, limiting the wide application of Sn-Zn solder.

[0003] Therefore, relevant researchers add Al element to Sn-Zn solder to form Sn-Zn-Al system solder to improve its oxidation resistance. This is because the chemical activity of Al is higher than that of Zn element, which will preferentially enrich on the surface of the solder during soldering and react with oxygen to form a dense Al2O3 oxide film, preventing further oxidation of the solder. However, the Al2O3 oxide film is ridge-shaped, and when the content of added Al element is small, the hollow area between the ridges will be large, and oxygen passing through the hollow will cause oxidation of the elements inside the solder. Excessive addition of Al element will thicken the oxide film, hinder the spreading of the solder and worsen the wettability of the solder. Therefore, there is a contradictory relationship between the oxidation resistance and wettability of Sn-Zn-Al system solder, which limits its further development. SUMMARY

[0004] The purpose of the present application is to provide a Sn-Zn-Al-Pt-Cu system lead-free solder, which realizes the common improvement of the oxidation resistance and wettability of Sn-Zn-Al system lead-free solder, and inhibits the excessive growth of solder joint interfacial compounds during aging.

[0005] Another purpose of the present application is to provide a preparation method of Sn-Zn-Al-Pt-Cu system lead-free solder.

[0006] The first technical solution of the present application is a Sn-Zn-Al-Pt-Cu lead-free solder, wherein the mass percentage of Zn is 9%, the mass percentage of Al is 0.4%-0.5%, the mass percentage of Cu is 0.1%, the mass percentage of Pt is 0.5%-0.8%, and the rest is Sn, and the mass percentages of the above components add up to 100%.

[0007] The second technical solution of the present application is a preparation method of the above-mentioned Sn-Zn-Al-Pt-Cu lead-free solder, which specifically comprises the following steps:

[0008] Step 1: cleaning and drying each component.

[0009] Step 2: weighing raw materials Sn and Zn according to a weight ratio of 4:1, placing them in a vacuum induction melting furnace for melting to obtain a Sn-Zn intermediate alloy.

[0010] Step 3: weighing raw materials Sn and Cu according to a weight ratio of 1:1, placing them in a vacuum induction melting furnace for melting to obtain a Sn-Cu intermediate alloy.

[0011] Step 4: weighing raw materials Sn and Al according to a weight ratio of 9:1, placing them in a vacuum induction melting furnace for melting to obtain a Sn-Al intermediate alloy.

[0012] Step 5: mixing the Sn-Zn intermediate alloy, the Sn-Cu intermediate alloy, the Sn-Al intermediate alloy and Pt, Sn prepared in the above steps according to the mass percentage of Zn being 9%, the mass percentage of Al being 0.4%-0.5%, the mass percentage of Cu being 0.1%, the mass percentage of Pt being 0.5%-0.8%, and the rest being Sn, placing them in a vacuum induction melting furnace for melting to obtain a Sn-Zn-Al-Pt-Cu lead-free solder.

[0013] The second technical solution of the present application is further characterized in that:

[0014] In step 1, each component is pure Sn, pure Zn, pure Cu, pure Al and pure Pt.

[0015] In step 1, the cleaning and drying are as follows: after being ultrasonically cleaned in alcohol for 15-20 min, the components are dried in a constant-temperature oven at 40-50℃ for 20-30 min.

[0016] In step 2, the melting process is as follows: after the vacuum induction melting furnace is vacuumized, argon is introduced and the gas pressure is kept at 10 -4 Pa, the melting temperature is 450℃-500℃, the melting time is 30 min-40 min, the alloy is repeatedly melted for 3 times, after the last remelting, it is poured into a metal mold and cooled and solidified in an argon atmosphere.

[0017] The smelting process in step 3 is as follows: after the vacuum induction smelting furnace is vacuumized, argon is introduced and the gas pressure is kept at 10 -4 Pa, the smelting temperature is 1100-1150℃, the smelting time is 30-40min, the alloy is repeatedly smelted for 3 times, after the last time of remelting, it is poured into a metal mold and cooled and solidified in an argon atmosphere.

[0018] The smelting process in step 4 is as follows: after the vacuum induction smelting furnace is vacuumized, argon is introduced and the gas pressure is kept at 10 -4 Pa, the smelting temperature is 700-750℃, the smelting time is 30-40min, the alloy is repeatedly smelted for 3 times, after the last time of remelting, it is poured into a metal mold and cooled and solidified in an argon atmosphere.

[0019] The smelting process in step 5 is as follows: after the vacuum induction smelting furnace is vacuumized, argon is introduced and the gas pressure is kept at 10 -4 Pa, the smelting temperature is 500-550℃, the smelting time is 30-40min, the alloy is repeatedly smelted for 3 times, after the last time of remelting, it is poured into a metal mold and cooled and solidified in an argon atmosphere.

[0020] The present application has the advantages of:

[0021] The present application adds 0.5-0.8% Pt in the Sn-Zn-Al brazing filler metal. The Pt element can interact with the Al element, promote uphill diffusion of the Al element, make it faster to form an oxide film on the surface of the molten brazing filler metal, thereby effectively prevent the oxidation of the brazing filler metal, and further improve the oxidation resistance of the brazing filler metal. Especially, the Pt element can make the Al2O3 oxide film more dense, reduce the hollow area between the Al2O3 ridges. At the same time, the thickness of the oxide film is reduced, the hindering effect of the oxide film on the spreading of the brazing filler metal is reduced, thereby the wettability of the brazing filler metal is improved, and therefore the oxidation resistance and wettability of the Sn-Zn-Al brazing filler metal are simultaneously enhanced. The Pt element will also form an interfacial intermetallic compound (Cu, Pt) 5Zn8 during brazing, slow down the diffusion rate of Cu atoms in the interfacial intermetallic compound layer, and thereby inhibit the excessive growth of the interfacial intermetallic compound.

[0022] The present application adds 0.1% Cu in the Sn-Zn-Al brazing filler metal. Since the Pt element cannot form compounds with Sn, Zn and Al, adding Pt alone to form a second phase cannot interact with the Al element. Therefore, the present application adds an appropriate amount of Cu, which can form stable compounds with Sn, Zn and Al. And the Pt can dissolve in the Cu element, so that the Pt element can interact with the Al. In addition, the addition of Cu itself can also improve the oxidation resistance of the brazing filler metal.

[0023] The melting point of the lead-free solder alloy of the present invention is not much different from that of the traditional Sn-Zn-Al solder. This is because the added elements are only added in trace amounts and have little effect on the melting point of the solder.

[0024] The Sn-Zn-Al-Pt-Cu lead-free solder of the present invention has a melting point close to that of a conventional Sn-Zn-Al solder, thereby overcoming the conflicting problem between the wettability and oxidation resistance of the Sn-Zn-Al lead-free solder. The solder can further improve its oxidation resistance while ensuring wettability, and can inhibit the excessive growth of compounds at the interface of the solder joint during the aging stage. DETAILED DESCRIPTION

[0025] The technical solution of the present invention is further described in detail below with reference to specific implementation examples, but the present invention is not limited to these embodiments.

[0026] Example 1

[0027] The invention discloses a Sn-Zn-Al-Pt-Cu lead-free solder, which is composed of the following components in weight percentage: Zn 9%, Al 0.4%, Cu 0.1%, Pt 0.5%, and the remainder Sn.

[0028] A method for preparing a Sn-Zn-Al-Pt-Cu lead-free solder is as follows:

[0029] Step 1: Place pure Sn, pure Zn, pure Cu, pure Al, and pure Pt in alcohol for ultrasonic cleaning for 15 minutes, and then place them in a constant temperature box at 40-50°C for drying for 20 minutes.

[0030] Step 2: weigh the raw materials Sn and Zn in a weight ratio of 4:1 and place them in a vacuum induction melting furnace. After evacuating the vacuum induction melting furnace, introduce argon gas and maintain the pressure at 10 -4 Pa, the melting temperature is 450℃, the melting time is 30min, the alloy is repeatedly melted 3 times, and after the final remelting, it is poured into a metal mold and cooled and solidified in an argon atmosphere to obtain a Sn-Zn master alloy.

[0031] Step 3: weigh the raw materials Sn and Cu in a weight ratio of 1:1 and place them in a vacuum induction melting furnace. After evacuating the vacuum induction melting furnace, introduce argon gas and maintain the pressure at 10 -4 Pa, the melting temperature is 1100℃, the melting time is 30min, the alloy is repeatedly melted 3 times, and after the final remelting, it is poured into a metal mold and cooled and solidified in an argon atmosphere to obtain a Sn-Cu master alloy.

[0032] Step 4, Sn and Al are weighed according to the weight ratio of 9:1 and placed in a vacuum induction melting furnace. After the vacuum induction melting furnace is vacuumed, argon is introduced and the gas pressure is kept at 10 -4 Pa, the melting temperature is 700℃, the melting time is 30min, the alloy is repeatedly melted for 3 times, after the last remelting, it is poured into a metal mold, and cooled and solidified in an argon atmosphere to obtain a Sn-Al master alloy.

[0033] Step 5, the Sn-Zn master alloy, Sn-Cu master alloy, Sn-Al master alloy and Pt, Sn prepared in the above steps are mixed according to the mass percentage of Zn 9%, the mass percentage of Al 0.4%, the mass percentage of Cu 0.1%, the mass percentage of Pt 0.5%, and the rest is Sn, and are placed in a vacuum induction melting furnace. After the vacuum induction melting furnace is vacuumed, argon is introduced and the gas pressure is kept at 10 -4 Pa, the melting temperature is 500℃, the melting time is 30min, the alloy is repeatedly melted for 3 times, after the last remelting, it is poured into a metal mold, and cooled and solidified in an argon atmosphere to obtain a Sn-Zn-Al-Pt-Cu lead-free solder.

[0034] Example 2

[0035] A Sn-Zn-Al-Pt-Cu lead-free solder, the lead-free solder is composed of the following components by weight percentage: Zn 9%, Al 0.4%, Cu 0.1%, Pt 0.6%, and the rest is Sn.

[0036] The preparation method of the lead-free solder alloy of the present example is consistent with the method of Example 1, the difference is only that the ultrasonic cleaning time in step 1 and the constant temperature box drying time are 20min and 30min respectively, and the weight percentage of each component in the Sn-Zn-Al-Pt-Cu lead-free solder is added according to the proportion in the present example.

[0037] Example 3

[0038] A Sn-Zn-Al-Pt-Cu lead-free solder, the lead-free solder is composed of the following components by weight percentage: Zn 9%, Al 0.4%, Cu 0.1%, Pt 0.7%, and the rest is Sn.

[0039] The preparation method of the lead-free solder alloy of the present example is consistent with the method of Example 1, the difference is only that the ultrasonic cleaning time in step 1 and the constant temperature box drying time are 20min and 30min respectively, and the weight percentage of each component in the Sn-Zn-Al-Pt-Cu lead-free solder is added according to the proportion in the present example.

[0040] Example 4

[0041] A Sn-Zn-Al-Pt-Cu lead-free solder, which is composed of the following components in percentage by weight: Zn 9%, Al 0.4%, Cu 0.1%, Pt 0.8%, and the rest is Sn.

[0042] The preparation method of the lead-free solder alloy of the present embodiment is consistent with the method of Embodiment 1, except that the melting temperature and the melting time in step 3 are 1150℃ and 40min respectively, and the weight percentage of each component in the Sn-Zn-Al-Pt-Cu lead-free solder is added according to the proportion in the present embodiment.

[0043] Embodiment 5

[0044] A Sn-Zn-Al-Pt-Cu lead-free solder, which is composed of the following components in percentage by weight: Zn 9%, Al 0.5%, Cu 0.1%, Pt 0.5%, and the rest is Sn.

[0045] The preparation method of the lead-free solder alloy of the present embodiment is consistent with the method of Embodiment 1, except that the melting temperature and the melting time in step 4 are 750℃ and 40min respectively, and the weight percentage of each component in the Sn-Zn-Al-Pt-Cu lead-free solder is added according to the proportion in the present embodiment.

[0046] Embodiment 6

[0047] A Sn-Zn-Al-Pt-Cu lead-free solder, which is composed of the following components in percentage by weight: Zn 9%, Al 0.5%, Cu 0.1%, Pt 0.6%, and the rest is Sn.

[0048] The preparation method of the lead-free solder alloy of the present embodiment is consistent with the method of Embodiment 1, except that the melting temperature and the melting time in step 5 are 550℃ and 40min respectively, and the weight percentage of each component in the Sn-Zn-Al-Pt-Cu lead-free solder is added according to the proportion in the present embodiment.

[0049] Embodiment 7

[0050] A Sn-Zn-Al-Pt-Cu lead-free solder, which is composed of the following components in percentage by weight: Zn 9%, Al 0.5%, Cu 0.1%, Pt 0.7%, and the rest is Sn.

[0051] The preparation method of the lead-free solder alloy of the present embodiment is consistent with the method of Embodiment 1, except that the weight percentage of each component in the Sn-Zn-Al-Pt-Cu lead-free solder is added according to the proportion in the present embodiment.

[0052] Embodiment 8

[0053] A Sn-Zn-Al-Pt-Cu based lead-free solder, which is composed of the following components in percentage by weight: Zn 9%, Al 0.5%, Cu 0.1%, Pt 0.8%, and the rest is Sn.

[0054] The preparation method of the lead-free solder alloy of the present embodiment is consistent with the method of Embodiment 1, with the only difference being that the weight percentages of the components in the Sn-Zn-Al-Pt-Cu based lead-free solder are added according to the proportions in the present embodiment.

[0055] Comparative Example 1

[0056] A Sn-Zn-Al based lead-free solder, which is composed of the following components in percentage by weight: Zn 9%, Al 0.1%, and the rest is Sn.

[0057] The preparation method of the Sn-Zn-Al based lead-free solder is as follows:

[0058] Step 1, pure Sn, pure Zn, and pure Al were placed in alcohol and ultrasonically cleaned for 15 min, and then dried in a constant temperature oven at 40℃ for 20 min.

[0059] Step 2, the raw materials Sn and Zn were weighed according to the weight ratio of 4:1 and placed in a vacuum induction melting furnace. After the vacuum induction melting furnace was evacuated, argon was introduced and the gas pressure was maintained at 10 -4 Pa, the melting temperature was 450℃, the melting time was 30 min, the alloy was repeatedly melted for 3 times, and after the last remelting, it was poured into a metal mold and cooled and solidified in an argon atmosphere to obtain a Sn-Zn intermediate alloy.

[0060] Step 3, the Sn-Zn intermediate alloy prepared in the above step and Al were mixed according to the mass percentage of Zn being 9%, the mass percentage of Al being 0.1%, and the rest being Sn, and were placed in a vacuum induction melting furnace. After the vacuum induction melting furnace was evacuated, argon was introduced and the gas pressure was maintained at 10 -4 Pa, the melting temperature was 700℃, the melting time was 30 min, the alloy was repeatedly melted for 3 times, and after the last remelting, it was poured into a metal mold and cooled and solidified in an argon atmosphere to obtain a Sn-Zn-Al based lead-free solder.

[0061] Comparative Example 2

[0062] A Sn-Zn-Al based lead-free solder, which is composed of the following components in percentage by weight: Zn 9%, Al 0.5%, and the rest is Sn.

[0063] The preparation method of the lead-free solder alloy of the present embodiment is consistent with the method of Comparative Example 1, with the only difference being that the weight percentages of the components in the Sn-Zn-Al lead-free solder are added according to the proportions in the present comparative example, which will not be repeated here.

[0064] Table 1 is the solder composition and main performance:

[0065]

[0066] Table 1 is the composition table of eight kinds of Sn-Zn-Al-Pt-Cu lead-free solders, and the components in the table are mass percentages. The melting point, wetting angle, oxidation weight gain and interfacial intermetallic compound (IMC) thickness of the solder of the present embodiment and the solder of the comparative example are also listed. As can be seen from the table, the melting point of the present embodiment 1-8 differs from the widely used Sn-Zn-Al solder, i.e. Comparative Example 1, by at most 3.9℃, and the melting points are very similar. The wetting angle, oxidation weight gain and IMC thickness of the present embodiment 1-8 are all lower than those of Comparative Examples 1-2. It is shown that the doping of trace Pt and Cu can simultaneously improve the wettability and oxidation resistance of the Sn-Zn-Al lead-free solder, and inhibit the excessive growth of the interfacial compound of the soldered joint in the aging stage.

[0067] It is necessary to point out that the steps for measuring the melting point of each solder in the present application are as follows:

[0068] Step 1, 20-25 mg of solder sample is placed in alcohol for ultrasonic cleaning for 15-20 min, and then placed in a constant temperature box at 40-50℃ for drying for 20-30 min;

[0069] Step 2, the dried solder sample is placed in MDSC2910 modulated differential scanning calorimetry, the sample chamber is evacuated, then argon is introduced and kept at atmospheric pressure, and the temperature is raised to 150℃ at a rate of 10℃ / min, and then raised to 250℃ at a rate of 2℃ / min. Draw the DSC curve and read the melting point of the solder.

[0070] It is necessary to point out that the steps for measuring the oxidation weight gain of each solder in the present application are as follows:

[0071] Step 1, 20-25 mg of solder sample is placed in alcohol for ultrasonic cleaning for 15-20 min, and then placed in a constant temperature box at 40-50℃ for drying for 20-30 min;

[0072] Step 2, the dried solder sample is placed in a corundum crucible and placed in a box-type resistance furnace for 24 h, with the temperature set at 260℃;

[0073] Step 3, after the corundum crucible containing the brazing filler metal is taken out and naturally cooled in air, it is weighed. The surface diameter of the brazing filler metal alloy is measured by using a vernier caliper, the surface area is calculated, and then the oxidation weight gain per unit surface area of the alloy is calculated.

[0074] It is necessary to point out that the steps of measuring the wetting angle and the IMC thickness of each brazing filler metal in the present application are as follows:

[0075] Step 1, the surface of the Cu substrate is polished by using W0.5 type diamond polishing paste after being polished by using 150 mesh, 400 mesh, 600 mesh, 800 mesh, 1000 mesh, 1200 mesh, 1500 mesh and 2000 mesh sandpaper in sequence, so as to ensure that the surface is flat and free of oxide film;

[0076] Step 2, the brazing filler metal sample with a volume of 3mm×3mm×3mm and the Cu substrate are placed in alcohol for ultrasonic cleaning for 15-20min, and then are placed in a constant temperature box at 40-50℃ for drying for 20-30min;

[0077] Step 3, the Cu substrate is taken out and 1 drop of rosin flux (the mass ratio of rosin to alcohol is 1:3) is dropped at the center of the substrate, the brazing filler metal sample is placed at the center of the Cu substrate, and they are placed in a high vacuum wetting angle goniometer. After being placed, the gas inlet valve and the gas outlet valve of the sample chamber are closed, the sample chamber is first pumped to low vacuum by using a mechanical pump, and then is pumped to high vacuum by using a molecular pump until the vacuum degree reaches 1×10 -3 Pa;

[0078] Step 4, the sample chamber is raised to 180℃ at a temperature raising rate of 5℃ / min, and then is raised to 250℃ at a temperature raising rate of 2℃ / min, and then is kept for 10min and is cooled with the furnace. The high-resolution camera system at the side end of the sample chamber is used to measure the wetting angle in combination with a graphic analysis software;

[0079] Step 5, the sample obtained in step 4 is taken out from the high vacuum wetting angle goniometer, is placed in the constant temperature zone of a VTCE-2585 type atmosphere protection furnace, and is heated to 150℃ after pure argon gas with a purity of 99.99% is flushed in. After being kept for 80h, the furnace is cooled, and the cooling speed is about 5-10℃ / min. When the furnace temperature drops to room temperature, the furnace door is opened and the sample is taken out;

[0080] Step 6, the sample obtained in step 5 is cut along the axial section, is polished after being polished by using sandpaper, and is prepared into a metallographic sample. The microstructure of the joint is observed by using a scanning electron microscope, and the IMC thickness is measured.

[0081] The above merely describes the best mode of the present application, but the protection scope of the present application is not limited thereto, any skilled person in the art can make equivalent substitution of similar materials, equipment or adjustment of relevant technical parameters according to the technical solution and inventive concept of the present application within the technical range disclosed by the present application, which should be covered in the protection scope of the present application.

Claims

1. A method for producing a Sn-Zn-Al-Pt-Cu-based lead-free solder, characterized by comprising: a step of adding a Pt-Cu alloy to a Sn-Zn-Al alloy. Specifically comprising the following steps: Step 1, cleaning and drying each component; Step 2, weighing raw materials Sn and Zn according to a weight ratio of 4:1 and placing them in a vacuum induction melting furnace for melting, the melting temperature is 450-500 DEG C, the melting time is 30-40 min, and a Sn-Zn intermediate alloy is obtained; Step 3, weighing raw materials Sn and Cu according to a weight ratio of 1:1 and placing them in a vacuum induction melting furnace for melting, the melting temperature is 1100-1150 DEG C, the melting time is 30-40 min, and a Sn-Cu intermediate alloy is obtained; Step 4, weighing raw materials Sn and Al according to a weight ratio of 9:1 and placing them in a vacuum induction melting furnace for melting, the melting temperature is 700-750 DEG C, the melting time is 30-40 min, and a Sn-Al intermediate alloy is obtained; Step 5, mixing Sn-Zn intermediate alloy, Sn-Cu intermediate alloy, Sn-Al intermediate alloy and Pt, Sn prepared in the above steps according to the mass percentage of Zn of 9%, the mass percentage of Al of 0.4-0.5%, the mass percentage of Cu of 0.1%, the mass percentage of Pt of 0.5-0.8%, and the rest of Sn, placing them in a vacuum induction melting furnace for melting, the melting temperature is 500-550 DEG C, the melting time is 30-40 min, and a Sn-Zn-Al-Pt-Cu lead-free solder is obtained.

2. The Sn-Zn-Al-Pt-Cu-based lead-free solder according to claim 1, wherein Each component in step 1 is pure Sn, pure Zn, pure Cu, pure Al and pure Pt.

3. The Sn-Zn-Al-Pt-Cu-based lead-free solder according to claim 1, wherein The cleaning and drying in step 1 is: after ultrasonic cleaning in alcohol for 15-20 min, drying in a constant temperature box at 40-50 DEG C for 20-30 min.

4. The Sn-Zn-Al-Pt-Cu-based lead-free solder according to claim 1, wherein The melting process described in Step 2 is as follows: the vacuum induction melting furnace is vacuumed, argon is introduced and the gas pressure is kept at 10 -4 Pa, the alloy is repeatedly melted for 3 times, and after the last time of remelting, it is poured into a metal mold, and cooled and solidified in an argon atmosphere.

5. The Sn-Zn-Al-Pt-Cu-based lead-free solder according to claim 1, wherein The melting process described in step 3 is as follows: the vacuum induction melting furnace is vacuumed, argon is introduced and the gas pressure is kept at 10 -4 Pa, the alloy is repeatedly melted for 3 times, after the last time of remelting, it is poured into a metal mold, and cooled and solidified in an argon atmosphere.

6. The Sn-Zn-Al-Pt-Cu-based lead-free solder according to claim 1, wherein The melting process described in Step 4 is as follows: After the vacuum induction melting furnace is vacuumized, argon is introduced and the gas pressure is kept at 10 -4 Pa, the alloy is repeatedly melted for 3 times, and after the last time of remelting, it is poured into a metal mold, and cooled and solidified in an argon atmosphere.

7. The Sn-Zn-Al-Pt-Cu-based lead-free solder according to Claim 1, wherein The melting process described in Step 5 is as follows: After the vacuum induction melting furnace is vacuumed, argon is introduced and the gas pressure is kept at 10 -4 Pa, the alloy is repeatedly melted 3 times, and after the last time of remelting, it is poured into a metal mold and cooled and solidified in an argon atmosphere.

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