Preparation method of Sn42-In58 alloy preformed solder sheet

Abstract

The invention discloses a preparation method of a Sn42-In58 alloy preform solder sheet, which belongs to the technical field of microelectronic welding connection material preparation. The method comprises the following steps: heating tin to 230-250°C and then adding indium to melt the preform to obtain an alloy solution; pouring the alloy solution to obtain an alloy ingot; subjecting the alloy ingot to rough rolling, first finishing rolling, and second finishing rolling to obtain a Sn42-In58 alloy thin strip with a thickness of less than 0.2mm; preparing a flux solution with ethanol, triethanolamine, nonylphenol polyoxyethylene, phenolic resin, and hydrogenated rosin; and punching and slitting the alloy thin strip and immersing it in the flux solution for 1-3min to remove the strip, drying it, and obtaining a Sn42-In58 alloy preform solder sheet. The Sn42-In58 alloy preform solder sheet prepared by the method of the present invention has a low alloy melting point and can effectively reduce the warpage of the mounted chip and the low solder void rate during the welding process.

Description

Technical Field

[0001] The invention belongs to the technical field of microelectronic welding connection material preparation, and particularly relates to a method for preparing a Sn42-In58 alloy preformed welding sheet. Background Art

[0002] Microelectronic soldering materials are a key component of the electronics industry, widely used in the assembly and interconnection of electronic devices. They primarily include solder paste, solder wire, solder bars, solder balls, solder preforms, and flux. These materials play a key role in multiple industry processes, including PCBA manufacturing, precision component connection, and semiconductor packaging.

[0003] Solder preforms are welding materials pre-fabricated into specific shapes and sizes. They are widely used in a variety of fields, including electronics, automotive, aerospace, and medical. Produced using precision mold technology and stamping processes, they significantly improve welding efficiency and quality. A key feature of solder preforms is their customizable shape and size, enabling more precise welding results. Compared to traditional welding materials, preforms reduce preparation time and errors during the welding process, improving the strength and reliability of welded joints. Furthermore, preforms offer excellent thermal conductivity, contributing to more uniform welds.

[0004] Solder is required to connect mounted chips (including those mounted using QFN, QFP, DO, LGA, SOP, VQFN, MOSP, etc.) to substrates, and between the middle pads of mounted chips and the surrounding pins. In the past, Sn-Ag-Cu solder (SAC) was mainly used for this connection. However, as mounted chips become thinner, using Sn-Ag-Cu solder for connection can cause the mounted chips to warp. At the same time, due to increasing reliability requirements, the void rate requirements for the solder joints between the mounted chips and substrates, and between the surrounding pins of the chips are becoming lower and lower, which cannot be met by ordinary solder paste.

[0005] In the field of modern surface mount chip manufacturing and packaging technology, as surface mount chips continue to shrink in size and thickness, traditional Sn-Ag-Cu solders are increasingly experiencing serious warping issues when connecting the chip to the substrate and the surrounding pins. This problem not only impacts the proper functioning of the surface mount chip but also poses a threat to the reliability of the entire electronic product. When using Sn-Ag-Cu solder, the solder undergoes significant thermal expansion and contraction during its transition from solid to liquid and back again. Due to its fragile structure, surface mount chips are unable to withstand the resulting thermal stress. Once the thermal stress exceeds the chip's tolerance threshold, the chip warps. This warping can cause gaps and misalignment in the previously tightly fitted connection interface, preventing the solder joint from properly transmitting electronic signals and ultimately leading to connection failure. Furthermore, warping can trigger a series of chain reactions, such as cracks and delamination within the package, increasing assembly complexity and reducing product reliability and service life.

[0006] The alloy composition of solder is the core factor determining its overall performance. Its physical properties (such as melting point, density, thermal conductivity, and resistivity), mechanical properties (such as tensile strength, hardness, elongation, and compressive strength), and processing characteristics (such as wettability, recrystallization temperature, and thermal expansion coefficient) are all directly related to the element ratio. Therefore, the alloy composition must be a key consideration when preparing alloy preforms. The comprehensive properties of the solder alloy influence the preform preparation method in various ways. For example, the melting point affects the temperature and method of smelting the alloy, the recrystallization temperature determines whether hot or cold rolling is suitable, the hardness and elongation affect the setting of rolling force and tension, and the wettability influences the choice of flux.

[0007] The prior art discloses some methods for preparing alloy preforms, such as a gold-tin preform and its preparation method with publication number CN118023765A, a process for producing ultra-thin gold-tin preforms with publication number CN116673637A, a method for preparing a difficult-to-deform tin-bismuth alloy preform with publication number CN109513747A, and a method for preparing a Sn-Ag-Cu alloy preform with publication number CN110512102A. These methods are all methods for preparing preforms for specific solder alloys with different properties, such as gold-tin alloy, tin-bismuth alloy, and Sn-Ag-Cu alloy. Due to the different alloy compositions, the preparation methods adopted are also different. These methods are not suitable for preparing preforms for Sn42-In58 alloy. Summary of the Invention

[0008] The purpose of the present invention is to provide a method for preparing a Sn42-In58 alloy preform solder sheet, which can effectively reduce the warpage and void rate of the mounted chip.

[0009] The technical solution adopted by the present invention is as follows:

[0010] A method for preparing a Sn42-In58 alloy preform solder sheet, wherein the composition and mass percentage of the Sn42-In58 alloy are In52±0.5%, and the balance is Sn; the preparation method is as follows:

[0011] (1) Add tin to a crucible, heat to 230-250°C, melt the tin, and keep it warm for 10-30 minutes. Then add indium and melt it completely. Raise the furnace temperature to 180-200°C and keep it warm for 10-30 minutes to obtain an alloy solution.

[0012] (2) pouring the alloy solution into an ingot mold to obtain a Sn42-In58 alloy ingot with a thickness of 50-80 mm;

[0013] (3) The obtained Sn42-In58 alloy ingot is subjected to rough rolling, and the reduction of each rough rolling pass is maintained at 2-10 mm and the rolling speed is 1.5-2 m / min; after multiple rolling passes, a Sn42-In58 alloy rough-rolled strip with a thickness of 2 mm to 8 mm is obtained;

[0014] (4) The Sn42-In58 alloy rough-rolled strip is subjected to the first finishing rolling, the tension at the unwinding end is controlled to be 100N-150N, the tension at the winding end is controlled to be 150N-200N, the rolling speed is 0.6-0.8m / min, and the reduction of each pass is maintained at 0.1-0.3mm; after multiple rolling passes, a Sn42-In58 alloy thick strip with a thickness of less than 1mm is obtained, and then the alloy thick strip is punched and slit;

[0015] (5) The Sn42-In58 alloy thick strip that has been punched and slit is subjected to a second finishing rolling. The tension at the unwinding end is controlled to be 10N-30N, the tension at the winding end is controlled to be 30N-50N, the rolling speed is 0.4-0.6m / min, and the reduction of each pass is maintained at 0.02-0.1mm. After multiple rolling passes, a Sn42-In58 alloy thin strip with a thickness of less than 0.2mm is obtained, and then the alloy thin strip is punched and slit;

[0016] (6) Place ethanol, triethanolamine, nonylphenol polyoxyethylene, phenolic resin, and hydrogenated rosin into a heating container, heat and stir at a temperature of 40-60°C to obtain a flux solution;

[0017] (7) Immerse the punched Sn42-In58 alloy thin strip in the flux solution for 1-3 minutes, take it out, and place it in an oven for drying at a temperature of 60-80°C for 20-50 minutes to obtain a Sn42-In58 alloy preformed solder sheet.

[0018] Furthermore, the components and mass percentages of the flux solution are 85-90% ethanol, 0.5-1% triethanolamine, 0.2-1% nonylphenol polyoxyethylene ether, 3%-8% phenolic resin, and 2%-7% hydrogenated rosin.

[0019] Furthermore, the flux solution is prepared by placing ethanol, triethanolamine, nonylphenol polyoxyethylene ether, phenolic resin, and hydrogenated rosin into a heating container, placing the container on a magnetic heating and stirring device for heating and stirring at a magnetic stirring speed of 50-200 rpm / min; after heating to 40-60°C, keeping the temperature and continuing stirring for half an hour.

[0020] Furthermore, before the first finishing rolling and the second finishing rolling, the surface oxide layer of the alloy rough-rolled strip and the alloy thick strip was corroded with dilute hydrochloric acid having a mass concentration of 1%, and then washed with clean water and wiped dry.

[0021] Furthermore, the remaining material after punching in the above steps (4) and (5) is remelted and recycled.

[0022] The Sn42-In58 alloy preform solder sheet prepared by the method of the present invention has an alloy melting point of 139°C, which is much lower than the melting point of Sn-Ag-Cu solder (217°C), and can effectively reduce the warpage and void rate of the mounted chip.

[0023] The Sn42-In58 alloy preformed solder sheet prepared by the method of the present invention has precise composition, stable performance, and is easy to store and transport. The preformed solder sheet has a complete shape, high dimensional accuracy, and the flux is evenly distributed on the surface of the solder sheet. The production method is simple and efficient, with high production efficiency and suitable for mass production. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a photo of the welding test results of Control Example 1;

[0025] Figure 2 This is a photo of the welding test results of Control Example 2;

[0026] Figure 3 This is a photo of the welding test results of Control Example 3;

[0027] Figure 4 This is a photo of the welding test results of Control Example 4;

[0028] Figure 5 This is a photo of the welding test results of Example 1;

[0029] Figure 6 This is a photo of the welding test results of Example 2;

[0030] Figure 7 This is a photo of the welding test results of Example 3;

[0031] Figure 8 This is a photo of the welding test results of Example 4. DETAILED DESCRIPTION

[0032] The present invention will be further described below with reference to the embodiments. Example 1

[0033] A method for preparing a Sn42-In58 alloy preform solder sheet is as follows:

[0034] (1) Weigh 294g Sn and 406g In. The purity of Sn and In is 99.99%. Add Sn to a crucible and place it in an intermediate frequency furnace. Raise the furnace temperature to 250°C to melt all the tin and keep it warm for 30 minutes. Then add indium and melt all the indium. Raise the furnace temperature to 200°C and keep it warm for 30 minutes to obtain an alloy solution.

[0035] (2) pouring the alloy solution into an ingot mold to obtain a Sn42-In58 alloy ingot with a length of 200 mm, a thickness of 80 mm, and a width of 6 mm;

[0036] (3) The obtained Sn42-In58 alloy ingot was rough rolled by a hot rolling mill. The reduction of each rough rolling pass was maintained at 2-10 mm and the rolling speed was 2 m / min. After multiple rolling passes (the thickness after each rolling pass was 70 mm, 60 mm, 50 mm, 40 mm, 35 mm, 30 mm, 25 mm, 20 mm, 18 mm, 16 mm, 14 mm, 12 mm, 10 mm, 8 mm, 6 mm, 4 mm, and 2 mm), a Sn42-In58 alloy rough-rolled strip with a thickness of 2 mm was obtained;

[0037] (4) The Sn42-In58 alloy rough sheet obtained by initial rolling was first corroded with dilute hydrochloric acid of 1% by mass, then washed with clean water and wiped dry. Then, the first finishing rolling was carried out on a hot rolling mill. The tension at the unwinding end of the hot rolling mill was controlled to be 150N, the tension at the winding end was controlled to be 200N, the rolling speed was 0.8m / min, and the reduction of each pass was maintained at 0.1mm. After multiple rolling passes (the thickness after each rolling pass was 1.9mm, 1.8mm, 1.7mm, 1.6mm, 1.5mm, 1.4mm, 1.3mm, 1.2mm, 1.1mm, 1.0mm, 0.9mm, 0.8mm, 0.7mm, 0.6mm, 0.5mm), a Sn42-In58 alloy thick strip with a thickness of 0.5mm was obtained, and then the alloy thick strip was punched into thick sheets with a width of 5mm using a punching device;

[0038] (5) The cut thick sheet is first etched with dilute hydrochloric acid with a mass concentration of 1%, then washed with clean water and wiped dry. Then, a second finishing rolling is carried out on a hot rolling mill. The tension at the unwinding end of the hot rolling mill is controlled to be 30N, the tension at the winding end is controlled to be 50N, the rolling speed is controlled to be 0.4m / min, and the reduction of each pass is maintained at 0.02-0.1mm. After multiple rolling passes (the thickness after each rolling pass is 0.45m, 0.40mm, 0.3mm, 0.25mm, 0.2mm, 0.18mm, 0.16mm, 0.14mm, 0.12mm, and 0.10mm respectively), a Sn42-In58 alloy thin strip with a thickness of 0.10mm is obtained, and the alloy thin strip is cut into thin sheets with a width of 2mm using a punching device;

[0039] (6) Punch the thin sheet into annular thin sheets with an outer diameter of φ (1 ± 0.01) mm, an inner diameter of φ (0.5 ± 0.01) mm, and a thickness of (0.1 ± 0.01) mm. The remaining material after punching is recycled and remelted for subsequent processing;

[0040] (7) Weigh 90g of ethanol, 1g of triethanolamine, 0.5g of nonylphenol polyoxyethylene ether, 6g of phenolic resin, and 2.5g of hydrogenated rosin, put the above raw materials into a beaker, place it on a magnetic heating and stirring device, set the magnetic stirring speed to 100rpm / min, heat to 50℃, keep warm and stir for half an hour to obtain a flux solution;

[0041] (8) Immerse the circular thin sheet in the flux solution for 2 minutes, then take it out and place it in an oven for drying at an oven temperature of 70°C for 30 minutes to obtain the required Sn42-In58 alloy preformed solder sheet. Example 2

[0042] A method for preparing a Sn42-In58 alloy preform solder sheet is as follows:

[0043] (1) Weigh 420g of Sn and 580g of In. The purity of both Sn and In is 99.99%. Add Sn to a crucible and place it in an intermediate frequency furnace. Raise the furnace temperature to 230°C to melt all the tin and keep it warm for 20 minutes. Then add indium and melt all the indium. Raise the furnace temperature to 180°C and keep it warm for 10 minutes to obtain an alloy solution.

[0044] (2) pouring the alloy solution into an ingot mold to obtain a Sn42-In58 alloy ingot with a length of 200 mm, a thickness of 50 mm, and a width of 10 mm;

[0045] (3) The obtained Sn42-In58 alloy ingot was subjected to rough rolling, with the reduction of each rough rolling pass maintained at 2-10 mm and the rolling speed at 1.5 m / min. After multiple rolling passes, a Sn42-In58 alloy rough-rolled strip with a thickness of 8 mm was obtained;

[0046] (4) The Sn42-In58 alloy rough strip obtained by primary rolling was subjected to the first finishing rolling. The tension at the unwinding end was controlled to be 100N, the tension at the winding end was controlled to be 150N, the rolling speed was 0.7m / min, and the reduction of each pass was maintained at 0.1mm-0.3mm. After multiple rolling passes, a Sn42-In58 alloy thick strip with a thickness of 1.0mm was obtained, and then the alloy thick strip was punched into thick sheets with a width of 10mm.

[0047] (5) The cut thick sheet is subjected to a second finishing rolling, the tension at the unwinding end is controlled to 20N, the tension at the winding end is controlled to 40N, the rolling speed is 0.5m / min, and the reduction of each pass is maintained at 0.02-0.1mm. After multiple rolling passes, a Sn42-In58 alloy thin strip with a thickness of 0.16mm is obtained, and the alloy thin strip is cut into thin sheets with a width of 2mm;

[0048] (6) Punch the thin sheet into a square ring-shaped sheet with an outer length and width of (5±0.01) mm × (5±0.01) mm, an inner length and width of (2±0.01) mm × (2±0.01) mm, and a thickness of 0.16±0.001 mm. The remaining material after punching is recycled and remelted for subsequent processing;

[0049] (7) Weigh 85g of ethanol, 1g of triethanolamine, 1g of nonylphenol polyoxyethylene ether, 8g of phenolic resin, and 5g of hydrogenated rosin, put the above raw materials into a beaker, place it on a magnetic heating and stirring device, set the magnetic stirring speed to 200rpm / min, heat to 40℃, keep warm and stir for half an hour to obtain a flux solution;

[0050] (8) Immerse the square ring sheet in the flux solution for 3 minutes, then take it out and place it in an oven for drying at an oven temperature of 60°C for 50 minutes to obtain the required Sn42-In58 alloy preformed solder sheet. Example 3

[0051] A method for preparing a Sn42-In58 alloy preform solder sheet is as follows:

[0052] (1) Weigh 378g Sn and 522g In. The purity of Sn and In is 99.99%. Add Sn to a crucible and place it in an intermediate frequency furnace. Raise the furnace temperature to 240°C to melt all the tin and keep it warm for 10 minutes. Then add indium and melt all the indium. Raise the furnace temperature to 190°C and keep it warm for 20 minutes to obtain an alloy solution.

[0053] (2) pouring the alloy solution into an ingot mold to obtain a Sn42-In58 alloy ingot with a length of 200 mm, a thickness of 60 mm, and a width of 15 mm;

[0054] (3) The obtained Sn42-In58 alloy ingot was subjected to rough rolling, with the reduction of each rough rolling pass maintained at 2-10 mm and the rolling speed at 1.8 m / min. After multiple rolling passes, a Sn42-In58 alloy rough-rolled strip with a thickness of 5 mm was obtained;

[0055] (4) The Sn42-In58 alloy rough sheet obtained by primary rolling was first etched with dilute hydrochloric acid of 1% by mass, then washed with clean water and dried. The first finishing rolling was carried out, with the tension at the unwinding end controlled at 120N and the tension at the winding end controlled at 180N. The rolling speed was 0.6m / min, and the reduction per pass was maintained at 0.1mm-0.3mm. After multiple rolling passes, a Sn42-In58 alloy thick strip with a thickness of 1.0mm was obtained, and then the alloy thick strip was punched into thick sheets with a width of 10mm.

[0056] (5) The cut thick sheet is subjected to a second finishing rolling, the tension at the unwinding end is controlled to be 10N, the tension at the winding end is controlled to be 30N, the rolling speed is 0.6m / min, and the reduction of each pass is maintained at 0.02-0.1mm. After multiple rolling passes, a Sn42-In58 alloy thin strip with a thickness of 0.12mm is obtained, and the alloy thin strip is cut into thin sheets with a width of 2mm;

[0057] (6) Punch the thin sheet into circular sheets with a diameter of 1 mm and a thickness of 0.12 ± 0.001 mm. The remaining material after punching is recycled and remelted for subsequent processing;

[0058] (7) Weigh 89g of ethanol, 0.5g of triethanolamine, 0.2g of nonylphenol polyoxyethylene ether, 3.3g of phenolic resin, and 7g of hydrogenated rosin, put the above raw materials into a beaker, place it on a magnetic heating and stirring device, set the magnetic stirring speed to 50rpm / min, heat to 60℃, keep warm and stir for half an hour to obtain a flux solution;

[0059] (8) Immerse the circular sheet in the flux solution for 1 minute, then take it out and place it in an oven for drying at an oven temperature of 80°C for 20 minutes to obtain the desired Sn42-In58 alloy preformed solder sheet. Example 4

[0060] A method for preparing a Sn42-In58 alloy preform solder sheet is as follows:

[0061] (1) Weigh 210g of Sn and 290g of In. The purity of both Sn and In is 99.99%. Add Sn to a crucible and place it in an intermediate frequency furnace. Raise the furnace temperature to 250°C to melt all the tin and keep it warm for 25 minutes. Then add indium and melt all the indium. Raise the furnace temperature to 200°C and keep it warm for 25 minutes to obtain an alloy solution.

[0062] (2) pouring the alloy solution into an ingot mold to obtain a Sn42-In58 alloy ingot with a length of 200 mm, a thickness of 70 mm, and a width of 10 mm;

[0063] (3) The obtained Sn42-In58 alloy ingot was subjected to rough rolling, with the reduction of each rough rolling pass maintained at 2-10 mm and the rolling speed at 2 m / min. After multiple rolling passes, a Sn42-In58 alloy rough-rolled strip with a thickness of 3 mm was obtained;

[0064] (4) The Sn42-In58 alloy rough strip obtained by primary rolling was subjected to the first finishing rolling. The tension at the unwinding end was controlled to be 150N, the tension at the winding end was controlled to be 180N, the rolling speed was 0.6m / min, and the reduction of each pass was maintained at 0.1mm-0.3mm. After multiple rolling passes, a Sn42-In58 alloy thick strip with a thickness of 0.8mm was obtained, and then the alloy thick strip was punched into thick sheets with a width of 10mm;

[0065] (5) The cut thick sheet is first etched with 1% mass concentration of dilute hydrochloric acid to remove the surface oxide layer, then washed with clean water and wiped dry. Then, a second finishing rolling is carried out, with the tension at the unwinding end controlled to 20N, the tension at the winding end to 30N, the rolling speed to 0.6m / min, and the reduction per pass to be maintained at 0.02-0.1mm. After multiple rolling passes, a Sn42-In58 alloy thin strip with a thickness of 0.1mm is obtained, and the alloy thin strip is cut into thin sheets with a width of 2mm.

[0066] (6) Punch the thin sheet into long thin strips with a length of 1 mm, a width of 0.8 mm, and a thickness of 0.12 ± 0.001 mm. The remaining material after punching is recycled and remelted for subsequent processing;

[0067] (7) Weigh 90 g of ethanol, 0.8 g of triethanolamine, 0.8 g of nonylphenol polyoxyethylene ether, 3 g of phenolic resin, and 5.4 g of hydrogenated rosin, put the above raw materials into a beaker, place it on a magnetic heating and stirring device, set the magnetic stirring speed to 50 rpm / min, heat to 60 ° C, keep warm and stir for half an hour to obtain a flux solution;

[0068] (8) Immerse the long thin sheet in the flux solution for 2 minutes, then take it out and place it in an oven for drying at an oven temperature of 70°C for 30 minutes to obtain the required Sn42-In58 alloy preformed solder sheet.

[0069] The Sn42-In58 alloy preformed solder sheet prepared in the above Examples 1-4 was used for chip mounting welding test. The welding test method was as follows: ① Ensure that the welding surface is clean and there are no impurities that affect the welding quality; ② Mount the tin-indium solder sheet on the PCB through a chip mounter; ③ Mount the chip on the PCB through the chip mounter; ④ Send it to the reflow soldering equipment for reflow soldering. The reflow soldering temperature is shown in Table 1; ⑤ After the welding is completed, the warpage is obtained by scanning point by point using a laser scanning profilometer; ⑥ After the welding is completed, the void rate is obtained using an x-ray detection device.

[0070] As a control, four soldering tests were repeated using SAC305 solder paste mounted chips. The four soldering tests followed the same method, with the PCB spacing and chip placement on the PCB identical to the previously described tin-indium solder chip soldering test. The soldering test procedures were as follows: ① Ensure the soldering surface is clean and free of impurities that could affect soldering quality; ② Print solder paste onto the PCB; ③ Use a chip mounter to mount the chip onto the PCB; ④ Use a reflow oven for reflow soldering, with the reflow temperature shown in Table 2; ⑤ After soldering, scan each point using a laser profilometer to determine warpage; ⑥ Use an X-ray machine to determine void ratio.

[0071] Table 1 Reflow temperature table for tin-indium solder sheets

[0072]

[0073] Table 2 Reflow temperature table for tin-silver-copper solder paste

[0074]

[0075] The chip warpage and void ratio of the embodiment and the control example are shown in Table 3 below.

[0076] Table 3 Chip warpage and void ratio

[0077]

[0078] The results show that compared with Sn-Ag-Cu solder, Sn42-In58 alloy preforms effectively reduce the warpage and solder void rate of mounted chips.

[0079] In the method of the present invention, the equipment and devices used, such as the medium frequency furnace, hot rolling mill, blanking equipment, magnetic heating and stirring equipment, and oven, are all prior art equipment. Raw materials used, such as tin, indium, ethanol, triethanolamine, nonylphenol polyoxyethylene ether, phenolic resin, and hydrogenated rosin, are all commercially available.

[0080] Unless otherwise specified, all percentages described in the present invention are by mass.

[0081] The above embodiments are only some embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any embodiments obtained by those skilled in the art based on data modifications within the scope defined by the claims of the present invention shall fall within the scope of protection of the present invention.

Claims

1. A method for preparing a Sn42-In58 alloy preform solder sheet, wherein the composition and mass percentage of the Sn42-In58 alloy are In58±0.5%, and the balance is Sn and unavoidable impurities; characterized in that: The preparation method is as follows: (1) Add tin to a crucible, heat to 230-250°C, melt the tin, and keep it warm for 10-30 minutes. Then add indium and melt it completely. Raise the furnace temperature to 180-200°C and keep it warm for 10-30 minutes to obtain an alloy solution. (2) pouring the alloy solution into an ingot mold to obtain a Sn42-In58 alloy ingot with a thickness of 50-80 mm; (3) The obtained Sn42-In58 alloy ingot is subjected to rough rolling, and the reduction of each rough rolling pass is maintained at 2-10 mm and the rolling speed is 1.5-2 m / min; after multiple rolling passes, a Sn42-In58 alloy rough-rolled strip with a thickness of 2 mm to 8 mm is obtained; (4) The Sn42-In58 alloy rough-rolled strip is subjected to the first finishing rolling, the tension at the unwinding end is controlled to be 100N-150N, the tension at the winding end is controlled to be 150N-200N, the rolling speed is 0.6-0.8m / min, and the reduction of each pass is maintained at 0.1-0.3mm; after multiple rolling passes, a Sn42-In58 alloy thick strip with a thickness of less than 1mm is obtained, and then the alloy thick strip is punched and slit; (5) The Sn42-In58 alloy thick strip that has been punched and slit is subjected to a second finishing rolling. The tension at the unwinding end is controlled to be 10N-30N, the tension at the winding end is controlled to be 30N-50N, the rolling speed is 0.4-0.6m / min, and the reduction of each pass is maintained at 0.02-0.1mm. After multiple rolling passes, a Sn42-In58 alloy thin strip with a thickness of less than 0.2mm is obtained, and then the alloy thin strip is punched and slit; (6) Put ethanol, triethanolamine, nonylphenol polyoxyethylene, phenolic resin, and hydrogenated rosin into a heating container, heat and stir, and the heating temperature is 40-60°C to obtain a flux solution; the components and mass percentages of the flux solution are 85-90% ethanol, 0.5-1% triethanolamine, 0.2-1% nonylphenol polyoxyethylene ether, 3%-8% phenolic resin, and 2%-5% hydrogenated rosin; (7) Immerse the punched Sn42-In58 alloy thin strip in the flux solution for 1-3 minutes, take it out, and place it in an oven for drying at a temperature of 60-80°C for 20-50 minutes to obtain a Sn42-In58 alloy preformed solder sheet.

2. The method for preparing a Sn42-In58 alloy preform solder sheet according to claim 1, characterized in that: The flux solution is prepared by placing ethanol, triethanolamine, nonylphenol polyoxyethylene ether, phenolic resin, and hydrogenated rosin into a heating container, placing the container on a magnetic heating and stirring device for heating and stirring at a magnetic stirring speed of 50-200 rpm / min; heating to 40-60°C, maintaining the temperature, and continuing stirring for half an hour.

3. The method for preparing a Sn42-In58 alloy preform solder sheet according to claim 1, characterized in that: Before the first finishing rolling and the second finishing rolling, the surface oxide layer of the alloy rough-rolled strip and the alloy thick strip was corroded with dilute hydrochloric acid with a mass concentration of 1%, and then washed with clean water and wiped dry.

4. The method for preparing a Sn42-In58 alloy preform solder sheet according to claim 1, characterized in that: The remaining material after punching in the above steps (4) and (5) is remelted and recycled.

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