A height-controlling preformed soldering piece and a preparation method thereof

Abstract

The application discloses a high-control preformed soldering sheet and a preparation method thereof. The high-control preformed soldering sheet comprises a tin-based soldering sheet and a metal wire mesh. The metal wire mesh is clamped in the tin-based soldering sheet and combined with the tin-based soldering sheet. The application effectively solves the problem of poor uniformity of the welding layer thickness by compounding a layer of metal wire mesh in the tin-based soldering sheet. Compared with the ordinary soldering sheet process, the post-welding penetration rate is usually 80-85%, tin overflow is easy to occur, and the requirements for the welding process and tooling are extremely high. The high-control preformed soldering sheet can improve the post-welding penetration rate to more than 95% under the same process conditions, can effectively control the tin overflow phenomenon, greatly reduces the rework rate, and improves the first-time pass rate.

Description

Technical Field

[0001] This invention belongs to the field of welding technology, and particularly relates to a height-controlled preformed welding sheet and its preparation method. Background Technology

[0002] With the rapid development of electronic information technology towards miniaturization, high frequency, and high-density integration, modern electronic packaging has placed unprecedentedly stringent demands on the precision and reliability of interconnect technologies. In advanced packaging structures such as System-in-Package (SiP), Chip-Scale Package (CSP), and Ball Grid Array (BGA), the vertical interconnection spacing between components has shrunk to the micrometer level, posing a severe challenge to the morphology control and process stability of soldering materials. Traditional solder pastes and pre-fabricated solder pads, due to their large morphological variability and uneven collapse height, struggle to ensure consistent and reliable connections within tiny gaps, easily leading to defects such as bridging, short circuits, and open circuits, becoming a key technical bottleneck restricting the improvement of yield in high-end electronic manufacturing. Reports indicate that soldering-related failures account for over 60% of all electronic device or complete system failures. Sintering is a widely used process technology in microwave micro-assembly, and its sintering overflow and penetration rate have always been significant issues hindering the improvement of sintering efficiency. For micro-assembled products, most of the sintering overflow cleaning needs to be done under a microscope; statistics show that sintering overflow cleaning accounts for about one-third of the time in the component sintering process. Therefore, effectively improving the penetration rate and reducing the tin overflow rate has become a barrier restricting the micro-assembly sintering process.

[0003] High-melting-point solder refers to a composite solder consisting of a tin-based solder body and high-melting-point metal particles or a metal mesh. During soldering, the tin-based solder body melts first, while the high-melting-point metal portion, due to its high melting point, does not melt during the soldering process, providing a certain degree of support and ensuring the consistency of the solder layer thickness. Simultaneously, the presence of the metal mesh effectively improves the solder penetration rate. Therefore, developing a solder that can solve the problem of low solder penetration rate while also effectively controlling solder overflow has significant practical and economic value for the microelectronics packaging industry. Summary of the Invention

[0004] Based on the above-mentioned technical problems, this invention provides a height-controlled preformed solder sheet and its preparation method. By composited with a metal mesh inside the tin-based solder sheet, the problem of poor uniformity of solder layer thickness is effectively solved. Compared with ordinary solder sheet processes, the solder penetration rate after soldering is usually 80-85%, and it is easy to overflow solder, which has extremely high requirements for soldering process and tooling. The height-controlled preformed solder sheet of this invention can increase the solder penetration rate to more than 95% under the same process conditions, and can effectively control the overflow solder phenomenon, greatly reducing the rework rate and improving the first pass rate.

[0005] The present invention proposes a height-controlled preformed solder sheet, comprising a tin-based solder sheet and a metal mesh, wherein the metal mesh is sandwiched inside the tin-based solder sheet and is bonded to the tin-based solder sheet.

[0006] In this invention, the melting point of pure tin is 231.9℃. The melting point of tin-based solder varies depending on the combination of tin with different alloys, and is generally preferred to be in the range of about 200-350℃. The melting point of nickel, copper, or silver metal mesh is about 1000℃. Thus, when the height-controlled preformed solder sheet is actually welded, the low-melting-point tin-based solder sheet is in a molten state, while the high-melting-point metal mesh does not melt or only partially melts. This not only increases the melting point of the solder sheet and reduces solder overflow, giving the solder the effect of "low-temperature welding and high-temperature service", but also forms a "skeleton" support because the metal mesh does not easily melt during the welding process, laying the foundation for maintaining a uniform weld height.

[0007] Preferably, the tin-based solder pad substrate material is at least one of SnAg, SnCu, SnBi, SnSb, SnZn, SnAu, SnAgCu, SnAgBi, SnAgIn, SnAgSb, SnAgCuBi, SnAgCuIn or SnAgCuSb.

[0008] In this invention, the preferred substrate material for the tin-based solder pad is Sn97.5Cu2.5, Sn99.3Cu0.7, Sn96.5Ag3.5, or Sn77.2In20Ag2.8.

[0009] Preferably, the wire mesh is formed by weaving metal wires; Preferably, the diameter of the metal wire is 10-100 μm; Preferably, the metal mesh is a nickel, copper, or silver metal mesh.

[0010] Preferably, the thickness of the metal wire is 30-80% of the thickness of the height-controlled preformed sheet.

[0011] In this invention, since the thickness of the metal wire mesh is 30-80% of the thickness of the height-controlled preformed sheet, when the thickness of the metal wire mesh is less than 30% of the thickness of the height-controlled preformed sheet, it is not conducive to generating a weld of the preset thickness and cannot provide sufficient support for the weld layer; when the thickness of the metal wire mesh is greater than 80% of the thickness of the height-controlled preformed sheet, since the hardness of the metal wire mesh is usually greater than the hardness of the tin-based sheet, it increases the difficulty of pressing the "rolled sheet" to the preset thickness.

[0012] Preferably, the surface of the metal wire mesh further includes a tin metal plating layer; Preferably, the thickness of the tin metal plating layer is 0.01-1 μm.

[0013] In this invention, the surface of the metal mesh also includes a tin metal plating layer. Thus, at a certain temperature, the surface of the metal mesh can undergo a metallurgical bonding reaction with the tin-based solder sheet, forming an intermetallic compound on the outer layer of the metal mesh to constitute a diffusion layer. This diffusion layer enables the aforementioned metal elements to better bond with each other, enhancing the strength and stability of the joint.

[0014] Preferably, the tin metal plating layer is obtained by chemical deposition reaction of a metal mesh and a tin ion source under a reducing agent; Preferably, the tin ion source includes a tin salt, which is at least one of tin chloride, tin nitrate, or tin sulfate; the reducing agent is at least one of sodium borohydride, ferrous sulfate, or chromium chloride.

[0015] Preferably, the tin-containing solution further includes a dispersing stabilizer; Preferably, the dispersant stabilizer is a polyvinylpyrrolidone diionic salt.

[0016] In this invention, the structural formula of the dispersant stabilizer is as follows:

[0017] n represents the degree of aggregation.

[0018] In this invention, the dispersant stabilizer is obtained by reacting polyvinylpyrrolidone with 3-dimethylamino-1-propylamine in an addition reaction, followed by reduction with sodium borohydride, and then quaternization with chloroacetic acid.

[0019] In this invention, the carboxyl groups in the dispersant stabilizer can form a complex with tin ions to prevent sedimentation, resulting in a more uniform tin plating effect; the amino groups act as proton relays to accelerate the transfer of atomic hydrogen (H·) to tin ions; the quaternary ammonium groups accelerate the diffusion and transfer of tin ions through the synergistic effect of anions and cations; and the polyvinylpyrrolidone can effectively disperse and ensure sufficient deposition reaction.

[0020] The present invention also proposes a method for preparing the above-mentioned height-controlled preformed solder sheet, comprising the following steps: S1. Place the metal wire mesh between two tin-based solder pads, and after preheating, obtain a sandwich laminate. S2. After rolling the sandwich laminate, it is then annealed to obtain the height-controlled preformed welding sheet.

[0021] Preferably, the preheating temperature is 150-200℃ and the time is 0.5-1h.

[0022] Preferably, the rolling temperature is 80-150℃; the annealing temperature is 90-110℃, and the annealing time is 0.5-1h.

[0023] The beneficial effects of this invention are as follows: Improving the yield and reliability of electronic manufacturing: The widespread application of the height-controlled solder pads described in this invention will effectively solve defects such as bridging and cold solder joints in the welding of micro-pitch components, improve the yield of high-end electronic packaging by 5-10 percentage points, and significantly improve the thermomechanical reliability of solder joints, thus extending the service life of electronic products.

[0024] Reducing Supply Chain Costs: Although the direct cost of the height-controlled solder sheet described in this invention is higher than that of traditional solder, the overall production costs of electronic manufacturing enterprises can be reduced through comprehensive benefits such as improved yield, reduced rework rate, and increased equipment utilization. It is estimated that in the field of high-end electronic manufacturing, the use of height-controlled solder sheets can reduce overall costs by 15-20%.

[0025] Expanding Applications: The height-controlled welding sheets developed to promote the localization of high-end equipment will be directly applied to high-end equipment such as 5G communication base stations, satellite payload systems, aerospace electronics, and automotive electronic control units, improving the reliability and independent controllability of these equipment and providing material support for the localization of equipment in key national sectors. Attached Figure Description

[0026] Figure 1 This is a cross-sectional view of the preformed welding sheet described in Embodiment 1 of the present invention; Figure 2 This is an enlarged view of the fracture surface of the preformed welding sheet described in Embodiment 1 of the present invention. Detailed Implementation

[0027] The present invention will now be described in detail through specific embodiments. However, these embodiments are clearly provided for illustrative purposes and are not intended to limit the scope of the present invention.

[0028] Example 1

[0029] A height-controlled preformed solder sheet includes a tin-based solder sheet and a nickel metal wire mesh, wherein the nickel metal wire mesh is sandwiched inside the tin-based solder sheet and bonded to the tin-based solder sheet.

[0030] In this invention, the tin-based solder sheet includes an upper substrate and a lower substrate, which are sandwiched on the upper and lower sides of a nickel metal wire mesh and rolled into one piece.

[0031] The preparation method of the above-mentioned height-controlled preformed welding sheet includes: (1) After obtaining a square ingot of Sn97.5Cu2.5 by vacuum melting of 99.9% tin and 99.9% copper at 500℃, it is rolled by a two-roll mill at a rolling temperature of 100℃ and a rolling speed of 3m / min to obtain a tin-based solder sheet with a thickness of 50μm. (2) A nickel metal wire mesh (250 mesh, 80 μm thick) woven from nickel metal wire with a diameter of 50 μm is placed between two tin-based solder sheets of the same size. After stacking to form a sandwich laminate, it is heated to 150°C in a nitrogen atmosphere and kept at that temperature for 1 hour to obtain the sandwich laminate. (3) The four corners of the sandwich laminate are fixed by stamping, and then the sandwich laminate is rolled. The rolling temperature is 100℃ and the rolling speed is 3m / min. The initial roll gap is set to 0.25mm. The roll gap is further shortened to eliminate the rolling springback. The final thickness of the sandwich laminate is 0.1mm. After leveling with an arc tool, it is annealed at 90℃ for 1h to obtain the preformed welding sheet.

[0032] The above-mentioned preformed weld sheet is shown in the following cross-sectional image. Figure 1 As shown, there are no voids between the upper and lower substrates of the weld sheet and the nickel metal wire mesh; the enlarged view of the fracture surface of the preformed weld sheet is shown below. Figure 2 As shown, the height control of the nickel metal wire mesh is clearly visible.

[0033] Example 2

[0034] A height-controlled preformed solder sheet includes a tin-based solder sheet and a nickel metal wire mesh, wherein the nickel metal wire mesh is sandwiched inside the tin-based solder sheet and bonded to the tin-based solder sheet.

[0035] In this invention, the tin-based solder sheet includes an upper substrate and a lower substrate, which are sandwiched on the upper and lower sides of a nickel metal wire mesh and rolled into one piece.

[0036] The preparation method of the above-mentioned height-controlled preformed welding sheet includes: (1) After obtaining a square ingot of Sn96.5Ag3.5 by vacuum melting of 99.9% tin and 99.9% silver at 500℃, it is rolled by a two-roll mill at a rolling temperature of 120℃ and a rolling speed of 2m / min to obtain a tin-based solder sheet with a thickness of 50μm. (2) A nickel metal wire mesh (250 mesh, 80 μm thick) woven from nickel metal wire with a diameter of 50 μm is placed between two tin-based solder sheets of the same size. After stacking to form a sandwich laminate, it is heated to 200°C in a nitrogen atmosphere and held for 0.5 h to obtain the sandwich laminate. (3) The four corners of the sandwich laminate are fixed by stamping, and then the sandwich laminate is rolled at a rolling temperature of 120°C and a rolling speed of 2m / min. The initial roll gap is set to 0.25mm. The roll gap is further shortened to eliminate rolling springback. The final thickness of the sandwich laminate is 0.1mm. After leveling with an arc tool, it is annealed at 110°C for 0.5h to obtain the preformed welding sheet.

[0037] Example 3 A height-controlled preformed solder sheet includes a tin-based solder sheet and a nickel metal wire mesh, wherein the nickel metal wire mesh is sandwiched inside the tin-based solder sheet and bonded to the tin-based solder sheet.

[0038] In this invention, the tin-based solder sheet includes an upper substrate and a lower substrate, which are sandwiched on the upper and lower sides of a nickel metal wire mesh and rolled into one piece.

[0039] The preparation method of the above-mentioned height-controlled preformed welding sheet includes: (1) After obtaining a square ingot of Sn97.5Cu2.5 by vacuum melting of 99.9% tin and 99.9% copper at 500℃, it is rolled by a two-roll mill at a rolling temperature of 100℃ and a rolling speed of 3m / min to obtain a tin-based solder sheet with a thickness of 50μm. (2) A nickel wire mesh (250 mesh, 80 μm thickness) woven from nickel wire with a diameter of 50 μm was ultrasonically cleaned in dilute sulfuric acid (5 wt%) for 5 min and then removed. It was then cleaned in deionized water and anhydrous ethanol and dried. The obtained nickel wire mesh was placed in a tin ion solution, which was obtained by dissolving tin(II) chloride in water and adjusting the pH to 0.2 with hydrochloric acid. Polyvinylpyrrolidone K30 was added and ultrasonically dispersed evenly. The concentration of tin chloride was 20 wt% and the concentration of polyvinylpyrrolidone K30 was 1 wt%. A 5 wt% chromium chloride solution was then added and ultrasonically mixed and reacted completely to obtain a nickel wire mesh with a tin metal coating on the surface with a thickness of 0.1 μm. The mesh was cleaned in anhydrous ethanol and dried to obtain a tin-plated nickel wire mesh. (3) The above-mentioned tin-nickel metal wire mesh is placed between two tin-based solder sheets of the same size, and stacked to form a sandwich laminate. Then, it is heated to 150°C under a nitrogen atmosphere and kept at that temperature for 1 hour to obtain the sandwich laminate. (4) The four corners of the sandwich laminate are fixed by stamping, and then the sandwich laminate is rolled. The rolling temperature is 100℃ and the rolling speed is 3m / min. The initial roll gap is set to 0.25mm. The roll gap is further shortened to eliminate the rolling springback. The final thickness of the sandwich laminate is 0.1mm. After leveling with an arc tool, it is annealed at 90℃ for 1h to obtain the preformed welding sheet.

[0040] Example 4

[0041] A height-controlled preformed solder sheet includes a tin-based solder sheet and a nickel metal wire mesh, wherein the nickel metal wire mesh is sandwiched inside the tin-based solder sheet and bonded to the tin-based solder sheet.

[0042] In this invention, the tin-based solder sheet includes an upper substrate and a lower substrate, which are sandwiched on the upper and lower sides of a nickel metal wire mesh and rolled into one piece.

[0043] The preparation method of the above-mentioned height-controlled preformed welding sheet includes: (1) After obtaining a square ingot of Sn97.5Cu2.5 by vacuum melting of 9.9% tin and 99.9% copper at 500℃, it is rolled by a two-roll mill at a rolling temperature of 100℃ and a rolling speed of 3m / min to obtain a tin-based solder sheet with a thickness of 50μm. (2) A nickel wire mesh (250 mesh, 80 μm thickness) woven from nickel wire with a diameter of 50 μm was ultrasonically cleaned in dilute sulfuric acid (5 wt%) for 5 min and then removed. It was then cleaned in deionized water and anhydrous ethanol and dried. The obtained nickel wire mesh was placed in a tin ion solution, which was obtained by dissolving tin(II) chloride in water and adjusting the pH to 0.2 with hydrochloric acid. Polyvinylpyrrolidone diionic salt was added and ultrasonically dispersed evenly. The concentration of tin chloride was 20 wt% and the concentration of polyvinylpyrrolidone diionic salt was 1 wt%. A 5 wt% chromium chloride solution was then added and ultrasonically mixed and reacted completely to obtain a nickel wire mesh with a tin metal coating on the surface with a thickness of 0.1 μm. The mesh was cleaned in anhydrous ethanol and dried to obtain a tin-plated nickel wire mesh. The polyvinylpyrrolidone diionic salt was synthesized by the following method: Polyvinylpyrrolidone K30 was dissolved in anhydrous ethanol, and formic acid was added at room temperature until complete dissolution. Then, an ethanol solution containing 3-dimethylamino-1-propylamine was added. The mass ratio of polyvinylpyrrolidone K30, formic acid, and 3-dimethylamino-1-propylamine was 1:0.12:0.04. The mixture was heated to 80°C and stirred for 5 hours. Then, a sodium hydroxide solution containing sodium borohydride (pH 8) was added. The mass ratio of polyvinylpyrrolidone K30 to sodium borohydride was 1:0.004. Then, deionized water was added and the mixture was stirred for 24 hours. After the solvent was evaporated by rotary evaporation, chloroform was added to dissolve the mixture. After washing with water, the intermediate was redissolved in anhydrous ethanol. Sodium hydroxide and chloroacetic acid were added in sequence. The mass ratio of polyvinylpyrrolidone K30 to sodium hydroxide and chloroacetic acid was 1:0.05:0.04. The mixture was heated to 60°C and stirred for 6 hours. After the solvent was evaporated by rotary evaporation, ethanol was added for recrystallization to obtain the polyvinylpyrrolidone diionic salt. (3) The above-mentioned tin-nickel metal wire mesh is placed between two tin-based solder sheets of the same size, and stacked to form a sandwich laminate. Then, it is heated to 150°C under a nitrogen atmosphere and kept at that temperature for 1 hour to obtain the sandwich laminate. (4) The four corners of the sandwich laminate are fixed by stamping, and then the sandwich laminate is rolled at a rolling temperature of 100°C and a rolling speed of 3m / min. The initial roll gap is set to 0.25mm. The roll gap is further shortened to eliminate rolling springback. The final thickness of the sandwich laminate is 0.1mm. After smoothing with an arc tool, it is annealed at 90°C for 1h to obtain the preformed welding sheet.

[0044] Comparative Example 1 A preformed solder pad, comprising a tin-based solder pad.

[0045] The above-mentioned method for preparing preformed solder sheets includes: After obtaining a square ingot of Sn97.5Cu2.5 by vacuum melting of 99.9% tin and 99.9% copper at 500℃, it is then rolled using a two-roll mill at a rolling temperature of 100℃ and a rolling speed of 3m / min to obtain a tin-based solder sheet with a thickness of 0.1mm.

[0046] Performance testing: The preformed solder pads described in the examples and comparative examples were placed between the chip and the top cover. A vacuum reflow soldering process was used, with vacuuming and nitrogen purging, preheating to 20°C below the melting point of the tin-based solder pad, followed by vacuuming again, and reflow soldering to 50°C above the melting point of the tin-based solder pad. The soldering time was 90 seconds, and the soldering pressure was 0.01 MPa, resulting in a test piece. The void ratio was detected using a SonoScan-D9600 ultrasonic scanner. The shear strength was obtained by averaging multiple experiments according to GB / T / 11363-2008, the test method for brazed joint strength. The results are shown in Table 1 below. Table 1 Test performance of the preformed sheets described in the examples and comparative examples

[0047] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A height-controlled preformed welding sheet, characterized in that, It includes a tin-based solder sheet and a metal wire mesh, wherein the metal wire mesh is sandwiched inside the tin-based solder sheet and bonded to the tin-based solder sheet.

2. The height-controlled preformed welding sheet according to claim 1, characterized in that, The tin-based solder pad substrate material is at least one of SnCu, SnAg, SnBi, SnSb, SnZn, SnAu, SnAgCu, SnAgBi, SnAgIn, SnAgSb, SnAgCuBi, SnAgCuIn or SnAgCuSb; Preferably, the thickness of the tin-based solder sheet is 10-500 μm.

3. The height-controlled preformed welding sheet according to claim 1 or 2, characterized in that, The wire mesh is formed by weaving metal wires; Preferably, the diameter of the metal wire is 10-100 μm; Preferably, the metal mesh is a nickel, copper, or silver metal mesh.

4. The height-controlled preformed welding sheet according to any one of claims 1-3, characterized in that, The thickness of the metal wire mesh is 30-80% of the thickness of the height-controlled preformed welding sheet.

5. The height-controlled preformed welding sheet according to any one of claims 1-4, characterized in that, The surface of the metal wire mesh also includes a tin metal plating layer; Preferably, the thickness of the tin metal plating layer is 0.01-1 μm.

6. The height-controlled preformed welding sheet according to claim 5, characterized in that, The tin metal coating is obtained by chemically depositing a metal mesh with a tin ion source under a reducing agent. Preferably, the tin ion source includes a tin salt, which is at least one of tin chloride, tin nitrate, or tin sulfate; the reducing agent is at least one of sodium borohydride, ferrous sulfate, or chromium chloride.

7. The height-controlled preformed welding sheet according to claim 6, characterized in that, The tin ion source also includes a dispersing stabilizer; Preferably, the dispersant stabilizer is a polyvinylpyrrolidone diionic salt.

8. A method for preparing a height-controlled preformed solder sheet according to any one of claims 1-7, characterized in that, Includes the following steps: S1. Place the metal wire mesh between two tin-based solder pads, and after preheating, obtain a sandwich laminate. S2. After rolling the sandwich laminate, it is then annealed to obtain the height-controlled preformed welding sheet.

9. The method for preparing the height-controlled preformed welding sheet according to claim 8, characterized in that, The preheating temperature is 150-200℃, and the time is 0.5-1h.

10. The method for preparing the height-controlled preformed welding sheet according to claim 8 or 9, characterized in that, The rolling temperature is 80-150℃; the annealing temperature is 90-110℃, and the annealing time is 0.5-1h.

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