Ag particle modified equal-atomic-ratio multi-element composite electronic paste and preparation method of high-shear-strength low-void-ratio packaging welding spots of Ag particle modified equal-atomic-ratio multi-element composite electronic paste

Abstract

The invention belongs to the technical field of electronic packaging brazing materials, and relates to Ag particle modified equal-atomic-ratio multi-element composite electronic paste and a preparation method of high-shear-strength low-void-ratio packaging welding spots of the Ag particle modified equal-atomic-ratio multi-element composite electronic paste. The Cu / InSnZnBi-xAg / Cu 3D packaging welding spot formed through modification by adding the nano Ag particles is good in microstructure compactness and reliability, the requirement for high-temperature service of the welding spot is met, the cost is reduced, and meanwhile the shear strength of the welding spot is improved.

Description

Technical Field

[0001] This invention belongs to the field of electronic packaging soldering materials technology. This invention relates to an Ag particle-modified equiatomic ratio multi-element composite electronic paste and a method for preparing high shear strength and low porosity packaging solder joints. Background Technology

[0002] With the popularization of 5G technology and the development of artificial intelligence, the integrated circuit industry is ushering in unprecedented development opportunities. Global semiconductor companies are actively pursuing diversified business development, forming a multi-layered industrial structure, continuously expanding their industrial scale, and driving the sustained expansion of the global semiconductor market. Against this backdrop, 3D packaging technology, with its significant advantages of miniaturization, high integration, and high efficiency, has become one of the most promising packaging solutions. However, due to the high integration and miniaturization characteristics of the packaging structure, significant heat accumulation occurs during device operation, placing higher demands on the thermal stability of electronic components. This is particularly true in high-end applications such as the automotive industry, new energy, aerospace, and nuclear power equipment, where the demand for high-temperature tolerance of electronic devices is even more pronounced. These applications often require electronic components to operate stably in extreme environments exceeding 300°C. Therefore, developing new high-temperature solders and packaging technologies has become a critical issue that urgently needs to be addressed.

[0003] In-48Sn solder, with its low melting point (118 ℃), good wettability, electrical conductivity, and thermal conductivity, is widely used in high-end electronic fields such as thermistors and chip-scale packaging. However, this solder is prone to coarsening of In-rich and Sn-rich phases under thermal conditions, which limits its high-temperature applications. Other binary or ternary solder systems, such as In-Sn, Sn-Zn-Cu, Sn-Bi, and Sn-Ag-Cu, also have similar issues regarding high-temperature reliability and cost.

[0004] SnBiInZn high-entropy solder, prepared using equiatomic ratios, exhibits broad application potential in the packaging of miniaturized and multifunctional electronic products due to its low melting point (approximately 80 °C), excellent wettability, and slow diffusion kinetics. The synergistic effect of In and Sn significantly lowers the solder's melting point; the addition of Zn inhibits interfacial oxidation and hinders the excessive growth of the Cu3Sn phase in interfacial IMCs; and the addition of Bi refines the IMC grains, thereby improving the mechanical properties of the solder joint. However, the high operating temperature required for preparing SnBiInZn high-entropy solder alloys via melting methods limits its application range to some extent.

[0005] For example, existing technologies CN 120170322 A and CN 119188017 A report SnBiInZnAg multi-component alloy solders, their preparation methods, and applications. CN 120170322 A introduces Ag to react with easily oxidized Zn, generating the compound AgZn3, which strengthens the alloy and reduces Zn oxidation to form an oxide film, thus improving solder wettability. CN 119188017 A, based on high-entropy alloy design principles, enhances the mechanical properties of low-melting-point alloy solders through solid solution strengthening and second-phase strengthening mechanisms. However, both technologies involve melting to prepare low-melting-point alloys, which suffers from high melting temperatures, complex processes, high costs, high oxidation risks, and phase segregation and coarseness in the alloy solder microstructure. Furthermore, the resulting solder joints cannot be used in high-temperature service environments.

[0006] However, Cu / InSnZnBi / Cu solder joints prepared using the TLP (Transient Liquid Phase) bonding process exhibit low shear strength (e.g., J Mater Sci: Mater Electron 36, 901 (2025), where the highest shear strength of the Cu / InSnZnBi / Cu solder joint is 9.28 MPa). During the TLP bonding process between InSnZnBi and the Cu substrate, brittle phases such as Cu6Sn5 (Cu-Sn IMC) and InBi (In-Bi IMC) are generated, and defects such as Kirkendall voids may occur. Due to the continuous distribution of brittle phases and the presence of voids, the plastic deformation capacity of the solder joint interface is significantly reduced, leading to a decrease in shear strength. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of existing technologies and provide an Ag particle-modified equiatomic ratio multi-element composite electronic paste and a Cu / InSnZnBi-xAg / Cu solder joint prepared by a TLP bonding process. This invention employs physical mixing to prepare InSnZnBi-xAg multi-element composite solder powder, overcoming the insufficient reliability of existing InSnZnBiAg solder alloy solder joints at high temperatures. By mixing the multi-element composite solder powder with flux, a multi-element composite electronic paste is obtained, solving the problem of low shear strength in Cu / InSnZnBi / Cu solder joints caused by the subsequent TLP bonding process. This not only meets the requirements for high-temperature service of the solder joints and reduces costs while improving their mechanical properties, but also simultaneously solves the defect of high porosity in Cu / InSnZnBi / Cu solder joints caused by the TLP bonding process.

[0008] According to a first aspect of the present invention, an InSnZnBi-xAg multi-component composite solder powder is provided, wherein nano-Ag particles are used for modification in the multi-component composite solder powder. The multi-component composite solder powder is prepared by a physical mixing method. Unlike existing technologies that require melting to prepare low-melting-point alloys, the present invention can directly obtain the multi-component composite solder powder through physical mixing, and subsequently use a wafer bonding machine to prepare solder joints using transient liquid-phase diffusion bonding technology.

[0009] Preferably, the multi-component composite solder powder contains Ag.

[0010] Preferably, the amount of Ag added to the multi-element composite solder powder is 20-70 wt.% of the weight of InSnZnBi, for example, it can be 20-60 wt.%, 20-50 wt.%, 20-40 wt.%, 20-30 wt.%, 30-70 wt.%, 30-60 wt.%, 30-50 wt.%, 30-40 wt.%, 40-70 wt.%, 40-60 wt.%, 40-50 wt.%, 50-70 wt.%, 50-60 wt.%, 60-70 wt.%.

[0011] Preferably, the raw materials used in the InSnZnBi-xAg multi-component composite solder powder are micron-sized In, Sn, Zn, and Bi particles; and the Ag is nanoparticles.

[0012] According to a second aspect of the present invention, a Cu / InSnZnBi-xAg / Cu solder joint is provided, wherein X is the weight percentage of Ag added to InSnZnBi. The InSnZnBi-xAg multi-component composite solder powder described in the first aspect is stirred evenly with flux to obtain a multi-component composite electronic paste. Then, the multi-component composite electronic paste is placed between two copper plates to form a sandwich structure. Finally, the solder joint is prepared by using a wafer bonding machine with transient liquid phase diffusion bonding technology.

[0013] In some embodiments of this invention, the Cu / InSnZnBi-xAg / Cu solder joint can solve the problem of low shear strength (below 10.05 MPa) of Cu / InSnZnBi / Cu solder joints prepared by TLP bonding process, achieving a shear strength of 23.27 MPa and a porosity as low as 0.94%. Although the solder joint shear strength reported in patent CN 119188017 A can reach up to 29 MPa, it uses alloy brazing filler metal prepared by traditional melting method, which has a high melting temperature but cannot be applied to high-temperature solder joint scenarios. This invention uses TLP bonding process combined with nano-Ag particle modification, effectively solving the problems of insufficient shear strength and high porosity that are easily caused by the TLP process itself, and significantly improving the reliability of the solder joint. This invention achieves low-temperature bonding and high-temperature service while ensuring excellent shear performance and low porosity.

[0014] Preferably, the flux is a rosin-based flux; According to a third aspect of the present invention, the present invention provides a method for preparing Cu / InSnZnBi-xAg / Cu solder joints, comprising the following steps: 1) Micron-sized In, Sn, Zn, and Bi particles are mixed in equal atomic ratios to obtain InSnZnBi equal atomic ratio multi-component composite solder powder; 2) Add nano-Ag particles of different mass ratios to InSnZnBi multi-element composite solder powder, stir thoroughly, and then add flux to obtain InSnZnBi-xAg (x=20~70 wt. %) multi-element composite electronic paste; 3) Cu / InSnZnBi-xAg / Cu (x=20~70 wt.%) solder joints were prepared using a TWB-100 wafer bonding machine with transient liquid phase diffusion bonding technology.

[0015] Preferably, the bonding time of the TWB-100 wafer bonding machine is 260℃~340℃; And / or, the bonding pressure of the TWB-100 wafer bonding machine is 0.1~5 MPa; Preferably, the bonding time is 60 min, the bonding temperature is 280℃, the bonding pressure is 3 MPa, and the vacuum degree is 50 Pa.

[0016] Preferably, the amount of nano-Ag particles added is 50-60 wt.% of the InSnZnBi multi-component composite solder powder in step 1), i.e., X = 50-60 wt.%.

[0017] Preferably, after bonding, the sample is cut in half using a DK77 EDM machine, and the solder joints are ground and polished for subsequent observation.

[0018] Preferably, a Zeisssupra 55 scanning electron microscope (SEM) was used to observe the microstructure, interfacial IMCs, and tensile fracture surface of the solder joints, and energy dispersive spectroscopy (EDS) was used to determine the chemical composition of different phases. A D8 Advance A25 X-ray diffractometer (XRD) was used to perform phase analysis on the solder joints, with a scanning range of 20–90° and a scanning speed of 2° / min. The SEM images of the solder joint microstructure were imported into ImageJ software to measure the porosity of the solder joints. A shear test was performed on the solder joints using an MTS EXCEED E44 electronic universal testing machine at a shear rate of 0.02 mm / min, and three samples were tested for each set of parameters to reduce errors.

[0019] Brief introduction to technical principles: This invention provides a method for preparing encapsulation solder joints using Ag particle-modified equiatomic ratio multi-component composite electronic paste and its technical principle. The method involves physically mixing four metal particles—In, Sn, Zn, and Bi—in equiatomic ratios, and further preparing an InSnZnBi multi-component composite electronic paste together with flux. Through a TLP bonding process, the low-melting-point components (In, Sn, etc.) melt and diffuse, reacting with the high-melting-point components (Cu, Zn, etc.) to generate high-melting-point IMC (such as Cu6Sn5, Cu3Sn, etc.), resulting in solder joints that "bond at low temperatures and operate at high temperatures (>300℃)," effectively reducing packaging costs and solving the technical problem that traditional low-melting-point alloy solders cannot meet the requirements of high-temperature operating environments.

[0020] However, during TLP bonding, voids may form inside the solder joint due to phase transitions, and Kirkendal voids may form at the interface due to mismatched element diffusion rates. These defects seriously affect the reliability of the solder joint. Compared with existing technologies CN120170322 A and CN 119188017 A, although both incorporate Ag, their technical principles differ. This invention introduces a high content (20-70 wt.%) of nano-Ag reinforcing particles into InSnZnBi multi-component electronic paste. On the one hand, these high-content nano-Ag particles can act as heterogeneous nucleation sites, effectively regulating the morphology and growth of IMC within and at the interface of the solder joint, promoting the formation of a more stable and uniform microstructure, and suppressing and reducing the generation of defects such as pores. On the other hand, the introduction of nano-Ag particles promotes the formation of the high-temperature stable phase Ag3(Sn, In) within the solder joint, which helps improve the stability of the solder joint under high-temperature operating conditions. Furthermore, by introducing a high content of nano-Ag particles, during the TLP bonding process, some incompletely reacted nano-Ag particles can act as physical barriers and be uniformly distributed within the solder joint, limiting the excessive coarsening and uneven growth of IMC, thereby playing a role in dispersion reinforcement in the solder joint and further improving its mechanical properties. However, in CN 120170322 A, Ag mainly improves the wettability of the solder by reacting chemically with easily oxidized Zn to form AgZn3 compounds. In CN 119188017 A, Ag forms a high-entropy alloy with In, Sn, Bi, and Zn, which enhances the mechanical properties of the low-melting-point alloy through solid solution strengthening and second-phase strengthening mechanisms.

[0021] Compared with the prior art, the significant advantages of this invention are: 1) This invention uses an equiatomic ratio and physical mixing method to prepare InSnZnBi multi-component composite solder powder; it avoids the problems of high temperature, complex process, high cost and oxidation risk required by the melting method, and broadens the application range of the material.

[0022] 2) This invention employs transient liquid phase (TLP) bonding to prepare solder joints, with a bonding time of 60 min, a bonding temperature of 280℃, and a bonding pressure of 3 MPa, meeting the requirements of "low-temperature bonding." The resulting high-melting-point IMCs meet the requirements for stable operation in extreme environments exceeding 300℃, making them suitable for high-end fields such as automotive, new energy, and aerospace.

[0023] 3) Compared to the low shear strength and high porosity of Cu / InSnZnBi / Cu solder joints, this invention modifies the joint by introducing a high content (20~70 wt.%) of nano-Ag particles to prepare Cu / InSnZnBi-xAg / Cu TLP solder joints. Specifically, the interface reaction zone of the Cu / InSnZnBi-55Ag / Cu solder joint is a Cu3(Sn, In) phase, while the in-situ reaction zone consists of a large amount of Ag3(Sn, In) phase, Ag particles, a Zn-rich phase, and a very small amount of InBi phase. The nano-Ag particles not only promote the formation of a high-temperature stable phase but also act as heterogeneous nucleation sites to regulate interfacial IMC growth, inhibit porosity formation, and play a role in dispersion strengthening within the solder joint, thus comprehensively improving the compactness and reliability of the solder joint.

[0024] 4) This invention found that the shear strength of the solder joint is as high as 23.27 MPa and the porosity is as low as 0.94% under a specific content of nano-Ag particles (50-60 wt.%), which is far more than satisfactory for most applications. Attached Figure Description

[0025] Figure 1 (a) Schematic diagram of the bonding process and sampling process of Cu / InSnZnBi-xAg / Cu (x=20~70 wt. %) 3D packaging solder joints; (b) Schematic diagram of shear test.

[0026] Figure 2 The images show the microstructure of Cu / InSnZnBi / Cu 3D package solder joints at different bonding temperatures, where (a) is 260℃, (b) is 280℃, (c) is 300℃, (d) is 320℃, and (e) is 340℃.

[0027] Figure 3 The images show the fracture morphology of the solder joints in Cu / InSnZnBi / Cu 3D packages at different bonding temperatures, where (a) is 260℃, (b) is 280℃, (c) is 300℃, (d) is 320℃, and (e) is 340℃; (D) is a magnified view of the corresponding (d).

[0028] Figure 4 Microstructure morphology of Cu / InSnZnBi / Cu 3D package solder joints under different bonding pressures, where (a) 0.1 MPa, (b) 1 MPa, (c) 2 MPa, (d) 3 MPa, and (e) 5 MPa.

[0029] Figure 5Fracture morphology of Cu / InSnZnBi / Cu 3D package solder joints under different bonding pressures, where (a) 0.1 MPa, (b) 1 MPa, (c) 2 MPa, (d) 3 MPa, (e) 5 MPa; (D) is a magnified view of the corresponding (d).

[0030] Figure 6 Microstructure morphology of solder joints in Cu / InSnZnBi-xAg / Cu (x=20~70 wt. %) 3D packaging, where (a) x=0 wt. %, (b) x=20 wt. %, (c) x=40 wt. %, (d) x=55 wt. %, and (e) x=70 wt. %.

[0031] Figure 7 for Figure 2 EDS point scan results of the marked points.

[0032] Figure 8 XRD analysis diagram of the Cu / InSnZnBi-55Ag / Cu fracture interface.

[0033] Figure 9 The properties of the solder joints for Cu / InSnZnBi-xAg / Cu (x=20~70 wt. %) 3D packaging are given, including (a) porosity and (b) shear strength.

[0034] Figure 10 Surface views of the fracture joints of Cu / InSnZnBi-xAg / Cu (x=20~70 wt. %) 3D packaged solder joints: (a) x=0 wt. %, (b) x=20 wt. %, (c) x=40 wt. %, (d) x=55 wt. %, (e) x=70 wt. %; (A)-(E) are magnified views of the corresponding (a)-(e). Detailed Implementation

[0035] Transient liquid phase (TLP) bonding technology achieves connection by forming a transient liquid phase at low temperatures, followed by isothermal solidification to generate high-melting-point intermetallic compounds (IMCs). This allows the solder joint to maintain structural stability even under high-temperature service conditions (>300 °C), achieving solder joint performance of "low-temperature bonding and high-temperature service". This application mixes In, Sn, Zn, and Bi particles in equal atomic ratios and adds nano-Ag particles for modification to prepare an InSnZnBi-xAg (x=20~70 wt.%) multi-element composite electronic paste. The TLP bonding process is used to prepare the solder joints, reducing packaging costs while providing an effective way to solve the challenges of high-temperature packaging.

[0036] During TLP bonding, the different phase compositions of the IMC particles and the interfacial IMC layer, as well as the mismatch in diffusion rates of elements such as Cu and Zn at the interface, can lead to various defects such as voids and cracks. These defects significantly weaken the mechanical properties of the solder joint, severely impacting its long-term reliability. To improve solder joint reliability, this application modifies the InSnZnBi multi-component composite electronic paste by introducing nano-Ag particles. Nano-Ag particles can regulate elemental diffusion during solder joint formation, disrupting the original phase equilibrium, promoting the formation of the high-temperature phase Ag3(Sn, In), and effectively suppressing voids, thus improving the solder joint's microstructure. Therefore, adding different mass percentages of nano-Ag particles to the InSnZnBi multi-component composite electronic paste with equal atomic ratios can effectively improve the shear strength of the solder joint. By optimizing the content of nano-Ag particles, the shear strength of the solder joint can be further improved and the porosity reduced, thereby enhancing the overall reliability and stability of the welded structure.

[0037] Raw materials and equipment: In particles, Sn particles, Zn particles, Bi particles and nano Ag particles. 10 mm × 10 mm × Pure Cu sheets (99.99% purity) of 4 mm and 12 mm × 12 mm × 4 mm. TWB-100 wafer bonding machine, DK77 EDM machine, Zeisssupra55 scanning electron microscope, D8 Advance A25 X-ray diffractometer, MTS EXCEED E44 electronic universal testing machine.

[0038] In this experiment, pure copper (99.99%) was used as the upper and lower substrates. Several copper blocks with dimensions of 10 mm × 10 mm × 4 mm (length × width × thickness) and 12 mm × 12 mm × 4 mm (length × width × thickness) were prepared using a wire cutting machine. These blocks were then ground, polished, and dried to remove oxides and oil. Micron-sized In, Sn, Zn, and Bi particles were mixed in equal atomic ratios; that is, the mass fractions of In particles were 22.61 wt.%, Sn particles 23.37 wt.%, Zn particles 12.87 wt.%, and Bi particles 41.16 wt.%. Based on this, nano-Ag particles (approximately 50 nm in diameter) of varying mass percentages (20–70 wt.%) are added and mechanically mixed for 60–90 minutes. Then, rosin-based flux, with a mass fraction of 13 wt.% of InSnZnBi-xAg, is added and mechanically stirred for 90–120 minutes until homogeneous to obtain a multi-element composite electronic paste. The obtained InSnZnBi-xAg (x = 20–70 wt.%) multi-element composite electronic paste is uniformly coated onto a lower copper plate with dimensions of 12 mm × 12 mm × 4 mm. Then, an upper copper plate with dimensions of 10 mm × 10 mm × 4 mm is placed on top to form a sandwich structure (e.g., ...). Figure 1 (a) is shown.

[0039] Solder joints were fabricated using a TWB-100 wafer bonding machine under a vacuum of 50 Pa. The bonding temperature and bonding pressure of the Cu / InSnZnBi / Cu solder joints were optimized using a single-variable method at a bonding time of 60 min. Based on the optimized parameters, Cu / InSnZnBi-xAg / Cu encapsulation solder joints were further fabricated.

[0040] The microstructure, interfacial IMCs, and tensile fracture surface of the solder joints were observed using a Zeisssupra 55 scanning electron microscope (SEM), and the chemical composition of different phases was determined by energy dispersive spectroscopy (EDS). Phase analysis of the solder joints was performed using a D8 Advance A25 X-ray diffractometer (XRD), with a scanning range of 20–90° and a scanning speed of 2° / min. The porosity of the solder joints was measured using ImageJ software. Shear tests were conducted on the solder joints using an MTS EXCEED E44 electronic universal testing machine at a shear rate of 0.02 mm / min, with three samples tested for each parameter group to minimize error.

[0041] Example I. Microstructure evolution and fracture morphology of Cu / InSnZnBi / Cu 3D package solder joints (i.e., without Ag addition) at different bonding temperatures Cu / InSnZnBi / Cu3D encapsulation solder joints were prepared at different bonding temperatures (260℃, 280℃, 300℃, 320℃, 340℃), with a bonding pressure of 1 MPa and a bonding time of 60 min.

[0042] The microstructure of solder joints at different bonding temperatures is as follows Figure 2 As shown. The solder joint height is approximately 35 μm. At 260℃ ( Figure 2 a) The IMCs at the solder joint interface consist of Cu5Zn8 and Cu6(Sn, In)5, and the in-situ reaction zone microstructure contains island-like InBi phase, Zn-rich phase, and Sn-rich phase. At 280℃ ( Figure 2 (b) The interfacial IMCs Cu5Zn8 and Cu6(Sn,In)5 phases tend to be stable, and the in-situ reaction zone has a dense structure without defects such as pores. At 300℃ ( Figure 2 c) In the in-situ reaction zone of the solder joint, the island-like InBi phase increases and gradually coarsens, and micropores appear at the interface between the InBi phase and the Sn-rich phase. At the interface, the Kirkendall effect occurs due to the difference in interdiffusion rates of Cu, Zn, and Sn atoms. After the bonding temperature continues to rise to 340℃ ( Figure 2 d) The island-like InBi phase breaks down, producing a large number of pores, and obvious cracks appear inside the solder joint.

[0043] Fracture morphology of solder joints at different bonding temperatures, as follows Figure 3 As shown. At a bonding temperature of 260°C ( Figure 3 a) The fracture surface is mainly composed of InBi phase. The weld joint has poor mechanical properties, exhibiting brittle fracture with a shear strength of only 5.32 MPa. At 280°C ( Figure 3 (b) The increased amount of Sn-rich phase and granular Cu5Zn8 phases improved the weld strength, and the fracture mode tended towards a mixed brittle-ductile fracture. The shear strength of the weld increased to 9.28 MPa. At 300℃ ( Figure 3 c) A small amount of whisker-like Zn-rich phase appeared in the fracture surface. The presence of the brittle phase made the fracture mode more brittle fracture, and the strength decreased to 6.99 MPa. At 320℃ ( Figure 3 d) A polyhedral prismatic structure and large blocky fragments were observed at the fracture surface, exhibiting a typical intergranular fracture mechanism, with a strength of 6.29 MPa. After 340℃ ( Figure 3 e) Island-like InBi fragmentation occurs, with an increase in Zn-rich phases and numerous defects. At this point, the microstructure of the weld joint is completely destroyed, the fracture mode is severe brittle fracture, and the strength is the worst, at 5.85 MPa.

[0044] II. Microstructural evolution and fracture morphology of Cu / InSnZnBi / Cu 3D encapsulation solder joints (i.e., without Ag addition) under different bonding pressures Solder joints for Cu / InSnZnBi / Cu 3D packaging were prepared under different bonding pressures (0.1 MPa, 1 MPa, 2 MPa, 3 MPa, 5 MPa), with a bonding temperature of 280°C and a bonding time of 60 min.

[0045] Solder joint microstructure under different bonding pressures, such as Figure 4 As shown. Bonding pressure has little effect on the microstructure of the solder joint. The microstructure of the shear fracture surface is as follows. Figure 5 As shown. When the bonding pressure is 3 MPa ( Figure 5 d) The fracture morphology exhibits a mixed ductile-brittle mode, under which the weld shear strength is the best, at 10.05 MPa. Under other pressures, the weld shear strength ranges from 7.59 MPa to 9.28 MPa.

[0046] III. Microstructural Evolution of Cu / InSnZnBi-xAg / Cu Packaging Solder Joints with Different Nano Ag Contents Cu / InSnZnBi-xAg / Cu (x=20~70 wt. %) 3D encapsulation solder joints with different Ag particle contents were prepared; the bonding process parameters were: bonding temperature 280°C, bonding time 60 min, and bonding pressure 3 MPa.

[0047] Microstructure of Cu / InSnZnBi-xAg / Cu (x=20~70 wt. %) 3D package solder joints as shown in the figure. Figure 6 As shown. This invention divides the solder joint into three parts: the Cu substrate, the interface diffusion reaction zone (Ⅰ), and the in-situ reaction zone (Ⅱ). According to EDS (… Figure 7 Results and XRD ( Figure 8 The results show that without the addition of nano-Ag particles ( Figure 6 In step a), the diffusion reaction zone at the Cu / InSnZnBi / Cu solder joint interface is Cu5Zn8 near the Cu substrate and Cu6(Sn, In)5 near the solder. The in-situ reaction zone includes InBi phase, Zn-rich phase, and Sn-rich phase. The content of nano-Ag particles is 20 wt.% ( Figure 6 In step b), the interfacial IMCs of the Cu / InSnZnBi-20Ag / Cu solder joint, Cu5Zn8 and Cu6(Sn, In)5, disappear, forming a very thin layer of Cu3(Sn, In). Numerous island-like Ag3(Sn, In) particles appear in the in-situ reaction zone, mainly formed by the reaction of Ag particles with Sn and In atoms in the slurry; a small amount of Ag particles are also observed. The formation of Ag3(Sn, In) leads to the disappearance of the Sn-rich phase and a reduction in the InBi phase in the in-situ reaction zone. The content of nano-Ag particles is 40 wt.% (…). Figure 6 At step c), the thickness of the interfacial IMC Cu3(Sn, In) layer increases, and the island-like Ag3(Sn, In) in the in-situ reaction zone gradually transforms into continuous blocky structures. With increasing nano-Ag particle content, the thickness of the interfacial IMC layer gradually increases, the proportion of Ag3(Sn, In) in the in-situ reaction zone increases, the proportion of InBi phase and Zn-rich phase decreases, and a small amount of Ag particles are observed to be dispersed. As the Ag particle content further increases to 55 wt.% (…),… Figure 6 At step d), the interfacial diffusion reaction zone of the Cu / InSnZnBi-55Ag / Cu solder joint is Cu3(Sn, In), and the in-situ reaction zone mainly consists of a large amount of Ag3(Sn, In), Ag particles, Zn-rich phase, and a very small amount of InBi phase. At this point, the interfacial IMC Cu3(Sn, In) thickness is moderate, showing a tendency to grow towards the in-situ reaction zone. Furthermore, the formation of a large amount of Ag3(Sn, In) phase consumes Sn and In atoms in the slurry, reducing the formation of pores. When the content of nano-Ag particles exceeds 70 wt.% (… Figure 6In step e), the thickness of the interfacial IMC Cu3(Sn, In) layer decreases. This is because the solder joint diffusion reaction mainly occurs under the influence of a concentration gradient. When there are sufficient Ag particles in the slurry to react completely with Sn and In, the Sn and In concentrations at the interface are low, leading to a thinner Cu3(Sn, In) layer. The in-situ reaction zone consists of Ag3(Sn, In) and a small amount of Zn-rich phase, while a very small amount of InBi phase accumulates at the Cu3(Sn, In) / Cu substrate interface, reducing solder joint reliability.

[0048] IV. Shear strength and fracture surface of Cu / InSnZnBi-xAg / Cu solder joints with different nano-Ag contents Voids cause stress concentration at solder joints and reduce mechanical properties. However, improving mechanical properties does not always come at the cost of reduced porosity. This study aims to optimize mechanical properties while effectively controlling porosity, thereby comprehensively enhancing solder joint reliability.

[0049] The porosity and shear strength values ​​of Cu / InSnZnBi-xAg / Cu (x=20~70 wt. %) 3D package solder joints are as follows: Figure 9 As shown in the figure, the results indicate that with the increase of Ag particle content, the porosity of the solder joint first decreases and then increases, while the shear strength shows a trend of first increasing and then decreasing. The solder joint porosity is highest (6.41%) and the shear strength is lowest (10.05 MPa) when no nano-Ag particles are added. At this point, the interfacial diffusion reaction zone is mainly composed of Cu5Zn8 and Cu6(Sn, In)5 phases. The relatively thick interfacial IMCs easily induce stress concentration during shearing, thus promoting further crack propagation and reducing the shear strength of the solder joint. The in-situ reaction zone contains a large amount of InBi, Zn-rich, and Sn-rich phases. The different thermal expansion coefficients of these phases lead to thermal stress between them during temperature changes, significantly affecting the shear strength of the solder joint. When the nano-Ag particle content is 55 wt.%, the solder joint porosity drops to the lowest level of 0.94%, and the shear strength reaches a peak of 23.27 MPa. This is because the addition of nano-Ag reacts with Sn and In atoms to form Ag3(Sn, In). In the interfacial diffusion reaction zone, only a dense and continuous IMC Cu3(Sn,In) layer is formed, with Ag particles dispersed in the in-situ reaction zone, thereby reducing the porosity of the solder joint and increasing its shear strength. When the content of nano-Ag particles exceeds 70 wt.%, the interfacial IMC layer becomes thinner, a large amount of Ag3(Sn,In) phase is generated in the in-situ reaction zone, its porosity increases to 1.67%, and the shear strength of the solder joint decreases to 18.97 MPa.

[0050] Figure 10SEM images of the shear fracture surface of the solder joint in a Cu / InSnZnBi-xAg / Cu (x=20~70 wt. %) 3D package. No nano-Ag particles were added. Figure 10 In case a), the fracture morphology of the weld joint contains Cu6(Sn, In)5 and InBi phases, exhibiting intergranular brittle fracture characteristics. The fracture occurs at the interface between the in-situ reaction zone and the interfacial diffusion reaction zone. The content of nano-Ag particles is 20–40 wt.% ( Figure 10 When the content of Ag particles increased to 55 wt.%, the fracture morphology transformed into Ag3(Sn, In) with needle-like Zn-rich phase and a small amount of Ag particles. Solder joint fracture mainly occurred in the in-situ reaction zone. Figure 10 d) Numerous dimple-shaped Cu3(Sn, In) phases were observed on the shear fracture surface, indicating a shift from brittle fracture to ductile fracture, resulting in optimal weld reliability. The fracture location shifted from the interface between the in-situ reaction zone and the interfacial diffusion reaction zone to the interfacial diffusion reaction zone. However, when the content of nano-Ag particles further increased to 70 wt. % ( Figure 10 In step e), a large amount of Ag3(Sn, In) appeared on the fracture surface. Tearing marks were observed on the fracture surface, indicating a clear brittle fracture mechanism. The weld fracture occurred in the in-situ reaction zone, and pores were formed.

[0051] This invention first investigated the effects of different bonding temperatures (260℃, 280℃, 300℃, 340℃) and different bonding pressures (0.1 MPa, 1 MPa, 2 MPa, 3 MPa, 5 MPa) on the microstructure and mechanical properties of Cu / InSnZnBi / Cu 3D encapsulation solder joints at a bonding time of 60 min, without the addition of Ag. It also examined the effects of different nano-Ag particle contents on the microstructure, porosity, and mechanical properties of Cu / InSnZnBi-xAg / Cu 3D encapsulation solder joints at optimal bonding temperature and pressure. The experimental analysis yielded the following conclusions: (1) Increased bonding temperature promotes the diffusion of Cu and Sn atoms, making the interfacial IMC layer more continuous and the solder joint structure more compact. However, when the temperature exceeds 300℃, a large number of pores or even obvious cracks appear in the solder joint, and the fracture mode changes from ductile-brittle mixed fracture to brittle fracture, with shear strength less than 6.99MPa. Therefore, 280℃ is the optimal bonding temperature, at which the interfacial IMC layer is continuous, the solder joint is dense and defect-free, and the shear strength reaches the highest value of 9.28MPa.

[0052] (2) Bonding pressure has little effect on the evolution of the microstructure and shear properties of the solder joint. When the bonding pressure is 3 MPa, the solder joint microstructure is denser and has a higher shear strength of 10.05 MPa compared to other pressures.

[0053] (3) At 280℃, 60min, and 3MPa, the diffusion reaction zone at the Cu / InSnZnBi / Cu solder joint interface consists of two layers: Cu5Zn8 and Cu6(Sn, In)5. The in-situ reaction zone includes InBi phase, Zn-rich phase, and Sn-rich phase. After adding nano-Ag particles, the interfacial IMC transforms into Cu3(Sn, In) phase. The presence of Ag3(Sn, In) phase and Ag particles can be observed in the in-situ reaction zone, while the Sn-rich phase disappears and the InBi and Zn-rich phases decrease. With the increase of nano-Ag particle content, the thickness of the interfacial IMC first increases and then decreases, showing a trend of growth towards the in-situ reaction zone. The Ag3(Sn, In) phase gradually changes from an island-like structure to a continuous blocky structure. When the nano-Ag particle content is 55wt.%, the solder joint microstructure exhibits the best density and reliability.

[0054] (4) The shear strength of the weld joint first increases and then decreases with the increase of the content of nano-Ag particles. When no nano-Ag particles are added, the interfacial IMCs are the thickest, and there are a large number of InBi, Sn-rich and Zn-rich phases in the in-situ reaction zone. At the same time, the porosity inside the weld joint is relatively high (6.41%), and the shear strength of the weld joint is the lowest, which is 10.05 MPa. When the content of nano-Ag particles is 55 wt.%, the thickness of Cu3(Sn, In) in the interfacial diffusion reaction zone is moderate, and the bonding strength with Ag3(Sn, In) in the in-situ reaction zone is high. At this time, the porosity is also at a low level (0.94%), and the shear strength reaches a peak of 23.27 MPa. The fracture mechanism changes from brittle fracture to ductile fracture, and then to brittle fracture.

[0055] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A powder for InSnZnBi equiatomic ratio multi-component composite solder, wherein the powder contains Ag, and the powder is prepared by physical mixing.

2. The InSnZnBi equiatomic ratio multi-component composite solder powder according to claim 1, wherein the amount of Ag added in the equiatomic ratio multi-component composite solder powder is 20-70 wt.% of the weight of InSnZnBi. And / or, the raw materials used in the InSnZnBi atomic ratio multi-component composite solder powder are micron-sized In, Sn, Zn, and Bi particles; the Ag is nanoparticles.

3. The InSnZnBi equiatomic ratio multi-component composite solder powder according to claim 2, wherein the amount of Ag added in the equiatomic ratio multi-component composite solder powder is 50-60 wt.% of the weight of InSnZnBi.

4. A Cu / InSnZnBi-xAg / Cu solder joint, wherein X is the weight percentage of Ag added to InSnZnBi, x = 20~70 wt.%; The multi-element composite electronic paste is prepared by uniformly mixing powder and flux of the InSnZnBi equiatomic ratio multi-element composite solder as described in claim 1, and then placing the multi-element composite electronic paste between two copper plates to form a sandwich structure. Finally, the solder joint is prepared by using a wafer bonding machine with transient liquid phase diffusion bonding technology.

5. The Cu / InSnZnBi-xAg / Cu solder joint according to claim 4, wherein the flux is a rosin-based flux.

6. A method for preparing the Cu / InSnZnBi-xAg / Cu solder joint as described in claim 4, comprising the following steps: 1) Micron-sized In, Sn, Zn, and Bi particles are mixed in equal atomic ratios to obtain InSnZnBi multi-component composite solder powder; 2) Add nano-Ag particles of different mass ratios and stir thoroughly. After mixing evenly, add flux to obtain InSnZnBi-xAg multi-component electronic paste; 3) Place the InSnZnBi-xAg multi-component electronic paste between two copper plates to form a sandwich structure, and use a TWB-100 wafer bonding machine to prepare Cu / InSnZnBi-xAg / Cu solder joints.

7. The method according to claim 6, wherein X = 50-60 wt.%; And / or, the bonding time of the TWB-100 wafer bonding machine is 260℃~340℃; And / or, the bonding pressure of the TWB-100 wafer bonding machine is 0.1~5 MPa.

8. The method according to claim 7, wherein the bonding time is 60 min; And / or, the bonding temperature is 280℃; And / or, the bonding pressure is 3 MPa.

9. The method according to claim 8, wherein X = 55 wt.%; and the coating height of the InSnZnBi-xAg multi-component electronic paste is 35 μm; And / or, after bonding, the sample is cut in half using a DK77 EDM machine, and the solder joints are ground and polished for subsequent observation; And / or, the microstructure, interfacial IMCs, and tensile fracture surface of the solder joints were observed using a Zeisssupra 55 scanning electron microscope, and the chemical composition of different phases was determined by energy dispersive spectroscopy. The phase composition of the solder joints was analyzed using a D8 Advance A25 X-ray diffractometer with a scanning range of 20–90° and a scanning speed of 2° / min. The porosity of the solder joints was measured using Image J. And / or, the solder joints are sheared using an MTS EXCEED E44 electronic universal testing machine at a shear rate of 0.02 mm / min, with three samples tested for each set of parameters to reduce error.

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