High electromigration lead-free composite solder

Abstract

This invention discloses a high electromigration lead-free composite solder, belonging to the field of material preparation and connection technology. The lead-free composite solder comprises Cu@Ag particles and SAC305 powder in a weight ratio of 1:(60-200). This invention prepares a novel core-shell structure Cu@Ag reinforcing particles and adds them to the lead-free solder to form a novel composite solder joint, giving the composite solder joint excellent anti-electromigration performance. The reinforcing particles can play a role in local refinement and can also reduce the thickness of the intermetallic compound layer at the interface, making it another option for practical applications. The new Cu@Ag core-shell structure material prepared by this invention further enhances the role of the reinforcing particles. Cu, as the core, is wrapped in an Ag shell. Due to its stable properties, Ag not only plays a protective role, but its addition as a shell layer to the solder can also reduce costs. The lead-free composite solder provided by this invention is suitable for use in connectors for electronic packaging connections.

Description

Technical Field

[0001] This invention belongs to the field of material preparation and joining technology, specifically relating to a high electromigration lead-free composite solder. Background Technology

[0002] Solder joints are an indispensable component of microelectronic interconnects, serving both mechanical connection and electrical signal transmission functions. Currently, as microelectronic packaging sizes trend towards miniaturization, chip heat generation intensifies, and the current density across solder joints continuously increases. Under high current density conditions, collisions between flowing electrons and metal atoms result in momentum exchange, leading to directional atomic motion. Driven by electron wind, metal atoms move from the negative electrode to the positive electrode of the solder joint, undergoing mass migration. Existing research indicates that when the current density passing through the solder joint reaches the threshold value (10⁻⁶) for electromigration to occur... 4 A / cm 2 When electromigration occurs, a large number of atoms diffuse from the cathode to the anode, forming voids in the cathode, which in turn induce microcracks, leading to solder joint failure. Additionally, because the thermal expansion coefficient of the solder joint does not match that of the PCB board, stress and strain are concentrated mainly at the solder joint, resulting in electronic microcracks during use. Sn-Ag-Cu series solders have attracted widespread attention due to their good solderability, reliability, and low cost. However, when the silver content in the solder is too high, a large amount of Ag3Sn compounds will exist in the solder joint matrix. These large, hard particles significantly affect the mechanical properties of the solder joint, thus greatly reducing its reliability. At the same time, the high Ag content also increases the cost of the solder joint, reducing its practical application potential. SAC305 is widely used due to its good overall mechanical properties and reliability. However, compared to SnPb solders, SAC305 has poor wetting properties and possesses higher surface tension and a higher melting point.

[0003] Another method to improve solder joint performance is to add reinforcing particles. Previous studies have involved adding inorganic materials such as SiC and CNTs to solder joints. These inorganic materials can act as a second-phase reinforcement within the solder joint matrix, increasing its strength and hardness. However, incompatibility between the inorganic materials and the metal can occur during use, causing the reinforcing particles to be repelled at the interface, thus failing to produce the desired effect. Summary of the Invention

[0004] To address the aforementioned problems in the prior art, this invention provides a high electromigration lead-free composite solder. By adding core-shell structured reinforcing particles Cu@Ag to SAC305 lead-free solder to form a composite solder, the microstructure of the solder joint can be effectively improved, thereby enhancing the reliability of components during application.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] This invention provides a high electromigration lead-free composite solder, comprising Cu@Ag particles and SAC305 powder in a weight ratio of 1:(60-200).

[0007] Furthermore, the Cu@Ag particles have a core-shell structure, and the preparation method includes the following steps:

[0008] S1: Add ammonium sulfate to ethylene glycol, heat and then add ammonia to dissolve it. Add Cu powder to the resulting solution and sonicate it.

[0009] S2: Add sodium citrate to the solution obtained by ultrasonic treatment. After it is completely dissolved, add polyvinylpyrrolidone (PVP), heat and stir until it is completely dissolved, and then cool. Add ethanol to wash the cooled solution. After washing, add water, heat and stir again, then add silver ammonia solution, stir and let stand. Centrifuge, wash and dry to obtain the Cu@Ag particles.

[0010] Further, in step S1, the mass-to-volume ratio of ammonium sulfate to ethylene glycol is 1g:(10-20)mL, the heating is to 60℃, the concentration of ammonia is 28wt%, the volume ratio of ammonia to ethylene glycol is 1:20, and the mass ratio of Cu powder to ammonium sulfate is 1.5:1.

[0011] Further, in step S2, the mass-to-volume ratio of sodium citrate to the solution obtained by ultrasonic treatment is 1g:100mL, the mass-to-volume ratio of polyvinylpyrrolidone to ethylene glycol in step S1 is 1g:10mL, the polyvinylpyrrolidone is a mixture of equal masses of polyvinylpyrrolidone with k=30 and polyvinylpyrrolidone with k=90, the heating and the reheating are both heated to 50-70℃, and the concentration of diamminesilver hydroxide in the solution obtained after adding the silver ammonia solution is 0.1-0.2mol / L.

[0012] Ammonium sulfate modifies Cu, and sodium citrate re-sensitizes it, eventually reacting with PVP to form a Cu-PVP film, which allows Ag to attach later.

[0013] Furthermore, the method for preparing the SAC305 powder includes the following steps:

[0014] (1) Add acetone to SAC305 solder paste, and remove the upper suspension after ultrasonic vibration;

[0015] (2) Add ethanol to the remaining solder paste, continue ultrasonic vibration, and remove the supernatant after the process is complete;

[0016] (3) Repeat steps (1) and (2) until the upper layer of solution is clear after ultrasonic vibration;

[0017] (4) The obtained solid is dried to remove the alloy flakes, thus obtaining the SAC305 powder.

[0018] Furthermore, the concentration of the ethanol is 95 vol.%.

[0019] Furthermore, intermittent stirring is performed during the ultrasonic vibration process.

[0020] The present invention also provides a method for preparing a high electromigration lead-free composite solder, which is obtained by uniformly mixing Cu@Ag particles and SAC305 powder in a weight ratio of 1:(60-200).

[0021] This invention also provides the application of the aforementioned high electromigration lead-free composite solder in electronic packaging connector materials.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] This invention prepares a novel core-shell structured Cu@Ag reinforcing particles and adds them to lead-free solder to form a novel composite solder joint, giving the composite solder joint excellent anti-electromigration properties. During the preparation stage, ammonia and ultrasonic vibration ensure uniform dispersion of copper particles and remove the surface oxide layer. The addition of sodium citrate enhances the surface activity of the Cu particles. This invention adds the alloy to the solder joint; during the melting process, the solder joint matrix reacts with the alloy to form intermetallic compounds, thereby improving performance. During the solder alloy powder preparation stage, repeated ultrasonication with acetone and ethanol completely strips the flux from the lead-free solder, while ensuring that the thin metal flakes on the alloy surface after drying do not affect the quality of the final composite solder joint. Furthermore, the improved electromigration performance of this novel composite solder can be observed through the angle between the Sn grain c-axis and the current direction during energization. In use, it was found that the reinforcing particles can play a role in local refinement and reduce the thickness of the intermetallic compound layer at the interface, making it another option for practical applications.

[0024] The novel Cu@Ag core-shell structure material prepared in this invention further enhances the role of reinforcing particles. Cu serves as the core, encapsulated within an Ag shell. Due to its stable properties, Ag not only provides protection but also reduces costs when added as a shell layer to the solder.

[0025] The lead-free composite solder provided by this invention is suitable for use in connectors of electronic packaging connections and can be applied to reliability testing and research of mechanical, thermal, and electrical aspects of microelectronic connections. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 The images show the microstructure of Cu@Ag particles prepared in step (2) of Example 1, where (a) is a surface view of the particles and (b) is a cross-sectional view of the particles.

[0028] Figure 2 SEM image of Cu@Ag particles prepared in Comparative Example 1;

[0029] Figure 3 SEM image of Cu@Ag particles prepared in Comparative Example 2;

[0030] Figure 4 This is a schematic diagram of a linear solder joint sample.

[0031] Figure 5 The images show the morphology of four solder joints (denoted as SAC305-x(0, 0.5, 1, 1.5)Cu@Ag solder joints) obtained from the solder pastes of Comparative Example 4 and Examples 1-3 after being energized for 0, 168, and 336 hours, respectively. Among them, (a)-(d) are the microscopic morphology images of the SAC305-x(0, 0.5, 1, 1.5)Cu@Ag solder joints after 0 hours of energization, (e)-(h) are the microscopic morphology images of the SAC305-x(0, 0.5, 1, 1.5)Cu@Ag solder joints after 168 hours of energization, and (i)-(l) are the microscopic morphology images of the SAC305-x(0, 0.5, 1, 1.5)Cu@Ag solder joints after 336 hours of energization.

[0032] Figure 6 The results are calculated for the thickness of the interface IMC layer before and after power-on of four solder joints (denoted as: SAC305-x(0, 0.5, 1, 1.5)Cu@Ag solder joints) obtained from the solder pastes of Comparative Example 4 and Examples 1 to 3, where (a) is the cathode and (b) is the anode. Detailed Implementation

[0033] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention. It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the present invention.

[0034] Furthermore, regarding the numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included within this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0035] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0036] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be obvious to those skilled in the art. This specification and embodiments are merely exemplary.

[0037] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0038] Example 1

[0039] (1) Weigh 1.03g of ammonium sulfate powder into a beaker and add 30mL of ethylene glycol. Then, add 1.5mL of 28wt% ammonia solution dropwise in a 60℃ oil bath and stir for 10min to completely dissolve the powder. Then, remove the beaker and add 1g of Cu powder to the solution. Ultrasonically vibrate for 3min to disperse the Cu particles evenly and activate the surface. After ultrasonic treatment, remove the beaker and add 0.3g of sodium citrate. Place it in a 60℃ oil bath and dissolve completely. Then add 3g of PVP (made by mixing PVP with k=30 and PVP with k=90 in a mass ratio of 1:1). Stir in a 60℃ oil bath for 30min until completely dissolved, then remove and air cool.

[0040] (2) After standing for 6 hours, the solution was washed with ethanol at 4000 rpm in a centrifuge. After washing, 50 ml of deionized water was mixed with the concentrated solution obtained from the washing and poured into a beaker. The mixture was stirred in an oil bath at 60°C. After stirring for 5 minutes, an appropriate amount of silver ammonia solution was added dropwise to make the concentration of diammonium silver hydroxide in the resulting solution 0.15 mol / L. The mixture was sealed and stirred for 3 hours, and then allowed to stand at room temperature for 12 hours. The solution was then washed with ethanol by centrifugation and dried to obtain the desired Cu@Ag particles.

[0041] Figure 1 The images show the microstructure of the prepared Cu@Ag particles, where (a) is the particle surface image and (b) is the particle cross-section image. Figure 1 It can be seen that the Cu@Ag particles exhibit good sphericity, and a clear core-shell structure can also be seen in the cross-sectional view.

[0042] (3) Preparation of SAC305 alloy powder: Take 15g of Senju SAC305 solder paste and place it at the bottom of a 50mL beaker. Then pour in 30mL of acetone to cover the solder paste. Place the beaker containing the solder paste and acetone into an ultrasonic device and set the ultrasonic time to 15min. During the ultrasonic process, use a stirring rod to stir the solution intermittently to ensure that the solder paste is fully ultrasonically vibrated. After the ultrasonic process is completed, pour out the upper suspension.

[0043] (4) Pour 30 mL of 95 vol% ethanol into the beaker after one sonication, and then sonicate it in the sonicator for 10 min. The sonication process also requires intermittent stirring with a stirring rod. After sonication, pour out the supernatant solution and repeat steps (3) and (4) until the supernatant solution is clear after sonication;

[0044] (5) Cover the ultrasonically treated beaker with plastic wrap to prevent oxidation and contamination of the powder during drying. Make several small holes in the surface to ensure complete evaporation of any remaining solution. Then place it in a drying oven at 60°C for 12 hours. Remove the beaker from the drying oven, remove the plastic wrap from the mouth of the beaker, and pour the alloy powder from the bottom onto clean weighing paper. Use tweezers, toothpicks, or other tools to remove the alloy flakes from the alloy powder. Repeat the above steps to prepare a sufficient amount of SAC305 alloy powder for later use.

[0045] (6) Weigh 8g of SAC305 alloy powder and 0.04g of Cu@Ag particles and put them into a 10mL transparent bottle. Mix them thoroughly by mechanical stirring to obtain a high electromigration lead-free composite solder containing 0.5wt% Cu@Ag particles.

[0046] (7) Add 1.04g of flux ALPHA POP 707 to the high electromigration lead-free composite solder obtained in step (6), and stir thoroughly at 300rpm for 10min to make it exhibit good adhesion and avoid the solder paste being too dry or too wet, thus obtaining composite solder paste.

[0047] Example 2

[0048] Same as in Example 1, except that steps (6) and (7) are as follows:

[0049] (6) Weigh 8g of SAC305 alloy powder and 0.0808g of Cu@Ag particles and put them into a 10mL transparent bottle. Mix them thoroughly by mechanical stirring to obtain a high electromigration lead-free composite solder containing 1.0wt% Cu@Ag particles.

[0050] (7) Add 1.05g of flux ALPHA POP 707 to the high electromigration lead-free composite solder obtained in step (6), and stir thoroughly at 300rpm for 10min to make it exhibit good adhesion and avoid the solder paste being too dry or too wet, thus obtaining composite solder paste.

[0051] The other steps, types of substances, and amounts are the same as in Example 1.

[0052] Example 3

[0053] Same as in Example 1, except that steps (6) and (7) are as follows:

[0054] (6) Weigh 8g of SAC305 alloy powder and 0.1218g of Cu@Ag particles into a 10mL transparent bottle, and mix thoroughly by mechanical stirring to obtain a high electromigration lead-free composite solder containing 1.5wt% Cu@Ag particles;

[0055] (7) Add 1.055g of flux ALPHAPOP 707 to the high electromigration lead-free composite solder obtained in step (6), and stir thoroughly at 300rpm for 10min to make it exhibit good adhesion and avoid the solder paste being too dry or too wet, thus obtaining composite solder paste.

[0056] The other steps, types of substances, and amounts are the same as in Example 1.

[0057] Comparative Example 1

[0058] Same as Example 1, except that step (1) is:

[0059] Weigh 1.03g of ammonium sulfate powder into a beaker and add 30mL of ethylene glycol. Then, stir in a 60℃ oil bath for 10min to completely dissolve the powder. Next, remove the beaker and add 1g of Cu powder to the solution. Ultrasonicate for 3min to disperse the Cu particles evenly and activate the surface. After ultrasonic treatment, remove the beaker and add 0.3g of sodium citrate. Place it in a 60℃ oil bath and dissolve completely. Then, add 3g of PVP (a mixture of k=30 and k=90 PVP in a 1:1 mass ratio). Stir in a 60℃ oil bath for 30min until completely dissolved, then remove and air cool.

[0060] The other steps, types of substances, and amounts are the same as in Example 1.

[0061] Figure 2 This is a SEM image of the Cu@Ag particles prepared in this comparative example.

[0062] Comparative Example 2

[0063] Same as Example 1, except that step (1) is:

[0064] Weigh 1.03 g of ammonium sulfate powder into a beaker and add 30 mL of ethylene glycol. Then, under 60°C oil bath conditions, add 1.5 mL of 28 wt% ammonia solution dropwise and stir for 10 min to completely dissolve the powder. Next, remove the beaker and add 1 g of Cu powder to the solution. Sonicate the solution for 3 min to disperse the Cu particles evenly and activate the surface. After sonication, remove the beaker and place it in a 60°C oil bath with stirring for 30 min, then air cool.

[0065] The other steps, types of substances, and amounts are the same as in Example 1.

[0066] Figure 3 This is a SEM image of the Cu@Ag particles prepared in this comparative example.

[0067] Depend on Figure 2 and Figure 3 It can be seen that if ammonia or sodium citrate is not used when preparing Cu@Ag particles, Ag cannot be deposited on the Cu surface to form a coating, and can only form fine Ag particles in the solution.

[0068] Comparative Example 3

[0069] Same as in Example 1, except that step (3) is:

[0070] Preparation of SAC305 alloy powder: 15g of Senju SAC305 solder paste was placed at the bottom of a 50mL beaker, and then 30mL of 95vol% ethanol was poured in to cover the solder paste. The beaker containing the solder paste and ethanol was placed in an ultrasonic device, and the ultrasonic time was set to 15min. During the ultrasonic process, the solution was intermittently stirred with a stirring rod to ensure that the solder paste underwent sufficient ultrasonic vibration. After the ultrasonic treatment was completed, the upper suspension was poured off. This comparative example only uses ethanol to treat the SAC305 solder paste.

[0071] The other steps, types of substances, and amounts are the same as in Example 1.

[0072] The results show that in this comparative example, without the use of acetone ultrasonic solution, the solution remains turbid and the quality of the obtained alloy powder is not accurate enough. In other words, acetone ultrasonication can quickly and effectively remove flux from solder paste.

[0073] Comparative Example 4

[0074] (1) Preparation of SAC305 alloy powder: Take 15g of Senju SAC305 solder paste and place it at the bottom of a 50mL beaker, then pour in 30mL of acetone to cover the solder paste. Place the beaker containing the solder paste and acetone into an ultrasonic device and set the ultrasonic time to 15min. During the ultrasonic process, use a stirring rod to stir the solution intermittently to ensure that the solder paste is fully ultrasonically vibrated. After the ultrasonic process is completed, pour out the upper suspension.

[0075] (2) Pour 30 mL of 95 vol% pure ethanol into the beaker after one sonication, and then sonicate it in the sonicator for 10 min. The sonication process also requires intermittent stirring with a stirring rod. After sonication, pour out the supernatant solution and repeat steps 1 and 2 until the supernatant solution is clear after sonication;

[0076] (3) Cover the ultrasonically treated beaker with plastic wrap to prevent oxidation and contamination of the powder during drying. Make several small holes in the surface to ensure complete evaporation of any remaining solution. Then place it in a drying oven at 60°C for 12 hours. Remove the beaker from the drying oven, remove the plastic wrap from the mouth of the beaker, and pour the alloy powder from the bottom onto clean weighing paper. Use tweezers, toothpicks, or other tools to remove the alloy flakes from the alloy powder. Repeat the above steps to prepare a sufficient amount of SAC305 alloy powder for later use.

[0077] (4) Weigh 8g of SAC305 alloy powder, add 1.04g of flux ALPHA POP 707, stir thoroughly until good adhesion is achieved, and avoid the solder paste being too dry or too wet to obtain lead-free solder paste.

[0078] Effect verification

[0079] Composite solder pastes prepared in equal amounts from Examples 1-3 and Comparative Examples 1-4 were used to prepare composite solder linear joints: A copper rod with both ends polished was fixed in place, leaving a 0.3mm gap at the end face joint. Solder paste was filled into the gaps, and then the rod was placed on a hot air welding station with a temperature profile set at 270℃ for 30 seconds. It was then removed and air-cooled.

[0080] Remove the one-dimensional linear solder joint, smooth the four surfaces of the joint, and then use resin to mount the joint onto the PCB board. A schematic diagram of the completed solder joint is shown below. Figure 4 As shown, the observation surface was then polished and initially characterized using SEM.

[0081] Connect the two ends of the linear solder joint to the two power supply stages using metal clips, and set the current to 8×10. 3 A / cm 2 The micro-interface was characterized again a week later.

[0082] Data analysis of the solder joints, Figure 5 The images show the morphology of four solder joints (denoted as SAC305-x(0, 0.5, 1, 1.5)Cu@Ag solder joints) obtained from the solder pastes of Comparative Example 4 and Examples 1-3 after being powered on for 0, 168 h, and 336 h, respectively. Among them, (a)-(d) are the microscopic morphology images of SAC305-x(0, 0.5, 1, 1.5)Cu@Ag solder joints after being powered on for 0 h, (e)-(h) are the microscopic morphology images of SAC305-x(0, 0.5, 1, 1.5)Cu@Ag solder joints after being powered on for 168 h, and (i)-(l) are the microscopic morphology images of SAC305-x(0, 0.5, 1, 1.5)Cu@Ag solder joints after being powered on for 336 h. It can be clearly observed that the surface morphology of the solder joints (a), (e), and (i) without added reinforcing particles changes drastically with the extension of the energizing time, and the intermetallic compound layer in the cross section is thicker. In contrast, the morphology of the solder joints with added reinforcing particles changes less, indicating that the solder joints have better anti-electromigration performance. In addition, the surface bumps found in Figures (g) and (h) are the effect of grain rotation, which indicates that the reinforcing particles have an influence on the rotation of Sn grains.

[0083] Figure 6 The results are calculated based on the thickness of the interface IMC layer of four solder joints (denoted as SAC305-x(0, 0.5, 1, 1.5)Cu@Ag solder joints) obtained from the solder pastes of Comparative Example 4 and Examples 1 to 3 before and after power-on. (a) is the cathode and (b) is the anode. It was found that the new composite solder joint with added reinforcing particles has a thinner IMC layer and better overall solder joint performance.

[0084] The above description is merely a preferred embodiment of the present invention, and 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 high electromigration lead-free composite solder, characterized in that, It consists of Cu@Ag particles and SAC305 powder in a weight ratio of 1:(60-200); The Cu@Ag particles have a core-shell structure, and the preparation method includes the following steps: S1: Add ammonium sulfate to ethylene glycol, heat and then add ammonia to dissolve it. Add Cu powder to the resulting solution and sonicate it. S2: Add sodium citrate to the solution obtained by ultrasonic treatment. After it is completely dissolved, add polyvinylpyrrolidone, heat and stir until it is completely dissolved, and then cool. Add ethanol to wash the cooled solution. After washing, add water, heat and stir again, then add silver ammonia solution, stir and let stand. Use alcohol to centrifuge and wash and dry to obtain the Cu@Ag particles. The preparation method of the SAC305 powder includes the following steps: (1) Add acetone to SAC305 solder paste, and remove the upper suspension after ultrasonic vibration; (2) Add ethanol to the remaining solder paste, continue ultrasonic vibration, and remove the supernatant after the process is complete; (3) Repeat steps (1) and (2) until the upper layer of solution is clear after ultrasonic vibration; (4) The obtained solid is dried to remove the alloy flakes, thus obtaining the SAC305 powder; In step S1, the mass-to-volume ratio of ammonium sulfate to ethylene glycol is 1 g: (20-40) mL, the heating is to 60°C, the concentration of ammonia is 28 wt%, the volume ratio of ammonia to ethylene glycol is 1:20, and the mass ratio of Cu powder to ammonium sulfate is 1.5:

1. In step S2, the mass-to-volume ratio of sodium citrate to the solution obtained by ultrasonic treatment is 1g:100mL, the mass-to-volume ratio of polyvinylpyrrolidone to ethylene glycol in step S1 is 1g:10mL, the polyvinylpyrrolidone is a mixture of equal masses of polyvinylpyrrolidone with k=30 and polyvinylpyrrolidone with k=90, the heating and the reheating are both heated to 50-70℃, and the concentration of diamminesilver hydroxide in the solution obtained after adding the silver ammonia solution is 0.1-0.2mol / L.

2. The high electromigration lead-free composite solder according to claim 1, characterized in that, The concentration of ethanol mentioned in step (2) is 95 vol.%.

3. The high electromigration lead-free composite solder according to claim 1, characterized in that, In step (3), intermittent stirring is performed during the ultrasonic vibration process.

4. A method for preparing the composite solder according to any one of claims 1-3, characterized in that, The Cu@Ag particles and SAC305 powder are mixed evenly in a weight ratio of 1:(60-200) to obtain the final product.

5. The application of the high electromigration lead-free composite solder according to any one of claims 1-3 in electronic packaging connector materials.

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