A method for in-situ growth of graphene during solder ball preparation and solder balls thereof.

Abstract

This invention provides a method for in-situ growth of graphene during solder ball preparation, belonging to the field of electronic packaging material preparation and in-situ construction technology of two-dimensional functional films. The method includes: preparing a solder ball preform; melting the preform into a liquid solder ball under a protective atmosphere using a heating treatment method; continuously introducing a gaseous carbon source, which decomposes at a preset reaction temperature to produce active carbon species, which nucleate and grow on the surface of the liquid solder ball, thus growing graphene in-situ on the surface of the liquid solder ball; stopping the introduction of the gaseous carbon source and cooling to room temperature to obtain a solder ball with a graphene film coating on its surface. This invention integrates solder ball forming and in-situ graphene growth, significantly reducing the surface oxidation of the solder ball during preparation, storage, and soldering, reducing flux usage, lowering the risk of voids and residual corrosion at the solder interface, and controlling the solidification and diffusion process at the solder interface to improve soldering quality.

Description

Technical Field

[0001] This invention relates to the field of electronic packaging material preparation and in-situ construction of two-dimensional functional thin films, specifically to a method for in-situ growth of graphene during solder ball preparation and solder balls. Background Technology

[0002] With the rapid development of technologies such as 5G mobile communication, artificial intelligence, the Internet of Things, power electronics, advanced driver assistance systems, and high-performance computing, electronic devices are continuously evolving towards high-density integration, high power density, high frequency and high speed, and miniaturization. As a key material for achieving electrical connections and mechanical support between chips, packaging substrates, and circuit boards, the reliability of solder joint interconnect structures directly affects the service life and operational stability of electronic packaged devices. In ball grid array packaging, wafer-level packaging, and flip-chip packaging, tin-based solder balls have become the mainstream interconnect material.

[0003] However, surface oxidation is a common problem in the preparation, storage, and reflow soldering of existing solder balls. Due to the high chemical reactivity of tin and tin-based alloys, they readily react with oxygen and moisture in the air during high-temperature preparation, transportation, and storage, forming a surface oxide film. The presence of this oxide film significantly reduces the wettability and solderability of the solder ball, increases interfacial contact resistance during soldering, leads to poor solder joint formation, and further induces defects such as pillow effect, cold solder joints, solder beads, and interface discontinuities.

[0004] To remove oxide films, existing processes typically rely on flux. While flux can reduce the surface oxide layer during soldering, it also introduces new problems. For example, flux residues are prone to hygroscopicity and the formation of corrosive substances, adversely affecting the solder joint interface and surrounding circuitry. Its volatilization and decomposition processes can also create voids within the solder joint, reducing its mechanical strength, thermal conductivity, and thermal cycling stability. For small-sized solder balls and high-density array packages, uniform flux coating and residue control are even more challenging, significantly narrowing the process window. Furthermore, as package sizes decrease and service conditions become more demanding, the growth of intermetallic compounds, element diffusion, and solidification evolution at the solder interface have an increasingly significant impact on solder joint reliability. Existing technologies primarily improve solder joint quality by adjusting alloy composition, soldering profiles, or flux systems, but their ability to continuously and stably control the interface microstructure remains limited. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention proposes a method for in-situ growth of graphene during solder ball preparation and a solder ball thereof. This addresses the technical problems of existing tin-based solder balls, which are prone to surface oxidation during preparation, storage, and soldering. The reliance on flux to remove the oxide layer leads to soldering defects and performance losses. Furthermore, existing control methods cannot stably manage the interface microstructure, ultimately resulting in a significant reduction in the reliability of solder joint interconnection.

[0006] The technical solution adopted in this invention is as follows: In a first aspect, a method for in-situ growth of graphene during solder ball preparation is provided, comprising the following steps: Preparation of welding ball preforms; Under a protective atmosphere, a heat treatment method is used to melt the preformed welding ball and transform it into a liquid welding ball; A gaseous carbon source is continuously introduced. After the gaseous carbon source is decomposed at a preset reaction temperature, it produces active carbon species. The active carbon species nucleate and grow on the surface of the liquid solder ball, and graphene grows in situ on the surface of the liquid solder ball. Stop introducing the gaseous carbon source and cool down to room temperature to obtain solder balls with a graphene film coating on the surface.

[0007] Furthermore, the raw materials for preparing the solder ball preform can be one or more of tin, tin-silver, tin-copper, and tin-silver-copper.

[0008] Furthermore, the heating treatment is performed under a protective atmosphere, wherein the protective atmosphere is argon and / or hydrogen.

[0009] Furthermore, the gaseous carbon source includes one or more of methane and ethylene; the volumetric flow rate of the gaseous carbon source is 0.5-10 sccm when it is introduced.

[0010] Furthermore, the preset reaction temperature is 700-1100℃.

[0011] Furthermore, the environmental pressure during the graphene growth process is 0.01-1 atm.

[0012] Furthermore, graphene is grown in situ on the surface of the liquid solder ball for a growth time of 0.1-10 hours.

[0013] Furthermore, the graphene has 1-5 layers.

[0014] Secondly, a graphene solder ball is provided, which is prepared using the method described in the first aspect.

[0015] Secondly, the application of the graphene solder balls described in the second aspect is provided in ball grid array packaging, wafer-level packaging, flip chip packaging, microelectronic interconnects, and high-reliability electronic packaging.

[0016] As can be seen from the above technical solution, compared with the prior art, the beneficial technical effects of the present invention are as follows: In-situ grown graphene films can continuously coat the surface of solder balls, forming an effective barrier layer during the cooling, storage and use of the solder balls, significantly inhibiting the oxidation of the solder ball surface; As the oxidation level on the surface of the solder ball decreases, the dependence on highly active flux during the welding process is reduced, which helps to reduce problems such as flux residue, interface corrosion and internal voids in the solder joint. The graphene coating can regulate the diffusion and solidification process at the welding interface, which helps to suppress abnormal growth of the interface structure and improve the integrity and uniformity of the weld interface. Meanwhile, the solder ball forming and graphene coating construction are coupled and completed in the same heat treatment process, eliminating the need for additional transfer, coating or post-treatment steps, which significantly simplifies the process flow. Attached Figure Description

[0017] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. In all the drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, the elements or parts are not necessarily drawn to scale.

[0018] Figure 1 This is a schematic diagram of the method for in-situ growth of graphene during the preparation of solder balls according to an embodiment of the present invention; Figure 2 The images shown are scanning electron microscope images and Raman spectroscopy characterization results of graphene in situ grown on the surface of solder balls in Example 1 of this invention. Figure 3 The images shown are scanning electron microscope images and Raman spectroscopy characterization results of graphene in situ grown on the surface of tin-copper solder balls in Example 2. Figure 4 The images show scanning electron microscope images and Raman spectral characterization results of the solder balls without graphene growth in Comparative Example 1. Figure 5 This is a schematic diagram of the welding interface between graphene solder balls and ordinary solder balls on a copper substrate according to the present invention. Figure 6 This is a schematic diagram comparing the shear properties of the graphene solder balls of this invention and ordinary solder balls after welding. Detailed Implementation

[0019] The embodiments of the technical solution of the present invention will now be described in detail with reference to the accompanying drawings. These embodiments are merely illustrative of the technical solution of the present invention and are therefore intended to limit the scope of protection of the present invention.

[0020] It should be noted that, unless otherwise stated, the technical or scientific terms used in this application should have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0021] The inventors of this application have discovered that graphene, as a typical two-dimensional carbon material, possesses excellent electrical conductivity, thermal conductivity, chemical stability, and high barrier properties against oxygen and moisture, and has received widespread attention in recent years in the fields of metal surface protection, functional coatings, and interface engineering. Further research by the inventors revealed that if graphene powder is dispersed and doped into solder, problems such as graphene agglomeration, poor dispersibility, and difficulty in forming a continuous surface barrier arise. Furthermore, if graphene is first prepared on other substrates and then transferred to the solder ball surface, the processing technology is complex, the interfacial adhesion is limited, and it is difficult to meet the requirements for mass production and high consistency of solder balls. Therefore, the inventors of this application considered that if a graphene film could be grown in situ directly on the surface of the liquid solder ball during the process of melting solid wafers into balls, it would be possible to construct a continuous and dense surface protective layer, endowing the solder ball with antioxidant and interfacial control capabilities from the initial stage of solder ball formation.

[0022] In view of the above research results, this application proposes a method for in-situ growth of graphene during solder ball preparation, comprising the following steps: S1. Preparation of welding ball preform In this embodiment, the raw material for preparing the solder ball preform can be selected from tin-based solder systems such as tin, tin-silver, tin-copper, and tin-silver-copper, and the preferred form of the raw material is foil. The metal foil is prepared into the solder ball preform, and the preparation method is not limited; it can be implemented in any feasible manner according to existing technology, such as by stamping, die-cutting, or laser cutting. The foil thickness is 10-500 mm. m, preferably 10-100 m.

[0023] The preform of the solder ball is preferably in the shape of a disc, which facilitates the formation of solder balls in subsequent steps. For the disc shape, those skilled in the art should understand that the preform as a whole presents a disc-shaped solid structure, and its overall shape falls within the category of circular. Its outer contour is not uniquely limited; it can be a standard circular shape with symmetrical edges and regular dimensions, or it can be a near-circular structure with undulating contour lines and an irregular shape. All of these appearances are classified as disc-shaped. The diameter of the disc-shaped solder ball preform can be set to 0.1-10 mm, preferably 1-5 mm, depending on the target solder ball size.

[0024] In some embodiments, the shape of the welding ball preform can also be square or triangular.

[0025] S2. Under a protective atmosphere, a heat treatment method is used to melt the circular weld ball preform into a liquid weld ball. The key point of this step is to heat-treat the disc-shaped solder ball preforms under a protective atmosphere to prevent oxidation during the melting and transformation of the disc-shaped solder ball preforms into liquid solder balls. The heat treatment method is not limited. In some embodiments, the disc-shaped preforms can be arranged in an orderly manner on a high-temperature resistant substrate, and then the substrate can be placed in the reaction chamber of a tube furnace. Under a protective atmosphere, the temperature inside the reaction chamber is raised above the melting point of the disc-shaped solder ball preforms. Different materials of the disc-shaped solder ball preforms correspond to different melting points. After the disc-shaped preforms melt, they shrink under surface tension to form liquid solder balls.

[0026] In specific implementations, the high-temperature resistant substrate can be a quartz plate, an alumina ceramic plate, or a boron nitride plate, or any of the above three types of plates with grooves, which facilitates the formation of liquid solder balls during the balling process and keeps them separated after balling.

[0027] In a specific implementation, argon and / or hydrogen are used as the protective atmosphere, with a volumetric flow rate of 50-3000 sccm. The target temperature for heating within the tubular furnace reaction chamber is 700-1100℃, with a heating rate of 5-30℃ / min; preferably, the target temperature is 850-1050℃, and the heating rate is 15-20℃ / min. The reason for setting the above target temperature is that the gaseous carbon source in the next step needs to be decomposed under high-temperature conditions, so heating to the target temperature in one go will result in better ball forming in subsequent steps.

[0028] S3. A gaseous carbon source is continuously introduced. After the gaseous carbon source decomposes at a preset reaction temperature, it produces active carbon species. These active carbon species nucleate and grow on the surface of the liquid solder ball, resulting in in-situ growth of graphene on the surface of the liquid solder ball. In this step, the pressure in the tubular furnace reaction chamber is adjusted to 0.01-1 atm, and a gaseous carbon source is introduced into the reaction chamber; the gaseous carbon source can be one or more of methane and ethylene, and the volumetric flow rate of the gaseous carbon source is 0.5-10 sccm.

[0029] In some embodiments, a gaseous carbon source may be introduced under a protective atmosphere, wherein the protective gas is argon and / or hydrogen, and the volume flow ratio of the protective gas to the gaseous carbon source is 1-104:1, preferably 10-103:1.

[0030] Gaseous carbon sources are pyrolyzed under high-temperature conditions (850-1050℃). The resulting active carbon species migrate, nucleate, and grow on the surface of liquid solder balls, thereby forming a graphene coating layer on the outer surface of the solder balls. Those skilled in the art should understand that active carbon species include highly active carbon-containing microparticles, carbon atoms, and carbon free radicals generated after the carbon source is pyrolyzed. These species possess chemical reactivity and can be deposited, nucleated, and grown into graphene on the substrate surface.

[0031] In this step, graphene is grown in situ on the surface of the liquid solder ball for 0.1-10 hours, preferably 0.2-4 hours. The graphene grown in situ on the surface of the liquid solder ball can be single-layer graphene, double-layer graphene, or 3-5-layer graphene. Excessive graphene layer thickness reduces the bonding strength of the welding interface; controlling the number of graphene layers to 1-5 layers provides effective interface control while ensuring the bonding strength of the welding interface.

[0032] S4. Stop introducing the gaseous carbon source and cool to room temperature to obtain solder balls with a graphene film coating on the surface. The gaseous carbon source is stopped, and the temperature is lowered to room temperature. The liquid solder balls with graphene grown in situ on the surface solidify, resulting in solder balls with a graphene film coating on the surface. The cooling rate is 5-100℃ / min, preferably 10-50℃ / min.

[0033] In some embodiments, cooling may be performed in a protective atmosphere, wherein the protective gas is argon and / or hydrogen, and the volumetric flow rate is 50-3000 sccm.

[0034] The key to the above technical solution lies in utilizing the liquid metal surface formed during the melting and spherical formation of solder ball alloy wafers at high temperatures as a dynamic substrate for in-situ graphene growth. The liquid solder ball surface possesses excellent fluidity and high flatness, reducing the adverse effects of solid grain boundaries, surface steps, and grain orientation on graphene nucleation and expansion. Simultaneously, the gaseous carbon source decomposes into active carbon species under the combined action of high temperature and the liquid metal surface. These active carbon species migrate and reconstruct in an orderly manner on the solder ball surface, ultimately forming a continuous and dense graphene film. The resulting graphene film remains on the outer surface of the solder ball after cooling and solidification, continuously blocking oxygen and moisture during subsequent storage and welding, significantly reducing the surface oxidation rate. Furthermore, this graphene interface layer can influence local interface diffusion, solidification nucleation, and microstructure evolution during welding, thereby improving the microstructure and service reliability of the solder joint. The following describes the method for in-situ graphene growth during solder ball preparation, based on specific experimental procedures: Example 1

[0035] Select a thickness of 10 Tin foil of size m was used as the solder ball alloy material, and tin disc-shaped preforms with a diameter of 0.1 mm were prepared by laser cutting. The obtained disc-shaped preforms were then arranged in a 3×10 array on a grooved quartz plate.

[0036] A quartz plate carrying a tin wafer-shaped preform was placed in the middle of a quartz sleeve and then placed in the isothermal zone of a tube furnace. First, 50 sccm of argon gas was introduced into the reaction system, and the temperature was raised to 700°C at a rate of 5°C / min. During this process, the tin wafer-shaped preform melted and formed liquid solder balls under surface tension. After the system stabilized, the pressure in the reaction chamber was adjusted to 0.01 atm, and 1 sccm of ethylene was introduced as a gaseous carbon source. The reaction was carried out at 700°C for 0.1 h. After the reaction was completed, the ethylene supply was stopped, and the protective atmosphere was maintained while the temperature was lowered to room temperature at a rate of 5°C / min, yielding solder balls with a graphene film coating on their surface.

[0037] Scanning electron microscopy (SEM) observation of the obtained samples revealed a uniform and continuous black thin film coating on the solder ball surface, exhibiting good coverage. Raman spectroscopy was performed at approximately 1350 cm⁻¹. -1 1580cm -1 and 2700cm -1 Distinct D, G, and 2D peaks were detected nearby, with the G and 2D peaks being clear and the D peak being relatively weak, indicating that the obtained carbon layer has a good degree of graphitization. Combined with peak shape analysis, the formed film is mainly composed of bilayer or at least layered (3-5 layers) graphene.

[0038] The surface morphology of the obtained graphene solder balls was observed after being stored in room temperature air for 7 and 30 days. The results showed that the surface of the solder balls still maintained high integrity, and only slight signs of oxidation were observed, indicating that the graphene coating layer prepared by the present invention can significantly reduce the degree of oxidation of the solder balls during storage.

[0039] Example 2

[0040] A 100μm thick tin-copper alloy foil was selected as the raw material and stamped into a circular preform using a 5mm diameter die. The preform was then arranged in a 4×15 array on a grooved boron nitride plate.

[0041] A boron nitride plate carrying a tin-copper alloy disc-shaped preform was placed in the middle of a quartz sleeve and then placed in the isothermal zone of a tube furnace. Argon gas at 1500 sccm was introduced into the reaction system, and the temperature was raised to 1100°C at a rate of 30°C / min, causing the tin-copper alloy disc-shaped preform to melt and form liquid solder balls. The chamber pressure was then adjusted to 0.5 atm, and ethylene at 5 sccm was introduced as a gaseous carbon source. The reaction was carried out at 1100°C for 4 hours. After the reaction, the ethylene supply was stopped, and the temperature was lowered to room temperature at a rate of 100°C / min, yielding tin-copper solder balls with two layers of graphene film coated on their surface.

[0042] The samples were characterized using scanning electron microscopy and Raman spectroscopy. The results showed that a relatively uniform graphene coating layer was formed on the surface of the solder balls, and the Raman spectrum exhibited typical graphene characteristic peaks. Compared with Example 1, under conditions of higher temperature and longer growth time, the graphene coverage was higher, and a more obvious bilayer structure was observed.

[0043] After reflow soldering tests on the graphene solder ball, observation of the solder joint interface revealed that the solder joint interface formed by the graphene solder ball was smoother and denser, and the number of voids and discontinuous defects at the interface was significantly reduced. This indicates that the method also has a positive effect on improving the soldering interface quality of tin-copper solder balls.

[0044] Example 3

[0045] A tin-silver-copper alloy foil with a thickness of 500μm was selected and stamped into a circular preform using a mold with a diameter of 10mm. The preform was then arranged in a 5×20 array on a grooved alumina ceramic plate.

[0046] An alumina ceramic plate carrying a circular preform was placed in the middle of a quartz sleeve and then placed in the isothermal zone of a tube furnace. Argon gas at 2800 sccm and hydrogen gas at 200 sccm were introduced, and the temperature was increased to 900℃ at a rate of 15℃ / min, causing the disc to melt and form liquid solder balls. The chamber pressure was then adjusted to 1 atm, and 10 sccm of methane was introduced, reacting at 900℃ for 10 hours. After the reaction was complete, the methane was turned off, but the protective atmosphere was maintained, and the temperature was lowered to room temperature at a rate of 50℃ / min, yielding tin-silver-copper solder balls with a surface coated with five layers of graphene film.

[0047] Characterization results show that methane, as a gaseous carbon source, can also form a graphene coating layer in situ on the surface of liquid solder balls. However, compared with ethylene, due to the lower cracking activity of methane, obtaining the same coverage usually requires a relatively higher temperature or a longer reaction time. This example further demonstrates that the method of the present invention has good applicability to different gaseous carbon sources.

[0048] Example 4: Verification of Process Parameter Window To verify the process stability and applicability of the method of the present invention, the reaction temperature, reaction pressure and carbon source flow rate were investigated.

[0049] (1) Temperature effect test With other conditions remaining essentially unchanged, the reaction temperatures were set to 700℃, 850℃, 950℃, and 1100℃, respectively. The test results showed that: At 700℃, the carbon source exhibits low degradation, resulting in limited graphene coverage on the solder ball surface and localized discontinuities. When the temperature rises to 850-950℃, the solder balls show good sphericity, more uniform graphene coating, and prominent Raman characteristic peaks, indicating that this temperature range is favorable for obtaining high-quality graphene coatings. While further increasing the temperature to 1100℃ increases the graphene growth rate, some areas may experience relatively thicker carbon layer deposition. Considering uniformity of coverage, film quality, and process stability, the preferred reaction temperature is 850-1050℃.

[0050] (2) Pressure effect test The reaction pressures were set to 1 atm, 0.5 atm, 0.1 atm, and 0.01 atm, respectively. The results showed that: Moderately reducing the reaction pressure is beneficial for improving gas transport efficiency and the migration ability of carbon active species on the surface of liquid solder balls, thereby improving the uniformity of the graphene coating. However, when the pressure is too low, the carbon supply in the system is insufficient, and the surface of some samples is not completely covered. Therefore, the preferred reaction pressure range is 0.5-1 atm.

[0051] (3) Experiment on the influence of carbon source flow rate The ethylene flow rate was set to 0.5 sccm, 1 sccm, 5 sccm, and 8 sccm, respectively. The results showed that: When the flow rate is too low, the nucleation density of graphene is insufficient; When the flow rate is 1-5 sccm, a relatively uniform and continuous graphene coating layer can be obtained. When the flow rate increases to 8 sccm, a more obvious tendency for multi-layered carbon deposition appears in local areas.

[0052] Therefore, the preferred gaseous carbon source flow rate is 0.5-5 sccm.

[0053] This indicates that the present invention has a wide process window, and the graphene coating on the surface of different solder ball systems can be controllably prepared by adjusting the temperature, pressure and gas flow rate.

[0054] (4) Compatibility of reflow soldering process Furthermore, to verify the compatibility of the graphene solder balls of this invention with existing electronic packaging processes, representative samples were selected within the aforementioned process parameter window for conventional reflow soldering compatibility verification. The results show that under the commonly used reflow soldering temperature profiles for existing tin-based solder balls, the graphene solder balls can successfully complete melting, spreading, and metallurgical connection with the pads, resulting in intact solder joints. No obvious solder rejection, solder shrinkage, abnormal dewetting, or interface delamination phenomena caused by the graphene coating were observed. The solder joint morphology, collapse state, and interface continuity after soldering are comparable to ordinary solder balls, indicating that the graphene solder balls prepared by this invention have good reflow soldering process compatibility and will not significantly adversely affect soldering performance. Conversely, because the graphene coating reduces the surface oxidation degree of the solder balls during storage, under the same storage conditions, the graphene solder balls are more likely to achieve consistent solder joint formation after reflow soldering, demonstrating good practical application potential.

[0055] Comparative Example 1 This comparative example is identical to Example 1 except that no gaseous carbon source is introduced, and ordinary solder balls without graphene film coating are finally obtained.

[0056] Scanning electron microscopy (SEM) observation of the obtained samples revealed that the solder ball surface exhibited a light color and obvious oxide film characteristics. Raman spectroscopy did not observe any graphene characteristic peaks. After being stored in room temperature air for 7 days, the surface of the ordinary solder ball gradually showed more obvious roughening and oxidation marks; after 30 days of storage, the oxidation degree further intensified.

[0057] Compared with the graphene solder balls obtained in Example 1, the surface oxidation resistance of the sample in Example 1 was significantly worse, indicating that the in-situ grown graphene coating layer in this invention has a significant effect on inhibiting solder ball oxidation.

[0058] Comparative Example 2 This comparative example uses a post-treatment coating method to prepare the graphene surface layer. First, ordinary solder balls are prepared according to conventional methods. Then, the solder balls are immersed in a graphene dispersion, removed, and dried to form a graphene coating layer attached to the surface.

[0059] Observations show that although this method can attach some graphene sheets to the surface of the solder ball, the graphene layer distribution is discontinuous and has poor uniformity, and it is prone to local detachment during subsequent storage and reflow soldering. Compared with the graphene coating layer formed by in-situ growth on the surface of liquid solder balls in this invention, Example 2 is significantly inferior in terms of surface coverage integrity, interfacial bonding stability, and oxidation resistance.

[0060] To further verify the effectiveness of the method of the present invention, the surface morphology, structural features, storage antioxidant properties, and welding interface quality of the samples from Examples 1-3 and Comparative Examples 1-2 were compared and analyzed as follows: (1) Structural characteristics of graphene The solder ball samples obtained in Examples 1, 2, and 3 all exhibited obvious G and 2D peaks in their Raman spectra, with the D peak being relatively weak, indicating that a graphene coating layer with a high degree of graphitization was successfully grown on the solder ball surface. Among them, the sample obtained in Example 1 was mainly composed of bilayer or at least layered graphene, while the sample obtained in Example 2 achieved a higher degree of coverage under higher temperature and longer growth time.

[0061] (2) Surface antioxidant capacity The graphene solder balls obtained in Example 1 were compared with the ordinary solder balls obtained in Comparative Example 1 after being stored in the same air environment for 7 days and 30 days. The results showed that the graphene solder balls exhibited less surface color change and lighter oxidation traces, while the ordinary solder balls showed more obvious oxide film and roughening phenomena on their surface. This result indicates that the graphene coating can effectively reduce the surface oxidation rate of solder balls during storage.

[0062] (3) Welding interface quality The graphene solder balls obtained in Example 2 and the ordinary solder balls obtained in Comparative Example 1 were welded under the same reflow soldering conditions, and the cross-sections of the weld joints were observed. The results showed that the solder joint interface formed by the graphene solder balls was more complete and dense, with fewer pores and discontinuous areas at the interface, a more uniform distribution of the solder joint microstructure, and a thin and continuous metal compound interconnection structure at the welding interface, without any abnormally grown metal compounds. Ordinary solder balls, on the other hand, were more prone to oxidation-related interface defects, and the metal compound interconnection structure at the welding interface was coarse with obvious voids in the middle. Further shear performance testing showed that the graphene solder balls effectively suppressed the abnormal growth of metal compounds while providing effective weld strength through a continuous and uniform weld microstructure. This indicates that the method of the present invention not only helps protect the surface of the solder balls but also improves the quality of the weld formation.

[0063] (4) Comprehensive technological advantages Compared with post-coating or graphene doping methods, the in-situ growth method of the present invention can directly construct a stable graphene surface layer during the solder ball formation stage, avoiding problems such as subsequent transfer, uneven coating and weak interface adhesion. The process flow is shorter, the repeatability is better, and it is suitable for large-scale preparation.

[0064] This invention provides a method for in-situ growth of graphene during solder ball preparation and the resulting graphene solder balls. The method utilizes the liquid surface formed when solder ball alloy discs are melted into balls as a graphene growth substrate, achieving direct in-situ construction of graphene under high temperature and gaseous carbon source conditions. The resulting graphene solder balls effectively suppress surface oxidation, reduce flux dependence, improve solder interface quality, and enhance long-term solder joint reliability because the graphene film can block oxygen and moisture from contacting the solder ball surface during storage and soldering, and regulate the solidification and diffusion process at the solder interface. This invention has advantages such as simple process, wide applicability, and strong industrial compatibility, making it suitable for advanced electronic packaging and high-reliability micro-interconnects. Specifically, graphene solder balls can be widely used in ball grid array packaging, wafer-level packaging, flip-chip packaging, microelectronic interconnects, and high-reliability electronic packaging.

[0065] 1. High degree of process integration This invention couples the forming of solder balls with the construction of graphene coatings in the same heat treatment process, eliminating the need for additional transfer, coating, or post-treatment steps, thus significantly simplifying the process.

[0066] 2. Significantly inhibits oxidation of solder ball surface In-situ grown graphene films can continuously coat the surface of solder balls, forming an effective barrier layer during the cooling, storage, and use of the solder balls, significantly reducing oxide film formation.

[0067] 3. Reduce dependence on flux As the oxidation level on the surface of the solder ball decreases, the reliance on highly active flux during the welding process is reduced, which helps to reduce problems such as flux residue, interface corrosion, and internal voids in the solder joint.

[0068] 4. Improve the quality of the welding interface The graphene coating can regulate the diffusion and solidification process at the welding interface, which helps to suppress abnormal growth of the interface structure and improve the integrity and uniformity of the weld interface.

[0069] 5. Improve overall performance and long-term reliability The graphene solder balls prepared by the method of this invention have significant advantages in terms of storage stability, soldering quality, mechanical properties, thermal conductivity and long-term service reliability.

[0070] 6. Wide range of applications, easy to industrialize This invention is applicable to various tin-based solder ball systems and is compatible with conventional tube furnaces and atmosphere control equipment. It has good process scale-up potential and is suitable for mass production in the field of electronic packaging.

[0071] 7. Excellent compatibility with existing reflow soldering processes. The graphene solder balls prepared by this invention can be directly adapted to the conventional reflow soldering process of existing tin-based solder balls without the need for significant adjustments to existing equipment and soldering temperature profiles. The graphene solder balls are suitable for conventional reflow soldering processes and have good engineering application feasibility. They can achieve solder ball melting, wetting and spreading, and metallurgical connection with the solder pads under peak reflow temperature conditions of 220-260℃.

[0072] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention.

Claims

1. A method for in-situ growth of graphene during solder ball preparation, characterized in that, Includes the following steps: Preparation of welding ball preforms; Under a protective atmosphere, a heat treatment method is used to melt the preformed welding ball and transform it into a liquid welding ball; A gaseous carbon source is continuously introduced. After the gaseous carbon source is decomposed at a preset reaction temperature, it produces active carbon species. The active carbon species nucleate and grow on the surface of the liquid solder ball, and graphene grows in situ on the surface of the liquid solder ball. The gaseous carbon source was stopped, and the temperature was lowered to room temperature to obtain solder balls with a graphene film coating on the surface.

2. The method for in-situ growth of graphene during solder ball preparation according to claim 1, characterized in that, The raw materials for preparing the solder ball preform can be one or more of tin, tin-silver, tin-copper, and tin-silver-copper.

3. The method for in-situ growth of graphene during solder ball preparation according to claim 1, characterized in that, The heating treatment is performed under a protective atmosphere, wherein the protective atmosphere is argon and / or hydrogen.

4. The method for in-situ growth of graphene during solder ball preparation according to claim 1, characterized in that, The gaseous carbon source includes one or more of methane and ethylene; the volumetric flow rate of the gaseous carbon source is 0.5-10 sccm when it is introduced.

5. The method for in-situ growth of graphene during solder ball preparation according to claim 4, characterized in that, The preset reaction temperature is 700-1100℃.

6. The method for in-situ growth of graphene during solder ball preparation according to claim 4, characterized in that, The environmental pressure during graphene growth is 0.01-1 atm.

7. The method for in-situ growth of graphene during solder ball preparation according to claim 1, characterized in that, The graphene is grown in situ on the surface of the liquid solder ball for 0.1-10 hours.

8. The method for in-situ growth of graphene during solder ball preparation according to claim 7, characterized in that, The graphene has 1-5 layers.

9. A graphene solder ball, characterized in that, It is prepared by the method described in any one of claims 1-8.

10. The graphene solder ball as described in claim 9, characterized in that, Applications in ball grid array packaging, wafer-level packaging, flip chip packaging, microelectronic interconnects, and high-reliability electronic packaging.

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