Composite solder ball, method of manufacture, and stacked package structure

Abstract

The application discloses a kind of composite solder ball, preparation method and stacked package structure, comprising: composite core, by continuous phase matrix and strengthening phase are constituted, the strengthening phase accounts for 15%~30% of the total volume of core, the compression modulus of the composite core is ≥3GPa and thermal expansion coefficient is ≤55ppm / ℃;Metal transition layer, is coated in the polymer core;Tin silver alloy outer layer covering the metal transition layer.Composite core is constituted by continuous phase polymer matrix and strengthening phase fiber network, realizes high-temperature pressure resistance and low thermal expansion characteristics by specific volume ratio and mass ratio, maintains solid rigid characteristics in welding high temperature interval, directly bears mechanical load, completely eliminates the risk of interlayer height collapse, metal transition layer forms and the mechanical interlocking combination interface of core, tin silver alloy outer layer provides weldability and electrical connection function, realizes that composite solder ball can play the role of support and also can play the role of welding dual-functional technology fusion.

Description

Technical Field

[0001] This invention relates to the field of microelectronic packaging technology, specifically to a composite solder ball, its preparation method, and a stacked packaging structure. Background Technology

[0002] In stacked packaging technology, traditional solid BGA solder balls achieve electrical interconnection between modules through molten soldering. Due to the inherent properties of the solder ball material, the molten solder cannot withstand the mechanical load of the upper package layer during high-temperature reflow, resulting in significant solder joint collapse. To maintain interlayer gaps, existing technologies require the introduction of plastic support structures for auxiliary positioning.

[0003] This support structure forces the packaging design to sacrifice space utilization efficiency and requires the underfill adhesive to cure in order to disperse thermal stress. However, the mismatch in the coefficient of thermal expansion causes interfacial shear stress concentration during temperature cycling, accelerating solder joint fatigue failure. More seriously, the cured body formed by the underfill adhesive and the plastic support greatly hinders the rework and replacement of the underlying chip. Engineering practice shows that there are irreconcilable structural contradictions between existing technical solutions in terms of packaging reliability, process complexity, and maintainability. Summary of the Invention

[0004] In order to overcome the shortcomings of the prior art, the present invention aims to provide a composite solder ball, a preparation method and a stacked packaging structure, to solve the problems of easy collapse, thermal stress concentration and high maintenance difficulty in the packaging technology using traditional BGA solder balls.

[0005] To solve the above problems, the technical solution adopted by the present invention is as follows:

[0006] In a first aspect, the present invention provides a composite solder ball, comprising:

[0007] The composite core is composed of a continuous phase matrix and a reinforcing phase, wherein the reinforcing phase accounts for 15% to 30% of the total volume of the core, and the composite core has a compressive modulus ≥3GPa and a coefficient of thermal expansion ≤55ppm / ℃.

[0008] A metal transition layer is formed, which encapsulates the polymer core.

[0009] A tin-silver alloy outer layer covering the metal transition layer.

[0010] In some embodiments, the reinforcing phase is a non-metallic fiber with an aspect ratio ≥ 20:1.

[0011] In some embodiments, the non-metallic fiber is a chopped fiber, which includes glass fiber, ceramic fiber, or carbon fiber.

[0012] In some embodiments, the strengthening phase accounts for 25-35 wt% of the total core mass.

[0013] In some embodiments, the silver content of the outer layer of the tin-silver alloy is 2.9-3.1 wt%.

[0014] In some embodiments, the diameter of the composite core is Φ0.18-0.22mm;

[0015] The thickness of the metal transition layer is 4-6 μm, and the surface roughness Ra≥0.6 μm;

[0016] The thickness of the tin-silver alloy outer layer is 35-45 μm.

[0017] In some embodiments, the continuous phase matrix is ​​a thermosetting polymer that satisfies: (a) glass transition temperature Tg ≥ 150 °C; (b) compression resilience ≥ 90%.

[0018] In some embodiments, the continuous phase matrix is ​​epoxy resin.

[0019] Secondly, the present invention provides a method for preparing a composite solder ball as described above, comprising:

[0020] Composite nucleation: The continuous phase matrix raw material and the reinforcing phase filler are mixed under shear emulsification conditions to form a composite slurry, which is then granulated into microspheres to obtain the core preform; Interface activation: The surface of the core preform is subjected to plasma irradiation treatment to form an active bonding surface;

[0021] Transition layer construction: Chemically depositing a metal transition layer on the active bonding surface;

[0022] Alloy layer shape control: A dual-source electroplating process is used to simultaneously deposit tin-silver alloy on the surface of the transition layer, in which the silver ion concentration is controlled in real time within ±5% deviation.

[0023] Thirdly, the present invention provides a stacked packaging structure, including a bottom package and a top package, wherein the bottom package and the top package are electrically connected and mechanically supported by a composite solder ball as described above.

[0024] Interlayer height fluctuation after reflow soldering ≤ ±2%.

[0025] Compared with the prior art, the present invention has at least the following beneficial effects:

[0026] 1. The composite core is composed of a continuous phase polymer matrix and a reinforcing phase fiber network. It achieves high temperature compressive strength and low thermal expansion characteristics through specific volume and mass ratios. It maintains solid rigidity in the high temperature range of welding, directly bears mechanical loads, and completely eliminates the risk of interlayer collapse. The metal transition layer forms a mechanically interlocked interface with the core. The tin-silver alloy outer layer provides solderability and electrical connection functions, realizing the dual-function technology integration of the composite solder ball, which can play both a supporting role and a welding role.

[0027] 2. The enhanced phase fiber network effectively constrains the expansion behavior of the matrix, making the thermal expansion coefficient of the composite core close to that of the organic packaging substrate. This characteristic reduces the interface stress concentration during thermal cycling from the source and improves the fatigue life of the solder joint.

[0028] 3. The composite solder balls independently assume the support function, eliminating the need for the plastic bracket installation process and the bottom filling process. This design gives the package structure reversible connection characteristics, and the underlying chip can be disassembled and replaced without damage.

[0029] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. Attached Figure Description

[0030] The present invention will be further described with reference to the accompanying drawings, but the embodiments in the drawings do not constitute any limitation on the present invention. For those skilled in the art, other drawings can be obtained based on the following drawings without creative effort.

[0031] Figure 1 This is a cross-sectional schematic diagram of a composite solder ball provided in one embodiment.

[0032] Figure 2 This is a schematic flowchart of a method for preparing a composite solder ball according to one embodiment. Detailed Implementation

[0033] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0035] In the description of this invention, when a specific device is described as being located between a first device and a second device, an intermediary device may or may not be present between the specific device and the first or second device. When a specific device is described as being connected to other devices, the specific device may be directly connected to the other devices without an intermediary device, or it may not be directly connected to the other devices but may have an intermediary device.

[0036] Techniques, methods, and equipment known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and equipment should be considered part of the specification.

[0037] The applicant discovered:

[0038] In the PoP (PoP) industry, traditional BGA solder balls have significant technical drawbacks:

[0039] 1. Low yield strength leads to thermal collapse and height fluctuation.

[0040] At the high temperatures of PoP reflow soldering (typically peak >220°C), the yield strength of conventional SnAgCu solid alloy solder balls drops sharply, becoming insufficient to support the weight of the top package module.

[0041] The solder balls were compressed and deformed (collapsed), resulting in significant fluctuations in interlayer height (±15%). This height inconsistency severely affected subsequent chip assembly, heat dissipation, mechanical stability, and signal integrity, and limited the increase in the number of PoP stack layers.

[0042] To address the collapse issue, the industry commonly uses plastic brackets as mechanical supports. However, this increases additional material costs (BoM), assembly steps (increasing complexity), package height, and severely hinders the rework and repair of the underlying chip, as the bracket is typically used in conjunction with underfill.

[0043] 2. CTE mismatch leads to thermal stress cracking

[0044] Because solder joints connect different materials (silicon chip ≈ 3ppm / ℃, substrate / PCB ≈ 16-18ppm / ℃, solder ≈ 20-25ppm / ℃), they expand and contract at different rates during temperature cycling (operational or environmental changes). Thermal stress concentrates at the weakest point of the connection (usually the neck where the solder joint connects to the pad or at the IMC layer), leading to solder joint fatigue cracking and a high failure rate (>2000ppm). Reliability is the primary challenge for PoP packaging, especially in demanding applications such as automotive and industrial applications.

[0045] 3. Difficulty in returning to work

[0046] To prevent thermal stress cracking and enhance mechanical stability, the bottom chip of a PoP (Polyboard in Packaging) is often reinforced with "underfill". However, underfill creates a strong bond between the chip and the substrate. If the bottom chip fails, removing the top package and underfill is extremely difficult and can easily damage the substrate, greatly increasing rework costs and workload.

[0047] In view of this, firstly, the applicant proposes a composite solder ball that fundamentally solves the above three main defects simultaneously:

[0048] 1. Composite core support structure to solve collapse and support problems.

[0049] A composite core with high compressive modulus (≥3GPa) and excellent resilience (≥90%) is used as the core material. At the high temperatures of reflow soldering, the composite core remains solid and exhibits extremely high rigidity (far exceeding that of molten solder). It supports the weight of the top package at high temperatures, significantly resisting collapse and ensuring interlayer height stability; it perfectly replaces the support structure, achieving the dual function of "connection + support" for a single ball, simplifying the process and reducing height and cost.

[0050] 2. Low CTE composite core to alleviate thermal stress problems

[0051] Because the continuous phase matrix itself has a high CTE, the CTE of the composite core can be significantly controlled by precisely adding a reinforcing phase, achieving specific volume and mass percentages. Compared to the high CTE of traditional solder balls, a CTE of 50 ppm / ℃ is closer to that of the packaging substrate (organic material, typical value 16-25 ppm / ℃) and PCB (typical value 16-18 ppm / ℃), greatly alleviating the mismatch of thermal expansion coefficients within the solder joint and at the connection with the PCB.

[0052] 3. The coating structure solves the problems of connection and rework.

[0053] By constructing a conductive and solderable layer through chemical copper plating (transition layer) and electroplating SnAg (outer layer), the high-strength composite core and optimized stress distribution reduce the dependence on underfill, so no underfill is needed for subsequent fixation. Without the fixation of underfill, and with the soldering occurring at the interface between the plating layer (molten) and the core (non-molten), rework of the bottom chip becomes possible and relatively easy. It can be separated simply by reheating and melting the plating solder, significantly reducing the amount of rework work.

[0054] Therefore, combining Figure 1 This embodiment proposes a composite solder ball, comprising:

[0055] The composite core 10 is composed of a continuous phase matrix and a reinforcing phase. The reinforcing phase accounts for 15% to 30% of the total volume of the core. The compressive modulus of the composite core 10 is ≥3GPa and the coefficient of thermal expansion is ≤55ppm / ℃.

[0056] Metal transition layer 20, encapsulating the polymer core;

[0057] A tin-silver alloy outer layer 30 covering a metal transition layer 20.

[0058] It should be noted that, due to the inability of traditional solder balls to simultaneously provide high-temperature support and adapt to thermal expansion, this embodiment addresses the issues of high-temperature collapse and thermal stress cracking in the composite core 10 by employing a continuous phase matrix and a reinforcing phase as a rigid framework to constrain thermal expansion behavior. The core maintains its peak compressive modulus in the 217-250℃ range, while effectively reducing CTE. The metal transition layer 20 chemically bonds to the core, and its rough interface provides mechanical anchoring points. The tin-silver alloy outer layer 30, after melting, resolidifies into spheres through surface tension, achieving electrical connection. In this design, the solid-state support of the core is decoupled from the liquid-state connection of the plating layer. At high temperatures, the molten plating layer wets the solder pads, forming an electrical path, while the rigid core independently bears the mechanical load, fundamentally preventing collapse and deformation.

[0059] In one implementation, the reinforcing phase is a non-metallic fiber with an aspect ratio ≥ 20:1, and the reinforcing phase accounts for 25-35 wt% of the total mass of the core. The non-metallic fiber is a chopped fiber, including glass fiber, ceramic fiber or carbon fiber, and the continuous phase matrix is ​​epoxy resin.

[0060] Since simply adding filler can lead to interface defects and molding difficulties, this embodiment limits the fiber aspect ratio to ≥20:1 and the mass to 25-35wt%. The high aspect ratio fibers form a three-dimensional mesh truss structure in the matrix. When the composite material is under pressure, the fibers distribute the load to the entire network through the shear force transfer mechanism, effectively improving the compressive strength. The stress in the micro-area at the fiber end is concentrated and reduced, avoiding the initiation of microcracks.

[0061] For example, chopped glass fibers can effectively increase the compressive modulus of epoxy resin matrix, giving it sufficient stiffness and strength to resist collapse at high temperatures. In addition, chopped glass fibers have extremely low CTE (about 5-6 ppm / ℃), and when they are uniformly dispersed in epoxy resin, they can significantly reduce the coefficient of thermal expansion of the overall resin core. This is the key to solving thermal stress, and the chopped form is easier to achieve uniform distribution in a spherical micro-space than continuous fibers.

[0062] Because epoxy resin needs to be manufactured into high-precision microspheres, adding short-cut glass fibers (micrometer-long) helps maintain good flowability during the epoxy resin melt-forming process, ensuring the sphericity and precision of the microspheres. Long fibers or excessive filler will severely impair flowability, making it impossible to form qualified microspheres.

[0063] Micron-sized chopped glass fibers can effectively transfer loads, and their short length makes it less likely for significant stress concentration points to form at both ends within the material. Compared to long fibers, they can better ensure the uniformity and long-term reliability of composite materials, especially under cyclic stress.

[0064] Furthermore, a glass fiber content of 25-35 wt% achieves a breakthrough in performance inflection point through the percolation threshold theory: when the mass content is <25 wt%, the isolated distribution of fibers cannot form a continuous force transmission network, and the improvement effect on the matrix CTE and modulus is not significant enough, making it difficult to effectively reduce the CTE, and the improvement in anti-collapse strength at high temperature may also be insufficient; when the mass content is >35 wt%, the matrix cannot completely cover the fibers, resulting in interface defects, the viscosity of the resin mixture increases sharply, and the fluidity becomes very poor, which poses a huge challenge to the highly precise microsphere molding process (requiring high roundness and no defects), glass fiber agglomeration and uneven distribution affect performance consistency, and it is impossible to form a perfect sphere.

[0065] Therefore, 25-35wt% is the optimal balance between "effective CTE / modulus improvement", "processability (good flowability and sphericity)" and "final core mechanical property reliability". Below the lower limit (25%), the effect is insufficient, while above the upper limit (35%), it is difficult to mass-produce high-quality microspheres.

[0066] In one implementation, the silver content of the tin-silver alloy outer layer 30 is 2.9-3.1 wt%.

[0067] It should be noted that pure tin (Sn) is relatively brittle. Adding an appropriate amount of silver (Ag) can significantly improve the ductility (toughness) and fatigue resistance of Sn-based solders. This is crucial for solder joints subjected to thermal cycling stress, helping to absorb some of the stress, delaying the initiation and propagation of cracks, and thus improving thermal cycling life.

[0068] Since silver content directly affects the melting point, 2.9-3.1 wt% Ag is a balanced ratio range that yields a near-eutectic or almost eutectic composition, keeping the melting point relatively constant (approximately 217-220℃). This allows the mechanical properties (strength, ductility) and fatigue resistance of the outer layer 30 of the tin-silver alloy to reach a relatively optimal balance. Below 2.9% Ag, ductility and fatigue resistance begin to decline; above 3.1% Ag, the resulting Ag3Sn particles are too large, which reduces ductility and may even slightly increase the melting point. By limiting the silver content, the following can be achieved:

[0069] The coating is precisely melted and wetted within a set temperature range to ensure the stability of the reflow process;

[0070] To avoid an increase in the solid-liquid coexistence zone due to component shift, and to prevent thermal tearing or void formation, i.e., to eliminate the risk of a pasty area;

[0071] Precise composition control ensures that the surface tension of the molten alloy is controllable. Within the rigid support framework provided by the resin core, the molten SnAg layer can be precisely resolidified under the action of surface tension to form a perfect sphere, thus ensuring reflow self-shaping.

[0072] As one implementation method, the diameter of the composite core 10 is Φ0.18-0.22mm, and the size fluctuation is controlled to ≤0.5μm by microfluidic granulation technology to ensure the consistency of interlayer height in the stacked packaging;

[0073] The thickness of the metal transition layer 20 is 4-6 μm, and the surface roughness Ra≥0.6 μm. Plasma irradiation generates micron-level pits on the epoxy surface, and the metal infiltrates into the transition layer to form a mechanical interlocking structure.

[0074] The outer layer 30 of the tin-silver alloy has a thickness of 35-45μm. It is electroplated using a current density gradient method to gradually change the grain size of SnAg from columnar to equiaxed, thereby eliminating the internal stress of the plating layer.

[0075] In one implementation, the continuous phase matrix is ​​a thermosetting polymer that satisfies the following:

[0076] (a) Glass transition temperature Tg≥150℃, ensuring that the matrix is ​​in the glass transition region before the peak reflux temperature (molecular chain segments are frozen), and the compressive elastic modulus retention rate>85%; (b) Compression resilience≥90%, this limitation is due to the control of epoxy crosslinking density, after unloading the polymer chain entropy elastic drive deformation recovery, completely eliminating the accumulation of plastic deformation.

[0077] Secondly, combining Figure 2 This embodiment provides a method for preparing a composite solder ball as described above, comprising:

[0078] Composite nucleation: The continuous phase matrix raw material and the reinforcing phase filler are mixed under shear emulsification conditions to form a composite slurry, which is then granulated into microspheres to obtain the core preform; Interface activation: The surface of the core preform is subjected to plasma irradiation treatment to form an active bonding surface;

[0079] Transition layer construction: A metal transition layer 20 is chemically deposited on the active bonding surface;

[0080] Alloy layer shape control: A dual-source electroplating process is used to simultaneously deposit tin-silver alloy on the surface of the transition layer, in which the silver ion concentration is controlled in real time within ±5% deviation.

[0081] It should be noted that during the composite nucleation stage, the reinforcing phase filler is subjected to dynamic fluid stress dispersion in the shear emulsification field, and the high shear rate peels off the fiber aggregates. Combined with the interfacial tension self-constraint effect of microfluidic granulation, 25-40 vol% of short-cut fibers are uniformly dispersed in the continuous phase matrix, achieving a rigid-thermal matched core with a compressive modulus ≥3 GPa and a thermal expansion coefficient ≤55 ppm / ℃. In the interfacial activation stage, oxygen-containing plasma is used to bombard the surface of the preform. Highly reactive oxygen free radicals preferentially etch the CH bonds in the epoxy resin, generating micron-sized pits on the surface and simultaneously grafting carboxyl functional groups. This process constructs a mechanical anchoring morphology and chemisorption sites with Ra≥0.6 μm. This lays a strong foundation for the subsequent metal layer; the transition layer is constructed using an electrochemical deposition process, which catalytically reduces metal ions on the activated surface and guides the directional deposition of metal atoms using surface active sites, achieving nanoscale coating integrity of the 4-6μm transition layer and avoiding core swelling caused by electrolyte penetration; the alloy layer shape control process innovatively adopts a dual-source electroplating architecture, where the tin source electrolyte and the silver source electrolyte are physically isolated by an ion exchange membrane but coupled in the current loop, and the pulse electroplating duty cycle is adjusted in real time with the help of a silver ion concentration sensor, suppressing the fluctuation of the deposited silver content within the range of ±0.1wt%, and simultaneously achieving uniform growth of a coating thickness of 35-45μm and precise control of the silver content of 2.9-3.1wt%.

[0082] Thirdly, this embodiment provides a stacked packaging structure, including a bottom package and a top package, wherein the bottom package and the top package are electrically connected and mechanically supported by a composite solder ball as described above;

[0083] Interlayer height fluctuation after reflow soldering ≤ ±2%.

[0084] The top package is a BGA or CSP package. In this embodiment, composite solder balls are used to achieve both connection and support. This is directly applied in the BGA / CSP field without using plastic support structures or bottom filler glue, thus eliminating auxiliary structures.

[0085] Specifically, composite solder balls form an array of support pillars in the PoP: during reflow, the outer SnAg layer melts and wets the pads, while the core remains solid, supporting the top package. Since the core's compressive modulus (3 GPa) is greater than the package modulus (1.5 GPa), height fluctuations are solely due to core size tolerances (±1.5 μm). This structure, replacing the traditional plastic support, reduces interlayer thermal resistance by 40°C, and the omission of the bottom filler process lowers the rework temperature from 200°C to 183°C (SnAg melting point), enabling non-destructive chip removal.

[0086] For example:

[0087] In this embodiment, a composite core 10 with a diameter of Φ0.20mm is used, which is composed of bisphenol A type epoxy resin and 30wt% chopped glass fiber reinforcement. The chopped glass fiber accounts for 35% of the total volume of the core, with a diameter of Φ0.5μm, an aspect ratio of 50:1, and a compression resilience of >95%.

[0088] After activation by oxygen-nitrogen plasma (O2 / N2 = 3:1, 300W / 5min), a 5μm copper transition layer is chemically deposited with a surface roughness Ra = 0.8μm to enhance adhesion. Then, a SnAg3.0 alloy outer layer is electroplated with a silver content of 3.0±0.1wt% and a thickness of 40μm, resulting in a finished product diameter of Φ0.30mm. Finally, the coating is reflowed and shaped at 230℃ for 30s to liquefy and solidify the coating into a perfect sphere.

[0089] The composite solder balls prepared through the above embodiments achieve a collapse resistance strength of 105 MPa at 250°C, while the traditional BGA solder balls only achieve a collapse resistance strength of 28 MPa at 250°C, representing a 275% improvement. This embodiment achieves a PoP interlayer height fluctuation of ≤±1.5%, while the traditional BGA solder balls have a PoP interlayer height fluctuation of ≤15%, a 10-fold reduction in fluctuation rate. After accelerated thermal cycling verification at -40~125°C, the solder joint life exceeds 5000 cycles, while the thermal cycling life of traditional BGA solder balls does not exceed 1500 cycles, representing a 233% improvement over traditional solutions. Simultaneously, three disruptive effects are achieved:

[0090] 1) The diameter of the solder ball is self-corrected to Φ0.300±0.001mm after reflow shaping (roundness error ≤0.3μm);

[0091] 2) Because the core CTE is approximately 50 ppm / ℃ (close to the PCB's 18 ppm / ℃), thermal stress is reduced by 70%;

[0092] 3) The single-ball integrated connection and support function replaces the plastic bracket and bottom filling process, which reduces the rework time of PoP packaging by 80% and the stacking thickness by 40%.

[0093] This embodiment, through the synergistic solution of "composite core 10-coating", systematically solves the technical contradictions of mechanical stability, thermal reliability and maintainability in stacked packaging by means of structural innovation and micron-level process control.

[0094] In summary, compared with the prior art, the above embodiments have at least the following technical advantages:

[0095] The composite core 10 is composed of a continuous phase polymer matrix and a reinforcing phase fiber network. It achieves high temperature compressive strength and low thermal expansion characteristics through specific volume and mass ratios. It maintains solid rigidity characteristics in the high temperature range of welding, directly bears mechanical loads, and completely eliminates the risk of interlayer collapse. The metal transition layer 20 forms a mechanically interlocked interface with the core. The tin-silver alloy outer layer 30 provides solderability and electrical connection functions, realizing the dual-function technology integration of the composite solder ball, which can play both a supporting role and a welding role.

[0096] The enhanced phase fiber network effectively constrains the expansion behavior of the matrix, making the thermal expansion coefficient of the composite core 10 close to that of the organic packaging substrate. This characteristic weakens the interface stress concentration during thermal cycling from the source and improves the fatigue life of the solder joint.

[0097] The composite solder balls independently provide support, eliminating the need for plastic bracket installation and bottom filling. This design enables the package structure to have reversible connection characteristics, allowing the underlying chip to be disassembled and replaced without damage.

[0098] The above embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention shall fall within the scope of protection claimed by the present invention.

Claims

1. A composite solder ball, characterized in that, include: The composite core is composed of a continuous phase matrix and a reinforcing phase, wherein the reinforcing phase accounts for 15% to 30% of the total volume of the core, and the composite core has a compressive modulus ≥3GPa and a coefficient of thermal expansion ≤55ppm / ℃. A metal transition layer is formed over the composite core; The tin-silver alloy outer layer covering the metal transition layer; The strengthening phase accounts for 25-35 wt% of the total core mass.

2. The composite solder ball as described in claim 1, characterized in that, The reinforcing phase is a non-metallic fiber with an aspect ratio ≥ 20:

1.

3. A composite solder ball as described in claim 2, characterized in that, The non-metallic fiber is a chopped fiber, which includes glass fiber, ceramic fiber or carbon fiber.

4. A composite solder ball as described in any one of claims 1 to 3, characterized in that, The silver content of the outer layer of the tin-silver alloy is 2.9-3.1 wt%.

5. A composite solder ball as described in claim 4, characterized in that, The diameter of the composite core is Φ0.18-0.22mm; The thickness of the metal transition layer is 4-6 μm, and the surface roughness Ra≥0.6 μm; The thickness of the tin-silver alloy outer layer is 35-45 μm.

6. A composite solder ball as described in claim 5, characterized in that, The continuous phase matrix is ​​a thermosetting polymer that satisfies the following: (a) Glass transition temperature Tg ≥ 150℃; (b) Compression resilience ≥90%.

7. A composite solder ball as described in claim 6, characterized in that, The continuous phase matrix is ​​epoxy resin.

8. A method for preparing a composite solder ball as described in any one of claims 1 to 7, characterized in that, include: Composite nucleation: The continuous phase matrix raw material and the reinforcing phase filler are mixed under shear emulsification conditions to form a composite slurry, which is then granulated into microspheres to obtain the core preform; Interface activation: The surface of the core preform is subjected to plasma irradiation treatment to form an active bonding surface; Transition layer construction: A metal transition layer is chemically deposited on the active bonding surface; Alloy layer shaping: A tin-silver alloy is simultaneously deposited on the surface of the transition layer using a dual-source electroplating process, wherein the silver ion concentration is controlled in real time within ±5% deviation.

9. A stacked packaging structure, comprising a bottom package and a top package, characterized in that, The bottom package and the top package are electrically connected and mechanically supported by a composite solder ball as described in any one of claims 1 to 7; Interlayer height fluctuation after reflow soldering ≤ ±2%.

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