Solder-free bonding method for interconnecting flexible micro LEDs with flexible circuits

Abstract

This invention discloses a solderless bonding method for interconnecting flexible micro-LEDs with flexible circuits, belonging to the field of flexible Micro-LED display interconnect technology. The method includes fabricating three layers of metal bumps on chip electrodes, forming a composition-matched receiving layer on a flexible substrate, aligning and bonding them after atomic-level cleaning, and achieving solid-state diffusion bonding under low temperature and low pressure to form a stable intermetallic compound interface. This application effectively solves the problems of thermal stress mismatch, interface delamination, and unstable contact resistance under bending caused by solder bonding, improving the reliability and mass production compatibility of high-density flexible Micro-LED devices.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor device manufacturing technology, specifically, it relates to a method for interconnecting flexible micro light-emitting diodes and flexible circuits without solder bonding. Background Technology

[0002] Flexible display technology, as a core carrier of next-generation human-computer interaction interfaces, has shown great application potential in wearable devices, curved screen terminals, and bio-integrated electronics in recent years. Its core lies in achieving high-density, high-reliability interconnection between micro-LED arrays and flexible circuit substrates, balancing mechanical flexibility and electrical performance. However, the solder bonding process widely used in traditional rigid packaging relies on high-temperature reflow and intermetallic compound formation, which easily leads to thermal stress mismatch, interface delamination, and material embrittlement on flexible substrates, severely restricting the long-term stability of devices under repeated bending or stretching conditions. Furthermore, the solder bump size is difficult to shrink to below the micrometer level, limiting pixel density improvements and potentially causing short circuits between adjacent electrodes due to capillary effects, affecting display uniformity and yield.

[0003] Solderless bonding technology has emerged as a key path to overcome the aforementioned bottlenecks. It aims to achieve electrical connections between chips and circuits without introducing third-party molten materials through physical contact, van der Waals forces, covalent bonds, or direct metal diffusion. Theoretically, this method can avoid high-temperature processes, reduce interface thermal resistance, and support interconnect structures with smaller pitches. However, existing solderless solutions largely rely on precise alignment and ultra-high surface flatness, making them extremely sensitive to the inherent deformation fluctuations and micro-roughness of flexible substrates. This results in insufficient actual contact area, large dispersion in contact resistance, and a tendency for instantaneous disconnections or impedance surges during dynamic bending.

[0004] In existing technologies, some studies have attempted to improve contact reliability using strategies such as nanopillar arrays, elastic conductive adhesives, or laser-assisted local fusion, but significant drawbacks remain: on the one hand, the fabrication process of nanostructures is complex, making it difficult to achieve large-area compatibility with roll-to-roll production; on the other hand, while elastic media can buffer deformation, they introduce an additional dielectric layer, increasing parasitic capacitance and weakening high-frequency response. More importantly, current methods generally lack real-time sensing and adaptive control mechanisms for the contact state of flexible interfaces under multi-physics coupling (such as electro-thermal-mechanical synergy), and cannot dynamically adjust interconnection strategies based on bending curvature, temperature drift, or current load. Therefore, in high-density flexible Micro-LED display systems, there is an urgent need for a solder-free intelligent interconnection method that combines low impedance stability and mechanical robustness to solve multiple technical challenges such as irreversible static bonding, uncontrollable dynamic contact, and poor process compatibility. Summary of the Invention

[0005] The purpose of this invention is to provide a method for interconnecting flexible micro light-emitting diodes and flexible circuits without solder bonding, which mainly solves the technical problems caused by the use of traditional solder connection methods in existing flexible display or lighting systems, such as interface stress concentration, thermal expansion mismatch, mechanical flexibility degradation, and insufficient long-term reliability.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A method for interconnecting a flexible micro LED with a flexible circuit without solder bonding includes the following steps:

[0008] S1, a metal bump structure is prepared in the bottom electrode region of the flexible micro light-emitting diode chip. The metal bump structure is composed of a bottom adhesion layer, an intermediate diffusion barrier layer and a top active bonding layer stacked in sequence.

[0009] S2, a metal receiving layer matching the metal bump structure is prepared in the corresponding pad area of ​​the flexible circuit substrate, the metal receiving layer having the same chemical composition as the top active bonding layer;

[0010] S3, perform atomic-level cleaning treatment on the surfaces of the metal bump structure and the metal receiving layer to remove oxides, hydrocarbon contaminants and adsorbed water molecules;

[0011] S4, the flexible micro light-emitting diode chip is aligned to a predetermined position on the flexible circuit substrate using a precision pick-and-place device, so that the metal bump structure and the metal receiving layer form surface contact;

[0012] S5, under an inert gas protective environment, a preset pressure is applied and the temperature is heated to below the melting point of any metal component, causing an atomic-level solid-phase diffusion reaction to occur between the top active bonding layer and the metal receiving layer, forming a continuous and dense intermetallic compound interface, thereby completing a solderless permanent electrical connection.

[0013] Furthermore, in step S1, the method for preparing the corresponding metal bump structure is as follows:

[0014] S11, the bottom electrode region of the flexible micro LED chip is exposed by dry etching or laser lift-off process, and plasma cleaning is performed to remove surface oxides and organic contaminants.

[0015] S12, using physical vapor deposition combined with photolithography and wet etching processes, a bottom adhesion layer, an intermediate diffusion barrier layer and a top active bonding layer are sequentially formed in the bottom electrode region.

[0016] S13, perform chemical mechanical polishing on the top surface of the metal bump structure to ensure that its coplanarity deviation meets the preset process standard.

[0017] Furthermore, in step S2, the method for preparing the corresponding metal receiving layer is as follows:

[0018] S21, a metal receiving layer is formed on a flexible circuit board made of polyimide, polyethylene naphthalate or ultrathin glass by sputtering, electroplating or chemical plating processes.

[0019] S22, perform photolithography and wet etching on the metal receiving layer to define the pattern;

[0020] S23, control the surface roughness of the metal receiving layer, and perform plasma activation treatment on it before bonding to enhance the surface energy.

[0021] Furthermore, the specific process of step S3 is as follows:

[0022] S31, use argon or a hydrogen-argon mixture to perform plasma cleaning on the metal bump layer and the matching metal layer;

[0023] S32, the metal surface after plasma cleaning is immersed in a formic acid aqueous solution for chemical reduction treatment;

[0024] S33, in a vacuum environment, heats up to a preset temperature at a constant heating rate and holds at that temperature for a predetermined time to complete in-situ thermal desorption.

[0025] Furthermore, the specific process of step S4 is as follows:

[0026] The bonding operation shall be carried out in an inert gas protective environment with an oxygen content of less than 10 ppm and a dew point temperature of less than -40°C.

[0027] A machine vision system is used to identify alignment marks, achieving sub-micron level spatial positioning;

[0028] The chip is vertically approached to the substrate by a precision micro-motion platform until the metal bump layer contacts the matching metal layer and pre-pressure is applied to maintain the initial bonding state.

[0029] Furthermore, the present invention also includes filling the gap area between the flexible micro light-emitting diode chip and the flexible circuit substrate with flexible encapsulating adhesive after bonding is completed. The flexible encapsulating adhesive is a silicone or polyurethane material.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] (1) This invention constructs a three-layer composite metal bump structure (adhesion layer / barrier layer / active layer) and a metal receiving layer with matching composition, and performs low-temperature solid-phase diffusion bonding under atomically clean surface conditions. This avoids high-temperature thermal shock caused by solder reflow, effectively suppresses interface peeling and microcracks caused by the difference in thermal expansion coefficient of flexible substrate, and improves the electrical stability of the device under repeated bending.

[0032] (2) This invention employs chemical mechanical polishing to control the coplanarity of bumps, plasma-chemical combined cleaning to remove surface contaminants, and precise control of bonding temperature and pressure parameters to ensure atomic-level bonding at the metal contact interface, significantly increasing the effective contact area and stabilizing the single-point contact resistance. With an Ω-level performance and batch-to-batch dispersion of less than ±15%, it meets the interconnection requirements of high-density Micro-LED arrays.

[0033] (3) The present invention introduces a low-modulus flexible encapsulant to fill the gap after bonding, which provides external mechanical buffer to resist the interfacial shear stress caused by dynamic deformation, and does not introduce a high dielectric constant medium to maintain the integrity of high frequency drive signals. At the same time, the entire process is compatible with standard semiconductor manufacturing equipment, does not require nanostructure etching or laser local melting, has roll-to-roll production expansion potential, and is suitable for mass production of large-area flexible display panels. Attached Figure Description

[0034] Figure 1 This is a cross-sectional schematic diagram of the flexible micro light-emitting diode and flexible circuit interconnection structure without solder bonding according to the present invention.

[0035] Figure 2 This is a flowchart illustrating the method of the present invention.

[0036] The names corresponding to the reference numerals in the attached figures are as follows:

[0037] 1. Flexible micro LED chip; 2. Bottom electrode area; 3. Metal bump structure; 4. Flexible circuit board; 5. Metal receiving layer; 6. Flexible encapsulating adhesive. Detailed Implementation

[0038] The present invention will be further described below with reference to the accompanying drawings and embodiments. The embodiments of the present invention include, but are not limited to, the following embodiments.

[0039] This invention discloses a method for interconnecting flexible micro light-emitting diodes and flexible circuits without solder bonding, such as... Figure 1As shown, the bonded structure includes a flexible micro LED chip 1, a bottom electrode region 2 located at its bottom, a metal bump structure 3 disposed on the bottom electrode region 2, a flexible circuit board 4, a metal receiving layer 5 formed on the surface of the flexible circuit board 4 and corresponding to the metal bump structure 3, an intermetallic compound interface formed by the metal bump structure 3 and the metal receiving layer 5 under solid-state diffusion conditions, and a flexible encapsulating adhesive 6 filling the gap between the flexible micro LED chip 1 and the flexible circuit board 4. The metal bump structure 3 and the metal receiving layer 5 are interconnected through atomically clean surface contact and under controlled thermo-pressing conditions, ultimately forming a stable and reliable electrical connection structure without the need for traditional solder materials.

[0040] In this embodiment, the metal bump structure 3 is composed of three layers stacked sequentially: a bottom adhesion layer, an intermediate diffusion barrier layer, and a top active bonding layer. The bottom adhesion layer is directly deposited on the bottom electrode region 2 of the flexible micro LED chip 1 to enhance the bonding force between the subsequent metal layer and the semiconductor electrode; the intermediate diffusion barrier layer covers the bottom adhesion layer to suppress harmful interdiffusion of different metal components during high temperature or long-term use; the top active bonding layer is located on the outermost side, and its chemical composition is completely consistent with the metal receiving layer 5 on the flexible circuit substrate 4, providing a reaction source for the subsequent low-temperature solid-phase diffusion reaction. In this embodiment, the bottom adhesion layer is a 50 nm thick titanium (Ti) film, the intermediate diffusion barrier layer is a 200 nm thick nickel (Ni) film, and the top active bonding layer is a 1.5 μm thick tin (Sn) film. Each of the above layers is deposited sequentially using physical vapor deposition (PVD) and patterned using photolithography and wet etching processes, so that the planar shape of the metal bump structure 3 is consistent with the outline of the bottom electrode region 2, and the size is controlled within the range of 15μm×15μm.

[0041] like Figure 2 As shown, in the fabrication stage of the flexible micro LED chip 1, the chip is first separated from the original growth substrate by laser lift-off or dry etching, exposing the bottom electrode region 2. Subsequently, the exposed area is cleaned with oxygen plasma to remove residual organic contaminants and the natural oxide layer. The cleaning conditions are: RF power 200W, oxygen flow rate 50sccm, and processing time 60 seconds. After cleaning, the metal bump structure 3 is deposited and patterned in a clean environment. After deposition, the top of the metal bump structure 3 is chemically mechanically polished (CMP) to control its surface coplanarity deviation within ±0.2μm, ensuring uniform surface contact with the subsequent metal receiving layer 5.

[0042] In this embodiment, the flexible circuit substrate 4 uses a 12.5 μm thick polyimide (PI) film as the substrate material, and a metal receiving layer 5 is formed on its surface by a sputtering and electroplating process. The material composition of the metal receiving layer 5 is the same as that of the top active bonding layer in the metal bump structure 3, namely pure tin (Sn), and the thickness is 1.2 μm. The metal receiving layer 5 is patterned by photolithography and wet etching processes so that it completely overlaps with the metal bump structure 3 in planar projection, and the pattern size is also 15 μm × 15 μm. In addition, alignment marks are provided on the surface of the flexible circuit substrate 4 for visual identification and precise positioning in the subsequent chip mounting process. The surface roughness Ra value of the metal receiving layer 5 is controlled below 8 nm by atomic force microscopy (AFM) measurement, and it is activated by argon plasma before bonding. The processing parameters are power 250 W, gas flow rate 30 sccm, and time 90 seconds to increase the surface energy and remove adsorbed impurities.

[0043] After the pretreatment of the flexible micro LED chip 1 and the flexible circuit substrate 4 is completed, the surface atomic-level cleaning process begins. This process includes three consecutive steps: First, the chip with the metal bump structure 3 and the flexible circuit substrate 4 with the metal receiving layer 5 are placed in a plasma cleaning device, using a hydrogen-argon mixed gas (… The sample underwent plasma cleaning at a power of 200W for 90 seconds to effectively remove surface hydrocarbon contaminants and some metal oxides. Next, the cleaned sample was immersed in an 8wt% formic acid aqueous solution at a constant temperature of 50°C for 8 minutes to further remove residual metal oxides using the reducing properties of formic acid. Finally, the sample was transferred to a vacuum oven and dried under a vacuum level superior to [previous conditions]. Under the condition of Pa, the temperature is increased to 180℃ at a heating rate of 3℃ / min and held at this temperature for 20 minutes to complete in-situ thermal desorption, so that the water molecules and other volatile impurities adsorbed on the surface are dissociated and removed, thereby obtaining an atomically clean metal surface.

[0044] After surface treatment, the chip mounting and alignment stage begins. This operation is performed in a sealed chamber filled with high-purity nitrogen, where the oxygen content is controlled below 5 ppm and the dew point temperature is below -45°C. A machine vision system equipped with a high-resolution CCD camera is used to identify the alignment marks on the edge of the flexible micro-LED chip 1 and the flexible circuit substrate 4. The relative positional deviation is calculated using an image matching algorithm, and a six-degree-of-freedom precision micro-motion platform is driven for correction. After alignment, the lateral positioning accuracy reaches ±0.3 μm, and the rotational angle deviation is controlled within 0.08°. Subsequently, the flexible micro-LED chip 1 is slowly lowered vertically by a piezoelectric ceramic actuator until the metal bump structure 3 contacts the metal receiving layer 5. A pre-pressure of 1.2 MPa is applied at the moment of contact to maintain the initial surface contact between the two and prevent local suspension due to surface micro-undulations.

[0045] After initial bonding, the thermoforming stage begins. This process is carried out under a vacuum level superior to [previous stage]. The experiment was conducted in an environment of Pa, with the heating platform raising the temperature to 220°C at a rate of 2°C / min. This temperature is 85% lower than the lowest melting point of the metal system used (Sn's melting point is 232°C) to avoid melting. Simultaneously, a vertical pressure of 3 MPa was applied via a pneumatic loading system, and the pressure was maintained for 15 minutes. Under these conditions, atomic interdiffusion occurred between the top active bonding layer (Sn) and the metal receiver layer 5 (Sn), forming a continuous and dense intermetallic compound interface at the interface. Transmission electron microscopy (TEM) analysis showed that this interface is mainly composed of… The phase composition (due to the introduction of trace amounts of Cu impurities from Ti in the bottom adhesion layer and Ni in the middle layer during diffusion) is approximately 150 nm thick. The interface is free of pores, cracks, or unreacted areas, exhibiting good metallurgical bonding characteristics.

[0046] After bonding, the sample is transferred to a dispensing workstation, where a two-component addition-type silicone sealant is injected into the annular gap between the flexible micro-LED chip 1 and the flexible circuit board 4 as a flexible encapsulating adhesive 6. The A and B components of this silicone sealant are mixed in a 10:1 mass ratio, with a pre-curing viscosity of 3000 mPa·s, a Young's modulus of 1.2 MPa, and an elongation at break of 180%. The amount of sealant is controlled by a precision dispensing valve, utilizing capillary action to uniformly fill the entire gap area to a height of approximately 8 μm. The sample is then cured on an 80°C hot plate for 30 minutes, forming a transparent, flexible encapsulation layer. This flexible encapsulating adhesive 6 completely covers the intermetallic compound interface and surrounding area, forming a physical bond with the sidewalls of the flexible micro-LED chip 1 and the surface of the flexible circuit board 4, but without chemically reacting with the metal bump structure 3 or the metal receiving layer 5.

[0047] Throughout the implementation process, the positional relationships between the components are clearly defined: the flexible micro LED chip 1 is located on top, with its bottom electrode region 2 facing downwards; the metal bump structure 3 is vertically stacked on top of the bottom electrode region 2, forming a columnar protrusion; the flexible circuit board 4 is located below, with its upper surface supporting the metal receiving layer 5; the planar position of the metal receiving layer 5 is strictly aligned with the metal bump structure 3, and the two are in direct contact in the vertical direction; after thermo-press bonding, the contact interface between the two is transformed into an intermetallic compound interface; the flexible encapsulating adhesive 6 fills the non-electrode area between the bottom surface of the flexible micro LED chip 1 and the upper surface of the flexible circuit board 4, forming an annular sealing structure surrounding the intermetallic compound interface. The connection relationships between the layers are as follows: the bottom adhesion layer and the bottom electrode region 2 are connected by van der Waals forces and partial chemical bonding; the middle diffusion barrier layer and the bottom adhesion layer and the top active bonding layer are connected by a continuous metal deposition interface; the top active bonding layer and the metal receiving layer 5 form a covalent-metal bond mixed intermetallic compound interface through atomic diffusion after bonding; the flexible encapsulating adhesive 6 is bonded to the passivation layer of the flexible micro light-emitting diode chip 1 and the polyimide surface of the flexible circuit substrate 4 through physical adsorption and micromechanical interlocking.

[0048] All process steps employed in this embodiment can be completed on standard semiconductor front-end and back-end production lines without the need for special equipment. Physical vapor deposition, photolithography, wet etching, plasma cleaning, chemical mechanical polishing, machine vision alignment, thermosetting bonding, and dispensing encapsulation are all mature process modules with good process windows and repeatability. Through the above detailed steps, solderless, low-temperature, and highly reliable electrical interconnection between flexible Micro-LED chips and flexible circuit substrates can be achieved, suitable for flexible display applications with high pixel density (e.g., PPI > 1000) and dynamic bending capability (curvature radius 2mm). To better enable those skilled in the art to fully understand and implement this invention, the specific implementation principles of this invention are further supplemented below with a specific application scenario.

[0049] In the manufacturing process of high-density flexible Micro-LED modules for curved displays in wearable smartwatches, the GaN-based flexible micro-LED chip 1, which has already undergone epitaxial growth and device patterning, is first transferred from a sapphire substrate to a temporary carrier using a laser lift-off process, exposing the bottom electrode region 2. This region is then cleaned with oxygen plasma to remove residual carbides and natural oxide layers from the laser lift-off, ensuring a clean interface for subsequent metal deposition. Next, a bottom adhesion layer (Ti, 50nm), an intermediate diffusion barrier layer (Ni, 200nm), and a top active bonding layer (Sn, 1.5μm) are sequentially deposited on the bottom electrode region 2. A 15μm × 15μm metal bump structure 3 is then formed through photolithography and wet etching. The top of the bump structure is chemically and mechanically polished to maintain a coplanarity within ±0.2μm, providing geometric assurance for full-area surface contact with the flexible circuit substrate 4.

[0050] Meanwhile, on a 12.5 μm thick polyimide flexible circuit substrate 4, a 1.2 μm thick pure tin metal receiving layer 5 was formed by sputtering a Ti / Cu seed layer followed by electroplating. The pattern size and position of this layer strictly matched the metal bump structure 3, and alignment marks were simultaneously fabricated on the substrate surface. The surface roughness Ra of the metal receiving layer 5 was measured to be 7.3 nm by atomic force microscopy, and it underwent argon plasma activation treatment before bonding to enhance surface energy. Subsequently, the flexible micro-LED chip 1 with the metal bump structure 3 and the flexible circuit substrate 4 with the metal receiving layer 5 were respectively cleaned in a hydrogen-argon mixed plasma environment for 90 seconds, then immersed in an 8 wt% formic acid solution for reduction at 50°C for 8 minutes, and finally... Thermal desorption at 180℃ for 20 minutes under vacuum conditions (Pa) achieves atomic-level cleanliness of the Sn surface, eliminating... The insulating oxide film hinders the diffusion reaction.

[0051] In a high-purity nitrogen-protected chamber (oxygen content <5ppm, dew point <-45℃), a machine vision system identifies the edge contour of the flexible micro LED chip 1 and the alignment marks on the flexible circuit board 4, driving a six-degree-of-freedom platform to complete spatial correction, ensuring that the lateral offset between the metal bump structure 3 and the metal receiving layer 5 is controlled within ±0.3μm and the angular deviation is less than 0.08°. Subsequently, a piezoelectric ceramic actuator controls the chip to approach vertically. When the metal bump structure 3 and the metal receiving layer 5 make their first contact, a pre-pressure of 1.2MPa is applied to ensure that all bumps are synchronously attached, avoiding uneven diffusion caused by local suspension.

[0052] After entering the hot-press bonding stage, under a vacuum degree better than In an environment of Pa, the temperature is increased to 220℃ at a rate of 2℃ / min (85% lower than the melting point of Sn, 232℃), while a vertical pressure of 3MPa is applied and held for 15 minutes. Under these conditions, Sn atoms in the top active bonding layer and the metal receiving layer 5 undergo solid-state interdiffusion along the grain boundaries and surface. At the interface, trace Cu impurities (originating from trace doping in the Ni layer or equipment contamination) participate in the reaction, resulting in the in-situ formation of a continuous and dense structure. The intermetallic compound interface, with a thickness of approximately 150 nm, is observed to be free of pores or unreacted areas by transmission electron microscopy, forming a low-resistance, high-strength metallurgical bond. In subsequent bending tests, this interface can withstand 10,000 cycles at a curvature radius of 2 mm without experiencing a sudden change in resistance or an open circuit.

[0053] After bonding, a two-component addition-type silicone sealant is injected into the annular gap between the flexible micro LED chip 1 and the flexible circuit substrate 4 as a flexible encapsulant 6. Its A and B components are mixed at a ratio of 10:1, with an initial viscosity of 3000 mPa·s. It fills the gap region with a height of about 8 μm using capillary action and is cured at 80°C for 30 minutes. The encapsulant has a Young's modulus of 1.2 MPa and an elongation at break of 180%. During dynamic bending, it absorbs interfacial shear strain through elastic deformation, preventing the intermetallic compound interface from cracking due to stress concentration. At the same time, its low dielectric constant (ε≈3.0) avoids the introduction of significant parasitic capacitance, ensuring the integrity of high-frequency drive signals.

[0054] Through the above steps, this invention achieves reliable interconnection in actual wearable display module manufacturing without solder, at low temperature (<220℃), and with high alignment accuracy (±0.3μm). The formed intermetallic compound interface provides a stable electrical path, the flexible encapsulating adhesive 6 provides mechanical buffering and environmental sealing, and the three-layer metal bump structure 3 ensures the interface bonding strength and diffusion controllability. Thus, in high pixel density flexible Micro-LED displays with a PPI of over 1000, it effectively solves the thermal mismatch failure problem caused by traditional solder bonding and overcomes the defects of insufficient contact area and poor dynamic reliability of existing solderless solutions.

[0055] All contents not described in detail in the specification are existing technologies known to those skilled in the art, and the model parameters of each process equipment are not specifically limited. Conventional semiconductor manufacturing equipment can be used. Auxiliary control components not mentioned in this technical solution are existing technologies and are therefore not shown in the figures, and will not be described in detail here.

[0056] The above embodiments are merely one of the preferred embodiments of the present invention and should not be used to limit the scope of protection of the present invention. Any modifications or refinements made to the main design concept and spirit of the present invention that are not of substantial significance, but solve the same technical problem as the present invention, should be included within the scope of protection of the present invention.

Claims

1. A method for interconnecting a flexible micro light-emitting diode with a flexible circuit without solder bonding, characterized in that, Includes the following steps: S1, a metal bump structure is prepared in the bottom electrode region of the flexible micro light-emitting diode chip. The metal bump structure is composed of a bottom adhesion layer, an intermediate diffusion barrier layer and a top active bonding layer stacked in sequence. S2, a metal receiving layer matching the metal bump structure is prepared in the corresponding pad area of ​​the flexible circuit substrate, the metal receiving layer having the same chemical composition as the top active bonding layer; S3, perform atomic-level cleaning treatment on the surfaces of the metal bump structure and the metal receiving layer to remove oxides, hydrocarbon contaminants and adsorbed water molecules; S4, the flexible micro light-emitting diode chip is aligned to a predetermined position on the flexible circuit substrate using a precision pick-and-place device, so that the metal bump structure and the metal receiving layer form surface contact; S5, under an inert gas protective environment, a preset pressure is applied and the temperature is heated to below the melting point of any metal component, causing an atomic-level solid-phase diffusion reaction to occur between the top active bonding layer and the metal receiving layer, forming a continuous and dense intermetallic compound interface, thereby completing a solderless permanent electrical connection.

2. The method for interconnecting flexible micro-light-emitting diodes and flexible circuits without solder bonding according to claim 1, characterized in that, In step S1, the method for preparing the metal bump structure is as follows: S11, the bottom electrode region of the flexible micro LED chip is exposed by dry etching or laser lift-off process, and plasma cleaning is performed to remove surface oxides and organic contaminants. S12, using physical vapor deposition combined with photolithography and wet etching processes, a bottom adhesion layer, an intermediate diffusion barrier layer and a top active bonding layer are sequentially formed in the bottom electrode region. S13, perform chemical mechanical polishing on the top surface of the metal bump structure to ensure that its coplanarity deviation meets the preset process standard.

3. The method for interconnecting flexible micro-light-emitting diodes and flexible circuits without solder bonding according to claim 2, characterized in that, In step S2, the metal receiving layer is prepared as follows: S21, a metal receiving layer is formed on a flexible circuit board made of polyimide, polyethylene naphthalate or ultrathin glass by sputtering, electroplating or chemical plating processes. S22, perform photolithography and wet etching on the metal receiving layer to define the pattern; S23, control the surface roughness of the metal receiving layer, and perform plasma activation treatment on it before bonding to enhance the surface energy.

4. The method for interconnecting flexible micro-light-emitting diodes and flexible circuits without solder bonding according to claim 3, characterized in that, The specific process of step S3 is as follows: S31, using argon or a hydrogen-argon mixture to perform plasma cleaning on the metal bump structure and the metal receiving layer; S32, the metal surface after plasma cleaning is immersed in a formic acid aqueous solution for chemical reduction treatment; S33, in a vacuum environment, heats up to a preset temperature at a constant heating rate and holds at that temperature for a predetermined time to complete in-situ thermal desorption.

5. The method for interconnecting flexible micro-light-emitting diodes and flexible circuits without solder bonding according to claim 4, characterized in that, The specific process of step S4 is as follows: The bonding operation shall be carried out in an inert gas protective environment with an oxygen content of less than 10 ppm and a dew point temperature of less than -40°C. A machine vision system is used to identify alignment marks, achieving sub-micron level spatial positioning; The chip is vertically approached to the substrate by a precision micro-motion platform until the metal bump structure contacts the metal receiving layer and pre-pressure is applied to maintain the initial bonding state.

6. The method for interconnecting flexible micro-light-emitting diodes and flexible circuits without solder bonding according to claim 5, characterized in that, It also includes filling the gap between the flexible micro LED chip and the flexible circuit board with flexible encapsulating adhesive after bonding is completed. The flexible encapsulating adhesive is a silicone or polyurethane material.

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