A low-temperature bonding method based on a hydrophobic copper micron layer

Abstract

The application provides a low-temperature bonding method based on a hydrophobic copper micron layer, a copper micron needle layer prepared by electrodepositing on a copper substrate is prepared; a mixture is added into an indium plating solution; the copper micron needle layer is placed in the indium plating solution containing the mixture for electroplating, and a nanometer indium layer in a pine wood shape is formed on the surface layer of the copper micron needle layer; a substrate with a pine wood shaped copper-indium secondary micro-nano layer is obtained; then, graphene is uniformly covered on the pine wood shaped copper-indium secondary micro-nano layer; the substrate is bonded with Sn-Ag-Cu alloy solder balls; the mixture is added to make the indium plating solution form a nanometer indium layer in a pine wood shape on the surface layer of the copper micron needle layer, and the shear strength after bonding with the solder is large; the graphene is added to avoid direct contact between copper and tin, and delay the growth of copper-tin compounds; the bonding temperature required by the application is low; by introducing ultrasonic energy, the bonding pressure is reduced, the bonding time is reduced, the transient bonding is realized, the reliability of the bonded interconnection is improved, the bonding does not need a protective atmosphere, and energy consumption is saved.

Description

Technical Field

[0001] This invention relates to sheet bonding in three-dimensional packaging of semiconductor devices, specifically to a low-temperature bonding method based on a hydrophobic copper micron layer. Background Technology

[0002] In electronic packaging, lead-free solders such as tin are generally used to connect copper. However, the soldering temperature between tin and copper is relatively high. When the molten tin solder comes into direct contact with the pad, an interfacial reaction occurs between copper and tin, forming intermetallic compounds. These intermetallic compounds are highly brittle, and the greater the thickness of the compound, the lower the strength of the solder joint and the reduced bond strength, thus affecting the reliability of the package. To address this issue, existing technologies insert a nickel layer or a Ni-W nickel-based alloy barrier layer between the copper and tin to restrict copper atom diffusion. For example, Chinese patent application CN202010942868.9, published on October 4, 2022, discloses a low-temperature copper-copper bonding method based on graphene / tin-modified copper nanoparticles. This method uses a composite of copper nanoparticles, tin nanoparticles, and graphene microsheets as the bonding material to achieve bonding between two copper-plated substrates at low temperatures. This invention also achieves low-temperature bonding by adding a tin nanolayer and a graphene microsheet structure to the bonding material.

[0003] For nickel layers, if a thin pure nickel layer is inserted between copper and tin as a barrier layer, the nickel will react with the tin and be consumed quickly, causing the thin barrier layer to fail. If an excessively thick nickel layer is inserted between copper and tin, the reliability of the bonding soldering will be reduced. For Ni-W nickel-based alloy barrier layers, nickel becomes the main diffusion element, and the formed Ni3Sn4 puts tensile stress on the barrier layer, causing cracks in the thin barrier layer, which in turn leads to the failure of the barrier layer. Summary of the Invention

[0004] This invention provides a low-temperature bonding method based on a hydrophobic copper micron layer. The addition of a compound agent causes the indium plating solution to form a pine-wood-like nano-indium layer on the surface of the copper micron needle layer, which has high shear strength after bonding with solder. The addition of graphene avoids direct contact between copper and tin and slows down the growth of copper-tin compounds.

[0005] To achieve the above objectives, the technical solution of the present invention is: a low-temperature bonding method based on a hydrophobic copper micron layer, comprising the following steps:

[0006] S1. Copper microneedle layer prepared by electrodeposition on a copper substrate.

[0007] S2. Add a mixture to the indium plating solution, the mixture including electrolyte, polyethylene glycol, Janus Green and CI ions.

[0008] S3. Electroplating is performed on the copper micron needle layer in an indium plating solution containing a mixture to form a pine-wood-like micro / nano indium layer on the surface of the copper micron needle layer; a substrate with a pine-wood-like copper-indium secondary micro / nano indium layer is obtained.

[0009] S4. Graphene is uniformly coated on a pine-wood-like copper-indium secondary micro / nano indium layer.

[0010] S5. Place the graphene-coated pine-wood-like copper-indium secondary micro / nano indium layer and the Sn-Ag-Cu alloy solder ball opposite each other on the ultrasonic bonding instrument, so that the graphene-coated pine-wood-like copper-indium secondary micro / nano indium layer and the Sn-Ag-Cu alloy solder ball form a contact area.

[0011] S6. Start the ultrasonic bonding machine and loading machine to bond the graphene-coated pine-wood-like copper-indium secondary micro / nano indium layer to the Sn-Ag-Cu alloy solder ball.

[0012] The above method involves a mixture containing electrolyte, polyethylene glycol, Janus Green, and Cl ions; the electrolyte contains H₂PO₂. - Because the copper micron needle layer is electroplated in an indium plating solution containing a mixture, H2PO2 - Attached to the copper microneedle layer, first through H2PO2 - With In 3+ The reaction causes In 3+ Deposited on the copper microneedle layer; simultaneously, Janus Green reacts with H2PO2 on the copper microneedle layer. - The reaction causes H2PO2 to... - Reduce and inhibit H2PO2 - With In 3+ Excessive reaction between them, thereby inhibiting In 3+ Deposition on copper microneedle layers; in H2PO2 - With In 3+ Reaction, Janus Green and H2PO2 -The combined effects of the reactions lead to the formation of refined grains, which in turn form a pine-like copper-indium secondary micro / nano layer. Graphene is then incorporated into the Sn-Ag-Cu alloy solder balls and the pine-like copper-indium secondary micro / nano indium layer substrate. This avoids direct contact between copper and tin, slows the growth of copper-tin compounds, and delays the aging effect of the microstructure. The addition of graphene also inhibits dislocation expansion in copper, improving shear strength. Simultaneously, the pine-like copper-indium secondary micro / nano indium layer reduces surface tension generated during the graphene drying process. Bonding is then performed under the lateral ultrasonic vibration of an ultrasonic bonding machine and the pressure of a loading machine. Because the tips of the copper micro-needle layer have a needle-like micro-structure, the tips of the pine-like copper-indium secondary micro-nano indium layer forming the micro-nano indium layer remain sharp. Consequently, the pine-like copper-indium secondary micro-nano indium layer easily inserts into the Sn-Ag-Cu alloy solder ball, and the copper needle array structure formed by the micro-nano indium layer and the copper micro-needle layer adheres together at the bonding interface. Simultaneously, the large surface area of ​​the pine-like nano-indium layer increases the contact area between the pine-like copper-indium secondary micro-nano indium layer substrate and the Sn-Ag-Cu alloy solder ball, resulting in high shear strength after bonding. Furthermore, under the action of friction, a small number of copper needle cones from the copper micro-needle layer break and disperse within the Sn-Ag-Cu alloy solder ball, improving the overall shear strength and ensuring reliable bonding between the pine-like copper-indium secondary micro-nano indium layer substrate and the Sn-Ag-Cu alloy solder ball. By using an ultrasonic bonding machine, the bonding temperature can be reduced, thereby reducing the risk of thermal deformation of the chip. At the same time, ultrasonic vibration accelerates the shrinkage and filling of the pores in the concave region of the pine-like copper-indium secondary micro / nano layer substrate, promotes the formation of copper-indium intermetallic compounds, and reduces the bonding time.

[0013] Furthermore, S4 also includes: preparing graphene, specifically: depositing graphene onto copper foil using low-pressure chemical vapor, then spin-coating a polymer onto the graphene surface for shaping, then baking the graphene mixture containing the polymer, and immersing the graphene mixture containing the polymer in a copper etchant to remove the copper foil, then using a pine-shaped copper-indium secondary micro-nano indium layer substrate coated with a nano-indium layer to scoop out the graphene mixture containing the polymer, then drying the pine-shaped copper-indium secondary micro-nano indium layer substrate carrying the graphene mixture containing the polymer, and then immersing the pine-shaped copper-indium secondary micro-nano indium layer substrate carrying the graphene mixture containing the polymer in xylene to remove the polymer, and transferring the polymer-removed and shaped graphene onto the pine-shaped copper-indium secondary micro-nano indium layer; wherein the polymer is ethylene-vinyl acetate.

[0014] The above method, due to the rough surface of the pine-wood-like copper-indium secondary micro / nano indium layer, avoids leaving voids when graphene covers the pine-wood-like copper-indium secondary micro / nano indium layer. ethylene-vinyl acetate is used to support and transfer the graphene onto the pine-wood-like copper-indium secondary micro / nano indium layer. The high elastic modulus of ethylene-vinyl acetate gives the graphene good ductility and makes it less prone to tearing, resulting in a high coverage of graphene on the pine-wood-like copper-indium secondary micro / nano indium layer. Then, the ethylene-vinyl acetate is removed, achieving graphene adhesion to the pine-wood-like copper-indium secondary micro / nano indium layer.

[0015] Furthermore, in S6, the loading speed of the loader is set to 2.0 mm / min.

[0016] Furthermore, in S6, the bonding pressure of the ultrasonic bonding instrument is set to 0.5 MPa-0.7 MPa, the bonding frequency is 10 kHz-40 kHz, the bonding time is 2 s-3 s, and the bonding temperature is 100℃-130℃.

[0017] Furthermore, in S6, the bonding pressure of the ultrasonic bonding instrument is set to 0.6 MPa, the bonding frequency to 20 kHz, the bonding time to 2.5 s, and the bonding temperature to 120 °C.

[0018] Furthermore, the copper microneedle has a conical structure, with a height of 3μm to 5μm and a root diameter of 1μm to 2μm; the thickness of the pine-like micro / nano indium layer is 250nm to 350nm.

[0019] Furthermore, the electroplating time for the indium plating solution containing the mixture is 15 min to 20 min. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of a pine-wood-like copper-indium secondary micro / nano indium layer substrate.

[0021] Figure 2 for Figure 1 A magnified view of 'a' in the middle.

[0022] Figure 3 Low-magnification electron microscope (SEM) image of this copper needle array structure.

[0023] Figure 4 This is a low-magnification electron microscope (SEM) image of the pine-wood-like copper-indium secondary micro / nano indium layer after indium coating.

[0024] Figure 5 This is a low-magnification electron microscope (SEM) image of conformal graphene covering a pine-wood-like copper-indium secondary micro / nano indium layer.

[0025] Figure 6This is a schematic diagram of the bonding between a pine-wood-like copper-indium secondary micro / nano indium layer substrate and a Sn-Ag-Cu alloy solder ball.

[0026] Figure 7 Low-magnification electron microscope (SEM) image of the bonding interface between the pine-wood-like copper-indium secondary micro / nano indium layer substrate and the Sn-Ag-Cu alloy solder ball after heat treatment at 180℃ for 20 h.

[0027] Figure 8 Low-magnification electron microscope (SEM) image of the bonding interface between the pine-wood-like copper-indium secondary micro / nano indium layer substrate and the Sn-Ag-Cu alloy solder ball after heat treatment at 180℃ for 100h.

[0028] Figure 9 The graph shows the relationship between the average shear strength of the Sn-graphene-In-Cu bonding interface and the bonding time in the ultrasonic bonding instrument. Detailed Implementation

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

[0030] like Figures 1-9 As shown; a low-temperature bonding method based on a hydrophobic copper microlayer includes the following steps:

[0031] S1. A copper microneedle layer 2 is electrodeposited on a copper substrate 1. In this embodiment, the microneedles are conical structures, with a height of 3μm to 5μm and a root diameter of 1μm to 2μm.

[0032] S2. A mixture is added to the indium plating solution. The mixture is formed by physical mixing of the electrolyte, polyethylene glycol, Janus Green, and Cl ions. The mixture is prepared by adding polyethylene glycol, Janus Green, and Cl ions to the electrolyte.

[0033] In this embodiment, the electrolyte is prepared by mixing analytical grade CuSO4-5H2O (0.04 mol / L), NiSO4-6H2O (0.0026 mol / L), NaH2PO2-H2O (0.24 mol / L), Na3C6H5O7-2H2O (0.05 mol / L), H3BO3 (0.50 mol / L), and H3BO3 (0.50 mol / L) with a mass-volume concentration of 0.50 mol / L. NaOH is added to adjust the pH value, and the pH value of the electrolyte is 9. The polyethylene glycol is PEG10000 with a content of 100 ppm. The content of Janus Green is 8 ppm, and the content of Cl ions is 60 ppm.

[0034] In this embodiment, the indium plating solution includes In2O12S3-6H2SO4 (50 g / L) and NaH2PO2 (1.5 mol / L), and PEG2000 at a concentration of 30 ppm is added.

[0035] S3. The copper micron needle layer is electroplated in an indium plating solution containing a mixture at a temperature of 60°C for 15-20 minutes. A pine-wood-like micro / nano indium layer 3 is formed on the surface of the copper micron needle layer, resulting in a substrate with a pine-wood-like copper-indium secondary micro / nano indium layer. In this embodiment, the thickness of the pine-wood-like micro / nano indium layer is 250 nm-350 nm.

[0036] S4. Graphene 4 is uniformly coated onto the pine-wood-like copper-indium secondary micro / nano indium layer 3. In this embodiment, the thickness of the graphene is the diameter of one carbon atom.

[0037] S5. Place the graphene-coated pine-wood-like copper-indium secondary micro / nano indium layer and the Sn-Ag-Cu alloy solder ball opposite each other on the ultrasonic bonding instrument, so that the graphene-coated pine-wood-like copper-indium secondary micro / nano indium layer and the Sn-Ag-Cu alloy solder ball form a contact area.

[0038] S6. Start the ultrasonic bonding machine and loading machine to preheat the contact area between the graphene-coated pine wood-like copper-indium secondary micro-nano indium layer and the Sn-Ag-Cu alloy solder ball for 20 minutes; then bond the graphene-coated pine wood-like copper-indium secondary micro-nano indium layer to the Sn-Ag-Cu alloy solder ball.

[0039] The above method involves a mixture containing electrolyte, polyethylene glycol, Janus Green, and Cl ions; the NaH2PO2-H2O in the electrolyte contains H2PO2. - H2PO2 - It will react with the In in the indium plating solution. 3+ The reaction, with the chemical equation: 2H₂PO₂ - + In 3+ + 20H - →In + H2PO3 - + 2H₂↑. Because the copper microneedle layer is electroplated in an indium plating solution containing a mixture, H₂PO₂... - Attached to the copper microneedle layer, first through H2PO2 - With In 3+ The reaction causes In 3+ It is deposited on a copper microneedle layer; meanwhile, Janus Green is a heterocyclic aromatic compound containing quaternary ammonium, and its inherent molecular structure allows Janus Green to react with H2PO2 on the copper microneedle layer. - The reaction causes H2PO2 to... - Reduce and inhibit H2PO2- With In 3+ Excessive reaction between them, thereby inhibiting In 3+ Deposition on copper microneedle layers; in H2PO2 - With In 3+ Reaction, Janus Green and H2PO2 - The combined effect of the reaction forms refined grains; which in turn forms a pine-wood-like copper-indium secondary micro / nano indium layer 3.

[0040] Then, conformal graphene was placed on the Sn-Ag-Cu alloy solder ball and the pine-shaped copper-indium secondary micro / nano indium layer substrate to avoid direct contact between copper and tin, delay the growth of copper-tin compounds, and slow down the aging effect of the structure. The addition of graphene 4 prevented dislocation expansion in copper and improved shear strength. At the same time, the pine-shaped copper-indium secondary micro / nano indium layer could reduce the surface tension generated during the graphene drying process. Bonding was then carried out under the action of transverse ultrasonic vibration of an ultrasonic bonding machine and the pressure of a loading machine. Since the tip of the copper micron needle layer has a needle-cone micron structure, the tip of the pine-shaped copper-indium secondary micro / nano indium layer forming the micro / nano indium layer can still remain sharp. As a result, the pine-shaped copper-indium secondary micro / nano indium layer can be easily inserted into the Sn-Ag-Cu alloy solder ball. At the same time, the large surface area of ​​the pine-shaped copper-indium secondary micro / nano indium layer 31 increased the contact area between the pine-shaped copper-indium secondary micro / nano indium layer substrate and the Sn-Ag-Cu alloy solder ball. The shear strength of the pine-shaped copper-indium secondary micro / nano indium layer substrate after bonding with the solder is high. Simultaneously, under the action of friction, a small amount of copper needle cones from the copper micron needle layer 3 break and disperse within the Sn-Ag-Cu alloy solder balls. This improves the overall shear strength, enabling reliable bonding between the pine-like copper-indium secondary micro / nano indium layer substrate and the Sn-Ag-Cu alloy solder balls. Using an ultrasonic bonding machine for bonding reduces the bonding temperature, thereby lowering the risk of thermal deformation of the chip. Simultaneously, ultrasonic vibration accelerates the shrinkage and filling of the pores in the concave region of the needle cones on the pine-like copper-indium secondary micro / nano layer substrate, promoting the formation of copper-indium intermetallic compounds and reducing bonding time.

[0041] In this embodiment, the Sn-Ag-Cu alloy solder ball has a diameter of 760 μm. In the Sn-Ag-Cu alloy solder ball, the weight percentage of Sn is 96.5%, the weight percentage of Ag is 3%, and the weight percentage of Cu is 0.5%.

[0042] In the above method, step S4 further includes: preparing graphene, specifically: depositing graphene onto a 25μm thick copper foil using low-pressure chemical vapor deposition; then spin-coating a polymer onto the graphene surface for shaping; then baking the polymer-containing graphene mixture in a 90℃ oven for 90 minutes; then etching the copper foil in a copper etchant for 30 minutes to remove the etchant; then rinsing the polymer-containing graphene with deionized water; and finally using a pine-wood-like copper-indium secondary micro / nano indium layer substrate. A graphene mixture containing a polymer is prepared, and then a copper substrate coated with a micro / nano indium layer supporting the graphene mixture containing the polymer is dried with nitrogen. Then, the pine-shaped copper-indium secondary micro / nano indium layer substrate supporting the graphene mixture containing the polymer is placed in an oven at 90°C and heated for 10 hours. Then, the graphene mixture containing the polymer is immersed in xylene for 30-40 minutes to remove the polymer. The polymer-removed and shaped graphene is transferred to the pine-shaped copper-indium secondary micro / nano indium layer. The polymer is ethylene-vinyl acetate.

[0043] The preparation method of ethylene-vinyl acetate is to dissolve 40 wt% of vinyl acetate in a 10 wt% xylene solution to form ethylene-vinyl acetate.

[0044] The above method addresses the issue of the rough surface of the pine-like copper-indium secondary micro / nano indium layer. To prevent voids from being left when removing the polymer from the pine-like copper-indium secondary micro / nano indium layer, ethylene-vinyl acetate is used to support and transfer the graphene onto the pine-like copper-indium secondary micro / nano indium layer. The high elastic modulus of ethylene-vinyl acetate results in good ductility of the graphene, making it less prone to tearing and allowing for a high coverage of graphene on the pine-like copper-indium secondary micro / nano indium layer. The ethylene-vinyl acetate is then removed, achieving graphene adhesion to the pine-like copper-indium secondary micro / nano indium layer.

[0045] In step S6, the loading speed of the loader is set to 2.0 mm / min, the fixed frequency of the ultrasonic bonding instrument is 20 kHz, the bonding pressure is set to 0.5 MPa-0.7 MPa, and the bonding time is 2 s-3 s. In this embodiment, the bonding pressure of the ultrasonic bonding instrument is set to 0.6 MPa, and the bonding time is 2.5 s.

[0046] Reference Figure 7 and Figure 8As shown, the bonding products of pine-like copper-indium secondary micro / nano indium layer substrates bonded to Sn-Ag-Cu alloy solder balls, after heat treatment at 180℃ for 20 h and at 150℃ for 100 h, showed no significant increase in copper-tin intermetallic compounds at the bonding interface. The interface morphology did not change significantly after aging treatment, and no further interfacial reaction occurred between tin and copper. The addition of graphene interlayer can effectively prevent the formation of copper-tin intermetallic compounds (Cu6Sn5, Cu3Sn), thereby preventing the aging of the Sn-Cu bonding interface. The bonding method has high reliability.

[0047] Reference Figure 9 As shown, during the bonding process between the pine-like copper-indium secondary micro / nano indium layer substrate and the Sn-Ag-Cu alloy solder ball, Sn-graphene-In-Cu bonding occurs. Within the bonding time range of 0.5-2.5 s, the average shear strength of the Sn-graphene-In-Cu bonding interface increases with the extension of time.

[0048] When the bonding time is greater than 3 s, the ultrasonic transverse vibration causes linear crack propagation due to the excessive bonding time, and the average shear strength of the Sn-graphene-In-Cu bonding interface decreases significantly. Therefore, in this embodiment, the bonding time of the ultrasonic bonding instrument is 2.5 s.

[0049] Compared to the Sn-In-Cu bonding formed by Sn-Ag-Cu alloy solder balls on a pine-like copper-indium secondary micro / nano indium layer substrate without graphene, the average shear strength of the Sn-graphene-In-Cu bonding interface is lower than that of the Sn-In-Cu bonding interface within the bonding time range of 0.5-2.5 s. Graphene hinders the bonding between Cu and Sn. However, since graphene is only one carbon atom thick, effective bonding can still be formed under pressure when the ultrasonic bonding time is 2.5 s. Therefore, setting graphene on the pine-like copper-indium secondary micro / nano indium layer can avoid direct contact between copper and tin, delay the growth of copper-tin compounds, and maintain effective bonding at the Sn-graphene-In-Cu bonding interface.

[0050] In this embodiment, the decomposition region of the pine-like copper-indium secondary micro / nano indium layer substrate bonded to the Sn-Ag-Cu alloy solder ball forms an indium-graphene boundary layer. The indium-graphene boundary layer contains an intermetallic compound layer with a thickness of 100-200 nm, including Cu2In and Cu6(Sn,In)5. Since Cu2In has good mechanical properties, it can improve the shear strength of the bonding interface.

Claims

1. A low-temperature bonding method based on a hydrophobic copper micron layer, characterized in that: Includes the following steps: S1. Copper microneedle layer electrodeposited on a copper substrate; S2. Add a mixture to the indium plating solution, the mixture including electrolyte, polyethylene glycol, Janus Green and CI ions; S3. Placing the copper micron needle layer in an indium plating solution containing a mixture for electroplating to form a pine-wood-like micro / nano indium layer on the surface of the copper micron needle layer; thus obtaining a substrate with a pine-wood-like copper-indium secondary micro / nano indium layer. S4. Graphene is uniformly coated on a pine-wood-like copper-indium secondary micro / nano indium layer; S5. The graphene-coated pine-wood-like copper-indium secondary micro-nano indium layer and the Sn-Ag-Cu alloy solder ball are placed opposite each other on the ultrasonic bonding instrument, and the graphene-coated pine-wood-like copper-indium secondary micro-nano indium layer and the Sn-Ag-Cu alloy solder ball form a contact area. S6. Start the ultrasonic bonding machine and loading machine to bond the graphene-coated pine-wood-like copper-indium secondary micro / nano indium layer to the Sn-Ag-Cu alloy solder ball.

2. The low-temperature bonding method based on a hydrophobic copper microlayer according to claim 1, characterized in that: S4 further includes: preparing graphene, specifically: synthesizing graphene by depositing it on copper foil using low-pressure chemical vapor, then spin-coating a polymer onto the graphene surface for shaping, then baking the graphene mixture containing the polymer, and then immersing the graphene mixture containing the polymer in a copper etchant to remove the copper foil, then using a pine-shaped copper-indium secondary micro-nano indium layer substrate coated with a micro-nano indium layer to scoop out the graphene mixture containing the polymer, then drying the pine-shaped copper-indium secondary micro-nano indium layer substrate carrying the graphene mixture containing the polymer, and then immersing the pine-shaped copper-indium secondary micro-nano indium layer substrate carrying the graphene mixture containing the polymer in xylene to remove the polymer, and transferring the polymer-removed and shaped graphene onto the pine-shaped copper-indium secondary micro-nano indium layer; wherein the polymer is ethylene-vinyl acetate.

3. The low-temperature bonding method based on a hydrophobic copper microlayer according to claim 1, characterized in that: In S6, the loading speed of the loader is set to 2.0 mm / min.

4. The low-temperature bonding method based on a hydrophobic copper microlayer according to claim 1, characterized in that: In S6, the bonding pressure of the ultrasonic bonding instrument is set to 0.5 MPa-0.7 MPa, the bonding frequency is 10 kHz-40 kHz, the bonding time is 2 s-3 s, and the bonding temperature is 100℃-130℃.

5. The low-temperature bonding method based on a hydrophobic copper microlayer according to claim 4, characterized in that: In S6, the bonding pressure of the ultrasonic bonding instrument is set to 0.6 MPa, the bonding frequency to 20 kHz, the bonding time to 2.5 s, and the bonding temperature to 120 ℃.

6. The low-temperature bonding method based on a hydrophobic copper microlayer according to claim 4, characterized in that: The copper microneedle has a conical structure with a height of 3μm to 5μm and a root diameter of 1μm to 2μm; the pine-like micro / nano indium layer has a thickness of 250nm to 350nm.

7. The low-temperature bonding method based on a hydrophobic copper microlayer according to claim 1, characterized in that: The electroplating time for indium plating solutions containing mixtures is 15 min to 20 min.

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