阅读说明：本技术 铜键合丝及其制备方法 (Copper bonding wire and preparation method thereof ) 是由 刘志权 李晓 李忠国 李哲 孙蓉 于 2020-12-04 设计创作，主要内容包括：本发明提供了一种铜键合丝,所述铜键合丝包括铜丝本体以及包覆在铜丝本体表面上的纳米孪晶铜外壳,所述纳米孪晶铜外壳由晶界界面垂直于所述铜丝本体表面的柱状晶组成,所述柱状晶内部包含层叠的纳米孪晶片层结构。所述铜键合丝的制备方法包括：将铜块依次经过真空熔炼、定向连铸以及拉拔工艺制备形成铜丝本体；将所述铜丝本体依次进行热处理和清洗处理；对清洗后的所述铜丝本体进行电镀工艺,在所述铜丝本体的表面上形成所述纳米孪晶铜外壳,获得所述铜键合丝。本发明通过在铜丝本体表面上形成纳米孪晶铜外壳,不仅提升了铜键合丝的抗氧化性,还增强了铜键合丝的抗拉强度,提高了键合丝抵抗断线的能力,满足芯片和外部封装基板的使用要求。(The invention provides a copper bonding wire which comprises a copper wire body and a nanometer twin crystal copper shell coated on the surface of the copper wire body, wherein the nanometer twin crystal copper shell is composed of columnar crystals with a crystal boundary interface vertical to the surface of the copper wire body, and the inside of the columnar crystals comprises a laminated nanometer twin crystal lamellar structure. The preparation method of the copper bonding wire comprises the following steps: sequentially carrying out vacuum melting, directional continuous casting and drawing processes on a copper block to prepare a copper wire body; sequentially carrying out heat treatment and cleaning treatment on the copper wire body; and carrying out an electroplating process on the cleaned copper wire body, and forming the nanometer twin crystal copper shell on the surface of the copper wire body to obtain the copper bonding wire. According to the invention, the nanometer twin crystal copper shell is formed on the surface of the copper wire body, so that the oxidation resistance of the copper bonding wire is improved, the tensile strength of the copper bonding wire is enhanced, the wire breakage resistance of the bonding wire is improved, and the use requirements of a chip and an external packaging substrate are met.)

1. The copper bonding wire is characterized by comprising a copper wire body and a nanometer twin crystal copper shell coated on the surface of the copper wire body, wherein the nanometer twin crystal copper shell is composed of columnar crystals with a crystal boundary interface vertical to the surface of the copper wire body, and the columnar crystals internally comprise laminated nanometer twin crystal lamellar structures.

2. The copper bonding wire according to claim 1, wherein the growth direction of the nano twin crystal layer in each columnar crystal is perpendicular or nearly perpendicular to the grain boundary interface of the corresponding columnar crystal, and the growth directions of the nano twin crystal layers in the same columnar crystal are the same.

3. The copper bonding wire according to claim 2, wherein the diameter of the copper wire body is 10 μm to 50 μm, and the thickness of the nano twin copper shell is 0.2 μm to 12 μm.

4. The copper bonding wire according to claim 3, wherein the thickness of the nano twin crystal layer is 10nm to 50nm, and the width of the columnar crystal is 0.5 μm to 10 μm.

5. The copper bonding wire according to any one of claims 1 to 4, wherein the material of the copper wire body is copper with a purity of not less than 99.99%, and the nano-twinned copper shell is formed on the surface of the copper wire body through an electrochemical deposition process.

6. A method of producing a copper bonding wire according to any one of claims 1 to 5, comprising:

sequentially carrying out vacuum melting, directional continuous casting and drawing processes on a copper block to prepare a copper wire body;

sequentially carrying out heat treatment and cleaning treatment on the copper wire body;

carrying out an electroplating process on the cleaned copper wire body, and forming the nanometer twin crystal copper shell on the surface of the copper wire body to obtain the copper bonding wire;

the electrolyte in the electroplating process comprises copper sulfate, sulfuric acid, sodium chloride, an electroplating additive and water.

7. The method for producing a copper bonding wire according to claim 6, wherein the concentration of copper sulfate in the electrolyte is 50g/L to 200g/L, the concentration of sulfuric acid is 20g/L to 50g/L, the content of sodium chloride is 30ppm to 50ppm, and the content of plating additives is 20ppm to 120 ppm.

8. The method for preparing a copper bonding wire according to claim 6, wherein the electroplating process is a direct current electroplating process with a current density of 1A/dm²～5A/dm²The electroplating time is 0.5 min-6 min.

9. The method for preparing the copper bonding wire according to claim 6, wherein the sequentially performing the heat treatment and the cleaning treatment on the copper wire body comprises:

carrying out heat treatment on the copper wire body at the temperature of 250-350 ℃ in a nitrogen atmosphere at the heat treatment speed of 1-3 m/s;

and (3) carrying out ultrasonic cleaning on the copper wire body subjected to heat treatment in a sodium hydroxide solution, a sulfuric acid solution and pure water in sequence.

10. The method for preparing the copper bonding wire according to claim 6, wherein the step of sequentially carrying out vacuum melting, directional continuous casting and drawing on the copper block to prepare the copper wire body comprises the following steps:

selecting a high-purity copper block with the purity of not less than 99.99 percent, and carrying out vacuum melting and directional continuous casting for 1-3 h at the temperature of 1000-1200 ℃ to form a copper rod with the diameter of 6-10 mm;

carrying out multiple times of rough drawing process on the copper bar to obtain a rough copper wire with the diameter of 0.2-2 mm;

and (3) carrying out multi-pass fine drawing process on the coarse copper wire to obtain a copper wire body with the diameter of 10-50 microns.

Technical Field

The invention belongs to the technical field of electronic device packaging, and particularly relates to a copper bonding wire and a preparation method thereof.

Background

In the field of packaging of integrated circuits or LEDs, electrical connections between the chip and the substrate (or lead frame) provide for the chip to deliver power and signals. In the current interconnection mode, the wire bonding technology occupies about 90%, which is to use a thin metal wire as a bonding wire, and use heat, pressure and ultrasonic energy to make the metal wire and a substrate pad tightly welded together, so as to realize the electrical interconnection between the chips and the substrate and the information intercommunication between the chips. The process is that the bonding wire is fixed on the bonding equipment through a special ceramic nozzle, the tail part of the bonding wire is provided with a bonding wire with a certain length, the tail part of the bonding wire is melted into a sphere through external arc discharge, then the spherical bonding wire is extruded and connected to an electrode of an electronic chip through the ceramic nozzle, finally the other end of the bonding wire is connected to an external lead frame through the movement of the bonding equipment, and the bonding wire is packaged by plastic resin.

At present, most bonding wires take gold with the purity of over 99.99 percent as a main material, and the gold as an inert metal has good oxidation resistance and excellent conductivity and stability. However, gold, as a precious metal, is very expensive, and is only used in high-end products with high reliability requirements at present. In order to adapt to the great trend of reducing the cost, copper bonding wires are developed in the industry. Copper has good application prospect in the field of bonding wires as a material with high electric conductivity, heat conductivity and relatively low cost, but has poor oxidation resistance and mechanical property, and is easy to cause the condition of insufficient soldering or wire breaking, thus causing poor service reliability of components.

Disclosure of Invention

In view of the defects in the prior art, the invention provides a copper bonding wire and a preparation method thereof, and aims to solve the problems of poor oxidation resistance and poor mechanical property of the existing copper bonding wire.

In order to achieve the above object, an aspect of the present invention provides a copper bonding wire, where the copper bonding wire includes a copper wire body and a nano-twin copper shell coated on a surface of the copper wire body, the nano-twin copper shell is composed of columnar crystals with a grain boundary interface perpendicular to the surface of the copper wire body, and the columnar crystals include a stacked nano-twin lamellar structure.

Specifically, the growth direction of the nano twin crystal layer in each columnar crystal is vertical or nearly vertical to the grain boundary interface of the corresponding columnar crystal, and the growth directions of the nano twin crystal layers in the same columnar crystal are the same.

Specifically, the diameter of the copper wire body is 10-50 μm, and the thickness of the nanometer twin crystal copper shell is 0.2-12 μm.

Specifically, the thickness of the nanometer twin crystal layer is 10 nm-50 nm, and the width of the columnar crystal is 0.5 μm-10 μm.

Specifically, the material of the copper wire body is copper with the purity of not less than 99.99%, and the nanometer twin crystal copper shell is formed on the surface of the copper wire body through an electrochemical deposition process.

Another aspect of the present invention provides a method for preparing a copper bonding wire as described above, comprising:

sequentially carrying out vacuum melting, directional continuous casting and drawing processes on a copper block to prepare a copper wire body;

sequentially carrying out heat treatment and cleaning treatment on the copper wire body;

carrying out an electroplating process on the cleaned copper wire body, and forming the nanometer twin crystal copper shell on the surface of the copper wire body to obtain the copper bonding wire;

the electrolyte in the electroplating process comprises copper sulfate, sulfuric acid, sodium chloride, an electroplating additive and water.

Specifically, the concentration of copper sulfate in the electrolyte is 50-200 g/L, the concentration of sulfuric acid is 20-50 g/L, the content of sodium chloride is 30-50 ppm, and the content of electroplating additives is 20-120 ppm.

Specifically, the electroplating process adopts a direct current electroplating process, and the current density is 1A/dm²～5A/dm²The electroplating time is 0.5 min-6 min.

Specifically, the sequentially carrying out heat treatment and cleaning treatment on the copper wire body comprises the following steps: carrying out heat treatment on the copper wire body at the temperature of 250-350 ℃ in a nitrogen atmosphere at the heat treatment speed of 1-3 m/s; and (3) carrying out ultrasonic cleaning on the copper wire body subjected to heat treatment in a sodium hydroxide solution, a sulfuric acid solution and pure water in sequence.

Specifically, the copper wire body is formed by sequentially carrying out vacuum melting, directional continuous casting and drawing processes on a copper block, and comprises the following steps:

selecting a high-purity copper block with the purity of not less than 99.99 percent, and carrying out vacuum melting and directional continuous casting for 1-3 h at the temperature of 1000-1200 ℃ to form a copper rod with the diameter of 6-10 mm;

carrying out multiple times of rough drawing process on the copper bar to obtain a rough copper wire with the diameter of 0.2-2 mm;

and (3) carrying out multi-pass fine drawing process on the coarse copper wire to obtain a copper wire body with the diameter of 10-50 microns.

According to the copper bonding wire provided by the embodiment of the invention, the nano twin crystal copper shell is formed on the surface of the copper wire body, and the nano twin crystal copper shell is composed of columnar crystals comprising laminated nano twin crystal sheets, so that: on one hand, the high-density nanometer twin crystal sheet layer is arranged in the shell structure, the twin crystal has lower Gibbs free energy and is more stable than pure copper coarse crystal, and meanwhile, the twin crystal replaces an easily oxidized crystal boundary, so that the surface of the copper bonding wire has better oxidation resistance; on the other hand, the shell structure is internally provided with a high-density nanometer twin crystal layer, and the twin crystal can play a role in hindering dislocation sliding in the metal deformation process, so that the tensile strength of the copper bonding wire is enhanced, and the wire breakage resistance of the bonding wire is improved. The preparation method of the copper bonding wire provided by the embodiment of the invention has the advantages of simple process flow and easy realization of process conditions, and is beneficial to large-scale industrial application.

Drawings

Fig. 1 is a schematic structural diagram of a copper bonding wire according to an embodiment of the present invention;

fig. 2 is an enlarged schematic cross-sectional view of a copper bonding wire according to an embodiment of the present invention;

fig. 3 is a process flow diagram of a method for manufacturing a copper bonding wire according to an embodiment of the present invention;

FIG. 4 is an SEM image of a nano-twin copper shell in a copper bonding wire according to example 1 of the present invention;

FIG. 5 is a TEM image of a nano-twin copper sheath in a copper bonding wire of example 1 of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, embodiments of the present invention are described in detail below with reference to the accompanying drawings. Examples of these preferred embodiments are illustrated in the accompanying drawings. The embodiments of the invention shown in the drawings and described in accordance with the drawings are exemplary only, and the invention is not limited to these embodiments.

It should be noted that, in order to avoid obscuring the present invention with unnecessary details, only the structures and/or processing steps closely related to the scheme according to the present invention are shown in the drawings, and other details not so relevant to the present invention are omitted.

The embodiment of the invention firstly provides a copper bonding wire, referring to fig. 1 and fig. 2, the copper bonding wire comprises a copper wire body 1 and a nanometer twin crystal copper shell 2 coated on the surface of the copper wire body 1, the nanometer twin crystal copper shell 2 is composed of columnar crystals 3 with a grain boundary interface vertical to the surface of the copper wire body 1, and the columnar crystals 3 internally comprise a laminated nanometer twin crystal lamellar structure.

Specifically, the growth direction of the nano twin crystal layer in each columnar crystal 3 is perpendicular or nearly perpendicular to the grain boundary interface of the corresponding columnar crystal 3, and the growth directions of the nano twin crystal layers in the same columnar crystal 3 are the same.

By forming the nano twin crystal copper shell on the surface of the copper wire body, the high-density nano twin crystal lamella organization structure is more stable than that of a pure copper coarse crystal, and meanwhile, the twin crystal replaces an easily-oxidized crystal boundary, so that the surface of the copper bonding wire has better oxidation resistance; in addition, the twin structure can play a role in hindering dislocation slippage in the metal deformation process, so that the tensile strength of the copper bonding wire is enhanced, and the wire breakage resistance of the bonding wire is improved.

In a preferable scheme, the diameter of the copper wire body can be set to be 10-50 μm, and the thickness of the nano twin crystal copper shell is set to be in the range of 0.2-12 μm.

In a preferable scheme, the thickness of the nanometer twin crystal lamella is 10 nm-50 nm, and the width of the columnar crystal is 0.5 μm-10 μm.

In a specific scheme, the copper wire body is made of copper with the purity of not less than 99.99%, and the nanometer twin crystal copper shell is formed on the surface of the copper wire body through an electrochemical deposition process.

The embodiment of the present invention further provides a method for manufacturing the copper bonding wire, which includes the following steps, with reference to fig. 3:

and step S10, sequentially carrying out vacuum melting, directional continuous casting and drawing processes on the copper block to prepare a copper wire body.

In a preferred technical solution, the step S10 specifically includes:

s11, selecting high-purity copper blocks with the purity not lower than 99.99%, and carrying out vacuum melting and directional continuous casting for 1-3 h at the temperature of 1000-1200 ℃ to form copper bars with the diameter of 6-10 mm.

S12, performing multiple times of rough drawing on the copper rod to obtain a rough copper wire with the diameter of 0.2-2 mm.

And S13, carrying out multi-pass fine drawing process on the coarse copper wire to obtain a copper wire body with the diameter of 10-50 microns.

And step S20, sequentially carrying out heat treatment and cleaning treatment on the copper wire body.

In a preferred embodiment, the heat treatment is specifically: and carrying out heat treatment on the copper wire body at the temperature of 250-350 ℃ in a nitrogen atmosphere, wherein the heat treatment speed is 1-3 m/s.

In a preferable scheme, the copper wire body after heat treatment is subjected to ultrasonic cleaning in a sodium hydroxide solution, a sulfuric acid solution and pure water in sequence. Among them, the concentration of the sodium hydroxide solution is preferably 10%, and the concentration of the sulfuric acid solution is preferably 10%.

Step S30, carrying out an electroplating process on the cleaned copper wire body, and forming the nanometer twin crystal copper shell on the surface of the copper wire body to obtain the copper bonding wire.

The electrolyte in the electroplating process comprises copper sulfate, sulfuric acid, sodium chloride, an electroplating additive and water. Specifically, in the electrolyte, the concentration of copper sulfate is 50-200 g/L, the concentration of sulfuric acid is 20-50 g/L, the content of sodium chloride is 30-50 ppm, and the content of electroplating additives is 20-120 ppm.

Such as wetting agents, levelers, brighteners, accelerators, surfactants, and the like.

Specifically, the electroplating process adopts a direct current electroplating process, and the current density is 1A/dm²～5A/dm²The electroplating time is 0.5 min-6 min.

As described above, according to the copper bonding wire and the method for manufacturing the same provided in the embodiments, the copper bonding wire is completely made of high-purity copper, and no alloying or plating of a dissimilar metal plating layer is performed, so that the conductivity of the copper bonding wire is close to that of pure copper, and the problem of conductivity reduction due to alloying is not caused. Further, the copper bonding wire is completely made of high-purity copper, and noble metal materials are not doped or electroplated, so that the cost has a great advantage.

The copper bonding wire prepared by the invention has the drawing rate of 10 at room temperature^-3s^-1The test is carried out under the condition, the tensile strength is up to 300 MPa-500 MPa, and the micro Vickers hardness is up to 1.5 GPa-2.5 GPa.

Example 1

(1) High-purity copper blocks with the purity of 99.99 percent are selected and subjected to vacuum melting at 1100 ℃ for 2 hours and directional continuous casting process to form copper rods with the diameter of 8 mm.

(2) And carrying out 15 times of rough drawing on the copper bar obtained by continuous casting to obtain a rough copper wire with the diameter of 1 mm.

(3) And carrying out multiple fine drawing on the thick copper wire to finally obtain a 15-micron copper wire body.

(4) And carrying out 350 ℃ heat treatment on the copper wire body in a nitrogen atmosphere, wherein the heat treatment speed is 2 m/s.

(5) And respectively carrying out ultrasonic cleaning on the copper wire body obtained by the heat treatment in 10% sodium hydroxide, 10% sulfuric acid and pure water.

(6) And forming a shell with the thickness of 2.5 mu m on the surface of the copper wire body in a direct current electroplating mode, wherein the shell is provided with a microstructure of the high-density nanometer twin crystal sheet layer.

Specifically, a copper sulfate system plating solution is used in the direct current, and a phosphor-copper ball is selected as an anode. The content of copper sulfate in the electrolyte is 200g/L, the content of sulfuric acid is 30mL/L, the content of sodium chloride is 50ppm, the content of gelatin as a twin crystal accelerator is 100ppm, and the content of SPS as a brightener is 5 ppm.

Specifically, the plating parameters of this embodiment are: the current density is 2A/dm²The electroplating time is 5min, and the ambient temperature is room temperature.

In this embodiment, a copper bonding wire with a diameter of 20 μm is finally prepared, and finally the copper bonding wire is rewound and packaged. FIG. 4 is an SEM image of a nano-twin copper shell in the copper bonding wire obtained in the embodiment; fig. 5 is a TEM image of a nano-twin copper shell in the copper bonding wire obtained in this example.

For the copper bonding wire prepared in this example: the electrochemical polarization curve measured a corrosion current density of 0.03mA/cm in a 3.5 wt.% NaCl solution²About 1/3 of coarse-grain pure copper, and has excellent oxidation resistance. At room temperature and a drawing rate of 10^-3s^-1Under the condition, the measured maximum tensile strength is 383MPa, the micro Vickers hardness is 1.9GPa, and the neck fracture resistance is greatly superior to that of a pure copper bonding wire.

Example 2

(1) High-purity copper blocks with the purity of 99.99 percent are selected and subjected to vacuum melting at 1200 ℃ for 1.5 hours and directional continuous casting process to form copper rods with the diameter of 10 mm.

(2) And carrying out 20 times of rough drawing on the copper bar obtained by continuous casting to obtain a rough copper wire with the diameter of 1.5 mm.

(3) And carrying out multiple fine drawing on the thick copper wire to finally obtain a 40-micron copper wire body.

(4) And carrying out heat treatment on the copper wire body at 300 ℃ in a nitrogen atmosphere, wherein the heat treatment speed is 1 m/s.

(5) And respectively carrying out ultrasonic cleaning on the copper wire body obtained by the heat treatment in 10% sodium hydroxide, 10% sulfuric acid and pure water.

(6) And forming a shell with the thickness of 5 mu m on the surface of the copper wire body in a direct current electroplating mode, wherein the shell is provided with a microstructure of the high-density nanometer twin crystal sheet layer.

Specifically, a copper sulfate system plating solution is used in the direct current, and a phosphor-copper ball is selected as an anode. The content of copper sulfate in the electrolyte is 150g/L, the content of sulfuric acid is 50mL/L, the content of sodium chloride is 40ppm, the content of gelatin as a twin crystal accelerator is 40ppm, and the content of SPS as a brightener is 2 ppm.

Specifically, the plating parameters of this embodiment are: the current density is 5A/dm²The electroplating time is 2min, and the environmental temperature is 30 ℃.

In this embodiment, a copper bonding wire with a diameter of 50 μm is finally prepared, and finally the copper bonding wire is rewound and packaged.

For the copper bonding wire prepared in this example: the electrochemical polarization curve measured a corrosion current density of 0.018mA/cm in a 3.5 wt.% NaCl solution²And the oxidation resistance is excellent. At room temperature and a drawing rate of 10^-3s^-1Under the condition of (1), the measured maximum tensile strength is 451MPa, the micro Vickers hardness is 2.1GPa, and the neck fracture resistance is greatly superior to that of a pure copper bonding wire.

In summary, according to the copper bonding wire provided by the embodiment of the invention, the nanometer twin crystal copper shell is formed on the surface of the copper wire body, so that the oxidation resistance of the copper bonding wire is improved, the tensile strength of the copper bonding wire is enhanced, the wire breakage resistance of the bonding wire is improved, and the use requirements of a chip and an external packaging substrate are met.

The foregoing is directed to embodiments of the present application and it is noted that numerous modifications and adaptations may be made by those skilled in the art without departing from the principles of the present application and are intended to be within the scope of the present application.