JP7774697B2 - Bonding wire, its preparation method and LED device - Google Patents

Description

The present invention belongs to the technical field of packaging materials, and in particular relates to bonding wires, their preparation methods, and LED devices.

Wire bonding is the most common interconnection method for IC packaging, serving as the vital path for chip connection lead frames, fulfilling the functions of signal transmission and electrical connection. It is also one of the essential basic raw materials for the repackaging manufacturing process of integrated circuits, semiconductor discrete devices, and LED light source devices. Bonding wires mainly include gold wire, silver wire, copper wire, aluminum wire, etc.

With the development of multi-lead, high-integration, and miniaturization in integrated circuits and semiconductor packaging, the impact of bonding wire on devices is becoming increasingly significant, necessitating the use of bonding wire with smaller wire diameters and better electrochemical performance for narrower pitches and longer distances. Gold bonding wire is expensive, copper bonding wire is highly susceptible to oxidation and has poor performance, and aluminum wire is used in low-end products. In contrast, silver bonding wire has excellent electrical and thermal performance, can reduce high-frequency noise in devices, can reduce heat generation in high-power LEDs, has good stability, and is cost-effective, making it widely used in microelectronic packaging. However, silver bonding wire often suffers from problems such as low bonding strength, unstable performance, poor corrosion resistance and high-temperature stability, and high-power devices becoming inoperable due to overheating, significantly limiting its development.
In view of this, the present invention has been devised.

The primary objective of the present invention is to provide a bonding wire with excellent mechanical properties, high-temperature stability, and reliability.

A second object of the present invention is to provide a method for preparing bonding wire that can improve the mechanical properties, high-temperature stability, and reliability of the bonding wire.

A third object of the present invention is to provide an LED device with excellent bonding reliability.

To achieve the above objectives of the present invention, the following technical solutions are particularly adopted.

The present invention provides a bonding wire. The bonding wire includes a core material containing, by mass fraction, 5 wt% to 10 wt% Cu, 2 wt% to 7 wt% graphene, 0.25 wt% to 0.5 wt% Sm, 1 wt% to 1.5 wt% Zr, and the remainder Ag.

Furthermore, the mass ratio of the Cu to the Sm is (19-21):1.

Furthermore, at least one of the following is included: (1) the graphene includes single-layer graphene; (2) the particle size of the single-layer graphene is 0.1 to 0.5 μm; and (3) the thickness of the single-layer graphene is less than 1 nm.

The core material may further include a protective layer provided on the surface thereof, and/or the protective layer provided on the surface thereof may include one or more of Al ₂ O ₃ , ZrO ₂ and SiO ₂ .

Furthermore, the bonding wire has at least one of the following characteristics: (1) a diameter of 15 to 25 μm; (2) a thickness of the protective layer of 0.3 to 2 μm; and (3) a ratio of the thickness of the protective layer to the diameter of (0.02 to 0.08):1.

The present invention further provides a method for preparing the above-mentioned bonding wire. The method includes step S1 of vacuum gas atomizing an Ag/Cu/Sm intermediate alloy to obtain intermediate alloy powder, and step S2 of mixing the intermediate alloy powder with Zr powder and graphene powder, followed by mold pressing, vacuum sintering, extrusion, and drawing, in that order, to obtain wire.

Furthermore, in step S1, the vacuum gas atomization pressure is 10 to 12 MPa, and/or the particle size D50 of the intermediate alloy powder is 35 to 50 μm.

Furthermore, step S2 includes at least one of the following: (1) the mold press pressure is 150 to 200 MPa; (2) the vacuum sintering includes sintering at 780 to 800°C for 3 to 5 hours; and (3) the extrusion temperature is 750 to 780°C and the extrusion speed is 4 to 7 mm/s.

Furthermore, the above-mentioned method for preparing bonding wire further includes a step of performing vapor phase growth on the surface of the wire to obtain a protective layer, and/or a step of performing vapor phase growth on the surface of the wire to obtain a protective layer, and then performing a wiredrawing process after the vapor phase growth.

The present invention further provides an LED device. The LED device includes the above-described bonding wire or a bonding wire prepared by the above-described method for preparing a bonding wire.

Compared with the prior art, the present invention has the following beneficial effects:
1. The bonding wire of the present invention optimizes the components of the silver alloy, and adds Zr and graphene to the silver alloy, in cooperation with Cu and Sm, to improve the mechanical properties of the silver alloy bonding wire, resulting in relatively high strength and tensile breaking strength, allowing for micro-machining, and improving the electromigration resistance, high temperature resistance, and reliability of the bonding wire, which can meet the requirements of high-power LED packaging and can be used for bonding high-power LED devices in complex bonding environments such as low loops and sustained high temperatures.
2. The bonding wire according to the present invention can further improve the corrosion resistance of the bonding wire by providing a protective layer on the surface of the silver alloy core material.
3. The method for preparing a bonding wire according to the present invention employs processes of atomization powder preparation, mold pressing, vacuum sintering, and extrusion, and introduces graphene with a high melting point to be uniformly distributed in the bonding wire system, thereby producing a bonding wire with excellent performance.

The following specific embodiments are used to clearly and completely explain the technical solutions of the present invention. Those skilled in the art will understand that the described examples are only some of the examples of the present invention, not all of the examples, and are intended only to illustrate the present invention and not to limit the scope of the present invention. All other examples obtained by those skilled in the art based on the examples of the present invention without using their inventive abilities also fall within the scope of protection of the present invention. In the examples, where specific conditions are not specified, they can be carried out under conventional conditions or conditions recommended by the manufacturer. For reagents or equipment for which the preparation manufacturer is not specified, conventional commercially available products can be used.

Note that the term "and/or" used in this specification represents a relationship between related objects, and indicates that a three-way relationship exists. For example, A and/or B represents a three-way relationship in which only A exists, both A and B exist, and only B exists.

Some embodiments of the present invention provide a bonding wire. The bonding wire includes a core material containing, by mass fraction, 5 wt% to 10 wt% Cu, 2 wt% to 7 wt% graphene, 0.25 wt% to 0.5 wt% Sm, 1 wt% to 1.5 wt% Zr, and the balance Ag.

The bonding wire according to the present invention includes a core material, which is a silver alloy. The addition of Zr to the core material contributes to the refinement of crystal grains and improves the high-temperature stability of the bonding wire. Graphene, as a nano-reinforcement phase, increases the strength of the bonding wire, pins stacking faults and grain boundaries, effectively inhibits the thermal movement of stacking faults and grain boundaries, and significantly improves the thermal stability of the bonding wire. The addition of Cu increases the ductility and strength of the bonding wire. The addition of Sm accumulates at the grain boundaries, reducing diffusion along the grain boundaries and improving electromigration resistance and reliability.

By adding Zr and graphene to the bonding wire and rationally controlling their content, the present invention can contribute to improving the strength and high-temperature stability of the bonding wire, and the cooperation of Cu and Sm can contribute to improving cycle temperature stability, strength, electromigration resistance, etc. As described above, the cooperation of each element can improve the basic performance and application reliability of the bonding wire.

The bonding wire of the present invention has excellent mechanical properties, relatively high strength and tensile breaking strength, is capable of being finely processed, and has excellent corrosion resistance, high temperature resistance and electromigration resistance, and can meet the requirements for bonding high-power LED devices in complex bonding environments such as low loops and sustained high temperatures.

In some embodiments of the present invention, as representative and non-limiting examples, the mass fraction of Cu in the core material is 5 wt%, 5.5 wt%, 6 wt%, 6.5 wt%, 7 wt%, 7.5 wt%, 8 wt%, 8.5 wt%, 9 wt%, 9.5 wt%, 10 wt%, or a value within a range consisting of any two values therein, and the mass fraction of graphene is 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, 5 wt%, 6 wt%, 7.5 wt%, 8 wt%, 8.5 wt%, 9 wt%, 9.5 wt%, 10 wt%, or a value within a range consisting of any two values therein. The mass fraction of Sm is 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, or a value within a range consisting of any two of these values; the mass fraction of Zr is 1 wt%, 1.1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%, or a value within a range consisting of any two of these values.

In some embodiments of the present invention, the core material contains, by mass fraction, 6.5 wt% to 7.5 wt% Cu, 4.5 wt% to 5.5 wt% graphene, 0.3 wt% to 0.4 wt% Sm, 1.1 wt% to 1.3 wt% Zr, and the remainder Ag.

The present invention further optimizes the components of the core material, and by keeping each component within the above range, it is possible to obtain a bonding wire with even better performance.

In some embodiments of the present invention, the mass ratio of Cu to Sm is (19-21):1, preferably 20:1. The cooperation of Cu and Sm elements can contribute to improving the strength and cycle temperature stability of the bonding wire.

In some embodiments of the present invention, the core material has a total mass fraction of Cu and graphene of 12%. The combination of Cu and graphene can contribute to improving the strength, high-temperature stability, and reliability of the bonding wire.

In some embodiments of the present invention, the graphene comprises single-layer graphene.

In some embodiments of the present invention, the particle size of the single-layer graphene is 0.1 to 0.5 μm.

In some embodiments of the present invention, the thickness of the single-layer graphene is less than 1 nm.

If the graphene particle size is too large, the mechanical properties of the alloy will deteriorate, and if the graphene particle size is too small, it will aggregate during melting and will not be uniformly distributed.

In some embodiments of the present invention, the bonding wire further includes a protective layer provided on the surface of the core material.

In some embodiments of the present invention, the protective layer comprises one or more of Al ₂ O ₃ , ZrO ₂ and SiO _2. For example, the protective layer is an Al ₂ O ₃ layer, a ZrO ₂ layer or a SiO ₂ layer.

The protective layer of the present invention has insulating, corrosion-resistant, and abrasion-resistant properties, and in combination with the core material can further improve the strength of the bonding wire.

In some embodiments of the present invention, the diameter of the bonding wire is 15-25 μm, typically and non-limitingly, for example, 15 μm, 20 μm, 25 μm, or a range consisting of any two values therein.

In some embodiments of the present invention, the thickness of the protective layer is 0.3 to 2 μm, and representative, but non-limiting examples include 0.3 μm, 0.5 μm, 1 μm, 1.5 μm, 2 μm, or a range consisting of any two of these values.

In some embodiments of the present invention, the ratio of the thickness of the protective layer to the diameter of the bonding wire is (0.02-0.08):1.

In some embodiments of the present invention, the tensile break strength of the bonding wire is 5 to 6 g, preferably 5.5 to 6 g.

In some embodiments of the present invention, the elongation of the bonding wire is 8% to 9%, preferably 8.5% to 9%.

In some embodiments of the present invention, the minimum loop height of the bonding wire is 80 μm, preferably less than 70 μm.

Some embodiments of the present invention further provide a method for preparing the above-mentioned bonding wire. The preparation method includes the following steps:

Step S1: Vacuum gas atomization is performed on the Ag/Cu/Sm intermediate alloy to obtain intermediate alloy powder.

Step S2: After mixing the intermediate alloy powder, Zr powder, and graphene powder, the mixture is mold pressed, vacuum sintered, extruded, and drawn in order to obtain a wire.

The bonding wire preparation method of the present invention employs the processes of atomization powder preparation, mold pressing, vacuum sintering, and extrusion to introduce graphene, which has a high melting point, into a silver alloy system and distribute it uniformly throughout the silver alloy. Utilizing the properties of graphene, including high strength, high thermal conductivity, and ultra-high temperature stability, the strength, high temperature stability, and electromigration resistance of the bonding wire can be improved.

In some embodiments of the present invention, the method for preparing an Ag/Cu/Sm intermediate alloy in step S1 includes the following:

The Ag, Cu, and Sm raw materials are weighed according to the blending ratio and placed in a crucible in a vacuum furnace. The furnace door is closed, the furnace is evacuated to 3×10 ⁻² Pa, and argon gas is added to the furnace until the pressure reaches 0.1-0.3 Pa. The temperature is raised to 600-800°C, and the furnace is again evacuated to 2×10 ⁻² Pa. Argon gas is then added to the furnace until the pressure reaches 0.1-0.3 Pa. The temperature is raised to 1150-1200°C and refined for 20-30 minutes, during which time the material is stirred in one direction using a magnetic stir bar. After cooling, an Ag/Cu/Sm intermediate alloy is obtained. Preferably, the purity of each of the Ag, Cu, and Sm raw materials is greater than 99.99%. The crucible includes a high-purity graphite crucible.

In some embodiments of the present invention, the vacuum gas atomization pressure in step S1 is 10 to 12 MPa.

In some embodiments of the present invention, the cooling rate of the molten metal during the vacuum gas atomization process in step S1 is 100 to 105°C/s.

In some embodiments of the present invention, the particle size D50 of the intermediate alloy powder in step S1 is 35 to 50 μm.

In some embodiments of the present invention, in step S2, mixing includes weighing the intermediate alloy powder, Zr powder, and graphene powder according to a formulation and ball milling them. Preferably, the rotation speed of the ball mill is 300 to 500 r/min. The ball milling time is 5 to 7 hours. The volume ratio of balls to materials in the ball milling is 3:1. Preferably, the Zr powder has a purity of 99.9% or more and a particle size of 35 to 50 μm.

In some embodiments of the present invention, the mold pressing pressure in step S2 is 150 to 200 MPa. Preferably, the mold pressing includes pre-press molding the mixed material using a mold with a diameter of 30 to 50 mm.

In some embodiments of the present invention, the vacuum sintering in step S2 includes sintering at 780-800° C. for 3-5 hours. Preferably, the vacuum degree in the vacuum sintering process is 2×10 ⁻² Pa.

In some embodiments of the present invention, the extrusion temperature in step S2 is 750 to 780°C, and the extrusion speed is 4 to 7 mm/s. Preferably, the extrusion produces a rod having a diameter of 12 to 15 mm.

In some embodiments of the present invention, the drawing includes at least two drawing processes, with a heat treatment being performed after each drawing process before the next drawing process. Preferably, the drawing includes a first drawing process, a heat treatment, and a second drawing process, in sequence.

In some embodiments of the present invention, in step S2, the extruded rod is subjected to a first wire drawing process to obtain a wire having a diameter of 0.6 to 1.0 mm. If the diameter of the wire exceeds 6 mm, the deformation rate of the wire is 12% to 15%, and if the diameter of the wire is less than 6 mm, the deformation rate is 8% to 10%.

In some embodiments of the present invention, the heat treatment in step S2 involves heat treating the wire rod after the first wiredrawing at 400 to 450° C. for 3 to 5 hours. Preferably, the heat treatment is performed at a temperature rise rate of 2 to 3.5° C./s and at a vacuum degree of more than 10 ⁻² Pa.

In some embodiments of the present invention, the second wiredrawing process in step S2 involves performing multiple passes of drawing on the heat-treated wire to obtain a wire with a diameter of 0.07 to 0.1 mm. If the wire diameter is greater than 0.5 mm, the deformation rate is 8% to 11%, and the wiredrawing speed is 7 to 10 m/s. If the wire diameter is less than 0.5 mm, the deformation rate is 7% to 10%, and the wiredrawing speed is 3 to 5 m/s.

In some embodiments of the present invention, the method for preparing a bonding wire includes vapor deposition on the surface of a core material to obtain a protective layer.

In some embodiments of the present invention, the method for preparing a protective layer comprises the following steps:

After the second wire drawing process, the wire is subjected to continuous vacuum deposition using high-purity Al, Si, or Ti as the target material, and high-purity _Ar2 and _O2 as the sputtering gas and reactive gas. Magnetron sputtering vacuum deposition technology is then used to uniformly sputter the surface of the wire to form a protective layer of 1 to 10 μm.

In some embodiments of the present invention, the method further includes a wire drawing process after vapor growth. Preferably, the vapor grown wire is subjected to a wire drawing process to obtain a bonding wire having a diameter of 15 to 25 μm. The wire drawing process is performed at a drawing speed of 2 to 4 m/s and a deformation ratio of 6% to 8%.

Some embodiments of the present invention further provide an LED device. The LED device includes the above-described bonding wire or a bonding wire prepared by the above-described method for preparing a bonding wire.

The bonding wire of the present invention can meet the requirements of high-power LED packaging and can be used to bond high-power LED devices in complex bonding environments such as low loops and sustained high temperatures.

Example 1
This example provides a method for preparing a bonding wire. The components and contents (mass fractions) of the core material of the prepared bonding wire are shown in Table 1.

Specifically, the above-mentioned bonding wire preparation method includes the following steps:

Step S1: Ag, Cu and Sm raw materials with a purity of over 99.99% are weighed out, and the weighed raw materials are placed in a high-purity graphite crucible in a vacuum furnace according to the formulation. The furnace door is closed and the furnace is evacuated to 3×10 ⁻² Pa, and argon gas is charged to 0.1-0.3 Pa. The temperature is raised to 600-800°C, and the furnace is evacuated again to 2×10 ⁻² Pa. Argon gas is charged to 0.1-0.3 Pa. The temperature is raised to 1150-1200°C and refined for 20-30 minutes, during which time the mixture is stirred in one direction using a magnetic stirrer bar, and the furnace is cooled to obtain an Ag/Cu/Sm intermediate alloy.

Step S2: Vacuum gas atomization was performed on the Ag/Cu/Sm intermediate alloy to obtain intermediate alloy powder with a particle size D50 of 35 to 50 μm. The atomization gas pressure was 10 to 12 MPa, and the cooling rate of the molten metal was 100 to 105°C/s.

Step S3: According to the formulation, the weighed intermediate alloy powder, Zr powder (purity: 99.9%, particle size: 35-50 μm), and single-layer graphene powder (particle size D50: 0.1-0.5 μm, thickness: less than 1 nm) were ball milled to obtain a mixed material. The volume ratio of balls to material was 3:1, the rotation speed was 300-500 r/min, and the ball milling time was 5-7 hours.

Step S4: The mixed material was press-molded into a mold having a diameter of 30 to 50 mm at a pressure of 150 to 200 MPa, and then sintered at a temperature of 780 to 800° C. under a vacuum of 2×10 ⁻² Pa for 3 to 5 hours.

Step S5: After sintering, extrusion was performed to obtain rods with a diameter of 12 to 15 mm. The extrusion temperature was 750 to 780°C, and the extrusion speed was 4 to 7 mm/s.

Step S6: The rod material with a diameter of 12 to 15 mm is drawn into a wire material with a diameter of 0.6 to 1.0 mm using a wire drawing machine. If the diameter of the wire material is greater than 6 mm, the deformation rate of the wire material is 12% to 15%, and if the diameter is less than 6 mm, the deformation rate is 8% to 10%.

Step S7: A wire rod having a diameter of 0.6 to 1.0 mm was placed in a vacuum annealing furnace, heated to 400 to 450° C. at a rate of 2 to 3.5° C./s under a vacuum of more than 10 ⁻² Pa, and heat-treated for 3 to 5 hours.

Step S8: The heat-treated wire is subjected to multiple passes of drawing using a multi-wire drawing machine to produce a wire with a diameter of 0.07 to 0.1 mm. If the wire diameter is greater than 0.5 mm, the deformation rate is 8% to 11% and the wire drawing speed is 7 to 10 m/s. If the wire diameter is less than 0.5 mm, the deformation rate is 7% to 10% and the wire drawing speed is 3 to 5 m/s.

Step S9: For wires with a diameter of 0.07 to 0.1 mm, a continuous vacuum deposition facility is used, Si is used as the target material, P-type single crystal Si is used, and high-purity _Ar2 and _O2 are used as the sputtering gas and reactive gas. Magnetron sputtering vacuum deposition technology is used to uniformly sputter the surface to form a 1 to 10 μm thick _SiO2 protective layer.

Step S10: After magnetron sputtering, the wire was drawn using a wire drawing machine to a diameter of 15 μm. The drawing speed was 2-4 m/s and the deformation rate was 6-8%. The wire was then ultrasonically cleaned for over 30 minutes, dried by spraying with nitrogen gas, and wound on a reel and packaged to obtain bonding wire.

<Comparative Example 1>
This comparative example provided a method for preparing a bonding wire. The components and contents (mass fractions) of the core material of the prepared bonding wire are shown in Table 2.

For the method of preparing the above bonding wire, refer to Example 1.

<Test Example 1>
The bonding wires of Example 1 and Comparative Example 1, each having a diameter of 15 μm, were subjected to mechanical property tests, and the results are shown in Table 3.

Tensile breaking strength and elongation tests were performed in accordance with the IPC-9702 standard.

Tests were conducted using bonding wires from Example 1 and Comparative Example 1 on the Al pads of the memory, and the results are shown in Table 3.

HTST (High Temperature Storage Test): Test conditions were 150°C, and standard JESD22-A103-A was referenced.

TCT (Temperature Cycle Aging Test): Test conditions were -55 to 125°C, and standard JESD22-A104-A was referenced.

As can be seen from Table 3, compared to Comparative Example 1, the bonding wire of the present invention had a higher tensile breaking strength and elongation, a relatively small minimum loop height, and better bonding reliability.

The above embodiments are merely intended to illustrate the technical solutions of the present invention and are not intended to limit the same. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art may modify the technical solutions described in the above embodiments and make equivalent substitutions for some or all of the technical features therein. These modifications or substitutions do not deviate from the essence of the relevant technical solutions and the scope of the technical solutions of the embodiments of the present invention.

Claims (10)

Including core material,
The core material contains, by mass fraction, Cu: 5 wt% to 10 wt%, graphene: 2 wt% to 7 wt%, Sm: 0.25 wt% to 0.5 wt%, Zr: 1 wt% to 1.5 wt%, and the balance is Ag. Bonding wire. The bonding wire described in claim 1, characterized in that the mass ratio of the Cu to the Sm is (19-21):1. (1) The graphene includes a single-layer graphene;
(2) the particle size of the single-layer graphene is 0.1 to 0.5 μm;
and (3) the thickness of the single layer graphene is less than 1 nm;
2. The bonding wire according to claim 1, comprising at least one of: Further comprising a protective layer provided on the surface of the core material,
Alternatively, the bonding wire according to claim 1 further comprises a protective layer provided on the surface of the core material, the protective layer comprising one or more of Al ₂ O ₃ , ZrO ₂ and SiO ₂ . (1) The diameter is 15 to 25 μm.
(2) The thickness of the protective layer is 0.3 to 2 μm.
and (3) the ratio of the thickness of the protective layer to the diameter is (0.02-0.08):1;
5. The bonding wire according to claim 4, comprising at least one of: A method for preparing a bonding wire according to any one of claims 1 to 5, comprising:
Step S1: subjecting the Ag/Cu/Sm intermediate alloy to vacuum gas atomization to obtain intermediate alloy powder;
and step S2 of mixing the intermediate alloy powder, Zr powder, and graphene powder, and then performing mold pressing, vacuum sintering, extrusion, and drawing in that order to obtain a wire. In step S1,
The pressure of the vacuum gas atomization is 10 to 12 MPa.
And/or, the particle size D50 of the intermediate alloy powder is 35 to 50 μm, characterized in that the method for preparing a bonding wire according to claim 6. In step S2,
(1) The pressure of the mold press is 150 to 200 MPa;
(2) The vacuum sintering includes sintering at 780 to 800°C for 3 to 5 hours;
and (3) the temperature of the extrusion is 750 to 780°C and the speed of the extrusion is 4 to 7 mm/s;
7. The method for preparing a bonding wire according to claim 6, further comprising at least one of: Further comprising a step of performing vapor deposition on the surface of the wire to obtain a protective layer.
Alternatively, the method for preparing a bonding wire according to claim 6 further comprises a step of performing vapor deposition on the surface of the wire to obtain a protective layer, and performing a wire drawing process after the vapor deposition. An LED device comprising the bonding wire described in any one of claims 1 to 5.