A bonding method of copper-based bonding wire and application thereof

Abstract

This invention belongs to the field of wire bonding technology and discloses a bonding method and application of copper-based bonding wires. The bonding method includes the following steps: depositing a composite metal interlayer at the bonding location on the chip; contacting the bonding end of the copper-based bonding wire with the composite metal interlayer and performing ultrasonic bonding to complete the bonding of the copper-based bonding wire; wherein, in the ultrasonic bonding step, three sets of ultrasonic power and bonding pressure are applied sequentially, satisfying the following conditions: second ultrasonic power > third ultrasonic power > first ultrasonic power, and second bonding pressure ≥ third bonding pressure > first ultrasonic power. This invention effectively overcomes the technical bottlenecks of easy chip damage and easy formation of brittle intermetallic compounds at the bonding interface when copper-based bonding wires are applied to IGBT chips, through the synergistic effect of the composite metal interlayer and the multi-stage gradient ultrasonic bonding process. It achieves a high-strength, non-destructive connection between the copper-based bonding wire and the chip pad, significantly improving the long-term reliability and stability of the bonding interface.

Description

Technical Field

[0001] This invention belongs to the field of wire bonding technology, and specifically relates to a bonding method and application of copper-based bonding wires. Background Technology

[0002] As a core component in the field of power conversion, the reliability of the electrical connection between the internal chip and terminals of the IGBT module plays a decisive role in the overall performance of the module. In related technologies, the industry commonly uses aluminum wire or aluminum strip to ultrasonically bond the IGBT chip and terminals. However, aluminum itself has drawbacks such as low electrical and thermal conductivity, as well as relatively insufficient mechanical strength. This directly leads to significant conduction losses in the IGBT module during operation, and the heat dissipation performance is insufficient for high-performance applications. Furthermore, during long-term power cycling, the mismatch in the thermal expansion coefficients of aluminum and related chip components makes the bonding points prone to fatigue failure, severely impacting the module's lifespan.

[0003] To improve this situation and enhance the performance of IGBT modules, the industry has begun to experiment with using copper, which has superior electrical conductivity and thermomechanical properties, as the bonding wire material, hoping to overcome the various drawbacks of aluminum bonding. However, copper faces two major technical bottlenecks in practical applications. First, copper is much harder than aluminum. When using traditional aluminum wire bonding process parameters for copper-based bonding wires, it is very easy to damage the passivation or metallization layer on the chip surface, thereby impairing the normal function of the chip. Second, copper reacts with the aluminum pads commonly used on the surface of IGBT chips under high-temperature conditions, forming brittle intermetallic compounds. These compounds severely reduce the long-term reliability of the bonding interface, leading to increased contact resistance and even cracking of the bonding interface. Summary of the Invention

[0004] The present invention aims to improve at least one technical problem in the prior art.

[0005] The first aspect of this invention provides a bonding method for copper-based bonding wires, comprising the following steps: Deposit a composite metal interlayer at the bonding sites on the chip; The bonding end of the copper-based bonding wire is brought into contact with the composite metal intermediate layer and ultrasonic bonding is performed to complete the bonding of the copper-based bonding wire. The composite metal interlayer comprises, from bottom to top, a first metal layer, a second metal layer, and a third metal layer, wherein the first metal layer is formed of titanium, the second metal layer is formed of nickel, and the third metal layer is formed of gold or silver. The ultrasonic bonding includes the following steps: Step S1: Apply a first ultrasonic power and a first bonding pressure to the bonding end of the copper-based bonding wire; Step S2: Apply a second ultrasonic power and a second bonding pressure to the bonding end of the copper-based bonding wire; Step S3: Apply a third ultrasonic power and a third bonding pressure to the bonding end of the copper-based bonding wire; The second ultrasonic power > the third ultrasonic power > the first ultrasonic power; The second bonding pressure is greater than or equal to the third bonding pressure and greater than the first bonding pressure.

[0006] The copper-based bonding wire bonding method provided in this application is applicable to copper-based bonding wire bonding of power semiconductor IGBT modules. It aims to solve the problems of high conduction loss, poor heat dissipation, and easy fatigue failure of bonding points in traditional aluminum wire bonding. Simultaneously, it overcomes the technical bottlenecks of high hardness of copper-based bonding wires, which easily damage the chip, and the easy formation of brittle intermetallic compounds between copper and the chip's aluminum pads. This application first deposits a composite metal interlayer at the chip bonding location. The first metal layer, formed of titanium, enhances the adhesion between the composite metal interlayer and the chip bonding location. The second metal layer, formed of nickel, prevents the interdiffusion of metal between the copper-based bonding wire and the chip bonding location. The third metal layer, formed of gold or silver, serves to prevent oxidation and promote bonding. The ultrasonic bonding performed after contacting the copper-based bonding wire bonding end with the composite metal interlayer (the third metal layer) is a multi-stage gradient ultrasonic bonding. This multi-stage gradient ultrasonic bonding is divided into three stages, corresponding to the sequential application of three different sets of ultrasonic power and bonding pressure. The second ultrasonic power is controlled to be greater than the third ultrasonic power, which is greater than the first ultrasonic power, and the second bonding pressure is greater than or equal to the third bonding pressure, which is greater than the first ultrasonic power. The first stage (step S1) is the contact breaking stage, where the applied first ultrasonic power and first bonding pressure are the lowest among the three stages, enabling the copper-based bonding wire to initially contact the composite metal interlayer and break down its surface contamination film. The second stage (step S2) is the plastic deformation stage, where the ultrasonic power and bonding pressure are increased to the highest of the three stages: the second ultrasonic power and the second bonding pressure, causing sufficient plastic deformation of the bonding interface and generating frictional heat. The third stage (step S3) is the diffusion stabilization stage, where the second ultrasonic power is reduced to the third ultrasonic power, and the bonding pressure is maintained at the second bonding pressure (at which point the third bonding pressure equals the second bonding pressure) or reduced, continuously for the corresponding duration to promote the mutual diffusion of interface atoms and form a stable metallurgical bond. The multi-stage gradient ultrasonic bonding method in this application avoids damage to the chip caused by a single high-energy impact while ensuring a high-strength, low-resistance bonding structure between the copper-based bonding wire and the chip, thereby improving the long-term reliability of the bonding interface, reducing the conduction loss of the power semiconductor module, and providing good process controllability to meet the needs of industrial production.

[0007] Preferably, the second ultrasonic power is 60W-175W, the ratio of the second ultrasonic power to the first ultrasonic power is (3-6):1, and the ratio of the second ultrasonic power to the third ultrasonic power is (1.5-3):1.

[0008] Preferably, the first bonding pressure is 0.5N-2N, the second bonding pressure is 2N-8N, and the ratio of the second bonding pressure to the third bonding pressure is 1:(1-0.5).

[0009] More preferably, the ratio of the second bonding pressure to the third bonding pressure is 1:(0.95-0.7).

[0010] Preferably, the duration of step S1 is no more than 15ms, the duration of step S2 is 15ms-50ms, and the duration of step S3 is 30ms-80ms.

[0011] Preferably, the thickness of the first metal layer is 0.1 μm-0.3 μm, the thickness of the second metal layer is 0.5 μm-3 μm, and the thickness of the third metal layer is 0.05 μm-0.2 μm. The total thickness of the composite metal interlayer is 0.65 μm-3.5 μm.

[0012] Preferably, the copper-based binding wire is a pure copper or zirconium copper round wire with a diameter of 100μm-500μm, or a copper strip with a thickness of 100μm-300μm and a width of 0.5mm-2mm.

[0013] Preferably, before ultrasonic bonding, the bonding ends of the copper-based bonding wire are subjected to plasma cleaning, which is performed under the protection of an inert gas.

[0014] During storage or processing, copper-based bonding wires are prone to surface adhesion to oxides and organic matter. These substances hinder atomic diffusion at the bonding interface, affecting the metallurgical bonding effect between the copper-based bonding wire and the composite metal interlayer. Plasma cleaning under inert gas protection can effectively remove oxides and organic matter from the bonding end surface, improving the surface cleanliness and creating favorable interface conditions for subsequent ultrasonic bonding. This, in turn, further enhances the strength and reliability of the bonding structure between the copper-based bonding wire and the chip.

[0015] Preferably, after ultrasonic bonding is completed, inert gas is purged onto the bonding site until the temperature at the bonding site is <150°C.

[0016] During the bonding process, the ultrasonic energy generates heat at the bonding site. The bonding interface, operating at high temperatures, is highly reactive and prone to oxidation upon direct contact with air. This can also promote the formation of brittle materials between the copper-based bonding wire and the composite metal interlayer, affecting the long-term stability of the bonding interface. By purging the bonding site with inert gas, air can be isolated, preventing oxidation of the bonding interface during cooling. Simultaneously, the cooling rate of the bonding site can be accelerated, ensuring stable formation of the bonding interface at low temperatures and thus guaranteeing the long-term performance of the copper-based bonding wire structure.

[0017] Preferably, the composite metal interlayer is obtained by magnetron sputtering deposition.

[0018] The second aspect of the present invention provides the application of the above-described copper-based bonding wire bonding method in the manufacturing of IGBT modules.

[0019] The beneficial effects of this invention are as follows: By combining a composite metal interlayer with a multi-stage gradient ultrasonic bonding process, this invention effectively overcomes the technical bottlenecks of easy chip damage and brittle intermetallic compound formation at the bonding interface when copper-based bonding wires are used for IGBT chip bonding. It achieves a high-strength, non-destructive connection between the copper-based bonding wires and the chip pads, significantly improving the long-term reliability and stability of the bonding interface. Simultaneously, this invention fully leverages the excellent electrical conductivity and thermomechanical properties of copper, improving the electrical performance and heat dissipation of the IGBT module and reducing energy loss during module operation. Furthermore, the entire process solution possesses good controllability and operability, adapting to the needs of industrial production. This provides strong technical support for the research and development and upgrading of high-performance IGBT modules, promoting the performance improvement and industrial development of related power conversion equipment. Attached Figure Description

[0020] Figure 1 This is a microscope image of the bonding process in the copper-based bonding wire bonding method of Example 1; Figure 2 This is a microscope image of the bonding process in the copper-based bonding wire bonding method of Comparative Example 1. Detailed Implementation

[0021] The present invention will be further described below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the description of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0022] Example 1 A bonding method for copper-based bonding wires includes the following steps: A composite metal interlayer is deposited at the bonding location (aluminum pad) of the IGBT chip (model: FF450R12ME4). Argon plasma cleaning was performed on the bonding ends of the copper-based bonding wire (pure copper round wire with a diameter of 300 μm). The plasma cleaning was carried out under the protection of an inert gas (nitrogen). The bonding ends of the copper-based bonding wires are brought into contact with the composite metal interlayer and ultrasonically bonded to complete the bonding of the copper-based bonding wires.

[0023] The composite metal interlayer comprises, from bottom to top, a first metal layer, a second metal layer, and a third metal layer. The first metal layer is formed of titanium, the second metal layer is formed of nickel, and the third metal layer is formed of silver. The first, second, and third metal layers are formed sequentially by magnetron sputtering deposition. The total thickness of the composite metal interlayer is 1.8 μm, the thickness of the first metal layer is 0.2 μm, the thickness of the second metal layer is 1.5 μm, and the thickness of the third metal layer is 0.1 μm.

[0024] Ultrasonic bonding includes the following steps: Step S1: Apply a first ultrasonic power (30W) and a first bonding pressure (1N) to the bonding end of the copper-based bonding wire for a duration of 15ms; Step S2: Apply a second ultrasonic power (120W) and a second bonding pressure (5N) to the bonding end of the copper-based bonding wire for a duration of 35ms; Step S3: Apply a third ultrasonic power (50W) and a third bonding pressure (4N) to the bonding end of the copper-based bonding wire for 30ms.

[0025] After ultrasonic bonding is completed, inert gas (nitrogen) is purged onto the bonding site until the temperature at the bonding site is <150°C.

[0026] Microscopic bonding images of the copper-based bonding wire bonding method in Example 1 are shown below. Figure 1 As shown, no cracks were observed.

[0027] Example 2 A bonding method for copper-based bonding wires includes the following steps: A composite metal interlayer is deposited at the bonding location (aluminum pad) of the IGBT chip (model: FF450R12ME4). Argon plasma cleaning was performed on the bonding ends of the copper-based bonding wire (pure copper round wire with a diameter of 200 μm). The plasma cleaning was carried out under the protection of an inert gas (nitrogen). The bonding ends of the copper-based bonding wires are brought into contact with the composite metal interlayer and ultrasonically bonded to complete the bonding of the copper-based bonding wires.

[0028] The composite metal interlayer comprises, from bottom to top, a first metal layer, a second metal layer, and a third metal layer. The first metal layer is formed of titanium, the second metal layer is formed of nickel, and the third metal layer is formed of silver. The first, second, and third metal layers are formed sequentially by magnetron sputtering deposition. The total thickness of the composite metal interlayer is 1.4 μm, the thickness of the first metal layer is 0.2 μm, the thickness of the second metal layer is 1.0 μm, and the thickness of the third metal layer is 0.2 μm.

[0029] Ultrasonic bonding includes the following steps: Step S1: Apply a first ultrasonic power (30W) and a first bonding pressure (1N) to the bonding end of the copper-based bonding wire for a duration of 15ms; Step S2: Apply a second ultrasonic power (120W) and a second bonding pressure (3N) to the bonding end of the copper-based bonding wire for a duration of 35ms; Step S3: Apply a third ultrasonic power (50W) and a third bonding pressure (3N) to the bonding end of the copper-based bonding wire for a duration of 30ms.

[0030] After ultrasonic bonding is completed, inert gas (nitrogen) is purged onto the bonding site until the temperature at the bonding site is <150°C.

[0031] Example 3 A bonding method for copper-based bonding wires includes the following steps: A composite metal interlayer is deposited at the bonding location (aluminum pad) of the IGBT chip (model: FF450R12ME4). Argon plasma cleaning was performed on the bonding ends of the copper-based bonding wire (pure copper round wire with a diameter of 100μm). The plasma cleaning was carried out under the protection of an inert gas (nitrogen). The bonding ends of the copper-based bonding wires are brought into contact with the composite metal interlayer and ultrasonically bonded to complete the bonding of the copper-based bonding wires.

[0032] The composite metal interlayer comprises, from bottom to top, a first metal layer, a second metal layer, and a third metal layer. The first metal layer is formed of titanium, the second metal layer is formed of nickel, and the third metal layer is formed of gold. The first, second, and third metal layers are formed sequentially by magnetron sputtering deposition. The total thickness of the composite metal interlayer is 0.65 μm, the thickness of the first metal layer is 0.1 μm, the thickness of the second metal layer is 0.5 μm, and the thickness of the third metal layer is 0.05 μm.

[0033] Ultrasonic bonding includes the following steps: Step S1: Apply a first ultrasonic power (30W) and a first bonding pressure (1N) to the bonding end of the copper-based bonding wire for a duration of 15ms; Step S2: Apply a second ultrasonic power (120W) and a second bonding pressure (2N) to the bonding end of the copper-based bonding wire for a duration of 35ms; Step S3: Apply a third ultrasonic power (50W) and a third bonding pressure (1.8N) to the bonding end of the copper-based bonding wire for 30ms.

[0034] After ultrasonic bonding is completed, inert gas (nitrogen) is purged onto the bonding site until the temperature at the bonding site is <150°C.

[0035] Example 4 A bonding method for copper-based bonding wires includes the following steps: A composite metal interlayer is deposited at the bonding location (aluminum pad) of the IGBT chip (model: FF450R12ME4). Argon plasma cleaning was performed on the bonding ends of the copper-based bonding wire (copper strip with a thickness of 300 μm and a width of 2 mm). The plasma cleaning was carried out under the protection of an inert gas (nitrogen). The bonding ends of the copper-based bonding wires are brought into contact with the composite metal interlayer and ultrasonically bonded to complete the bonding of the copper-based bonding wires.

[0036] The composite metal interlayer comprises, from bottom to top, a first metal layer, a second metal layer, and a third metal layer. The first metal layer is formed of titanium, the second metal layer is formed of nickel, and the third metal layer is formed of silver. The first, second, and third metal layers are formed sequentially by magnetron sputtering deposition. The total thickness of the composite metal interlayer is 3.5 μm, the thickness of the first metal layer is 0.3 μm, the thickness of the second metal layer is 3.0 μm, and the thickness of the third metal layer is 0.2 μm.

[0037] Ultrasonic bonding includes the following steps: Step S1: Apply a first ultrasonic power (30W) and a first bonding pressure (1N) to the bonding end of the copper-based bonding wire for a duration of 15ms; Step S2: Apply a second ultrasonic power (120W) and a second bonding pressure (8N) to the bonding end of the copper-based bonding wire for a duration of 35ms; Step S3: Apply a third ultrasonic power (50W) and a third bonding pressure (4N) to the bonding end of the copper-based bonding wire for 30ms.

[0038] After ultrasonic bonding is completed, inert gas (nitrogen) is purged onto the bonding site until the temperature at the bonding site is <150°C.

[0039] Comparative Example 1 A bonding method for copper-based bonding wires includes the following steps: The bonding end of the copper-based bonding wire (a pure copper round wire with a diameter of 300μm) is brought into contact with the bonding position (aluminum pad) of the IGBT chip (model: FF450R12ME4), and ultrasonic bonding is performed (ultrasonic power of 350W, bonding pressure of 5N, ultrasonic bonding duration of 80ms) to complete the bonding of the copper-based bonding wire.

[0040] Microscopic bonding images of the copper-based bonding wire bonding method in Comparative Example 1 are shown below. Figure 2 As shown, cracks have been formed.

[0041] Characterization test experiment The products obtained by bonding using the bonding methods of Examples 1-4 and Comparative Example 1 were subjected to the following characterization tests: Bond strength and shear strength: tested using a universal testing machine (model: Instron 5969); Conduction loss: Tested using an impedance analyzer (model: Agilent 4294A); High-temperature cycling test: The test was conducted in a constant temperature oven (model: Binder MK53) with temperature fluctuation controlled at ±2℃. The cycle was: "heating from 25℃ room temperature to 150℃ for 1 hour; holding at 150℃ for 2 hours; cooling from 150℃ to 25℃ room temperature for 1 hour", for 1000 cycles. The contact resistance before and after the high-temperature cycling was measured using an impedance analyzer (model: Agilent 4294A), and the rate of change of contact resistance was calculated.

[0042] The test results are shown in Table 1.

[0043] Table 1 Referring to the data in Table 1, it can be seen that in Comparative Example 1, the direct ultrasonic bonding using traditional processes lacks the diffusion barrier effect of the composite metal interlayer. Cu and Al atoms rapidly interdiffuse to form a large amount of brittle Cu-Al IMC (Intermetallic Compound Layer), such as CuAl2 and CuAl4, resulting in poor interfacial bonding. Furthermore, single high-power ultrasonic bonding is prone to local stress concentration, exacerbating interfacial defects. After high-temperature cycling, the defects further expand, leading to a sharp deterioration in electrical performance, which cannot meet the long-term reliable operation requirements of high-performance IGBT modules.

[0044] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several improvements and additions without departing from the method of the present invention, and these improvements and additions should also be considered within the scope of protection of the present invention.

Claims

1. A bonding method of a copper-based bonding wire, characterized by, Includes the following steps: Deposit a composite metal interlayer at the bonding sites on the chip; The bonding end of the copper-based bonding wire is brought into contact with the composite metal intermediate layer and ultrasonic bonding is performed to complete the bonding of the copper-based bonding wire. The composite metal interlayer comprises, from bottom to top, a first metal layer, a second metal layer, and a third metal layer, wherein the first metal layer is formed of titanium, the second metal layer is formed of nickel, and the third metal layer is formed of gold or silver. The ultrasonic bonding includes the following steps: Step S1: Apply a first ultrasonic power and a first bonding pressure to the bonding end of the copper-based bonding wire; Step S2: Apply a second ultrasonic power and a second bonding pressure to the bonding end of the copper-based bonding wire; Step S3: Apply a third ultrasonic power and a third bonding pressure to the bonding end of the copper-based bonding wire; The second ultrasonic power > the third ultrasonic power > the first ultrasonic power; The second bonding pressure is greater than or equal to the third bonding pressure and greater than the first bonding pressure.

2. The copper-based bond wire bonding method of claim 1, wherein, The second ultrasonic power is 60W-175W, the ratio of the second ultrasonic power to the first ultrasonic power is (3-6):1, and the ratio of the second ultrasonic power to the third ultrasonic power is (1.5-3):

1.

3. The copper-based bond wire bonding method of claim 1, wherein, The first bonding pressure is 0.5N-2N, the second bonding pressure is 2N-8N, and the ratio of the second bonding pressure to the third bonding pressure is 1:(1-0.5).

4. The copper-based bond wire bonding method of claim 1, wherein, The duration of step S1 is no more than 15ms, the duration of step S2 is 15ms-50ms, and the duration of step S3 is 30ms-80ms.

5. The copper-based bond wire bonding method of claim 1, wherein, The thickness of the first metal layer is 0.1μm-0.3μm, the thickness of the second metal layer is 0.5μm-3μm, and the thickness of the third metal layer is 0.05μm-0.2μm.

6. The copper-based bond wire bonding method of claim 1, wherein, The copper-based binding wire is a pure copper or zirconium copper round wire with a diameter of 100μm-500μm, or a copper strip with a thickness of 100μm-300μm and a width of 0.5mm-2mm.

7. The copper-based bond wire bonding method of claim 1, wherein, Before ultrasonic bonding, the bonding ends of the copper-based bonding wire are subjected to plasma cleaning, which is performed under the protection of an inert gas.

8. The copper-based bond wire bonding method of claim 1, wherein, After ultrasonic bonding is completed, inert gas is blown onto the bonding site until the temperature at the bonding site is <150°C.

9. The bonding method for copper-based bonding wires according to claim 1, characterized in that, The composite metal interlayer was obtained by magnetron sputtering deposition.

10. The application of the copper-based bonding wire bonding method as described in any one of claims 1-9 in the manufacture of IGBT modules.

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