Method for brazing copper-aluminum dissimilar metals using zinc-modified sn material as an intermediate layer

Abstract

This invention discloses a composite welding method for copper-aluminum dissimilar metals using zinc-modified Sn material as an intermediate layer, belonging to the field of welding technology. This invention addresses the problem of insufficient welding performance of copper-aluminum dissimilar metals in semiconductor packaging technology. The preparation of the zinc-modified Sn material involves: passivating Zn particles under argon protection to obtain pretreated Zn particles; then, under nitrogen protection, uniformly mixing the pretreated Zn particles and Sn alloy powder to obtain the zinc-modified Sn material; wherein the Sn alloy powder, by mass percentage, comprises 0.06–0.5% Sb. The composite welding method of copper and aluminum dissimilar metals using zinc-modified Sn material as the intermediate layer, provided by this invention, yields joints with excellent tensile and shear strength, making the welded joint less prone to failure under load. When applied to semiconductor heat dissipation systems, it provides excellent airtightness, ensuring the normal operation of semiconductor devices.

Description

Technical Field

[0001] This invention relates to the field of welding technology, and more specifically to a composite welding method for copper and aluminum dissimilar metals with zinc-modified Sn material as the intermediate layer. Background Technology

[0002] Semiconductor devices such as chips and power modules rely on the efficient connection of "semiconductor materials - metal electrodes - external circuits" for operation, and copper and aluminum are the most commonly used metal materials in this process. In semiconductor device heat dissipation systems, copper and aluminum dissimilar metal connections are frequently used to ensure efficient heat dissipation and support the functionality of the semiconductor device. The semiconductor packaging process can be simplified as: chip bonding → wire bonding → encapsulation → heat dissipation structure connection. The heat dissipation path is typically: semiconductor chip → copper substrate → aluminum heat sink. In this path, the connection between the copper substrate and the aluminum heat sink is the core link. Its function is to efficiently transfer the heat generated by the chip from the copper substrate inside the package to the external aluminum heat sink, and finally dissipate it into the environment. Its thermal conductivity directly determines whether the device can operate stably within a safe junction temperature range (silicon chips <150℃, SiC chips <200℃). Copper has excellent electrical and thermal conductivity and is widely used in the power industry. Aluminum has good electrical and thermal conductivity, a lower density than copper, and a lower price. Joining dissimilar alloys like copper and aluminum presents significant challenges. Copper has a melting point of 1083℃, while aluminum has a melting point of 658℃. Direct welding results in a large amount of brittle interfacial phases at the joint, increasing the risk of cracking and compromising long-term stability and reliability. Furthermore, the significant difference in the coefficients of linear expansion between copper and aluminum leads to thermal stress concentration at the joint during welding and subsequent use, further increasing the risk of cracking and damage. Direct welding of copper and aluminum also results in the formation of complex intermetallic compounds at the interface. These compounds are often inferior to the base metal, significantly reducing the joint's mechanical properties and thermal conductivity.

[0003] To address this technical deficiency, a solution is proposed. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a composite welding method for copper and aluminum dissimilar metals with zinc-modified Sn material as the intermediate layer. By introducing zinc-modified Sn material as the intermediate layer, the performance of the copper-aluminum weld joint is improved, the welding quality and the reliability of the joint are enhanced, and it is suitable for semiconductor packaging.

[0005] To achieve the above objectives, the present invention provides a composite welding method for copper-aluminum dissimilar metals with zinc-modified Sn material as the intermediate layer, comprising the following steps:

[0006] The heating platform is heated to the preheating temperature. The zinc-modified Sn material is placed between the welding interfaces of the aluminum base material and the copper base material to be welded, and makes contact with the welding interfaces respectively to obtain the component to be welded. The component to be welded is placed on the processing platform of the ultrasonic assisted welding device. The heating platform is heated to the set temperature of 200-260℃ and the ultrasonic tool head applies pressure in the longitudinal direction of the component to be welded to perform ultrasonic welding assistance. After welding is completed, it is allowed to cool naturally to obtain the welded sample.

[0007] In this process, the aluminum base material to be welded is in contact with the heating platform;

[0008] The ultrasonic-assisted welding device includes a vertical ultrasonic generator, a tilting ultrasonic generator, and a heating platform.

[0009] Among them, the tilted ultrasonic generator is tilted at a 60° angle to the ground;

[0010] Among them, the preparation of zinc-modified Sn materials:

[0011] Under argon protection, Zn particles are passivated to obtain pretreated Zn particles; under nitrogen protection, the pretreated Zn particles and Sn alloy powder are mixed evenly to obtain zinc-modified Sn material.

[0012] The Sn alloy powder, by mass percentage, comprises Sb 0.06–0.08%, Cu 0.7–0.9%, Bi 0.03–0.05%, Fe 0.02–0.04%, Cd 0.008%, Ag 0.3–0.6%, Al 0.01–0.1%, with the balance being Sn.

[0013] The pretreated Zn particles account for 2 to 5% of the mass of the Sn alloy powder.

[0014] Preferably, the preparation of both the aluminum base material to be welded and the copper base material to be welded adopts the following steps, specifically:

[0015] The base material was polished sequentially with 800#, 1200#, 2500# and 4000# sandpaper, then placed in an ethanol aqueous solution with a mass concentration of 40-60% and sonicated for 5 minutes, and dried with nitrogen gas for later use.

[0016] Preferably, the ultrasonic welding assistance is as follows: first, the vertical ultrasonic generator is started and held for 2-10 seconds, then the tilting ultrasonic generator is started and held for 8-30 seconds; wherein the vertical ultrasonic generator applies a pressure of 2.5-8 MPa to the substrate to be tested.

[0017] Preferably, in the ultrasonic-assisted welding device, the vertical ultrasonic generator and the tilting ultrasonic generator have the same power and range from 600 to 1600 W, and the frequency is 20-22 kHz.

[0018] Preferably, the preparation of the pretreated Zn particles includes the following steps: introducing argon gas with a purity of 99.9% at a flow rate of 0.8–1.2 L / min, continuously purging for 10 min to remove oxygen from the system, placing the Zn particles in a dynamic fluidized bed reactor, heating to 80–100 °C at a rate of 3–5 °C / min, maintaining the temperature for 30–45 min; heating to 120–130 °C, maintaining the temperature for 60–90 min, to obtain the pretreated Zn particles.

[0019] Preferably, the pretreated Zn surface contains a passivation layer with a thickness of 50–70 nm.

[0020] Preferably, the passivation layer on the surface of the pretreated Zn particles is zinc oxide.

[0021] Preferably, the preheating temperature of the heating platform is 120–140°C.

[0022] Preferably, the thickness of the zinc-modified Sn material sandwiched at the welding interface between the aluminum base material and the copper base material to be welded is 5μm-1mm.

[0023] Preferably, the pretreated Zn particles have a particle size of 40–50 μm; the Sn alloy powder has a particle size of 20–25 μm.

[0024] Preferably, a method for fabricating a semiconductor device includes a composite welding method for copper-aluminum dissimilar metals, in which the zinc-modified Sn material is used as an intermediate layer in the heat dissipation connection.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] 1. In this invention, the Zn particles in the zinc-modified Sn material undergo passivation treatment, resulting in a passivation layer on the surface that protects the internal Zn. Simultaneously, when mixed with Sn alloy powder, the pre-treated Zn particles refine the grain size and inhibit excessive growth of intermetallic compounds (IMCs) during welding. This allows for a more stable and high-strength bond at the copper-aluminum welding interface, improving the overall mechanical properties of the joint and enhancing its tensile shear strength. This makes the welded joint less prone to failure under load. The combined use of vertical and inclined ultrasonic generators in the ultrasonic-assisted welding device promotes better spreading and wetting of the base material surface by the intermediate zinc-modified Sn material. Furthermore, during welding, ultrasonic vibration promotes uniform distribution of the intermediate material at the welding interface, preventing localized stress concentration caused by agglomeration and avoiding localized component segregation or poor bonding. This results in a more uniform and stable welded joint quality at different locations, reducing the risk of failure due to joint quality variations.

[0027] 2. In this invention, the passivation layer on the surface of the pretreated Zn particles is zinc oxide. Zinc oxide has a high melting point and can effectively physically isolate the direct contact and diffusion between the active elements Cu and Al during welding. This physical barrier effectively slows down the formation rate and thickness growth of intermetallic compounds (IMCs). Furthermore, during welding, under the dual action of ultrasonic vibration and heating, the surface zinc oxide of the pretreated Zn particles is broken down, and the internal Zn dissolves into the intermediate layer, participating in the alloying process of the intermediate layer. This optimizes the composition and structure of the welding interface. The zinc oxide, due to its high melting point, remains dispersed in the intermediate layer in a solid state, continuing to act as a physical barrier and further hindering the excessive diffusion of Cu and Al atoms, thus synergistically controlling the growth thickness of IMCs. By adjusting parameters such as welding temperature, welding time, and ultrasonic power, the dissolution and diffusion behavior of Zn particles can be precisely controlled, thereby controlling the type, morphology, and distribution of IMCs. Lower welding temperatures help reduce excessive evaporation and oxidation of Zn particles, while effectively controlling the growth rate of IMCs. A suitable welding time ensures that Zn particles fully exert their effects on grain refinement and inhibiting IMC growth, avoiding excessive welding time that could lead to joint performance degradation. Appropriate ultrasonic power enhances the dispersion of Zn particles in the interlayer, promoting atomic diffusion and interfacial reactions between the interlayer and the base material. Through synergistic optimization of these welding process parameters, the overall performance of copper-aluminum welded joints can be significantly improved, meeting the stringent requirements of high performance and high reliability for dissimilar metal welded joints in semiconductor heat dissipation systems and other applications, thus facilitating the normal operation of semiconductor devices.

[0028] 3. The zinc-modified Sn material of this invention possesses several excellent properties. The Sn matrix itself has a low melting point and good plasticity, which allows it to better fill the weld interface during welding and provide good wettability. The addition of Zn particles can further refine the grains, inhibit the growth of IMCs, and enhance interfacial bonding, thus optimizing the performance of the weld joint. In addition, the addition of alloying elements such as Ag, Cu, Sb, Bi, Fe, and Cd optimizes the melting point, wettability, strength, and thermal stability of the material, effectively improving the overall performance of the weld joint. Elements Ag and Cu optimize the melting point, wettability, and strength; Sb inhibits grain coarsening and improves high-temperature stability; Bi optimizes fluidity and reduces welding temperature sensitivity; Fe inhibits the formation of the Cu-Sn brittle phase; and Cd improves wettability. The brittle phase reduces thermal conductivity and accelerates thermal fatigue failure. Through reasonable composition design and preparation process, the characteristics of various material components are fully utilized and synergistically improved, enhancing the overall performance of the interlayer material. Ag optimizes the interfacial heat conduction path by forming a strengthening phase; Cu improves thermal contact performance and facilitates thermal conductivity through solid solution strengthening and promoting interfacial diffusion. Sb inhibits Sn grain coarsening, which helps reduce interfacial resistance, suppresses IMCs growth, and lowers interfacial thermal resistance. This is particularly important for power semiconductor devices, as it can lower junction temperatures and improve device reliability. Al has high thermal conductivity and low density, which can reduce the overall package weight, making it suitable for weight-sensitive applications.

[0029] 4. The zinc-modified Sn material of this invention not only enables low-temperature welding but also avoids the damage to semiconductor materials that may be caused by traditional high-temperature welding, particularly the problem that high temperatures can lead to the diffusion of dopant atoms in silicon chips or intensified interfacial reactions with electrodes. Under low-temperature welding conditions, the Sn material can effectively fill the welding interface, avoiding the adverse effects on semiconductor materials that may occur during traditional high-temperature welding. Simultaneously, the use of zinc-modified Sn material optimizes the performance of Sn, especially at the copper-aluminum welding interface, effectively suppressing the formation of brittle phases. The presence of brittle phases typically reduces the strength and conductivity of the joint, while zinc modification reduces the formation of such brittle phases, thereby improving the joint's strength and conductivity. Furthermore, zinc modification also improves the mechanical strength and thermal stability of Sn, ensuring the reliability and stability of the welded joint during long-term use. Attached Figure Description

[0030] Figure 1 The tensile load-displacement curves are shown for the joints in Examples 3-5 and the comparative examples of this invention.

[0031] Figure 2 The bar chart shows the impact energy absorption test results of the joints and comparative examples in Examples 3-5 of this invention. Detailed Implementation

[0032] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] Example 1

[0034] This embodiment provides a method for preparing an aluminum base material to be welded, including the following steps:

[0035] The aluminum substrate was polished with 800#, 1200#, 2500# and 4000# sandpaper for 2 min, 4 min, 2 min and 5 min respectively. Then it was placed in a 40% ethanol aqueous solution and sonicated for 5 min. It was then dried with nitrogen gas for later use.

[0036] Example 2

[0037] This embodiment provides a method for preparing a copper base material to be welded, including the following steps:

[0038] The copper substrate was polished with 800#, 1200#, 2500# and 4000# sandpaper for 2 min, 4 min, 2 min and 5 min respectively. Then it was placed in a 40% ethanol aqueous solution and sonicated for 5 min. It was then dried with nitrogen gas for later use.

[0039] Example 3

[0040] This embodiment provides a composite welding method for copper and aluminum dissimilar metals with zinc-modified Sn material as the intermediate layer, including the following steps:

[0041] The heating platform is heated to a preheating temperature of 120℃. A 1mm thick zinc-modified Sn material is clamped between the welding interfaces of the aluminum and copper base materials to be welded, and in contact with the welding interfaces to obtain the component to be welded. The component to be welded is placed on the processing platform of the ultrasonic-assisted welding device. The heating platform is heated to 200℃. The vertical ultrasonic generator is started, and a pressure of 5.5MPa is applied to the copper base material to be welded to press the component. The ultrasonic frequency is maintained at 20kHz and the power is 1400W for 10s. Then the tilting ultrasonic generator is started, and the ultrasonic frequency is maintained at 20kHz and the power is 1400W for 30s. The ultrasonic generator is then turned off, and the sample is allowed to cool naturally to obtain the welded sample.

[0042] In this process, the aluminum base material to be welded is in contact with the heating platform;

[0043] Among them, the tilted ultrasonic generator is tilted at a 60° angle to the ground;

[0044] The aluminum base material to be welded and the copper base material to be welded have a diameter of 15mm and a height of 3mm.

[0045] Among them, the preparation of zinc-modified Sn materials:

[0046] Under nitrogen protection, pretreated Zn particles and Sn alloy powder are mixed evenly to obtain zinc-modified Sn material;

[0047] Among them, the pretreated Zn particles account for 2% of the mass of the Sn alloy powder;

[0048] The Sn alloy powder, by mass percentage, comprises 0.06% Sb, 0.7% Cu, 0.03% Bi, 0.02% Fe, 0.008% Cd, 0.3% Ag, 0.01% Al, with the balance being Sn.

[0049] The preparation of pretreated Zn particles includes the following steps:

[0050] Argon gas with a purity of 99.9% was introduced at a flow rate of 0.8 L / min and continuously purged for 10 min to remove oxygen from the system. The Zn particles were then placed in a dynamic fluidized bed reactor and heated to 80 °C at a rate of 3 °C / min and held at that temperature for 30 min. The temperature was then increased to 120 °C and held at that temperature for 60 min to obtain Zn particles with a passivation layer pretreatment with a thickness of 50 nm.

[0051] The pretreated Zn particles have a particle size of 40 μm; the Sn alloy powder has a particle size of 20 μm.

[0052] Example 4

[0053] This embodiment provides a composite welding method for copper and aluminum dissimilar metals with zinc-modified Sn material as the intermediate layer, including the following steps:

[0054] The heating platform is heated to a preheating temperature of 130℃. A 1mm thick zinc-modified Sn material is clamped between the welding interfaces of the aluminum and copper base materials to be welded, and in contact with the welding interfaces to obtain the component to be welded. The component to be welded is placed on the processing platform of the ultrasonic-assisted welding device, and the heating platform is heated to 240℃. The vertical ultrasonic generator is started, and a pressure of 6.5MPa is applied to the copper base material to be welded to press the component. The ultrasonic frequency is maintained at 21kHz and the power is 1500W for 8 seconds. Then the tilting ultrasonic generator is started, and the ultrasonic frequency is maintained at 21kHz and the power is 1500W for 20 seconds. The ultrasonic generator is then turned off, and the sample is allowed to cool naturally to obtain the welded sample.

[0055] In this process, the aluminum base material to be welded is in contact with the heating platform;

[0056] Among them, the tilted ultrasonic generator is tilted at a 60° angle to the ground;

[0057] The aluminum base material to be welded and the copper base material to be welded have a diameter of 15mm and a height of 3mm.

[0058] Among them, the preparation of zinc-modified Sn materials:

[0059] Under nitrogen protection, pretreated Zn particles and Sn alloy powder are mixed evenly to obtain zinc-modified Sn material;

[0060] Among them, the pretreated Zn particles account for 3.5% of the mass of the Sn alloy powder;

[0061] The Sn alloy powder, by mass percentage, comprises 0.07% Sb, 0.8% Cu, 0.04% Bi, 0.03% Fe, 0.008% Cd, 0.45% Ag, 0.05% Al, with the balance being Sn.

[0062] The preparation of pretreated Zn particles includes the following steps:

[0063] Argon gas with a purity of 99.9% was introduced at a flow rate of 1 L / min and continuously purged for 10 min to remove oxygen from the system. The Zn particles were then placed in a dynamic fluidized bed reactor and heated to 90 °C at a rate of 4 °C / min and held at that temperature for 37 min. The temperature was then increased to 125 °C and held at that temperature for 75 min to obtain Zn particles with a passivation layer pretreatment with a thickness of 60 nm.

[0064] The pretreated Zn particles have a particle size of 45 μm; the Sn alloy powder has a particle size of 22 μm.

[0065] Example 5

[0066] This embodiment provides a composite welding method for copper and aluminum dissimilar metals with zinc-modified Sn material as the intermediate layer, including the following steps:

[0067] The heating platform is heated to a preheating temperature of 140℃. A 1mm thick zinc-modified Sn material is clamped between the welding interfaces of the aluminum and copper base materials to be welded, and in contact with the welding interfaces to obtain the component to be welded. The component to be welded is placed on the processing platform of the ultrasonic-assisted welding device. The heating platform is heated to 260℃. The vertical ultrasonic generator is started, and an 8MPa pressure is applied to the copper base material to be welded to press the component. The ultrasonic frequency is 22kHz and the power is 1600W for 5s. Then the tilting ultrasonic generator is started, and the ultrasonic frequency is 22kHz and the power is 1600W for 10s. The ultrasonic generator is then turned off, and the sample is allowed to cool naturally to obtain the welded sample.

[0068] In this process, the aluminum base material to be welded is in contact with the heating platform;

[0069] Among them, the tilted ultrasonic generator is tilted at a 60° angle to the ground;

[0070] The aluminum base material to be welded and the copper base material to be welded have a diameter of 15mm and a height of 3mm.

[0071] Among them, the preparation of zinc-modified Sn materials:

[0072] Under nitrogen protection, pretreated Zn particles and Sn alloy powder are mixed evenly to obtain zinc-modified Sn material;

[0073] Among them, the pretreated Zn particles account for 5% of the mass of the Sn alloy powder;

[0074] The Sn alloy powder, by mass percentage, comprises 0.08% Sb, 0.9% Cu, 0.05% Bi, 0.04% Fe, 0.008% Cd, 0.6% Ag, 0.1% Al, with the balance being Sn.

[0075] The preparation of pretreated Zn particles includes the following steps:

[0076] Argon gas with a purity of 99.9% was introduced at a flow rate of 1.2 L / min and continuously purged for 10 min to remove oxygen from the system. The Zn particles were then placed in a dynamic fluidized bed reactor and heated to 100 °C at a rate of 5 °C / min, and held at that temperature for 45 min. The temperature was then increased to 130 °C and held at that temperature for 90 min to obtain Zn particles with a passivation layer pretreatment with a thickness of 70 nm.

[0077] The pretreated Zn particles have a particle size of 50 μm; the Sn alloy powder has a particle size of 25 μm.

[0078] Example 6

[0079] This embodiment provides a composite welding method for copper and aluminum dissimilar metals with zinc-modified Sn material as the intermediate layer, including the following steps:

[0080] The heating platform is heated to a preheating temperature of 120℃. A 60μm thick zinc-modified Sn material is placed between the welding interfaces of the aluminum plate and the copper plate to be welded, and makes contact with the welding interfaces to obtain the component to be welded. The component to be welded is placed on the processing platform of the ultrasonic-assisted welding device. The heating platform is heated to 200℃. The vertical ultrasonic generator is started, and a pressure of 2.5MPa is applied to the copper plate to be welded to press the component. The ultrasonic frequency is maintained at 20kHz and the power is 600W for 4s. Then the tilting ultrasonic generator is started, and the ultrasonic frequency is maintained at 20kHz and the power is 600W for 10s. The ultrasonic generator is then turned off, and the sample is allowed to cool naturally to obtain the welded sample.

[0081] The aluminum plate to be welded is in contact with the heating platform.

[0082] Among them, the tilted ultrasonic generator is tilted at a 60° angle to the ground;

[0083] The thickness of the aluminum plate to be welded and the copper plate to be welded is 2mm.

[0084] The aluminum plate and copper plate were polished with 800#, 1200#, 2500# and 4000# sandpaper respectively, and then placed in an ethanol aqueous solution with a mass concentration of 40% and sonicated for 5 minutes. They were then dried with nitrogen gas and set aside to obtain the aluminum plate and copper plate to be welded.

[0085] Among them, the preparation of zinc-modified Sn materials:

[0086] Under nitrogen protection, pretreated Zn particles and Sn alloy powder are mixed evenly to obtain zinc-modified Sn material;

[0087] Among them, the pretreated Zn particles account for 2% of the mass of the Sn alloy powder;

[0088] The Sn alloy powder, by mass percentage, comprises 0.06% Sb, 0.7% Cu, 0.03% Bi, 0.02% Fe, 0.008% Cd, 0.3% Ag, 0.01% Al, with the balance being Sn.

[0089] The preparation of pretreated Zn particles includes the following steps:

[0090] Argon gas with a purity of 99.9% was introduced at a flow rate of 0.8 L / min and continuously purged for 10 min to remove oxygen from the system. The Zn particles were then placed in a dynamic fluidized bed reactor and heated to 80 °C at a rate of 3 °C / min and held at that temperature for 30 min. The temperature was then increased to 120 °C and held at that temperature for 60 min to obtain Zn particles with a passivation layer pretreatment with a thickness of 50 nm.

[0091] The pretreated Zn particles have a particle size of 40 μm; the Sn alloy powder has a particle size of 20 μm.

[0092] Example 7

[0093] The heating platform is heated to a preheating temperature of 120℃. A 60μm thick zinc-modified Sn material is placed between the welding interfaces of the aluminum plate and the copper plate to be welded, and makes contact with the welding interfaces to obtain the component to be welded. The component to be welded is placed on the processing platform of the ultrasonic-assisted welding device. The heating platform is heated to 210℃. The vertical ultrasonic generator is started, and a pressure of 3MPa is applied to the copper plate to be welded to press the component. The ultrasonic frequency is 21kHz and the power is 650W for 3s. Then the tilting ultrasonic generator is started, and the ultrasonic frequency is 21kHz and the power is 650W for 9s. The ultrasonic generator is then turned off, and the sample is allowed to cool naturally to obtain the welded sample.

[0094] The aluminum plate to be welded is in contact with the heating platform.

[0095] Among them, the tilted ultrasonic generator is tilted at a 60° angle to the ground;

[0096] The thickness of the aluminum plate to be welded and the copper plate to be welded is 2mm.

[0097] The aluminum plate and copper plate were polished with 800#, 1200#, 2500# and 4000# sandpaper respectively, and then placed in an ethanol aqueous solution with a mass concentration of 40% and sonicated for 5 minutes. They were then dried with nitrogen gas and set aside to obtain the aluminum plate and copper plate to be welded.

[0098] Among them, the preparation of zinc-modified Sn materials:

[0099] Under nitrogen protection, pretreated Zn particles and Sn alloy powder are mixed evenly to obtain zinc-modified Sn material;

[0100] Among them, the pretreated Zn particles account for 2% of the mass of the Sn alloy powder;

[0101] The Sn alloy powder, by mass percentage, comprises 0.06% Sb, 0.7% Cu, 0.03% Bi, 0.02% Fe, 0.008% Cd, 0.3% Ag, 0.01% Al, with the balance being Sn.

[0102] The preparation of pretreated Zn particles includes the following steps:

[0103] Argon gas with a purity of 99.9% was introduced at a flow rate of 0.8 L / min and continuously purged for 10 min to remove oxygen from the system. The Zn particles were then placed in a dynamic fluidized bed reactor and heated to 80 °C at a rate of 3 °C / min and held at that temperature for 30 min. The temperature was then increased to 120 °C and held at that temperature for 60 min to obtain Zn particles with a passivation layer pretreatment with a thickness of 50 nm.

[0104] The pretreated Zn particles have a particle size of 40 μm; the Sn alloy powder has a particle size of 20 μm.

[0105] Example 8

[0106] The heating platform is heated to a preheating temperature of 120℃. A 60μm thick zinc-modified Sn material is placed between the welding interfaces of the aluminum plate and the copper plate to be welded, and makes contact with the welding interfaces to obtain the component to be welded. The component to be welded is placed on the processing platform of the ultrasonic-assisted welding device. The heating platform is heated to 220℃. The vertical ultrasonic generator is started, and a pressure of 3.5MPa is applied to the copper plate to be welded to press the component. The ultrasonic frequency is maintained at 22kHz and the power is 700W for 2 seconds. Then the tilting ultrasonic generator is started, and the ultrasonic frequency is maintained at 22kHz and the power is 700W for 8 seconds. The ultrasonic generator is then turned off, and the sample is allowed to cool naturally to obtain the welded sample.

[0107] The aluminum plate to be welded is in contact with the heating platform.

[0108] Among them, the tilted ultrasonic generator is tilted at a 60° angle to the ground;

[0109] The thickness of the aluminum plate to be welded and the copper plate to be welded is 2mm.

[0110] The aluminum plate and copper plate were polished with 800#, 1200#, 2500# and 4000# sandpaper respectively, and then placed in an ethanol aqueous solution with a mass concentration of 40% and sonicated for 5 minutes. They were then dried with nitrogen gas and set aside to obtain the aluminum plate and copper plate to be welded.

[0111] Among them, the preparation of zinc-modified Sn materials:

[0112] Under nitrogen protection, pretreated Zn particles and Sn alloy powder are mixed evenly to obtain zinc-modified Sn material;

[0113] Among them, the pretreated Zn particles account for 2% of the mass of the Sn alloy powder;

[0114] The Sn alloy powder, by mass percentage, comprises 0.06% Sb, 0.7% Cu, 0.03% Bi, 0.02% Fe, 0.008% Cd, 0.3% Ag, 0.01% Al, with the balance being Sn.

[0115] The preparation of pretreated Zn particles includes the following steps:

[0116] Argon gas with a purity of 99.9% was introduced at a flow rate of 0.8 L / min and continuously purged for 10 min to remove oxygen from the system. The Zn particles were then placed in a dynamic fluidized bed reactor and heated to 80 °C at a rate of 3 °C / min and held at that temperature for 30 min. The temperature was then increased to 120 °C and held at that temperature for 60 min to obtain Zn particles with a passivation layer pretreatment with a thickness of 50 nm.

[0117] The pretreated Zn particles have a particle size of 40 μm; the Sn alloy powder has a particle size of 20 μm.

[0118] The aluminum base materials to be welded in Examples 3-5 were all prepared using the aluminum base materials to be welded in Example 1.

[0119] The copper base material to be welded in Examples 3-5 was the copper base material to be welded prepared in Example 2.

[0120] Performance testing:

[0121] (1) Tensile shear test: The joints from Examples 3-5 were processed into 10mm × 10mm specimens using wire electrical discharge machining. After grinding and polishing, the specimens were ultrasonically cleaned by immersion in ethanol and dried with nitrogen gas. For the comparative example, copper and aluminum were directly welded using conventional methods. The tensile shear test was conducted on an MTSC MT4304 microcomputer-controlled universal testing machine at a tensile speed of 1mm / min. The test was repeated three times, and the average value was recorded. Specific test results are as follows: Figure 1 As shown;

[0122] from Figure 1 It can be seen that the joints in Examples 3-5 of this invention have higher shear strength and better toughness, indicating that by optimizing the welding process, the bonding quality of the copper-aluminum welding interface is effectively improved, brittle intermetallic compounds are suppressed, and the mechanical properties of the joint are enhanced. The joints prepared by the composite welding method of copper-aluminum dissimilar metals with zinc-modified Sn material as the intermediate layer provided by this invention have good maximum load-bearing limits. The higher the strength, the better the joint can resist interface slippage or fracture caused by tension, indicating better welding results. Among them, the curve of Example 4 has a higher peak value and a slower decline, indicating better overall performance.

[0123] (2) Impact Energy Absorption Test: The impact load-displacement curves of the joints in Examples 3-5 were collected, and the mean energy absorption was calculated using Matlab programming. The specific results are as follows: Figure 2 As shown;

[0124] from Figure 2 It can be seen that the larger the average impact energy absorption value, the stronger the joint's ability to resist fracture under impact load, and the better its impact resistance. The impact energy absorption values ​​of Embodiments 3-5 of the present invention are all greater than those of the comparative example, indicating that their impact resistance is superior.

[0125] (3) Thermal conductivity test: The copper-aluminum dissimilar metal composite welding method with zinc-modified Sn material as the intermediate layer in Examples 6-8 was used in semiconductor packaging. It served as the connection link between the heat dissipation copper substrate and the aluminum heat sink. It was then combined with GaN chip, wire bonding, etc. to form a complete package and obtain semiconductor device. These were recorded as samples 1-3. The comparative example used conventional ultrasonic bonding and was combined with chip, wire bonding, etc. to form a complete package and obtain semiconductor device. This was recorded as sample 4. The thermal resistance of samples 1-4 was tested and 20,000 cycles were performed. One cycle was 6 minutes, including 3 minutes of heating and 3 minutes of cooling. The thermal resistance decay rate after the cycle test was measured. The test results are shown in Table 1.

[0126] in,

[0127] The thermal resistance detection method is as follows: first, the temperature sensitivity coefficient (i.e., K coefficient) of the chip is calibrated by the K coefficient, and then the thermal resistance is calibrated by the K coefficient.

[0128] The parameters for calibrating the chip's temperature sensitivity coefficient (K coefficient) using the K coefficient are set as follows: the maximum current and voltage drop are the standard rated values ​​or maximum values ​​in the datasheet, the minimum current is -100mA, VGS(on) is 15V, VGS(OFF) is -5V, and the temperature rise range is 25℃ to 85℃, with each 20℃ point representing a point. The parameters for calibrating the thermal resistance using the K coefficient are set as follows: import the K coefficient, set the transient heating current to 1 / 5 of the rated current, and set the heating and cooling time to 150s.

[0129] Table 1

[0130]

[0131] As can be seen from the test results in Table 1, the composite welding method of copper-aluminum dissimilar metals with zinc-modified Sn material as the intermediate layer provided by the present invention has good thermal conductivity and heat dissipation performance in semiconductor packaging, which is better than the traditional ultrasonic bonding in the comparative example. At the same time, the present invention can ensure that the junction temperature is lower than that of the chip, which is beneficial to the operation of semiconductor devices, and the lower thermal resistance attenuation rate is beneficial to stability.

[0132] (4) Air tightness test: The copper-aluminum dissimilar metal composite welding method with zinc-modified Sn material as intermediate layer in Examples 6-8 was used in semiconductor packaging. It served as the connection link between the heat dissipation copper substrate and the aluminum heat sink. It was then combined with GaN chip, wire bonding, etc. to form a complete package and obtain semiconductor device, which was recorded as samples 1-3. The comparative example used conventional ultrasonic bonding and was combined with chip, wire bonding, etc. to form a complete package and obtain semiconductor device, which was recorded as sample 4. The air tightness of samples 1-4 was tested according to GB / T25915.1-2010 "Air tightness test - Part 1: Helium mass spectrometry leak detection". The specific test results are shown in Table 2.

[0133] Table 2

[0134]

[0135] As shown in Table 2, the airtightness of samples 1-3 is better than that of sample 4, and the leakage rate of samples 1-3 is ≤1×10⁻⁶. -6 Pa·m 3 / s, which meets the national standards for semiconductor devices.

[0136] The above description is merely an example and illustration of the structure of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the structure of the invention or exceed the scope defined in the claims, all of which should fall within the protection scope of the present invention.

[0137] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0138] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to specific implementations. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A composite welding method for copper and aluminum dissimilar metals using zinc-modified Sn material as the intermediate layer, characterized in that, Includes the following steps: The heating platform is heated to the preheating temperature. The zinc-modified Sn material is placed between the welding interfaces of the aluminum base material and the copper base material to be welded, and makes contact with the welding interfaces respectively to obtain the component to be welded. The component to be welded is placed on the processing platform of the ultrasonic assisted welding device. The heating platform is heated to the set temperature of 200-260℃ and the ultrasonic tool head applies pressure in the longitudinal direction of the component to be welded to perform ultrasonic welding assistance. After welding is completed, it is allowed to cool naturally to obtain the welded sample. In this process, the aluminum base material to be welded is in contact with the heating platform; The ultrasonic-assisted welding device includes a vertical ultrasonic generator, a tilting ultrasonic generator, and a heating platform. Among them, the tilted ultrasonic generator is tilted at a 60° angle to the ground; Among them, the preparation of zinc-modified Sn materials: Under argon protection, Zn particles are passivated to obtain pretreated Zn particles; under nitrogen protection, the pretreated Zn particles and Sn alloy powder are mixed evenly to obtain zinc-modified Sn material. The Sn alloy powder, by mass percentage, comprises Sb 0.06–0.08%, Cu 0.7–0.9%, Bi 0.03–0.05%, Fe 0.02–0.04%, Cd 0.008%, Ag 0.3–0.6%, Al 0.01–0.1%, with the balance being Sn. The pretreated Zn particles account for 2 to 5% of the mass of the Sn alloy powder.

2. The composite welding method for copper-aluminum dissimilar metals with zinc-modified Sn material as the intermediate layer according to claim 1, characterized in that, The preparation of both the aluminum base material and the copper base material to be welded adopts the following steps, specifically: The base material was polished sequentially with 800#, 1200#, 2500# and 4000# sandpaper, then placed in an ethanol aqueous solution with a mass concentration of 40-60% and sonicated for 5 minutes, and dried with nitrogen gas for later use.

3. The composite welding method for copper-aluminum dissimilar metals with zinc-modified Sn material as the intermediate layer according to claim 1, characterized in that, The ultrasonic welding assistance is as follows: first, start the vertical ultrasonic generator and hold it for 2-10 seconds, then start the tilting ultrasonic generator and hold it for 8-30 seconds; wherein the vertical ultrasonic generator applies a pressure of 2.5-8 MPa to the base material to be tested.

4. The composite welding method for copper-aluminum dissimilar metals using zinc-modified Sn material as the intermediate layer according to claim 1, characterized in that, In the ultrasonic-assisted welding device, the vertical ultrasonic generator and the tilting ultrasonic generator have the same power and range from 600 to 1600W, and the frequency is 20-22kHz.

5. The composite welding method for copper-aluminum dissimilar metals using zinc-modified Sn material as the intermediate layer according to claim 1, characterized in that, The preparation of the pretreated Zn particles includes the following steps: purging with 99.9% pure argon gas at a flow rate of 0.8–1.2 L / min for 10 min to remove oxygen from the system; placing the Zn particles in a dynamic fluidized bed reactor and heating them to 80–100°C at a rate of 3–5°C / min, maintaining the temperature for 30–45 min; then heating them to 120–130°C and maintaining the temperature for 60–90 min to obtain the pretreated Zn particles.

6. The composite welding method for copper-aluminum dissimilar metals using zinc-modified Sn material as the intermediate layer according to claim 1, characterized in that, The pretreated Zn surface contains a passivation layer with a thickness of 50–70 nm.

7. The composite welding method for copper-aluminum dissimilar metals using zinc-modified Sn material as the intermediate layer according to claim 6, characterized in that, The passivation layer on the surface of the pretreated Zn particles is zinc oxide.

8. The composite welding method for copper-aluminum dissimilar metals with zinc-modified Sn material as the intermediate layer according to claim 1, characterized in that, The preheating temperature of the heating platform is 120-140℃.

9. The composite welding method for copper-aluminum dissimilar metals with zinc-modified Sn material as the intermediate layer according to claim 1, characterized in that, The pretreated Zn particles have a particle size of 40–50 μm; the Sn alloy powder has a particle size of 20–25 μm.

10. A method for fabricating a semiconductor device, characterized in that, The heat dissipation connection includes a composite welding method for copper and aluminum dissimilar metals, with zinc-modified Sn material as the intermediate layer as described in any one of claims 1-9.

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