Palladium-coated copper-based bonding wire and process for making same

Abstract

The application relates to a palladium-plated copper-based bonding wire and a preparation process thereof. A nickel-phosphorus layer is plated on the surface of the copper-based bonding wire as a transition layer, and then a palladium layer is plated. The nickel-phosphorus layer has good adhesion with the copper-based layer and the palladium layer, and has good conductivity, thereby improving the bonding force between the copper-based layer and the palladium layer. The nickel element can increase the ductility of the bonding wire and has sulfurization resistance. The copper-based bonding wire is doped with palladium elements, and the doped palladium elements are beneficial to improving the corrosion resistance and oxidation resistance of the bonding wire and improving the conductivity. Meanwhile, the palladium elements have good adhesion, and can make the copper-based bonding wire and the nickel-phosphorus layer form better adhesion. In the process of plating the nickel-phosphorus layer, free phosphorus ions in a nickel-phosphorus alloy electroplating solution combine with the palladium elements to form palladium phosphide. The palladium phosphide has high conductivity and can enhance the bonding force with the matrix.

Description

Technical Field

[0001] This invention relates to the field of bonding wire technology, specifically to a palladium-plated copper-based bonding wire and its preparation process. Background Technology

[0002] Bonding materials are a micro-connection technology that can tightly bond to substrate pads using heat, pressure, and ultrasonic energy. As a key material for wire bonding, it plays a role in connecting semiconductor chips and pins, transmitting current and signals. It dominates the connection method due to its advantages such as simple process, low cost, and suitability for various packaging forms. Currently, it is mainly used in integrated circuits, discrete semiconductor devices, LEDs, etc.

[0003] Currently, copper bonding wire is widely used. Compared to gold wire, it is less expensive and has better electrical and thermal conductivity, gradually replacing gold wire bonding materials. However, research has revealed that copper wire has poor oxidation resistance, high hardness, and low tensile strength, which may lead to poor device stability, low operating efficiency, and low bonding yield, limiting its application range. A plating layer is usually applied to its surface to improve its performance. Palladium-plated copper-based bonding wire can improve the oxidation and corrosion resistance of bonded copper wire. However, the poor compatibility between the palladium plating and copper, and the poor interlayer adhesion, lead to plating peeling, flaking, or bending during the production and use of palladium-plated copper wire, affecting its application. Designing a palladium-plated copper-based bonding wire with good adhesion between the plating and copper is a pressing problem that needs to be solved. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings and deficiencies of the existing technology and to provide a palladium-plated copper-based bonding wire and its preparation process.

[0005] The technical solution adopted by the present invention is as follows: The first aspect of the present invention provides a palladium-plated copper-based bonding wire, including a copper-based busbar, and further including a nickel-phosphorus alloy transition layer and a palladium layer sequentially plated on the surface of the copper-based busbar.

[0006] Preferably, the thickness of the nickel-phosphorus alloy transition layer is 5-15 nm, and the thickness of the palladium layer is 40-60 nm.

[0007] Preferably, the copper-based busbar contains 97-99.9% copper and 0.1-3% palladium.

[0008] A second aspect of the present invention provides a process for preparing palladium-plated copper-based bonding wire, comprising the following steps:

[0009] (A) Nickel-phosphorus alloy transition layer: A layer of NiP is plated onto the surface of the surface-active copper-based busbar as a transition layer using a nickel-phosphorus alloy electroplating solution.

[0010] (B) Palladium plating layer: A layer of metallic palladium is plated onto the surface of the copper-based busbar, which is plated with a nickel-phosphorus alloy transition layer, using a palladium electroplating solution;

[0011] (C) Annealing: Wire annealing is adopted, in which the wire passes through a furnace protected by hydrogen and nitrogen gas. The furnace temperature is 400-600℃ and the speed is 0.5-2m / s.

[0012] Preferably, in step (A), the nickel-phosphorus alloy electroplating solution comprises 15-25 g / L nickel sulfate, 20-30 ml / L sodium hypophosphite, and 20%-25% ammonia.

[0013] Preferably, in step (A), the electroplating current density is 0.1–5 A / dm². 2 The electroplating temperature is 60-80℃, and the electroplating speed is 15-40m / s.

[0014] Preferably, in step (B), the electroplating current density is 0.5–5 A / dm². 2 The electroplating temperature is 55-75℃, and the electroplating speed is 25-40m / s.

[0015] Preferably, in step (C), the hydrogen-nitrogen gas is a mixture of hydrogen and nitrogen, and the mixing ratio of hydrogen and nitrogen is (4.5-7):(93-95.5).

[0016] Preferably, the copper-based busbar is prepared by the following method:

[0017] S1. Raw material preparation and pretreatment: Ultrasonic cleaning and drying of the metal;

[0018] S2. Substrate melting and casting: The dried metal is first vacuum-melted in a high-purity argon atmosphere with a vacuum degree of 10. -3 ~10 -2 MPa, melting temperature of 1050~1250℃, melting time of 50~80 minutes, followed by directional continuous casting to obtain copper-based busbars with a diameter of 6-10mm;

[0019] S3. Cold drawing: The copper-based busbar is cooled to 150-200℃, and then coarsely drawn to a diameter of 60-120μm, and then finely drawn to a diameter of 30-60μm;

[0020] S4. Surface activation treatment: The surface of the copper-based busbar is cleaned and deoxygenated using an organic solvent, and then the copper-based busbar is immersed in an acidic solution for activation.

[0021] Preferably, the acidic solution comprises a mixture of sulfuric acid, nitric acid and succinic acid, wherein the mixing ratio of sulfuric acid, nitric acid and succinic acid is (1-2):(1-2):(3-5), the concentration of sulfuric acid and nitric acid is 5-10 mol / L, and the concentration of succinic acid is 20-25 mol / L.

[0022] The beneficial effects of this invention are as follows:

[0023] 1. The present invention first deposits a nickel phosphorus layer as a transition layer on the surface of a copper-based bonding wire, and then deposits a palladium layer. The nickel phosphorus has good adhesion to both the copper base and the palladium layer, and also has good electrical conductivity, thereby improving the bonding force between the copper base and the palladium layer. At the same time, the nickel element can increase the ductility of the bonding wire and also has anti-sulfurization properties.

[0024] 2. The nickel-phosphorus alloy electroplating solution of the present invention uses nickel sulfate as the main salt and sodium hypophosphite as the reducing agent. The free nickel used for the reduction reaction in the plating solution is controlled by lactic acid. The plating solution has high stability. The nickel hypophosphite formed by hypophosphite and nickel ions is easier to remove than nickel phosphite. The resulting amorphous nickel-phosphorus alloy electroplating layer has good wettability and high corrosion resistance to various corrosive media.

[0025] 3. The present invention further incorporates palladium doping into the copper-based bonding wire. The doped palladium element is beneficial for improving the corrosion resistance and oxidation resistance of the bonding wire, as well as its conductivity. At the same time, palladium has good adhesion, which enables the copper-based bonding wire to form a better adhesion and bonding with the phosphate nickel layer. Furthermore, during the phosphate nickel plating process, free phosphorus ions in the nickel-phosphorus alloy electroplating solution will combine with palladium to form palladium phosphide. Palladium phosphide not only has high conductivity but also enhances the bonding force with the substrate. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, obtaining other drawings based on these drawings without creative effort still falls within the scope of the present invention.

[0027] Figure 1 The following are the test results of the tape in Examples 1-4 and Comparative Example 1 of the present invention: (a) Example 1, (b) Example 2, (c) Example 3, (d) Example 4; (e) Comparative Example 1. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings.

[0029] Example 1

[0030] A process for preparing palladium-plated copper-based bonding wire includes the following steps:

[0031] S1. Raw material preparation and pretreatment: All metal raw materials are cleaned and dried using anhydrous ethanol with ultrasonic technology; all metal raw materials are copper.

[0032] S2. Substrate casting: The dried metal raw materials are mixed and vacuum-melted in a high-purity argon atmosphere. The vacuum degree is 0.001MPa, the melting temperature is 1050℃, and the melting time is 50 minutes. Then, directional continuous casting is carried out to obtain a copper-based busbar with a diameter of 8mm.

[0033] S3. Cold drawing: The copper-based master alloy is cooled to 150°C, and then coarsely drawn to a diameter of 90μm, and then finely drawn to a diameter of 45μm;

[0034] S4. Surface activation treatment: The surface of the copper-based busbar is cleaned and deoxygenated using an organic solvent, and then the copper-based busbar is immersed in an acidic solution for activation. The mixing ratio of sulfuric acid, nitric acid and succinic acid in the acidic solution is 1:2:3. The temperature of the copper-based bonding wire during immersion is 70℃ and the immersion time is 8s.

[0035] S5. NiP Transition Layer Plating: A NiP transition layer is plated onto the surface of the surface-active treated copper-based busbar. A nickel-phosphorus alloy electroplating solution is used, with the following formula: nickel sulfate: 20 g / L, sodium hypophosphite: 25 g / L, lactic acid: 20 ml / L, ammonia: 20%–25%, pH value 4.8; the electroplating current density is 0.5 A / dm³. 2 The electroplating temperature was 70℃, the electroplating speed was 20m / s, and the thickness of the NiP transition layer was 10nm.

[0036] S6. Target Layer Plating: A layer of palladium is plated onto the surface of the copper-based bonding wire with the NiP transition layer. A palladium plating solution is used, with the following formula: alkaline palladium plating solution, pH 7-8, and a plating current density of 1 A / dm³. 2 The electroplating temperature was 60℃, the electroplating speed was 30m / s, and the thickness of the palladium layer was 50nm.

[0037] S7. Annealing: Linear annealing is adopted, with the wire passing through a furnace protected by hydrogen and nitrogen gas. The temperature is controlled at 500℃ and the speed is controlled at 1m / s. The mixing ratio of hydrogen and nitrogen in the hydrogen and nitrogen gas is 4:96.

[0038] S8. Winding and Packaging: The winding is a standard operation in the field. A dedicated winding machine can be used to wind the copper-based bonding wire to a fixed length onto a two-inch diameter spool at a suitable speed. Finally, ordinary packaging can be used for storage at room temperature.

[0039] Example 2

[0040] The difference between this embodiment and Embodiment 1 is that the thickness of the NiP transition layer deposited in step S5 is 15 nm, and the thickness of the palladium layer deposited in step S6 is 45 nm.

[0041] Example 3

[0042] The difference between this embodiment and Embodiment 1 is that the thickness of the NiP transition layer deposited in step S5 is 5 nm, and the thickness of the palladium layer deposited in step S6 is 55 nm.

[0043] Example 4

[0044] The difference between this embodiment and Embodiment 1 is that, in step S1, the metal raw material contains 99.8% copper and 0.2% palladium.

[0045] Comparative Example 1

[0046] A process for preparing palladium-plated copper-based bonding wire includes the following steps:

[0047] S1. Raw material preparation and pretreatment: All metal raw materials are cleaned and dried using anhydrous ethanol with ultrasonic technology; all metal raw materials are copper.

[0048] S2. Substrate casting: The dried metal raw materials are mixed and vacuum-melted in a high-purity argon atmosphere. The vacuum degree is 0.001MPa, the melting temperature is 1050℃, and the melting time is 50 minutes. Then, directional continuous casting is carried out to obtain a copper-based busbar with a diameter of 8mm.

[0049] S3. Cold drawing: The copper-based master alloy is cooled to 150°C, and then coarsely drawn to a diameter of 90μm, and then finely drawn to a diameter of 45μm;

[0050] S4. Surface activation treatment: The surface of the copper-based busbar is cleaned and deoxygenated using an organic solvent, and then the copper-based busbar is immersed in an acidic solution for activation. The mixing ratio of sulfuric acid, nitric acid and succinic acid in the acidic solution is 1:2:3. The temperature of the copper-based bonding wire during immersion is 70℃ and the immersion time is 8s.

[0051] S5. Target plating: A layer of palladium is plated onto the surface of the copper-based bonding wire using a palladium plating solution with the following formula: alkaline palladium plating solution with a pH of 7-8, and a plating current density of 0.5 A / dm³. 2 The electroplating temperature was 60℃, the electroplating speed was 25m / s, and the thickness of the palladium layer was 50nm.

[0052] S6. Annealing: Linear annealing is adopted, with the wire passing through a furnace protected by hydrogen and nitrogen gas. The temperature is controlled at 400℃ and the speed is controlled at 0.5m / s. The mixing ratio of hydrogen and nitrogen in the hydrogen and nitrogen gas is 4:96.

[0053] S7. Winding and Packaging: The winding is a standard operation in the field. A dedicated winding machine can be used to wind the copper-based bonding wire to a fixed length onto a two-inch diameter spool at a suitable speed. Finally, ordinary packaging can be used for storage at room temperature.

[0054] Tape tests were performed on samples from Examples 1-4 and Comparative Example 1, see [link to relevant documentation]. Figure 1 As shown in (ae), the plating layers in Examples 1, 2, and 4 did not peel off, while Example 3 showed some slight peeling. Comparative Example 1 showed more severe peeling. This indicates that by using the composite plating system and thickness settings selected in this invention, the electroplated nickel-phosphorus transition layer can greatly enhance the adhesion between the copper-based bonding wire surface and the palladium layer, thereby improving the durability of the bonding wire.

[0055] Annealing performance and electrical properties of the samples from Examples 1-4 and Comparative Example 1 were tested, and the results are shown in Table 1 below:

[0056] Table 1

[0057]

[0058] The standard reference for tensile strength and elongation in the table is GB / T 34507-2017.

[0059] The above description discloses only preferred embodiments of the present invention and should not be construed as limiting the scope of the present invention. Therefore, equivalent variations made in accordance with the claims of the present invention are still within the scope of the present invention.

Claims

1. A palladium-plated copper-based bonding wire, comprising a copper-based busbar, characterized in that: It also includes a nickel-phosphorus alloy transition layer and a palladium layer that are sequentially plated on the surface of the copper-based busbar.

2. The palladium-plated copper-based bonding wire according to claim 1, characterized in that: The thickness of the nickel-phosphorus alloy transition layer is 5-15 nm, and the thickness of the palladium layer is 40-60 nm.

3. The palladium-plated copper-based bonding wire according to claim 1, characterized in that: The copper-based busbar contains 97-99.9% copper and 0.1-3% palladium.

4. The preparation process of a palladium-plated copper-based bonding wire as described in any one of claims 1-3, characterized in that, Includes the following steps: (A) Nickel-phosphorus alloy transition layer: A layer of NiP is plated onto the surface of the surface-active copper-based busbar as a transition layer using a nickel-phosphorus alloy electroplating solution. (B) Palladium plating layer: A layer of metallic palladium is plated onto the surface of the copper-based busbar, which is plated with a nickel-phosphorus alloy transition layer, using a palladium electroplating solution; (C) Annealing: Wire annealing is adopted, in which the wire passes through a furnace protected by hydrogen and nitrogen gas. The furnace temperature is 400-600℃ and the speed is 0.5-2m / s.

5. The preparation process of a palladium-plated copper-based bonding wire according to claim 4, characterized in that: In step (A), the nickel-phosphorus alloy electroplating solution includes 15-25 g / L nickel sulfate, 20-30 ml / L sodium hypophosphite, and 20%-25% ammonia.

6. The preparation process of a palladium-plated copper-based bonding wire according to claim 4, characterized in that: In step (A), the electroplating current density is 0.1–5 A / dm². 2 The electroplating temperature is 60-80℃, and the electroplating speed is 15-40m / s.

7. The preparation process of a palladium-plated copper-based bonding wire according to claim 4, characterized in that: In step (B), the electroplating current density is 0.5–5 A / dm². 2 The electroplating temperature is 55-75℃, and the electroplating speed is 25-40m / s.

8. The preparation process of a palladium-plated copper-based bonding wire according to claim 4, characterized in that: In step (C), the hydrogen-nitrogen gas is a mixture of hydrogen and nitrogen, and the mixing ratio of hydrogen and nitrogen is (4.5-7):(93-95.5).

9. The preparation process of a palladium-plated copper-based bonding wire according to claim 4, characterized in that: The copper-based busbar is prepared by the following method: S1. Raw material preparation and pretreatment: Ultrasonic cleaning and drying of the metal; S2. Substrate melting and casting: The dried metal is first vacuum-melted in a high-purity argon atmosphere with a vacuum degree of 10. -3 ~10 -2 MPa, melting temperature of 1050~1250℃, melting time of 50~80 minutes, followed by directional continuous casting to obtain copper-based busbars with a diameter of 6-10mm; S3. Cold drawing: The copper-based busbar is cooled to 150-200℃, and then coarsely drawn to a diameter of 60-120μm, and then finely drawn to a diameter of 30-60μm; S4. Surface activation treatment: The surface of the copper-based busbar is cleaned and deoxygenated using an organic solvent, and then the copper-based busbar is immersed in an acidic solution for activation.

10. The preparation process of a palladium-plated copper-based bonding wire according to claim 9, characterized in that: The acidic solution comprises a mixture of sulfuric acid, nitric acid and succinic acid, wherein the mixing ratio of sulfuric acid, nitric acid and succinic acid is (1-2):(1-2):(3-5), the concentration of sulfuric acid and nitric acid is 5-10 mol / L, and the concentration of succinic acid is 20-25 mol / L.

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