A method for preparing single crystal copper bonding wire

Abstract

The present invention discloses a method for preparing a single crystal copper bonding wire, comprising the following steps: preparing a polycrystalline copper rod by extrusion treatment to prepare a polycrystalline copper thin rod; preparing a polycrystalline copper thin rod by multiple drawing steps to prepare a polycrystalline copper thin wire; and preparing a single crystal copper bonding wire by annealing the polycrystalline copper thin wire. The method uses a polycrystalline copper billet as the initial raw material, abandons the limitation of using expensive single crystal copper rods as the raw material, and has simple operation and low cost.

Description

Technical Field

[0001] The invention relates to a method for preparing an electronic packaging bonding wire, and in particular to a novel method for preparing a single crystal copper bonding wire. Background Art

[0002] As the inner lead for electronic packaging, bonding wire is one of the essential basic materials in the manufacturing process of integrated circuits and discrete semiconductor devices. It is a bridge connecting the silicon wafer electrode and the external lead terminal of the lead frame, and plays the role of transmitting chip electrical signals and dissipating the internal heat of the chip. The important function of the bonding wire determines that the material used as the bonding wire needs to have good electrical conductivity, thermal conductivity, good mechanical properties and chemical stability. At present, the commonly used bonding wires include gold wire, copper wire, aluminum wire and alloy wire. Among them, compared with gold wire, copper bonding wire is cheap, which is only 20%-40% of the price of gold wire, but copper bonding wire has higher resistivity and thermal conductivity (second only to silver wire). In addition, during the welding process, copper is not easy to form intermetallic compounds with aluminum, and the reliability is also high. Therefore, copper wire is an important material for semiconductor packaging leads instead of gold wire.

[0003] In recent years, with the development of the semiconductor electronics industry, it is moving towards higher chip density, lower price, and lower power consumption. Seeking a new generation of copper bonding wires with low cost and good performance has become an important goal of the electronic packaging industry. Single-crystal copper bonding wires can effectively further reduce electron and phonon scattering due to the lack of polycrystalline grain boundaries. Compared with polycrystalline copper bonding wires, they have better electrical conductivity and heat dissipation performance, and will become the mainstream product in the future electronic packaging field. At present, single-crystal copper bonding wires are usually made of more expensive continuous-cast single-crystal copper rods as the initial raw material, and are drawn through multiple passes. However, during the drawing process, it is usually accompanied by severe work hardening and defects, which affect the electrical and mechanical properties of single-crystal copper wires. Moreover, in the process of drawing copper wires, it is necessary to melt, continuously cast, and form at a temperature above the melting point of copper (1085°C). The process is relatively complicated, so the cost is high and it is difficult to achieve large-scale manufacturing. Therefore, it is of great significance to seek a low-cost preparation technology for high-performance single-crystal copper bonding wires. Summary of the invention

[0004] In order to solve the above problems, the present invention provides a novel method for preparing single crystal copper bonding wire, which uses polycrystalline rods as initial raw materials, abandons the limitation of using expensive single crystal rods as raw materials, is relatively simple to operate, and has low cost.

[0005] To solve the above technical problems, the purpose of the present invention is achieved as follows:

[0006] A method for preparing a single crystal copper bonding wire according to the present invention comprises the following steps:

[0007] The polycrystalline copper rod is processed by extrusion to obtain a polycrystalline copper thin rod;

[0008] The polycrystalline copper thin rod is drawn through multiple passes to obtain a polycrystalline copper thin wire;

[0009] The polycrystalline copper thin wire is annealed to obtain a single crystal copper bonding wire.

[0010] On the basis of the above scheme and as a preferred scheme of the above scheme: comprising the following steps:

[0011] (1) pickling the oxygen-free copper blank and then heat treating it to obtain polycrystalline copper with equiaxed grains;

[0012] (2) extruding the polycrystalline copper prepared in the previous step to obtain a polycrystalline copper rod;

[0013] (3) extruding the polycrystalline copper rod prepared in the previous step to obtain a polycrystalline copper thin rod;

[0014] (4) passing the polycrystalline copper thin rod prepared in the previous step through a wire drawing machine to draw a polycrystalline copper wire;

[0015] (5) preheating the polycrystalline copper wire prepared in the previous step, and drawing it into a polycrystalline copper thin wire through a wire drawing machine;

[0016] (6) The polycrystalline copper wire prepared in the previous step is pickled and annealed; after the annealing treatment, it is cold-water quenched, pickled and polished to obtain a finished single crystal copper bonding wire.

[0017] On the basis of the above scheme and as a preferred scheme of the above scheme: in step (1), the purity of the polycrystalline copper billet is 99.999%;

[0018] In step (2), the polycrystalline copper billet is drawn and extruded at a temperature of 800°C, No. 45 engine oil plus 25% flake graphite is used as a lubricant, and the speed of flowing out of the die hole is controlled at 35 / m·min -1 , the obtained polycrystalline thick copper rod has a diameter of 8 mm.

[0019] On the basis of the above scheme and as a preferred scheme of the above scheme: in step (3), the polycrystalline copper rod is extruded again into a polycrystalline thin copper rod with a diameter of 2 mm, wherein the setting conditions are an extrusion temperature of 850°C and a flow rate out of the die hole of 50 / m·min -1 , using No. 45 engine oil plus 25% flake graphite as lubricant, the diameter of the polycrystalline copper rod obtained is 2mm.

[0020] On the basis of the above scheme and as a preferred scheme of the above scheme: in step (5), the polycrystalline copper wire is preheated and then drawn into a polycrystalline copper thin wire with a diameter of 0.018-0.025 mm in multiple passes on a small wire drawing machine.

[0021] Based on the above scheme and as a preferred scheme of the above scheme: in step (6), the polycrystalline copper wire is pickled, and the polycrystalline copper wire after pickling and drying is vacuum packaged using a quartz tube, and the vacuum degree is less than 10 -3 Pa; annealing heat treatment is performed at 200°C below the melting point; wherein the annealing temperature is 885°C, the time is 24 hours, the heating rate is 10°C / min, and after the annealing is completed, the copper bonding wire is directly taken out together with the quartz tube, quenched in cold water, and the surface of the annealed copper bonding wire is pickled and polished to obtain a finished single crystal copper bonding wire.

[0022] The beneficial effects of the present invention are as follows: the method for preparing a single crystal copper bonding wire of the present invention uses polycrystalline copper billets as initial raw materials, abandons the limitation of using expensive single crystal copper rods as raw materials, and has simple operation and low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solution implemented in the present invention, the following is a brief introduction to the drawings used in the implementation. It is obvious that the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0024] Figure 1 Schematic diagram of the process of preparing a single crystal copper bonding wire in one embodiment of the present invention;

[0025] Figure 2 A scanning electron microscope (SEM) image of a single crystal copper bonding wire prepared in one embodiment of the present invention;

[0026] Figure 3 This is an electron backscattering (EBSD) image of a single crystal copper bonding wire prepared in one embodiment of the present invention. DETAILED DESCRIPTION

[0027] Combination Figures 1 to 3 The present invention is described in detail. The present invention relates to a method for preparing a single crystal copper bonding wire, and the specific process flow is as follows:

[0028] Step (1): After pickling 99.999% high-purity oxygen-free copper billet, heat treatment is performed at 800°C, and the pressure in the furnace is less than 10 -3 Pa. The heating rate was 10°C / min, the heat treatment time was 12 hours, and then the polycrystalline copper with equiaxed grains was obtained by furnace cooling.

[0029] Step (2): Extrusion the equiaxed polycrystalline copper billet annealed in step (1) to obtain a polycrystalline copper rod with a diameter of 8 mm. The setting conditions are as follows: the extrusion temperature is set at 800°C and the flow rate out of the die hole is 35 / m·min. -1 ,Using No. 45 engine oil plus 25% flake graphite as lubricant, the diameter of the obtained polycrystalline copper rod is 8mm. The added flake graphene accounts for 25% of the volume of No. 45 engine oil, that is, 25% is the volume percentage.

[0030] Step (3): The 8 mm diameter polycrystalline copper rod obtained in step (2) is extruded again into a 2 mm diameter polycrystalline thin copper rod. The setting conditions are as follows: the extrusion temperature is 850°C, the flow rate out of the die hole is 50 / m·min -1 Similarly, using No. 45 engine oil plus 25% flake graphite as a lubricant, the obtained polycrystalline thin copper rod has a diameter of 2 mm. In this step, 25% is also a volume percentage.

[0031] Step (4): The thin copper rod with a diameter of 2 mm obtained in step (3) is drawn into a polycrystalline copper wire with a diameter of 0.2 mm by a wire drawing machine controlled by a microcomputer and driven by an AC motor;

[0032] Step (5): preheat the polycrystalline copper wire with a diameter of 0.2 mm obtained in step (4), and then draw it into a polycrystalline copper fine wire with a diameter of 0.018-0.025 mm in multiple passes on a small wire drawing machine.

[0033] Step (6): pickling the polycrystalline copper wire obtained in step (5), and vacuum packaging the pickled and dried polycrystalline copper wire using a quartz tube, with a vacuum degree of less than 10 -3 Pa. Annealing heat treatment is performed at 200°C below the melting point to obtain a single crystal copper bonding wire. The annealing temperature is 885°C and the time is 24 hours. The heating rate from room temperature to 885°C is 10°C / min. After the annealing is completed, it is directly taken out together with the quartz tube, quenched in cold water, and the surface of the annealed copper bonding wire is pickled and polished to obtain a finished single crystal copper bonding wire.

[0034] Take the single crystal copper bonding wire with a diameter of 0.018mm as an example, and conduct the test. Figure 2 and Figure 3 , and the scanning electron microscope (SEM) images and electron backscattering (EBSD) images were tested respectively.

[0035] Depend on Figure 2 It can be seen from the scanning electron microscope image of the single crystal copper bonding wire that the prepared single crystal copper bonding wire has no obvious grain boundaries, a relatively smooth surface, and a single crystal morphology, overcoming the processing defects caused by using continuous casting single crystal copper rods as the initial raw material to process single crystal copper bonding wire.

[0036] Depend on Figure 3 The electron backscattering image of the single crystal copper bonding wire shows that the prepared single crystal copper bonding wire presents a single crystal structure without obvious lattice distortion, but is accompanied by a small amount of common annealing twins.

[0037] The resistivity of the single crystal copper bonding wire with a diameter of 0.018 mm was tested by the four-probe method. The results showed that the resistivity of the single crystal copper bonding wire was 1.48×10 -8 Ω·m, compared with the typical resistivity of polycrystalline copper bonding wire in the prior art, which is 1.75~1.94×10 -8 Compared with the single crystal copper bonding wire, the resistivity of the single crystal copper bonding wire decreased by 15-23%, indicating that the single crystal copper bonding wire prepared by this method has better electrical properties.

[0038] The preferred specific embodiments of the present invention are described in detail above. It should be understood that a person skilled in the art can make many modifications and changes based on the concept of the present invention without creative work. Therefore, any technical solution that can be obtained by a person skilled in the art through logical analysis, reasoning or limited experiments based on the concept of the present invention on the basis of the prior art should be within the scope of protection determined by the claims.

Claims

1. A method for preparing a single crystal copper bonding wire, characterized in that: The steps include: (1) The oxygen-free copper billet is pickled and then heat treated to obtain polycrystalline copper with equiaxed grains; (2) extruding the equiaxed grain polycrystalline copper prepared in the previous step to obtain a polycrystalline copper rod; (3) extruding the polycrystalline copper rod prepared in the previous step to obtain a polycrystalline copper thin rod; (4) passing the polycrystalline copper thin rod prepared in the previous step through a wire drawing machine to draw a polycrystalline copper wire; (5) preheating the polycrystalline copper wire prepared in the previous step, and drawing it into a polycrystalline copper thin wire through a wire drawing machine; (6) pickling and annealing the polycrystalline copper wire prepared in the previous step; after annealing, cold water quenching, pickling and polishing are performed to obtain a finished single crystal copper bonding wire; In step (1), the purity of the oxygen-free copper blank is 99.999%; In step (2), the extrusion temperature of the polycrystalline copper is 800°C, 45# engine oil plus 25% flake graphite is used as lubricant, and the speed of the polycrystalline copper out of the die hole is controlled at 35 m•min. -1 , the diameter of the obtained polycrystalline copper rod is 8 mm; In step (3), the polycrystalline copper rod is extruded again into a polycrystalline thin copper rod with a diameter of 2 mm, wherein the setting conditions are an extrusion temperature of 850°C and a flow rate out of the die hole of 50 m•min -1 , using No. 45 engine oil plus 25% flake graphite as lubricant, the diameter of the polycrystalline copper thin rod is 2 mm; The 25% mentioned in step (2) and step (3) is a volume ratio; In step (5), the polycrystalline copper wire is preheated and then drawn on a wire drawing machine in multiple passes into a polycrystalline copper thin wire with a diameter of 0.018-0.025 mm.

2. The method for preparing a single crystal copper bonding wire according to claim 1, characterized in that: In step (6), the polycrystalline copper wire is pickled, and the pickled and dried polycrystalline copper wire is vacuum packaged using a quartz tube, with a vacuum degree of less than 10 -3 Pa; annealing heat treatment is performed at 200°C below the melting point; wherein the annealing temperature is 885°C, the time is 24 hours, the heating rate is 10°C / min, and after the annealing is completed, the copper bonding wire is directly taken out together with the quartz tube, quenched in cold water, and the surface of the annealed copper bonding wire is pickled and polished to obtain a finished single crystal copper bonding wire.

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