ABSTRACT: Copper has been widely used in electronic components manufacturing because of its excellent thermal conductivity and good processing performance. With the development of electronic component industry and the improvement of material properties, it is the trend that a large number of common copper materials are replaced by oxygen-free copper and copper-silver alloy materials. Keywords: oxygen-free Copper; Electronic Copper; development trend; drawing classification number: TM205.1 Literature Identification Number: a article number: 1671-8887(2006)01-0010-041. Copper and copper alloys have excellent electrical and thermal conductivity and good technological properties, corrosion resistance, easy processing, good weldability and relatively low price, it is widely used in wire and cable, electric contact and electronic component manufacturing industry. In order to meet the needs of the development of the electronics industry, in recent years, significant progress has been made in the research and development of new copper and copper alloy materials, such as oxygen-free copper and copper-silver alloy electrical contact materials, copper-iron Alloy lead frame materials and single crystal copper materials. This paper introduces the preparation methods of oxygen-free Copper and discusses the development trend of electronic copper. 2. The metallurgical principle and technological characteristics of producing oxygen-free copper by up-drawing method the production of oxygen-free copper billets (slab, tube billets and wire billets) by up-drawing method is an increasingly mature technology in the 1980s. The technological process of up-drawing continuous casting is essentially a continuous casting process. After melting and refining (mainly deoxidization and degassing) in the power frequency or intermediate frequency furnace, the copper liquid enters the holding furnace through a bridge. The graphite mould is inserted into the crystallizer of the copper liquid (Fig. 1) , driven by the traction of the seed Crystal Rod, the formed slabs and wire slabs are finally rolled by a transmission mechanism and a winding mechanism. The weight of a single roll is cut at will by a plasma cutting machine according to the capacity of the equipment in the subsequent process, and the production process is continuous. Quality Inspection shall be conducted once per shift, including impurity analysis, oxygen content determination, billet dimensional accuracy and appearance quality, etc. . The technical parameters are adjusted by the technical personnel according to the production conditions within the prescribed range. The unqualified blank can be remelted due to its purity, and the qualified blank is transferred to the later working procedure. The raw material for preparing oxygen-free copper is high-quality electrolytic copper, and the raw material needs to be treated strictly. The temperature of liquid copper, drawing speed and water cooling effect of crystallizer are the key factors affecting the quality of billet.

The temperature of the copper solution in the holding furnace has a great influence on the quality of the billet. Too High temperature will coarsen the grains and increase the oxygen content, which will have a bad effect on the service life of the graphite mould, easy to appear cold separation and crack as well as loose and broken billet, etc. . The results show that the optimum temperature is (1150 ± 5) °C. The molten copper is covered from beginning to end with charcoal and flake-like graphite during melting and refining. The charcoal needs to be baked before it is put into the furnace, the water content is & Lt; 8% , the granularity is 30 ~ 50mm. The following reactions occur during the refining process: 4Cu + o 2 * 2Cu2O, 2Cu2O + c * 4cu + Co 2, and Deoxidation is finally achieved. The copper liquid enters the mold graphite mold, the heat mainly passes through the graphite mold circulation cooling water to radiate outwards. The solid-liquid interface during solidification is shown in Fig. 2. In the solidification process of copper liquid, the faster the cooling rate is, the smaller the columnar crystal is and the denser the structure is. Therefore, rapid solidification is an important method to obtain refined crystal structure, improve the segregation and obtain better quality billet. The practice shows that the large columnar crystal can be obviously improved by reducing the temperature difference between the inlet and outlet water from 12 °C to about 7 °C under the condition of equipment.

It was found that if the drawing speed was too slow, not only the yield would be affected, but also the quality of billet would not be improved. The casting billet with good quality can be obtained with general guide rod speed of 1180 ~ 1200 MM/MIN, guide plate speed of 80 ~ 100 MM/MIN and pitch of 3 ~ 4 mm. In addition, the environmental conditions such as temperature, humidity and weather conditions in the workshop will affect the production of oxygen-free copper, which must be adjusted by process parameters. 3. The main technical characteristics of oxygen-free copper and copper-silver Alloy oxygen-free copper and copper-silver alloy wires and strips are widely used in the manufacture of switches, relays, connectors and other electronic components and household appliances, electric tools, automobiles, motorcycles, such as the commutator. The grades, chemical compositions and mechanical properties of oxygen-free copper and copper-silver alloy products are shown in Table 1. The main properties of oxygen-free copper and copper-silver alloys are: 1 good conductivity and thermal conductivity, resistivity ≤0.017593 mm2/m at 20 °C, relative conductivity ≥98% , 2 products in t, Y, y 2 and M states, 3 low oxygen content of the materials, oxygen Content ≤0.0210-3, with good oxidation resistance, corrosion resistance; 4 good forming technology, in the processing of complex components, there are no cracks, peeling and distortion defects; 5 High Strength, good plasticity, it is helpful to improve the wear resistance and service life of components. 4. Development trend of electronic copper electronic copper is the basic material for manufacturing electronic components. With the development of electronic component manufacturing industry, the requirement for the dimensional accuracy and surface quality of electronic copper materials has been raised, especially, it is the trend to improve the mechanical properties of copper alloys without affecting the intrinsic properties of copper (such as excellent conductivity and thermal conductivity) .

4.1 adding a small amount of silver into the oxygen-free copper of copper-silver alloy can strengthen the copper by proper heat treatment without much influence on its conductivity and thermal conductivity. At present, this kind of material is mainly used in the commutator of micro-motor and the contact wire of traction locomotive. It not only keeps the conductivity and thermal conductivity of oxygen-free copper, but also improves its strength and wear resistance. 4.2 with the development of microelectronic technology, lead frame materials for IC packaging have become a series of electronic alloy materials, mainly copper alloy and iron-nickel alloy. Due to the excellent thermal conductivity of copper, with the development of low alloy strengthening technology and the requirement of high density packaging technology, the lead frame material of copper alloy has replaced fe-ni alloy in the range of 90% . Among them, cu-fe alloy is a kind of solid solution reinforced lead frame material series. According to the investigation, the consumption of lead frame materials for IC packaging in China is above 2000t each year. Because domestic copper-based lead frame materials are still in the development stage and have not been mass-produced, so they are basically dependent on imports. Table 2 and Table 3 are the chemical composition and main performance index of common IC packaging lead frame materials.

The dimension accuracy of C lead frame material is very strict, which can not be achieved by ordinary metal material production equipment. The main dimensional accuracy indexes are: thickness tolerance: ± 0.01 mm when the product thickness is 0.25ー0.45 mm; width tolerance: ± 0.05 mm when the product width is ≤100 mm; lateral bending: Product Width & Lt; 60 mm when the product is ≤1mm; width ≥60 mm, ≤1.5 MM/M; lateral bending: Product Width & Lt; 43 mm, ≤0.1 MM/M; width ≥43 ~ 60 mm, ≤0.15 MM/M; deflection ≤10 °/m; coil bending ≤1.5 mm/200 mm; Burr & Lt; 0.01 mm. 4.3 The hot mold Continuous Casting technology of single crystal copper was invented by Toshimi Ono of Japan, also called Ohno Continuous Casting. The Slab can be produced by continuous casting because of unidirectional solidification in the mould and continuous drawing by traction machine, which creates favorable conditions for large-scale production. The schematic diagram of the directional solidification device is shown in fig

The characteristics of single crystal copper are: 1 No grain boundary or less grain boundary. The whole section is composed of one or more parallel crystals arranged along the axis, which is called single crystal or unidirectional crystal structure. Due to the complete structure of the single crystal, the defects such as shrinkage, porosity, porosity and inclusion are basically eliminated. 3 the surface of the cast billet is smooth and crack-free, which is convenient for the post-processing 4 The electrical resistivity of single crystal copper processed at 20 °c ≤0.01690 MM2/M, relative conductivity ≥102% , tensile strength 140ー250 MPA, elongation 28% ー75% , oxygen content ≤110-5, hydrogen content ≤110-6. Single Crystal Copper has been widely used abroad, especially in Japan. The development trend of electronic Copper materials is illustrated from ordinary Copper (T1, T2) to oxygen-free Copper (TU1, Tu2) and then to single crystal Copper (TG1, TG2, PuRe, Copper OCC) . This not only represents the technical progress of electronic functional materials, but also is the inevitable result of the higher technical requirements for electronic materials with the development of electronic component industry. The main application fields of single crystal copper are: (1) audio and video equipment. Because single crystal copper has no grain boundary or few grain boundary, the transmission of signal is not affected by the reflection and refraction of grain boundary, so the distortion, distortion and attenuation of signal are reduced, and the audio and video quality is improved obviously. (2) components and transmission systems for communications equipment. The related components and transmission lines are made of single crystal copper, and the transmission effect is improved fundamentally. (3) computer network systems and peripherals. Because the computer network must transmit high-efficiency digital signal, using ordinary copper or even oxygen-free copper to make relevant components and transmission lines, its strong skin effect and grain boundary loss will cause signal attenuation and distortion, therefore, it is necessary to use single crystal copper to obtain perfect transmission effect. (4) integrated circuit leads. It is required to use 0.05 ~ 0.019 mm fine copper wire. Only single crystal copper can process the fine wire and gradually replace the gold wire to reduce the cost. (5) manufacturing of electronic components. With the development of electronic industry, the requirements for high performance, miniaturization and lightweight of electronic components such as switches, relays, connectors, loudspeakers, buzzers, mid-week and mini-transformers are becoming higher and higher, in this field, it is an inevitable trend to use single crystal copper instead of ordinary copper or even oxygen-free copper. 

Source: Chinanews.com, by Yu Chaoqing

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