Tailoring the Surface Morphology and Microstructure of Electrodeposited Copper Foil with Organic Additives,ECS Meeting Abstracts |
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Tailoring the Surface Morphology and Microstructure of Electrodeposited Copper Foil with Organic Additives,ECS Meeting Abstracts
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Copper foil manufactured by high-speed electrochemical deposition (ED) is an essential material for its extensive applications such as the negative current collector for lithium-ion batteries (LIBs) or building up the designed connection pattern on the printed circuit boards (PCBs). Thus, producing copper foil with optimal quality and machinability depending on the end products is necessary. For example, the thickness of Cu foils for LIBs should be thin (< 10 µm) to reduce the volume and weight of batteries but the mechanical properties should remain strong enough to go through the roll-to-roll manufacturing process without fracture. In addition, the surface roughness on both sides should be identically smooth and glossy to provide the coating carbon materials with acceptable wetability and adhesion. On the other hand, Cu foils for the fifth generation (5G) high-frequency wireless devices should be exceedingly smooth because the skin depth of copper caused by the so-called skin effect is merely 0.266 µm when the transmitting frequency of signals is up to 60 GHz. Thus, a great majority of electric current passing through the conductor will flow extremely near the surface. Under such circumstances, coarse surface roughness has a significant detrimental effect on the signal loss of wireless communication devices, and consequently, the surface morphology and mechanical properties of copper foils should be further improved in order to meet the requirements for the next generation electronic devices. The microstructure of copper fabricated by ED depends highly on plating parameters, including current density, convection rate of the electrolyte, pulsed/direct current deposition, or using appropriate organic additives to ameliorate the nucleation behavior of Cu from cupric ions. Manufacturing of ED copper foils ought to operate with very high current density and high temperature to promote the yield rate for mass production, and the gelatin-based additive has been used for a long time. However, grain structure and surface roughness are coarse and mechanical properties are merely acceptable with around 250 MPa tensile strength and a 4% elongation rate for a normal 18 µm foil. In this work, we demonstrate the copper foil fabricated by high-speed electrodeposition with a current density of 450 mA/cm2 (average growth rate > 150 nm/s) from a 54oC bath, which meets the required yield rate for genuine mass-production, and tailoring the microstructure of copper with selective additives. The surface morphology of the foil facing the electrolyte side is smooth by our designed additives, and surface roughness values, Ra and Rq, are less than 100 nm, which are as smooth as foils manufactured via rolling process. In addition, the structure of copper is further tuned by a specific additive, and the grain size of copper is getting smaller as the concentration of this additive is increased. When the concentration of this additive is up to 800 ppm, the average grain size of copper is shrunk from 3 µm to 0.3 µm, and extremely unique copper texture with nearly single (220) orientation is constructed. Owing to such delicate microstructure, considerable improvement in mechanical properties with more than 40 % increase in tensile strength and 4 times increase in the elongation rate compared to the conventional gelatin-based copper foil is achieved. The surface morphology and structure of copper foil are properly characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), electron back-scattered diffraction (EBSD), transmission electron microscopy (TEM) and tensile testing machine, and the applied additive to tailor the structure of copper will be clearly revealed and discussed. Finally, a novel and commercially realizable scheme to fabricate copper foil with ultra smooth surface morphology and ductile mechanical properties by high-speed ED is proposed.
中文翻译：
通过高速电化学沉积 (ED) 制造的铜箔是其广泛应用的重要材料，例如锂离子电池 (LIB) 的负极集流体或在印刷电路板 (PCB) 上构建设计的连接图案。因此，有必要根据最终产品生产具有最佳质量和可加工性的铜箔。例如，用于锂离子电池的铜箔厚度应该很薄（< 10 µm），以减少电池的体积和重量，但机械性能应该保持足够强，以便在卷对卷制造过程中不会断裂。此外，两侧的表面粗糙度应相同光滑和有光泽，以使涂层碳材料具有可接受的润湿性和附着力。另一方面，用于第五代（5G）高频无线设备的铜箔应该非常光滑，因为当信号传输频率高达 100 kHz 时，由所谓趋肤效应引起的铜的趋肤深度仅为 0.266 µm。 60GHz。因此，流过导体的绝大多数电流将在极其靠近表面的地方流动。在这种情况下，粗糙的表面粗糙度对无线通信设备的信号损耗具有显着的不利影响，因此，需要进一步改善铜箔的表面形貌和机械性能以满足下一代电子设备的要求。通过 ED 制造的铜的微观结构在很大程度上取决于电镀参数，包括电流密度、电解质的对流速率、脉冲/直流沉积，或使用适当的有机添加剂来改善铜离子的铜成核行为。 ED铜箔的制造需要在非常高的电流密度和高温下进行，以提高批量生产的良率，并且明胶基添加剂已经被使用了很长时间。然而，晶粒结构和表面粗糙度很粗糙，机械性能仅能接受，普通 18 µm 箔的拉伸强度约为 250 MPa，伸长率为 4%。在这项工作中，我们展示了通过电流密度为 450 mA/cm 的高速电沉积制备的铜箔2（平均生长速率 > 150 nm/s）从 54哦C浴，满足真正量产所需的良率，并通过选择性添加剂定制铜的微观结构。通过我们设计的添加剂，面向电解质侧的箔的表面形貌变得光滑，表面粗糙度值Ra和Rq小于100 nm，与通过轧制工艺制造的箔一样光滑。此外，特定添加剂进一步调整了铜的结构，并且随着该添加剂浓度的增加，铜的晶粒尺寸变得更小。当该添加剂的浓度达到800 ppm时，铜的平均晶粒尺寸从3 µm缩小到0.3 µm，并构建出极其独特的几乎单（220）取向的铜织构。由于这种精细的微观结构，与传统明胶基铜箔相比，机械性能得到了显着改善，拉伸强度提高了 40% 以上，伸长率提高了 4 倍。通过扫描电子显微镜（SEM）、原子力显微镜（AFM）、X射线衍射（XRD）、电子背散射衍射（EBSD）、透射电子显微镜（TEM）和拉伸试验机，以及用于定制铜结构的添加剂将被清楚地揭示和讨论。最后，提出了一种新颖且可商业实现的方案，通过高速电火花加工制造具有超光滑表面形貌和延展机械性能的铜箔。 |
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