Effect of dimethylglyoxime on microstructure of electrodeposited cobalt coating and growth of interfacial IMC at cobalt/solder joint
Jiteng Wang;Xiaoxi He;Wei Cao;Yuyao Luo;Mingji Zhou;Yuanming Chen;[Objective] Cobalt is an important material for next-generation interconnect metals, and it is of great significance to study the growth behavior of intermetallic compounds(IMC) at the interface between cobalt and solder. [Method] The electrochemical inhibition behavior of DMG on cobalt deposition was analyzed by chronopotentiometry and cyclic voltammetry. Cobalt electrodeposition was conducted by adding 150 mg/L DMG to the basic bath. The surface roughness, grain size and crystal structure of cobalt coatings obtained without and with DMG were characterized by scanning electron microscopy, laser confocal microscopy and electron backscatter diffraction. The cobalt coating was soldered with SAC305 solder at 250 ℃ for 1 min, and then isothermally aged at 150 ℃ for 0-12 d. The morphological evolution and growth kinetics of the interfacial IMC(CoSn3) were compared and analyzed by energy-dispersive spectroscopy and scanning electron microscopy. [Result] The obtained Co coating had a surface roughness(Sa) of 0.324 μm, an average grain size of 0.296 μm, and the proportions of HCP(hexagonal close-packed) and FCC(facecentered cubic) cobalt phases were 79.7% and 20.3%, respectively. The IMC formed after soldering was prismatic CoSn3, which gradually thickened with isothermal aging time. After isothermal aging for 12 days, the CoSn3 grains on the Co coating obtained with 150 mg/L DMG became more uniform in size, with small Ag_3Sn grains attached on the surface. [Conclusion] The additive DMG can effectively reduce the surface roughness of Co coating, refine the grains and regulate the crystal structure. The obtained smooth cobalt coating helps to form a stable and uniform IMC layer with tin solder, which is beneficial to improving the reliability of electronic products in high-density interconnection and packaging.
Effect of binary composite additive on microstructure of ultra-low profile electrolytic copper foil
Mengmeng Wang;Xiang Li;Ran Xu;Peng Xu;Qianqian Zhu;Weiwei Lu;Kexing Song;[Objective] Ultra-low profile copper foil for high-frequency high-speed printed circuit board(PCBs) is required to have a surface roughness Rz no higher than 0.5 μm(HVLP4 grade). However, conventional additives often contain three or more components, suffering from complexity, instability, and difficulty in process control, and typically require low current densities for preparation, which limits production efficiency. This study aims to prepare ultra-low profile copper foil at high current density by designing a binary additive system comprising polyethylene glycol(PEG) and a novel additive Q(a water-soluble organic sulfur compound containing mercapto groups). [Method] Copper foils were electrodeposited on a titanium cathode with a platinum-coated titanium anode in an electrolyte containing 90 g/L Cu2+, 110 g/L sulfuric acid, and 40 mg/L Cl~-at 45 ℃ and a current density of 25 A/dm2. The effect of single and composite additives on the surface morphology(SEM) and roughness Rz of the rough side were studied by varying the concentrations of PEG and additive Q in bath. The action mechanisms of the additives on copper electrodeposition were analyzed by cyclic voltammetry(CV), chronopotentiometry(CP), and electrochemical impedance spectroscopy(EIS), and the grain orientation and size distribution of the copper foils were characterized by electron backscatter diffraction(EBSD). [Result] With PEG alone, the surface roughness of the rough side of copper foil increased with increasing PEG concentration. After fixing the PEG mass concentration at 15 mg/L and introducing additive Q, the surface of copper foil became smoother and denser; when the concentration of additive Q reached 20 mg/L, the Rz of the copper foil decreased to 0.36 μm, meeting the HVLP4 standard. Electrochemical measurements revealed that additive Q shifted the deposition potential of copper positively and reduced the charge transfer resistance, exhibiting a depolarizing acceleration effect, whereas PEG shifted the deposition potential negatively and increased the charge transfer resistance, exhibiting an inhibiting effect. EBSD results showed that the addition of additive Q promoted preferred grain growth along the deposition direction, with refined and more compactly arranged grains on the rough side. [Conclusion] PEG and additive Q exert opposite effects on copper deposition, with PEG inhibiting the deposition process while additive Q accelerating it. Their synergistic interaction regulates the electrocrystallization process of copper. This binary additive system, featuring a simple composition, enables the preparation of ultra-low profile copper foil at a high current density of 25 A/dm2, providing a feasible pathway for the industrial production of copper foil for high-frequency high-speed PCB applications.
Optimization of shot peening process for CuCrZr crystallization rolls: simulation analysis and experimental verification
Chang'an Zhao;Mingxue Zhang;Yuzheng Song;Junjie Yang;Yiming Xiao;Zheng Chang;Xujie Gao;Na'na Guo;Jinhua Ding;Guangming Zhu;[Objective] For CuCrZr alloy crystallization rolls used in twin-roll strip casting, the surface roughness Ra must be controlled within 2.0-3.5 μm prior to electroplating. However, there is a conflict between the surface roughening induced by shot peening and the desired increase in subsurface compressive stress layer depth. This study aims to maximize the residual compressive stress strengthening layer depth under the given roughness constraint through coordinated regulation of process parameters, thereby providing an optimized shot peening pretreatment scheme for electroplating. [Method] A finite element model of multi-shot random impact was established using Abaqus/Explicit to obtain the responses of surface roughness and residual stress field under various shot peening parameters. First, orthogonal experiments were conducted to identify the dominant influencing factors. Then, single-factor experiments were performed to clarify the influence trends of each parameter on surface integrity and to define the process window. Finally, a desirability function regression model was constructed based on the Box–Behnken design to globally optimize the compressive stress layer depth under the roughness constraint. The optimization results were validated by surface profilometry and X-ray diffraction(XRD) layer-by-layer residual stress measurements. [Result] The orthogonal experimental results showed that shot diameter had the most significant effect on both surface roughness and compressive stress layer depth of the CuCrZr alloy, followed by shot velocity, while the influence of coverage was negligible. The preferred process parameters were: shot velocity 10 m/s, impact angle 60°, and shot diameter 0.4 mm. Validation experiments under these conditions gave a measured Ra of 2.03 μm, a peak residual compressive stress of-389.1 MPa, and a compressive stress layer depth of 250 μm. The relative errors between simulation and experimental values were all below 7%. Microstructural observation revealed a gradient deformation layer from the surface inward and a high-density dislocation structure, with no over-peening damage. [Conclusion] The optimization framework proposed in this study effectively resolves the trade-off between surface roughening caused by high-intensity shot peening and the demand for deep strengthening, providing a basis for the design of shot peening processes.
Cyanide-free cadmium electroplating with low hydrogen embrittlement and high corrosion resistance based on an amino-carboxylate complex system
Chen Chen;Jihua Cheng;Hai Ji;Yilin Yao;Qi Zhang;Zhongwei Zhan;AVIC Jincheng Nanjing Engineering Institute of Aircraft System;[Objective] To address the challenge that existing cadmium(Cd) coating preparation processes cannot simultaneously satisfy the requirements of low hydrogen embrittlement, high corrosion resistance, and low maintenance demand, a new additive CFG-D was introduced into an amino-carboxylate complex cyanide-free cadmium electroplating bath to develop a novel process with both low hydrogen embrittlement and superior corrosion resistance. [Method] The effects of CFG-D volume fraction(0-16 mL/L) on coating appearance, thickness, and microstructure were investigated. With the CFG-D volume fraction fixed at 12 mL/L, the corrosion resistance of Cd coatings deposited on different substrates(i.e. brass, 30 CrMnSiA, 45 steel, 17-4 PH, and 65 Mn) was evaluated by neutral salt spray(NSS) and acidic salt spray(ASS) tests. The hydrogen embrittlement susceptibility of the process was assessed by sustained tensile loading(using 30 CrMnSiA, 30 CrMnSiNi2A, and 4340 specimens as substrate) and a hydrogen analyzer method. The influence of the electroplating process on the fatigue performance of 4340 steel substrate was examined via axial tension fatigue tests. [Result] The additive CFG-D significantly improved coating appearance, promoted deposition, and induced dense grain stacking. At 12 m L/L CFG-D, the Cd coating was compact and nearly white. After being subjected to 1 000 h of NSS test and 10 cycles of ASS test, the Cd coatings on various substrates exhibited no corrosion, with corrosion resistance far surpassing the standard specifications. Hydrogen embrittlement test results indicated that the process falls into the low-hydrogen-embrittlement category. Moreover, the cyanide-free cadmium electroplating process had no negative effect on the fatigue performance of the substrate. [Conclusion] The given cyanide-free cadmium electroplating process successfully combines excellent corrosion resistance with low hydrogen embrittlement and does not adversely affect substrate fatigue, showing great application potential in the aerospace field.
Effect of heat treatment on properties of wear-resistant and heat-conductive Ni–Co alloy coating on pure copper surface
Chao Zhang;Ming Zhang;[Objective] To address the issue of easy wear and failure of metallurgical copper components, a Ni–Co alloy coating was electroplated on the copper surface and subjected to heat treatment at 900 ℃. The high-temperature wear resistance and thermal conductivity of the coating was studied. [Method] The microstructure and phase composition of Ni–Co alloy coating were analyzed using scanning electron microscopy(SEM) and X-ray diffraction(XRD). The microhardness, wear resistance, and thermal conductivity of the coating was measured using a microhardness tester, a high-temperature friction and wear tester, and a laser flash apparatus, respectively. [Result] The as-plated Ni–Co alloy coating was smooth and mainly composed of Ni Co solid solution, with a microhardness 6.4 times that of the copper substrate. After heat treatment, a “fish-scale” oxide layer formed on the coating surface, with the main phases being 3 CoO·NiO and a small amount of NiCo_2O4, and the microhardness increased by 6.8% compared to that before heat treatment. This oxide layer provided protective and lubricating effects, improving the wear resistance of the coating to 4.5 times that before heat treatment, with the wear mechanism being oxidative wear. In addition, due to the small thickness of the coating and oxide layer, the overall thermal conductivity of the coated specimen was approximately 93.5% that of pure copper. [Conclusion] After appropriate heat treatment, the Ni–Co alloy coating on copper exhibits both high-temperature wear resistance and thermal conductivity. The findings of this study can provide a reference for the surface strengthening of metallurgical copper components.
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