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    28 June 2022, Volume 28 Issue 6
    Special Issue on Electronic Electroplating
    Introduction of Development and Application Technology of Organic Additives for Acid Copper Electroplating
    Hao-Bin Zou, Chao-Li Tan, Wei Xiong, Dao-Lin Xi, Bin-Yun Liu
    2022, 28(6):  2104531.  doi:10.13208/j.electrochem.210453
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    Acid copper electroplating is one of the key technologies in buildup multilayer PCB (BUM-PCB) manufacture process and the most important technique to achieve electrical interconnection between any layer and high-density interconnection in a substrate. This article introduces the research focus of organic additives used in acid copper electroplating, and developing different kinds of micro-via filling copper electroplating technique applied in various scenarios, and some other technical problems from applications. First of all, according to the chronopotentiometric (CP) experiment results, the levelers with different polymeric molecular structures exhibited various responses of cupric deposition potential along with their increased concentrations, which is the critical information for studying the absorption and desorption behaviors of organic additives, and provides reasonable advices for additives formula design. Linear sweeping voltammetric (LSV) study is very helpful for studying the absorption behavior of organic additives under different potentials and quantitatively describing the degree of current change because of potential polarization that helps evaluate the stability of micro-via filling performance of particular additive formular. Secondly, with the use of gel permeation chromatography (GPC) we have widely studied polymer molecular structure in the aspect of molecular weight and polydispersity, which includes carrier and leveler. The precise information of polymeric molecular structure obtained from experiments can greatly enhance comprehension of the absorption mechanism of polymer additives. Corresponding electrochemical experiment results show that there is obvious correlation between molecular weight of carrier and its suppression effect. Examples of polymerization reaction of some levelers with novel molecular structure are presented, which aims at studying the influence of steric hindrance on electrochemical or electroplating performance by adjusting the length of carbon chain between two aminos and the number of heteroatom, like oxygen atom. Thirdly, different kinds of micro-via filling copper electroplating technique applied in various scenarios have been developed, which includes high-speed micro-via filling copper electroplating technique, ultrathin thickness controlled micro-via filling copper electroplating technique, highly uniform pattern line and micro-via filling copper electroplating technique, through hole and micro-via filling copper electroplating technique and through hole filling copper electroplating technique. Finally, technical problems from application of additives are simply introduced here. Copper plating equipment is the workplace for plating solution and its structure design and process parameters will profoundly affect the micro-via filling performance in the aspect of flow field and electric field. Large void is very easy to be formed inside micro-via under improper convection and deposition velocity. Virgin make-up solution (VMS) components also affect micro-via filling performance obviously in coordination with organic additives by changing overpotential of cupric reduction reaction. Precise determination of organic additives in aged plating solution is very challengeable because byproducts accumulated during manufacture have completely different absorption mechanisms compared to fresh plating solution.

    Research Progresses of Cobalt Interconnect and Superfilling by Electroplating in Chips
    Li-Jun Wei, Zi-Han Zhou, Yun-Wen Wu, Ming Li, Su Wang
    2022, 28(6):  2104431.  doi:10.13208/j.electrochem.210443
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    Copper interconnect using dual damascene technology has always been the main means for metallization in the back end of line process. However, with the size effect becoming more and more obvious due to feature size reduction, copper interconnect can no longer meet the demand for high circuit speed in Post-Moore era. Following copper interconnection, cobalt interconnection in chips attracts much attention as an interconnect technology by the next generation, which has been introduced in 7 nm node of integrated circuit manufacturing and below. The electron mean free path of cobalt (~10 nm) is much shorter than copper’s (39 nm), thus exhibiting the potential to further shrink the critical dimension without increasing line resistance and RC delay especially for contacts or local interconnects in the first few stack layers. Also, cobalt is considered as a suitable barrier/liner material, which means implementing cobalt interconnects needs no such layers and gives more space for conductive metal. Besides, higher melting point of cobalt makes it more favorable with good electromigration resistance compared with copper interconnects. Cobalt interconnection mainly adopts the wet electrodeposition method and the quality of the electrodeposite matters a lot to the reliability of the metal interconnects. For the reason of confidentiality and the limitation of research conditions, there are few research reports about cobalt interconnection. Based on existing patents and literature reports, this paper systematically introduces the advantages and current developments of cobalt interconnection. To better understand the behavior of the metal ions during electroplating process, this paper reviews the basic technology, bath composition and additives used in the electrolyte for cobalt electroplating from the point of view of solution chemistry and electrochemistry. For superconformal electroplating, there are several superfilling mechanisms for bottom-up electrodeposition with different emphasis, this paper gives a brief summary about three mechanisms and makes a comparison. Furthermore, this paper introduces the annealing control of cobalt deposition and the influence of impurities, since the evolution of grains and migration of impurities determine the sheet resistance. Finally, further study of cobalt interconnection technology is prospected. Cobalt interconnect is expected to be a proper alternative to extend Moore’s Law and promises to play a part in next advanced technology node. More researches about cobalt interconnection are worthwhile to be carried out in the future.

    Microstructure of Electrodeposited Copper Foil: Discussion on the Mechanism Model of Three-Dimensional Electrocrystallization
    Ren-Zhi Liu, Ping-Ling Xie, Chong Wang
    2022, 28(6):  2104481.  doi:10.13208/j.electrochem.210448
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    The manufacturing of electrolytic copper foil has attracted more and more attention with the extensive applications of printed circuit board and lithium battery. The industrial scale is still extending. Compared with the developments of electroplating equipment and electroplating process, there is limited research on the mechanism of electrodeposition. This paper summarizes the manufacturing process of electrodeposited copper foil and analyzes the differences of various electroplating parameters in different electrodeposited copper technologies, and points out the important role of electrodeposition current density in the formation of copper foil. By showing and comparing the microstructures of different electrodeposited copper foils, the influences of various factors in electrodeposition on the microstructures of copper foils and the corresponding macroscopic mechanical properties are discussed. From previous research results, it is found that the electrodeposition conditions and the composition of the plating solution have a significant impact on the microstructure and morphology of the copper foil, as well as the macroscopic mechanical properties. It is difficult to establish an effective relationship between the microstructures such as crystallite size and plane and the mechanical properties, which brings great challenge to the theoretical framework of the macro-mechanical properties of copper foils by using the microstructure of the coating as a bridge to establish electrodeposition conditions. Much effort has been tried to solve this problem by studying the mechanism of copper foil electrodeposition. The classical metal electrodeposition theory reveals that increasing the overpotential can increase the number of instantaneous nucleation and reduce the average grain size, however, it cannot explain the preferred orientation in crystallization. Watanabe found the similarity between electrodeposition and metallurgy, and believed that the microstructure of electrodeposited metal is related to the melting point of the metal, but this “microstructure control” theory still has some defects, such as the inability to explain the refining effect of additives on grains, etc. The author suggests that the relationship between the electrodeposition mechanism and the macroscopic properties of copper foil can be reshaped from the perspectives of valence bond and energy band theory. Influence of the macroscopic properties of copper foil can then be discussed.

    Development Status of Copper Electroplating Filling Technology in Through Glass Via for 3D Interconnections
    Zhi-Jing Ji, Hui-Qin Ling, Pei-Lin Wu, Rui-Yi Yu, Da-Quan Yu, Ming Li
    2022, 28(6):  2104461.  doi:10.13208/j.electrochem.210446
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    With the slow development of Moore's Law, the high density and miniaturization of microelectronic devices put forward higher requirements for advanced packaging technology. As a key technology in 2.5D/3D packaging, interposer technology has been extensively studied. According to different interposer materials, it is mainly divided into organic interposer, silicon interposer and glass interposer. Compared with the through silicon via (TSV) interconnection, the through glass via (TGV) interposer has received extensive attention in the 2.5D/3D advanced packaging field for its advantages of excellent high-frequency electrical characteristics, simple process, low cost, and adjustable coefficient of thermal expansion (CTE). However, the thermal conductivity of glass (about 1 W·m-1·K-1) is much lower than that of silicon (about 150 W·m-1·K-1), thus, the glass interposer has serious heat dissipation problems. In order to obtain a high-quality TGV interposer, not only an efficient and low-cost via preparation process, but also a defect-free filling process is required. The challenges faced by glass interposer is mainly concentrated in these two aspects. This review firstly introduces the preparation process of TGV, such as ultra-sonic drilling (USD), ultra-sonic high speed drilling (USHD), wet etching, deep reactive ion etching (DRIE), photosensitive glass, laser etching, laser induced deep etching (LIDE), etc. Then it summarizes the defect-free filling of TGV, and outlines several filling mechanisms and some current filling processes of TGV, such as bottom-up filling mechanisms, butterfly filling mechanisms and conformal filling mechanisms. Among the filling mechanisms of the above three filling methods, the filling method of bottom-up is the most studied one, and many scholars have given relevant explanations. Currently, the main ones that are commonly used are the diffusion-consumption mechanism, curvature enhanced adsorbate coverage mechanism (CEAC), convection dependent adsorption mechanism (CDA), and S-shaped negative differential resistance theory. In the process of TGV filling, the type and concentration of base bath, additives and electroplating process will affect the filling status of TGV. At present, the constant current plating mode is most commonly used in the process of TGV filling. Then the research progress of TGV electroplating additives is introduced, including the action mechanism of typical additives and the current research status of some new additives. Through glass via technology can be filled with the synergistic action of accelerators, suppressors and levelers. Finally, the practical application of TGV is briefly reviewed, for example, glass interposer is used in 3D integrated passive device (IPD), embedded glass fan-out technology (eGFO), integrated antenna packaging, micro-electro-mechanical system (MEMS), multi-chip module packaging, as well as the applications in the field of optical integration technology.

    Study on Low Voltage Electrodeposition of Diamond-like Carbon Film
    Li Wang, Min-Xian Wu, Jun Li, Yan-Li Chen, Wen-Chang Wang, Zhi-Dong Chen
    2022, 28(6):  2104441.  doi:10.13208/j.electrochem.210444
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    Diamond-like carbon (DLC) films are receiving a lot of attention from the scientific community, thanks to the promise of DLC films for applications in microelectronics and optoelectronics. Usually, electrodeposition is the preferred common technique because of low cost, large deposition area and simplicity of the setup. However, when carbon films are electrodeposited on a stainless steel, high cell voltages (≥1000 V) are required owing to the low electric conductivity of the organic solvents. This work has developed a new electrolyte system that could achieve carbon deposition on a stainless steel under a low applied cell voltage. The DLC films were electrodeposited from 230 g·L-1 formic acid and 17 g·L-1 sodium formate in 1:1 (v/v) water-dimethyl sulfoxide mixture with the applied voltages ranged from 4.0 V to 8.0 V on the stainless steel substrate. The effects of the applied voltage on film morphology have been investigated. Dimethyl sulfoxide (DMSO) can broaden the electrochemical window of the solvents, inhibit hydrogen evolution and improve current efficiency. Nevertheless, the current efficiency was still low. X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy, probe surface profiler, and four-point probe resistivity tester were employed to analyze the structure, morphology, surface chemical composition, film thickness, and electric conductivity of the DLC films. It was found that the dense and uniform hydrogenated DLC films were successfully prepared on the stainless steel substrate. The film thickness was sensitive to the cell voltage and decreased with the increase in cell voltage. The Raman spectra of these films indicated the three broad peaks. Presences of D and G peaks near 1330 cm-1 and 1570 cm-1, respectively, revealed that the as-deposited films were typical DLC films. The average grain size and sp3 carbon content of the film increased with the increase in deposition voltages. The FTIR results showed that the peaks observed at 2850 cm-1, 2920 cm-1 and 2960 cm-1 were related to the C-H symmetric and asymmetric stretching of CH2 and CH3 groups. Because of deionized water added in the solution, the infrared spectroscopic measurements supported that the DLC films were hydrogenated carbon films. The XPS results demonstrated that the two peaks for C1s at 284.5 eV and 285.2 eV with the comparatively lower intensity corresponded to C=C and C-C, respectively. The third peak at 288.5 eV may be associated with ester or carboxyl groups. The electric conductivity of the DLC film decreased with the increase in deposition voltage, falling between those of metal and semiconductor.

    Electrochemical SERS study of Benzotriazole and 3-mercapto-1-propanesulfonate in Acidic Solution on Copper Electrode
    Yin-Fei Shen, Yan-Li Chen, Sheng-Xu Wang, Ye Zhu, Wen-Chang Wang, Min-Xian Wu, Zhi-Dong Chen
    2022, 28(6):  2104451.  doi:10.13208/j.electrochem.210445
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    Since the development of acid copper plating technology, the role of additives is indispensable. In addition to the main salt copper sulfate and supporting electrolyte sulfuric acid, suppressors, accelerators, levelers and chlorine ions (Cl-) are also required to be added into the plating solution. Appropriate additive system can have a significant impact on the coating or the plating solution, which can help improve the quality of the coating and increase the brightness of the coating. Through electrochemical measurement, vibrational spectroscopy, scanning probe microscopy, molecular dynamics simulation and other methods, researches have a deeper understanding in the adsorption configuration of some additives on the copper electrode surface and the changes in the electroplating process. Surface-enhanced Raman spectroscopy (SERS) is a powerful technique that yields vibrational information with ultra-high sensitivity. Enhancements of up to 1010 have been achieved in some systems, which provides sensitivity up to single molecule level. Therefore, SERS technique is one of the main methods to study the adsorption structure and mechanism of additives. In this paper, the competitive adsorption behaviors of benzotriazole (BTAH), 3-mercapto-1-propanesulfonate (MPS) and Cl- in an acidic solution on the copper electrode were investigated by in-situ electrochemical surface-enhanced Raman spectroscopy (EC-SERS). It was found that in the positive potential range, the adsorption behavior of BTAH molecules was mainly through the formation of [Cu(BTA)]n polymer film on the copper electrode surface by the triazole ring; with the negative shift of the potential, the polymer film was gradually transformed into the BTAH molecular. The MPS was mainly adsorbed on the copper electrode by the sulfhydryl end. Cl- mainly existed in the form of Cu-Cl, and the active sites occupying the surface of the electrode had a synergistic effect with MPS. The electroplating process on the copper foil also verified the strong adsorption of BTAH, and the presence of small copper particles on the copper foil also confirmed that MPS and Cl- have a synergistic effect, which promotes the local deposition of copper. As the only technical method that can realize nano-level electronic interconnection, electronic electroplating is the main direction of future research. Related additive basic research is also indispensable. In the process of copper electroplating, the interfacial competitive adsorption of additives and their mechanism of action need more in-depth study. It is hoped that this study will play an important guiding role in the development of electroplating additives and the improvement of electroplating technology in the future.

    An Investigation on the Interface Corrosion Behaviors of Cobalt Interconnects in Chemical Mechanical Polishing Slurry
    Kai-Xuan Qin, Peng-Fei Chang, Yu-Lin Huang, Ming Li, Tao Hang
    2022, 28(6):  2104471.  doi:10.13208/j.electrochem.210447
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    Cobalt is widely regarded as the most promising interconnect material for 10 nm node and beyond. The development of a chemical mechanical planarization (CMP) slurry suitable for cobalt interconnect is a critical component for the application of cobalt interconnect. During CMP process of the interconnect layer, the achievement of high-quality surface after planarization is greatly challenged by the metal corrosion in CMP slurry. In this contribution, the corrosion behavior of cobalt in a slurry with potassium persulfate (KPS) as an oxidizer, glycine as a complexing agent, and benzotriazole (BTA) as an inhibitor was investigated. Static erosion rates (SER) of cobalt in the slurry at various pH values with and without the inhibitor were examined. The result showed that SER of cobalt increased slightly with increasing pH, whereas BTA clearly inhibited the corrosion of cobalt in the slurry. Scanning electronic Microscopic analysis revealed that BTA could improve the morphology of cobalt surface which was deteriorated due to corrosion in planarization slurry of pH = 9. Electrochemical corrosion measurements were conducted to further investigate the effects of BTA. The potentiodynamic polarization curves indicated that as the BTA concentration increased, the corrosion potential increased, while the corrosion current density decreased. The corrosion of cobalt was effectively inhibited by adding 0.4wt% BTA in the slurry, with an inhibition efficiency of 99.02%. The electrochemical impedance data showed that the Nyquist plots of cobalt contained two rings in the slurry without BTA. The high-frequency ring was formed by cobalt oxide, and the low-frequency ring was formed by double layers. While in the BTA-containing slurry, the Nyquist plots contained only one ring at a high frequency formed by double layers, with a significantly larger diameter than that in the slurry without BTA. It can be concluded that BTA is capable of preventing cobalt from forming an oxide layer, and thereby, reducing electrochemical corrosion. Finally, the X-ray photoelectron spectroscopy was implemented to quantitatively analyze the surface's valence composition of cobalt in various solutions. The results showed that when the KPS was added as an oxidizer, a double-layer of passivation was formed on the surface of cobalt, with a Co2+ rich inner layer and Co3+ rich outer layer. The addition of glycine resulted in the dissolution of the outer layer oxide, reducing the content of Co3+ in the passivation layer. The addition of BTA could suppress the oxidation of Co by KPS, and lowered the Co3+ content on the cobalt surface. It can be demonstrated that the CMP slurry developed in this work effectively inhibited the corrosion of cobalt in an acid solution, which may solve the problem of galvanic corrosion between the cobalt interconnect and barrier layer in CMP process.

    Effect of Sodium Alcohol Thiyl Propane Sulfonate on Electrolysis of High Performance Copper Foil for Lithium Ion Batteries
    Sen Yang, Wen-Chang Wang, Ran Zhang, Shui-Ping Qin, Min-Xian Wu, Naotoshi Mitsuzaki, Zhi-Dong Chen
    2022, 28(6):  2104501.  doi:10.13208/j.electrochem.210450
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    Electrolytic copper foils have been widely used in printed circuit boards and lithium-ion batteries due to their simple production process and high economic value. In the process of electrolysis foil making, additives can greatly improve the performance of electrolytic copper foils. In this work, the copper foils were prepared in a self-designed plate electrodeposition device of which the operating principles were in accordance with those of actual industrial production. A series of the Virgin Make-up Solution (VMS: 312.5 g·L-1 CuSO4·5H2O, 100 g·L-1 H2SO4, 50 mg·L-1 Cl-) containing different additives was investigated to study the electrochemical behaviors of the electrolytes and their effects on the surface morphology, structure, and properties of the electrolytic copper foils. The results showed that HP had a strong depolarization effect in the combined additive system, which can accelerate the growth of copper nuclei, and had the optimal growth orientation of the enhanced copper (200) crystal surface. HVP had adsorption effect on the cathode surface and formed a barrier layer on the cathode active site, which inhibits the electrical deposition of copper. DPS had a strong depolarization effect at low concentration, with the high concentration, a polarization effect reduced the grain size. When HP and DPS coexisted, there was a competitive adsorption, showing certain polarization effect. The synergistic effect of HP with DPS and HVP could further reduce the grain size of electrolytic copper foils, reduce the surface roughness, and improve the mechanical properties and corrosion resistance of the coatings. The obtained electrolytic copper foils were uniformly dense, with an average grain size of 29.2 nm, an average roughness of 1.12 μm. and an average tensile strength of 399.5 MPa. The electrolytic copper foils obtained exhibited the superior corrosion resistance, became the ideal materials for lithium-ion battery anode fluid collection, and had high commercial value. Subsequently, the effects of DPS and HVP in the combined additive system on the surface morphology and physical properties of copper foil will be investigated to further explore the action mechanism of the combined additive and improve the electrodeposition model.

    Influences of Suppressing Additive Malachite Green on Superconformal Cobalt filling and Nucleation
    Xiao-Chuan Ma, Ya-Qiang Li, Pei-Xia Yang, Jin-Qiu Zhang, Mao-Zhong An
    2022, 28(6):  2104521.  doi:10.13208/j.electrochem.210452
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    As the semiconductor integrated circuits evolve into 7 nm technology and beyond, the resistance of the Cu filling at back-end-of-line interconnects no longer linearly scales with dimension. The metal Co with lower mean free path can be used to replace Cu for reducing the line resistance caused by the scattering on the outer surface and grain boundary in the smaller and smaller size. In this study, CoSO4 was used as the main salt, boric acid as a buffer and malachite green (MG) as an inhibitor for further research. According to the electrochemical cyclic voltammetric (CV) curves by using a rotating disk electrode, the reductive overpotential of the metal Co shifted negatively and the reduction process was gradually suppressed with the increasing concentration of the additive MG. Besides, the deposition current density decreased and the current efficiency of the reduction process declined after adding MG from the electrochemical quartz crystal microbalances (EQCM) test. This is because of the MG adsorption on the surface and complexation with the metal Co ion in the bath. Hence, MG has a significant inhibition effect in the deposition process, which reduces the deposition efficiency. At -1.27 V, the current density of the total reduction process gradually decreased with the applying higher rotation rate and returned to the initial value within a few minutes after suspending. The current density was heavily influenced by the convection process. At last, the bottom-up superfilling of blind via from an aqueous solution containing 0.4 mol·L-1 CoSO4, 0.5 mol·L-1 H3BO3, a small amount of Cl-, 20 mg·L-1 MPS and 10 mg·L-1 MG at -1.27 V with the pH 4. From the chronoamperometric curves, the appearance of two peaks was mainly attributed to the hydrogen evolution process and the nucleation process of Co2+ reduction, and the nucleation process was three-dimensional instantaneous nucleation process. In order to further studying the construction of the MG, and the bonding between additive MG and cobalt ions, the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of MG are obtained by quantum chemical calculation, indicating the active site distributed on the conjugate structure of aniline and amido cyclohexadiene for adsorbing on the cathode surface. The electrostatic potential (ESP) diagram is obtained by molecular dynamics simulation, and the results point out that the potential distributes at 35 ~ 78 kcal·mol-1, meaning the easily adsorption of additive MG on the cathode surface. The complex of CoMG was formed from delocalized pi-bond of phenyl of MG and free Co ion in the bath.

    Optimization of Pulse Plating Additives and Plating Parameters for High Aspect Ratio Through Holes
    Kai Yang, Ji-Da Chen, Shi-Jin Chen, Wei-Lian Xu, Mao-Gui Guo, Jin-Chao Liao, Zeng-Kun Wu
    2022, 28(6):  2104491.  doi:10.13208/j.electrochem.210449
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    As an important component in electronic products, printed circuit board (PCB) plays a supporting and interconnecting role for the electronic components in it. With the development of communication technology, electronic products are developing in the direction of “thin, light and small”, and high density interconnection (HDI) comes into being. Due to the high-density interconnection characteristics of HDI boards, the thickness of the board is increasing. At the same time, in order to reserve space for the laying of fine lines on the subsequent board surface, the diameter of the through holes on the board is also decreasing, so the depth-diameter ratio of the through holes is increasing. In order to ensure the electrical interconnection between the middle layers of the HDI board, the through-hole plating technology has become the key. In the process of through-hole electroplating, due to the relatively small diameter of the through-hole, the current density distribution inside and outside the hole is uneven, and the dispersion ability of the plating solution is poor, resulting in uneven copper plating layer and thick surface copper layer, which is not conducive to subsequent fine circuits laying. An effective way to overcome this drawback is to add electroplating additives to the bath, and to use bidirectional pulse electroplating technology. Therefore, 2, 2'-dithiodipyridine (DTDP) with low toxicity and low cost was used as an additive in the plating solution, and its application in pulse plating of high aspect ratio through holes was studied. The additive concentration and pulse plating parameters were optimized. It was concluded that DTDP could be applied to pulse plating of high aspect ratio through holes. And through orthogonal optimization experiments, the optimal concentration of additives suitable for the high aspect ratio (14.5:1) through-hole electroplating was obtained. Finally, the throwing power of the plating solution was measured at about 86%, and the average thickness of surface copper was about 38 μm. It is not conducive to the operation of the subsequent process, and the through hole is in the shape of a “dog bone”; then the single factor analysis of the pulse parameters was carried out, and finally, the optimal single-stage pulse plating parameters were obtained. At this time, the throwing power of the plating solution was about 75%, and the average thickness of the surface copper was about 27.6 μm, which is convenient for the subsequent processing and solves the above-mentioned “dog bone” phenomenon. SEM test and tin immersion thermal stress test were performed on the experimental boards of the two experiments separately. The SEM images found that the coating particles of the two experimental boards were fine and uniform, and relatively flat; the tin immersion thermal stress test results did not find any cracks. These phenomena are all in line with industry requirements, so it provides a certain basis for the research of high aspect ratio through-hole pulse electroplating. Further experiments are needed in the follow-up to make the plating solution higher in throwing power and at the same time reduce the surface copper thickness.

    Keywords: plating additive; pulse electroplating; high aspect ratio through hole; orthogonal design tests; throwing power

    Study on Weak Alkaline Cyanide-Free Silver Plating Process for Etching Lead Frame
    Jian-Wei Zhao, Hai-Feng Zhu, Xiao-Hui Yu, Gui-Yun Yuan, Zhi Sun
    2022, 28(6):  2104551.  doi:10.13208/j.electrochem.210455
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    As a new development direction of integrated circuit chip carrier, etched lead frame has been gradually applied in microelectronics industry in recent years. Since the preparation of the etched lead frame requires the use of multiple layers of non-alkali-resistant photoresist films with specific patterns, and the traditional cyanide silver plating is unable to meet this requirement, making that the development of weakly alkaline cyanide free silver plating process has great significance. In this paper, a weak alkaline silver plating process based on 5,5-dimethylhydantoin (DMH) cyanide-free silver plating system was studied. The electrodeposition behavior of the system and the nucleation mechanism of silver crystallization were investigated by cyclic voltammetry (CV) and chronoamperometry (CA); By changing a series of conditions, the effective working range of the process was determined, and the properties of the coating and the bath were characterized under the optimized process conditions. The results showed that the crystals of the silver plating layer were fine, and the average particle size was 16.7 ± 3.6 nm. From the XRD test results, the effective grain size was 43.6 ± 3 nm, and the (200) crystal surface was the preferred orientation crystal plane. Coating performance tests included whiteness, brightness and hardness, which were 7.2%, 117 Gs and 74 ± 4 Hv, respectively. In addition, the performance test of the bath showed that the current efficiency of the bath reached 99.2% with the temperature was 30 oC and the current density was 0.6 ASD, and the throwing power was about 83% at 30 oC. The results of the above tests and the actual etched lead frame samples have demonstrated that this process is of great value in practical application.

    Keywords: cyanide-free silver plating; lead frame; nucleation mechanism; bath properties; coating properties

    Application of Numerical Simulation Method in Periodic Pulse Reverse Electroplating Through Hole
    Yuan-Hang Zhang, Mao-Zhong An, Pei-Xia Yang, Jin-Qiu Zhang
    2022, 28(6):  2104511.  doi:10.13208/j.electrochem.210451
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    The upgrade of the fifth generation (5G) communication technology increases the number of communication backplane layers and the aspect ratio of through holes on the board, making it more difficult to use traditional direct current deposition for interconnection. Direct current electrodeposition is more prone to uneven coating in the hole, resulting in poor contact between the coating and components, and open circuit. This has a serious impact on the stability of printed circuit board. The periodic pulse reverse plating method can significantly improve the uniformity of high aspect ratio through-hole plating and improve the production quality of through-hole plating through the dissolution and electromigration of the coating in the reverse pulse process. Compared with direct current method, periodic reverse pulse has multiple controllable parameters. Changing these parameters will have different effects on the quality of through-hole electroplating. However, to study all parameters one by one, the number of experiments is huge and time-consuming. Numerical simulation is a newly developing research method, which intuitively studies the influence of a variety of physical fields. And it can be completed only by calculation, which avoids the loss of a large number of experiments. In this work, the influences of periodic pulse reverse parameters in through hole electroplating were studied by numerical simulation. Based on the orthogonal experiments, the influence order and rule of the periodic pulse reverse parameters on throwing power (TP) of through hole were analyzed. Among them, the reverse pulse duty ratio has a great influence on the TP of through-hole. The optimal combination is screened as: Forward peak current density 1 A·dm-2, ratio of positive and reverse peak current density 1:4, reverse peak width 1ms, ratio of positive and reverse peak width 30:1, forward duty cycle 1, reverse duty cycle 1, number of forward peak 2, number of reverse peak 3. Using the optimized parameter combination in the simulation results, TP is greatly improved as compared with direct current electrodeposition. The parameters of periodic pulse reverse electroplating optimized by numerical simulation method can effectively improve the uniform plating capacity of through holes, and can be applied to actual electrodeposition of through holes. Using the optimized parameters, the TP of through hole with the aspect ratio of 1:10 is improved efficiently. The experimental results provide theoretical support and new ideas for the optimization of periodic pulse reverse electroplating by numerical simulation method.

    Study on the Effect of Additives in the Electrodeposition of Sn-Ag-Cu Ternary Alloy Solder
    Hua Miao, Ming-Rui Li, Wen-Zhong Zou, Guo-Yun Zou, Shou-Xu Wang, Xiao-Jing Ye, Kai Zhu
    2022, 28(6):  2104411.  doi:10.13208/j.electrochem.210441
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    Sn-Ag-Cu ternary alloy is the most ideal substitute for Sn-Pb alloy at present, and can be prepared by electrodeposition with high production efficiency, simple equipment, easy maintenance and excellent coating performance. The coordination system of the electroplating solution was investigated through the Hull cell experiment. The type of brighteners used in the plating solution and the ratio of the two brighteners were determined through the microscopic morphologic characterization, electrochemical corrosion test and cathodic polarization curve test. In addition, the dispersant and stabilizer were studied by observing the microscopic morphology and measuring the concentration change of Sn2+ ions in the plating solution, respectively. The results showed that when ammonium citrate and thiourea were used as the complexing agents, benzylidene acetone and polyethylene glycol as the brighteners, poly propylene glycol as the dispersing agent, and ascorbic acid as the stabilizer, the wide current density range of the plating solution and excellent stability were obtained. Furthermore, the resulted coating was dense and smooth with high corrosion resistance.