Electroless Copper Plating Process By Applying Alternating One-Side Air Stirring Method for High-Aspect-Ratio through-Holes

Electroless (ELS) copper plating process has been commonly used for printed circuit board (PCB) metallization. The traditional ELS copper plating process uses tin/palladium colloid or complexed palladium ion as catalysts for ELS copper deposition. But the price of palladium catalyst is much higher than that of gold. Herein, we use complexed copper(II) ion to replace the palladium catalyst in order to greatly reduce the process cost but maintain the performance and the reliability of the complexed copper(II) ion as good as palladium. The synthesis process of the complexed copper ion is simple and its cost, which compared with palladium, is cheap. Especially, they have no oxidation issue because they are not metallic copper nanoparticles but copper(II) ions. Before ELS copper plating, the grafted copper(II) ion that is chemically adsorbed onto the substrate surface is reduced to copper atom, so they can catalyze ELS copper deposition. In this work, we optimize the experimental parameters such as operating temperature, reaction time, copper ion concentration and the pH of the plating solution. After ELS plating process, the backlight test of through holes (THs) of a PCB and the morphology of the ELS copper deposited onto the sidewalls of the THs are evaluated by optical microscope (OM) and scanning electron microscope (SEM), respectively. The thermal reliability of the ELS copper deposition catalyzed by the grafted copper catalyst was examined after copper electroplating using thermal shock in a tin bath at 288℃ for ten seconds and repeated it for 5 times. Results show that it can pass the thermal shock test. Therefore, the application of complexed copper(II) ion as the catalyst of ELS copper plating is expected to replace the expensive palladium for PCB fabrication.

Couette and Poiseuille flows in a low viscosity asthenosphere: Effects of internal heating rate, Rayleigh number, and plate representation

Modeling and simulation for a drop-impact analysis of multi-layered printed circuit boards

The work is devoted to the study of the effect of various compounds on the stability of electroless copper plating solution containing Trilon B. as a chelating agent. The stability of electroless copper plating solutions was estimated by the accelerated method as the time before the start of intensive decomposition of the solution after the introduction of 0.15 ml of colloidal palladium activator solution heated to 75 °C in 250 ml. As stabilizers, both known, currently used, and newly selected compounds were investigated. Sulfur- and/or nitrogen-containing organic and inorganic compounds such as: sodium diethyldithiocarbamate, 2,2’–dipyridyl, thiosemicarbazide, potassium hexacyanoferrate (III), potassium hexacyanoferrate (II), thiourea, thioglycolic acid, dimethylglyoxime, potassium rhodanide in concentrations in the range of 1 - 50 μmol/l were among the first studied. It is shown that when the stabilizers are contained in the solution at the optimal concentrations set (for each compound), solutions containing sodium diethyldithiocarbamate, thioglycolic acid, thiosemicarbazide, thiourea (in descending order of stabilizing action), i.e. compounds containing a sulfur-carbon bond, have the greatest stability. With this in mind, other sulfur-containing compounds, including heterocyclic ones, were selected and studied as stabilizers: α-lipoic acid, thiamine chloride, methyl orange, nitroso-p-salt, methylene blue and SPADNS (sodium salt of 2-(psulfophenylazo)-1,8- dihydroxynaphthalene-3,6- disulfonic acids). In addition, nitrogen-containing compounds that were not previously used in electroless copper plating solutions as stabilizers were also studied: nicotine, pyridoxine, Janus Green B (8-(4-dimethylaminophenyl) diazenyl-N, N-diethyl-10-phenylphenazine-10-ium-2-amine chloride), nigrosine, however. Solutions of electroless copper plating in the presence of these compounds did not show high stability. It has been established that the most effective, comparable in effect to the stabilizers currently used, are α-lipoic acid and thiamine chloride. The advantages of the latter are their availability and low toxicity. For citation: Solopchuk M.S., Grigoryan N.S., Asnis N.A., Vagramyan T.A., Shmelkova P.O., Bardina O.I. Stabilizers of solutions of chemical copper plating. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2023. V. 66. N 3. P. 100-107. DOI: 10.6060/ivkkt.20236603.6708.

The micro-hole is a key structure in multilayer printed circuit board (PCB), as it enables the effective transmission of electrical signals. At present, the most common way to machine PCB micro-holes is mechanical drilling using micro-bit. However, in the mechanical drilling of micro-holes, these holes are prone to burring at the hole mouth due to the micro-bit failing to cleanly cut through the first layer of copper foil on the PCB. Hole mouth burr can seriously affect the performance of the PCB, resulting in potential short circuiting or even ruining the PCB. To solve the above problems, this paper proposed to machine the first layer of copper foil on the PCB via micro electro-discharge machining (micro-EDM) to eliminate hole mouth burr. Compared with the mechanical drilling, micro-EDM is a form of non-contact machining, and the high temperature generated from the electric spark discharge can erode the first layer of copper foil, thus fully eliminating hole mouth burr. This paper performed a detailed study of the influence of spindle speed, machining voltage, pulse width, and pulse interval on hole mouth quality. After that, the technological parameters for eliminating hole mouth burr were obtained. Finally, under the effects of 20,000 rpm spindle speed, 26 V machining voltage, 4 μs pulse width, and 8 μs pulse interval, a micro-bit with a diameter of 200 μm was used to perform micro-EDM of the first layer of copper foil. From the machining results, it can be known that the PCB micro-hole was possessed of overall good quality, with good hole wall surface quality and almost no visible hole mouth burr.

The advent of High Density Printed Circuit Board (HD PCB) into electronic assemblies has enabled the evolution of mobile computing devices like smartphones and tablets. System level failure analysis to understand quality and reliability issues of such products is challenging. The presence of blind and buried vias stacked in a multi-layer Printed Circuit Board (PCB) coupled with double sided assemblies without test or probe points for electrical continuity access adds to the complexity. This paper presents one such case study where a detailed failure analysis approach was adopted to identify the root cause of failures. Coupling software and complimentary electrical techniques the problem was isolated to the PCB part of the system assembly. Deep dive material analysis of the fault isolated signals revealed cracks in inner layers of the PCB. The study also highlighted the fact that marginal PCB manufacturing issues could worsen during the thermal exposures associated with motherboard assembly and product usage.

Edge plating and via stitching connecting ground planes are two common edge treatments to suppress electromagnetic interference (EMI) from multilayer printed circuit boards (PCB). One critical parameter for stitching via is the spacing between vias. At higher frequencies, it is desirable to plate the edges of PCB, and a gap is required in the plating to accommodate the break-off tabs. In this paper, the shielding performance of these two scenarios are studied in both simulation and measurement. By sweeping the parameters of via pitch size and the length of each plated edge, the near-field shielding effectiveness (SE) of these different cases are compared. In general, the edge plating cases have much better shielding performance than the stitching via ones. Since edge plating implements the shielding on PCB walls, it leaves no interference with signals and moreover saves space for dropping GND stitching vias, with a trade-off of 5% more cost. Design guidelines for PCB edge treatments are provided in the end of the paper.

Recently, electric circuits may be become small, and also high-density electrical technologies have advanced. In order to place many elements on the small printed circuit board (PCB), a high-density multi-layered PCB may be used. Many vias are used in such multi-layered PCB to connect lines on each layer. If many vias are placed in narrow area, they make ground slots. If a ground slot exists near a transmission line, the distortion of the signal may be occurred. Then, existence of slots is issue for high-speed circuit designs. In this paper, we analyzed the transmission characteristic of a microstrip line above a ground slot on a PCB using multiconductor transmission-line (MTL) method. First, we measured it for various slot width. And also, we analyzed it using FDTD method. Comparing the results of measurement value and analysis value, a validity of the model of the FDTD method was confirmed. Next, we derived the characteristic impedance of the microstrip line using spectral domain approach (SDA). We calculated the transmission characteristics of the microstrip line above the slot by applying MTL method. And, the analysis values of MTL and FDTD are almost same in the case of small slot up to high frequency.

The copper-coated polyester fabric can be used to prepare electromagnetic shielding materials. At present, electroless copper plating mainly using formaldehyde as the reducing agent. But the stability of the bath is poor and it is also volatile and toxic. Using hypophosphite as reducing agent has more advantages for its stability and the plating process does not release any toxic gases. In this paper, The copper-coated polyester fabric was prepared by electroless plating with the sodium hypophosphite as reducing agent. The roughening condition before plating and the deposition process were optimized through orthogonal test. The surface resistances of conductive polyester fabrics, the deposition rate and the coating adhesion were investigated respectively. The optimum roughening conditions obtained are as following: sodium hydroxide concentration of 250g/L; temperature 70 D; time 15min, and the lightweight rate of the plating layer is 0.43% under the experimental conditions. The optimum conditions of electroless copper plating using sodium hypophosphite as reducing agent are: copper sulfate 8g/L; nickel sulfate 1.0g/L; sodium hypophosphite 35g/L; citric acid 20g/L; boric acid 30g/L; pH 9.0; temperature 75D. With these conditions, the deposition rate reaches 1.274g/(m2·min) and the uniform and compact copper layer with excellent electro-conductivity was obtained.

A compact common-mode suppression filter is proposed by employing the modified ground structure (MGS) for high speed digital interconnects using differential signals on the multi-layered printed circuit board (PCB). It consists of two folded U-shaped slot resonators and arranged via-holes. It has compact size of 0.073λ <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</inf> × 0.225λ <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</inf> when the center frequency is 5.2 GHz. A test board is fabricated on four-layered PCB through an optimizing process for verifying effects of the proposed MSG structure. The proposed MGS can suppress the common-mode noise over 10 dB from 4.34 to 6.07 GHz in the frequency domain and over 52% of amplitude in the time domain. Furthermore, the proposed filter still keeps good signal integrity characteristics with regard to the insertion loss of differential-mode signals. It is clear that the proposed filter structure can apply to the multi-layered PCB of commercial mobile devices due to its compact size and have some advantages such as wide bandwidth, gigahertz frequency range, low cost, and PCB embedded design‥

We have analyzed the effect of via in multilayer printed circuit boards (PCBs) on signal integrity and signal delay time of high-speed digital systems. First, the techniques of the circuit modeling of via are discussed. Electrical behaviors of via in interconnects according to its circuit model are characterized through HSPICE simulation. Based on these results, we show that via can behave as being capacitive or inductive according to the characteristic impedance of signal lines, which is different from the fact that via is generally regarded as being only capacitive. The proposed electrical characteristic of via is verified by results of TDR/TDT measurement of through-hole type via in 8-layer PCBs. Second, the methodology of measurement of delay caused by via is proposed. Because it is so difficult to measure the electrical delay of signal passing through one via, we extract the delay caused by single via from measuring the delay when the signal passes through several vias. For an example, we obtained the signal delay time of 12 psec caused by a throughhole type via in 8-layer PCBs. For just two vias, the delay time is about 24 psec and it is about 8% of flight time of 5 cm signal line.

Plated though-hole (PTH) vias are extensively adopted in multilayer printed circuit boards (PCBs). Unused portions of PTH vias become open stubs, which excite the resonance mode and degrade signal integrity (SI). This work investigates how open via stubs in multilayer PCBs affect the time-domain transmission (TDT) waveform and eye diagram. Exactly how time-domain reflection affects the open via stubs on TDT waveform is also studied using the lattice diagram. Additionally, the R and RL terminations of open via stubs are developed to improve SI in previous studies. Moreover, the RC termination of open via stubs is proposed to improve the performance of SI, which is the same as that of the R termination in this work. RC termination is also characterized by its nearly zero DC power consumption. Furthermore, different terminations are compared with respect to how they improve the TDT waveforms and eye diagrams.

Possibilities of improvement in detection and characterisation accuracy concerning internal defects in multi-layered printed circuit boards (PCB) and electronic components by applying the ultrasonic immersion technique have been investigated. The experiments have been carried out on a real PCB with a mounted defective microchip. Defect-free and defective high-voltage semiconductor components have also been investigated. The investigations have been performed using the acoustic microscope produced by Ultrasonic Science Ltd and ultrasonic measurement system developed at the Ultrasound Institute of Kaunas University of Technology. The novel signal processing method based on the adaptive numerical model of ultrasonic wave propagation through a multi-layered electronic component and respective selection of signal components in time and frequency domains have been proposed. Two different signal processing techniques have been used to increase the contrast of defective regions and so improve reliability of ultrasonic inspection.

A set of commonly used food additives was evaluated for their antifungal activity against the brown rot disease of fruits caused by the fungal pathogen Monilinia fructigena, which is one of the most economically important agents, causing important damage to pome fruits, such as pears and apples. The radial mycelial growth of the fungal pathogen was assessed in PDA amended with different concentrations (0.5, 2, 2.5, and 5%) of each additive. The results underlined that most of the additives displayed a significant inhibition of mycelial growth, with the extent of inhibition varying depending on the specific additive and concentration used. Five food additives showed high inhibition rates (above 88%), of which sodium bicarbonate, sodium carbonate, copper sulphate, and sodium hydroxide were the most effective, whereas ammonium carbonate, magnesium chlorite, and citric acid were the least effective. Interestingly, the coatings containing sodium bicarbonate, copper sulphate, and ammonium bicarbonate significantly reduced the incidence of brown rot disease in apples, but other additives were not effective, such as ammonium carbonate and magnesium sulphate. The anhydrous sodium sulphate used at a concentration of 2%, was found to be one of the least effective additives, with a reduction rate of 20%. Subsequently, food additives showing good growth inhibition rates and reduction in disease severity were then tested in semi-commercial trials at temperatures of 4 °C and 22 °C. The results indicated that these additives demonstrate effectiveness in controlling M. fructigena at specific concentrations, and lower temperatures (4 °C) can improve the efficiency of the control measures. In addition, the selected food additives exhibited significant antimicrobial activity against M. fructigena, suggesting their application as a promising alternative for managing brown rot disease in apple fruits.

Gearless and compact motors rotating at speeds above 10,000 rpm are finding many applications nowadays. This study presents the multiphysics modelling and analysis of a multilayer printed circuit board (PCB) stator for high‐speed, low‐power axial flux permanent magnet motor. The possibility of circulating current in the multilayer PCB is studied. The two major effects of eddy currents at high frequencies: skin effect and proximity effect are investigated for the PCB winding. The losses in the PCB stator are estimated, and thermal analysis is performed to ensure reliable operation of the motor. MagNet 3‐D and COMSOL Multiphysics are used, respectively for the finite element analysis and optimisation of the motor; and the simulation results are presented. A prototype of the motor is fabricated and tested to validate the simulation results.