Electroless Copper Research Articles

Electro-discharge machining using copper-coated additively-manufactured AlSi10Mg electrodes

Customized fabrication of electrodes for electro-discharge machining (EDM) is considered as a useful emerging application of metal additive manufacturing technologies for building complex shaped tools in a short period of time. This approach of producing electrodes not only effectively addresses the design flexibility and complexity issues of the tools but also enables the use of various materials so as to ingrain the desired properties in them. The current study explores the production of laser powder bed fusion (LPBF) AlSi10Mg tools for machining of titanium alloy. Moreover, it explicitly assesses the machining performance of additively manufactured electrodes when the tools are subjected to a thin layer of copper coating. Three types of acidic baths are used for electroless coating of tools. The machining performance of the tools in terms of material removal rate, tool wear rate, surface crack density, surface roughness, white layer thickness, and microhardness of the white layer is compared for different electroless copper coating processes. It is observed that the coated tools significantly enhance material removal rate; however, uncoated LPBF tools exhibit superior surface morphology and surface roughness.

Electroless Copper Patterning on TiO2-Functionalized Mica for Flexible Electronics

The formation of conductive copper patterns on mica holds promise for developing cost-effective flexible electronics and sensing devices, though it is challenging due to the low adhesion of mica’s atomically flat surface. Herein, we present a wet-chemical method for copper patterning on flexible mica substrates via electroless copper deposition (Cu-ELD). The process involves pre-functionalizing 50 µm thick muscovite mica with a titanium dioxide (TiO2) layer, via a sol–gel dip-coating method with a titanium acetylacetonate-based sol. Photolithography is employed to selectively activate the TiO2-coated mica substrates for Cu-ELD, utilizing in situ photodeposited silver (Ag) nanoclusters as a catalyst. Copper is subsequently plated using a formaldehyde-based Cu-ELD bath, with the duration of deposition primarily determining the thickness and electrical properties of the copper layer. Conductive Cu layers with thicknesses in the 70–130 nm range were formed within 1–2 min of deposition, exhibiting an inverse relationship between plating time and sheet resistance, which ranged from 600 to 300 mΩ/sq. The electrochemical thickening of these layers to 1 μm further reduced the sheet resistance to 27 mΩ/sq. Finally, the potential of Cu-ELD patterning on TiO2-functionalized mica for creating functional sensing devices was demonstrated by fabricating a functional resistance temperature detector (RTD) on the titania surface.

Maillard Type Reaction for Electroless Copper Plating onto Ceramic Nanoparticles

A high demand for oxide dispersion strengthened (ODS) materials arose in wide fields of application. The electroless plating method has been presented as an elegant way to overcome different surface energies and obtain metal‐plated ceramics. However, copper electroless plating is still performed under harsh conditions with toxic and expensive reagents, including noble metals and harsh reducing agents like formaldehyde and hydrazine. To create a pure copper metal matrix in an environmentally friendly and efficient way a previously reported method is advanced in a way that naturally occurring amino acids are utilized. A screening of several amino acids leads to an improvement in phase purity and atomic efficiency. Therefore, a Maillard type reaction with lysine as amino compound is reported to show the best results in the particle coating for all ceramic nanoparticles evaluated. The metal plating results in uniform round micro particles showing a homogeneous coating. In order to obtain copper matrix composites, the prepared particles are successfully implemented in a PBF‐LB/M process after mixing with a highly conductive copper alloy. The resulting products were investigated by transmission electron microscopy, scanning electron microscopy, powder X‐ray diffraction, and optical density measurements.

Fabrication of copper coated aminated graphene oxide based textiles for electromagnetic interference shielding applications

The issue of electromagnetic radiation pollution and interference has been triggered due to rapid progress in electronic and telecommunication technologies. Serious health issues such as cancer, headaches, and improper development of the brain take place due to long-term exposure to dangerous radiation. Therefore, materials are required to provide efficient protection against electromagnetic interference (EMI). This study aimed to protect humans from dangerous radiations of different frequency by developing EMI shielding textiles. For this, a bilayer textile structure was fabricated by the electroless plating of copper on aminated GO cotton fabric. GO was applied on cotton fabric by simple dip and dry method and then amine groups were generated by solvothermal reaction. After that, copper electroless plating was done on aminated GO fabric. According to the results, remarkable EMI SE in different frequency bands was observed in developed fabrics and the maximum EMI SE was about 34 dB at 13.6 GHz. In all the frequency bands ranging between (100 MHz and 13.6 GHz), more than 99.9 % of EMI shielding observed in the developed fabric. Moreover, the developed fabric exhibited high thermal stability and surface resistance of about ~0.18 Ω/cm. The results of this study clearly showed that the efficacy of EMI shielding developed fabric is a remarkable strategy for controlling electromagnetic radiation pollution exposing humans.

Fabrication of conductive polyimide/metal composite fibers for high temperature EMI shielding

Surface metallization of high-performance polymer fibers via electroless plating represents a significant advancement in producing lightweight, flexible and durable electromagnetic interference (EMI) shielding fabrics. The conventional process for metallization of polyimide (PI) fibers faces challenges, including complex procedures and insufficient interfacial adhesion between the metal layer and fiber matrix. Herein, carboxylate-containing PI (PIC) fibers were developed to mitigate the mechanical degradation caused by traditional alkaline etching. Conductive composite fibers (PIC/Cu) were successfully produced through a continuous electroless copper plating process. The robust PIC/Cu interfacial bonding achieved based on nanoscale mechanical interlocking through Ni nanoparticles imparts excellent flexibility and durability, evidenced by only a 4 % increase in electrical resistance after 5000 bending cycles. The dense, uniform copper layer provides high conductivity (1.3 × 104 S/cm), resulting in an optimal EMI shielding efficiency of 63.4 dB for the corresponding fabric. Moreover, PIC/Cu-Ni fibers prepared by further electroless plating of nickel layer on the surface of PIC/Cu fibers demonstrate remarkable electrical stability across temperatures ranging from 50 to 350°C, with only a 1.2 % reduction in conductivity after exposure to 350°C for 1 h. These findings advance the development of high-performance conductive PI fibers for applications in aerospace vehicles and high-temperature environments.

Optimising Electroless Copper Plating Parameters on Insulative Substrate for Enhanced Efficiency and Quality

Optimising Electroless Copper Plating Parameters on Insulative Substrate for Enhanced Efficiency and Quality

Effect of Ni addition and bath temperature on electroless Cu microstructure in microvia preparation for HDI substrate

In this work, we investigated the microstructure evolution of electroless copper (Cu) deposition under different nickel (Ni) additions and reaction temperatures. It was found that the grain structure of electroless Cu is significantly influenced by the addition of Ni due to its inhibitory effect on Cu self-diffusion, while bath temperature had no impact on the electroless Cu grain growth. Additionally. nanovoids were observed in the electroless layer, primarily at the interface between the Cu trace and electroless layer, which is caused by the attachment of hydrogen bubbles during the electroless Cu reaction. These nanovoids do not affect the epitaxial grain growth in the microvia structure as observed through transmission electron microscopy (TEM). The nanovoids in the electroless Cu under different deposition conditions were also investigated through TEM images with the assistance of ImageJ. We found that the dimension of nanovoids initially increases with the reaction rate, as a result of the higher deposition rate introducing large hydrogen bubbles. However, as the reaction rate further increases, the size of the nanovoids stabilizes because larger hydrogen bubbles more easily escape the surface. This work may offer insights into potential approaches to enhance the quality of electroless Cu deposition for microvia preparation.

The design of nano-porous photocatalytic intermediate layer to fabricate the copper layer on AlN ceramic with high bonding strength through the interlocking microstructure

AlN ceramic is the potential substrate for high-performance printed circuit board with the rapid development of electronic industry due to the superior thermal and electrical property, while its metallization still faces the issues of thermal stress and weak interface bonding with existing technology. Herein, a convenient design is proposed to achieve the Cu deposition on the surface of AlN substrate, the TiO2 containing photocatalytic intermediate layer is prefabricated on AlN substrate with silica and titania mixed sol, and induces the autocatalytic deposition of electroless copper plating under ultraviolet irradiation. Compared with Cu deposition with Pd activation treatment, the bonding strength between Cu layer and AlN substrate is significantly enhanced with the intermediate layer, this is ascribed to the formed nano-porous microstructure of the sintered intermediate layer facilitating the penetration of plating bath, and the mechanical anchoring effect derived from the interlocking microstructure between Cu layer and intermediate layer contributes to the improved bonding strength. This new method realizes the metallization of AlN ceramic with high interfacial bonding strength and low cost compared with the traditional joining technology, and provides a potential reference for the surface metallization of inert material.

Printable and filament-drawable PDMS based adhesive assisted manufacturing of highly conductive copper micro-patterns

Manufacturing of copper micro-patterns is crucial in electronics for its utilization as high conductivity transparent conductive films (TCFs) and circuits. In the preparation process of current TCFs, a plethora of materials have emerged that can replace traditional indium tin oxide (ITO). However, even for the most promising metal-based nanowire materials, there are issues such as high cost, complex welding, and high contact resistance. To address these problems, this paper proposes a printable and filament-drawable polydimethylsiloxane (PDMS)-based adhesive, which, through a novel additive patterning technology, efficiently and economically manufactures self-welding copper micro-meshes and circuits. The adhesive can be processed into micro-patterns through printing and filament drawing, on which ionic Ag can be in situ reduced and anchored, thereby eliminating the need for tedious pre- and post-treatment steps. The fully exposed Ag particles dramatically minimize the usage of precious metal catalyst, thus efficiently catalyzing electroless copper deposition (ECD) reaction. Highly conductive (1.03 × 107 S m−1) copper circuits can be fabricated on the printed adhesive patterns, exhibiting versatile applicability to diverse substrates. Highly precise copper micro-meshes (∼50 μm) can be fabricated on the filament networks drawn by the adhesive. The copper meshes undergo complete self-welding at junctions during the ECD process, thus exhibiting ultra-low square resistance of 0.45 Ω sq−1 while maintaining a high transmittance of 82.2 %. This is far superior to most of TCFs in published literature.

Partial Applicability of Mixed Potential Theory in Unsteady Regime for Cu Electroless Deposition on Pt

Electroless deposition (ELD) has been practiced over many decades, but its underlying mechanism is incompletely understood. We explore the applicability of Mixed Potential Theory (MPT) in the unsteady regime during the electroless copper deposition (ELCD) on Pt surface pretreated by dipping Pt in SnCl2 and PdCl2. We demonstrate that ELCD occurs in the low and high potential zone (LPZ & HPZ) at two different reaction rates due to the under-potential deposition of Cu on pretreated Pt in LPZ. The Nyquist plot in HPZ shows one semicircle, while LPZ shows two semicircles. Single semicircle in HPZ suggests dependency only on catalytic potential available on the surface over which ELCD occurs. The two semicircles in LPZ indicate that besides the surface catalytic potential, the dependency is on the reaction intermediate of formaldehyde oxidation, limiting the relevance of MPT. MPT posits that reduction and oxidation in Cu ELD are independent of each other and the role of the surface is only in establishing the catalytic potential. To check the pertinence of MPT, we obtained the polarization resistance (RP) from the Nyquist plot of (a) ELCD solution, (b) CuSO4 with Tartrate and without Formaldehyde i.e. electrochemical copper deposition (ECCD). The RP so obtained shows a significant difference only in LPZ but not in HPZ because of which we argue that MPT is applicable only in the HPZ.

Multifunctional PDMS/Schiff base/SiO2 gel assisted fabrication of printed, stretchable and straight copper conductors

Printable, stretchable, and highly conductive metal conductors have emerged as potentially promising interconnects in the field of soft electronics. However, current techniques relying on geometric engineering have been criticized for complicated fabrication process and defective geometric structure. Here, we report a printed, straight, and omnidirectionally stretchable copper conductor, which is facilely fabricated on a flat substrate without requiring prestretching, assisted by a multifunctional gel medium layer. The PSS gel, composited by polydimethylsiloxane, Schiff base and fumed SiO2, offers a unique combination of stretchability, printability, and moldability. Additionally, this gel enables the reduction of silver ions directly on its surface by partially bonded crosslinker molecules. The fully exposed catalyst exhibits excellent activity in catalyzing electroless copper deposition reaction, on which high-quality copper coating is facilely achieved. The produced copper patterns exhibit high conductivity (4.93 × 107 S m−1) and excellent stretchability with fracture strains of ∼ 191 % and ∼ 135 % for the uni- and omni-directionally stretchable patterns respectively, which are superior to the majority of stretchable metals in published literature. The stretchable wrinkles derive form the gel medium layer molded by templates, realizing straight metal lines on flat substrate. This process combines the advantages of traditional in-plane and out-of-plane strategies, demonstrating great potential in practical application.

Electroless Copper Plating on a Cotton Surface: Effect of Metal Ion Ligand Stability Constant on Reduction Deposition.

Electroless plating facilitates the metallization of nonconductive substrate surfaces, and of note, the precise control of the bath stability constant influences the deposition process of metal particles. In this paper, trisodium citrate, potassium sodium tartrate, nitrogen triacetic acid, thiourea, and ethylenediamine tetraacetic acid disodium were selected as coordination agents, and the effect of the metal ion ligand stability constant on the reduction deposition was studied. Coordination bonds can be established between the Cu2+ and O/N/S particles in the ligand because paired electrons in O/N/S hybrid orbitals tend to occupy empty Cu2+ hybrid orbitals and establish coordination bonds. More importantly, the copper-potassium sodium tartrate ligand exhibits the lowest stability constant and lowest reduction barrier. As an exception, a consecutive Cu-plated coating with an excellent crystallinity property was deposited on the cotton surface when potassium sodium tartrate was used as the coordination agent in the plating solution. The deposition amounts are 55.2% and 74.1% after 1 and 4 h of electroless copper plating, respectively. The surface resistivity of Cu-plated cotton is 0.38 Ω/cm2, and additionally, the surface resistivity ratio before and after 1000 cycles fluctuated between 0.9 and 1.1, indicating that the Cu-plated cotton exhibits outstanding flexibility. In this paper, the deposition rate can be optimized by adjusting the copper particle ligand stability constant in the plating solution, aiming to achieve optimal results.

Selective metallization of polymer based on nanoscale tungsten oxide laser activators for advanced electronics

In recent years, laser-induced selective metallization (LISM) has been widely used to fabricate complex metal patterns and circuits due to its superior precision. Laser sensitizers known as laser-activated for electroless copper plating (ECP) are a significant premise in LISM. Herein, we confirmed that tungsten oxides (WO2.72, WO2.92, and WO3) exhibited excellent LISM activity due to oxygen vacancies (OVs) in their lattice. Moreover, non-stoichiometric tungsten (WO2.72, WO2.92) presented higher activity due to a higher concentration of OVs than the stoichiometric form of WO3, indicating the importance of OVs to the activity of laser sensitizers in LISM. Moreover, a higher OVs concentration in the laser sensitizer resulted in a higher LISM activity. This finding points out the direction for future laser sensitizer screening, synthesis, and development. After 30 min ECP, the square resistance of the prepared copper layer on ABS/WO2.72, ABS/WO2.92, and ABS/WO3 are 0.014, 0.035, and 0.176 Ω/sq, respectively. The nanoscale tungsten oxides with excellent LISM activity enabled the rapid fabrication of metal patterns and circuits in various scenarios, which expands the research field and application prospect of LISM technology. We demonstrate the advantages of LISM with tungsten oxides in fabricating advanced electronics. A strategy for replacing hand-wound windings in electromagnetic generators with 2D on-chip planar inductor arrays from LISM was proposed. The generated current reached a high level of 193 mA, and can be directly connected to wireless sensor networks to supply power. This work is the first research ever reporting laser sensitizers of tungsten oxides and introducing LISM technology into self-powered electronics.

Electroless copper plating of 3D-printed polymer foam: A promising method to fabricate electrodes for denitrification

This work involves processing porous copper structures through electroless plating/metallization on 3D-printed polymer foam (PF) and exploiting them as electrode material for denitrification studies. A sustainable electroless plating process using KOH and H2SO4 for etching and copper seed crystals for surface activation is presented as an alternative to conventional chromic acid and palladium. This etching process increased average surface roughness (Ra) from 58.7 to 287 nm and amplification of hydrophilic functional groups. These modifications enhance the surface’s wettability by reducing the contact angle from 96.35 to 37.5°, thereby facilitating uniform deposition. After activation, Cu deposition was accomplished by immersing the foam in the bath. The resulting Cu-metallized polymer foams (Cu/PF) were investigated as electrodes for nitrate reduction, showing a sensitivity of 5.86 mA/mM within a nitrate concentration range of 2.5–10 mM, also demonstrated good stability in durability tests.

Altering the percolation threshold of PA66‐copper hybrid in an electroless copper deposition process by surface activation of the polymer

AbstractIn this study, the impact of three different principles of surface activation techniques for polyamide fibers on the formation of conductive percolation during the subsequent electroless copper deposition process was investigated. The techniques used are (1) polyamide complexation using a solution mixture of calcium chloride, ethanol and water, (2) atmospheric plasma surface treatment and (3) grafting of 2‐hydroxyethylmethacrylate by radical induced polymerization. As a result, the percolation threshold was shifted to lower copper contents. The copper content required to form conductive structures was reduced ranged between 59% and 89%, depending on the activation techniques. Furthermore, the deposition time was reduced by 37%–57%, resulting in a faster build‐up of the percolation on the fabric. Changes in wetting behavior and substrate surface topography were identified to be the main reasons for these observations. While all applied surface activation techniques led to higher copper contents compared to unmodified reference, the atmospheric plasma modification led to the highest copper contents during the deposition process and a more uniform appearance of the metallised layer.Highlights Three different fiber surface activation methods are evaluated. Fiber surface activation increases wetting and polymer‐metal adhesion. Activated polymer surface leads to faster copper deposition and percolation. Atmospheric plasma modification is the most efficient technique.

In situ reduction of copper nanoparticles in porous carbonized wood for efficiently enhancing electromagnetic interference shielding performance

In this study, porous carbonized wood was used as the substrate, and a multi-layer composite of copper/carbonized wood/copper (Cu/CW/Cu) layer with light weight, flame retardancy, and efficient electromagnetic shielding effectiveness was prepared by electroless copper method. The results showed that the copper particles can be filled in the layered porous structure of the carbonized wood. The metal Cu layer was evenly covered on the surface of the whole carbonized wood, and the average surface roughness was 7.62 µm. The absorption peak at 2340 cm−1 was significantly enhanced, which proved that the increase of the number of electroless Cu on the carbonized wood surface promoted the improvement of Cu autocatalytic ability. After three depositions of Cu, the conductivity of the composite material reached 1154 S/cm, showing good electrical properties. The shielding effectiveness in the X-band from 8.2 to 12.4 GHz was up to 55.97 dB at low density (0.27 g/cm3). Specific shielding effectiveness SSE/t was as high as 581.69 dB cm2 g−1. Through the “absorption–reflection–absorption” path, high absorption and low reflection are achieved, shielding a large number of incident electromagnetic waves.

An innovative approach for the passive cooling of batteries: An empirical investigation of copper deposition on polyurethane foam for the enhancement of phase change material

A proof-of-concept utilising Copper-Plated Polyurethane Foam (CPPF) and Phase Change Material (PCM) for passive thermal management of lithium-ion batteries is demonstrated in this study. The aim of this research is to assess the effectiveness of CPPF when utilised as a constituent substance in PCM/Foam composites. Six distinct configurations of PCM/Foam composites are presented in this work using 10-pore-per-inch foam. A total of four deposition foam samples were produced. Of these, three were created by gradually increasing the immersion time in an electroless copper plating solution. For the fourth sample, an electroless plating technique was utilised for 80 min, followed by an electroplating procedure to deposit an additional layer of copper. The evaluation entails examining each plated sample in comparison to a copper foam that is commercially available with a purity level of 99.99 %. The findings reveal that the electroless-plated specimens exhibit improved effectiveness after being subjected to a prolonged plating period of 80 min. The electroplated sample exhibited the greatest degree of effectiveness, as evidenced by a 64.4 % reduction in battery cell surface temperature(10.98 °C), which is almost identical to the 64.5 % decrease in temperature (11.03 °C) observed with commercial foam but coupled with 88.1 % decrease in mass. The results suggest that the CPPF-PCM composites offer effective passive cooling properties for batteries.

Incorporating pre-stretching into electroless copper plating for conductivity improvement of elastic nylon fabric: application in ECG electrode

Incorporating pre-stretching into electroless copper plating for conductivity improvement of elastic nylon fabric: application in ECG electrode

Enhancement of deposition rate by accelerators employing D-Mannitol as complexing agent

Copper possesses better conductivity which makes it an ideal plating choice for the electronics and semiconductor industries. Copper electroless plating can be carried easily on non-conductors like plastics, ceramics, fabrics, glasses etc. One of the limitations of electroless plating is its very low plating rate, which is further reduced by the addition of stabilizers which is quite essential for the plating process. A stabilizer improves stability of bath and deposit qualities, but slows down the plating rate. The current study focuses on the enhancement of plating rate by the addition of accelerators in eco-friendly copper methane sulphonate bath. It is observed that accelerators like guanidine hydrochloride and 2,6-diaminopyridine improves the rate of deposition with good deposit quality. It was studied with weight gain method and analyzed with tafel polarization studies. The surface of the deposit was analyzed with X-ray diffraction (XRD) and scanning electrode microscope (SEM). KEY WORDS: Copper, Methane sulphonic acid, Accelerators, Guanidine hydrochloride, 2,6- Diaminopyridine Bull. Chem. Soc. Ethiop. 2024, 38(4), 901-908. DOI: https://dx.doi.org/10.4314/bcse.v38i4.7

Design and Analysis of a Textured Cu-Encapsulated Ni Tube for Low-Reflection Electromagnetic Interference Shielding Material.

With the frequent increase and update of electromagnetic interference (EMI) shielding materials, a low-resolution material that can absorb most electromagnetic waves, thereby effectively reducing the secondary pollution, is urgently needed. However, the excellent performance, flexibility, and low cost of these methods are usually incompatible with current reports. To address the above dilemma, we reported a facile solution for fabricating a low-reflection and high-performance EMI shielding composite by means of electroless nickel plating (EP-Ni), electroless copper plating (EP-Cu), annealing, and coating with a polydimethylsiloxane (PDMS) polymer with the structure of a Ni@Cu tube encapsulated with PDMS. The results indicate that the active groups on vegetable wool can act as active sites for the absorption of the Pd catalyst, thereby catalyzing the reduction of Ni2+, Cu2+, and the subsequent deposition on the plant fiber surface. Notably, the Ni@Cu-encapsulated plant fibers decreased during annealing at 100 °C. According to the segregated network and synergistic effect of the porous structure, the as-fabricated EMI shielding material demonstrated high absorption and low reflection, in which the power coefficient of the T value was approximately 0.0001, the R value was about 0.1764 (a decrease of 27.5% compared that of EP-Ni cotton), and the A value was approximately 0.8235.