Chromic Acid Etching Research Articles

Towards decoupling chemical and mechanical adhesion at the electroplated metal/polymer interface via precision surface texturing

Electroplating is the most widely used method for coating metals on polymers, the adhesion of which is ensured by chemical and mechanical interactions of their surface. Unfortunately, the relative contributions of these factors to the overall adhesion was debated over the past century with no quantitative arguments. This study decouples the contribution of polymer chemistry from other adhesion factors by using non-interlocking micro-textures with variated actual surface area. We used state-of-the-art photolithography to micro-texture nine molds with 2, 4 and 6 µm wide and 2, 4 and 6 µm tall pillars (1) hot embossing to replicate the pillars on the ABS polymer (2), electroplating to deposit copper on the textured and etched ABS polymer (3), and peeling test to measure the adhesion strength (4). In the absence of mechanical interlocking, the measured adhesion can be fully ascribed to the surface-amplified chemical adhesion between the metal and the polymer. In result, the chemical adhesion appeared linearly proportional to the actual interfacial area, yet it contributed only a minor fraction (1/7) to the overall adhesion strength in electroplating with classical chromic acid etching. Evidently, chemical adhesion is not the dominant factor in polymer electroplating.

STUDY OF ELECTROLESS NICKEL PLATING ON RAPID PROTOTYPING MODEL USING ACRYLONITRILE BUTADIENE STYRENE

Electroless plating on Acrylonitrile Butadiene Styrene (ABS) is a metallization process that involves a reduction and oxidation reaction between the nickel source and the substrate material. The purpose of this research is to determine the ability of nickel deposition in the nickel electroless plating process with a specific etching time variation. This nickel electroless procedure begins with a chromic acid etching process that can last anywhere from 15 to 55 minutes and is useful for increasing roughness and creating submicroscopic cavities. After the etching process is finished, the surface roughness test is performed with a Mitutoyo SJ-210. Additionally, the activation step is carried out for 5 minutes in order for the polymer to become a conductor, allowing the plating process to proceed. The electroless plating process was then carried out for 55 and 75 minutes, with the goal of depositing nickel metal on the ABS surface. The coating results were analyzed using Fourier Transform Infrared (FTIR) spectroscopy IRSpirit/ATR-S serial No. A224158/Shimadzu to determine the functional groups formed both before and after the coating process, X-Ray Diffraction (XRD) to determine the character of the crystal structure, and phase analysis of a solid material using PANalytical type E'xpert Pro, To determine the surface morphology, the Zeiss EVO MA 10 was used to perform scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) at 1000x magnification. The test findings demonstrate that, based on a range of investigations, etching variations of 15,25,35,45, and 55 minutes etching time 55 minutes are the best nickel deposited substrates, as evidenced by EDS data, where this treatment has the largest weight fraction of nickel. As a result, the longer the etching period, the rougher the surface becomes, affecting the capacity of nickel deposition to increase. Furthermore, it can be demonstrated in this investigation that the nickel deposited is in an amorphous form.

Adhesion improvement of ABS resin by MnO2-H3PO4-H2SO4 colloid with ultrasound-assisted etching treatment

The adhesion strength between electroless copper and acrylonitrile-butadiene-styrene (ABS) resin could be improved significantly by MnO2-H3PO4-H2SO4 colloid system. In this paper, when the concentrations of H3PO4 and H2SO4 in the colloid were 4.2 and 10.4 M, respectively, the effect of the ultrasound-assisted etching (UAE) time on the etching performance of ABS resin were investigated. With the UAE for 10 min, much more uniform cavities formed on the ABS surface, the average surface roughness (Ra ) decreased from 143 to 107 nm, which was much lower than etched by CrO3-H2SO4 colloid (420 nm). Though the average surface roughness (Ra ) was decreased, the average adhesion strength between the electroless copper film and ABS substrate increased from 1.39 to 1.60 kN m−1, which was also higher than chromic acid etching treatment (1.42 kN m−1). The density of the hydrophilic groups and the uniformity of cavities on the ABS surface were increased with the UAE, which resulted in high adhesion strength and low average surface roughness.

Catalytic C–H Oxidation Enhances Polyethylene Bonding

Selectively adding functionality to commodity plastics is an abiding challenge in polymer science. In this issue of Chem, Hartwig and co-workers describe a selective, catalytic oxidation of polyethylene C–H bonds by using high-valent ruthenium-oxo species. The transformation increases polyethylene’s adhesive properties without significantly modifying its thermal stability or mechanical strength.

Selective, Catalytic Oxidations of C–H Bonds in Polyethylenes Produce Functional Materials with Enhanced Adhesion

Summary The synthesis of functional and processable polyethylenes from simple vinyl monomers with controlled molecular weights and architectures has been a grand challenge of polymer chemistry. Post-polymerization modification of the homopolymers of ethylene is attractive for this purpose but has been hampered by the lack of efficient methods for the selective functionalization of C–H bonds in polyolefins. We report the selective, catalytic oxidation of C–H bonds in commodity polyethylenes with varying molecular weights and architectures. Remarkably, the functionalized materials, even at low levels of functionalization, exhibit physical properties that are absent in unmodified polyolefins, such as strong adhesion and the ability to be painted with common waterborne latex paint. Such observations indicate that selectively modified polyethylenes as described here may help to transform existing commodity plastics into more valuable and potentially more sustainable materials.

Effect of surface morphology change of polystyrene microspheres through etching on protein corona and phagocytic uptake

Surface physicochemistry properties of polymer particles are crucial for protein corona formation and macrophage phagocytosis when they contact with living body. In this work, polystyrene microspheres (PS-MSs) were selected as a model of polymer microparticles and fabricated by chromic acid etching through controlling conditions to obtain different surface morphology structures and to investigate their effect on the protein adsorption and phagocytic uptake of PS-MSs. The adsorption of bovine serum albumin (BSA) and fibrinogen (FIB) on PS-MSs showed almost the same tendency, i.e. the etched PS-MSs presented lower protein adsorption compared with original microspheres. The adsorption of BSA and FIB was the lowest when the protuberances on the etched surfaces were maximum and the size of the protuberances was minimum. Furthermore, the surface morphologies of PS-MSs were influenced in return not only by the amounts of proteins but also by protein types. Meanwhile, the macrophages phagocytosis of PS-MSs depended on the amounts and kinds of adsorbed proteins, especially the albumin content. In a word, phagocytosis and protein adsorption can be regulated by microsphere morphologies through etching, which provides a promising strategy to avoid invalid uptake for polymer particles such as drug delivery carriers.

Completely Aqueous Route for Metallization of Structural Polymeric Materials in Micro-Electro-Mechanical Systems

Recent developments in the fabrication of micro-electro-mechanical systems (MEMS) are moving away from the deposition/mask/etch paradigm and instead exploiting useful properties of polymers. Many polymeric insulating materials, such as Parylene, PMMA, HSQ, SU-8 and KMPR, have attracted attention in microfabrication lately, because of their low cost and significantly easy processing procedures [1,2]. Metallization of these polymers is required for their integration in MEMS technology. While conventional microfabrication methods for preparing metallic thin films on insulating substrates are limited to vapor deposition techniques, it has recently demonstrated that electroless deposition can be considered as an alternative and efficient approach [3,4]. Presently used process of electroless plating onto plastics requires a pretreatment based on chromic acid etching for oxidizing the surface. This pretreatment increases the surface energy and wettability for the subsequent step of surface activation with noble metal catalysts. Thus, the development of simple, cost-effective and environment friendly strategies, such as avoiding chromic acid etching and/or minimizing the gravimetric use of noble metal, to metallize the surface of insulating substrates is of huge interest. Here, we report a simple one step covalent amination of the surface of commercial structural polymers employing diazonium-based aqueous chemistry. These amine-terminated functionalities allow minimizing the quantity of palladium cations used as catalyst for the subsequent electroless nickel deposition, as well as offer excellent adhesion between the polymer substrate and the nickel film. X-ray photoelectron spectroscopy is carried out to elucidate the mechanism of surface functionalization with amine groups. We then focus our attention on the comprehensive characterization of the metallic thin film through scanning electron microscopy, energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy techniques. Keywords: Metallization of plastics, diazonium chemistry, covalent grafting, environment plating process, MEMS fabrication Reference W. Dai et al., Sensors and Actuators A 135 (2007) 300–307.Y. Liu et al., Progress in Polymer Science 52 (2016) 79–106.Y. Shacham-Diamand et al. Microelectron. Eng. 132 (2015) 35–45.G. Zeb et al., Applied Surface Science 407 (2017) 518–525.

Metallisation on ABS plastics using fine-bubbles low ozonated water complying with REACH regulations

Traditionally, a highly concentrated mixed solution of chromic acid and sulphuric acid has been used as an etchant for electroplating on ABS plastics. However, this etchant is hazardous and the subject of impending legislation. Therefore, the fine-bubbles low ozonated water treatment as an alternative to the chromic acid etching process has been investigated. Adhesion strengths of 0.9–1.0 kN m−1 were obtained for treatment of 30 min. From the observation of surface morphology, dimples of several hundred nanometres were formed after surface modification. Cross-sectional observation of the interface suggested that formation of a thin nano-porous anchor layer on the ABS surface was responsible for plating adhesion. This method with low ozonated water treatment provides an environmentally friendly process for plating on ABS.

Environmentally Friendly Copper Metallization of ABS by Cu-Catalysed Electroless Process

Abstract An environment-friendly surface etching and activation technique for ABS surface metallization were investigated as a replacement for conventional chromic acid etching bath and palladium catalyst. After etching by H2SO4-MnO2 colloid, the ABS surfaces became rough; meanwhile the carboxyl and hydroxyl groups were formed on the surface. With absorption and reduction by a sodium borohydride solution, copper particles were deposited on the ABS surface, which serve as a catalyst replacement for SnCl2/PdCl2 colloid. The effects of CuSO4 concentration, NaBH4 concentration, reduction temperature and reduction time on the adhesion strength between the ABS surface and the electroless copper film were investigated. The average adhesion strengths reaches 0.87 kN·m−1.

Chemical modification on UHMWPE microparticles to improve the interfacial and tribological properties of UHMWPE/carbon fabric/phenolic laminate in water environment

Carbon fabric (CF)/phenolic laminates filled with pristine and chromic acid treated ultra high molecular weight polyethylene (UHMWPE) microparticles were fabricated. Their interfacial and tribological properties in water environment were comparatively investigated. The interlaminar shear strength (ILSS) of the laminates was tested on a universal testing machine (DY35), and the tribological properties were evaluated by a block-on-ring tribo-tester. The worn surfaces and the interfaces of the laminates were respectively analyzed by scanning electron microscope (SEM) and field emission SEM (FESEM). The change of the chemical composition of UHMWPE microparticles after chromic acid etching was analyzed by Fourier transform infrared spectroscopy (FTIR). The chemical state of carbon fiber surface was examined using X-ray photoelectron spectroscopy (XPS). The results revealed that the chromic acid treated UHMWPE microparticles had more remarkable effect than the pristine ones on improving not only ILSS and wear resistance of CF/phenolic laminate, but also its immunity to water environment. This should be attributed to the strengthened interfaces in treated UHMWPE/CF/phenolic laminate, which were characterized by the drawn dendritic UHMWPE fibrils firmly clinging on the surfaces of carbon fibers and resin in a Boston ivy-like manner. Copyright © 2015 John Wiley & Sons, Ltd.

Plasma and chromic acid treatments of polycarbonate surface to improve coating–substrate adhesion

The influence of Ar/O2 plasma activation and chromic acid etching of polycarbonate (PC) surface on the adhesion of coating to substrate was systematically studied by cross‐cut and tape peel methods through temperature‐shock aging tests. The differences between the wettabilities and elemental compositions of plasma‐treated and chromic acid‐treated PC surfaces prior to coating deposition were evaluated by contact angle measurements and X‐ray photoelectron spectroscopy. To elucidate the adhesion failure of the coatings, nanoindentation technique was employed for the quantitative assessment of the nanomechanical changes of coating depositions on PCs after temperature‐shock aging tests. The two surface treatments can significantly improve the hydrophilicity and polarity of the PC surface, resulting in excellent adhesion of the coating on the PC substrate. Temperature‐shock aging tests reveal that the adhesion of coating on plasma‐modified substrates is superior to that of chromic acid‐etched substrates. We propose that the improved adhesion of the coating on the plasma‐modified PC can be attributed to the higher wettability and more cross‐linking of C–O–Si bonds at the coating–substrate interface. Copyright © 2013 John Wiley & Sons, Ltd.

Adhesion improvement of electroless copper to ABS resin by low environmental pollution surface etching system

The adhesion strength between acrylonitrile–butadiene–styrene (ABS) resin and electroless copper can be improved significantly by a low environmental pollution etching system containing H2SO4–MnO2–Na4P2O7–H2O colloid as a replacement for conventional chromic acid etching solutions. In this paper, the effects of the H2SO4 concentration and Na4P2O7 content on the surface topography, surface roughness and the adhesion strength were studied. When the H2SO4 concentration was 12·9M, good etching performance was obtained. The average adhesion strength between the electroless copper and ABS substrate reached 1·30 kN m−1. The surface contact angle measurement indicated that the ABS surface became hydrophilic and the contact angle decreased from 92·1 to 31·2°.

Study of an environment-friendly surface pretreatment of ABS-polycarbonate surface for adhesion improvement

In this paper, an environmentally friendly etching system containing MnO2–H3PO4–H2SO4 colloid was used to investigate surface etching for ABS- polycarbonate (PC/ABS) as a replacement for conventional chromic acid etching solutions. In order to obtain a good etching performance, a swelling system, containing tetramethylammonium hydroxide (TMAH), and 1-Methyl-2-pyrrolidinone (NMP), was used to investigate the surface swelling for PC/ABS resin. Then the effects of H2SO4 concentration, and etching time on the surface topographies and surface contact angle were investigated. After the optimal swelling and etching treatment, the surface contact angle of PC/ABS resin decreased from 95.7° to 28.3°, and the adhesion strength between electroless copper film and PC/ABS resin reached to 1.04KNm−1. The FT-IR spectra and XPS analyses indicated that hydroxyl and carboxyl groups formed on the PC/ABS surface as a result of the swelling and etching treatment, which improved the adhesion strength between PC/ABS substrate and elctroless copper film.

Adhesion improvement of electroless copper to PC substrate by a low environmental pollution MnO2–H3PO4–H2SO4–H2O system

A low environmental pollution etching system, MnO2–H2SO4–H3PO4–H2O colloid, was used to investigate surface etching performance of polycarbonate (PC) as a replacement for the chromic acid etching solution. The effects of H2SO4 concentrations, H3PO4 concentrations and etching times upon the surface topography, surface chemistry and surface roughness were studied. With the appropriate etching treatment, the surface average roughness (Ra) of PC substrates increased from 3 to 177nm, and the adhesion strength between the electroless copper and PC substrate also reached 1.10KNm−1. After the etching treatment, the PC surface became hydrophilic and the surface contact angle decreased from 95.2° to 24.8°. The intensity of C–O groups increased and the new functional groups (–COOH) formed on the PC surface with the etching treatment, which improved the adhesion strength between PC substrate and elctroless copper film.

A New Palladium-Free Surface Activation Process for Cu Electroless Plating on ABS Plastic

An environment-friendly surface etching and activation technics for ABS surface metallization were investigated as a replacement for conventional chromic acid etching bath and palladium catalyst. After etching by H2SO4-MnO2 colloid, the ABS surfaces became roughness; meanwhile the carboxyl and hydroxyl groups were formed on the surface. With absorption and a reduction by a dimethylamineborane solution, nickel particles were deposited on the ABS surface, which serves as a catalyst replacement for SnCl2/PdCl2 colloid. The effects of NiSO4 concentration, (CH3) 2NHBH3 concentration, reduction temperature and reduction time on the adhesion strength between the ABS surface and the electroless copper film were investigated.

Environment-friendly Pd free surface activation technics for ABS surface

An environment-friendly surface etching and activation technics for acrylonitrile–butadiene–styrene (ABS) surface metallization were investigated as a replacement for conventional chromic acid etching bath and palladium catalyst. After etching by H2SO4–MnO2 colloid, the ABS surfaces became roughness; meanwhile the carboxyl and hydroxyl groups were formed on the surface. With absorption and a reduction by a dimethylamineborane solution, copper particles were deposited on the ABS surface, which serves as a catalyst replacement for SnCl2/PdCl2 colloid. The effects of CuSO4 concentration, (CH3)2NHBH3 concentration, reduction temperature and reduction time on the adhesion strength between the ABS surface and the electroless copper film were investigated. And the average adhesion strengths reached 1.31kNm−1, which is near the values (1.19kNm−1) obtained by SnCl2/PdCl2 colloid.

Adhesion Improvement of ABS Resin to Electroless Copper by H2SO4–MnO2 Colloid with Ultrasound-Assisted Treatment

The adhesion strength between electroless copper and acrylonitrile-butadiene-styrene (ABS) resin can be improved significantly by an environmentally friendly etching system containing H2SO4–MnO2 colloid as a replacement for conventional chromic acid etching solutions. In this paper, the effects of the H2SO4 concentration and ultrasound-assisted treatment (UAT) on the surface roughness and adhesion strength were investigated. When the H2SO4 concentration was 11.8∼12.7 M, good etching was obtained. With UAT, many uniform cavities formed on the ABS surface with the average surface roughness (R a) and maximum roughness (R max) of ABS substrates decreasing from 386 and 397 nm to 278 and 285 nm, respectively, which were much lower than that etched by CrO3–H2SO4 colloid (420 and 510 nm, respectively). The average adhesion strength increased from 1.29 to 1.39 kN/m, which was close to that obtained with chromic acid etching treatment (1.42 kN/m). The surface contact angle measurement indicated that the density of the polar groups on the ABS surface increased with increasing time of UAT. The results indicated that surface etching with UAT not only improved the uniformity of cavities, but also enhanced the oxidation rate of ABS resin, which in turn resulted in greater adhesion strength and a lower surface roughness.

Study of an Environmentally Friendly Surface Etching System of ABS for Improving Adhesion of Electroless Cu film

In this paper, an environmentally friendly system containing H2SO4-MnO2 colloid was used to investigate surface etching of acrylonitrile-butadiene-styrene (ABS) resin as a replacement for the chromic acid etching solutions. The effects of the H2SO4 concentrations, bath temperatures and etching times on the etching effectiveness were studied. The surface roughness and surface hydrophilicity of ABS substrates were improved greatly with the etching treatment. After the electroless plating of copper, the adhesion strength between the electroless copper and ABS substrate reached 1.19 KN m−1, which was much higher than that required in PCB process (over 0.7 KN m−1). Electrical potential measurements indicated that the etching performance depended strongly on the oxidation potential of MnO2 and the “soluble” MnO2 concentration in the colloid. The FT-IR spectra and XPS results demonstrated that the C=C bonds of butadiene on the ABS surface were oxidized, and –COOH and –OH groups were formed on the ABS surface with the etching treatment. Meanwhile, some –C≡N groups of acrylonitrile were changed to –CONH2 groups with etching treatment, and the –CONH2 groups increased with the etching time. The formation of –COOH, –OH and –CONH2 groups on the surface enhanced hydrophilicity and decreased surface contact angle, which was beneficial to improve the adhesion strength. These results suggest that the H2SO4-MnO2 colloid is an effective and environment-friendly surface etchant for ABS surface etching.

Microscopic Study of a Ligand Induced Electroless Plating Process onto Polymers

The ligand induced electroless plating (LIEP) process was recently developed and thoroughly demonstrated with one of the most used polymers for plating processes: acrylonitrile-butadiene-styrene (ABS). This generic process is based, thanks to the use of diazonium salts as precursors, on the covalent grafting of a thin layer of poly(acrylic acid) (PAA) acting as ligand for metallic salts onto pristine polymer surfaces. This strategy takes advantage of the PAA ion exchange properties. Indeed, carboxylate groups contained in PAA allow one to complex copper ions which are eventually reduced and used as catalysts of the metallic deposition. Essentially based on ABS, ABS-PC (ABS-polycarbonate) and PA (polyamide) substrates, the present paper focuses on the role of the polymer substrate and the relationships between the macroscopic properties and microscopic characterizations such as infrared (IR), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and scanning electron microscopy (SEM). The adhesion strength of the metallic layer deposited via that LIEP process with the bulk polymer substrates was successfully compared with the adhesion of similar copper films deposited by the usual process based on chromic acid etching and palladium-based seed layer, by measuring the T-peel adhesion strength, and by carrying out the common industrial scotch tape test. Lastly, the electrical properties of the deposited layer were studied thanks to a four-point probe and scanning tunneling microscopy (STM) measurements.

ABS Polymer Electroless Plating through a One-Step Poly(acrylic acid) Covalent Grafting

A new, efficient, palladium- and chromium-free process for the electroless plating of acrylonitrile-butadiene-styrene (ABS) polymers has been developed. The process is based on the ion-exchange properties of poly(acrylic acid) (PAA) chemically grafted onto ABS via a simple and one-step method that prevents using classical surface conditioning. Hence, ABS electroless plating can be obtained in three steps, namely: (i) the grafting of PAA onto ABS, (ii) the copper Cu(0) seeding of the ABS surface, and (iii) the nickel or copper metallization using commercial-like electroless plating bath. IR, XPS, and SEM were used to characterize each step of the process, and the Cu loading was quantified by atomic absorption spectroscopy. This process successfully compares with the commercial one based on chromic acid etching and palladium-based seed layer, because the final metallic layer showed excellent adhesion with the ABS substrate.