Surface characteristics and adhesion performance of black oxide coated copper substrates with epoxy resins

Black oxide is a conversion coating applied onto the copper substrate to improve its interfacial adhesion with polymeric adhesives. A comprehensive study is made to characterize the black oxide coating using various characterization techniques, including SEM, XPS, AFM, XRD, Auger electron spectroscopy, TEM, D-SIMS, RBS and contact angle measurements. It was found that the oxide coating consisted of cupric and cuprous oxide layers from the top surface to inside. The cuprous oxide layer was formed on the copper crystal surface, on which densely-packed fibrillar cupric oxide grew continuously until saturation. The cupric oxide had a fibrillar structure with high roughness at the nanoscopic scale, whereas the cuprous oxide was rather flat and granular. There was a continuous change in oxide composition with no distinct boundary between the two oxide layers. The bond strength between the epoxy resin and the oxide coated copper substrate increased rapidly at a low level of oxide thickness, and became saturated at thicknesses greater than about 800 nm. There were similar dependences of bond strength on surface roughness, oxide thickness especially of cupric oxide and surface energy, reflecting the importance of these surface characteristics in controlling the interfacial adhesion.     

Vacuum metallization of polyetherimide: Interfacial chemistry and adhesion

Vacuum deposition of metal coatings on polyetherimide was investigated. High levels of adhesion (>170 g/mm) with evaporated copper were achieved through a primarily chemical interaction. Changes in the interfacial chemistry were correlated with metal/polymer adhesion. Vacuum deposition of aluminum onto polyetherimide was also examined and found to yield much lower adhesion.     

Improvement in the adhesion between copper metal and polyimide substrate by plasma polymer deposition of cyano compounds onto polyimide

The surface modification of Kapton film by means of plasma polymer deposition is discussed from the viewpoint of improving the adhesion between copper metal and Kapton film substrate. Plasma polymers of AN (acrylonitrile) and FN (fumaronitrile) were used for the surface modification, and the adhesion between the copper metal and the plasma polymer-coated Kapton film was evaluated by the T-peel strength measurement. The surfaces of peeled layers were analyzed by X-ray photoelectron spectroscopy (XPS) and the failure mode is discussed. The plasma polymer deposition of AN and FN shows an effective improvement in the adhesion between the copper metal and Kapton film; in particular, the AN plasma polymer deposition increased the peel strength 4.3 times. Failure occurred mainly in the Kapton film, and the adhesion between the AN plasma polymer and the Kapton film and that between the copper metal and the AN plasma polymer were found to be quite strong.     

A study of the adhesion between steel and an ethylene-acrylic acid-acrylate terpolymer

The interfacial interaction of an ethylene-acrylic acid-t-butyl acrylate (EAA) terpolymer with metals (mild steel) has been studied by spectroscopic techniques (XPS, AES, and IR), SEM, and mechanical testing. Using peel tests it was shown that the copolymerization of small quantities of acrylic acid and t-butyl acrylate with ethylene induces polymer/metal adhesion values rather higher than in plain polyethylene. The fracture surfaces were analyzed by XPS, AES, and SEM. It was shown that the fracture is cohesive and occurs within the polymer. Some specimens were aged under various conditions. In this case, the failure was located at the polymer/metal interface. In fact, SEM, XPS, and AES did not show the presence of polymer on the metal surface. Iron corrosion is then considered responsible for the failure of the joint. Since a thin layer of metal oxide covers the surface of mild steel, so to understand the polymer/ metal interfacial interaction better, IR spectroscopy was performed on polymer/metal oxide (goethite and hematite) composites. It was shown that the carboxyl groups of the polymer react with hydroxyl groups present at the metal surface. Adsorption isotherms of the polymer on iron oxides were also obtained, showing remarkable EAA terpolymer chemisorption, while there was no evidence of bonding between iron oxides and plain polyethylene.     

An FT-IR Study on Interfacial Interactions in Ethylene Copolymers/Aluminium Laminates in Relation to Adhesion Properties

The effect of three different functional groups in ethylene copolymers on the adhesion with aluminium was studied. The interface in polymer/metal laminates was analyzed by FT-IR, and the adhesion mechanism for each functional group was evaluated. Laminate samples were prepared by solution casting or by hotpressing polymeric film onto the aluminium substrate. In the latter case, the interface was exposed by solvent extraction. The interfacial structures developed by the different copolymers were correlated to the mechanical strength of hotpressed laminates, which was measured by a peel test. The polymer surfaces were further characterized by contact angle measurements.

Polar functional groups, carboxylic acid and butyl ester in hotpressed laminates were found to form Lewis acid/base interactions with the aluminium oxide. The strength of the interfacial interactions was correlated to the concentration and acidity/basicity of the group, the acid group being the most efficient. A silane functional group provided strong adhesion to the laminates at a much lower concentration than the polar groups. Silanols as well as Al-O-Si linkages were detected at the polymer/aluminium interface.     

An FT-IR Study on Interfacial Interactions in Ethylene Copolymers/Aluminium Laminates in Relation to Adhesion Properties

The effect of three different functional groups in ethylene copolymers on the adhesion with aluminium was studied. The interface in polymer/metal laminates was analyzed by FT-IR, and the adhesion mechanism for each functional group was evaluated. Laminate samples were prepared by solution casting or by hotpressing polymeric film onto the aluminium substrate. In the latter case, the interface was exposed by solvent extraction. The interfacial structures developed by the different copolymers were correlated to the mechanical strength of hotpressed laminates, which was measured by a peel test. The polymer surfaces were further characterized by contact angle measurements.

Polar functional groups, carboxylic acid and butyl ester in hotpressed laminates were found to form Lewis acid/base interactions with the aluminium oxide. The strength of the interfacial interactions was correlated to the concentration and acidity/basicity of the group, the acid group being the most efficient. A silane functional group provided strong adhesion to the laminates at a much lower concentration than the polar groups. Silanols as well as Al-O-Si linkages were detected at the polymer/aluminium interface.     

XPS/AFM study of the PET surface modified by oxygen and carbon dioxide plasmas: Al/PET adhesion

The formation of the interface between aluminium and O₂ or CO₂ plasma-modified poly(ethylene terephthalate) (PET) has been investigated by X-ray photoelectron spectroscopy (XPS). As demonstrated by the changes in the C 1s, O 1s, and A1 2p core level spectra upon A1 deposition, the metal was found to react preferentially with the original ester, with the plasma-induced carboxyl and carbonyl groups to form interfacial complexes. The phenyl ring at the modified PET surface was seen to be involved in the formation of the interface, but to a lesser extent. This confirms the high reactivity of the oxygen-containing groups towards the deposited A1 atoms. The adhesion between A1 and the plasma-modified PET films was evaluated by means of a 180° peel test. A considerable (up to ten times) improvement in adhesion was achieved by plasma treatment of the PET substrate, but for either plasma gas the adhesion strength was found to depend strongly on the plasma power and treatment time. The results are discussed in terms of the concentration of oxygen-containing groups at the polymer surface, the surface topography, and the possible presence of low-molecular-weight materials at the metal-polymer interface.     

Influence of corona treatment on adhesion and mechanical properties in metal/polymer/metal systems

The effect of corona treatment (CT) on the adhesion at the metal–polymer interface was studied. Metal/polymer/metal laminates were manufactured by the laboratory roll‐bonding process with preliminary corona surface treatment of the polymer core: a polyethylene and polypropylene sheet as well as steel sheet. It was treated with corona discharge to increase its surface energy and the adhesion to metal, an austenitic steel. The adhesion, which was measured by T‐peel and shear tests, was increased by 43% of crack peel and 22% of mean peel resistance respectively, after 120 s CT. On the basis of scanning electron spectroscopy observations, improvements in the adhesive properties were attributed to the change in the interfacial morphology. In mechanical tests, yield and tensile strengths were strongly influenced by CT, indicating that these laminates were sensitive to interfacial phenomena. However, elongation at rupture of the composites was found to be unchanged. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.     

Analysis of the Molecular Structure at the PPS/Copper Interphase and its Role in Adhesion

X-ray photoelectron spectroscopy (XPS) was used to examine the interfacial chemistry in polyphenylene sulfide (PPS)/copper bonded laminates. Several surface pretreatments were studied including a simple methanol wash, two acid etches, thermal oxidation and chemical oxidation. Peel test analysis showed poor adhesion to the methanol-washed and acid-etched foils, giving a peel strength of only 3-5 g/mm. XPS analysis of the failure surfaces revealed a large amount of inorganic sulfide at the interface with reduction of the copper oxide. Chemical oxidation using an alkaline potassium persulfate solution gave a matt-black surface consisting of primarily cupric oxide. These samples showed improved adhesion and XPS analysis of the failure surfaces revealed fracture through a mixed PPS/cuprous oxide layer. A simple thermal oxidation yielded a cuprous oxide surface layer and laminates bonded to these surfaces showed a more than ten-fold increase in peel strength. XPS analysis of the failure surfaces showed much lower amounts of interfacial copper sulfide and it was postulated that excess sulfide at the interface was responsible for the poor adhesion observed for other pretreatments.     

Plasma graft polymerization of vinylimidazole onto Kapton film surface for improvement of adhesion between Kapton film and copper

Kapton film was modified by means of the plasma graft polymerization of vinylimidazole for the improvement of the adhesion with copper metal. Argon plasma exposure generated hydroperoxides at the surface of the Kapton film. Hydroperoxides generated by the argon plasma exposure could initiate the graft polymerization of vinylimidazole. The graft polymerization was restricted at the surface of the Kapton film and never occurred on the inside of the Kapton film. The graft polymer layer was 150–200 nm thick. The surface modification by the plasma graft polymerization of vinylimidazole led to the improvement of adhesion between Kapton film and copper metal. A part of the copper metal made a complex with imino groups in the vinylimidazole chains graft-polymerized onto Kapton film. The complex is considered to contribute to the improvement of the adhesion. © 1995 John Wiley & Sons, Inc.     

Surface modification of polymers and improvement of the adhesion between evaporated copper metal film and a polymer. I. Chemical modification of PET

To improve the interfacial adhesion between evaporated copper film and poly(ethylene terephthalate) (PET), the surface of PET films was modified by treating with hydrazine monohydrate. The effect of the treatment time in the range of 5-20 min with 80 wt% hydrazine monohydrate at 60 °C on the number of polar groups created on PET was investigated. The surface topography of and water contact angle on the PET film surface, the mechanical properties of the PET film, and the adhesion strength of evaporated copper metal film to the PET film surface were also investigated. The introduction of polar groups on the modified PET film surface was examined by FT-IR and ESCA analyses. The amount of polar groups increased to the maximum value with increasing treatment time to 10 min, and thereafter it decreased markedly. The surface roughness increased with increasing treatment time up to 10 min and cracks occurred after 20 min. The water contact angle and tensile properties decreased with increasing treatment time. Using the scratch test, the adhesion between Cu film and PET was found to increase with increasing treatment time up to 10 min and thereafter there was a remarkable decrease in adhesion. From these results, it was concluded that the optimum treatment time with hydrazine monohydrate (80 wt%) at 60°C was about 10 min to improve copper-PET adhesion.     

Interfacial Adhesion of Polyamide 66 Fibres to an Aqueous Polyurethane–Acrylic Hybrid Polymer Adhesive

In this work, the interfacial adhesion between a polyamide 66 fibre, and an aqueous polyurethane–acrylic hybrid polymer adhesive was investigated. Silane and air plasma treatments were introduced to modify the surface of the polyamide 66 fibre. The surface chemistry was characterised using X-ray photoelectron spectroscopy (XPS). There were more oxygen-containing functional groups, –OH or –COOH, introduced by air plasma and silane treatments on the surface of polyamide fibre to increase its chemical activity. The microbond test was used to measure the interfacial shear strength (IFSS) between the waterborne polyurethane–acrylic hybrid polymer adhesive and a polyamide fibre. It has been found that air plasma and silane surface treatments can be used to improve interfacial adhesion. IFSS at 8.7 and 5.9 MPa, respectively, were higher than that of the control, 5.0 MPa. After water immersion at 50°C for 48 h, IFSS dropped to 7.0 MPa for air plasma-treated specimen and to 4.4 and 4.1 MPa for silanised and control specimens, respectively. Air plasma surface treatment is more effective than silane treatment to improve the interface adhesion in the polymer fibre–polymer composite.     

Metal–polymer nanocomposites produced by the melt‐compounding interaction of an aliphatic polyamide with metal particles

Composites prepared at 200°C by the melt compounding of copolymer polyamide 6/66 and ferric chloride, ferric oxalate, cupric chloride, cupric formiate, cupric acetate, Cr‐carbonyl, Mo‐carbonyl, or W‐carbonyl have been studied. The solution stability and aggregation suppression for nanoparticles in a polyamide can be explained by the formation of stable polymer–metal complexes. The nitrogen atoms of amide and amine groups of polymers serve as ligands for the coordination compounds that form. The dynamic viscosity of the solutions suggests that Cr‐carbonyl forms mostly intermolecular complexes, whereas ferric oxalate, ferric chloride, cupric formiate, cupric acetate, cupric chloride, Cr‐carbonyl, Mo‐carbonyl, and W‐carbonyl form intramolecular complexes. The critical concentrations for metal‐containing compounds at which a dispersion rises to nanodimensions without aggregating in the polymer matrix under the experimental conditions are 0.024 wt % for ferric oxalate, 0.12 wt % for ferric chloride, 0.08 wt % for cupric formiate, 0.096 wt % for cupric acetate, and 0.19 wt % for cupric chloride. Metal carbonyls undergo dispersion (with their concentration up to 5 wt %) in polyamide 6/66 without aggregating into larger formations. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Photochemical surface modification of poly(ethylene terephthalate)

To elucidate the role of chemical interactions in the promotion of metal–polymer adhesion, a poly(ethylene terephalate)/copper system was studied. Surface photografting of unsaturated monomers containing different chemical functional groups onto a three-mil poly(ethylene terephthalate) film provided a means of examining a variety of copper-polymer interfaces. Initial graft verification was accomplished via contact angle measurements. Adhesion strengths to vacuum-deposited copper were determined using 90° peel tests. Graft analysis, as well as investigation of the interfacial interaction between copper and the grafted moieties, was accomplished using X-ray photoelectron spectroscopy.     

Adhesion Improvement of Poly(Phenylene-Vinylene) Substrates Induced by Argon-Oxygen Plasma Treatment

Copper films evaporated on argon-oxygen plasma-treated poly(phenylene-vinylene) films have been studied by scratch test, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The adhesion of the metallic film to the polymer substrate was greatly enhanced after treatment and found to increase with the treatment time. SEM observation of the treated samples revealed that the morphology of the polymer surface was gradually changed with the treatment time as compared with that of the bare polymer film. On the other hand, XPS analysis of the polymer-metal interface showed that the bonding between carbon, oxygen and copper were subsequently modified as compared with those obtained in untreated samples. The high adhesion strength observed on these substrates was related to the modification in the surface morphology on the one hand and to the formation of new compounds at the polymer-metal interface on the other. The nature of the interfacial layer and its influence on the adhesion of the copper layer was discussed by comparing the results with those obtained in poly(phenylene-vinylene) (PPV)-Al systems.     

Adhesion Improvement of Poly(Phenylene-Vinylene) Substrates Induced by Argon-Oxygen Plasma Treatment

Copper films evaporated on argon-oxygen plasma-treated poly(phenylene-vinylene) films have been studied by scratch test, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The adhesion of the metallic film to the polymer substrate was greatly enhanced after treatment and found to increase with the treatment time. SEM observation of the treated samples revealed that the morphology of the polymer surface was gradually changed with the treatment time as compared with that of the bare polymer film. On the other hand, XPS analysis of the polymer-metal interface showed that the bonding between carbon, oxygen and copper were subsequently modified as compared with those obtained in untreated samples. The high adhesion strength observed on these substrates was related to the modification in the surface morphology on the one hand and to the formation of new compounds at the polymer-metal interface on the other. The nature of the interfacial layer and its influence on the adhesion of the copper layer was discussed by comparing the results with those obtained in poly(phenylene-vinylene) (PPV)-Al systems.     

Dissolution of copper scrap in hydrochloric acid

The dissolution of copper scrap has been investigated as a possible approach to the production of copper chloride solutions for certain metallurgical purposes. The principal stages involved in the dissolution have been found to be (1) diffusion-controlled attack of cupric ions on the surface of the copper, and (2) re-oxidation of cuprous ions by oxygen. The effects of chloride concentration, acidity, temperature, agitation, metal surface area and oxygen partial pressure are described.     

Microstructure,adhesion strength and failure path at a polymer/roughened metal interface

Metals and polymers are extensively used in microelectronics packaging where they are joined together. Since both the yield and reliability of packages are strongly affected by the interfacial adhesion between polymers and metals, extensive studies have been performed in order to improve the resistance to debonding of many resulting interfaces. In the present work, the interfacial fracture energy of representative polymer/metal interfaces commonly encountered in micoroelectronics packaging was characterized. A copper-based alloy leadframe was used as the metal and an epoxy molding compound (EMC) was used as the polymer. The leadframe surfaces were roughened by chemical oxidation in a hot alkaline solution and molded with the EMC. In general, roughening of metal surfaces enhances their adhesion to polymers by mechanical interlocking, yet often produces a cohesive failure in the polymer. Sandwiched double-cantilever beam (SDCB) specimens were employed to measure the adhesion strength in terms of interfacial fracture energy. After the adhesion test, the microstructures of metal surfaces before molding with the EMC were correlated to the adhesion strength, and the fracture surfaces were analyzed using various techniques to determine the failure path.     

Physicochemical and Adhesion Characteristics of High-Density Polyethylene when Treated in a Low-Pressure Plasma under Different Electrodes

The present investigation studys the effects of different electrodes such as copper, nickel, and stainless steel under low-pressure plasma on physicochemical and adhesion characteristics of high-density polyethylene (HDPE). To estimate the extent of surface modification, the surface energies of the polymer surfaces exposed to low-pressure plasmas have been determined by measuring contact angles using two standard test liquids of known surface energies. It is observed that the surface energy and its polar component increase with increasing exposure time, attain a maximum, and then decrease. The increase in surface energy and its polar component is relatively more important when the polymer is exposed under a stainless-steel electrode followed by a nickel and then a copper electrode. The dispersion component of surface energy remains almost unaffected. The surfaces have also been studied by optical microscopy and electron spectroscopy for chemical analysis (ESCA). It is observed that when the HDPE is exposed under these electrodes, single crystals of shish kebab structure form, and the extent of formation of crystals is higher under a stainless-steel electrode followed by nickel and then copper electrodes. Exposure of the polymer under low-pressure plasma has essentially incorporated oxygen functionalities on the polymer surface as detected by ESCA. Furthermore the ESCA studies strongly emphasize that higher incorporation of oxygen functionalities are obtained when the polymer is exposed to low-pressure plasma under a stainless-steel electrode followed by nickel and then copper electrodes. These oxygen functionalities have been transformed into various polar functional groups, which have been attributed to increases in the polar component of surface energy as well as the total surface energy of the polymer. Therefore, the maximum increase in surface energy results in stronger adhesion of the polymer when the polymer is exposed under a stainless-steel electrode rather than nickel and copper electrodes.     

The level of matrix-filler interfacial adhesion in metal and polymer nanocomposites reinforced with carbon nanotubes

In this paper, the interfacial adhesion between metal matrix and carbon nanotubes (CNTs) is determined in various metal/CNT nanocomposites by several models. The models apply the experimental data to calculate the interfacial parameters. A good correlation is acquired between theoretical and experimental results which validates the current analysis. The calculated parameters reveal the formation of a perfect adhesion at the interface between the metal matrix and CNT in all reported samples. In addition, the calculations are compared with similar results for polymer nanocomposites which show a stronger adhesion at metal–CNT interface in comparison to polymer–filler interfacial adhesion in polymer nanocomposites.