Improved adhesion between Kapton film and copper metal by silane-coupling reactions

Kapton film, poly[(N,N′-oxydiphenylene)pyromellitimide], was modified by silane-coupling reactions using 3′(trimethoxysilyl)propoxy-2-hydroxypro-pyl-1,3-diazole (Si–imidazole) to improve the adhesion with copper metal. The Kapton film surface was first treated with argon plasma for 30 s, then dipped into a methanol solution of Si–imidazole (0.01 wt %), followed by heating at 110°C for 90 min. The Kapton surfaces, modified by the argon plasma and Si–imizadole coupling reactions, were analyzed by water contact-angle measurement, atomic force microscopy, and XPS. The Si–imidazole modification showed a large increase in adhesion between the copper metal and the Kapton film. The peel strength of the copper metal/Kapton film joint increased from 0.94 to 2.4 N/5 mm. The failure occurred at the interface between the Si–imidazole and the Kapton film layer. We conclude that the Si–imidazole modification is an effective treatment for improvement of the adhesion between copper metal and Kapton film. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1645–1654, 1999     

Effect of the type of plasma on the polydimethylsiloxane/collagen composites adhesive properties

Polydimethylsiloxane (PDMS) films were treated with either oxygen (O₂), nitrogen (N₂) or argon (Ar) plasma between 40 W and 120 W for 5–15 min and their surface properties studied by contact angle measurements, infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and atomic force microscopy (AFM). Lower contact angles and increases in surface roughness, assessed by SEM and AFM, were observed for all used gases when plasma power and time increased, with argon treatment being the one that showed the most significant change in roughness.PDMS/collagen type I composites obtained after treating PDMS with oxygen at 80 W for 13 min or nitrogen and argon at 80 W for 14 min showed a peel strength of 0.1N/mm (oxygen plasma), 0.08 N/mm (nitrogen plasma) and 0.09 N/mm (argon plasma). In all cases, peel strength was higher than that measured for the untreated bilayer composite. An increase in adhesion strength, after oxygen and nitrogen plasma, was mostly attributed to chemical interaction between functional groups introduced on the PDMS surface and the functional groups on collagen as detected by FTIR. In contrast, the high peel strength observed on PDMS treated with argon plasma was attributed to its increased roughness which in turn increased mechanical interlocking. The properties of these composites render them suitable for adhesive free skin substitutes.     

Changes in the Peeled Surfaces of Copper Thin Films Deposited on Polyimide Substrates After Heat Treatment

Peel strength between a copper (Cu) thin film and a polyimide (pyromellitic dianhydride-oxydianiline, or PMDA-ODA) substrate is reduced by heat treatment at 150°C in air. In this work, we investigated the peel strength, the morphology of the interface between Cu films and polyimide substrates using optical microscopy and electron microscopy, and chemical change of the interface using Auger electron spectroscopy (AES) and micro X-ray photoelectron spectroscopy (XPS). The analysis showed that CuO “lumps” were present on the peeled surface of PMDA-ODA after heat treatment at 150°C in air. The peeled surfaces of other polyimide substrates were also analyzed: biphenyl dianhydride-para phenylene diamine (BPDA-PDA) and biphenyl dianhydride-oxydianiline (BPDA-ODA). CuO lumps were present on the peeled surface of BPDA-ODA after the heat treatment, but not that of BPDA-PDA. Compared with the adhesion strength for the Cu thin film, the adhesion strength was high for the Cu/PMDA-ODA and Cu/BPDA-ODA laminates, but the adhesion strength was very low for the Cu/BPDA-PDA laminate. This low strength is the reason that CuO lumps were not detected on the peeled surface of the BPDA-PDA substrate. These CuO lumps were related to the adhesion degradation of the Cu/polyimide laminates after the heat treatment.     

Study on brown oxidation process with imidazole group,mercapto group and heterocyclic compounds in printed circuit board industry

The adhesion strength of the interface between copper foil and resin is an important technological parameter for applications in microelectronics. In this study, a new brown oxidation solution of copper foil, including the recipe composition and reliability tests, was fully discussed. We provided an overview of brown oxidation process used in the semi-flexible printed circuit boards production industry by investigating the brown oxide film. The morphology of the copper oxide film was changed from lamellar structure to honeycomb structure with the increasing of oxidation time. The peel adhesion strength of the Cu/polyimide laminates was increased from about 2–16 N/cm by altering the immersion time and the concentration of inhibitors in brown oxidation solution. Scanning electron microscopy, peel tests and X-ray diffraction indicated that the higher adhesion strength was resulted from the rougher surface and the proper etching depth of copper foil, which was caused by chemical reactions on the interface surface of copper foil.     

Preparation and characterization of novel film adhesives based on cyanate ester resin for bonding advanced radome

In this paper, the novel film adhesives based on phenolphthalein poly(ether sulfone) (PES-C) and epoxy (EP) modified cyanate ester resin (CE) were prepared for bonding an advanced radome. The film adhesives are convenient for applying to manufacture, possessing good adhesion strength, thermal durability and excellent dielectric property. The curing behaviors were confirmed by differential scanning calorimetry (DSC), showing that the main reaction pathways are not varied with adding PES-C but the reaction rates are evidently accelerated, and the film adhesives can be well cured at lower temperature of 177 °C. The adhesion strength was evaluated in lap shear strength and peel strength, indicating that the better adhesion strength is obtained with increasing in PES-C. The maximum value of lap shear strength is 33 MPa at room temperature. The thermal durability was determined by thermal aging tests of lap shear specimens, showing that the decrease in strength gets faster with adding PES-C, and the usability of film adhesives over 2000 h at 200 °C. The dielectric properties were measured by dielectric resonator methods, finding that the introduction of PES-C brings a positive effect on dielectric properties. The lowest value of determined dielectric loss is 0.0075 at 10 GHz.     

Improvement in the adhesion of polyimide/epoxy joints using various curing agents

An improvement in the adhesion strength of polyimide/epoxy joints was obtained by (1) introducing a functional group on the polyimide surface, (2) improving the mechanical properties of the epoxy adhesive, (3) increasing the curing temperature, and (4) using polyamic acid as an adhesion‐promoting layer. The functional group on polyimide was introduced via treatment with aqueous KOH. An adhesion‐promoting layer was formed by spin coating polyamic acid onto a modified polyimide surface. The maximum adhesion strength of the polyimide/epoxy joint was obtained using polyamic acid as both the adhesion‐promoting layer and as the curing agent. The surface energy of the modified polyimide was examined using contact angle measurements and Fourier transform infrared spectroscopy, and the peel strength was determined by the T‐peel method. The peeled surfaces were analyzed using scanning electron microscopy and X‐ray photoelectron spectroscopy.© 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 812–820, 2002     

Adhesion improvement of electroless copper to a polyimide film substrate by combining surface microroughening and imide ring cleavage

In order to enhance the adhesion strength of copper metal film to a polyimide (PI) film substrate, a method combining surface microroughness formation and imide ring cleavage was investigated. The results showed that imide rings were cleaved with a KOH treatment while carboxyl and amide groups were formed on the surface of the PI film. The surface micro-roughness did not change with the KOH treatment, and the adhesion strength of the copper metal film to the PI film was slightly improved to 30 g/mm, which could be attributed to the interaction of both carboxyl and amide groups with the copper atoms. When the PI films were successively treated with an alkaline permanganate and a KOH solution, many recesses were formed on the surface in an alkaline permanganate solution, and the size and depth of the recesses increased with alkaline permanganate treatment time. The results of the AFM measurements showed that the average roughness (R) increased from 3.54 to 10.23 nm after combined treatment with alkaline permanganate and KOH solutions. The adhesion strength of the copper metal film to the PI film reached 150 g/mm, which was five times greater than that achieved with the KOH treatment only.     

Hydrothermal stability of Cr/polyimide interfaces

The hydrothermal stability of both Cr/polyimide and C₇₅Cr₂/polyimide interfaces has been studied using Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and peel testing. It was found that RF sputter treatment of the polyimide surface prior to metal deposition leads to an enhancement of adhesion through chemical bonding of the metal with polyimide. Owing to the enhanced chemical bonding at the interface, failure always occurs cohesively in the polyimide. The RF sputter treatment of the polyimide surface also simultaneously modifies the polyimide underneath the surface. The adhesion strength of the Cr/polyimide interface is degraded significantly upon exposure to high temperature and high humidity (85°C/81% relative humidity, T/H) environment. It is suggested that this degradation results from the hydrolysis of polyimide. The hydrolysis is facilitated by the presence of unstable modified polyimide near the interface. This degradation of adhesion strength can be minimized by converting the unstable modified polyimide to a stable state by reheating the Cr/polyimide interface at 400°C for 40 min before exposure to the T/H environment.     

Adhesion Properties and Structure of Ion-Beam Modified Polyimide Films

Polyimide (PI) surface modification was carried out by an ion beam treatment to improve the adhesion between the polyimide film and copper. The PI film surface was treated with an ion-beam source at ion doses ranging from 1.96 × 10¹³ to 2.38 × 10¹³ ions/cm² using a mixture of nitrogen (N₂) and hydrogen (H₂). Contact angle measurement, atomic force microscopy and X-ray photoelectron spectroscopy, respectively revealed an increase in the surface roughness, a decrease in contact angle, and the formation of oxygen complexes and functional groups on the treated PI surfaces. Adhesion between the copper and PI film treated with the beam was superior to that of the untreated PI film. The 90° peel test revealed the highest peel strength of 7.8 N/cm.     

Temperature effect on PI/Cu interface

The interfacial reaction and peel strength of polyimide with copper foil at various cure schedules have been investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and peel test to determine the temperature effect on polyimide/copper interface diffusion and adhesion. SEM studies indicate that the polyimide/copper interfaces are fairly smooth for all samples studied in this experiment. The TEM microstructure reveals the existence of a copper-polyimide interaction zone at the interface when it is cured at a temperature higher than 250°C, which also results in a high peel strength. XPS spectra revealed higher copper and carbonyl carbon contents at the polyimide interface when it is cured at a high-temperature schedule (350°C). From the results of these interface studies, it is concluded that chemical bonding resulting from the interaction of copper oxide and polyimide carbonyl group provides the binding force for polyimide and copper foil. © 1993 John Wiley & Sons, Inc.     

Metallization of polyimide film by wet process

The interfacial adhesion strength of metallized polyimide (BPDA/ODA/PDA) has been studied with respect to polyimide surface molecular structure, reactions during electroless nickel deposition, baking, copper electroplating, and thickness of polyimide film. Each factor is discussed in terms of its influence on the peel strength. For practical application, operation at optimized conditions for each step of the metallization process is essential for sustaining the mechanical integrity of the copper/polyimide laminate. © 1994 John Wiley & Sons, Inc.     

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 1.04 KN m⁻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.     

Surface modification of polyimide films by argon plasma for copper metallization on microelectronic flex substrates

Surface modification of polyimide films such as Kapton E(N) and Upilex S by argon plasma was investigated because of the enhanced adhesive strength with sputtered copper. Peel tests demonstrated this improvement, with a peel strength of 0.7 and 1.2 g/mm for unmodified Kapton E(N) and Upilex S, respectively, and 110.3 and 98 g/mm for argon plasma–modified Kapton E(N) and Upilex S, respectively, in certain plasma conditions. This study showed that the enhanced adhesive strength of polyimide films with sputtered copper by argon plasma was strongly affected by the surface characteristics such as surface morphology and surface energy of polyimide films. Atomic force microscopy and the sessile drop method indicated that the surface roughness and surface energy of the polyimide films were greatly increased by argon plasma, resulting in highly increased peel strength of the polyimide films with sputtered copper. It was observed in electron spectroscopy for chemical analysis (ESCA) that the increased surface energy of the polyimide films from argon plasma was a result of more of the surface being composed of O and N and of the increased number of C? O, C?O, and C? N chemical bonds. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 744–755, 2006     

Thermal graft copolymerization of 4-vinyl pyridine on polyimide to improve adhesion to copper

The surface of poly[N,N′-(oxydiphenylene)pyromellitimide] film, Kapton^® HN, was modified to improve its adhesion to copper metal. The polyimide surface was argon plasma activated and then exposed to air. A nitrogen-containing monomer, 4-vinyl pyridine, was then polymerized at elevated temperature under constant pressure between the argon plasma activated polyimide film and copper foil without any added photoinitiator. Optimization of the argon pretreatment time, curing temperature and curing duration resulted in almost doubling of the single lap shear strength. It is postulated that failure occurred mainly between the polyimide and the poly(4-vinyl pyridine).     

Synthesis of bamboo-like carbon nanotubes on a copper foil by catalytic chemical vapor deposition from ethanol

Bamboo-like carbon nanotubes (CNTs) were synthesized on a copper foil by catalytic chemical vapor deposition (CVD) from ethanol. The effects of temperature (700–1000 °C) and duration (5–60 min) on the growth of CNTs were investigated. Morphology and structure of the CNTs were characterized by scanning and transmission electron microscopy and Raman spectroscopy. The yield and size of the CNTs increased with temperature. Those prepared at 700 °C had a copper droplet tip and those at 800–900 °C had a copper nanoparticle inside. An amorphous carbon film consisted of a porous and non-porous layer was observed on the surface of the copper substrate, and the CNTs were really grown from this carbon film. The thickness of the carbon film increased from 187 to 900 nm when the duration increased from 5 to 60 min. It was also found that the copper foil became porous after ethanol CVD treatment. The growth mechanism of the CNTs, carbon film and motion of copper catalyst were discussed. It is proposed that a carbon film first deposited on the top surface of the copper foil while the top surface of the copper foil partially melted and migrated across the carbon film, where CNTs formed.     

Chitosan-grafted nonwoven geotextile for heavy metals sorption in sediments

Functionalized polypropylene nonwoven (PP) geotextiles can be used as a new eco-friendly way to trap heavy metals in sediments. Chitosan was chosen as sorbent because of its ability to trap heavy metals, its natural origin (from shells) and its low cost. PP was first functionalized with acrylic acid using a low pressure cold plasma process, in order to bring reactive carboxylic functions onto the surface. Chitosan was then covalently grafted on the acrylic acid modified PP. The functionalized surfaces were characterized by Fourier Transform Infrared Spectroscopy–Attenuated Total Reflectance (FTIR–ATR) and X-ray Photoelectron Spectroscopy (XPS) and evidence of chitosan grafting was given. The ability of the functionalized geotextile to trap heavy metals was then investigated. Copper was chosen as a model heavy metal, and artificial solutions of CuSO₄ were prepared for the experiments. Sorption studies were carried out at 20 °C with Polypropylene-grafted-Acrylic acid-Chitosan (PP-g-AA-chitosan) varying the concentration of copper in polluted solutions to evaluate the maximum of adsorption of the surface: the textile can chelate copper increasingly as a function of the initial copper concentration until 830 ppm. At this concentration, it reaches a plateau at about 30 mg of trapped copper per gram of geotextile. The effects of pH and of the ionic strength (adsorption in a NaCl containing solution) were finally investigated. The trapping of Cu²⁺ decreases slowly when the ionic strength increases. When there are 30 g/L NaCl in the artificial polluted solution (like in seawater), only 20 mg of Cu²⁺ can be trapped per g of geotextile. Finally, the optimum pH to trap the maximum amount of copper was determined to be 4.8, which corresponds to the optimum pH for the chitosan solubility.     

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.     

Development of hydroxyapatite coatings on laser textured 316 LSS and Ti-6Al-4V and its electrochemical behavior in SBF solution for orthopedic applications

The current work focused on the development of hydroxyapatite (HAP) coating on laser textured metallic implants using electrophoretic deposition. HAP was synthesized by sol-gel technique and its phase purity and surface morphology were confirmed by FT-IR, XRD and SEM analysis. 316 L SS and Ti-6Al-4V metal implants were polished and the surface was modified using Nd-YAG laser operating at a pulse interval of 10 ns at various overlapping rate of 0%, 25% and 50%. The laser treated surface was characterized for its surface roughness using surface profilometry and surface morphology. The surface roughness of the metallic implants was increased by increase in the overlapping rate. The prepared HAP powder was electrophoretically deposited on bare and laser textured Ti-6Al-4V and 316 L stainless steel followed by vacuum sintering at 300 °C for 2 h. Scratch analysis results showed an improvement in adhesion strength for the HAP coatings on laser treated specimens than untreated metal. Corrosion efficiency of the coated samples was studied in SBF solution using EIS and potentiodynamic polarization studies. The result from the corrosion experiments proved increased corrosion resistance property of laser textured coated samples when compared to bare alloy due to higher adhesion of HAP coating on the metal surface.     

Carboxymethylated polysaccharide-based films as carriers for acrylic pressure-sensitive adhesives

A novel application of a biodegradable polysaccharide-based film as a pressure-sensitive acrylic adhesive carrier has been reported. For film preparation carboxymethyl derivatives of starch (CMS) and cellulose (CMC) have been used. Based on physicochemical tests results (solubility in water, moisture absorption, mechanical properties) the most promising CMS/CMC 50/50 wt% film was selected as a carrier for an acrylic pressure-sensitive adhesive tape. Prepared double-sided self-adhesive tapes were characterized by good tack 5 N/2.5 cm, peel adhesion 12 N/2.5 cm and shear strength 90 N/6.25 cm² at 20 °C. Such acrylic self-adhesive tapes could find application in the paper industry.     

Microsphere pressure sensitive adhesives—acrylic polymer/montmorillonite clay nanocomposite materials

In this study, the synthesis and characterization of acrylic polymer/montmorillonite (MMT) clay nanocomposite pressure sensitive adhesives (PSA) are presented. Different types and amounts of modified and unmodified montmorillonite clays were dispersed in ethyl acrylate (EA)/2-ethylhexyl acrylate (2-EHA) monomer mixture, which was then polymerized using a suspension polymerization technique. Polymerization was monitored in-line using attenuated total reflectance-fourier transform infrared (ATR-FTIR) spectroscopy. The adhesion properties of the synthesized nanocomposite materials were determined using standard measurements of tack, peel and shear strength. Viscoelastic properties of dried adhesive films were analyzed using dynamic mechanical analysis (DMA). The results showed that the kinetics of suspension polymerization was independent of the addition of MMT clays. On the other hand, adhesive properties were strongly influenced by the type and the amount of MMT clay added. While peel strength and tack gradually decreased with higher amount of modified MMT clay, a substantial increase in shear strength was determined with a maximal value at 1 wt% of added MMT clay. Moderate influence on tack, peel and shear strength was observed when the unmodified type of MMT clay was used. DMA analysis showed an increase in storage modulus (G′) for adhesives synthesized with MMT clay addition, but no significant differences were determined between particular types of MMT clays. A decrease in tan δ value for adhesives with 1 wt% of added MMT clay was observed, which also concurs with higher shear strength and implies to the improved cohesion of adhesive.