Adhesion of Polyethylene to Copper: Importance of Substrate Topography

In order to get good adhesion between polyethylene and copper previous workers have oxidized the metal in alkaline solution to give a matt black oxide film. In this paper it is shown that the good adhesion obtained is associated with the very rough, fibrous nature of the matt black oxide film. Adhesion rises as the layer develops on the copper. If the fibres are damaged to alter the topography without changing the chemical nature of the substrate, the adhesion falls markedly. If the chemical nature of the oxide film is changed by electrolytic reduction, with minimum change in topography, the adhesion is still substantial. Adhesion to these matt black oxide films is still good if oxidation of the polymer is suppressed either by incorporation of stabilizers or by coating in a nitrogen atmosphere. This further points to the importance of topography in adhesion to these surfaces.     

The influence of cooling rate on the adhesion of polyethylene coatings applied to metals as a hot melt

The quenching from the melt of polyethylene coatings on steel, polished copper and black-oxidized copper increased their adhesion. The fracture surfaces examined in a scanning electron microscope showed the quenched polymer had a more fibrous texture. Quenching lowered the crystallinity and yield strength of the polymer but greatly increased its elongation at break requiring a greater energy for fracture. The tear strength also was higher. The increased adhesion is attributed to the changed mechanical properties of the quenched polymer, particularly to its increased fracture energy.     

Surface modification of polyether ether ketone (peek) films for flexible printed circuit boards

The surface of polyether ether ketone (PEEK) films was modified using plasma treatment, corona, or surface etching to improve their adhesion with regard to glued copper foils and copper layers generated by physical vapor deposition. After the pretreatments, surface chemical analysis was performed by X-ray photoelectron spectroscopy (XPS). The wetting behavior was qualitatively investigated by contact angle measurements. Surface topography was monitored by laser scanning microscopy (LSM). After coating, the adhesion strength of the copper layer was measured by a peel force test. Plasma treatment, corona discharge, or etching lead to a significant increase in adhesion. This increase is caused by a change in surface topography as well as by the incorporation of polar groups into the surface.     

Surface modification of polyether ether ketone (peek) films for flexible printed circuit boards

The surface of polyether ether ketone (PEEK) films was modified using plasma treatment, corona, or surface etching to improve their adhesion with regard to glued copper foils and copper layers generated by physical vapor deposition. After the pretreatments, surface chemical analysis was performed by X-ray photoelectron spectroscopy (XPS). The wetting behavior was qualitatively investigated by contact angle measurements. Surface topography was monitored by laser scanning microscopy (LSM). After coating, the adhesion strength of the copper layer was measured by a peel force test. Plasma treatment, corona discharge, or etching lead to a significant increase in adhesion. This increase is caused by a change in surface topography as well as by the incorporation of polar groups into the surface.     

SURFACE MODIFICATION OF POLYETHER ETHER KETONE (PEEK) FILMS FOR FLEXIBLE PRINTED CIRCUIT BOARDS

The surface of polyether ether ketone (PEEK) films was modified using plasma treatment, corona, or surface etching to improve their adhesion with regard to glued copper foils and copper layers generated by physical vapor deposition. After the pretreatments, surface chemical analysis was performed by X-ray photoelectron spectroscopy (XPS). The wetting behavior was qualitatively investigated by contact angle measurements. Surface topography was monitored by laser scanning microscopy (LSM). After coating, the adhesion strength of the copper layer was measured by a peel force test. Plasma treatment, corona discharge, or etching lead to a significant increase in adhesion. This increase is caused by a change in surface topography as well as by the incorporation of polar groups into the surface.     

SURFACE MODIFICATION OF POLYETHER ETHER KETONE (PEEK) FILMS FOR FLEXIBLE PRINTED CIRCUIT BOARDS

The surface of polyether ether ketone (PEEK) films was modified using plasma treatment, corona, or surface etching to improve their adhesion with regard to glued copper foils and copper layers generated by physical vapor deposition. After the pretreatments, surface chemical analysis was performed by X-ray photoelectron spectroscopy (XPS). The wetting behavior was qualitatively investigated by contact angle measurements. Surface topography was monitored by laser scanning microscopy (LSM). After coating, the adhesion strength of the copper layer was measured by a peel force test. Plasma treatment, corona discharge, or etching lead to a significant increase in adhesion. This increase is caused by a change in surface topography as well as by the incorporation of polar groups into the surface.     

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.     

The adhesion between electrolessly deposited copper and a photoimageable polymer

We investigated the relationship between the peel adhesion of copper, deposited by electroless plating, to a photoimageable polymer and the time of chemical etching before plating. Mechanical interlocking is generally considered as being the adhesion mechanism between deposited metals and substrates. However, we found that the peel strength decreased with an increase in the etching time though the polymer roughness did not change. The glass transition temperature of the photoimageable polymer became lower as the etching time increased. The pretreatment not only roughened the surface of the photoimageable polymer, but also affected the bulk polymer and the adhesion.     

Effects of solvent exposure on the adhesion of grafted PE to EVOH copolymer

Multilayer polymers are gaining popularity in many industrial applications, where the combination of various advantages of the individual materials may be exploited (e.g. mechanical strength and chemical resistance). Such materials rely heavily on the quality of interfacial adhesion and this in turn may alter with solvent exposure. Here, we study the ageing of a multilayer high density polyethylene, grafted polyethylene (PEg), ethylene/vinyl alcohol copolymer (EVOH) assembly in organic solvents, and its effect on the T-peel resistance of the EVOH/PEg interface (interphase). Apolar solvents absorb essentially in the polyethylenic materials leading to reduced peel strength due to modification of polymer bulk properties, rather than to changes in intrinsic adhesion strength. Ethanol diffuses readily into the EVOH leading to an intrinsic drop in energy of adhesion. In the cases studied, reduction of interfacial, peel strength was found to be largely reversible on drying the polymer assembly.     

The effect of fluorination on the surface characteristics and adhesive properties of polyethylene and polypropylene

Polyethylene and polypropylene have been treated with fluorine/nitrogen or fluorine/oxygen/nitrogen mixtures at atmospheric pressure. Changes in surface chemistry and topography as well as depth of fluorination have been examined using Fourier transform infra-red analysis, X-ray photoelectron spectroscopy (X.p.s.), atomic force microscopy (AFM) and ellipsometry. Even very short exposure times caused a large substitution of the hydrogen atoms by fluorine. No change in surface topography was noticed at magnifications of up to 5000 times with the scanning electron microscope (SEM), but AFM showed that fluorination led to an increase of microroughness. The influence of fluorine or fluorine/oxygen concentration, as well as time of treatment and time of storage before adhesive bonding, on adhesion of polypropylene to steel was investigated with a bending peel test. Significant improvement in peel strength was already achieved with minor fluorination intensity. Increase of fluorination intensity did not lead to further improvement in peel strength. Analysis of the fracture surfaces was carried out with the SEM and by energy dispersive X-ray spectroscopy and X.p.s. The findings showed that the samples failed cohesively in the polymer or directly beneath the fluorinated layer. A model to describe the formation of specific interactions between substrate and adhesive is suggested.     

Adhesion to Plasma-Modified LaRC-TPI II. Effect of Plasma Treatment on Peel Strength

LaRC-TPI, an aromatic thermoplastic polyimide, was exposed to oxygen, argon and ammonia plasmas as pretreatments for adhesive bonding. A 180[ddot] peel test with an acrylate-based pressure sensitive adhesive tape as an adherend was utilized to study the interactions of the plasma-treated polyimide surface with another polymeric material. The peel strengths of the pressure sensitive adhesive tape on the plasma-treated LaRC-TPI fell below the level of the non-treated controls, regardless of the plasma treatment used. Failure surface analysis by XPS revealed the presence of polyimide on the pressure sensitive adhesive failure surface, indicating failure in the plane of a weak boundary layer created by plasma treatment. The removal of the weak boundary layer by a solvent rinse restored the peel strength to the level of the control. Comparison with tape adhesion peel strengths of oxygen plasma-treated high density polyethylene showed that the physical condition of a polymer surface following plasma treatment plays an important role in determining the level of adhesion which can be achieved.     

Aqueous pretreatment of polyetherimide to facilitate the bonding of electrolessly deposited metals. Part 2. Solubilizer-free systems

An aqueous method for chemically pretreating polyetherimide substrates to promote adhesion to electrolessly deposited copper or nickel is described. The process consists of cleaning the polymer surface followed by surface normalization and debris removal. In contrast to previously developed processes, no separate adhesion promotion step is required. Peel strengths between 150-250 and 120-150 g/mm were achieved for copper and nickel, respectively. Scanning electron microscopy and X-ray photoelectron spectroscopy were utilized to investigate changes in the polymer surface morphology and chemistry during processing. Possible candidates for the different steps are presented, as are analyses of the failure loci following peel strength assessment.     

A study of the adhesion of polyethylene to porous alumina films using the scanning electron microscope

An adhesive bond was formed by sintering low-density polyethylene onto aluminum with a porous anodic film. The topography of the polymer surface in contact with the anodized aluminum was studied in a scanning electron microscope, having removed the aluminum and alumina by dissolution in aqueous sodium hydroxide. The surface of the polymer appeared very rough with large projections of various forms, all of which were many times larger than the pores revealed in the anodic films by transmission electron microscopy. These projections are shown to consist, most probably, of “stacks” or “tufts” of much smaller polyethylene fibers, each of which had entered a pore in the anodic film. Thus, the scanning electron-microscopic investigation confirms the keying mechanism for the adhesionof polyethylene to porous anodic films on aluminum proposed in an earlier paper.     

Surface modification of plasma‐pretreated high density polyethylene films by graft copolymerization for adhesion improvement with evaporated copper

Surface modification of Ar plasma‐pretreated high density polyethylene (HDPE) film via UV‐induced graft copolymerization with glycidyl methacrylate (GMA) and 2‐hydroxyethylacrylate (HEA) was carried out to improve the adhesion with evaporated copper. The surface compositions of the modified HDPE surfaces were characterized by X‐ray photoelectron spectroscopy (XPS). The adhesion strengths of evaporated copper with the graft‐copolymerized HDPE films were affected by the Ar plasma pretreatment time, the monomer concentration used for graft copolymerization, and the graft concentration. Post‐treatments, such as plasma post‐treatments after graft copolymerization and thermal treatment (curing) after metalization, further enhanced the adhesion strength of the Cu/HDPE laminates. The T‐type peel strengths of the laminates involving the graft‐modified and plasma posttreated HDPE films were greater than 15 N/cm. The enhanced adhesion strength resulted from the strong affinity of the graft chains for Cu and the fact that the graft chains were covalently tethered on the HDPE surface. XPS characterization of the delaminated surfaces of the Cu/HDPE laminates revealed that the failure mode of the laminates with T‐peel adhesion strengths greater than 5 N/cm was cohesive in nature.     

Adhesion of flame-treated polyolefins to styrene butadiene rubber

Samples of polyethylene and polypropylene have been submitted to repeated short duration (75 ms) flame treatments, at optimum flaming conditions. Surface energies of untreated and flamed specimens were determined by liquid contact angle measurements. It appears that the surface energy of polyethylene increases much more than that of polypropylene after flame treatment. The flamed polymer surfaces were further examined by electron spectroscopy, Fourier Transform IR spectroscopy and secondary ions mass spectrometry. The adhesion properties of modified polymer surfaces were studied by testing in peel the bonded Styrene Butadiene Rubber/polyolefins assemblies. Scanning electron microscopy (SEM) and water contact angle measurements have been used to observe the locus of failure. Good correlations were obtained between surface energy and adhesion strength, the increase in adhesion strength being particularly important for flamed PE/SBR assemblies. In addition, the peeling in a liquid medium allowed the determination of the respective contribution to adhesion of chemical and physical interactions. It is shown that a major part of the adhesion strength increase is of chemical origin, particularly for the bonded flamed PE/SBR assemblies.     

Mechanical factors in the adhesion of polyethylene to aluminium

The adhesion of low-density polyethylene to porous anodic films on aluminum was studied using the 180° peel test. Relative values of bond strengths, obtained by using polymer with and without antioxidant and by forming the bond in air or in vacuo, indicated that good adhesion could be obtained, despite previous evidence to the contrary, in conditions where oxidation of the polyethylene was suppressed. The relation between peel strength and anodic film thickness and film-forming voltage implied that the polyethylene entered pores in the film during bond formation. This was supported by the change of the category of the adhesion to one dependent upon polymer oxidation when the pores in the anodic film were sealed prior to bond formation. It is suggested that the mechanism of adhesion to porous anodic films on aluminum involves keying of the polymer into the pores in the film.     

Effect of grafting of acrylic acid onto PET film surfaces by UV irradiation on the adhesion of PSAs

To improve the peel strength between a pressure-sensitive adhesive (PSA) and its substrate, grafting of acrylic acid (AA) onto the surface of poly(ethylene terephthalate) (PET) film was carried out. After AA was coated onto the surface of PET films using a spin coater, the coated PET films were irradiated by UV. To investigate the surface chemistry and topography of the PET-g-AA films, the grafted surface of the PET films was characterized by FT-IR spectroscopy, X-ray photoelectron spectroscopy (XPS) and scanning probe microscopy (SPM). From these investigations, the effects of grafting of AA at the surface of PET by UV irradiation were discussed. In addition, to determine the effect of grafting on the adhesion between PSA polymer and PET-g-AA films, peel strength was measured after the PSA/PET-g-AA system was cured at various temperatures. As the esterification between PSA polymer and PET-g-AA films occurred in the interfacial region, the peel strength of the PSA/PET-g-AA system generally increased with increasing curing temperature.     

Electroplating on crystalline polypropylene. I. Compression molding and adhesion

A direct relationship between polymer processing and metal adhesion is evident from studies of compression-molded isotactic polypropylene (PP). Cooling rate, nature of the mold surface, and after-plated annealing are shown to affect the peel adhesion of the plated components. This report described (1) the relation of compression molding variables to polymer surface morphology, (2) the oxidative cracking behavior of the surface due to pretreatment with chromic–sulfuric acid in terms of crystallite orientation and crystallinity, and (3) the effect of surface crack patterns on adhesion. The nature of the mold surface is the single most important variable for controlling the surface morphology of PP. Compression molding PP against oxidized aluminum or copper produces a spherulitic surface, whereas molding the polymer against Mylar or Teflon produces a transcrystalline surface. Surface etching of PP homopolymer produces sponge-like crack patterns characteristic of the morphology. Radial patterns are observed on spherulitic surfaces and random patterns, on transcrystalline ones. The various surface patterns are developed in the oxidative process by swelling of amorphous material followed by oxidative stress cracking and dissolution. Metal-to-polymer adhesion, as measured by the peel test, may involve failure at the interface or within the polymer. Three factors are shown to be important: (a) the geometry of the interface, (b) the diminished strength of the polymer surface arising from attack by the oxidizing acid, and (c) the crystallinity of the fissured polymer surface. The highest peel values are associated with conditions that lead to deep and frequent fissuring of the polymer surface and minimum oxidative damage.     

Improved cathodic disbondment performance of polyethylene blends

Cathodic disbondment (CD) performance of a range of modified polyethylenes (PE) compression molded on to steel plates at 320°C is reported. Adhesion strength was measured by the 90° peel test and good dry adhesion strength was obtained for all modified polyethylene materials and blends, as well as for the neat polymer. It is shown that dry bond strength does not correlate with CD performance. Initial results of wet peel tests of samples in various concentrations of NaOH are presented where it is observed that for samples with improved wet adhesion strength, CD performance was also improved. Surface polarity was determined from contact angle measurements, and it is shown that increased surface polarity of the coating was not the only determinant for improved CD performance. Inorganic fillers such as talc were also found to improve CD performance by changing the bulk properties, with little measurable change in polarity. Some mechanistic aspects of CD performance are also discussed.     

Thermodynamics of polymer-paper adhesion: a review

A review of studies of polymer-paper adhesion illustrates the thermodynamic nature of the bondability of polymers to plain, uncoated paper surfaces. The bond strength depends strongly on the chemical nature of the polymer surface and on that of the fibrous paper surface. Adhesion to paper may be characterized indirectly through thermodynamic analysis of the paper substrate, or directly through paper laminate or adhesion tape peel testing. The need for adequate paper adhesion is emphasized, particularly for some of the newer printing processes (electrophotographic and thermal imaging). It is concluded that some of the indirect methods of adhesion characterization (surface energetics analysis via contact angle measurements or the inverse gas chromatography technique) may serve to characterize paper adhesion in these processes.