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.     

Electroless plating of copper on fluorinated polyimide films modified by surface graft copolymerization with 1‐vinylimidazole and 4‐vinylpyridine

Electroless plating of copper via a tin‐free activation process was carried out effectively on two types of fluorinated polyimide (FPI) films modified by UV‐induced surface graft copolymerization with N‐containing monomers, such as 1‐vinylimidazole (VIDz) and 4‐vinyl pyridine (4VP). The graft copolymerization of VIDz and 4VP was carried out on the argon (Ar) plasma‐pretreated FPI films via a solvent‐free process under atmospheric conditions. X‐ray photoelectron spectroscopy (XPS) results showed that the VIDz graft‐copolymerized FPI surface (the VIDz‐g‐FPI surface) and 4VP graft‐copolymerized FPI surface (the 4VP‐g‐FPI surface) were much more susceptible to the electroless deposition of metals via the Sn‐free process than the pristine FPI surfaces, and the FPI surfaces modified by Ar plasma pretreatment alone. T‐peel adhesion strengths above 9 N/cm were achieved for the electrolessly deposited copper on both VIDz‐g‐FPI surfaces (the Cu/VIDz‐g‐FPI assemblies) and 4VP‐g‐FPI surfaces (the Cu/4VP‐g‐FPI assemblies). These adhesion strength values were much higher than those obtained for assemblies involving electrolessly deposited copper on pristine or on Ar plasma pretreated FPI films. The high adhesion strength of the Cu/VIDz‐g‐FPI and Cu/4VP‐g‐FPI assemblies was attributed to the synergistic effect of spatial interactions of the grafted VIDz or 4VP polymer chains with the copper atoms, and the fact that the VIDz or 4VP polymer chains were covalently tethered on the FPI surfaces. XPS results also revealed that the Cu/VIDz‐g‐FPI and Cu/4VP‐g‐FPI assemblies delaminated by cohesive failure inside the FPI films.     

Surface modification of low‐density polyethylene films by UV‐induced graft copolymerization with a fluorescent monomer

Surface modification of argon plasma–pretreated low‐density polyethylene (LDPE) film via UV‐induced graft copolymerization with a fluorescent monomer, (pyrenyl)methyl methacrylate (Py)MMA, was carried out. The chemical composition and morphology of the (Py)MMA‐graft‐copolymerized LDPE [(Py)MMA‐g‐LDPE] surfaces were characterized, respectively, by X‐ray photoelectron spectroscopy (XPS) and by atomic force microscopy (AFM). The concentration of the surface‐grafted (Py)MMA polymer increased with Ar plasma pretreatment time and UV graft copolymerization time. The photophysical properties of the (Py)MMA‐g‐LDPE surfaces were measured by fluorescence spectroscopy. After graft copolymerization with the fluorescent monomer, the surface of the LDPE film was found to have incorporated new and unique functionalities. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1526–1534, 2001     

Adhesion enhancement of thermally evaporated aluminum to surface graft copolymerized poly(tetrafluoroethylene) film

Surface modifications of Ar plasma-pretreated poly(tetrafluoroethylene) (PTFE) film via UV-induced graft copolymerization with glycidyl methacrylate (GMA) and 1-vinylimidazole (VIDz) were carried out to improve the adhesion with evaporated aluminum metal. The surface compositions of the graft copolymerized PTFE films were studied by X-ray photoelectron spectroscopy (XPS). The adhesion strength of the evaporated aluminum to the surface graft copolymerized PTFE film was affected by the type of monomer used for graft copolymerization, the graft concentration, the plasma post-treatment of the graft copolymerized PTFE surface prior to metallization, and the extent of thermal treatment after metallization. The optimum T-peel adhesion strengths of the Al/PTFE laminates were in excess of 10 and 5 N/cm, respectively, for the GMA and VIDz graft copolymerized PTFE films. These adhesion strengths are significantly higher than those obtained between the evaporated aluminum and the pristine or plasma-pretreated PTFE film. The mechanism of adhesion enhancement and the failure of the metal-polymer assembly were also investigated. It was observed that the failure occurred within the PTFE film. The strong adhesion between Al and PTFE arises from the charge-transfer interaction between the Al atom and the epoxide moiety of the grafted GMA polymer, as well as from the fact that the graft chains are covalently tethered on the PTFE film surface as a result of the grafting process.     

Lamination of conductive polypyrrole films to poly(tetrafluoroethylene) films via interfacial graft copolymerization

A simple technique for the lamination of a conductive polymer film to an inert dielectric polymer film was demonstrated. The electrochemically synthesized and p‐toluenesulfonic acid‐doped polypyrrole (PPY) film was laminated simultaneously to the argon plasma‐pretreated PTFE film during the thermally induced graft copolymerization of the PTFE surface with a functional monomer. The graft copolymerization was carried out using glycidyl methacrylate (GMA) monomer containing 20% v/v hexamethyldiamine (HMDA) and in the absence of any polymerization initiator. Thermally induced graft copolymerization of the GMA monomer on the PPY surface was minimal. The lap shear and T‐peel adhesion strengths of the laminates were found to be dependent on the GMA graft concentration on the PTFE surface, which, in turn, was affected by the plasma pretreatment time of the film. To increase the GMA graft concentration for the enhancement of adhesion strength, the plasma‐pretreated PTFE surfaces were premodified via UV‐induced graft copolymerization with GMA prior to the simultaneous thermal graft copolymerization and lamination process. The modified surfaces and interfaces were characterized by X‐ray photoelectron spectroscopy (XPS). Through XPS measurements of the delaminated surfaces, it was found that the PPY/PTFE laminates failed predominantly by cohesive failure inside the PTFE substrate. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 716–727, 2001     

Surface photografting of low-density polyethylene films and its relevance to photolamination

Surface modifications of pristine and ozone-pretreated low-density polyethylene (LDPE) films were carried out via UV-induced graft copolymerization with a photoinitiator-containing, epoxy-based commercial monomer (DuPont Somos? 6100 for solid imaging and optical lithography) and also with the photoinitiator-free acrylic acid (AAc). The chemical composition and microstructure of the graft copolymerized surfaces were studied by angle-resolved X-ray photoelectron spectroscopy (XPS). The concentration of surface grafted polymer increased with the UV illumination time and the monomer concentration. For LDPE films graft copolymerized with the epoxy-based monomer, surface chain rearrangement was not observed or was less well pronounced, due to the partial crosslinking of the grafted chains. Simultaneous photografting and photolamination between two LDPE films, or between a LDPE film and a poly(ethylene terephthalate) (PET) film, in the presence of either monomer system, were also investigated. The photolamination rates and strengths depend on the ozone pretreatment time, the UV illumination time, and the UV wavelength, as well as on the nature of the substrate materials. A shear adhesion strength approaching 150 N/cm² could be achieved with either monomer system, provided that the polymer films were pretreated with ozone. The failure mode of the photolaminated surfaces was cohesive in nature in the case of the photoinitiator-containing epoxy monomer, but was either cohesive or adhesional in nature (depending on the substrate assembly) in the case of the photoinitiator-free AAc monomer.     

Grafting of Epoxy Resin on Surface-modified Poly(tetrafluoroethylene) Films

An epoxy/PTFE composite was prepared by curing the epoxy resin on the surface-modified PTFE film. Surface modification of PTFE films was carried out via argon plasma pretreatment, followed by UV-induced graft copolymerization with glycidyl methacrylate (GMA). The film composite achieved a 90°-peel adhesion strength above 15 N/cm. The strong adhesion of the epoxy resin to PTFE arose from the fact that the epoxide groups of the grafted GMA chains were cured into the epoxy resin matrix to give rise to a highly crosslinked interphase, as well as the fact that the GMA chains were covalently tethered on the PTFE film surface. Delamination of the composite resulted in cohesive failure inside the PTFE film and gave rise to an epoxy resin surface with a covalently-adhered fluoropolymer layer. The surface composition and microstructures of the GMA graft-copolymerized PTFE (GMA-g-PTFE) films and those of the delaminated epoxy resin and PTFE film surfaces were characterized by X-ray photoelectron spectroscopy (XPS), water contact angle and scanning electron microscope (SEM) measurements. The delaminated epoxy resin surfaces were highly hydrophobic, having water contact angles of about 140°C. The value is higher than that of the pristine PTFE film surface of about 110°. The epoxy resin samples obtained from delamination of the epoxy/GMA-g-PTFE composites showed a lower rate of moisture sorption. All the fluorinated epoxy resin surfaces exhibited rather good stability when subjected to the Level 1 hydrothermal reliability tests.     

Grafting of Epoxy Resin on Surface-modified Poly(tetrafluoroethylene) Films

An epoxy/PTFE composite was prepared by curing the epoxy resin on the surface-modified PTFE film. Surface modification of PTFE films was carried out via argon plasma pretreatment, followed by UV-induced graft copolymerization with glycidyl methacrylate (GMA). The film composite achieved a 90°-peel adhesion strength above 15 N/cm. The strong adhesion of the epoxy resin to PTFE arose from the fact that the epoxide groups of the grafted GMA chains were cured into the epoxy resin matrix to give rise to a highly crosslinked interphase, as well as the fact that the GMA chains were covalently tethered on the PTFE film surface. Delamination of the composite resulted in cohesive failure inside the PTFE film and gave rise to an epoxy resin surface with a covalently-adhered fluoropolymer layer. The surface composition and microstructures of the GMA graft-copolymerized PTFE (GMA-g-PTFE) films and those of the delaminated epoxy resin and PTFE film surfaces were characterized by X-ray photoelectron spectroscopy (XPS), water contact angle and scanning electron microscope (SEM) measurements. The delaminated epoxy resin surfaces were highly hydrophobic, having water contact angles of about 140°C. The value is higher than that of the pristine PTFE film surface of about 110°. The epoxy resin samples obtained from delamination of the epoxy/GMA-g-PTFE composites showed a lower rate of moisture sorption. All the fluorinated epoxy resin surfaces exhibited rather good stability when subjected to the Level 1 hydrothermal reliability tests.     

Electroless Plating of Copper on Fluorinated Polyimide Films Modified by Plasma Graft Copolymerization and UV‐induced Graft Copolymerization with 4‐Vinylpyridine

Surface modification of two types of fluorinated polyimide (FPI) films, either by plasma polymerization and deposition of 4‐vinylpyridine (4VP) or by UV‐induced graft copolymerization with 4VP under atmospheric conditions, was carried out for adhesion enhancement with the electrolessly deposited copper. X‐ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) results revealed that the pyridine groups in the plasma polymerized 4VP (pp‐4VP) layer could be preserved to a large extent under proper glow discharge conditions. The grafted 4VP layer with well‐preserved pyridine groups was used not only as the chemisorption sites for the palladium complexes (without the need for prior sensitization by SnCl₂) during the electroless plating of copper, but also as an adhesion promotion layer for the electrolessly deposited copper. The T‐peel adhesion strength of the electrolessly deposited copper with both the 4VP plasma‐polymerized FPI (pp‐4VP‐FPI) film and the 4VP graft‐copolymerized FPI (4VP‐g‐FPI) film was much higher than that of the electrolessly deposited copper with the pristine or the Ar plasma‐treated FPI films. The high adhesion strength between the electrolessly deposited copper and the surface‐modified FPI film was attributed to the fact that the plasma‐polymerized and the UV graft‐copolymerized 4VP chains were covalently tethered on the FPI surfaces, as well as the fact that these grafted 4VP polymer chains were spatially and reactively distributed into the copper matrix.

     

Low‐temperature thermal graft copolymerization of 1‐vinyl imidazole on fluorinated polyimide films with simultaneous lamination of copper foils

A simple technique of thermal graft copolymerization of 1‐vinyl imidazole (VIDZ) on pristine and argon plasma pretreated fluorinated polyimide (FPI) films with simultaneous lamination of copper foils was demonstrated. The simultaneous thermal grafting and lamination process was carried out in the temperature range of 80–140°C under atmospheric conditions and in the complete absence of a polymerization initiator. Three different FPI samples of different chemical structures were employed in the present study. An optimum T‐peel strength about 15 N/cm was achieved for the copper/FPI laminate. The adhesion strength, however, decreased with increasing fluorine content in the FPI film. The onset of cohesive failure occurred in the FPI film for assemblies with T‐peel strength greater than 6 N/cm. The T‐peel strengths are reported as a function of the argon plasma pretreatment time of the FPI films and thermal lamination temperature. The adhesion strengths were compared to that of the similarly prepared copper/polyimide (Kapton HN) laminate. Time‐dependent water contact angle (Θ) measurements indicated that the surfaces of FPI films are significantly more hydrophobic and more resistant to water diffusion or hydration than the Kapton HN films. The surface compositions of the pristine FPI films, as well as the delaminated FPI films and copper foils were studied by X‐ray photoelectron spectroscopy. The thickness of the graft VIDZ polymer layer was in the order of 200 nm, as derived from the cross‐sectional view of the scanning electron micrograph. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1478–1489, 1999     

Thermal imidization of poly(amic acid) precursors on surface-modified poly(tetrafluoroethylene) films via graft copolymerization with glycidyl methacrylate

A novel method for preparing composites of polyimides (PI) laminated to poly(tetrafluoroethylene) (PTFE) films is reported. PI/PTFE composites were developed through thermal imidization of poly(amic acid) (PAA) precursors on surface-modified PTFE films. Surface modification of PTFE films was carried out via Ar plasma pretreatment of the films, followed by UV-induced graft copolymerization with glycidyl methacrylate (GMA). The surface composition and topography of the graft copolymerized PTFE films and the delaminated PI and PTFE surfaces were characterized by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM), respectively. The adhesion strengths of the PI (imidized PAA) on the GMA graft copolymerized PTFE films were evaluated as a function of various thermal imidization schedules. The adhesion reliability of the PI/PTFE composites was tested by a series of hydrothermal cycles. The development of strong Tpeel adhesion strengths of about 8 N/cm with excellent reliability for the PI/PTFE composites was attributable to the synergistic effect of coupling the curing of the epoxide functional groups of the grafted GMA chains with the imidization process of the PAA and the fact that the GMA chains were covalently tethered onto the PTFE surface. The PI/PTFE composites delaminated via cohesive failure inside the PTFE substrates. The delaminated PI film with a covalently adhered 'rough' PTFE surface layer exhibited a water contact angle as high as 140°.     

Modification of poly(tetrafluoroethylene) and gold surfaces by thermal graft copolymerization for adhesion improvement

The adhesion between a poly(tetrafluoroethylene) (PTFE) film and a gold substrate was achieved by surface graft copolymerization of glycidyl methacrylate (GMA) on an argon plasma-pretreated PTFE film at elevated temperature with simultaneous lamination to a surface-modified gold substrate. The plasma pretreatment introduces peroxides which are thermally degraded into radicals to initiate the graft copolymerization of GMA on the PTFE surface. The gold surface, on the other hand, was first pretreated with 3-mercaptopropionic acid (MPA), 3-mercaptopropionic acid-2-ethylhexyl ester (MPAEE), or (3-mercaptopropyl)trimethoxysilane (MPTMS) to form self-assembled monolayers (SAMs) and then subjected to Ar plasma treatment. The simultaneous graft copolymerization and lamination of the PTFE film to the gold surface was carried out in the presence of GMA and an amine hardener at an elevated temperature under atmospheric conditions. The modified surfaces and interfaces were characterized by X-ray photoelectron spectroscopy (XPS) and contact angle measurements. The gold/GMA/PTFE assembly exhibited a T-peel adhesion strength above 10 N/cm and the joint delaminated by cohesive failure inside the bulk of the PTFE film. The strong adhesion of the Au/PTFE laminate is the result of concurrent graft copolymerization on both the Ar plasma-pretreated PTFE surface and the SAM of the Au surface to form a covalent network. The network is further strengthened by the crosslinking reaction promoted by the presence of the hardener.     

Surface Graft Copolymerization of Poly(vinylidene fluoride) Film with Simultaneous Lamination to Copper Foil

Surface thermal graft copolymerization with concurrent lamination was carried out between an Ar plasma pretreated poly(vinyh'dene fluoride) (PVDF) film and a copper foil in the presence of a small quantity of a N-containing monomer, such as 4-vinyl pyridine (4-VPN) and acryloyl morpholine (ACMO), under atmospheric conditions and in the complete absence of an added polymerization initiator and system degassing. The adhesion strength, as reported by T-peel strength, was dependent on the argon plasma pretreatment time of the PVDF film, the thermal lamination temperature and the type of monomer. An optimum T-peel adhesion of about 10 N/cm was readily achieved in the Cu/PVDF laminate for grafting and lamination carried out in the presence of 4-VPN. A lower adhesion strength was obtained using ACMO and other N-containing monomers. The chemical compositions of the graft copolymerized and delaminated sample surfaces were studied by X-ray photoelectron spectroscopy (XPS). The failure mode of the Cu/4-VPN/PVDF assembly was a combined adhesional and cohesive failure. The strong adhesion between the Cu foil and the PVDF film arises from the strong charge transfer interaction between Cu and the pyridine ring, as well as the fact that the graft chains are covalently tethered on the PVDF films surfaces as a result of surface graft copolymerization.     

Surface studies of pristine and surface-modified polypyrrole films

Polypyrrole (PPY) films having high conductivity were synthesized electrochemically in acetonitrile at low temperature and low current density. Pristine, deprotonated, and ozone-pretreated PPY films were subjected to either thermally induced or near-UV-light-induced graft copolymerization with acrylic acid (AAc), or sodium salt of 4-styrenesulfonic acid (NaSS). Surface structures and redox states of the pristine, deprotonated, reprotonated, and surface-modified polypyrrole films were studied by angle-dependent X-ray photoelectron spectroscopy (XPS). The morphology of the PPY surface after modification by graft co-polymerization was revealed by atomic force microscopy (AFM). The results showed that the density of surface grafting decreased with ozone pretreatment. Surface grafting of the two polymeric acids also gave rise to a self-protonated surface structure. A substantial proportion of the grafted protonic acid groups at the surface remained free for further surface functionalization. The surface characteristics, in particular the charge-transfer interactions and the changes in the intrinsic redox states of the substrate films, associated with the external protonation and surface self-protonation processes were also discussed. © 1996 John Wiley & Sons, Inc.     

Low-temperature graft copolymerization of 1-vinyl imidazole on low-density polyethylene films with simultaneous lamination of copper foils

Surface modification of argon plasma-pretreated low-density polyethylene (LDPE) films by graft copolymerization with 1-vinyl imidazole (VIDz) and with concurrent lamination of copper foils at room temperature and at an elevated temperature were carried out. The adhesion strengths were reported as lap shear adhesion strengths and T-peel strengths. The surfaces of the graft copolymerized films and the mechanically delaminated LDPE and Cu surfaces were characterized by X-ray photoelectron spectroscopy (XPS). It was found that plasma pretreatment of LDPE alone, and in the absence of VIDz, could give rise to strong lap shear adhesion between the polymer and copper. Significant T-peel strengths, however, were obtained only for LDPE/Cu laminates obtained from the simultaneous graft copolymerization and lamination technique. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 1977–1983, 1998     

Surface structures and adhesion enhancement of poly(tetrafluoroethylene) films after modification by graft copolymerization with glycidyl methacrylate

Surface modifications of Ar plasma-pretreated poly(tetrafluoroethylene) (PTFE) film were carried out via near-UV light-induced graft copolymerization with glycidyl methacrylate (GMA). The structure and chemical composition of the copolymer surface and interface were studied by angle-resolved X-ray photoelectron spectroscopy (XPS). For PTFE substrate with a substantial amount of grafting, the grafted GMA polymer penetrates or becomes partially submerged beneath a thin surface layer of dense substrate chains to form a stratified surface microstructure. The concentration of the surface-grafted GMA polymer increases with the plasma pretreatment time, the near-UV light illumination time, and the monomer concentration. The GMA graft copolymerized PTFE surfaces adhere strongly to one another when brought into direct contact and cured (i) in the presence of a diamine alone or (ii) in the presence of an epoxy adhesive (epoxy resin plus diamine curing agent). In the presence of diamine alone, failure occurs in the interfacial region. For epoxy adhesive-promoted adhesion, the failure mode is cohesive, i.e. it takes place in the bulk of one of the delaminated PTFE films. The lap shear strengths in both cases increase with the amount of surface-grafted epoxide polymer. The development of the adhesion strength depends on the concentration of the surface graft, the microstructure of the graft copolymerized PTFE surface, the interfacial reactions, and the nature of the bonding agent.     

Surface modification of polyethylene by plasma pretreatment and UV‐induced graft polymerization for improvement of antithrombogenicity

The purpose of this study was to enhance blood compatibility of polyethylene (PE) films. Glycidyl methacrylate (GMA) was grafted onto the surface of PE by Ar plasma pretreatment and UV‐induced graft polymerization without photo‐initiator, then heparin was immobilized onto the poly (glycidyl methacrylate) segments. The surface compositions and microstructure of GMA graft polymerized PE films were studied by X‐ray photoelectron spectroscopy (XPS) and Attenuated Total Reflectance Fourier Transfer Infrared (ATR‐FTIR) spectroscopy. It was confirmed that heparin was successfully immobilized onto the surface of PE films by XPS analysis. The antithrombogenicity of the samples was determined by the activated partial thromboplastin time (APTT), prothrombin time (PT), thrombin time (TT), and plasma recalcification time (PRT) tests and platelet adhesion experiment. Results indicated that the antithrombogenicity of modified PE was improved remarkably. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2014–2018, 2004     

Lamination of polytetrafluoroethylene films via surface thermal graft copolymerization with ionic and zwitterionic monomers

Surface thermal graft copolymerization with concurrent lamination was carried out between two argon plasma‐pretreated polytetrafluoroethylene (PTFE) films in the presence of aqueous zwitterionic solutions of N,N‐dimethyl‐N‐methacrylamidopropyl‐N‐(3‐sulfopropyl)ammonium betain (DMASAB), N,N‐dimethyl(methacryloylethyl)ammonium propansulfonate (DMAPS), and 1‐(3‐sulfopropyl)‐2‐vinylpyridinium betaine (SVPB), as well as an aqueous ionic solution of potassium‐2‐sulfopropylacrylate (SPA) and potassium‐2‐sulfopropyl methacrylate (SPM), under atmospheric conditions and in the complete absence of an added initiator and system degassing. The lap shear adhesion strength between the PTFE films from simultaneous grafting and lamination depended on the argon plasma pretreatment time of PTFE films, the thermal lamination temperature, the concentration of the monomer solution, and the ionic nature of the grafted chains. Lap shear adhesion strength greater than 120 N/cm² and exceeding the yield strength of the PTFE substrate used could be readily obtained in most PTFE/zwitterion/PTFE assemblies after simultaneous thermal graft copolymerization and lamination. The chemical compositions of the graft‐copolymerized surfaces were studied by X‐ray photoelectron spectroscopy (XPS). © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 816–824, 1999     

Surface modification of poly(tetrafluoroethylene) films by plasma polymerization and UV-induced graft copolymerization for adhesion enhancement with electrolessly-deposited copper

Surface modification of H₂ plasma-pretreated poly(tetrafluoroethylene) (PTFE) films, either by plasma polymerization and deposition of GMA, or by UV-induced graft copolymerization with glycidyl methacrylate (GMA), was carried out for adhesion enhancement with the electrolesslydeposited copper. XPS and FTIR results revealed that the epoxide groups in the plasma-polymerized GMA (pp-GMA) layer had been preserved to various extents, depending on the glow discharge conditions. The T-peel adhesion test results showed that the adhesion strengths of the electrolesslydeposited copper on both the pp-GMA modified PTFE (pp-GMA-PTFE) film and the GMA graftcopolymerized PTFE (GMA-g-PTFE) film were much higher than that of the electrolessly-deposited copper on the pristine or the H₂ plasma-treated PTFE film. The high adhesion strength between the electrolessly-deposited copper and the surface-modified PTFE film was attributed to the fact that the plasma-polymerized and the UV graft-copolymerized GMA chains were covalently tethered on the H₂ plasma-pretreated PTFE surface, as well as the fact that these GMA chains were spatially and interactively distributed into the copper matrix.     

Surface modification of poly(tetrafluoroethylene) films by graft copolymerization for adhesion enhancement with electrolessly deposited copper

The surface modification of Ar plasma-pretreated poly(tetrafluoroethylene) (PTFE) films via UV-induced graft copolymerization with either 3-(trimethoxysilyl)propyl methacrylate (TM-SPMA) or glycidyl methacrylate (GMA) was carried out to enhance their adhesion to electrolessly deposited copper. The surface compositions of the PTFE films at various stages of surface modification and electroless plating were studied by X-ray photoelectron spectroscopy (XPS). The adhesion strength of the graft-copolymerized PTFE film to the electrolessly deposited copper was affected by the type of monomer used for graft copolymerization, the graft concentration, the plasma post-treatment time after graft copolymerization, and the extent of thermal post-treatment after metallization. The maximum T-peel strength achieved between the electrolessly deposited copper and the GMA graft-copolymerized PTFE film was about 11 N/cm. This adhesion strength represented a more than 20-fold increase over what could be achieved when the PTFE film was treated by Ar plasma alone. The mechanisms of the adhesion strength enhancement and the failure mode in the metal-polymer laminates were also investigated. It was found that the failure was cohesive in nature within the PTFE film.