Enhanced adhesion and thermal stability of Al/Cr film on indium-tin-oxide (ITO)-coated glass

Metallization of indium-tin-oxide (ITO)-coated glass using an Al/Cr composite thin film is a common practice for chip-on-glass packaging. However, the reliability of the Cr/ITO interface is always a problem because of poor adhesion due to the chemical inertness of ITO. In this study, the adhesion strength between a Cr film and ITO coated glass was enhanced by forming an intermediate oxide layer at the interface. To find out the optimal interface condition, various amounts of oxygen were doped at the interface. The results show that the adhesion strength and thermal stability are both enhanced by the interfacial doping of oxygen. This enhancement is found to be related to the flow rate of oxygen and, therefore, to the oxide thickness. Maximum improvement occurs when the flow rate of oxygen is set at 6 sccm during doping, and at this rate the interface oxide thickness also reaches its maximum value. Under this condition, the Cr/ITO interface also shows the best thermal stability. Wire bond testing shows that the wire pull strength is affected by the thickness of Al film. The results of this study show that the Al film should not be thicker than 1 μm.     

The aging effects of repeated oxygen plasma treatment on the surface rearrangement and adhesion of LDPE to aluminum

The effects of aging temperature and time on the adhesion properties of oxygen plasmatreated low-density polyethylene (LDPE) were investigated. As the aging temperature and time increased, surface rearrangement and the migration of molecules containing polar functional groups into the bulk were accelerated to the surface to form a hydrophobic surface. The adhesion strength of oxygen plasma-treated LDPE/aluminum joints was measured using a 90° peel test by varying the plasma treatment time and aging temperature. The adhesion strength was constant, regardless of the plasma treatment time. As the aging temperature increased, the adhesion strength of the LDPE/aluminum joints decreased and the locus of failure changed from cohesive to interfacial failure. It was also found that the polar functional groups buried in the bulk could be reoriented to the surface in a polar environment. This study also investigated whether repeated oxygen plasma treatment would increase the concentration of polar functional groups at the surface and reduce the surface rearrangement and the migration of molecules containing polar functional groups during aging. Contact angle measurements and X-ray photoelectron spectroscopy (XPS) showed that repeated oxygen plasma treatments increased the concentration of polar functional groups at the surface. However, the aging time between plasma treatments had a negligible effect on the concentration of polar functional groups at the surface.     

Influence of Laser Surface Modification on Bonding Strength of Al/Mg Adhesive Joints

Key properties of magnesium alloys, such as the high strength-to-density ratio, are driving the production of lightweight structural components in the automotive and aeronautical industries. Many efforts have been carried out on various aspects of processing and fabrication, but the joining of Mg alloys to dissimilar materials is a subject which attracted much research interest in the last decades. In the present work a preliminary investigation on the strength of Al/Mg (AA6082/AZ31B) single-lap epoxy bonded joints was carried out. To this aim, Mg and Al substrates were laser irradiated using a pulsed ytterbium fiber laser. For comparison, and in order to estimate the beneficial action of the laser surface treatment, single lap joints with grit-blasted substrates were prepared and tested. The interaction between laser treated surfaces and two different epoxy adhesives was also analyzed. Finally, the results and discussion were supported by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) executed on treated and post-failure sample surfaces.     

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.     

Characterization of an evaporated Al/PET interface by TEM and correlation with adhesion measured by a peel test

Transmission electron microscopy (TEM) has been used to characterize thin Al films thermally evaporated (vacuum around 10^-4 Torr) onto polyethylene terephthalate (PET) (Mylar?). The morphology of the Al/PET system has been correlated with the adhesion as measured by a peel test of the Al films. A special cross-section preparation revealed the exact thickness of the thin Al film, the roughness of the interfaces (Al/PET and Al/vacuum), the presence of precipitates or the diffusion of Al in the PET, the morphology of the Al layer (small grains or rod-like structure), the size of the grains or the columns (also checked with plane section), and the structure (crystalline or amorphous) of the PET at the Al/PET interface. The results suggest that the grain size and the roughness of the Al/PET interface decrease as the adhesion of the Al increases. Some spherical precipitates and diffusion of Al into PET were also observed for the films which had a low adhesion strength.     

Chemical modification combined with corona treatment of UHMWPE fibers and their adhesion to vinylester resin

The influence of corona treatment on the near-surface structures of treated ultra-high-molecular-weight polyethylene (UHMWPE) fibers was studied first by atomic force microscopy (AFM). AFM pictures showed that the pits on the corona-treated PE fiber surfaces had different change characteristics in depth compared with in length and breadth with variations of corona power. Then the UHMWPE fibers were subjected to chemical modification following the corona treatment, named the two-stage treatment. Surface morphologies and chemical properties of the treated fibers were analyzed by scanning electron microscopy (SEM), FT-IR–ATR spectroscopy and Raman spectroscopy. The results obtained suggested that some carbon–carbon double bonds had been introduced on the surfaces of the PE fibers after the two-stage treatment. These unsaturated groups could participate in free-radical curing of vinylester resin (VER), and this resulted in improvement of interfacial adhesion strength in the PE fiber/VER composites. In addition, the mechanical properties of the UHMWPE fibers reduced after corona treatment did not reduce further after subsequent chemical treatment with increase of corona power. In short, the two-stage treatment proved to be effective in improving the interfacial adhesion of the composites and maintaining the high mechanical properties of the PE fibers, as this treatment method did not destroy the bulk structure of the UHMWPE fibers.     

氦检漏法在PET热态真空测试中的应用

阐述了氦检漏在PET热态真空测试中的作用、氦检仪的工作原理、氦检仪的使用方法和氦检漏的具体实施步骤,并根据应用进行了经验总结,提出了注意事项。     

Using heterogeneous silane patterns to maintain adhesion and decrease water penetration into epoxy/aluminum interfaces

Silanes are used for surface modification to improve dispersion, bind biomaterials, improve adhesion, etc. Their use in improving adhesion in composite materials is widespread, and for these systems there is a growing need for both increased adhesion performance and resistance to water penetration across polymer/oxide interfaces. The present work reports adhesion results obtained using patterned, binary combinations of adhesion-promoting and non-adhesion-promoting silanes patterned onto an oxide surface. The effects of pattern shape, texture (feature size) and the fractional coverage of the adhesion promoter are explored for the bonding of epoxy matrices to aluminum oxide surfaces using combinations of γ-glycidoxypropyltrimethoxysilane (GPS), an adhesion promoter, and either octadecyltrichlorosilane (ODTS) as a hydrophobic non-adhesion promoter, or vinyltrimethoxysilane (VMS) as a water scavenger. In addition to dry tests, samples are submerged in boiling water for 48 h, and in 50°C water for 4 h to determine if water penetrated into the interface, thereby reducing the adhesion. Climbing drum peel tests reveal that heterogeneity of silane primer substrates can influence the adhesion and increase the durability to water penetration. Adhesion enhancement is attributed to the blocking of lateral diffusion of water by barriers due to the presence of the hydrophobic silane. Results show that due to exposure to water at 50°C for 4 h, the adhesion is reduced by 46% in the homogeneous samples but only by 20% in the heterogeneous samples. In contrast, the use of VMS was ineffective in preventing the loss of adhesion due to water penetration.     

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.     

聚对苯二甲酸乙二醇酯/聚丙二醇共聚醚酯热性能研究

采用熔融缩聚法制备了聚对苯二甲酸乙二醇酯/聚丙二醇共聚醚酯（PET/PPG）,并采用核磁共振氢谱（1H-NMR）、热重分析（TGA）、差示扫描量热分析（DSC）、动态热分析（DMA）等研究了材料的结构与热性能,1H NMR结果证明了PET/PPG共聚物结构的存在,而且共聚物的组成与投料比非常接近;热分析的结果表明,聚醚链段的引入对热稳定性和熔融温度的影响不大,而玻璃化转变温度、冷结晶温度、冷结晶焓、储能模量、损耗正切的峰温均有明显下降.     

Improvement of paint adhesion to a polypropylene bumper by plasma treatment

Improvement of the paint adhesion to a polypropylene (PP) bumper has been investigated without using a primer by treating the bumper surface with O₂, H₂O, and acetylene plasmas. All the plasma treatments resulted in an increase of the adhesion strength in dry conditions. The adhesion strength could be increased up to a value comparable to that obtained by applying a primer. The treated surfaces were quite stable for 7 days in air. After exposure to wet conditions, however, the adhesion strengths for both O₂ and H₂O plasma-treated samples decreased significantly, while the adhesion strength for the acetylene plasma-treated sample did not change much.     

The role of interfacial interactions and loss function of model adhesives on their adhesion to glass

The measurement of adhesion and the evaluation of influencing factors are of great scientific and technological importance. There are two distinct viewpoints on adhesion: (i) surface chemistry, and (ii) fracture mechanics. For elucidation of the relative importance of mechanical properties in the bonding of adhesives, the strength of adhesion between model adhesives and glass plates was measured by the wedge cleavage (WC) test method. Copolymers of methyl methacrylate (MMA) with n-butyl acrylate (nBA) and methyl methacrylate with styrene (S) were prepared as model adhesives. The results show that in MMA-nBA copolymers, by increasing the amount of nBA, both the loss function and the adhesion energy of the adhesives increase. However, by increasing the amount of nBA above a certain level, the adhesion strength begins to decrease. In this situation, the cohesive strength of the adhesive dominates the failure mechanism. On the other hand, a decrease in adhesion was expected upon increasing the amount of styrene in the poly(styrene-co-methyl methacrylate) adhesive, because methyl methacrylate, an interactive monomer with glass, is replaced by a non-interacting styrene monomer, while the loss function of the adhesive is almost constant. But our practical adhesion measurement technique was not sensitive enough to detect this adhesion loss.     

Photochemical surface modification of polypropylene for adhesion enhancement by using an excimer laser

Polypropylene (PP) surface in water was photochemically modified to render it hydrophilic using ArF excimer laser radiation. The chemical stability of PP is attributed to the C-H and C-H₃ bonds present. Thus, it is considered that H atoms are selectively pulled out from the area irradiated with ArF excimer laser light and are replaced with OH functional groups in the presence of water. In this treatment, the irradiated sample becomes hydrophilic with enhanced adhesion properties. The experimental conditions for this surface treatment were ArF laser fluence of 12.5 mJ/cm² and a shot number of 10000. The treated PP and stainless steel were bonded with epoxy adhesive and the tensile shear strength was 46 kg/cm².     

Study on PET fiber modified by nanomaterials: Improvement of dimensional thermal stability of PET fiber by forming PET/MMT nanocomposites

Poly(ethylene terephthalate) (PET) and PET/montmorillonite(MMT) (2.5 wt %) nanocomposites with high molecular weight were prepared by solid‐state polycondensation and their fiber was spun and drawn under various conditions. The influence of MMT nanomaterials on the thermal shrinkage of PET fiber was investigated and the structure was studied using the methods of WAXD, DSC, fiber orientation measurement, etc. The results showed that the MMT nanomaterials improved the thermal stability of microstructure of PET fiber. The fusion heat of PET/MMT was higher than that of PET, which generally implied the high orientation or high crystallinity. However, the degree of orientation and the crystallinity of PET/MMT fiber measured by WAXD were lower than that of pure PET fiber. It is suggested that the strong interaction between MMT layer and PET restricted the motions of PET molecular chains, which developed “a special continuous network structure” and prohibited the thermal shrinkage of PET fiber. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 2247–2252, 2005     

The critical humidity effect in the adhesion of epoxy to glass: role of hydrogen bonding

Adhesion between an epoxy [diglycidyl ether of bisphenol F (DGEBF) cured with diethylene triamine] and glass was lowered abruptly when the epoxy was equilibrated with air whose relative humidity (RH) exceeded a critical value of approximately 70% RH. The critical humidity marking the onset of adhesion loss was also associated with a sudden increase of water uptake by the epoxy. In earlier work, it was shown that this 'transition' was not due to capillary condensation, osmotic cell formation or a decrease in the T _g of the material. Instead, it was speculated that the critical humidity effect was due to the trapping of water by hydroxyl groups which become available as inter-chain hydrogen-bonded structures are broken. To verify the above hypothesis, two model compounds were synthesized. One closely mimicked the cured DGEBF resin and the other had all of its hydroxyl groups replaced by hydrogen. Comparison of the water sorption isotherms of these two model compounds clearly suggested that hydroxyl groups played a key role in the critical humidity effect. Using molecular simulation software, hydrogen bonding between the various polar sites of the hydroxylated model compound was also studied. In the dry state or at low water concentrations, simulations predicted the formation of hydrogen bonds between polar sites. These hydrogen bonds always involved one or more hydroxyl groups. At higher water concentrations, molecular simulations showed that water tended to displace the hydrogen bond network of the epoxy, and in the process, water-mediated 'bridges' between polar groups were formed. The large decrease in entropy associated with the formation of such macrocyclic conformers is thought to be offset by the decreased enthalpy of condensation of water made possible by multiple hydrogen bonding. This suggests that the critical humidity effect might be an 'order-disorder' transition associated with the formation of ring structures closed by hydrogen-bonded water linkages between polar groups. The first-order energetics of this type of transition is consistent with the abrupt nature of the critical humidity effect.     

Influence of glass mechanical strengthening on the adhesion properties of poly(vinyl butyral) films to a float glass surface

The effects of various methods of mechanical strengthening of glass on the adhesion properties of poly(vinyl butyral) (PVB) film to a float glass surface were investigated. The mechanisms of the influence of the strengthening processes on the adhesion properties were analyzed. The influence of different types of pretreatment of the glass surface on the adhesion of the polymer films was also considered. It was shown that ion-exchange strengthening followed by treatment with an alkaline water solution provided the best combination of high mechanical strength of glass and good adhesion of the PVB films to the glass surface. Metal-oxide coatings on float glass increased the mechanical strength of glass but decreased the adhesion strength between the polymer and glass. The adhesion of PVB to the metal-oxide layers was determined not only by the chemical composition of the layers, but also by the method of layers formation, the type of glass surface pretreatment, and the nature of the intermediate layer between the metal-oxide layer and the glass surface.     

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.     

The role of water in delamination in electronic packages: degradation of interfacial adhesion

Polymeric electronic packages subjected to standard Joint Electron Device Engineering Council (JEDEC) reliability testing are known to exhibit weakening and failures at the polymeric adhesive interfaces. Coupling agents are typically used as additives in epoxy-based materials to improve package reliability. Coupling agent chemistry and environment conditions, including pH, temperature and applied stress, are known factors that affect the rate of adhesion degradation and jeopardize the long-term reliability of the package. In this study, the subcritical interfacial debonding process is described. The debonding rates of polymers with silane, titanate and zirconate coupling agents were characterized at different temperatures by shear fracture tests and tapered double cantilever beam tests under mechanical loading and simultaneous exposure to controlled acidic environments. An analytical procedure was developed to delineate the material parameters governing adhesion degradation. Elevated temperature and acidity were shown to have a strong effect on package reliability, but mechanical loading was found to have a minimal effect on the rate of adhesion degradation. The effects of the JEDEC testing conditions on interfacial bond degradation are discussed using the chemical kinetic model.     

The role of joint viscoelastic function in the adhesion of low-density polyethylene to thermoplastic starch

Measured adhesion energies of low-density polyethylene (LDPE) to thermoplastic starch (TPS) joint and of joints in presence of poly(ethylene-co-vinyl acetate) (EVA), polyethylene grafted with maleic anhydride (PE-g-MAH) and styrene-ethylene-butadiene-styrene grafted with maleic anhydride (SEBS-g-MAH) compatibilizers were investigated. The compatibilizers were introduced to the interface via their pre-mixing with the adherend (PE) or adhesive (TPS). The results showed adhesion energy improvement from 41 J/m² for PE/TPS to 118, 151 and 272 J/m² by adding 3.3 wt% of EVA, SEBS-g-MAH and PE-g-MAH to the PE adherend, respectively. On the other hand, by raising the compatibilizers to 5.75 wt%, similar joint adhesion energies of about 250 J/m² were found for all studied systems. The measured adhesion energy increments were attributed to the migration of the compatibilizers to the interface during high temperature joint preparation. In addition, the observed efficacies of various compatibilizers were ascribed to their interfacial stress transfer capabilities. Joint viscoelastic function, i.e., joint adhesion energy divided by its thermodynamic work of adhesion, showed similar dependence on adherend tan δ divided by the adhesive tan δ (A) divided by the compatibilizer tan δ as the measured adhesion energy. This interesting finding supports the hypothesis that the main viscoelastic loss effects in joints with stiff adherends are localized in the interphase adjacent to the crack tip.     

Surface modifications of EVA copolymers induced by low pressure RF plasmas from different gases and their relation to adhesion properties

Two ethylene vinyl acetate (EVA) copolymers (12 and 20 wt% of vinyl acetate,VA, content) have been treated with low pressure RF plasmas from non-oxidizing gases (Ar, N₂) and oxidizing gases (air, a mixture of 4N₂: 6O₂ (v/v), O₂ and CO₂). The formation of polar moieties on both EVAs was more noticeable by treatment with plasmas from non-oxidizing gases than from oxidizing ones (the higher the reactivity, the lower the difference with respect to untreated EVA surfaces). The surface etching with the non-oxidizing plasmas, giving rise to a high roughness, depends on the wt% of VA in the composition of the copolymer because of the different resistances of VA (low) and PE (high) to the non-oxidizing plasma particles bombardment. The adhesion properties obtained using a polyurethane adhesive (PU) showed high T-peel strength values and adhesion failure in EVAs treated with plasmas from oxidizing gases, due to roughness produced causing mechanical interlocking of the adhesive. Lower T-peel strength values were obtained with non-oxidizing plasmas: the values for EVA12 being, in general, lower than those obtained for EVA20. The durability of the treated EVAs/PU adhesive joints after ageing in humidity and temperature was quite good.