Enhanced adhesion of plasma-sputtered copper films on polyimide substrates by oxygen glow discharge for microelectronics

Enhanced plasma-sputtered copper film adhesion onto polyimide substrates treated by oxygen glow discharge was investigated. The peel test demonstrates this improvement, with peel strengths of 0.7-1.2 g/mm for copper films prepared on un-modified polyimide substrates and 195.5-262.2 g/mm for copper films on oxygen plasma-modified polyimide substrates at certain plasma conditions. The enhanced adhesive strengths of plasma-sputtered copper films onto polyimide substrates by oxygen plasmas are due mainly to the increased surface energies of the polyimide substrates. Contact angle measurements indicate that the surface energies of polyimide substrates were greatly increased by oxygen plasmas. X-ray photoelectron spectroscopy analysis shows that the increased surface energies of polyimide substrates using oxygen plasmas occur because of the increased oxygen surface concentration and the increased C-O bond proportion.     

Effects of heat treatment at 350°C on the adhesion of Cu-Cr alloy films to polyimide

CuCr alloys with varying Cr content were sputter deposited on polyimide films, and the metal/polyimide films were maintained under 350°C/N₂ environment up to 10 hours for the reliability measurements. The Cr contents of the alloy layer prepared were 0, 8.5, 17, 25, 34, and 100 atomic %, respectively. Before exposures to 350°C, the peel strength increased proportionally with the Cr content in the alloy layer up to 17 atomic % and saturated. The failure occurred inside polyimide near the metal/polyimide interface by the cohesive failure mode except for the specimen with no Cr. After exposures to 350°C, the peel strength dropped for all the specimens, but most drastically for the specimens with 8.5% Cr which failed along the Cr-oxide/polyimide interface by the interfacial failure mode. Through AES and XPS analyses, it was shown that the decrease of the peel strength during the heat treatment was primarily caused by the formation of brittle Cr₂O₃ at the metal/polyimide interface, which was accompanied by the reduction of carbidic bonds responsible for the good adhesion.     

A fracture approach to thick film adhesion measurements

The constant-compliance double cantilever beam test for adhesive fracture energy has been adapted to the measurement of the adhesion of thick film metallizations on alumina. The test involves a single beam soldered to metallization strips and measures the opening-mode fracture energy, G _Ic. Solder-wire peel tests were also made on the same metallizations. Both the fracture and peel tests indicated failure in the thick films but near the film/alumina boundary and both sets of data exhibited a bimodal distribution. The magnitude of the fracture energies indicated failure usually occurred in the glass phase of the film but that film adherence was greatly enhanced by interlocking between the metal and glass phases. This interlocking, and thus the film adhesion, was strongly dependent on the firing temperature.     

Effects of diffusion on interfacial fracture of gold-chromium hybrid microcircuit films

In this study, the effects of diffusion on gold-chromium film durability was determined from interfacial fracture energy measurements on laboratory samples aged to simulate long term service. The samples were prepared by sputter deposition of gold films and chromium adhesive layers on sapphire substrates. Some films were left in the as-deposited condition while others were given an accelerated age to drive the chromium off the interface and into the gold film. Stressed overlayers and nanoindentation were then used to induce interfacial delamination and blister formation from which interfacial fracture energies were determined using mechanics-based models. These tests showed that the fracture energies for interfacial failure of the as-deposited and annealed films occurred near 1.3 J m^–2 even when diffusion had driven all chromium into solution. These results clearly demonstrate that chromium in solution is as effective in promoting adhesion as continuous chromium adhesive layers.     

In vitro bioactivity and osteoblast-like cell test of zinc containing fluoridated hydroxyapatite films

Zinc containing fluoridated hydroxyapatite (ZnFHA) films on Ti6Al4V substrates was prepared using sol–gel dip-coating method. The release of zinc ions from ZnFHA film was controlled mainly by the zinc content in the film. The release behavior showed an initial rapid increase release followed by a tapering-off and directed to a constant value at longer time. After soaking in SBF for 8 days, a layer was deposited and completely covered the original surface of the ZnFHA film, indicating good in vitro “bioactivity.” The osteoblast-like MG63 cells were seeded on the ZnFHA films; FHA film and Ti6Al4V substrate were used as control. The cell culture result showed that cell adhesion and proliferation on ZnFHA films were significantly increased compared with the controls. The results in this work suggest that ZnFHA films on Ti6Al4V substrates can function as an implant with good bioactivity and cytocompatibility.     

Humidity effect on polyimide film adhesion

A 90° peel tester with substrate heating capability has been built to evaluate the adhesion strength of polyimide film to silicon substrate. The peel strength of polyimide film is not only a function of film thickness or peeling rate, but also a function of ambient humidity. A mechanism is proposed. The peel strength decreases with increasing relative humidity due to the hydrolysis of polyimide, reaches a minimum, and then increases with increasing relative humidity due to the hydrogen bonding at the weak boundary layer. In a high-humidity environment, peel crack tips are attacked by moisture and result in weak adhesion measurement. Water adsorbed by polyimide film near the crack tip and diffused into the peel crack tip is the main mode of moisture attack. The peel behaviour of polyimide film at the elevated temperature is almost the same as peeling at room temperature in a low-humidity environment.     

Nanoindentation of LaCrO3 thin films

Nanoindentation of LaCrO₃ thin films deposited by radio-frequency magnetron sputtering onto stainless steel substrates was performed using an XP Nanoindenter. The “as-deposited” film was amorphous but transformed to an orthorhombic LaCrO₃ perovskite structure after annealing at 1073 K for 1 h. The film thickness in the “as-deposited” state was 800 nm. Single loading/unloadings were performed in the displacement control mode on the crystalline film using different maximum displacements (50, 200, 400, and 800 nm). Therefore, the integral response of the film−substrate system was probed at different distances from the substrate. Nanoindentation experiments on LaCrO₃ perovskite films revealed sharp “pop-in” events at certain loads. Such “pop-ins”, are most likely caused by the orthorhombic-to-rhombohedral phase transition which is known to occur in a LaCrO₃ perovskite structure under pressure. However, such discontinuities have never been observed upon indentation of the amorphous “as-deposited” La-Cr-O thin films, and the pressure found to be typical of this transition in the LaCrO₃ thin films is higher than previous bulk LaCrO₃ sample studies. Mechanical characteristics of the films, such as hardness and Young’s modulus, were also measured.     

Effect of damage on the interlaminar shear properties of hybrid composite laminates at cryogenic temperatures

This paper presents the experimental and numerical characterization of the interlaminar shear failure of hybrid composite laminates at cryogenic temperatures. Cryogenic short beam shear tests were performed on hybrid laminates consisting of woven glass fiber reinforced polymer (GFRP) composites and polyimide films to evaluate their interlaminar shear strength. Microscopic observations of damage accumulation and failure mechanisms were also made on failed specimens. In addition, a progressive damage analysis was conducted to predict the initiation and growth of damage in the specimens, and the interlaminar shear strength was determined from the maximum shear stress in the failure region. The damage effect on the interlaminar shear properties of hybrid laminates at cryogenic temperatures was examined based on the experimental and numerical results.     

Practical Approach in Developing Desirable Peel–Seal and Clear Lidding Films Based on Poly(Lactic Acid) and Poly(Butylene Adipate‐Co‐Terephthalate) Blends

In this research, poly(lactic acid) (PLA) blend with poly(butylene adipate‐co‐terephthalate) (PBAT) were selected to fabricate peelable lidding films. In general, blending PLA with PBAT results in hazy films; however, desirable low haze films (<10%) could be achieved in this study by designing proper blend composition and cast film process under optimum conditions. Based on various blends containing PBAT ranging from 15 to 30% by weight, it could be seen that a PBAT/PLA blend of 20/80 showed desired optical and peel–seal property, which had a haze of <10% and low peel strength in an easy‐peel characteristic. It was also observed that not only the blend composition but also the film thickness could influence both optical and peel–seal behaviours because the bulk morphology and surface irregularities of the films could vary by changing films' thicknesses. Thus, cast extruded pristine and PBAT/PLA (20/80) blend films of three different thicknesses (20, 35 and 50 μm) were studied. Peel–seal behaviour and optical properties of these films were examined. An I‐peel test (180°) of films sealed on PLA sheet (thickness of ~350 μm) with different interfacial sealing temperature illustrated failure mechanism of four types, i.e. tearing, partial tearing, cohesive and adhesive failure. Based on this study, the PBAT/PLA of 20/80 wt% films with thickness of 20 μm can be used as easy‐peel lidding film sealed with PLA container. Such PBAT/PLA blend films possess a low haze of ~4% and a low peel strength of 8–10 N/15 mm at a broad range of interfacial sealing temperature of 76–105°C. Copyright © 2017 John Wiley & Sons, Ltd.     

Effect of basalt fiber hybridization on the impact behavior under low impact velocity of glass/basalt woven fabric/epoxy resin composites

The low velocity impact behavior of E-glass/basalt reinforced hybrid laminates, manufactured by resin transfer moulding technique, was investigated. Specimens prepared with different stacking sequences were tested at three different impact energies, namely 5 J, 12.5 J and 25 J. Residual post-impact mechanical properties of the different configurations were characterized by quasi static four point bending tests. Post-impact flexural tests have been also monitored using acoustic emission in order to get further information on failure mechanisms. Results showed that basalt and hybrid laminates with an intercalated configuration exhibited higher impact energy absorption capacity than glass laminates, and enhanced damage tolerance capability. Conversely, the most favorable flexural behavior was shown by laminates with symmetrical sandwich-like configuration (E-glass fiber fabrics as core and basalt fiber fabrics as skins).     

A critical investigation of the use of a mandrel peel method for the determination of adhesive fracture toughness of metal-polymer laminates

The application of peel tests for the measurement of adhesive fracture toughness of metal-polymer laminates is reviewed and the merits of a mandrel peel method are highlighted. The mandrel method enables a direct experimental determination of both adhesive fracture toughness (G_A) and the plastic bending energy (G_P) during peel, whilst other approaches require a complex calculation for G_P. In this method, the peel arm is bent around a circular roller in order to develop a peel crack and an alignment load attempts to ensure that the peel arm conforms to the roller.The conditions for peel arm conformance are thoroughly investigated and the theoretical basis for conformation are established. Experimental investigations involve the study of the roller size (radii in the range 5-20 mm are used), the peel arm thickness (varied from 0.635 to 2.0 mm) and the magnitude of the alignment load. In addition, the plane of fracture is studied since fractures can vary from cohesive to interfacial and this has a profound influence on the value of G_A and on interpretation of results.A test protocol for conducting mandrel peel is developed such that the roller size for peel arm conformance can be established from preliminary fixed arm peel tests.The work is conducted on two epoxy/aluminium alloy laminates suitable for aerospace applications. Comparative results of adhesive fracture toughness from mandrel peel and multi-angle fixed arm peel are made with cohesive fracture toughness from a tapered double cantilever beam test.     

Atomic oxygen resistant phosphorus-containing polyimides for LEO environment

In this study, a series of polyimides had been prepared from bis-(4-aminophenoxyl) phenoxyl phosphine oxide (p-DAPO₄) with corresponding dianhydrides via two-stage polycondensation method. The inherent viscosities of the polyamide acid were in range of 0.43–0.92 dL/g, and atomic oxygen (AO) exposure experiment was conducted in a ground-based atomic oxygen effects simulation facility with the filament charge and bound of magnetic field to determine the AO erosion-resistant properties of the polyimide films. Field emission scanning electron microscopy (FE-SEM), attenuated total-reflection Fourier transform infrared spectrometer and X-ray photoelectron spectrometer were employed to characterize the change on the surface of films after AO exposure, and the mass loss of some phosphorus-containing polyimide films reduced to about 20% that of Kapton^? HN film as AO fluence of 4.14 × 10²⁰ atoms/cm². The morphologies of heave residues of the polyimide films acting as a barrier to further erosion could be obtained from FE-SEM. The results indicated that a phosphate-type layer was left on the surface of phosphorus-containing polyimide films after AO exposure.     

Local metallic conductivity of thin polyimide films as a result of “soft” electrical breakdown

The electrical breakdown of a thin polyimide film between metal electrodes has been investigated under conditions of strong confinement of the breakdown current. The result of this “soft” electrical breakdown is a local, highly conducting channel in the insulating film implanted in the polymer and consisting of a compound of carbon and metal from the electrodes. It is shown that the polymer channel is converted to the superconducting state by the superconducting properties of the metal from the electrodes. Pis’ma Zh. Tekh. Fiz. 23, 8–12 (July 26, 1997)     

Refractive index of polymethylmethacrylate oriented by fluid temperature under electrical field

We prepared micron and submicron polymethylmethacrylate (PMMA) layers by the spin-coating method. We investigated the possibility to orientate polymer dipoles in electric field in the glass transition area (T _g) and the fluid temperature of PMMA with the aim to increase its refractive index (n) after the layer is cooled below T _g. We have studied the effect of electric field (up to 12 kV cm⁻¹) on change of surface morphology of the layer, dependence of n and contact angle (surface wettability) on the field and dependence of layers orientation on orientation of electric field. The surface morphology was examined using atomic force microscopy (AFM), contact angles were measured by goniometer, film thickness was measured by profilometer, refractive index of films was determined using refractometer. The change of refractive index as dependent on the PMMA layer orientation in electric field depends on temperature and electric field. The highest change in n was found for electric field 11 kV cm⁻¹. The change in contact angle (wettability) on surface of an orientated PMMA layer confirms the dipoles orientation in electric field unambiguously. The orientation of layers causes a “slight” change in their morphology and a “slight” increase of surface roughness only for one direction of field effect. Change in colour for oriented layers does not depend on orientation of electric field.     

缺陷对单搭胶接接头力学性能的影响

通过单向拉伸试验对比分析了两种接头的破坏模式及载荷-位移曲线, 研究了T700/TDE85复合材料单向层合板单搭接胶层内缺陷对接头破坏行为的影响。试验结果表明, 接头破坏的主导模式为界面破坏, 胶层中微小缺陷对接头强度的影响不大。为研究接头的失效机制, 采用有限元方法对两种接头失效进行数值分析, 模拟了接头搭接区界面剥离应力及剪切应力分布情况, 并分析了缺陷位置变化及面积变化对接头强度的影响。结果表明, 随着缺陷位置距接头搭接区自由端部越近, 接头强度越小, 且缺陷位置距接头搭接区自由端部2.5 mm以内, 缺陷对接头强度影响较大; 接头强度随缺陷面积的增大而减小, 并且缺陷面积占搭接区面积的比率在4.4%以内, 缺陷对接头强度的影响较小; 数值计算结果与实验结果吻合较好。     

多壁碳纳米管对Ti-碳纤维/反应型聚酰亚胺超混杂层板力学性能的影响

为了改善Ti/反应型聚酰亚胺（PMR）树脂界面的黏结强度,从而提高Ti-碳纤维（CF）/PMR超混杂层板的力学性能,本文探究了添加多壁碳纳米管（MWCNTs）对Ti-CF/PMR超混杂层板力学性能的影响。将不同质量分数（0wt%、2.5wt%、5.0wt%和7.5wt%）的MWCNTs利用超声分散法均匀分散于PMR树脂中,随后进行Ⅰ型断裂韧性试验,探究添加MWCNTs对Ti-CF/PMR超混杂层板界面性能的影响,最后选取最优含量的MWCNTs同时添加到PMR胶层和CF/PMR树脂中,并进行弯曲试验,探究添加MWCNTs对Ti-CF/PMR超混杂层板力学性能的影响。通过SEM观察和分析了相应的失效模式和增强机制。结果表明:当MWCNTs含量为5.0wt%时,Ⅰ型层间断裂韧性提高了74%;同时添加5.0wt% MWCNTs于PMR胶层和CF/PMR复合材料树脂中,Ti-CF/PMR超混杂层板的弯曲性能较未添加MWCNTs提高了42%。这是由于MWCNTs在PMR胶层和CF/PMR树脂中的分布均匀性较高,且能分散并承受界面层转移到纤维层的载荷,并利用自身拔出、断裂、桥接、脱黏来吸收并消耗断裂能量,进一步提升Ti-CF/PMR超混杂层板的弯曲性能。      

固化剂对聚酰亚胺挠性覆铜板剥离强度的影响

采用双氰胺(DICY)、间苯二胺(m-PDA)、长链柔性二胺(DAMI)固化双酚A型环氧树脂(E-51),制备了三种环氧胶粘剂,分别考察了三种固化剂对挠性覆铜板剥离强度的影响。根据差示扫描量热仪(DSC)曲线,通过t-β外推法得到了各固化剂固化环氧胶粘剂的固化工艺。采用扫描电子显微镜(SEM)考察其不同的破坏形式。结果表明,采用双氰胺固化的环氧胶粘剂粘接的挠性覆铜板,剥离后聚酰亚胺薄膜、铜箔表面都留有大量的胶粘剂,此破坏形式属于内聚破坏。同时双氰胺固化的环氧胶粘剂剥离强度最高,粘接强度达到0.74 N/mm,符合日本JPAC行业标准。     

Growth and characterization of high resistivity c-axis oriented ZnO films on different substrates by RF magnetron sputtering for MEMS applications

In the present work, we report the deposition of high resistivity c-axis oriented ZnO films by RF magnetron sputtering. The deposition parameters such as RF power, target-to-substrate spacing, substrate temperature, and sputtering gas composition affect the crystallographic properties of ZnO films, which were evaluated using XRD analysis. The self-heating of the substrate in plasma during film deposition was investigated and we report that highly “c-axis oriented” ZnO thin films can be prepared on different substrates without any external heating under optimized deposition parameters. The post-deposition annealing of the film at 900 °C for 1 h in air ambient increases the intensity of (002) peak corresponding to c-axis orientation in addition with the decrease in full width at half maxima (FWHM). Bond formation of ZnO was confirmed by FTIR analysis. Grains distribution and surface roughness have been analyzed using SEM and AFM. The DC resistivity of the films prepared under different deposition conditions was measured using MIS/MIM structures and was found to be in the range of 10¹¹–10¹² Ω cm at low electric field of 10⁴ V/cm. The ZnO film of 1 μm thickness has transmittance of over 85% in the visible region. Applications of these films in MEMS devices are discussed.     

基于表面改性的国产T800碳纤维/高韧性环氧树脂复合材料胶接性能

本文通过打磨、喷砂、等离子处理方法对国产T800碳纤维/高韧性环氧树脂复合材料的待胶接面进行改性,分别制备了J-116B胶膜和J-375胶膜的浮辊剥离性能及拉伸剪切性能试验件。测试了不同处理条件下J-116B胶膜和J-375胶膜的剥离和剪切性能。采用SEM对老化前后、未经刻蚀和刻蚀后的剥离试样形貌进行观察。采用接触角测试仪测试了不同表面处理方法对国产T800碳纤维/高韧性环氧树脂复合材料胶接面润湿性的影响,并采用XPS光电子能谱分析仪对等离子处理前后的国产T800碳纤维/高韧性环氧树脂复合材料胶接面表面理化性能进行研究。结果表明:尽管J-375胶膜的室温剥离性能不如J-116B胶膜,但J-375胶膜具有更好的湿热老化性能。等离子处理后的国产T800碳纤维/高韧性环氧树脂复合材料的破坏模式由黏附破坏为主转变为内聚破坏为主,因此使两种胶膜的拉剪和剥离性能均有明显提高。这是由于等离子体处理能够重组复合材料表面的分子链,在胶接表面形成新的活性基团。      

热和化学亚胺化对ODPA/ODA聚酰亚胺薄膜性能的影响

以4,4'-二胺基二苯醚(ODA)和3,3',4,4'-二苯醚四酸二酐(ODPA)为单体,采用两步法,分别经热亚胺化和化学亚胺化过程制备了两种聚酰亚胺(PI)薄膜,并对两种薄膜的性能进行了表征.傅立叶红外光谱(FT-IR)表明两种薄膜均已完全亚胺化.化学亚胺化的PI薄膜的玻璃化温度、热稳定性均高于热亚胺化的薄膜.拉伸性能测试表明热亚胺化的薄膜具有较高的断裂伸长率,而化学亚胺化的薄膜的拉伸强度、弹性模量较大.