Analysis of mold insert fabrication for the processing of microfluidic chip

The microfluidic chip has been used as an example to discuss different mold insert materials by micro hot‐embossing molding. For the mold insert, this study uses the SU‐8 photoresist to coat on the silicon wafer, then uses UV light to expose the pattern on the surface of SU‐8 photoresist, and coat the seed layer on the SU‐8 structure using thermal evaporation. The micro electroforming technology has been combined to fabricate the mold inserts (Ni, Ni‐Co) followed by replicating the microstructure from the metal mold insert by micro‐hot embossing molding. Different processing parameters (Embossing temperature, embossing pressure, embossing time, and demolding temperature) for the properties of COP film of microfluidic chip have been discussed. The results show that the most important parameter is the embossing temperature for replication properties of molded microfluidic chip. The demolding temperature is the most important parameter for surface roughness of the molded microfluidic chip. The Ni‐Co mold insert is the most suitable mold material for molded microfluidic chip by microhot embossing molding. The bonding temperature is the most important factor for the bonding strength of sealed microfluidic chip by tensile bonding test. POLYM. ENG. SCI., 2009. © 2008 Society of Plastics Engineers     

Optimization of electrospinning an SU‐8 negative photoresist to create patterned carbon nanofibers and nanobeads

The optimization of electrospinning SU‐8 2100 negative photoresist was performed to create carbon micro/nanofibers and beads that can be patterned after electrospinning by using UV radiation. The fiber diameters had a range of 300 nm to 1 μm, based upon the selected electrospinning parameters. Low concentrations of the SU‐8 2100 resulted in beads while specific higher concentrations produced well‐defined fibers. Fibers and beads were converted to carbon through pyrolysis and retained their three dimensional structure. By utilizing the photosensitive properties of the SU‐8 negative photoresist, the electrospun fibers were patterned by UV photolithography. The fibers and beads were characterized by SEM and Raman microscopy, respectively. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

High dielectric constant SU8 composite photoresist for embedded capacitors

A novel, photodefinable, high dielectric constant (high‐k) nanocomposite material was developed for embedded capacitor applications. It consists of SU8 as the polymer matrix and barium titanate (BT) nanoparticles as the filler. The UV absorption characteristics of BT nanoparticles were studied with a UV‐Vis spectrophotometer. The effects of BT nanoparticle size, filler loading, and UV irradiation dose on SU8 photopolymerization were systematically investigated. The dielectric properties of the photodefined SU8 nanocomposites were characterized. Embedded capacitors using the novel high dielectric constant SU8 composite photoresist were demonstrated on a flexible polyimide substrate by the UV lithography method. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1523–1528, 2007     

The effects of thermoplastic poly(olefin) (TPO) morphology on subsequent paintability and thermal shock performance

Adhesion to thermoplastic olefin (TPO) substrates is strongly influenced by the type and amount of solvent contained within paint applied. Morphological changes in the TPO substrate are accomplished in the presence of solvent from the topcoat and vary depending upon paint bake times and temperatures. These morphological changes at and near the surface of TPO affect not only the paint adhesion to the substrate but also the cohesive integrity of the painted plastic composite. This paper attempts to delineate the influence of paint and paint processes on the adhesion/cohesion and mechanical properties of coated TPO parts, in particular, the performance of 2K topcoated TPO substrates under thermal shock conditions. It was found that the most important attribute contributing to thermal shock resistance of painted TPO parts was the bake temperature of the topcoat. A temperature of 250 °F in either the adhesion promoter bake or the topcoat bake is necessary to afford acceptable thermal shock performance. It is postulated that the rearrangement of poly(propylene) crystallites at the uppermost surface of the TPO under a 250 °F bake accounts for the increased cohesive strength of the painted composite.     

Investigating the optimum parameters of a negative photoresist to prepare a V-grooved diffraction grating on Si using photolithography and reactive ion etching techniques

In this study, the deposition parameters of the SU8 2000.5 negative photoresists have been investigated and optimized for the photolithographic technique. Then, applied the inductive coupled plasma reactive ion etching (ICP RIE) to produce V-shaped groove diffraction grating on a silicon substrate. Spin coater (speed: 1000 rpm) was used to coat the photoresist over the Si substrate. The observed photoresist film thickness was measured by ellipsometry and found to be 800 nm. Interestingly, the film exhibited some stability with increasing the spin speed. The thermogravimetric analysis was used to optimize the baking temperature which was found to be ~105 °C. Contrast curves were obtained experimentally and used to optimize the exposure energy along with the images obtained from the field emission scanning electron microscopy (FESEM). The optimized energy fluence was found to be 17 mJ/cm². It was interesting to observe that the thickness of the photoresists film was increasing with the elevation of the exposure energy fluence. The FESEM images were used to optimize the ICP RIE etching process and the best etching conditions for the Si substrate were ICP power: 150 W, bias power: 100 W, and SF₆ gas flow rate: 32 SCCM (standard cubic centimeters per minute), O₂ gas flow: 8 SCCM, and Ar gas flow of 8 SCCM. It is worth to mention that well-defined V-shaped grooves were observed with a depth of 2 μm under the same experimental conditions.     

Preparation of a nanosilica‐modified negative‐type acrylate photoresist

A new type of negative photoresist, which incorporated nanosized silica into a photosensitive acrylic resin, was developed. First, free‐radical polymerization was employed to synthesize the acrylic resin, poly[methyl methacrylate/methacrylic acid/3‐(trimethoxysilyl) propyl methacrylate], and then a silica precursor, prepared by hydrolysis and condensation of tetraethoxysilane in a sol–gel process, was introduced into the as‐formed resin solution. After the addition of photosensitive monomers and photoinitiators, a negative‐type organic–inorganic photoresist was produced. The morphology of the UV‐cured photoresist, as observed by field emission scanning electron microscopy, indicated that the size of the silica domain in the material could be reduced from 300 to about 50 nm by appropriate dosage of 3‐(trimethoxysilyl) propyl methacrylate. Thermogravimetric analysis, dynamic mechanical analysis, differential scanning calorimetry, and thermal mechanical analysis were used to evaluate the thermal and dimensional stabilities of the cured photoresists. It was found that the thermal decomposition temperature and glass‐transition temperature increased, whereas the thermal expansion coefficients before and after the glass transition decreased, with increasing silica content. The incorporation of 3‐(trimethoxysilyl) propyl methacrylate also enhanced the thermal and dimensional stabilities; however, the level of enhancement was moderate for the thermal decomposition temperature and thermal expansion coefficient and low for the glass‐transition temperature. In addition, a photoresist coated on a copper substrate demonstrated high hardness (5H) and strong adhesion (100%) with a resolution of 30 μm. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Two‐component photoresists containing thermally crosslinkable photoacid generators

Bis{4‐[2′‐(vinyloxy)ethoxy]phenyl}‐4‐methoxyphenylsulfonium triflate (TPS‐2VE‐Tf) and tris{4‐[2′‐(vinyloxy)ethoxy]phenyl}sulfonium triflate (TPS‐3VE‐Tf) were synthesized as thermally crosslinkable photoacid generators (PAGs) and used in a two‐component chemically amplified photoresist system. The photoresist films formulated with poly(p‐hydroxystyrene) (PHS) as a binder polymer and a thermally crosslinkable PAG are insolubilized in aqueous base by prebaking due to the thermal crosslinking reaction between PHS and the PAG. The insolubilization temperature of the resists and conversion of vinyl ether groups are greatly influenced by the PAG concentration and prebaking temperature, respectively. Upon exposure to deep UV and subsequent postexposure bake, the crosslinks are cleaved by photogenerated acid, leading to effective solubilization of the exposed areas. Photoresists containing TPS‐2VE‐Tf and TPS‐3VE‐Tf exhibited sensitivities of 12 and 45 mJ/cm², respectively. Positive‐tone images were obtained using a 2.38 wt% aqueous tetramethylammonium hydroxide developer.     

Adhesion properties of nanoparticle-coated emulsion aggregation toner

Toner is the key material in printing and copying processes. Fundamental understanding of toner detachment and adhesion during the printing process is critical to improve both the efficiency of toner usage and the quality of print. To control their adhesion property, toner particles can be surface-coated with nanoparticle additives to modify their surface roughness, and consequently, to tune their adhesion properties. In this study, a technique based on the rolling resistance moment of the particle-substrate adhesion bond is used to quantify the effect of nanoparticle surface area coverage (SAC) on the effective work of adhesion of individual toner particles. Nanoparticle-coated model emulsion aggregation (EA) toner microparticles with the specified SAC levels of 0%, 10%, 50% and 100% were studied and the corresponding particle-substrate work of adhesion values were determined and compared. It is quantitatively demonstrated that the work of adhesion between a surface-coated toner particle and a flat silicon substrate decreases significantly with increasing nanoparticle SAC, which provides an effective means to tailor the adhesion performance of the EA toner. Also, based on the experimental data, for a nanoparticle-coated microparticle on a flat substrate, two possible modes of contact formation were identified and discussed.     

Investigation of the “Surface” and “Interphase” Composition of Adhesion Promoter/Thermoplastic Olefin Systems: The Effect of Adhesion Promoter Bake Temperature

The interfacial chemistry of model systems consisting of two adhesion promoting primers and a single Thermoplastic Olefin (TPO) substrate was examined. Two commercial adhesion promoter (AP) materials were applied to a commercially-available TPO material and either flash dried at room temperature or baked at 100°C. The surface composition of the AP films and TPO substrate, and the interfacial compositions of the AP/TPO systems were characterized using x-ray photoelectron spectroscopy (XPS). The AP films studied were based upon a chlorinated polyolefin (CPO). For one adhesion promoter film (AP-1), no chlorine was present at the surface suggesting a nonhomogeneous system. For the second adhesion promoter film (AP-2), the surface composition was about 15% CPO and 85% AP matrix. No changes in AP surface composition were evident for the different bake conditions for either AP. Interfacial compositions of the room temperature flashed materials were found to be very similar for both AP/TPO systems, with CPO being present for each and at similar concentrations. Interfacial compositions for the baked materials were also similar for the two systems, although the level of CPO at the interface increased for both the AP-1 and AP-2 relative to the unbaked materials. The relative increases observed were 46% and 41% for the AP-1 and AP-2 systems, respectively. The increase in the relative concentration of CPO at the interface with bake temperature suggests that there is a stronger interaction between the AP and TPO. The implication of these data is that a baked AP should result in a more robust paint system with respect to AP/TPO adhesion.     

Fabrication and characterization of well-aligned and ultra-sharp silicon nanotip array

Well-defined, uniform, and large-area nanoscaled tips are of great interest for scanning probe microscopy and high-efficiency field emission. An ultra-sharp nanotip causes higher electrical field and, hence, improves the emission current. In this paper, a large-area and well-aligned ultra-sharp nanotip arrays by reactive ion etching and oxidation techniques are fabricated. The apex of nanotips can be further sharpened to reach 3-nm radius by subsequent oxidation and etching process. A schematic model to explain the formation of nanotip array is proposed. When increasing the etching time, the photoresist on top of the nanotip is also consumed, and the exposed silicon substrate is etched away to form the nanotip. At the end, the photoresist is consumed completely and a nanotip with pyramid-like shape is developed. The field emission property was measured, and the turn-on field and work function of the ultra-sharp nanotip was about 5.37 V/μm and 4.59 eV, respectively. A nanotip with an oxide layer capped on the sidewall is also fabricated in this paper. Comparing to the uncapped nanotip, the oxide-capped sample exhibits stable and excellent field emission property against environmental disturbance.     

Modelling and analysis of the electrostatic adhesion performance considering a rotary disturbance between the electrode panel and the attachment substrate

In real-world applications of electrostatic adhesion technology, the electrostatic adhesion force decreases when the electrode panel slides or rotates relative to the attachment substrate due to an external disturbance. However, little work has been done to study this phenomenon. This paper presents a model and analysis method to evaluate the electrostatic adhesion performance considering a rotary disturbance between the electrode panel and the attachment substrate. First, dynamic variations of the electric fields for any point on the attachment substrate are analysed. Then the decrease in the electrostatic adhesion force is explained based on the analysis results and our previous work. The analysis results and explanations are experimentally validated on three different attachment substrates. The fundamental cause of the decrease in adhesion force is the loss of the lined layer polarization due to the rotary disturbance. The results provide a good explanation to the phenomenon and make the existing electrostatic adhesion theory more self-consistent.     

Work of Adhesion as a Dominant Factor in Formation of Composition‐Gradient Thermosensitive Gel

By copolymerizing a thermosensitive primary component, N‐isopropylacrylamide (NIPA), and an ionic secondary component, 2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid (AMPS) between two substrates of hydrophilic glass and hydrophobic polytetrafluoroethylene (Teflon), a novel composition‐gradient copolymer gel, in which the AMPS content decreases gradually towards Teflon, is prepared. The formation of the composition‐gradient in NIPA‐co‐AMPS gels is discussed in terms of the work of adhesion between a solution and a substrate, i.e., the liquid‐solid interfacial free energy. The work of adhesion is determined from the Young‐Dupré equation on the basis of the measured contact angle and the surface tension in the system consisting of an aqueous solution containing NIPA or AMPS monomers or polymers and glass or Teflon as the substrate. The values of the work of adhesion of AMPS monomer and polymer on Teflon were lower than those on glass. Thus, AMPS remains relatively stable at the glass interface and unstable at the Teflon interface. This repulsion of AMPS due to the hydrophobicity of the Teflon wall generates the composition‐gradient.     

Fabrication of Photonic/Microfluidic Integrated Devices Using an Epoxy Photoresist

Using a single layer of SU‐8 photoresist to fabricate optical waveguide cores and microfluidic channels on Pyrex glass is an ideal way to achieve photonic/microfluidic integration on a single chip. To address the problem of poor bonding, a thin nanoscale intermediate polymer layer was applied to reduce the stress generated from the material processing while maintaining strong adhesion between the patterning polymer layer and Pyrex. It was found that a 186–600 nm thick intermediate layer of a specialty epoxy photoresist effectively served the purpose without deteriorating the optical performance of the involved waveguides. Quality photonic/microfluidic integrated devices with satisfied optical performance were fabricated.

     

Fiber-stretching test: a new technique for characterizing the fiber–matrix interface using direct observation of crack initiation and propagation

A new micromechanical technique for experimental determination of fiber-matrix interfacial properties is presented. This technique consists in tensile loading of the fiber, with a matrix droplet on it, at both ends, accompanied by continuous direct observation of interfacial crack propagation. In comparison with the well-known microbond test, the new method has two important advantages. First, crack propagation is stable for any embedded fiber length and any relation between adhesion and friction at the interface. Second, compliance of the test equipment does not affect the results, and specimens with long free fiber ends can be successfully tested. A similar result can be reached using the pull-out or microbond test with an 'infinite' (very long) embedded fiber length. An algorithm for separate determination of the interfacial adhesion and friction from experimental relationships between the crack length and applied load is described. The new test was employed to determine the interfacial parameters for composites of glass fibers with polypropylene, polystyrene, and polycarbonate. For each fiber-polymer system investigated, the following parameters were calculated: ultimate interfacial shear strength; critical energy release rate for crack propagation; and adhesional pressure. Our approach to the estimation of the work of adhesion, WA, from micromechanical tests, based on the concept of adhesional pressure, allowed us to calculate the WA values for several thermoplastic matrix-glass fiber pairs and to obtain values consistent with previous estimations made according to other approaches.     

On oxidation and adhesion of copper‐filled PE

The IR‐spectroscopy and MVCIR technique were used to study the role of technological factors (filler content, film thickness) in oxidation of polyethylene coatings filled with copper powder. It was learned that copper powder introduced into polyethylene reduces the ultimate level of oxidation of both the outer surface layer and deep‐seated layers of the polymer; also, the layer thickness of the specimens oxidized at diffusion conditions was observed to be decreased. Besides, the oxidation gradient determined through the specimen thickness was decreased on increasing the filler content. For example, with copper concentration over 3 vol %, the ultimate level of oxidation within the polymer layer that undergoes diffusive oxidation remains unchanged. The filler exerts its influence on bonding of the coatings, first of all through variations in the oxidation level of the polymer layer bordering on the substrate. For example, at the filler concentration above 3 vol %, the achievable level of adhesional strength does not depend on the coat thickness (the coat thickness being smaller than that of the diffusively oxidized layer). In thicker coatings, oxidative transformations do not, in fact, take place in the zone of adhesional contact, and the adhesion strength remains unchanged during thermal treatment. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2047–2052, 2001     

How Compliance Compensates for Surface Roughness in Fibrillar Adhesion

Fibrillar interfaces play an important role in the ability of many small animals to adhere to surfaces. Surface roughness is generally deleterious to adhesion because it hinders the ability of mating surfaces to make contact, but fibrillar surfaces compensate for surface roughness by virtue of their enhanced compliance. We examine the relationship between roughness and compliance by analyzing the mechanics of detaching an array of fibrils from a substrate. The theory of Johnson, Kendall, and Roberts is used to describe the interfacial adhesion of each fibril, and roughness is modeled by making the fibril length a random variable subject to a probability distribution. We solve for the mean force response of a fibrillar array as a function of the displacement of the entire array. From these results we extract the mean fibrillar pull-off force and work to separate the fibrillar array and substrate. We show how the mean fibrillar pull-off force decreases with increasing roughness-height standard deviation: the relationship is linear for small height standard deviation, and the pull-off force trails off to zero for very rough surfaces. Conversely, the work of separation is shown to be unaffected by small roughness-height standard deviation, although it decreases toward zero for rougher surfaces. The effects of roughness may be offset by increasing fibrillar compliance; for small roughness-height standard deviation, we show that the reduction in pull-off force is inversely proportional to the normalized compliance. We also show that the work of separation increases linearly with the compliance when the compliance is large compared with the roughness-height standard deviation.     

How Compliance Compensates for Surface Roughness in Fibrillar Adhesion

Fibrillar interfaces play an important role in the ability of many small animals to adhere to surfaces. Surface roughness is generally deleterious to adhesion because it hinders the ability of mating surfaces to make contact, but fibrillar surfaces compensate for surface roughness by virtue of their enhanced compliance. We examine the relationship between roughness and compliance by analyzing the mechanics of detaching an array of fibrils from a substrate. The theory of Johnson, Kendall, and Roberts is used to describe the interfacial adhesion of each fibril, and roughness is modeled by making the fibril length a random variable subject to a probability distribution. We solve for the mean force response of a fibrillar array as a function of the displacement of the entire array. From these results we extract the mean fibrillar pull-off force and work to separate the fibrillar array and substrate. We show how the mean fibrillar pull-off force decreases with increasing roughness-height standard deviation: the relationship is linear for small height standard deviation, and the pull-off force trails off to zero for very rough surfaces. Conversely, the work of separation is shown to be unaffected by small roughness-height standard deviation, although it decreases toward zero for rougher surfaces. The effects of roughness may be offset by increasing fibrillar compliance; for small roughness-height standard deviation, we show that the reduction in pull-off force is inversely proportional to the normalized compliance. We also show that the work of separation increases linearly with the compliance when the compliance is large compared with the roughness-height standard deviation.     

杂环硅烷自组装膜改性的聚丙烯表面镀铜研究

通过在电晕放电处理的聚丙烯(PP)表面自组装6-(3-三乙氧基硅基丙基氨)-1,3,5-三嗪-2,4-二硫醇单钠盐(TES)纳米膜后,进行了化学镀铜研究。考察了施镀温度、镀液pH值对镀速的影响,施镀时间对镀层厚度的影响,确定了最优工艺参数。在优化的工艺条件下制备镀层,用扫描电镜对镀层的形貌进行分析,并做了粘接性能测试。结果表明:最佳工艺为施镀温度为50℃,pH为13,施镀时间为50 min。采用此优化工艺条件制备的镀层,表观光亮,均匀致密,与基体结合力良好。     

Study on interfacial interaction energy of Cu–SAM–epoxy systems in a hot and humid environment

Due to poor adhesion, the interfacial delamination is one of the typical failure modes in electronic packages. In this paper, two kinds of self-assembly monolayers (SAMs), SAMA and SAME, are added to Cu–epoxy interface and the effects of temperature, moisture, and cross-link conversion on the modified interfaces are investigated with molecular dynamics (MD) simulation. The results show that the interfacial interaction energy of the systems with SAMA increases with the increasing temperature, decreasing moisture content, and cross-link conversion. However, the interfacial interaction energy of the systems with SAME decreases with the increasing temperature and moisture content, while it is reluctant to the cross-link conversion. In addition, the simulation reveals that the covalent bonds between SAMA and epoxy enhance the interfacial adhesion of Cu–epoxy. However, the nonbond interactions of SAME and epoxy resin weaken the interfacial adhesion. This paper provides a new method for research and valuation the effects of SAM or other adhesive on interfacial adhesion. MD simulation is an efficient tool in predicting the performances of materials.     

Structure-property relationships of hydrido organo siloxane polymer (HOSP)

Summary The structure and properties of Hydrido Organo Siloxane Polymer (HOSP) as a function of cure conditions have been analyzed. Fourier transform infrared spectroscopy, dielectric constant, and mechanical properties all indicated a dependence on the bake sequence of HOSP. FT-IR analysis indicated that the ratio of Si-O bonds in a caged (or ordered) configuration to Si-O bonds in a non-caged (or disordered) configuration changed as a function of both pre-cure hot plate bake conditions and cure temperature. The dielectric constant was lower for samples that received a high temperature hot plate bake (400°C) prior to the furnace cure independent of the furnace cure temperature, compared with samples that did not undergo the high temperature hot plate bake. In addition, adhesion was significantly improved with an increase in the cure temperature from 400°C to 430°C. These results indicate that both pre-cure hot plate bake conditions, and cure temperature affect the structure and therefore the properties of HOSP. Optimum properties are achieved when both the 400°C hot plate bake and a 430°C furnace cure are employed. Received: 8 January 2002/Revised version: 27 February 2002/ Accepted: 27 February 2002